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Agboola FA and Bridges J (2004), "Jet Noise Source Localization Using Linear Phased Array" (NASA/TM—2004-213041)
Abstract: A study was conducted to further clarify the interpretation and application of linear phased array microphone results, for localizing aeroacoustics sources in aircraft exhaust jet. Two model engine nozzles were tested at varying power cycles with the array setup parallel to the jet axis. The array position was varied as well to determine best location for the array. The results showed that it is possible to resolve jet noise sources with bypass and other components separation. The results also showed that a focused near field image provides more realistic noise source localization at low to mid frequencies.
BibTeX:
@techreport{Agboola_Bridges2004,
  author = {Agboola, F. A. and Bridges, J.},
  title = {Jet Noise Source Localization Using Linear Phased Array},
  year = {2004},
  number = {NASA/TM—2004-213041},
  url = {http://gltrs.grc.nasa.gov/reports/2004/TM-2004-213041.pdf}
}
Ahlefeldt T and Koop L (2010), "Microphone-Array Measurements in a Cryogenic Wind Tunnel", AIAA J.. Vol. 48(7), pp. 1470-1479.
Abstract: Based on previous studies with microphones and electronic equipment in a cryogenic environment, a test array for cryogenic application has been developed. Electret microphones, electronic equipment, and fairing material have been successfully tested by the authors under cryogenic conditions and have demonstrated long-term stability. Subsequently, acoustic array measurements performed in a cryogenic wind tunnel for various temperatures in the range of 100 to 300 K, using a single-rod configuration, are described in this paper. The Mach number was in the range 0.1 to 0.3, and the Reynolds number (based on the cylinder diameter of 2.5 mm) was in the range of 5 10^3 to 8 10^4. The experiments demonstrated the technical feasibility of performing aeroacoustic array measurements at these low temperatures. A systematic study of Reynolds- and Mach-number effects on the radiated noise of a singlerod configuration has been conducted. The results showed good agreement between theory and measured sound radiation. A Reynolds number dependency of the measured and predicted sound power can be shown.
BibTeX:
@article{AhlefeldKoop2010,
  author = {Ahlefeldt, T. and Koop, L.},
  title = {Microphone-Array Measurements in a Cryogenic Wind Tunnel},
  journal = {AIAA J.},
  year = {2010},
  volume = {48},
  number = {7},
  pages = {1470--1479},
  doi = {10.2514/1.50871}
}
Ahlefeldt T and Koop L (2009), "Microphone Array Measurements in a Cryogenic Wind Tunnel", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3185., May, 2009.
Abstract: Based on previous studies with microphones and electronic equipment in a cryogenic environment, a test array for cryogenic application has been developed. Electret microphones, electronic equipment and fairing material have been successfully tested by the authors under cryogenic conditions and have demonstrated long-term stability. Subsequently, in this paper, acoustic array measurements performed in a cryogenic wind tunnel for various temperatures in the range 100 K to 300 K using a single rod configuration are described. The Mach number was in range 0.1 to 0.3 and the Reynolds number (based on the cylinder diameter of 2.5 mm) was in the range 5·103 to 8·104 . The experiments demonstrated the technical feasibility of performing aeroacoustic array measurements at these low temperatures. A systematic study of Reynolds and Mach number effects on the radiated noise of a single rod configuration has been conducted. The results showed reasonably good agreement between theory and measured sound radiation. A Reynolds number dependency of the measured and predicted sound power can be shown. At a later stage, a large array for cryogenic application, which was modeled on the test array used here, has been constructed and preliminary results of measurements on a Dornier DO-728 half-model are also presented here.
BibTeX:
@inproceedings{AhlefeldtKoop2009,
  author = {Ahlefeldt, T. and Koop, L.},
  title = {Microphone Array Measurements in a Cryogenic Wind Tunnel},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3185.pdf}
}
Ahlefeldt T, Koop L, Lauterbach A and Spehr C (2010), "Advances in microphone array measurements in a cryogenic wind tunnel", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-03., February, 2010.
Abstract: The prediction of full-scale airframe noise based on small-scale model measurements via the phased microphone array technique is well known and in common use in closed test sections. Since conventional wind tunnels cannot generally achieve full-scale Reynolds numbers, measurements are often performed in cryogenic and pressurized wind tunnels which are capable of higher Reynolds number flows. Thus, the characteristics of the moving fluid are adapted to the scale of the model. At the DLR Institute of Aerodynamics and Flow Technology the microphone array measurement technique was further developed to perform measurements in a cryogenic wind tunnel at temperatures down to 100 K. To this end, a microphone array consisting of 144 microphones was designed and constructed. In order to use a microphone array in a cryogenic environment, coming to grips with cold hardiness and ensuring long term stability of the array fairing and the electronic devices, especially the microphones, are the primary challenge. Measurements of the radiated noise from a single rod configuration have been conducted. The results showed very good agreement between theory and measured sound radiation. A Reynolds number dependency of the measured and predicted sound power can be shown.
BibTeX:
@inproceedings{Ahlefeld_etal2010,
  author = {Ahlefeldt, T. and Koop, L. and Lauterbach, A. and Spehr, C.},
  title = {Advances in microphone array measurements in a cryogenic wind tunnel},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-03.pdf}
}
Ahlefeldt T, Lauterbach A and Koop L (2010), "Aeroacoustic Measurements of a Scaled Half Model at High Reynolds Numbers", In 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010., AIAA-2010-3748., June, 2010.
Abstract: The measurement of airframe noise on small-scale models is well known and common practice in conventional wind tunnels. Since conventional wind tunnels cannot generally achieve full-scale Reynolds numbers, measurements during the development process of modern aircraft are often performed in cryogenic and/or pressurized wind tunnels which are capable of higher Reynolds number flows. Thus, the characteristics of the moving fluid are better adapted to the scale model. At the DLR Institute of Aerodynamics and Flow Technology the microphone array measurement technique was further developed to perform measurements in a cryogenic wind tunnel at temperatures down to 100 K. A microphone array consisting of 144 microphones was designed and constructed for this purpose. In this paper, acoustic array measurements performed in a cryogenic wind tunnel are described for various Reynolds numbers using a 9.24% Dornier-728 half model. Additionally, the background noise of the empty test section was measured within the range of the measurements performed on the Dornier-728 half model. Our results seems to indicate a Reynolds number dependency of the measured sound power for various sources.
BibTeX:
@inproceedings{Ahlefeld_etal2010b,
  author = {Ahlefeldt, T. and Lauterbach, A. and Koop, L.},
  title = {Aeroacoustic Measurements of a Scaled Half Model at High Reynolds Numbers},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010},
  year = {2010}
}
Alexander WN, Devenport W, Glegg S and Van Buren R (2010), "Directivity of Noise from Discrete Elements in a Turbulent Boundary Layer", In 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010., AIAA-2010-3773., June, 2010.
Abstract: Measurements were taken in the Virginia Tech Anechoic Wall Jet Facility to study the directivity of roughness noise produced by single 8mm and 3mm cubes and varying size grid patterns of 3mm cubes. Boundary layer thickness to roughness height ratios varied from 2-5.3 over the examined conditions. An arrangement of 8 far field microphones creating two arcs overtop and around the side of the roughness were used in combination with a linear microphone array of 32 sensors which was resting on the flat plate of the wall jet. Single microphone data, beamformed source images, and a least-squares method were used to characterize the noise produced by the rough surfaces. The least-squares method was used to estimate the source strengths of both streamwise and spanwise dipoles originating from the cubic roughness by minimizing the error between the measured spectra and model spectra. This method was validated for frequencies above 10kHz by comparison with single microphone measurements. The results show that the strength of the streamwise dipole emanating from a single element was found to be equal to or stronger than the spanwise dipole. Finally, the lead row of a multi-row fetch of cubic roughness elements produced the strongest spanwise dipole and the strength of the spanwise dipole decreased with each succeeding row.
BibTeX:
@inproceedings{Alexander_etal2010,
  author = {Alexander, W. N. and Devenport, W. and Glegg, S. and Van Buren, R.},
  title = {Directivity of Noise from Discrete Elements in a Turbulent Boundary Layer},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010},
  year = {2010}
}
Alscher H (1989), "Aeroacoustic Investigation of the Magnetic Train Transrapid 06", In International conference on magnetically levitated systems and linear drives (Maglev '89), Yokohama (Japan), 7-11 Jul 1989., July, 1989.
Abstract: Dominant sources of aero-acoustic noise are identified on the surface of the magnetic train Transrapid 06 by microphone array measurements, in order to minimize the aerodynamic drag and the noise. Wind tunnel tests were carried out for a specific area near the nose of the train and led to local reshaping. For the measurements, a linear equidistant arrangement of 13 microphones with omnidirectional characteristic. The various signals received are recorded in parallel for later digital processing. Such acoustic investigations necessitate many parameters to be varied: position of array, microphone distances for different frequency ranges, different speeds of the vehicle and different types of guideway construction. A complete combination of all parameters adds up to a great number of test runs.
BibTeX:
@inproceedings{Alscher1989,
  author = {Alscher, H.},
  title = {Aeroacoustic Investigation of the Magnetic Train Transrapid 06},
  booktitle = {International conference on magnetically levitated systems and linear drives (Maglev '89), Yokohama (Japan), 7-11 Jul 1989},
  year = {1989}
}
Arcondoulis E, Doolan C, Brooks L and Zander A (2011), "A Modification to Logarithmic Spiral Beamforming Arrays for Aeroacoustic Applications", In 17th AIAA/CEAS Aeroacoustics Conference, 05 - 08 June 2011, Portland, Oregon., AIAA-2011-2720., June, 2011.
Abstract: Acoustic beamforming is an experimental tool that can be used to locate and quantify aeroacoustic noise sources. Much of the available aeroacoustic beamforming literature presents beamforming results of noise at relatively high frequencies. There are few experimental acoustic beamforming results for acoustic frequencies between 1 kHz and 5 kHz, although much of the literature for airfoil self noise at low to moderate Reynolds number fits in this frequency range. One difficulty with acoustic beamforming of relatively low frequency noise is the large size of the main lobe in the beamformer output, resulting in a potential inability to resolve acoustic sources within close proximity to each other. This paper provides a detailed comparison between grid, randomized, logarithmic spiral and modified logarithmic spiral arrays and a discussion of the performance of each array type over a range of low frequencies (1 kHz-5 kHz). The spiral arrays were found to have lower sidelobe levels over a wider frequency range than the grid and random array. For frequencies less than 4.84 kHz and greater than 12.36 kHz, the modified logarithmic spiral exhibited smaller sidelobe magnitudes than the unmodified logarithmic spiral. An experimental verification of a modified logarithmic spiral using a small headphone in an anechoic environment is also provided. This showed that the error of the measured noise source locations placed 600 mm from the array plane is within 20 mm for the series of locations studied. The estimation error was shown to be dependent on the source location and direction from the center of the array.
BibTeX:
@inproceedings{Arcondoulis_etal2011,
  author = {Arcondoulis, E.J.G. and Doolan, C.J. and Brooks, L.A. and Zander, A.C.},
  title = {A Modification to Logarithmic Spiral Beamforming Arrays for Aeroacoustic Applications},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference, 05 - 08 June 2011, Portland, Oregon},
  year = {2011}
}
Arcondoulis E, Doolan C, Zander A and Brooks L (2010), "Design and Calibration of a Small Aeroacoustic Beamformer", In Proceedings of 20th International Congress on Acoustics, ICA 2010, 23-27 August 2010, Sydney, Australia.
BibTeX:
@inproceedings{Arcondoulis_etal2010,
  author = {Arcondoulis, E.J.G. and Doolan, C.J. and Zander, A.C. and Brooks, L.A.},
  title = {Design and Calibration of a Small Aeroacoustic Beamformer},
  booktitle = {Proceedings of 20th International Congress on Acoustics, ICA 2010, 23-27 August 2010, Sydney, Australia},
  year = {2010}
}
Avarvand FS, Ziehe A and Nolte G (2012), "Self-consistent MUSIC algorithm to localize multiple sources in acoustic imaging", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-22., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The Multiple Signal Classification (MUSIC) algorithm is a standard method to localize acoustic sounds as well as brain sources in electroencephalography (EEG) and magnetoencephalography (MEG). In one of its variants used for EEG/MEG source analysis, called RAP-MUSIC, sequential projections were proposed to properly identify local maxima of the gain function as origins of true sources. The purpose of this paper is twofold: a) we introduce the concept of RAP-MUSIC to the acoustic community, and b) we extend the RAP-MUSIC approach to a fully recursive algorithm. The latter highly suppresses distortions of the estimate of each source due to the presence of other sources. The method is demonstrated for a measurement of the sounds of two loudspeakers placed on a table in a reverberant room. We presented the localization results for Delay and Sum(DAS) beamformer, RAP-MUSIC and SC-MUSIC. In contrast to both DAS beamformer and RAP-MUSIC the new method correctly localizes and separates four sources: the two loudspeakers and the two respective echoes
BibTeX:
@inproceedings{Avarvand_etal2012,
  author = {Avarvand, F. S. and Ziehe, A. and Nolte, G.},
  title = {Self-consistent MUSIC algorithm to localize multiple sources in acoustic imaging},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-22.pdf}
}
Bahr C, Jian L and Cattafesta L (2011), "Aeroacoustic Measurements in Open-jet Wind Tunnels - An Evaluation of Methods Applied to Trailing Edge Noise", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2771., June, 2011.
Review: Open jet wind tunnels have become commonplace in aeroacoustic testing, as having an open-jet test section in an anechoic chamber can provide a near-anechoic environment when ttempting to measure acoustic field levels due to an aeroacoustic source. Additionally, reduced flow is present over installation microphones, so SNR gains are observed versus equivalent closed test section experiments. However, open-jet wind tunnels and their acoustic treatment introduce additional noise sources which may contaminate a given signal of interest. To overcome this limitation, multiple-microphone processing techniques involving coherent power and/or beamforming are often leveraged. These techniques can isolate the behavior of an aeroacoustic noise source using different types of assumptions. However, depending on the facility background noise characteristics and measurement setup these assumptions may be violated. A comparison of these techniques is conducted using a NACA 63-215 Mod-B airfoil in UFAFF, and shows that when the signal of interest, trailing edge noise, is not the dominant noise source, facility flow noise can introduce aberrant behavior to the coherent power and array processing techniques. This behavior leads to correspondingly large uncertainty bounds in output power spectra. Modifications to the wind tunnel facility and experimental setup are proposed to mitigate these problems, and a new experiment set with a smaller NACA 0012 airfoil is designed. Results show that modifications appear to improve the behavior of coherent power methods, specifically those tailored to trailing edge noise measurements, significantly. Major disagreement between coherent power techniques and delay-and-sum integration is found even with significant mitigation of facility contaminating noise sources. Uncertainty analysis does not account for the difference visible between the methods, suggesting that further analysis involving deconvolution and coherent source behavior is warranted.
BibTeX:
@inproceedings{Bahr_etal2011,
  author = {Bahr, Christopher and Li Jian and Cattafesta, Louis},
  title = {Aeroacoustic Measurements in Open-jet Wind Tunnels - An Evaluation of Methods Applied to Trailing Edge Noise},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Bahr C, Zawodny N, Bertolucci B, Woolwine K, Liu F, Li J, Sheplak M and Cattafesta L (2011), "Measurement of Phased Array Point Spread Functions for Use with Beamforming", In 17th AIAA/CEAS Aeroacoustics Conference, 5-8 June 2011, Portland, Oregon., AIAA-2011-2767., June, 2011.
BibTeX:
@inproceedings{Bahr_etal2011b,
  author = {Bahr, C. and Zawodny, N. and Bertolucci, B. and Woolwine, K. and Liu, Fei and Li, Jian and Sheplak, M. and Cattafesta, L.},
  title = {Measurement of Phased Array Point Spread Functions for Use with Beamforming},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference, 5-8 June 2011, Portland, Oregon},
  year = {2011},
  doi = {10.2514/6.2011-2767}
}
Bahr C, Zawodny NS, Yardibi T, Liu F. Wetzel D, Bertolucci B and Cattafesta L (2010), "Shear Layer Correction Validation using a Non-Intrusive Acoustic Point Source", In 16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden., AIAA-2010-3735., June, 2010.
Abstract: Microphone arrays can be used to localize and estimate the strengths of acoustic sources present in a region of interest. In general, microphone array processing algorithms assume line-of-sight acoustic wave propagation from each source to each microphone. However, when the microphone array is placed outside the jet in an open-jet test section, the presence of the shear layer refracts the acoustic waves and causes the wave propagation times (from each source to each microphone) to be different than in the case without the shear layer. With a known source location in space, the change in propagation times can be determined by using Amiet’s method (J. Sound Vib., Vol. 58, 1978). We investigate the effects of shear layer refraction on the conventional delay-and-sum beamforming algorithm by using a pulsed laser system to generate a plasma point source in space and time within the test section at several different test section flow speeds and configurations with varying levels of complexity. The results indicate that Amiet’s method properly corrects for shear layer refraction effects when the source is in the inviscid core of the open-jet test section, as well as when the source is located in a simple thin wake. When the source is in a complex wake region, the quantitative agreement degrades although overall trends are correct.
BibTeX:
@inproceedings{Bahr_etal2010,
  author = {Bahr, C. and Zawodny, N. S. and Yardibi, T. and Liu, F. Wetzel, D. and Bertolucci, B. and Cattafesta, L.},
  title = {Shear Layer Correction Validation using a Non-Intrusive Acoustic Point Source},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden},
  year = {2010}
}
Bai L and Huang X (2010), "Observer-Based Method in Acoustic Array Signal Processing", In 16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden., AIAA-2010-3813., June, 2010.
Abstract: Acoustic arrays have become an important testing tool in noise identification for industry applications, where the typical beamforming algorithm has been adopted as a classical processing technique. In most practical cases the beamforming computations have to be conducted off-line due to the excessive computational requirements. An alternative algorithm with a real-time capability is proposed. The algorithm is similar to a classic observer while array processing is performed in the frequency domain. The performance of this observer-based algorithmis studied here through comparing with the typical beamforming method, particulary for a case of coherent noise sources. In this paper it is shown that the observer-based algorithm could resolve the coherence restriction between the background noise and the signal of interest. The proposed algorithm is also beneficial for its capability of operating over sampling blocks recursively. The convergence rate of this recursive algorithm is fast enough to satisfy the requirements for practical cases. The experimental efforts could be saved extensively as any testing defects could be revealed instantaneously and corrected on site. In addition, this innovative approach provides an alternative perspective, from which many techniques already developed in control and filtering could be extended to this new application area of array processing.
BibTeX:
@inproceedings{BaiHuang2010,
  author = {Bai, Long and Huang, Xun},
  title = {Observer-Based Method in Acoustic Array Signal Processing},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden},
  year = {2010}
}
Bai MR and Chen CC (2013), "Application of convex optimization to acoustical array signal processing", J. Sound. Vol. 332, pp. 6596-6616.
Abstract: This paper demonstrates that optimum weighting coefficients and inverse filters for microphone arrays can be accomplished, with the aid of a systematic methodology of mathematical programming. Both far-field and near-field array problems are formulated in terms of convex optimization formalism. Three application examples, including data-independent far-field array design, nearfield array design, and pressure field interpolation, are presented. In far-field array design, array coefficients are optimized to tradeoff Directivity Index for White Noise Gain or the coefficient norm, while in nearfield array convex optimization is applied to design Equivalent Source Method-based Nearfield Acoustical Holography. Numerical examples are given for designing a far-field two-dimensional random array comprised of thirty microphones. For far-field arrays, five design approaches, including a Delay-And-Sum beamformer, a Super Directivity Array, three optimal arrays designed using ℓ1,ℓ2, and ℓ∞-norms, are compared. Numerical and experimental results have shown that sufficiently high White Noise Gain was crucial to robust performance of array against sensor mismatch and noise. For nearfield arrays, inverse filters were designed in light of Equivalent Source Method and convex optimization to reconstruct the velocity field on a baffled spherical piston source. The proposed nearfield design is benchmarked by those designed using Truncated Singular Value Decomposition and Tikhonov Regularization. Compressive Sampling and convex optimization is applied to pressure field reconstruction, source separation and modal analysis with satisfactory performance in both near-field and far-field microphone arrays.
BibTeX:
@article{BaiChen2013,
  author = {Bai, M. R. and Chen, C. C.},
  title = {Application of convex optimization to acoustical array signal processing},
  journal = {J. Sound},
  year = {2013},
  volume = {332},
  pages = {6596--6616},
  doi = {10.1016/j.jsv.2013.07.029}
}
Ballesteros J, Quintana S, Fernández M and Martínez L (2012), "Application of beamforming and SONAH to airborne noise insulation measurements", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-16., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: According to ISO 140-4, pressure level measurements are usually carried out to evaluate the airborne noise insulation. This standard provides no information about parts of the element under test that present a reduced insulation. To solve this problem, intensity measurements based on ISO 15186-2 can be taken. Nevertheless, this solution implies a long time due to the high number of measurement points required. This paper introduces different tests to assess the in-situ airborne noise insulation through SONAH and Beamforming techniques. This makes it easier and quicker the calculation of the insulation of these parts of interest. In these experiments, the intensity magnitude has been obtained through SONAH or Beamforming measurements to derive the airborne noise insulation of a separating element, or a part of it, applying the calculation procedure indicated by the ISO 15186-2 for that. The experiments have been carried out for four constructive elements: a double-wall and three doors made up of common materials (wood, glass, sheet). To determine the accuracy obtained with these experiments, the insulation of the tested elements has been determined in advance by the standardized procedures of pressure and intensity, so that a valid comparison with the results given by SONAH and Beamforming could be established
BibTeX:
@inproceedings{Ballesteros_etal2012,
  author = {Ballesteros, J.A. and Quintana, S. and Fernández, M.D. and Martínez, L.},
  title = {Application of beamforming and SONAH to airborne noise insulation measurements},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-16.pdf}
}
Ballesteros J, Sarradj E, Fernandes M, Geyer T and Ballesteros M (2014), "Methodology for Pass-By Measuremtns with Beamforming on Cars", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-30., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Traffic noise is one of the most important noise sources in industrialized countries. In order to control this kind of noise, it is important to identify and to quantify the noise sources during the pass-by of a car. Standardised methods for vehicle and tyre/road noise measurements only provide results about the time history of the sound, the sound pressure level emitted or the spectrum, but it is impossible to identify the main noise sources. Other advanced measurement methods, as sound intensity, identify the noise source but have the problem of positioning the transducers during the pass-by measurements. In this paper, a new methodology to apply Beamforming for pass-by measurements on cars is described. To define this methodology, simulations were performed in order to design the array, the measurement scenario and to choose the beamforming algorithm most suited to process the pass-by measurement data. Once the methodology was established, it was applied to a real measurement. The results obtained were similar to other published in the literature and therefore, the applicability of the new methodology was confirmed.
BibTeX:
@inproceedings{Ballesteros_etal2014,
  author = {Ballesteros, J. and Sarradj, E. and Fernandes, M. and Geyer, T. and Ballesteros, M.J.},
  title = {Methodology for Pass-By Measuremtns with Beamforming on Cars},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-30.pdf}
}
Barsikow B (1996), "Experiences with various configurations of microphone arrays used to locate sound sources on railway trains operated by the DB AG", J. Sound Vib.. Vol. 193, pp. 283-293.
Abstract: This paper gives an overview of the results and conclusions from measurements made with various configurations of microphone arrays designed to locate sound sources on trains operated by the Deutsche Bahn AG at speeds up to 280 km/h. These arrays comprised one- and two-dimensional arrangements of up to 29 microphones. The characteristics peculiar to microphone arrays will be mentioned only briefly here, because the theoretical background of array measurements is available in other publications. Within the context of the present paper, the sound sources located are those generated mechanically, principally by wheel/rail interactions, and those produced by aerodynamic fluctuations. In addition, noise radiation from cooling systems was also measured during passages of the trains. Examples are given of results obtained with different kinds of arrays during pass-bys of dedicated ICEs and goods trains. These examples demonstrate the usefulness of array measurements for producing detailed information pertaining to the characteristics of individual sound sources. With respect to these individual sound sources particularly on moving vehicles, array technology provides a much more efficient and capable tool for investigating these sources than does the more conventional technique employing single microphones.
BibTeX:
@article{Barsikow1996,
  author = {Barsikow, B.},
  title = {Experiences with various configurations of microphone arrays used to locate sound sources on railway trains operated by the DB AG},
  journal = {J. Sound Vib.},
  year = {1996},
  volume = {193},
  pages = {283--293},
  doi = {10.1006/jsvi.1996.0269}
}
Barsikow B and King III WF (1988), "On Removing the Doppler Frequency Shift from Array Measurements of Railway Noise", J. Sound Vib.. Vol. 120(1), pp. 190-196.
BibTeX:
@article{BarsikowKing1988,
  author = {Barsikow, B. and King III, W. F.},
  title = {On Removing the Doppler Frequency Shift from Array Measurements of Railway Noise},
  journal = {J. Sound Vib.},
  year = {1988},
  volume = {120},
  number = {1},
  pages = {190--196},
  note = {Letter to the editor},
  doi = {10.1016/0022-460X(88)90344-6}
}
Barsikow B, King III WF and Pfizenmaier E (1987), "Wheel/Rail Noise Generated by a High-Speed Train Investigated with a Line Array of Microphones", J. Sound Vib.. Vol. 118, pp. 99-122.
Abstract: Radiated noise generated by a high-speed electric train travelling at speeds up to 250 km/h has been measured with a line array of microphones mounted along the wayside in two different orientations. The test train comprised a 103 electric locomotive, four Intercity coaches, and a dynamo coach. Some of the wheels were fitted with experimental wheel-noise absorbers. By using the directional capabilities of the array, the locations of the dominant sources of wheel/rail radiated noise were identified on the wheels. For conventional wheels, these sources lie near or on the rim at an average height of about 0·2 m above the railhead. The effect of wheel-noise absorbers and freshly turned treads on radiated noise were also investigated.
BibTeX:
@article{Barsikow_etal1987,
  author = {Barsikow, B. and King III, W. F. and Pfizenmaier, E.},
  title = {Wheel/Rail Noise Generated by a High-Speed Train Investigated with a Line Array of Microphones},
  journal = {J. Sound Vib.},
  year = {1987},
  volume = {118},
  pages = {99--122},
  doi = {10.1016/0022-460X(87)90257-4}
}
Barsikow B and Klemenz M (1998), "Diagnosis of noise sources on high-speed trains using the microphone-array technique", In Proc. 16th ICA and 135th Meeting ASA, Seattle. Vol. IV, pp. 2229-2230.
BibTeX:
@inproceedings{BarsikowKlemenz1998,
  author = {Barsikow, B. and Klemenz, M.},
  title = {Diagnosis of noise sources on high-speed trains using the microphone-array technique},
  booktitle = {Proc. 16th ICA and 135th Meeting ASA, Seattle},
  year = {1998},
  volume = {IV},
  pages = {2229--2230}
}
Barsikow B and Klemenz M (1998), "Pantograph noise - a sound source relevant to high-speed trains?", In Proc. International EAA/EEAA Symposium "Transport Noise and Vibration", Tallinn, 1998. , pp. 69-74.
BibTeX:
@inproceedings{BarsikowKlemenz1998b,
  author = {Barsikow, B. and Klemenz, M.},
  title = {Pantograph noise - a sound source relevant to high-speed trains?},
  booktitle = {Proc. International EAA/EEAA Symposium "Transport Noise and Vibration", Tallinn, 1998},
  year = {1998},
  pages = {69--74}
}
Barsikow B, Klemenz M and Schüttpelz M (1997), "Verification of sound-abatement measures applied to a high-speed pantograph during passbys of an ICE test train.", In Proc. 2nd International Workshop on the AeroAcoustics of High-Speed Trains (AAT), Berlin, 1997.
BibTeX:
@inproceedings{Barsikow_etal1997,
  author = {Barsikow, B. and Klemenz, M. and Schüttpelz,M.},
  title = {Verification of sound-abatement measures applied to a high-speed pantograph during passbys of an ICE test train.},
  booktitle = {Proc. 2nd International Workshop on the AeroAcoustics of High-Speed Trains (AAT), Berlin, 1997},
  year = {1997}
}
Berry A, Khatami I, Joshi N and Meslioui S-A (2012), "Source identification of gas turbine engine using an inverse method with beamforming matrix regularization", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-24., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper addresses the discrimination of inlet / exhaust noise of aero-engines in free-field static tests using far-field semi-circular microphone arrays. Three approaches are considered for this problem: focused beamforming, inverse method with Tikhonov regularization and inverse method with beamforming matrix regularization (called hybrid method). The classical beamforming method is disadvantaged due to need for a high number of measurement microphones in accordance to the requirements. Similarly, the Inverse methods are disadvantaged due to their need of having an a-priori source information. The classical Tikhonov regularization provides improvements in solution stability, however continues to be disadvantaged due to its requirement of imposing a stronger penalty for undetected source positions. The proposed hybrid method builds upon the beneficial attributes of both the beamforming and inverse methods, and has been validated using experiments conducted in hemi-anechoic conditions with a small-scale waveguide system simulating a gas turbine engine. The method has further been applied to the measured noise data from a Pratt & Whitney Canada turbo-fan engine and has been observed to provide better spatial resolution and solution robustness with a limited number of measurement microphones compared to the existing methods. More validation work is ongoing.
BibTeX:
@inproceedings{Berry_etal2012,
  author = {Berry, A. and Khatami, I. and Joshi, N. and Meslioui, S.-A.},
  title = {Source identification of gas turbine engine using an inverse method with beamforming matrix regularization},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-24.pdf}
}
Billingsley J (1978), "A comparison of the source location techniques of the acoustic telescope and polar correlation", J. Sound Vib.., December, 1978. Vol. 61(3), pp. 419-425.
Abstract: Previous papers have described the principles of two acoustic source location techniques, those of polar correlation and the acoustic telescope. In this paper the techniques are compared in terms of their computational procedures with the aim of displaying similarities rather than enlarging on their difference. From these consideration, some guidelines emerge for choosing between them according to the particular application, and methods are suggested for combining the techniques to obtain improvements in both.
BibTeX:
@article{Billingsley1978,
  author = {Billingsley, J.},
  title = {A comparison of the source location techniques of the acoustic telescope and polar correlation},
  journal = {J. Sound Vib.},
  year = {1978},
  volume = {61},
  number = {3},
  pages = {419--425},
  doi = {10.1016/0022-460X(78)90389-9}
}
Billingsley J (1974), "An acoustic telescope", Aeronautical Research Council ARC 35/364, 1974.
BibTeX:
@misc{Billingsley1974,
  author = {Billingsley, J.},
  title = {An acoustic telescope},
  howpublished = {Aeronautical Research Council ARC 35/364, 1974},
  year = {1974}
}
Billingsley J and Kinns R (1976), "The Acoustic Telescope", J. Sound Vib.. Vol. 48, pp. 485-510.
Abstract: A system has been developed for real-time sound source location on full-size jet engines. It consists of an array of microphones connected to a small digital computer, via a sequence of preamplifiers, analog filters and analog to digital converters and multiplexer. Microphone signals can be processed on-line to give displays of time varying source distributions or statistical averages with respect to position and frequency, by using a colour television as well as a display screen and printer/plotter. The whole system can be transported in a small estate car and can be used on both model scale and full size engine test rigs. A theoretical analysis of system performance is in terms of a line source of generally correlated omni-directional sound radiators, which shares the measurable far-field properties of a jet engine noise source. The general properties of the system are described, including its use to correlate spatially separated sound sources, application in the presence of ground reflections and use in a moving airstream. The statistical properties of apparent source distributions are also discussed. A series of experiments on a Rolls-Royce/SNECMA Olympus engine is described, in order to illustrate pplication of the system.
BibTeX:
@article{BillingsleyKinns1976,
  author = {Billingsley, J. and Kinns, R.},
  title = {The Acoustic Telescope},
  journal = {J. Sound Vib.},
  year = {1976},
  volume = {48},
  pages = {485--510},
  doi = {10.1016/0022-460X(76)90552-6}
}
Bin Ahmad ZA and Bin Raja Hamzah I (2014), "Low Cost Beam Forming Solutiuon for a Developing Country", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-20., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Beamforming is an effective method for sound localization problem. In developing countries like Malaysia, most of the acoustic and beamforming equipment is typically supplied by established United States or European manufacturers. They are very expensive equipment with cost comparable to our houses. Only universities aided with special grants from the government can afford it. Even the basic building block of a beamforming system, the microphone is very expensive, more than our monthly salary. Armed with internet, a low cost microphone and beamforming system is being developed in the Faculty of Mechanical Engineering, Universiti Teknologi Malaysia. This is our attempt to start the open hardware movement here which should follow the open source (software) movement that is being widely embraced worldwide. Our microphones and beamforming system are developed using the available resources in our university.
BibTeX:
@inproceedings{BinAhmadBinRajaHamzah2014,
  author = {Bin Ahmad, Z. A. and Bin Raja Hamzah, I.},
  title = {Low Cost Beam Forming Solutiuon for a Developing Country},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-20.pdf}
}
Blacodon D (2011), "Array Processing for Noisy Data: Application for Open and Closed Wind Tunnels", AIAA J.. Vol. 49(1), pp. 55-66.
Abstract: Array processing represents an extremely important area in aeroacoustics: in particular, in the development of methods to extract the useful characteristics of acoustic sources, such as their locations and absolute levels, starting from the received sound field. Generally, the methods are based on a deconvolution operation to remove the undesirable effects of smearing produced by array response. This process should be carried out after the additive noise has been suitably attenuated and, ideally, the deconvolution operator should amplify the noise as little as possible. We show that, when a noise reference is known beforehand, and under certain assumptions, that it is possible to both remove the smearing effect produced by array response and to reduce the noise contamination of the results using a method called the spectral estimation method with additive noise. This method has been applied to computer and experimental simulations involving acoustic sources radiating in a noisy environment. The levels of the sources were found with good accuracy, and the background noise was highly reduced, confirming the validity of the approach and the good performance of the proposed method.
BibTeX:
@article{Blacodon2011,
  author = {Blacodon, D.},
  title = {Array Processing for Noisy Data: Application for Open and Closed Wind Tunnels},
  journal = {AIAA J.},
  year = {2011},
  volume = {49},
  number = {1},
  pages = {55--66},
  doi = {10.2514/1.53148}
}
Blacodon D (2010), "Spectral estimation noisy data using a reference noise", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-07., February, 2010.
Abstract: The development of array processing methods to extract the useful characteristics of acoustic sources such as their locations and absolute levels, starting from the measured sound field is one of the main issues in aero-acoustics. Generally, the methods are based on a deconvolution operation to remove the undesirable effects of smearing produced by array response. This process should be carried out after the additive noise has been suitably attenuated and, ideally, the deconvolution operator should amplify the noise as little as possible. We show that when a reference of noise is known beforehand, and under certain assumptions, that it is possible both to remove the smearing effect produced by array response and to reduce the noise contamination of the results using a method called Spectral Estimation Method With Additive Noise. This method has been applied to computer and experimental simulations involving acoustic sources radiating in a noisy environment. The levels of the sources were found with a good accuracy and the background noise highly reduced, confirming the validity of the approach and the good performance of the proposed method.
BibTeX:
@inproceedings{Blacodon2010,
  author = {Blacodon, D.},
  title = {Spectral estimation noisy data using a reference noise},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-07.pdf}
}
Blacodon D (2009), "Combustion-Noise Characterization of a Turbofan Engine with a Spectral Estimation Method", Journal of Propulsion and Power 2009. Vol. 25(2), pp. 374-379.
Abstract: A full-scale test on a turbofan engine has been carried out in the framework of a European project to assess the acoustic benefits of new exhausts and novel hot-stream streamliners in the reduction of the overall jet noise level radiated in the far field. The purpose of the tests is also to provide a better understanding of combustion noise, which is one of the main issues for turbofan engines because of the significant noise reduction obtained for other acoustic sources such as the fan and jet by using innovative efficient silencers and acoustics liners. This work investigates the use of the so-called spectral estimation method to separate the combustion noise from other noise sources measured with a near-field array of microphones. The comparisons between the estimated and measured spectra downstream, at the location at which the combustion noise is dominant, yield promising results, suggesting that the procedure of discrimination is relevant.
BibTeX:
@article{Blacodon2009,
  author = {Blacodon, D.},
  title = {Combustion-Noise Characterization of a Turbofan Engine with a Spectral Estimation Method},
  journal = {Journal of Propulsion and Power 2009},
  year = {2009},
  volume = {25},
  number = {2},
  pages = {374--379},
  doi = {10.2514/1.37013}
}
Blacodon D (2008), "Characterization of Combustion Noise of a Turbofan Engine with SEM Method", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, British Columbia, May 5-7, 2008., AIAA-2008-2945., May, 2008.
Abstract: A full-scale test on a turbofan engine has been carried out in the framework of the European SILENCE(R) project. In the present work, it is investigated the use the so-called Spectral Estimation Method (SEM) to separate the combustion noise from others noise sources measured with a near field phased array. The comparisons between the estimated spectra with the SEM and measured downstream at location where the combustion noise is dominant yields promising results suggesting that the procedure of discrimination is relevant.
BibTeX:
@inproceedings{Blacodon2008,
  author = {Blacodon, D.},
  title = {Characterization of Combustion Noise of a Turbofan Engine with SEM Method},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, British Columbia, May 5-7, 2008},
  year = {2008},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO08_1871/PV2008_2945.pdf}
}
Blacodon D (2007), "Analysis of the Airframe Noise of an A320/A321 with a Parametric Method", Journal of Aircraft. Vol. 44, pp. 26-34.
Abstract: A spectral estimation method based on measurements by a phased array was developed to estimate absolute power levels radiated by compact or extended sources. After a brief recall of its principle, numerical simulations involving several source regions are presented to illustrate the accuracy and the high-resolution performances of this new method. Tests were carried out with a 1:11th scale A320/A321 Airbus model in the anechoic wind tunnel CEPRA 19. The characteristics of source regions from inboard to outboard of the wing slat and flap, and the main and nose landing gear subregions are examined. The dependence in level and frequency of the model subregions with the flow speed, the effects of the attack angle, and the effects of the flap or slat deployment are studied. The different trends revealed by the integrated power levels are also discussed. Examples of the localization of noise sources identified with conventional beam forming and the new method are presented. The consistency of the results is examined by comparing the integrated power levels for the complete wing and the measured spectra with the phased array. Finally, we show that the spectral estimation method is quite reliable in computing the far-field directivity of airframe noise sources.
BibTeX:
@article{Blacodon2007a,
  author = {Blacodon, D.},
  title = {Analysis of the Airframe Noise of an A320/A321 with a Parametric Method},
  journal = {Journal of Aircraft},
  year = {2007},
  volume = {44},
  pages = {26--34},
  doi = {10.2514/1.20295}
}
Blacodon D (2005), "Spectral analysis of airframe noise of an aircraft model A320/A321", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California (USA), 23-25 May 2005,., AIAA-2005-2809., May, 2005.
BibTeX:
@inproceedings{Blacodon2005,
  author = {Blacodon, D.},
  title = {Spectral analysis of airframe noise of an aircraft model A320/A321},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California (USA), 23-25 May 2005,},
  year = {2005},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO05_1140/PV2005_2809.pdf}
}
Blacodon D, Caplot M and Élias G (1989), "Source localization technique for impulsive multiple sources", Journal of Aircraft. Vol. 26(2), pp. 154-156.
Abstract: An improved multimicrophone array technique for the localization of helicopter rotor impulsive noise sources is described and validated by experiment. Two types of data processing are presented: a linear beam forming method and a multiplicative method. For a single source, both techniques give good results, but in the case of multiple-point sources, only the multiplicative method is sufficiently accurate. The multiplicative processing is applied to a helicopter rotor noise test in the CEPRA19 anechoic wind tunnel. In the experiment the rotor blades are equipped with pressure transducers to give the blade/vortex interaction loci. Comparison between the array technique and the measured values presents good agreement when the flow effects (i.e., convection and refraction) are taken into account.
BibTeX:
@article{Blacodon_etal1989,
  author = {Blacodon, D. and Caplot, M. and Élias, G.},
  title = {Source localization technique for impulsive multiple sources},
  journal = {Journal of Aircraft},
  year = {1989},
  volume = {26},
  number = {2},
  pages = {154--156},
  doi = {10.2514/3.45737}
}
Blacodon D, Caplot M and Élias G (1987), "A source localization technique for helicopter rotor noise", In 11th Aeroacoustics Conference, Sunnyvale, CA., AIAA-1987-2743., Oct, 1987.
Abstract: A multimicrophone array technique for the localization of helicopter rotor impulsive noise sources is developed and applied here to the acoustic radiation of blade-vortex interaction. To isolate correctly the phenomenon, the analysis is made in the time domain rather than in the frequency one. Two kinds at array processing are presented: a linear beamforming and a multiplicative processing. For the case of a simple source, both techniques give good results. But in the case of multiple point sources, only the second processing is accurate: the linear beamforming cannot detect two sources which are closely spaced, especially if their amplitudes are different. Comparisons of computed siaulations with an anechoic chamber experiment show a very good agreement. Finally. the multiplicative processing is applied to a helicopter rotor noise test in the CEPRA 19 anechoic wind tunnel. In this experiment. the rotor blades were equipped with blade pressure transducers which give the blade-vortex interaction loci. Comparison, for one interaction. between the array technique and the measured values presents a good agreement, when the flow effects (i.e. convection and refraction) are taken into account.
BibTeX:
@inproceedings{Blacodon1987a,
  author = {Blacodon, D. and Caplot, M. and Élias, G.},
  title = {A source localization technique for helicopter rotor noise},
  booktitle = {11th Aeroacoustics Conference, Sunnyvale, CA},
  year = {1987}
}
Blacodon D, Caplot and Élias G (1989), "Source localization technique for impulsive multiple sources", Journal of Aircraft. Vol. 26(2), pp. 154-156.
BibTeX:
@article{Blacodon_etal1998,
  author = {Blacodon, D. and Caplot and Élias, G.},
  title = {Source localization technique for impulsive multiple sources},
  journal = {Journal of Aircraft},
  year = {1989},
  volume = {26},
  number = {2},
  pages = {154--156},
  doi = {10.2514/3.45737}
}
Blacodon D, Caplot and Élias G (1987), "A source localization technique for helicopter rotor noise", Journal of Aircraft., In 11th AIAA Aeroacoustics Conference, Sunnyvale, CA, 19--21 October 1987.
Abstract: A multimicrophone array technique for the localization of helicopter rotor impulsive noise sources is developed and applied here to the acoustic radiation of blade-vortex interaction. To isolate correctly the phenomenon, the analysis is made in the time domain rather than in the frequency one. Two kinds of array processing are presented: a linear beam forming and a multiplicative processing. For the case of a simple source, both techniques give good results. But in the case of multiple-point sources, only the second processing is accurate; the linear beam forming cannot detect two sources which are closely spaced. Comparisons of computed simulations with an anechoic chamber experiment show a very good agreement. Finally, the multiplicative processing is applied to a helicopter rotor noise test in the CEPRA 19 anechoic wind tunnel. In this experiment, the rotor blades were equipped with blade pressure transducers which give the blade-vortex interaction loci. Comparison, for one interaction, between the array technique and the measured values presents a good agreement, when the flow effects (i.e., convection and refraction) are taken into account.
BibTeX:
@inproceedings{Blacodon1987,
  author = {Blacodon, D. and Caplot and Élias, G.},
  title = {A source localization technique for helicopter rotor noise},
  booktitle = {11th AIAA Aeroacoustics Conference, Sunnyvale, CA, 19--21 October 1987},
  journal = {Journal of Aircraft},
  year = {1987},
  doi = {10.2514/6.1987-2743}
}
Blacodon D and Élias G (2004), "Level Estimation of Extended Acoustic Sources Using a Parametric Method", Journal of Aircraft. Vol. 41, pp. 1360-1369.
Abstract: Array processing is a powerful tool to extract the noise source characteristics from the acoustic signals measured during wind-tunnels tests. For many years, this measurement technology is commonly being used to study airframe noise. Conventional beam forming methods have proven their efficiency in source localization, but it is well known that they are limited in the estimation of the power levels of extended sources. An approach based on a spectral estimation method (SEM) is proposed in order to determine the actual sound-pressure levels of the acoustic sources found by the localization method. The SEM is based on the array cross-spectral matrix, which contains an indirect measurement of the source power levels of interest and on a modeling of this matrix. Optimal estimates of the actual source power levels can be obtained by minimizing the mean square error between the measurement and model matrices. However, the direct minimization suffers from the sensitivity to noise inherent in the ill-posed nature of the problem. To obtain meaningful results, the problem is regularized by using a priori information. Numerical simulations involving multiple source areas are provided to illustrate the effectiveness of the estimation procedure. The method is successfully applied to compute the power levels of the main sources on a 1/11th-scaled model of the Airbus A320/A321 tested in CEPRA 19 wind tunnel.
BibTeX:
@article{BlacodonElias2004,
  author = {Blacodon, D. and Élias, G.},
  title = {Level Estimation of Extended Acoustic Sources Using a Parametric Method},
  journal = {Journal of Aircraft},
  year = {2004},
  volume = {41},
  pages = {1360--1369},
  doi = {10.2514/1.3053}
}
Blacodon D and Élias G (2003), "Level Estimation of Extended Acoustic Sources Using an Array of Microphones", In 9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003., AIAA-2003-3199., May, 2003.
Abstract: Array Processing ( AP ) is a powerful tool to extract the noise source characteristics from the signals that are measured during tests performed in wind tunnel facility. This kind of means of investigation has been intensively used to study the airframe noise generated by a 1/11th scaled model Airbus A320/A321 during an experiment conducted in the CEPRA 19 anechoic wind tunnel. In particular, a Localization Method (LM ) has allowed to identity the main noise sources on the aircraft model with a good accuracy. This paper proposes a Spectral Estimation Method (SEM ) in order to associate the actual Power Spectral Density ( PSD ) of the acoustic sources found by the LM . The SEM is based on the measurement of the Cross-Spectral Density Matrix (CSDM ) which contains the PSD of interest and on a model of this matrix. A minimization of the mean square error between the two CSDM is adopted to obtain the estimates of the actual PSD . However, the direct minimization may lead to non acceptable PSD . The a priori knowledge on the positivity of the PSD is incorporated in the algorithm to compute the desired solutions. Numerical and experimental results demonstrate the effectiveness of the estimation procedure.
BibTeX:
@inproceedings{BlacodonElias2003,
  author = {Blacodon, D. and Élias, G.},
  title = {Level Estimation of Extended Acoustic Sources Using an Array of Microphones},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003}
}
Blacodon D, Élias G, Prieur J and Papillier D (2004), "Noise Source Localization on a Dauphin Helicopter in Flight", Journal of the American Helicopter Society. Vol. 49(4), pp. 425-435.
Abstract: A flight test campaign with a Dauphin helicopter has been conducted by ONERA, in cooperation with Istres Flight Test Center (CEV). The objective was to investigate the possibility of localizing the noise sources radiated by the helicopter from measurements performed with an array of ground fixed microphones. This study is based on a method that works in frequency domain to successfully localize the airframe noise sources on an aircraft in flight. The acoustic sources identified in this framework are localized on the main rotor disk or on the fenestron depending on the frequency band and on the flight conditions. The results demonstrate the effectiveness of the method. Particularly the method has been applied to localize the blade vortex interaction noise sources that are dominant during descending flight. The results obtained for this flight condition are compared with the locations found by another method in the time domain from data collected with on-board microphones. Both methods give consistent source distributions on the main rotor disk.
BibTeX:
@article{Blacodon_etal2004,
  author = {Blacodon, D. and Élias, G. and Prieur, J. and Papillier, D.},
  title = {Noise Source Localization on a Dauphin Helicopter in Flight},
  journal = {Journal of the American Helicopter Society},
  year = {2004},
  volume = {49},
  number = {4},
  pages = {425--435},
  doi = {10.4050/JAHS.49.425}
}
Blake WK and Donovan P (2008), "A New Road-Side Array-.Based Method for Characterization of Truck Noise During Passby", In Proc. NoiseCon 2008/ASME NCAD, Dearborn, Mich., American Society of Mechanical Engineers, July 2008.., Paper NCAD2008-73056., July, 2008.
BibTeX:
@inproceedings{BlakeDonovan2008a,
  author = {Blake, W. K. and Donovan, P.},
  title = {A New Road-Side Array-.Based Method for Characterization of Truck Noise During Passby},
  booktitle = {Proc. NoiseCon 2008/ASME NCAD, Dearborn, Mich., American Society of Mechanical Engineers, July 2008.},
  year = {2008},
  note = {Proc. NoiseCon 2008/ASME NCAD, Dearborn, Mich., American Society
of Mechanical Engineers, July 2008.} }
Blumrich R and J. A (2000), "Medium-range localisation of aircraft via triangulation", Applied Acoustics. Vol. 61, pp. 65-82.
BibTeX:
@article{BlumrichAltmann00,
  author = {Blumrich, R. and Altmann J.},
  title = {Medium-range localisation of aircraft via triangulation},
  journal = {Applied Acoustics},
  year = {2000},
  volume = {61},
  pages = {65--82}
}
Böhning P and Michel U (2004), "Study on Source Localisation Techniques using circular and linear Microphone Arrays, Automatic Source Breakdown Methods and Array Design." (92517-04/B10)
BibTeX:
@techreport{BoehningMichel2004,
  author = {Böhning, P. and Michel, U.},
  title = {Study on Source Localisation Techniques using circular and linear Microphone Arrays, Automatic Source Breakdown Methods and Array Design.},
  year = {2004},
  number = {92517-04/B10}
}
Böhning P and Siller H (2007), "Study of a de-convolution method for aircraft flyover measurements", In 13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007., AIAA-2007-3474., May, 2007.
Abstract: Noise source distributions calculated using beamforming methods are biased by properties of the array and the processing algorithm such as the beamwidth or spatial sidelobes. De-convolution methods are able to compensate for these characteristics and make the interpretation of the results easier. However, when de-convolution methods are applied to moving sources, additional difficulties arise. These are, for example, the spectral spreading of the point spread function and the very short averaging times. In this study, the specific problems with the analysis of moving sources are addressed. A point spread function for moving sources is formulated and applied to the simple de-convolution method CLEAN. In the analysis of flyover measurement data of an Airbus A320, this method significantly improves the quality of the source distributions. The modified point spread functions are also successfully tested with the DAMAS algorithm for simulated moving point sources.
BibTeX:
@inproceedings{BoehningSiller2007,
  author = {Böhning, P. and Siller, H.},
  title = {Study of a de-convolution method for aircraft flyover measurements},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007},
  year = {2007}
}
Böhning P, Siller H, Holland K, Arnold F, Kempton A and Michel U (2006), "Novel Methods for Acoustic Indoor Measurements and Applications in Aero-Engine Test Cells", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-04., November, 2006. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The research institutes DLR in Germany and ISVR in Great Britain are developing together with Rolls-Royce, one of the major aero-engine manufacturers, methods for acoustic indoor measurements. These methods will allow acoustic tests to be performed in semi-reverberant aero-engine test cells. Currently, static noise tests are performed on open-air test beds in order to ensure free-field condition. However, open-air tests are prone to delays due to unfavorable whether conditions. Also, expensive noise protection installations might be required if the test bed is located close to communities. The presentation first introduces two novel methods developed by DLR and ISVR. Their effectiveness will be demonstrated using the results obtained in simulations and in experiments using loud speakers as noise sources. Both methods will be verified by comparing the radiated far-field noise of a Rolls-Royce BR715 engine measured under free field conditions and the far-field noise estimated from measurements taken in one of the standard development and production pass off test beds at Rolls-Royce Deutschland in Dahlewitz. This final test is going to be performed under the framework of the German research project LEXMOS.
BibTeX:
@inproceedings{Boehning_etal2006,
  author = {Böhning, P. and Siller, H. and Holland, K. and Arnold, F. and Kempton, A. and Michel, U.},
  title = {Novel Methods for Acoustic Indoor Measurements and Applications in Aero-Engine Test Cells},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-04_Boehning_Siller_etal.pdf}
}
Bondant L and Malbequi P (1994), "Localisation de sources acoustiques complexes par antenne focalisee a l'aide d'un modele a deux sources. (Localization of complex acoustic sources using an antenna focused with the aid of a two-source model.)"
BibTeX:
@techreport{BondantMalbequi94,
  author = {Bondant, Luc and Malbequi, Patrice},
  title = {Localisation de sources acoustiques complexes par antenne focalisee a l'aide d'un modele a deux sources. (Localization of complex acoustic sources using an antenna focused with the aid of a two-source model.)},
  year = {1994}
}
Boone MM and Berkhout AJ (1984), "Theory and Application of a High-Resolution Synthetic Acoustic Antenna for Industrial Noise Measurements", Noise Control Engineering Journal. Vol. 23, pp. 60-68.
BibTeX:
@article{BooneBerkhout1984,
  author = {Boone, M. M. and Berkhout, A. J.},
  title = {Theory and Application of a High-Resolution Synthetic Acoustic Antenna for Industrial Noise Measurements},
  journal = {Noise Control Engineering Journal},
  year = {1984},
  volume = {23},
  pages = {60--68}
}
Boone MM, Kinneging N and van den Dool T (2000), "Two-dimensional noise source imaging with a T-shaped microphone cross array", J. Acoust. Soc. Am.., December, 2000. Vol. 108(6), pp. 2884-2890.
Abstract: Spatial cross-correlation beamsteering with a T-shaped sparse array can provide an efficient procedure to identify the directions and to obtain the emission levels of multiple uncorrelated noise sources. The procedure can be applied to stationary or moving sources. It provides two-dimensional image resolution equivalent to that of a full array, but requires significantly fewer microphones. This results in substantially reduced requirements for data acquisition and signal processing, with a material cost reduction. Simulation, laboratory measurement, and field measurement of a train moving at high speed illustrate application of the procedure.
BibTeX:
@article{Boone_etal2000,
  author = {Boone, M. M. and Kinneging, N. and van den Dool, T.},
  title = {Two-dimensional noise source imaging with a T-shaped microphone cross array},
  journal = {J. Acoust. Soc. Am.},
  year = {2000},
  volume = {108},
  number = {6},
  pages = {2884--2890}
}
Booth E and Humphreys W (2005), "Tracking and Characterization of Aircraft Wakes Using Acoustic and Lidar Measurements", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-2964., May, 2005.
Abstract: Data from the 2003 Denver International Airport Wake Acoustics Test are further examined to discern spectral content of aircraft wake signatures, and to compare three dimensional wake tracking from acoustic data to wake tracking data obtained through use of continuous wave and pulsed lidar. Wake tracking data derived from acoustic array data agree well with both continuous wave and pulsed lidar in the horizontal plane, but less well with pulsed lidar in the vertical direction. Results from this study show that the spectral distribution of acoustic energy in a wake signature varies greatly with aircraft type.
BibTeX:
@inproceedings{BoothHumphreys2005,
  author = {Booth, E. and Humphreys, W.},
  title = {Tracking and Characterization of Aircraft Wakes Using Acoustic and Lidar Measurements},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Brühl S and Röder A (2000), "Acoustic noise source modelling based on microphone array measurements", J. Sound Vib.. Vol. 231, pp. 611-617.
BibTeX:
@article{Bruhl2000,
  author = {Brühl, S. and Röder, A.},
  title = {Acoustic noise source modelling based on microphone array measurements},
  journal = {J. Sound Vib.},
  year = {2000},
  volume = {231},
  pages = {611--617}
}
Brühl S and Schmitz K-P (1993), "Noise Source Localization on Highspeed Trains Using Different Array Types", In Proceedings of Internoise 93. , pp. 1311-1314.
BibTeX:
@inproceedings{BruehlSchmitz93,
  author = {Brühl, S. and Schmitz, K.-P.},
  title = {Noise Source Localization on Highspeed Trains Using Different Array Types},
  booktitle = {Proceedings of Internoise 93},
  year = {1993},
  pages = {1311--1314}
}
Brandes TS and Benson RH (2007), "Sound source imaging of low-flying airborne targets with an acoustic camera array", Applied Acoustics. Vol. 68(7), pp. 752-765.
Abstract: Two-dimensional images of sound source distribution from near-ground airborne sounds are created using an array of 32 microphones and time-domain beamforming. The signal processing is described and array configurations spanning a square area with a side length of 3.45 m, approximately five wavelengths for a 500 Hz sound, are examined. Simulations of a 32-element under-populated log6 × log6 spaced array are given for sound sources centered over the array at 250 Hz, 500 Hz, and 1000 Hz. Stochastically optimized array geometry with a simulated annealing algorithm is discussed and a 32-element array optimized for a 500 Hz source is given along with a simulated image for direct comparison with the log6 spaced array. Images from field testing a 32-element under-populated log6 × log6 spaced array are provided for a small aircraft flyover. Results show that this type of acoustic camera generates accurate images of sound source location. Suggested uses include monitoring small aircraft flying too low to be detected by radar as well as monitoring ecological events, such as bird migration.
BibTeX:
@article{BrandesBenson2007,
  author = {Brandes, T. S. and Benson, R. H.},
  title = {Sound source imaging of low-flying airborne targets with an acoustic camera array},
  journal = {Applied Acoustics},
  year = {2007},
  volume = {68},
  number = {7},
  pages = {752--765},
  doi = {10.1016/j.apacoust.2006.04.009}
}
Brick H, Kohrs T, Sarradj E and Geyer T (2011), "Noise from high-speed trains: Experimental determination of the noise radiation of the pantograph", In Forum Acusticum 2011, Aalborg.
BibTeX:
@inproceedings{Brick2011,
  author = {Brick, H. and Kohrs, T. and Sarradj, E. and Geyer, T.},
  title = {Noise from high-speed trains: Experimental determination of the noise radiation of the pantograph},
  booktitle = {Forum Acusticum 2011, Aalborg},
  year = {2011}
}
Brooks T, Humphreys Jr WM and Plassman GE (2010), "DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory", In 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010., AIAA-2010-3780., June, 2010.
Abstract: A jet noise measurement study was conducted using a phased microphone array system for a range of jet nozzle configurations and flow conditions. The test effort included convergent and convergent/divergent single flow nozzles, as well as conventional and chevron dual-flow core and fan configurations. Cold jets were tested with and without wind tunnel co-flow, whereas, hot jets were tested only with co-flow. The intent of the measurement effort was to allow evaluation of new phased array technologies for their ability to separate and quantify distributions of jet noise sources. In the present paper, the array post-processing method focused upon is DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) for the quantitative determination of spatial distributions of noise sources. Jet noise is highly complex with stationary and convecting noise sources, convecting flows that are the sources themselves, and shock-related and screech noise for supersonic flow. The analysis presented in this paper addresses some processing details with DAMAS, for the array positioned at 90° (normal) to the jet. The paper demonstrates the applicability of DAMAS and how it indicates when strong coherence is present. Also, a new approach to calibrating the array focus and position is introduced and demonstrated.
BibTeX:
@inproceedings{Brooks_etal2010,
  author = {Brooks, T. and Humphreys, Jr, W. M. and Plassman, G. E.},
  title = {DAMAS Processing for a Phased Array Study in the NASA Langley Jet Noise Laboratory},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010},
  year = {2010}
}
Brooks TF and Humphreys Jr WM (2006), "A deconvolution approach for the mapping of acoustic sources (DAMAS) determined from phased microphone array", J. Sound Vib.., July, 2006. Vol. 294(4-5), pp. 856-879.
Abstract: Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic sources. Traditional array results represent noise sources that are convolved with array beamform response functions, which depend on array geometry, size (with respect to source position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent noise sources. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift airframe component noise studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration sources. Presentations are explicit and straightforward, as the noise radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.
BibTeX:
@article{BrooksHumphreys2006,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {A deconvolution approach for the mapping of acoustic sources (DAMAS) determined from phased microphone array},
  journal = {J. Sound Vib.},
  year = {2006},
  volume = {294},
  number = {4-5},
  pages = {856--879},
  doi = {10.1016/j.jsv.2005.12.046}
}
Brooks TF and Humphreys Jr WM (2006), "Extension of DAMAS Phased Array Processing for Spatial Coherence Determination (DAMAS-C)", In 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2654.
Abstract: The present study reports a new development of the DAMAS microphone phased array processing methodology that allows the determination and separation of coherent and incoherent noise source distributions. In 2004, a Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) was developed which decoupled the array design and processing influence from the noise being measured, using a simple and robust algorithm. In 2005, three-dimensional applications of DAMAS were examined. DAMAS has been shown to render an unambiguous quantitative determination of acoustic source position and strength. However, an underlying premise of DAMAS, as well as that of classical array beamforming methodology, is that the noise regions under study are distributions of statistically independent sources. The present development, called DAMAS-C, extends the basic approach to include coherence definition between noise sources. The solutions incorporate cross-beamforming array measurements over the survey region. While the resulting inverse problem can be large and the iteration solution computationally demanding, it solves problems no other technique can approach. DAMAS-C is validated using noise source simulations and is applied to airframe flap noise test results.
BibTeX:
@inproceedings{BrooksHumphreys2006a,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {Extension of DAMAS Phased Array Processing for Spatial Coherence Determination (DAMAS-C)},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference, Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006}
}
Brooks TF and Humphreys Jr WM (2005), "Three-Dimensional Applications of DAMAS Methodology for Aeroacoustic Noise Source Definition", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-2960.
Abstract: At the 2004 AIAA/CEAS Aeroacoustic Conference, a breakthrough in acoustic microphone array technology was reported by the authors. A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) was developed which decouples the array design and processing influence from the noise being measured, using a simple and robust algorithm. For several prior airframe noise studies, it was shown to permit an unambiguous and accurate determination of acoustic source position and strength. As a follow-on effort, this paper examines the technique for three-dimensional (3D) applications. First, the beamforming ability for arrays, of different size and design, to focus longitudinally and laterally is examined for a range of source positions and frequency. Advantage is found for larger array designs with higher density microphone distributions towards the center. After defining a 3D grid generalized with respect to the array’s beamforming characteristics, DAMAS is employed in simulated and experimental noise test cases. It is found that spatial resolution is much less sharp in the longitudinal direction in front of the array compared to side-to-side lateral resolution. 3D DAMAS becomes useful for sufficiently large arrays at sufficiently high frequency. But, such can be a challenge to computational capabilities, with regard to the required expanse and number of grid points. Also, larger arrays can strain basic physical modeling assumptions that DAMAS and all traditional array methodologies use. An important experimental result is that turbulent shear layers can negatively impact attainable beamforming resolution. Still, the usefulness of 3D DAMAS is demonstrated by the measurement of landing gear noise source distributions in a difficult hard-wall wind tunnel environment.
BibTeX:
@inproceedings{BrooksHumphreys2005,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {Three-Dimensional Applications of DAMAS Methodology for Aeroacoustic Noise Source Definition},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Brooks TF and Humphreys Jr WM (2004), "A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) Determined from Phased Microphone Arrays", In 10th AIAA/CEAS Aeroacoustics Conference, Manchester, Great Britain, May 10-12, 2004., AIAA-2004-2954.
Abstract: Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic sources. Traditional array results represent noise sources that are convolved with array beamform response functions, which depend on array geometry, size (with respect to source position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent noise sources. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift airframe component noise studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration sources. Presentations are explicit and straightforward, as the noise radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.
BibTeX:
@inproceedings{BrooksHumphreys2004,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {A Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) Determined from Phased Microphone Arrays},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference, Manchester, Great Britain, May 10-12, 2004},
  year = {2004}
}
Brooks TF and Humphreys Jr WM (2003), "Flap-edge aeroacoustic measurements and predictions", J. Sound Vib.., March, 2003. Vol. 261(1), pp. 31-74.
Abstract: An aeroacoustic model test has been conducted to investigate the mechanisms of sound generation on high-lift wing configurations. This paper presents an analysis of flap side-edge noise, which is often the most dominant source. A model of a main element wing section with a half-span flap was tested at low speeds of up to a Mach number of 0.17, corresponding to a wing chord Reynolds number of approximately 1.7 million. Results are presented for flat (or blunt), flanged, and round flap-edge geometries, with and without boundary-layer tripping, deployed at both moderate and high flap angles. The acoustic database is obtained from a small aperture directional array (SADA) of microphones, which was constructed to electronically steer to different regions of the model and to obtain farfield noise spectra and directivity from these regions. The basic flap-edge aerodynamics is established by static surface pressure data, as well as by computational fluid dynamics (CFD) calculations and simplified edge flow analyses. Distributions of unsteady pressure sensors over the flap allow the noise source regions to be defined and quantified via cross-spectral diagnostics using the SADA output. It is found that shear layer instability and related pressure scatter is the primary noise mechanism. For the flat edge flap, two noise prediction methods based on unsteady-surface-pressure measurements are evaluated and compared to measured noise. One is a new causality spectral approach developed here. The other is a new application of an edge-noise scatter prediction method. The good comparisons for both approaches suggest that the prediction models capture much of the physics. Areas of disagreement appear to reveal when the assumed edge noise mechanism does not fully define the noise production. For the different edge conditions, extensive spectra and directivity are presented. The complexity of the directivity results demonstrate the strong role of edge source geometry and frequency in the noise radiation. Significantly, for each edge configuration, the spectra for different flow speeds, flap angles, and surface roughness were successfully scaled by utilizing aerodynamic performance and boundary-layer scaling methods developed herein.
BibTeX:
@article{BrooksHumphreys2003,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {Flap-edge aeroacoustic measurements and predictions},
  journal = {J. Sound Vib.},
  year = {2003},
  volume = {261},
  number = {1},
  pages = {31--74},
  doi = {10.1016/S0022-460X(02)00939-2}
}
Brooks TF and Humphreys Jr WM (1999), "Effect of Directional Array Size on the Measurement of Airframe Noise Components", In Fifth AIAA/CEAS Aeroacoustics Conference, May 10-12, 1999, Bellevue, Washington., AIAA-1999-1958.
Abstract: A study was conducted to examine the effects of overall size of directional (or phased) arrays on the measurement of aeroacoustic components. An airframe model was mounted in the potential core of an open-jet windtunnel, with the directional arrays located outside the flow in an anechoic environment. Two array systems were used; one with a solid measurement angle that encompasses 31.6° of source directivity and a smaller one that encompasses 7.2°. The arrays, and sub-arrays of various sizes, measured noise from a calibrator source and flap edge model setups. In these cases, noise was emitted from relatively small, but finite size source regions, with intense levels compared to other sources. Although the larger arrays revealed much more source region detail, the measured source levels were substantially reduced due to finer resolution compared to that of the smaller arrays. To better understand the measurements quantitatively, an analytical model was used to define the basic relationships between array to source region sizes and measured output level. Also, the effect of noise scattering by shear layer turbulence was examined using the present data and those of previous studies. Taken together, the two effects were sufficient to explain spectral level differences between arrays of different sizes. An important result of this study is that total (integrated) noise source levels are retrievable and the levels are independent of the array size as long as certain experimental and processing criteria are met. The criteria for both open and closed tunnels are discussed. The success of special purpose diagonal-removal processing in obtaining integrated results is apparently dependent in part on source distribution. Also discussed is the fact that extended sources are subject to substantial measurement error, especially for large arrays.
BibTeX:
@inproceedings{BrooksHumphreys1999,
  author = {Brooks, T. F. and Humphreys, Jr, W. M.},
  title = {Effect of Directional Array Size on the Measurement of Airframe Noise Components},
  booktitle = {Fifth AIAA/CEAS Aeroacoustics Conference, May 10-12, 1999, Bellevue, Washington},
  year = {1999},
  doi = {10.1.1.31.2108}
}
Brooks TF, Marcolini MA and Pope DS (1987), "A Directional Array Approach for the Measurement of Rotor Noise Source Distributions with Controlled Spatial Resolution", J. Sound Vib.. Vol. 112, pp. 192-197.
BibTeX:
@article{Brooks_etal1987,
  author = {Brooks, T. F. and Marcolini, M. A. and Pope, D. S.},
  title = {A Directional Array Approach for the Measurement of Rotor Noise Source Distributions with Controlled Spatial Resolution},
  journal = {J. Sound Vib.},
  year = {1987},
  volume = {112},
  pages = {192--197},
  doi = {10.1016/S0022-460X(87)80105-0}
}
Brühl S (1997), "Source Density Modelization of 2D Array Measurement Data", March, 1997. (1F 7M11 T1.DB (DeuFraKo, Annex K2))
BibTeX:
@techreport{Bruehl1997a,
  author = {Brühl, S.},
  title = {Source Density Modelization of 2D Array Measurement Data},
  year = {1997},
  number = {1F 7M11 T1.DB (DeuFraKo, Annex K2)}
}
Brühl S and Röder A (2000), "Acoustic noise source modelling based on microphone array measurements", J. Sound Vib.. Vol. 231(3), pp. 611-617.
Abstract: A method will be presented which allows a construction of an acoustic source model based on the analysis of microphone array measurements during a train pass-by. The conventional array beam-forming technique is used as a kind of pre-processing or first order analysis to calculate in a second step the true source strengths by a back-projection method. The final equation to be solved connects the source power distribution on the vehicle surface with the measured microphone array amplitudes via a Green's function transfer matrix. By these means the side-lobe effects of the array characteristics as well as the Doppler frequency shift and amplitude augmentation of the sources are removed. The model is updated for consecutive time slices during the pass-by so that it is possible to study directional and time-dependent effects on the source characteristics. The method has been applied to measurements on the ICE-V train where three known artificial noise sources (loudspeakers) had been mounted on the outside of the sidewall. The source power distribution function gives a much better source separation than the conventional beam-forming result. The calculated source strengths show a good agreement with the true values.
BibTeX:
@article{BruehlRoeder2000,
  author = {Brühl, S. and Röder, A.},
  title = {Acoustic noise source modelling based on microphone array measurements},
  journal = {J. Sound Vib.},
  year = {2000},
  volume = {231},
  number = {3},
  pages = {611--617},
  doi = {10.1006/jsvi.1999.2548}
}
Brühl S and Schmitz K-P (1993), "Noise Source Localization on Highspeed Trains Using Different Array Types", In Proceedings of Internoise 93. , pp. 1311-1314.
BibTeX:
@inproceedings{BruehlSchmitz1993,
  author = {Brühl, S. and Schmitz, K.-P.},
  title = {Noise Source Localization on Highspeed Trains Using Different Array Types},
  booktitle = {Proceedings of Internoise 93},
  year = {1993},
  pages = {1311--1314}
}
Brusniak L (2008), "DAMAS2 validation for flight test airframe noise measurements", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-11. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The DAMAS2 algorithm is a deconvolution method which can be used to quantify aircraft noise subcomponent spectral levels obtained using phased array measurements. This paper examines the effectiveness of the DAMAS2 algorithm for accurately determining flight test aircraft noise subcomponent spectral levels. First, the DAMAS2 subcomponent spectral levels are shown to be qualitatively correct through comparison with the expected behavior as seen in the phased array beamform maps. The DAMAS2 spectra are then compared to sample output from the original DAMAS algorithm and are seen to be generally within 0.1 dB of DAMAS algorithm spectral levels. Lastly, the shape of the cumulative DAMAS2 spectral levels are compared with single microphone spectra and are seen to be in very good agreement. The DAMAS2 algorithm is seen to be an effective tool for flight test aircraft noise subcomponent spectral measurement.
BibTeX:
@inproceedings{Brusniak2008,
  author = {Brusniak, L.},
  title = {DAMAS2 validation for flight test airframe noise measurements},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-11_Brusniak.pdf}
}
Brusniak L, Shur ML and Spalart PR (2006), "Phased-Array Imaging of Jet Noise Sources in a Large-Eddy Simulation", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), 8 - 10 May 2006, Cambridge, Massachusetts., AIAA-2006-2444., May, 2006.
Abstract: Time-series pressure data were saved on a surface in the near acoustic region of the Large-Eddy Simulation (LES) of a Mach 0.9 round-nozzle jet-flow. The data amount to sampling from an ideal acoustic phased array (with zero self noise and perfect frequency response, within the known limitations of the LES). The data were converted into crossspectral matrices and beamformed using frequency-domain conventional beamforming as in experiments. Only a small sub-set of the points available from the LES has been used so far. The results demonstrate the feasibility of obtaining beamformer acoustic maps using LES solution pressure time series data. Potential benefits of this type of exercise include, but are not limited to: a) improved phased-array designs for given test configurations; b) improved array-processing algorithms; c) improved understanding of processing algorithm output (beamform maps) and relationship to flowfield; d) insight into the physics of the flowfield; and e) insight into possible flaws of the LES. The paper describes the procedure used for obtaining the beamformed data and the various issues which need to be addressed in this type of approach.
BibTeX:
@inproceedings{Brusniak_etal2006a,
  author = {Brusniak, L. and Shur, M. L. and Spalart, P. R.},
  title = {Phased-Array Imaging of Jet Noise Sources in a Large-Eddy Simulation},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), 8 - 10 May 2006, Cambridge, Massachusetts},
  year = {2006}
}
Brusniak L, Underbrink J and Stoker R (2006), "Acoustic Imaging of Aircraft Noise Sources Using Large Aperture Phased Arrays", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2715., May, 2006.
Abstract: Increased restrictions on large commercial aircraft noise levels during takeoff and approach have spawned increased interest in the localization of subcomponent noise sources and quantification of their levels. Landing gear are the dominant sources of airframe noise during approach, with additional contributions from deployed slats, flaps, flaperons and so on. Jet noise, of course, dominates during takeoff. The acoustic phased array is a powerful flight test tool for imaging the noise sources on the aircraft. The acoustic phased array is a spatially distributed set of microphones which simultaneously sample the acoustic field. By appropriately time delaying the output of individual microphones, the origin and level of a given noise source can potentially be determined. The success of this approach depends largely on 1) the actual character of the source (monopole, dipole, etc.), 2) the phased array design, and 3) the array data processing method. This paper focuses on aspects of the latter two areas. The objectives of this paper are to a) present the flight test benefits accrued using large aperture phased arrays and, b) examine the utility of recently developed array processing methods for quantifying flight test aircraft subcomponent noise source levels.
BibTeX:
@inproceedings{Brusniak_etal2006b,
  author = {Brusniak, L. and Underbrink, J. and Stoker, R.},
  title = {Acoustic Imaging of Aircraft Noise Sources Using Large Aperture Phased Arrays},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006}
}
Brusniak L, Underbrink JR, Nesbitt E, Lynch D and Martinez M (2007), "Phased Array Measurements of Full-Scale Engine Exhaust Noise", AIAA-2007-3612., May, 2007.
Abstract: Three configurations of ground-mounted microphones have been used to obtain phased array measurements of the exhaust noise from a full-scale GE90-115B engine. The configurations included the standard 150-foot polar arc array present at all static engine acoustic tests, a second, linear distribution of microphones designed to localize and quantify the jet noise sources at and downstream of the exhaust nozzles, and a third, multi-arm logspiral array designed to resolve the fan and core exhaust noise sources at the nozzle exits. These data represent perhaps the most extensive and comprehensive collection of phased array measurements of full-scale engine exhaust noise ever acquired. The present results focus exclusively on baseline nozzle measurements made at a high engine power level setting. The arc array is shown to provide basic information on jet noise source structure. The log spiral array is shown to be capable of resolving the fan and core exhaust noise sources at the nozzle exits. The linear array is shown to provide the capability for describing the variation in jet noise source location with temporal frequency and emission angle. This paper seeks to illustrate the benefits and numerous challenges associated with the use of this powerful technology within the complexities of a full-scale test.
BibTeX:
@inproceedings{Brusniak_etal2007,
  author = {Brusniak, L. and Underbrink, J. R. and Nesbitt, E. and Lynch, D. and Martinez, M.},
  title = {Phased Array Measurements of Full-Scale Engine Exhaust Noise},
  year = {2007}
}
Burnside N, Jaeger S, Reinero B, Horne W and Soderman P (2002), "Array Design and Performance for a Large Scale Airframe Noise Study", In 8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2576., June, 2002.
Abstract: Two phased microphone arrays were developed for an aeroacoustic test of a 26 % scale model of a Boeing 777 commercial airliner. Model size and a broad frequency range of interest required that two custom arrays be used in tandem during the STAR (Subsonic Transport Aeroacoustic Research) test. A 70-microphone, 244 cm (96 in) array provided a spatial resolution of 3.4 λ with moderate sidelobes under 10 kHz. A smaller 102 cm (40 in) traversing array was used to measure source directivity and provide accurate sound pressure levels with a useful range of 1 to 25 kHz and a spatial resolution of 6.5 λ . The acoustic performance of both arrays was optimized using a simulated annealing method to minimize sidelobe levels and beamwidth. Both arrays used a recessed microphone Kevlar™ drumhead design to reduce microphone self-noise. Recessing the array below Kevlar™ reduces background noise by as much as 20 dB by isolating the microphones from the turbulent boundary layer. The array data must be corrected for effects of the resonance created between the array plates and the Kevlar™. Broadband speaker sources as well as airframe noise sources were used to evaluate the effectiveness of the two phased arrays. Numerous airframe noise sources and noise reduction technologies were thoroughly documented using these two custom arrays in the large-scale STAR test.
BibTeX:
@inproceedings{Burnside_etal2002,
  author = {Burnside, N. and Jaeger, S. and Reinero, B. and Horne, W. and Soderman, P.},
  title = {Array Design and Performance for a Large Scale Airframe Noise Study},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Cadula F (2011), "High Resolution Acoustic Source Localization for Aeroacoustic Arrays", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2717., June, 2011.
Abstract: This paper presents results of an alternative method for locating sound sources in acoustic imaging applications. It is named 2D-ESPRIT and possesses high resolution together with high background noise rejection. One of its chief merits is that it avoids elaborate array geometry design to achieve high resolution compared to commonly used delay-and-sum beamforming. Another important feature is that it dispenses with direction scanning to determine sound source location. Simulations are used to contrast both methods.
BibTeX:
@inproceedings{Cadula2011,
  author = {Cadula, Flavio},
  title = {High Resolution Acoustic Source Localization for Aeroacoustic Arrays},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Camargo HE, Ravetta PA, Burdisso RA and Smith AK (2009), "Application of Phased Array Technology for Identification of Low Frequency Noise Sources", Low Frequency Noise & Vibration and Active Control., December, 2009. Vol. 28(4), pp. 237-244.
Abstract: Noise Induced Hearing Loss (NIHL) is the most common occupational disease in the U.S. with devastating consequences particularly in the mining industry. A study conducted by the National Institute for Occupational Safety and Health (NIOSH) revealed that 90% of coal miners have hearing impairment by age 50, compared to only 10% of those not exposed to occupational noise. According to the Mine Safety and Health Administration (MSHA), Continuous Mining Machine (CM) operators account for 30% of workers exposed to noise doses exceeding the Permissible Exposure Level (PEL). This number becomes more dramatic considering that 49% of the total national underground coal production is extracted using these machines. In this context, NIOSH is conducting research to identify and control dominant noise sources in CMs. Previous noise source identification was performed using a Brüel &Kjær (B&K) 1.92-m diameter, 42-microphone phased array. These measurements revealed that the impacts from the conveyor chain onto the tail roller, and the impacts from the conveyor chain onto the upper deck are the dominant noise sources at the tailsection of the CM. The objectives of the work presented in this paper were: 1) To rank the noise radiated by the different sections of the conveyor, and 2) to determine the effect of a urethane-coated tail roller on the noise radiated by the tail-section. This test was conducted using an Acoustical and Vibrations Engineering Consultants (AVEC) 3.5-m diameter, 121-microphone phased array. The results from this new test show that a urethane-coated tail roller yields reductions in the tail-section of 2 to 8 dB in Sound Pressure Level in the frequency range of 1 kHz to 5 kHz. However, integration of the acoustic maps shows that the front-section and mid-section of the conveyor also contain dominant noise sources. Therefore, a urethane-coated tail roller in combination with a chain with urethane-coated flights that reduces the noise sources in the front and mid sections of the conveyor is required to yield a significant noise reduction on the CM operator's overall exposure. These results show the applicability of phased array technology for low frequency noise source identification.
BibTeX:
@article{Camargo_etal2009,
  author = {Camargo, H. E. and Ravetta, P. A. and Burdisso, R. A. and Smith, A. K.},
  title = {Application of Phased Array Technology for Identification of Low Frequency Noise Sources},
  journal = {Low Frequency Noise & Vibration and Active Control},
  year = {2009},
  volume = {28},
  number = {4},
  pages = {237--244},
  doi = {10.1260/0263-0923.28.4.237}
}
Camier C, Blais J-F and Berry A (2012), "A time-domain analysis of acoustic sources in 3D non uniform motion: Application to source identification and absolute quantification via Beamforming", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-30., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: When applying acoustical imaging techniques of wave fields produced by sources in arbitrary, high-speed motion and sampled by a fixed microphone array, it is necessary to de-dopplerise the microphone signals. A careful examination of the related literature reveals a confusion when applying Doppler formulation in term of sound pressure to a monopole source. The aim of this paper is first to carefully detail the analytical and explicit developments of the Doppler effect in term of acoustic pressure for the general case of a density distribution source in a non-uniform and non-rectilinear motion. In the case of arbitrary motion, Lorentz transform is unapplicable and Green’s function procedure seems to be the only mathematical tool. An original vectorial closed-form expression of Doppler effect in time-domain has been obtained. The acoustic pressure radiated by a moving monopole has been simulated. Back and forth propagations with other Green functions presented in the literature highlight the impact of the source signal de-dopplerisation on the recovered amplitude. The transfer function introduced in this paper is applied to Delay-And-Sum Beamforming. Although, with respect to the implemented methods, the localisation performances are unchanged. A significant effect on the amplitude is shown and studied with respect to different motion parameters.
BibTeX:
@inproceedings{Camier_etal2012,
  author = {Camier, C. and Blais, J.-F. and Berry, A.},
  title = {A time-domain analysis of acoustic sources in 3D non uniform motion: Application to source identification and absolute quantification via Beamforming},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-30.pdf}
}
Capon J (1969), "High-resolution frequency-wavenumber spectrum analysis", Proc. IEEE. Vol. 57(8), pp. 1408-1418.
Abstract: The output of an array of sansors is considered to be a homogeneous random field. In this case there is a spectral representation for this field, similar to that for stationary random processes, which consists of a superposition of traveling waves. The frequency-wavenumber power spectral density provides the mean-square value for the amplitudes of these waves and is of considerable importance in the analysis of propagating waves by means of an array of sensors. The conventional method of frequency-wavenumber power spectral density estimation uses a fixed-wavenumber window and its resolution is determined essentially by the beam pattern of the array of sensors. A high-resolution method of estimation is introduced which employs a wavenumber window whose shape changes and is a function of the wavenumber at which an estimate is obtained. It is shown that the wavenumber resolution of this method is considerably better than that of the conventional method. Application of these results is given to seismic data obtained from the large aperture seismic array located in eastern Montana. In addition, the application of the high-resolution method to other areas, such as radar, sonar, and radio astronomy, is indicated.
BibTeX:
@article{Capon1969a,
  author = {Capon, J.},
  title = {High-resolution frequency-wavenumber spectrum analysis},
  journal = {Proc. IEEE},
  year = {1969},
  volume = {57},
  number = {8},
  pages = {1408--1418}
}
Carballo-Crespo A. and Takeda K (2009), "An Investigation of Microphone Array Installation Effects", In 47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 5-8, 2009., AIAA-2009-0883., January, 2009.
Abstract: The ability to perform aeroacoustic measurements in hard-walled, closed section wind tunnels is desirable for the development of quiet aircraft, to supplement dedicated acoustic testing in open-jet anechoic facilities. One of the restrictions of such testing is the poor signal-to-noise ratio (SNR) when using arrays of microphones mounted on the wind tunnel wall. This can limit the ability to discern acoustic sources which are near, or below, the background noise level of the facility. Increasing the number of sensors can help to improve SNR. In this paper we investigate how sensor mounting details can help to improve SNR. A systematic study of microphone mounting strategies is presented. The performance of individual microphone recessing, using straight and countersunk holes, is investigated and compared with flush-mounted microphone performance. The effects of placing the microphones out of the flow by recessing the whole array behind a cloth are described. A parametric study of the effect of recess depth and cloth type has been carried out, along with the effect of adding an acoustic foam liner within the recess enclosure. Results show that recessing individual microphones by the depth of the microphone diameter (d) up to 2d can provide up to 3dB improvement. Increasing the recess depth beyond 2d provided up to 10dB improvement, with recessing to 10d depth providing up to 20dB improvement. The greatest improvements occur below 25kHz, although there is improvement across the 0 to 48kHz range. The effect of countersunk recessing was either no improvement, or an increase in the background noise level of up to 20dB, possibly due to cavity mode oscillations within the recess aperture. Significant differences in SNR were observed between Kevlar cloths of different densities, and with a silk covering. A reduction in background noise level of 5 to 10dB was observed when acoustic foam lining was added to the floor of the recessed array. Overall this study concludes that the use of recessed arrays with acoustic foam lining may significantly improve microphone array SNR in hard-walled wind tunnel testing.
BibTeX:
@inproceedings{Carballo-Crespo2009,
  author = {Carballo-Crespo, A., and Takeda, K.},
  title = {An Investigation of Microphone Array Installation Effects},
  booktitle = {47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 5-8, 2009},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMASM09_1811/PV2009_883.pdf}
}
Cariou C, Delverdier O, Paillasseur S and Lamotte L (2012), "Tool for interior noise sources detection in aircraft with comparison of configuration", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-13., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Identification of interior noise sources during flight tests becomes a necessary step in aircraft industry to improve acoustic comfort. In the case of the cabin, it can be interesting to use mobile tools such as microphones rackets to explore all corners. In many other cases, a static tool can be more efficient, for example where access is prohibited during flight, when sources are transient, or when successive flight configurations are compared. For several years Airbus and MicrodB have developed a spherical rigid antenna. It was used in trouble shooting activity and gave good results in presence of complex acoustic
field thanks to favourable scattering effect on the sphere. In order to improve at same time detection performance and ability to be used in difficult access areas, Airbus and MicrodB recently developed a new tool, based on a multi-antenna concept. It is composed of a smaller spherical antenna and extension arms. Beamforming treatments had to be adapted to this special microphones layout. Different methods were explored in order to evaluate true levels of localized sources for the different types of sources encountered and their degree of correlation. This tool was recently tested in flight and produced promising results.
BibTeX:
@inproceedings{Cariou_etal2012,
  author = {Cariou, Ch. and Delverdier, O. and Paillasseur, S. and Lamotte, L.},
  title = {Tool for interior noise sources detection in aircraft with comparison of configuration},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-13.pdf}
}
Castellini P and Martarelli M (2008), "Acoustic beamforming: Analysis of uncertainty and metrological performances", Mechanical Systems and Signal Processing., April, 2008. Vol. 22(3), pp. 672-692.
Abstract: In this paper, the metrological performances of the acoustic beamforming technique have been investigated, and in particular, its accuracy in estimating the acoustic power of sources and in localizing their spatial position has been analysed. The uncertainty of the system has been determined combining the statistical effects of input parameters uncertainty under the basic hypothesis that the sound source can be represented as a distribution of independent monopoles. This analysis was performed using a Type B approach based on an analytical model according to the ISO Guide of the expression of uncertainty in measurement and subsequently using a numerical model based on Monte Carlo simulation. Systematic errors due to deviations of input parameters (e.g. speed of sound or source–array distance), affecting output level and spatial accuracy have been analysed. Once these inaccuracies were quantified, suggestions to minimize them were given. Finally a criterion to optimize focussing of the beamforming technique based on acoustic image contrast maximization has been developed.
BibTeX:
@article{CastellinaMartarelli2008,
  author = {Castellini, P. and Martarelli, M.},
  title = {Acoustic beamforming: Analysis of uncertainty and metrological performances},
  journal = {Mechanical Systems and Signal Processing},
  year = {2008},
  volume = {22},
  number = {3},
  pages = {672--692},
  doi = {10.1016/j.ymssp.2007.09.017}
}
Chen JC, Yao K and Hudson RE (2003), "Acoustic Source Localization and Beamforming: Theory and Practice", EURASIP Journal on Applied Signal Processing. Vol. 4, pp. 359-370.
Abstract: We consider the theoretical and practical aspects of locating acoustic sources using an array of microphones. A maximum-likelihood (ML) direct localization is obtained when the sound source is near the array, while in the far-field case, we demonstrate the localization via the cross bearing from several widely separated arrays. In the case of multiple sources, an alternating projection procedure is applied to determine the ML estimate of the DOAs from the observed data. The ML estimator is shown to be effective in locating sound sources of various types, for example, vehicle, music, and even white noise. From the theoretical Cramér-Rao bound analysis, we find that better source location estimates can be obtained for high-frequency signals than low-frequency signals. In addition, large range estimation error results when the source signal is unknown, but such unknown parameter does not have much impact on angle estimation. Much experimentally measured acoustic data was used to verify the proposed algorithms.
BibTeX:
@article{Chen_etal2003,
  author = {Chen, J. C. and Yao, K. and Hudson, R. E.},
  title = {Acoustic Source Localization and Beamforming: Theory and Practice},
  journal = {EURASIP Journal on Applied Signal Processing},
  year = {2003},
  volume = {4},
  pages = {359--370},
  url = {http://downloads.hindawi.com/journals/asp/2003/926837.pdf}
}
Cho TH (2008), "Beamforming in closed test section", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-08. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The acoustic test results in the environment like closed test section may interfere with the reflected sources. A series of acoustic test with point source was conducted in KARI low speed wind tunnel with 4mx3m closed test section to find out the reflected source effect. The test was conducted with various frequency and source position. CBF method was mainly used for data analysis. Test results were compared with simulation results. Test results shows that there are errors in source poisoning under certain frequency region. The critical frequency from test results is inside the band of 1 & 2 wave length of maximum phase difference for all source position.
BibTeX:
@inproceedings{Cho2008,
  author = {Cho,Tae Hwan},
  title = {Beamforming in closed test section},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-08_Cho.pdf}
}
Choi Y-C, Park J-H, Yoon D-B and Kwon H-S (2008), "Noise source identification in a reverberant field using spherical beamforming", Modern Physics Letters B (MPLB). Vol. 22, pp. 1147-1151.
Abstract: Identification of noise sources, their locations and strengths, has been taken great attention. The method that can identify noise sources normally assumes that noise sources are located at a free field. However, the sound in a reverberant field consists of that coming directly from the source plus sound reflected or scattered by the walls or objects in the field. In contrast to the exterior sound field, reflections are added to sound field. Therefore, the source location estimated by the conventional methods may give unacceptable error. In this paper, we explain the effects of reverberant field on interior source identification process and propose the method that can identify noise sources in the reverberant field.
BibTeX:
@article{Choi_etal2008,
  author = {Choi, Y-C. and Park, J.-H. and Yoon, D.-B. and Kwon, H.-S.},
  title = {Noise source identification in a reverberant field using spherical beamforming},
  journal = {Modern Physics Letters B (MPLB)},
  year = {2008},
  volume = {22},
  pages = {1147--1151},
  doi = {10.1142/S021798490801598X}
}
Christensen JJ and Hald J (2004), "Beamforming", Technical Review No. 1 - 2004.
BibTeX:
@misc{ChristensenHald2004,
  author = {Christensen, J. J. and Hald, J.},
  title = {Beamforming},
  howpublished = {Technical Review No. 1 - 2004},
  year = {2004},
  note = {Brüel & Kjæ r Sound & Vibration Measurements A/S}
}
Chu N, Gac N, Picheral J and Mohammad-Djafari A (2014), "2D-Convolution Model Using (In)variant Kernels for Fast Acoustic Imaging", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-05., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Acoustic imaging is an advanced technique for acoustic source localization and power reconstruction using limited measurements at microphone sensors. The acoustic imaging methods often involve in two aspects: one is to build up a forward model of acoustic power propagation which requires tremendous matrix multiplications due to large dimension of the power propagation matrix; the other is to solve an inverse problem which is usually ill-posed and time consuming. In this paper, our main contribution is to propose to use 2D convolution model for fast acoustic imaging. We find out that power propagation matrix seems to be a quasi-Symmetric Toeplitz Block Toeplitz (STBT) matrix in the far-field condition, so that the (in)variant convolution kernels (sizes and values) can be well derived from this STBT matrix. For method validation, we use simulated and real data from the wind tunnel S2A (France) experiment for acoustic imaging on vehicle surface.
BibTeX:
@inproceedings{Chu_etal2014,
  author = {Chu, N. and Gac, N. and Picheral, J. and Mohammad-Djafari, A.},
  title = {2D-Convolution Model Using (In)variant Kernels for Fast Acoustic Imaging},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-05.pdf}
}
Chu N, Mohammad-Djafari A and Picheral J (2012), "Two robust super resolution approaches in aeroacoustic imaging for near-field wideband extended sources", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-29., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Recently deconvolution-based methods, like the DAMAS, have greatly improved spatial resolutions of the Beamforming in aeroacoustic imaging. But most of existing methods are not robust to background noise. In this paper, we propose two robust super-resolution approaches using Sparsity Constraint (SC-RDAMAS) and Sparse Regularisation (SR-RDAMAS) respectively to simultaneously estimate source powers and positions, and the variance of background noise. In proposed SC-RDAMAS, sparsity constraint on source power is obtained by considering eigenvalue distributions of observed covariance matrix. When sparsity constraint is hard to determine in strong noise interference, proposed SR-RDAMAS applying ℓ1 regularisation with proper regularisation parameter can greatly improve resolutions and robustness of proposed SC-RDAMAS. Moreover, proposed SC-RDAMAS can work well even if the source number is over-estimated, but our SR-RDAMAS does not require source number at all. Proposed methods are shown to be robust to noise, wide dynamic range, super resolution and feasibility to use for near-field wideband extended source imaging based on 2D non-uniform microphone array by simulated and wind tunnel data. Our methods are compared with the state-of-art methods: Beamforming, DAMAS, Diagonal Removal DAMAS, DAMAS with sparsity constraint, Covariance Matrix Fitting and CLEAN.
BibTeX:
@inproceedings{Chu_etal2012,
  author = {Chu, N. and Mohammad-Djafari, A. and Picheral, J.},
  title = {Two robust super resolution approaches in aeroacoustic imaging for near-field wideband extended sources},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-29.pdf}
}
Cigada A, Lurati M, Francesco Ripamonti F and Vanali M (2008), "Moving microphone arrays to reduce spatial aliasing in the beamforming technique: Theoretical background and numerical investigation", J. Acoust. Soc. Am.., December, 2008. Vol. 124(6), pp. 3648-–3658.
Abstract: This paper introduces a measurement technique aimed at reducing or possibly eliminating the spatial aliasing problem in the beamforming technique. Beamforming main disadvantages are a poor spatial resolution, at low frequency, and the spatial aliasing problem, at higher frequency, leading to the identification of false sources. The idea is to move the microphone array during the measurement operation. In this paper, the proposed approach is theoretically and numerically investigated by means of simple sound propagation models, proving its efficiency in reducing the spatial aliasing. A number of different array configurations are numerically investigated together with the most important parameters governing this measurement technique. A set of numerical results concerning the case of a planar rotating array is shown, together with a first experimental validation of the method.
BibTeX:
@article{Cigada_etal2008,
  author = {Cigada, A. and Lurati, M. and Francesco Ripamonti, F. and Vanali, M.},
  title = {Moving microphone arrays to reduce spatial aliasing in the beamforming technique: Theoretical background and numerical investigation},
  journal = {J. Acoust. Soc. Am.},
  year = {2008},
  volume = {124},
  number = {6},
  pages = {3648-–3658},
  doi = {10.1121/1.2998778}
}
Cigada A, Ripamonti F and Vana (2007), "The delay & sum algorithm apllied to microphone array measurement: Numerical analysis and experimental validation", Mechanical System and Signal Processing., August, 2007. Vol. 21(6), pp. 2645-2664.
Abstract: The experimental validation of the beamforming technique applied to microphone array measurements is investigated in this paper. At first the method theoretical background is presented, highlighting the main parameters affecting its performances and studying their influence with the aim of producing an instrument useful in designing an efficient experimental set-up. Then, in order to prove the theory assessment and to give a first estimation of the method uncertainty, an experimental campaign is carried out to validate the exposed theory under controlled and repeatable conditions. The obtained results highlight a very good correspondence between the theoretical model and the “in field” tests, giving the possibility to correctly design microphones array for future experimental campaigns.
BibTeX:
@article{Cigada_etal2007,
  author = {Cigada, A. and Ripamonti, F. and Vana},
  title = {The delay & sum algorithm apllied to microphone array measurement: Numerical analysis and experimental validation},
  journal = {Mechanical System and Signal Processing},
  year = {2007},
  volume = {21},
  number = {6},
  pages = {2645--2664},
  doi = {10.1016/j.ymssp.2007.01.001}
}
Comparin RJ (1991), "Acoustic Intensity Measurements in the presence of Mean Flow with Application to Noise Measurements in a Wind Tunnel", J. Acoust. Soc. Am.. Vol. 90, pp. 1733-1741.
Abstract: Wind tunnels are frequently used in the experimental study of moving sound sources. Although a number of techniques are currently used to determine the radiation characteristics of a sound source in a wind tunnel, they are usually limited by a lack of explicit directional information and/or a requirement that measurements be made in a free field. The multiple microphone acoustic intensity technique provides explicit directional information and can be used to measure sound fields in the near field of a source and, therefore, represents a possible alternative to the current measurement techniques used in wind tunnels. The formulations currently used to measure acoustic intensity are limited to either zero flow or plane waves in a one-dimensional mean flow. A new formulation has been developed that extends the method to the case of a spherically spreading wave in a uniform one-dimensional flow. Using an analytical simulation, the intensity distributions for a monopole and dipole source are studied. Initial results suggest that the formulation is suitable for the analysis of compact sources. Although a more detailed study will be required to develop a practical measurement tool, this study provides additional insight into the problem of intensity measurement in the presence of mean flow.
BibTeX:
@article{Comparin1991,
  author = {Comparin, R. J.},
  title = {Acoustic Intensity Measurements in the presence of Mean Flow with Application to Noise Measurements in a Wind Tunnel},
  journal = {J. Acoust. Soc. Am.},
  year = {1991},
  volume = {90},
  pages = {1733--1741}
}
Comparin RJ (1991), "Acoustic Intensity Measurements in the presence of Mean Flow with Application to Noise Measuremtns in a Wind Tunnel", J. Acoustical Society of America. Vol. 90, pp. 1133-1741.
BibTeX:
@article{Comparin1991a,
  author = {Comparin, R. J.},
  title = {Acoustic Intensity Measurements in the presence of Mean Flow with Application to Noise Measuremtns in a Wind Tunnel},
  journal = {J. Acoustical Society of America},
  year = {1991},
  volume = {90},
  pages = {1133--1741}
}
Dassen T, Parchen R, Bruggeman J and Hagg F (1996), "Results of a wind tunnel study on the reduction of airfoil self-noise by the application of serrated blade trailing edges", May, 1996. (NLR TP 96350)
Abstract: Wind tunnel measurements on the self-noise of a series of airfoils and flat plates were performed to explore the previously reported noise reducing potential of serrated trailing edges in case of more realistic flows and geometries. For this purpose, different types of airfoils, and flat plates with varying planforms and orientations of the teeth at the trailing edge were used. All serrated airfoils yield reduced trailing-edge noise levels, the reductions ranging from 3 dB up to 8 dB. Spectral shape and dependency on the flow speed and angle-of-attack appeared to be different for every airfoil type. The serrated flat plates were found to give reductions up to 10 dB (1 kHz - 6 kHz). Inclination of the complete flat plate by 10 degrees or a swept trailing edge affected this reduction to a very limited extend only (<2 dB). The same holds for a 10 degrees misalignment of the teeth with respect to the flow direction but in the chord plane. However, misalignment of the teeth by 15 degrees with respect to the chord plane caused an increase of the radiated noise.
BibTeX:
@techreport{Dassen_etal1996,
  author = {Dassen, T. and Parchen, R and Bruggeman, J. and Hagg, F.},
  title = {Results of a wind tunnel study on the reduction of airfoil self-noise by the application of serrated blade trailing edges},
  year = {1996},
  number = {NLR TP 96350},
  note = {1996 European Union Wind Energy Conference and Exhibition, Gothenburg, 20-24 May 1996},
  url = {http://www.nlr.nl/id~8253/lang~en.pdf}
}
Davy R, Moens F and Remy H (2002), "Aeroacoustic Behaviour of a 1:11 Scale Airbus Model in the Open Anechoic Wind Tunnel CEPRA 19", In 8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2412., June, 2002.
Abstract: This paper presents the analysis of aeroacoustic experiments performed with an Airbus 1/11th scaled aircraft model in the open anechoic wind tunnel CEPRA 19. This study aimed at checking the aerodynamic condition on the wing and characterizing the airframe noise sources. The results have shown that the flight aerodynamic conditions can be well reproduced in the wind tunnel by adjusting slightly the model pitch angle for each configuration. The main noise sources have been localized using a 2D cross-shaped array of microphones. Near-field/farfield correlations have been performed in order to study the spectral shape of these sources, completed in high frequencies with the analysis of the signals of flush mounted transducers. Different behavior were exhibited between low and high frequency range, for the wing leading edge noise and in the slotted flap region. The wind tunnel data have been transposed at full scale: using a geometric scaling factor, or a one based on Amiet's model for slat noise prediction. Depending on the scaling method used, the transposed data surround the flight data.
BibTeX:
@inproceedings{Davy_etal2002,
  author = {Davy, R. and Moens, F. and Remy, H.},
  title = {Aeroacoustic Behaviour of a 1:11 Scale Airbus Model in the Open Anechoic Wind Tunnel CEPRA 19},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Day B and Suzuki T (2011), "Mode identification in a rectangular duct using an L1 generalized inverse beam-forming approach", In 17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference); Portland, OR; United States; 5 June 2011 through 8 June 2011; Code 98125.
Abstract: To identify multiple duct acoustic modes, the L1 generalized inverse beam-forming algorithm is applied to phased-array pressure data. This algorithm has been proven to detect multipole modes regardless of their coherency in previous studies. A tone signal of a prescribed mode or broadband signal is generated upstream of a curved rectangular duct, and acoustic fields formed in both upstream and downstream stations of the test section are measured with identical wall-mounted microphone arrays. Amplitude distributions of several horizontal and vertical modes including upstream- and downstream-propagating waves can be identified, and the results are compared with those processed with conventional beam-forming. The comparison using synthetic data demonstrates that the L1 generalized inverse beam-forming approach can substantially suppress undesirable noise levels regardless of the prescribed modes and the noise levels. The comparison using test data acquired in the curved duct test rig (CDTR) at the NASA Langley Research Center suggests that L1 generalized inverse beam-forming can improve the dynamic range of the detected mode by more than 10 dB relative to conventional beam-forming even with mean flow of M = 0.5.
BibTeX:
@inproceedings{Day-Suzuki-2011,
  author = {Day, B.J. and Suzuki, T.},
  title = {Mode identification in a rectangular duct using an L1 generalized inverse beam-forming approach},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference 2011 (32nd AIAA Aeroacoustics Conference); Portland, OR; United States; 5 June 2011 through 8 June 2011; Code 98125},
  year = {2011}
}
Deblauwe F, Beguet B and Robin M (2008), "Combining acoustic imaging techniques to localize and identify sources", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-21. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper deals with recent advances in acoustic experimental methods and especially acoustic imaging. The paper covers two areas of interest to acousticians. In the first part, it is explained how near-field acoustic holography (NAH) can be extended with beamforming in the near-field, focalization. The combination of the two methods is providing now a source localization solution with a good spatial resolution over the complete frequency range without the burden of measuring a large number of points as would be required if only NAH was used. In the second part of the paper, a method is described that goes one step beyond source localization. It is interesting to locate the noise sources, but from an engineering standpoint it is even more interesting to know the internal sources/forces causing these noise sources. In this part is explained how source localization techniques in conjunction with artificial excitation of the structure can provide information on the internal sources of the structure.
BibTeX:
@inproceedings{Deblauwe_etal2008,
  author = {Deblauwe, F. and Beguet, B. and Robin, M.},
  title = {Combining acoustic imaging techniques to localize and identify sources},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-21_Deblauwe_Beguet_Robin.pdf}
}
Debrouwere M, Uyttersprot L, Verwilligen J, Probsting S, Simons D and Scarano F (2012), "Imaging of rod-airfoil aeroacoustics using a low-cost acoustic camera", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-20., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Along with stricter noise regulations in aviation comes the requirement to identify and eliminate sources of noise in aerodynamic designs. For this purpose, a phased array and data acquisition system (acoustic camera) was designed and built by students of the Faculty of Aerospace Engineering of Delft University of Technology. The performance of the phased array and different beamforming algorithms is evaluated with a variety of test cases, representative for the experiments conducted in moderate size wind tunnels (models of 10 cm to 30 cm, working distance of 1 m to 2 m) as typically available in university aboratories. The considered test cases are rod-airfoil combinations, which produce low-frequency tonal noise. The scaled models are tested in an open jet non-anechoic vertical wind tunnel at flow speeds ranging from 15 m/s to 40 m/s. The experiments present several challenges, namely the low level of the emitted noise, the required high spatial resolution and the refraction of sound waves travelling through the shear layer. The study discusses the specific developments and optimization of the low-cost acoustic camera for use in the non-anechoic open jet wind tunnel of moderate size
BibTeX:
@inproceedings{Debrouwere_etal2012,
  author = {Debrouwere, M. and Uyttersprot, L. and Verwilligen, J. and Probsting, S. and Simons, D.G. and Scarano, F.},
  title = {Imaging of rod-airfoil aeroacoustics using a low-cost acoustic camera},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-20.pdf}
}
DiBiase JH, Silverman HF and Brandstein MS (2001), "Robust Localization in Reverberant Rooms", In Microphone Arrays. , pp. 157-180. Springer-Verlag.
BibTeX:
@incollection{DiBiase_etal2001,
  author = {DiBiase, J. H. and Silverman, H. F. and Brandstein, M. S.},
  editor = {Brandstein, M. and Ward, D},
  title = {Robust Localization in Reverberant Rooms},
  booktitle = {Microphone Arrays},
  publisher = {Springer-Verlag},
  year = {2001},
  pages = {157--180}
}
Di Claudio ED and Parisi R (2001), "Multi-Source Localization Strategies", In Microphone Arrays. , pp. 181-201. Springer-Verlag.
BibTeX:
@incollection{DiClaudioParisi2001,
  author = {Di Claudio, E. D. and Parisi, R.},
  editor = {Brandstein, M. and Ward, D},
  title = {Multi-Source Localization Strategies},
  booktitle = {Microphone Arrays},
  publisher = {Springer-Verlag},
  year = {2001},
  pages = {181--201}
}
Dine C, Gely D and Élias G (1992), "Caracterisation de jets subcritique et supercritiques par une methode d'imagerie acoustique (Characterization of subcritical and supercritical jets by an acoustic imagery method)", In 2nd Congres Francais d'Acoustique, Arcachon, France, Apr. 14-16, 1992., ONERA, TP No. 1992-34, 1992.
BibTeX:
@inproceedings{Dine_etal92,
  author = {Dine, C. and Gely, D. and Élias, G.},
  title = {Caracterisation de jets subcritique et supercritiques par une methode d'imagerie acoustique (Characterization of subcritical and supercritical jets by an acoustic imagery method)},
  booktitle = {2nd Congres Francais d'Acoustique, Arcachon, France, Apr. 14-16, 1992},
  year = {1992}
}
Döbler D and Heilmann G (2010), "New method for positioning of microphones", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-15., February, 2010. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Acoustic imaging methods for sound source localization use microphone arrays. The quality of the results is strongly influenced by an accurate determination of the positions of the array microphones. Assurance of the required precision solely by means of exact design and construction is expensive, and the determination of the geometric sensor coordinates with classical methods is a time-consuming task and it is often not applicable in the field. The paper gives an estimation of the necessary precision of the positions and it proposes an algorithm which can determine unknown source positions as well as unknown sensor positions simultaneously. There is no need for reference speakers in this method, so it is useful for flexible array designs and their fast calibration in the field. Simulations and application examples are demonstrated, and the limits of the method will be discussed.
BibTeX:
@inproceedings{DoeblerHeilmann2010,
  author = {Döbler, D. and Heilmann, G.},
  title = {New method for positioning of microphones},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-15.pdf}
}
Döbler D and Heilmann G (2008), "Time-domain beamforming using zeropadding", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-04.
Abstract: Zeropadding is an approved method in signal processing to get additional samples or to suppress undesirable signals without changing essential signal properties. Beamforming in the frequency domain also uses zeropadding to transform the time signals into the frequency domain. The advantage of beamforming in the time domain compared with beamforming in frequency domain is the providing of high time resolution additional to positioning resolution (acoustical movie). But by use of high resolution in the time domain in combination with non stationary, impulse containing signals the delay and sum beamformer produces overlaps between acoustic events that are well separated in time domain. The analysis of short and small impulses can be complicate or impossible. An acoustic movie shows this overlays by apparently inversely moving patterns that can hide noise sources completely. This paper describes these moving patterns as an artifact of the delay and sum algorithm. Some examples show the limitations of spatio-temporally resolution. An enhanced algorithm using zeropadding suppresses the patterns and improves the spatio-temporally resolution considerably. A comparison of analyses with and without zeropadding shows the advantages of the enhanced algorithm. It enables new areas of applications, e.g. in architectural acoustics.
BibTeX:
@inproceedings{DoeblerHeilmann2008,
  author = {Döbler, D. and Heilmann, G.},
  title = {Time-domain beamforming using zeropadding},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-04_Doebler_Heilmann.pdf}
}
Döbler D and Schröder R (2012), "Contrast improvement and source separation enhancement using High Dynamic Range Algorithm", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-12., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The maximum contrast of a standard beamforming result (acoustic photo) is characterized by the difference between mainlobes and sidelobes. Typical values for a standard beamforming system are 8 dB up to 15 dB, quieter sound sources are covered. Contrast improvement by simply increasing the number of microphone s is expensive and ineffective. On the other hand, the increase in computational power allows the use of more complex algorithms to improve the acoustic map. Two years ago we presented at the BeBeC 2010 an algorithm to discover the masked sources, called “Acoustic eraser” [1] . This paper introduces a time domain beamforming algorithm based on the acoustic eraser algorithm . The algorithm provides an automatically, successively decomposition of the sound field with a high dynamic range. That allows contrast improvements up to 50 dB . Due to this high contrast quiet source can be discovered and a very accurate sound reconstruction is practicable.
BibTeX:
@inproceedings{DoeblerSchroeder2012,
  author = {Döbler, D. and Schröder, R.},
  title = {Contrast improvement and source separation enhancement using High Dynamic Range Algorithm},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-12.pdf}
}
Döbler D and Schröder R (2010), "Contrast improvement of acoustic maps by successive deletion of the main sources", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-19., February, 2010.
Abstract: Beamforming for acoustic imaging is a well established, fast and practical method for acoustic source localization. A disadvantage of the method is the still relatively low image contrast due to sidelobes in the map. Weaker sources may be masked by stronger ones. Therefore, algorithmic contrast improvements in acoustic maps are an ongoing topic of research. Many algorithms developed for this purpose are computationally very expensive. The paper presents a simple and fast time domain method which successively deletes the dominant sources in the beamforming map and hence uncovers weaker sound sources. The contrast improvements are partially very dramatic and they offer the advantage of an interactive analysis of the acoustic emissions nearly in real time. The properties of the algorithm are discussed, and application examples and simulations are shown.
BibTeX:
@inproceedings{DoeblerSchroeder2010,
  author = {Döbler, D. and Schröder, R.},
  title = {Contrast improvement of acoustic maps by successive deletion of the main sources},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-19.pdf}
}
Dolph CL (1946), "A Current Distribution of Broadside Arrays which Optimizes the Relationship between Beam Width and Sidelobe Level", Proc. Inst. Radio Eng.. Vol. 34, pp. 335-348.
BibTeX:
@article{Dolph1946,
  author = {Dolph, C. L.},
  title = {A Current Distribution of Broadside Arrays which Optimizes the Relationship between Beam Width and Sidelobe Level},
  journal = {Proc. Inst. Radio Eng.},
  year = {1946},
  volume = {34},
  pages = {335--348},
  url = {http://garfield.library.upenn.edu/classics1982/A1982NG43600001.pdf}
}
Dougherty RP (2002), "Beamforming in Acoustic Testing", In Aeroacoustic Measurements. , pp. 62-97. Springer-Verlag Berln Heidelberg New York.
BibTeX:
@incollection{Dougherty2002a,
  author = {Dougherty, R. P.},
  editor = {Mueller, T. J.},
  title = {Beamforming in Acoustic Testing},
  booktitle = {Aeroacoustic Measurements},
  publisher = {Springer-Verlag Berln Heidelberg New York},
  year = {2002},
  pages = {62--97}
}
Dougherty RP (2014), "Functional Beamforming", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-01., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: A new beamforming algorithm is introduced. It is called Functional Beamforming because it uses the mathematics of functions of matrices. The algorithm depends on an exponent parameter. The array Cross Spectral Matrix is raised to the power of the reciprocal of this exponent in the functional sense. Conventional Frequency Domain Beamforming is applied using the modified CSM, and the values of the resulting beamform map are raised to power of the non-reciprocal exponent. For large values of the exponent, array sidelobes are essentially eliminated. This increases flexibility in array design and dramatically increases the dynamic range of the system so that new sources may be discovered. Theory is given that proves that the method will not eliminate or even reduce true sources if the steering vector is accurate. This depends on the quality the array calibration, but the requirements are not extraordinary. Examples are given comparing the method with Robust Adaptive Beamforming, CLEAN-SC, Orthogonal Beamforming, and to some degree, Linear Programming. A previously unknown noise source of Boeing 747 desk models is shown.
BibTeX:
@inproceedings{Dougherty2014,
  author = {Dougherty, R. P.},
  title = {Functional Beamforming},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-01.pdf}
}
Dougherty RP (2012), "Directional acoustic attenuation of planar foam rubber windscreens for phased arrays", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-05., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Use of a porous layer, such as foam rubber, over a phased array is proposed to reduce background noise in wind tunnel acoustic measurements. As previous work has shown, this reduces boundary layer noise by displacing the flow from the array by the thickness of the layer. The new idea is that it can also reduce the impact of noise from the wind tunnel drive system and other flow control features because that noise appears to originate from far away in the wind tunnel, usually upstream. Due to its oblique incidence on the porous layer, the interfering noise sees more transmission loss in passing through the layer than the sound from the model does. A disadvantage of such a layer is that the attenuation can increase rapidly with frequency, possibly complicating the interpretation of the data. Shop tests of several materials have been performed. It is observed that viscoelastic "memory foam” has lower and more linear attenuation than the other samples tested. Elements of the shop results have been validated in a wind tunnel test.
BibTeX:
@inproceedings{Dougherty2012,
  author = {Dougherty, R. P.},
  title = {Directional acoustic attenuation of planar foam rubber windscreens for phased arrays},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-05.pdf}
}
Dougherty RP (2012), "Improved Generalized Inverse Beamforming for Jet Noise", Int. J. Aeroacoustics. Vol. 11(3-4), pp. 259-290.
Abstract: The acoustic holography/generalized inverse method of microphone array processing is improved in two ways: the linear algebra is simplified to avoid separate processing of cross spectral matrix eigenvalues, and a new regularization technique is introduced to produce reasonable results when the problem is underdetermined. Model-scale testing has shown that the improved method can map coherent sources and extrapolate directivity patterns using a modest 2D nearfield array and one data acquisition in a warehouse with no acoustic treatment. Tests with shop air jets show that rectangular jets can have asymmetric radiation patterns and the flight deck and jet blast deflector dramatically alter the radiation pattern in a configuration representing an aircraft carrier launch operation.
BibTeX:
@article{Dougherty2012a,
  author = {Dougherty, R. P.},
  title = {Improved Generalized Inverse Beamforming for Jet Noise},
  journal = {Int. J. Aeroacoustics},
  year = {2012},
  volume = {11},
  number = {3-4},
  pages = {259--290},
  doi = {10.1260/1475-472X.11.3-4.259}
}
Dougherty RP (2012), "Deconvolution Beamforming Analysis of Low Frequency Wind
Turbine Noise"
, In 15th International Meeting on Low Frequency Noise and Vibration and its Control, Stratford upon Avon UK 22nd – 24th May 2012., Meeting Paper., May, 2012.
Abstract: Two simple, field deployable phased arrays of microphones were used to evaluate their capability for locating low frequency and audio frequency wind turbine noise. The low frequency array was a 10 m triangular arrangement of three microphones on plywood boards the ground. The second system was a commercial 24-channel planar array with an aperture of 0.7 m, placed on the ground in the center of the triangle. By combining the two systems and applying advanced beamforming algorithms, wind turbine sound sources were located over the range of 2 Hz – 4 kHz.
BibTeX:
@inproceedings{Dougherty2012b,
  author = {Dougherty, R. P.},
  title = {Deconvolution Beamforming Analysis of Low Frequency Wind
Turbine Noise}, booktitle = {15th International Meeting on Low Frequency Noise and Vibration and its Control, Stratford upon Avon UK 22nd – 24th May 2012}, year = {2012} }
Dougherty RP (2011), "Improved Generalized Inverse Beamforming for Jet Noise", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2769., June, 2011.
Abstract: The acoustic holography/generalized inverse method of microphone array processing is improved in two ways: the linear algebra is simplified to avoid separate processing of cross spectral matrix eigenvalues, and a new regularization technique is introduced to produce reasonable results when the problem in underdetermined. Low-TRL testing has shown that the improved method can map coherent sources and extrapolate directivity patterns using a modest 2D nearfield array and one data acquisition in a warehouse with no acoustic treatment. Tests with shop air jets show that rectangular jets can have asymmetric radiation patterns and the flight deck and jet blast deflector dramatically alter the radiation pattern in a configuration representing an aircraft carrier launch operation.
BibTeX:
@inproceedings{Dougherty2011,
  author = {Dougherty, Robert P.},
  title = {Improved Generalized Inverse Beamforming for Jet Noise},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Dougherty RP (2010), "Jet noise beamforming with several techniques", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-17., February, 2010. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: Advanced techniques can enhance beamforming results. Deconvolution methods can improve low frequency resolution and reduce sidelobes. Matrix analysis approaches can separate statistically independent sources. This paper presents the results of applying 3D CLEAN-SC, DAMAS, TIDY, and eigenvalue cancellation to cage array data for turbofan engine jet noise from the NASA Engine Validation of Noise and Emission Reduction program.
BibTeX:
@inproceedings{Dougherty2010,
  author = {Dougherty, R. P.},
  title = {Jet noise beamforming with several techniques},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-17.pdf}
}
Dougherty RP (2008), "What is Beamforming?", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-01. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Beamforming is an imaging technique that has found many applications in aeroacoustics, and continues to evolve to meet greater challenges. It has elements in common with other methods such as nearfield acoustic holography, but its strength is distributed, broadband, incoherent sources at arbitrary distance from the array. The formulation of the classical technique in the frequency domain is simple and lends itself to many types of analysis. A derivation is given here that leads to an expression for the variance of the beamform map when the integration time is finite and not all of the elements of the cross spectral matrix are included.
BibTeX:
@inproceedings{Dougherty2008,
  author = {Dougherty, R. P.},
  title = {What is Beamforming?},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-01_Dougherty.pdf}
}
Dougherty RP (2008), "Noise Source Imaging by Beamforming", SAE Technical Paper 2008-36-0518. March, 2008.
Abstract: Beamforming using phased arrays of microphones is a popular technique for noise source imaging in certain applications in aerospace. Scale models tests of airframe noise, for example, use the method extensively because the acoustic source distribution is complicated and matches the assumptions of the algorithm. Beamforming can be done in the frequency domain or the time domain. The time domain version adapts easily to moving sources including aircraft flyover and ground vehicle pass-by tests. Frequency domain formulations have been extended to in many ways. Recent versions improve resolution by deconvolution and treat extended, coherent sources seen, for example, in aircraft engine tests.
BibTeX:
@misc{Dougherty2008b,
  author = {Dougherty, R. P.},
  title = {Noise Source Imaging by Beamforming},
  howpublished = {SAE Technical Paper 2008-36-0518},
  year = {2008},
  url = {http://www.sae.org/technical/papers/2008-36-0518}
}
Dougherty RP (2005), "Extensions of DAMAS and Benefits and Limitations of Deconvolution in Beamforming", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-2961.
Abstract: The DAMAS deconvolution algorithm represents a breakthrough in phased array imaging for aeroacoustics, potentially eliminating sidelobles and array resolution effects from beamform maps . DAMAS is an iterative non-negative least squares solver. The original algorithm is too slow and lacks an explicit regularization method to prevent noise amplification. Two extensions are proposed, DAMAS2 and DAMAS3. DAMAS2 provides a dramatic speedup of each iteration and adds regularization by a low pass filter. DAMAS3 also provides fast iterations, and additionally, reduces the required number of iterations. It uses a different regularization technique from DAMAS2, and is partially based on the Wiener filter. Both DAMAS2 and DAMAS3 restrict the point spread function to a translationally-invariant, convolutional, form. This is a common assumption in optics and radio astronomy, but may be a serious limitation in aeroacoustic beamforming. This limitation is addressed with a change of variables from (x,y,z) to a new set, (u,v,w). The concepts taken together, along with appropriate array design, may permit practical 3D beamforming in aeroacoustics.
BibTeX:
@inproceedings{Dougherty2005,
  author = {Dougherty, R. P.},
  title = {Extensions of DAMAS and Benefits and Limitations of Deconvolution in Beamforming},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Dougherty RP (2004), "Advanced Time-domain Beamforming Techniques", In 10th AIAA/CEAS Aeroacoustics Conference, Manchester, Great Britain, May 10-12, 2004., AIAA-2004-2955.
Abstract: Aeroacoustic beamforming for static sources like wind tunnel models is usually performed in the frequency-domain because special techniques that exploit the structure of the cross spectral matrix are formulated in the frequency-domain. This usually restricts the analysis to narrowband processing. Simple time-domain beamforming formulas that implement the diagonal deletion and cross-array beamforming techniques are presented. Examples using synthetic data show that the techniques are effective and that increasing the processing bandwidth can reduce the array sidelobes and improve the performance of diagonal deletion in removing the effects of microphone self noise.
BibTeX:
@inproceedings{Dougherty2004,
  author = {Dougherty, R. P.},
  title = {Advanced Time-domain Beamforming Techniques},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference, Manchester, Great Britain, May 10-12, 2004},
  year = {2004}
}
Dougherty RP (2003), "Turbulent Decorrelation of Aeroacoustic Phased Arrays: Lessons from Atmospheric Science and Astronomy", In 9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003., AIAA-2003-3200.
Abstract: Aeroacoustic phased array and mirror microphones are known to suffer a loss of sensitivity due to passage of the sound waves through the wind tunnel shear layer or boundary layer. It is common practice to use smaller arrays than might otherwise be desired in order to limit this effect. A quantitative model of the scattering and its impact on the results would permit improved array designs and increase the accuracy of the spectra from these tests. A well developed formalism for wave propagation in random media supports the astronomical, underwater acoustics, and especially the atmospheric science fields. Initial steps have been taken to apply the this theory to the aeroacoustic phased array domain. An expression of the von Kármán turbulence model in the parabolic and Markov approximations has been adapted for phased array beamforming in open and closed wind tunnels. A simple formula for the effect of turbulence on the beamforming peak level has been derived. The theory and previous experimental work suggest correlation based on Mδ/λ. The effect of array diameter on the turbulence scattering is predicted. If the diameter exceeds several times the boundary layer thickness, then further increases in size should not change the scattering. Comparisons with measurements show good agreement in some cases, but not all. A need for more detailed investigation of hot wire data from wind
tunnel shear and boundary layers and more complete numerical simulations has been recognized.
BibTeX:
@inproceedings{Dougherty2003,
  author = {Dougherty, R. P.},
  title = {Turbulent Decorrelation of Aeroacoustic Phased Arrays: Lessons from Atmospheric Science and Astronomy},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003}
}
Dougherty RP (2003), "Beamforming for aircraft noise measurements", Acoustical Society of America Journal. Vol. 114(4), pp. 2339-2339.
Abstract: Phased array beamforming for aircraft noise source location has a long history, including early work on jet noise, wind tunnel measurements, and flyover testing. In the last 10 years, advancements in sparse 2-D and 3-D arrays, wind tunnel test techniques, and computer power have made phased array measurements almost common. Large aerospace companies and national research institutes have an advantage in access to major facilities and hundreds of measurement microphones, but universities and even consulting companies can perform tests with electret microphones and PC data acquisition systems. The type of testing remains a blend of science and art. A complex noise source is approximated by a mathematical model, and the microphones are deployed to evaluate the parameters of the model. For example, the simplest, but often the best, approach is to assume a distribution of mutually incoherent monopoles. This leads to an imaging process analogous to photography. Other models include coherent distributions of multipoles or duct modes. It is sometimes important to simulate the results that would have been obtained from single microphone measurements of part of the airplane in an ideal environment, had such measurements been feasible.
BibTeX:
@article{Dougherty2003a,
  author = {Dougherty, R. P.},
  title = {Beamforming for aircraft noise measurements},
  journal = {Acoustical Society of America Journal},
  year = {2003},
  volume = {114},
  number = {4},
  pages = {2339--2339}
}
Dougherty RP (1997), "Source location with sparse acoustic arrays: interference cancellation", DNW.
BibTeX:
@misc{Dougherty1997,
  author = {Dougherty, R. P.},
  title = {Source location with sparse acoustic arrays: interference cancellation},
  howpublished = {DNW},
  year = {1997}
}
Dougherty RP, Fonseca WD and Gerges SNY (2008), "Beamforming in reflecting environments: an experiment in a reverberation chamber", In NoiseCon2008, Dearborn MI, July 28-30, 2008.., ASME Paper NCAD2008-73020., July, 2008.
Abstract: Beamforming in reverberant environments is important to locate and quantify noise sources in turbofan engine nacelles, automobile interiors, factories, and architectural settings. In order to validate and explore the limits of this approach, a beamforming experiment was conducted in a reverberation chamber using a 32 channel planar phased array and B&K sound power source. In the reference configuration, the source was located 2 m from the 1.1 m diameter array, and neither was close to the chamber walls. A less-demanding case was constructed by adding some foam absorber to the room to reduce reverberation. A difficult case resulted when the source was placed 5 m from the array, about 1 m from a corner of the chamber. Conventional frequency-domain beamforming with diagonal deletion was applied. The sound source was accurately located at the 2 m distance, with and without the added absorber. In the 5 m case, the sound source could be located at only a few frequencies and only when the processing bandwidth was increased from 48.8 Hz to 781 Hz. Processing individual eigenvectors of the CSM separated the direct and reflected source in 5 m case. The error in the deduced broadband sound power was 0.72 dB in the baseline case, 1.47 dB with the added absorber, and 5.41 dB with the speaker in the corner. Application of CLEAN-SC did not improve the accuracy of the corner results. Use of a Green’s function that attempts to account for reflections was ineffective. It is concluded that beamforming in highly reverberant environment with the free space Green’s function is practical, provided the array is designed and positioned correctly for the environment and source location.
BibTeX:
@inproceedings{Dougherty_etal2008,
  author = {Dougherty, R. P. and Fonseca, W. D. and and Gerges, S. N. Y.},
  title = {Beamforming in reflecting environments: an experiment in a reverberation chamber},
  booktitle = {NoiseCon2008, Dearborn MI, July 28-30, 2008.},
  year = {2008}
}
Dougherty RP and Mendoza J (2008), "Nacelle In-Duct Beamforming Using Modal Steering Vectors", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, British Columbia, May 5-7, 2008., AIAA-2008-2812., May, 2008.
Abstract: A mode measurement array of 119 Kulite transducers was installed in an inlet duct section and tested with a Honeywell Tech977 turbofan engine. 2D mode analysis was performed using conventional beamforming and CLEAN-SC. The modes were determined in terms of sound power level. In-duct spatial source imaging was also performed using free space steering vectors and an annular duct Green’s function. CLEAN-SC is found to be a powerful enhancement for mode measurements, completely removing several types of array artifacts and facilitating reliable sound power estimates. An interesting feature of CLEANSC is that the resulting mode map potentially combines the powers of several modes into a single spot. Applying CLEAN-SC to the spatial imaging results in a confusing distribution of apparent point sources. A need to improve the way CLEAN-SC represents extended sources has been identified.
BibTeX:
@inproceedings{DoughertyMendoza2008b,
  author = {Dougherty, R. P. and Mendoza, J.},
  title = {Nacelle In-Duct Beamforming Using Modal Steering Vectors},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference), Vancouver, British Columbia, May 5-7, 2008},
  year = {2008}
}
Dougherty RP and Mendoza JM (2008), "Phased Array Beamforming with 100-foot Polar Arc Microphones in a Śtatic Engine Noise Test", In 46th AIAA Aerospace Sciences Meeting and Exhibit, 7-10 January 2008, Reno, Nevada., AIAA-2008-0051., January, 2008.
Abstract: Ground microphones from static engine testing of a Honeywell Tech977 turbofan engine were used for phased array beamforming. Two arrays were included: the polar array and the “high frequency” array. The polar array consisted of the standard 32 5° microphones covering inlet angles from 5° through 160°, and the “high frequency” array comprised 23 microphones nonuniformly spaced over 60° through 90°. All of the microphones were spaced 100 feet from a point below the engine inlet highlight on the tarmac. The primary objectives were to separate source components and to determine the feasibility of beamforming with the standard microphones. An unexpected case-radiation source was identified and characterized. Conventional beamforming as well as DAMAS and CLEAN-SC were applied. It was found that CLEAN-SC is a powerful tool for reducing sidelobes, dealing with coherent sources, and mitigating the effects of turbulent decorrelation, all of which are important in this application.
BibTeX:
@inproceedings{DoughertyMendoza2008a,
  author = {Dougherty, R. P. and Mendoza, J. M.},
  title = {Phased Array Beamforming with 100-foot Polar Arc Microphones in a Śtatic Engine Noise Test},
  booktitle = {46th AIAA Aerospace Sciences Meeting and Exhibit, 7-10 January 2008, Reno, Nevada},
  year = {2008}
}
Dougherty RP, Panda J and Lee SS (2005), "Non-intrusive jet noise study combining Rayleigh scattering and phased array measurement techniques", In 11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference), 23 - 25 May 2005, Monterey, California., AIAA-2005-2843., May, 2005.
Abstract: A one-inch diameter cold jet at the NASA-Glenn Research Center was studied with a Rayleigh scattering technique to measure the unsteady density in selected probe volume locations and, simultaneously, with a phased array of 32 microphones arranged in a partial cylinder that was centered on the jet and the probe volume. Phased array beamforming was performed to visualize the jet noise sources and test the effect of ray tracing for array steering and the DAMAS2 deconvolution technique. Correlation coefficients between the microphone signals and between the acoustic data and the unsteady density from the Rayleigh probe were examined. The primary goal was to determine whether the array would increase the correlation coefficient relative to previous work in which the unsteady density from the Rayleigh system was correlated with the output of individual microphones. Results are presented for the case of M = 0.95. Increased correlation was observed, but, contrary to expectations, the optimal array steering points were not coincident with the probe volume. At low frequency, the highest correlation coefficient was seen when then array was steered upstream of the probe volume . At high frequency, significant correlation between the microphones and the de nsity occurred only when the probe volume was in the jet shear layer. In this case, the delay between the density signal and the acoustic pressure was negative, i.e., the density fluctuations in the probe volume lagged the pressure waves at the microphones. The optimal array steering point in this case was downstream of the probe volume, and coincided with peak acoustic source region seen in beamforming with array by itself.
BibTeX:
@inproceedings{DoughertyPanda2005,
  author = {Dougherty, R. P. and Panda, J. and Lee, S. S.},
  title = {Non-intrusive jet noise study combining Rayleigh scattering and phased array measurement techniques},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference), 23 - 25 May 2005, Monterey, California},
  year = {2005}
}
Dougherty RP and Podboy G (2009), "Improved Phased Array Imaging of a Model Jet", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 11 - 13 May 2009, Miami, FL., AIAA-2009-3186., May, 2009.
Abstract: An advanced phased array system, OptiNav Array 48, and a new deconvolution algorithm, TIDY, have been used to make octave band images of supersonic and subsonic jet noise produced by the NASA-Glenn SHJAR rig. The results are much more detailed than previous jet noise images. Shock cell structures and the production of screech in an underexpanded supersonic jet are observed directly. Some trends are similar to observations using spherical and elliptic mirrors that partially informed the two-source model of jet noise, but the radial distribution of high frequency noise near the nozzle appears to differ from expectations of this model. The beamforming approach has been validated by agreement between the integrated image results and the conventional microphone data
BibTeX:
@inproceedings{DoughertyPodboy2009,
  author = {Dougherty, R. P. and Podboy, G.},
  title = {Improved Phased Array Imaging of a Model Jet},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 11 - 13 May 2009, Miami, FL},
  year = {2009}
}
Dougherty RP, Ramachandran RC and Raman G (2013), "Deconvolution of Sources in Aeroacoustic Images from Phased Microphone Arrays Using Linear Programming", In 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, 27th-29th May 2013., AIAA-2013-2210., May, 2013.
Abstract: A new deconvolution strategy for aeroacoustic beamforming based on linear programming (LP) is introduced. Results of an aeroacoustic test show that it produces virtually the same results as DAMAS in much less time. DAMAS, DAMAS2 and LP display superresolution, which is expressed in terms of the Sparrow resolution limit from optics. CLEAN-SC and TIDY did not achieve superresolution in the test, but did produce higher dynamic range than DAMAS and LP at high frequency.
BibTeX:
@inproceedings{Dougherty_etal2013b,
  author = {Dougherty, R. P. and Ramachandran, R. C. and Raman, G.},
  title = {Deconvolution of Sources in Aeroacoustic Images from Phased Microphone Arrays Using Linear Programming},
  booktitle = {19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany, 27th-29th May 2013},
  year = {2013},
  doi = {10.2514/6.2013-2210}
}
Dougherty RP and Stoker RW (1998), "Sidelobe suppression for phased array aeroacoustic measurements", In 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, June 2-4, 1998., AIAA-1998-2242.
Abstract: Phased array test techniques are becoming increasingly popular in aeroacoustics. This is due, in part, to the use of optimized array designs (e.g., spiral shapes) which can operate over usefully wide frequency ranges with acceptable resolution and sidelobe rejection characteristics with practical numbers of microphones. Sometimes constraints such as limited space for microphone installation prevent the use of optimum array designs, raising the prospect of high sidelobe levels. Several modifications to classical beamforming which may reduce sidelobe levels for imperfect arrays (and possibly improve the performance of optimized arrays) are available. The effectiveness of these techniques is explored by applying three of them to four array designs using simulated wind tunnel data. The three bearnforrning techniques are robust adaptive beamforming, cross spectral matrix element weighting, and the CLEAN algorithm. The array designs are a cross, an array of four crosses, a filled square, and a spiral array
BibTeX:
@inproceedings{DoughertyStoker1998,
  author = {Dougherty, R. P. and Stoker, R. W.},
  title = {Sidelobe suppression for phased array aeroacoustic measurements},
  booktitle = {4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, June 2-4, 1998},
  year = {1998}
}
Dougherty RP and Walker B (2009), "Virtual Rotating Microphone Imaging of Broadband Fan Noise", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3121., May, 2009.
Abstract: An in-duct beamforming technique for imaging rotating broadband fan sources has been developed. A phased array consisting of one or more rings of microphones is employed. Thedata are mathematically resampled to a frame of reference rotating with the fan and subsequently used in a conventional beamforming technique in the rotating frame. The steering vectors for the beamforming are derived from annular duct modes, so that effects of reflections from the duct walls are reduced. In contrast with other work, the steering vectors represent the effect of the unsteady pressure at the fan, rather than the Green’s function. This improves the condition of the formulation and provides a connection to analytical studies. The method has been tested by applying it to data from the NASA-Glenn ANCF rig. The test included a condition in which two of the fan blades were altered to create noise sources at known locations. CLEAN-SC was applied in an attempt to remove array resolution effects from the results.
BibTeX:
@inproceedings{DoughertyWalker2009,
  author = {Dougherty, R. P. and Walker, B.},
  title = {Virtual Rotating Microphone Imaging of Broadband Fan Noise},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  year = {2009}
}
Dougherty RP, Walker BE and Sutliff DL (2010), "Locating and Quantifying Broadband Fan Sources using In-Duct Microphones", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3736., June, 2010.
Abstract: In-duct beamforming techniques have been developed for locating broadband noise sources on a low-speed fan and quantifying the acoustic power in the inlet and aft fan ducts. The NASA Glenn Research Center’s Advanced Noise Control Fan was used as a test bed. Several of the blades were modified to provide a broadband source to evaluate the efficacy of the in-duct beamforming technique. Phased arrays consisting of rings and line arrays of microphones were employed. For the imaging, the data were mathematically re-sampled in the frame of reference of the rotating fan. For both the imaging and power measurement steps, array steering vectors were computed using annular duct modal expansions, selected subsets of the cross spectral matrix elements were used, and the DAMAS and CLEAN-SC deconvolution algorithms were applied.
BibTeX:
@inproceedings{Dougherty_etal2010,
  author = {Dougherty, R. P. and Walker, B. E. and Sutliff, D. L.},
  title = {Locating and Quantifying Broadband Fan Sources using In-Duct Microphones},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Dougherty RP, Wang F, Booth E, Watts M, Fenichel N and D'Errico R (2004), "Aircraft Wake Vortex Measurements at Denver International Airport", In 10th AIAA/CEAS Aeroacoustics Conference , Manchester, Great Britain, May 10-12, 2004., AIAA-2004-2880., May, 2004.
Abstract: Airport capacity is constrained, in part, by spacing requirements associated with the wake vortex hazard. NASA’s Wake Vortex Avoidance Project has a goal to establish the feasibility of reducing this spacing while maintaining safety. Passive acoustic phased array sensors, if shown to have operational potential, may aid in this effort by detecting and tracking the vortices. During August/September 2003, NASA and the USDOT sponsored a wake acoustics test at the Denver International Airport. The central instrument of the test was a large microphone phased array. This paper describes the test in general terms and gives an overview of the array hardware. It outlines one of the analysis techniques that is being applied to the data and gives sample results. The technique is able to clearly resolve the wake vortices of landing aircraft and measure their separation, height, and sinking rate. These observations permit an indirect estimate of the vortex circulation. The array also provides visualization of the vortex evolution, including the Crow instability.
BibTeX:
@inproceedings{Dougherty_etal2004,
  author = {Dougherty, R. P. and Wang, F. and Booth, E. and Watts, M. and Fenichel, N. and D'Errico, R.},
  title = {Aircraft Wake Vortex Measurements at Denver International Airport},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference , Manchester, Great Britain, May 10-12, 2004},
  year = {2004},
  url = {http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040070828_2004063387.pdf}
}
Ehrenfried K and Koop L (2008), "Microphone-array processing for wind-tunnel measufrements with strong background noise", In 14th CEAS/AIAA Aeroacoustics Conference, Vancouver, British Columbia, Canada, 5-7 May 2008., AIAA-2008-2907.
Abstract: Acoustic array measurements have been carried out in a wind tunnel with a closed test-section on a swept constant-chord half-model. The experiments show that strong background noise present in the test section disturbs the array measurements and causes artefacts in source maps obtained with conventional beamforming (CB). By analyzing the components of the wavenumber spectrum in the array plane using the delay-and-sum beamforming with an infinite focal distance it is shown that this noise consists mainly of upstream propagating spurious waves. They can be reduced either by modifications to the wind tunnel test-section or by the BiCLean algorithm, a more advanced array processing technique. In a second step the robustness of deconvolution algorithms is investigated with respect to the noisy data obtained from the closed test-section measurements. The new deconvolution algorithms E-DAMAS2 proposed by Ehrenfried and Koop and the CLEAN-SC algorithm introduced by Sijtsma are applied to the present experimental data. The results show that the spatial resolution can be increased considerably by applying these algorithms and that side lobes are successful suppressed. The integrated spectra obtained from the deconvolution source-powers agree very well with standard source-power integration results based on CB. The background noise which is present in the CB results is detected also with the deconvolution algorithms. But no instabilities have been observed in the deconvolution process due to this noise.
BibTeX:
@inproceedings{EhrenfriedKoop2008,
  author = {Ehrenfried, K. and Koop, L.},
  title = {Microphone-array processing for wind-tunnel measufrements with strong background noise},
  booktitle = {14th CEAS/AIAA Aeroacoustics Conference, Vancouver, British Columbia, Canada, 5-7 May 2008},
  year = {2008}
}
Ehrenfried K and Koop L (2007), "Comparison of Iterative Deconvolution Algorithms for the Mapping of Acoustic Sources", AIAA Journal. Vol. 45(7), pp. 1584-1595.
Abstract: The DAMAS algorithm is compared with the DAMAS2 method and two other Fourier-based deconvolution approaches. One is the Richardson–Lucy method, which is widely used for the deconvolution of astronomical images. The second is a gradient-type nonnegative least-squares (NNLS) approach, in which spectral procedures are implemented to accelerate the computations. It is described how the DAMAS2 and the Fourier-based NNLS algorithms can be embedded in an outer iteration loop to take the variation of the point-spread function into account. All methods are tested with synthetic data. An initial example with a simple linear array and a small opening angle is considered, where the variation of the point-spread function in the source region is negligible. In this test case the results of the DAMAS2, the Fourier-based NNLS, the Richardson–Lucy, and the original DAMAS algorithm are compared. It is shown that all algorithms more or less introduce oscillations in the reconstructed source distribution. The effect of background noise on the results is investigated. A subsequent test case with a planar array and a large opening angle is presented, to demonstrate the influence of a strong variation of the point-spread function. It is shown that the methods that neglect the variation of the point-spread function lead to distorted results, whereas the embedded Fourier-based methods and the DAMAS algorithm give a significantly better reconstruction of the source distribution
BibTeX:
@article{EhrenfriedKoop2007,
  author = {Ehrenfried, K. and Koop, L.},
  title = {Comparison of Iterative Deconvolution Algorithms for the Mapping of Acoustic Sources},
  journal = {AIAA Journal},
  year = {2007},
  volume = {45},
  number = {7},
  pages = {1584--1595},
  doi = {10.2514/1.26320}
}
Ehrenfried K and Koop L (2006), "A comparison of iterative deconvolution algorithms for the mapping of acoustic sources", In 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, Massachusetts (USA), 8-10 May 2006., AIAA-2006-2711.
Abstract: The DAMAS2 algorithm is compared with several other Fourier-based deconvolution approaches. One is the Richardson-Lucy method, which is widely used for the deconvolution of astronomical images. The second is a modified gradient-type NNLS approach, where spectral procedures are implemented to accelerate the computations. Both methods require a computational effort similar to the DAMAS2 algorithm. All three algorithms use an approximate shift invariant point-spread function. Furthermore it is described how the DAMAS2 and the Fourier-based NNLS algorithms can be embedded in an outer iteration loop to take the variation of the point-spread function into account. The resulting methods have two nested iterations, which require much more numerical effort than a single DAMAS2 iteration loop. All methods are tested with synthetic data. At first an example with a simple linear array and a small opening angle is considered, where the variation of the point-spread function in the source region is negligible. In this test case the results of the DAMAS2, the modified gradient-type NNLS, and the Richardson-Lucy algorithm are compared. It is shown that these algorithms more or less introduce oscillations in the reconstructed source distribution. A second test case with a planar array and a large opening angle is presented, to demonstrate the influence of a strong variation of the pointspread function. It is shown that the approximate methods lead to distorted results, while the methods with nested iterations give a significantly better reconstruction of the source distribution.
BibTeX:
@inproceedings{EhrenfriedKoop2006,
  author = {Ehrenfried, K. and Koop, L.},
  title = {A comparison of iterative deconvolution algorithms for the mapping of acoustic sources},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference, Cambridge, Massachusetts (USA), 8-10 May 2006},
  year = {2006}
}
Ehrenfried K, Koop L, Henning A and Käpernick K (2006), "Effects of wind-tunnel noise on array measurements in closed test section.", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-07. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Past experiments have shown that aeroacoustic measurements are possible in wind tunnels with closed test sections, although there are several drawbacks compared to measurements in open test sections. Problems can arise from reflections at the hard side walls, the flow about the microphones, and background noise which propagates through the wind tunnel. To investigate the latter effect, array measurements are carried out in the large wind tunnel of the Hermann-Föttinger-Institute at the TU Berlin. This wind tunnel has a closed test section with a size of 2 m by 1.4 m. A microphone array is mounted at one side wall in the test section. The array has a diameter of about 1m and consists of 144 microphones. Experiments are done at flow velocities of 30 m/s with a wing model installed. The tests show that the background noise which is present in the test section has a characteristic wavenumber spectrum. Typically stronger waves are found which propagate in upstream direction. Their signals can cause strange artifacts in the source maps at focus points downstream of the array. A method is proposed to reduce these artifacts by a more sophisticated array evaluation.
BibTeX:
@inproceedings{Ehrenfried_etal2006b,
  author = {Ehrenfried, K. and Koop, L. and Henning, A. and Käpernick, K.},
  title = {Effects of wind-tunnel noise on array measurements in closed test section.},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-07_Ehrenfried_Koop_etal.pdf}
}
Élias G (1995), "Source localization with a two-dimensional focussed array: optimal signal processing for a cross-shaped array", In INTER-NOISE 95; Proceedings of the 1995 International Congress on Noise Control Engineering, Newport Beach, CA; UNITED STATES; 10-12 July 1995. , pp. 1175-1178.
Abstract: In order to overcome the poor performance of a focused cross-shaped array for 2D localization, a new array processing method based on discarding part of the array cross-spectral density matrix is presented. Numerical simulations show that it leads to acoustic source images close to those obtained with a full square array.
BibTeX:
@inproceedings{Elias1995,
  author = {Élias, G.},
  title = {Source localization with a two-dimensional focussed array: optimal signal processing for a cross-shaped array},
  booktitle = {INTER-NOISE 95; Proceedings of the 1995 International Congress on Noise Control Engineering, Newport Beach, CA; UNITED STATES; 10-12 July 1995},
  year = {1995},
  pages = {1175--1178}
}
Eret P and Meskell C (2012), "Microphone arrays for compressed air leakage detection", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-17., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Compressed air energy is expensive, but common in industrial manufacturing plant. However, up to 30% of the generated compressed air energy is lost due to leakage. Best practice requires ongoing leak detection and repair. Leak detection in the ultrasonic frequency range using hand held devices is possible only over short distances as associated high-frequency waves with do not propagate well. Pressurized air escaping to ambient also generates frequencies below 20kHz. In this paper, beamforming in the audible frequency range is tested as a tool for localization of compressed air leaks at larger distances. Both advanced time and frequency domain beamforming methods have been implemented in a variety of situations on a laboratory experimental rig with several open blows representing leakage in a noisy environment typical of a factory setting. The advanced time domain broadband beamformer gives clearer initial noise maps than narrowband frequency domain approach as the broadband nature of the leakage is better exploited. The advanced beamforming in frequency domain is more effective in spatial resolution. Based on these initial results it is concluded that the microphone array approach has the potential to be a robust leak identification tool
BibTeX:
@inproceedings{EretMeskell2012,
  author = {Eret, P. and Meskell, C.},
  title = {Microphone arrays for compressed air leakage detection},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-17.pdf}
}
Eric M and Miškovic M (2012), "Novel methods for acoustic indoor measurements and applications in aero-engine test cells", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-04., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Concept of steered covariance matrix (STCM) was proposed in far-field wideband beamforming but to the authors' best knowledge this approach is not widely exploited in near-field beamforming applied in acoustic mapping. In this paper we will give theoretical background of steered covariance matrix approach applied in near-field signal scenario combined with classical Bartlett and high-resolution spectral method MUSIC in order to see if this approach can improve resolution properties as well as dynamic range in near-field array processing applied in acoustic mapping. Results provided by simulations and measurements will be compared and presented in this paper.
BibTeX:
@inproceedings{EricMiskovic2012,
  author = {Eric, M. and Miškovic, M.},
  title = {Novel methods for acoustic indoor measurements and applications in aero-engine test cells},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-04.pdf}
}
Erić M and Mišković M (2014), "Laboratory ModeI of Acoustic Camera Based on Direct Localization Methods: Concept, Implementation and Some Experimental Results", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-21., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In previous BeBeC 2012 conference authors proposed direct localization method based on steered covariance matrix approach, as an innovative method which can be applied for acoustical mapping in acoustic camera. Meanwhile, the authors realized low cost laboratory model of acoustic camera, named it LM-ERA. It integrates hardware components such as microphone array, signal processing platform with multichannel signal acquisition daughter boards, video camera and PC computer. Application software with Graphical User Interface is developed in MATLAB. Concept and practical implementation of laboratory model of acoustic camera LM-ERA are shortly presented in the paper. Some experimental results of acoustical mapping in real indoor environment are also presented in the paper. In order to illustrate functionality and performances of the realized LM-ERA acoustic camera preliminary experimental results provided by the use LM-ERA acoustic camera are compared with results provided by Brüel & Kjær acoustic camera for the same signal scenario.
BibTeX:
@inproceedings{EricMiskovic2014,
  author = {Erić, M. and Mišković, M.},
  title = {Laboratory ModeI of Acoustic Camera Based on Direct Localization Methods: Concept, Implementation and Some Experimental Results},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-21.pdf}
}
Faszer A, Hynes T, Blaabjerg C and Shin H-C (2006), "Acoustic Beamforming and Holography Measurements of Modified Boundary Layer Trailing-Edge Noise", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2566., May, 2006.
Abstract: This paper investigates how the trailing-edge noise mechanism is affected by manipulation of the turbulent boundary layer by means of suction and blowing. By manipulating the boundary layer (the noise source) and determining the effect on trailing-edge noise, better understanding of the trailing-edge noise generation mechanism can be gained. A 0.5 m chord, 0.585 m span NACA 0012 aerofoil was tested on an acoustically treated open-jet wind tunnel. Changeable plates were used on a hollow trailing-edge to allow suction and blowing manipulation of the boundary layer near the trailing-edge. Suction/blowing was achieved using an industrial vacuum/blower with an inline acoustic silencer to minimize noise contamination due to the vacuum/blower. Acoustic measurements were obtained using a Brüel & Kjær 60-channel sector-wheel-array suited for both beamforming and acoustic holography measurements. The two acoustic measurement techniques, were used to obtain measurements over the frequency range of interest for trailing-edge noise. Hotwire anemometry was used for aerodynamic measurements of the boundary layer noise source. The results in this paper detail: 1) the effect on trailing-edge noise of the different trailing-edge plate geometries 2) the effect on trailing-edge noise of manipulating the boundary layer using suction and blowing 3) the aerodynamic effect of suction and blowing on the boundary layer velocity fluctuations.
BibTeX:
@inproceedings{Faszer_etal2006,
  author = {Faszer, A. and Hynes, T. and Blaabjerg, C. and Shin, H.-C.},
  title = {Acoustic Beamforming and Holography Measurements of Modified Boundary Layer Trailing-Edge Noise},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO06_1268/PV2006_2566.pdf}
}
Fenech BA (2009), "Accurate aeroacoustic measurements in closed-section hard-walled wind tunnels". Thesis at: University of Southampton, School of Engineering Sciences.
Abstract: Noise emissions from aircraft are of major concern to aircraft manufacturers. There are various analytical, empirical and numerical tools to help in the design of quieter aircraft, however aeroacoustic measurements in wind tunnels are still required. There is a growing interest in simultaneous aerodynamic and aeroacoustic measurements in hard-walled closed-section wind tunnels. The research hypothesis of this work is whether accurate aeroacoustic measurements are possible in this type of wind tunnel. Two issues are of particular concern: the reverberation sound field and high background noise levels. De-reverberation, based on an Image Source Model (ISM), is proposed to tackle the first issue by incorporating the reflections in the focused beamformer. This technique is computationally fast and easy to implement. Source Power Integration and deconvolution techniques are shown to be still valid in de-reverberation. Measurements in a closed section wind tunnel have shown that an ISM gives a better estimate of the Green's functions, when compared to free-space Green's functions. Furthermore de-reverberation yielded more accurate source strength estimates from the beamformer. Qualitatively, de-convolved results were no different than when using free-space Green's functions. Simulations have shown that the ISM can become unstable at high frequencies if position errors are present. It is therefore recommended to limit the application of the ISM to frequencies below 10 kHz. At low frequencies the accuracy of beamforming levels is highly dependent on the level of noise contamination of the input data. Removing the diagonal of the cross spectral matrix might not be sufficient to eliminate this noise.
BibTeX:
@phdthesis{Fenech2009,
  author = {Fenech, B. A.},
  title = {Accurate aeroacoustic measurements in closed-section hard-walled wind tunnels},
  school = {University of Southampton, School of Engineering Sciences},
  year = {2009},
  url = {http://eprints.soton.ac.uk/71636/}
}
Fenech B and Takeda K (2008), "Beamforming accuracy in closed-section wind tunnels", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)., AIAA-2008-2908., May, 2008.
Abstract: The ability to perform aeroacoustic measurements in closed-section wind tunnels is important in vehicle design, but presents significant problems compared with anechoic open-jet tunnel testing. The use of microphone arrays and beamforming processing can yield useful source localisation information, but there are concerns as to the consistency of quantitative results from such methods. Most of the limitations are due to the assumption of uncorrelated monopoles having uniform spherical directivity patterns. However there are other effects, such as the acoustic properties of the measuring environment and the position of the source with respect to nearby rigid boundaries. These effects are investigated in this paper using a calibration source with a known sound power level. It was found that the errors in the beamformer levels are frequency dependent, and also depend on the position of the source with respect to nearby boundaries. An image source model can give improvements in the beamformer accuracy, however the frequency-dependence of the errors could only be minimised by using measured transfer functions.
BibTeX:
@inproceedings{FenechTakeda2008,
  author = {Fenech, B. and Takeda, K.},
  title = {Beamforming accuracy in closed-section wind tunnels},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)},
  year = {2008},
  doi = {10.2514/6.2008-2908}
}
Fenech B and Takeda K (2007), "Towards more Accurate Beamforming Levels in Closed-Section Wind Tunnels via De-Reverberation", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), Rome, Italy, 21 - 23 May 2007., AIAA-2007-3431., May, 2007.
Abstract: The ability to perform aeroacoustic measurements in closed-section wind tunnels is important in vehicle design, but presents signi¯cant problems compared with anechoic open-jet tunnel testing. The use of microphone arrays and beamforming processing can yield useful source localisation information, but there are concerns as to the consistency of quantitative results from such methods. In this paper some of the de¯ciencies of current beamforming practice are highlighted; in particular, inaccuracies in levels arising from the reverberant sound ¯eld in hard-walled wind tunnels. Notably, the use of free-space Green's functions when beamforming in such conditions is shown to be a signi¯cant source of error, and an image source method is proposed to improve accuracy by de-reverberating the measuring environment. Comparisons are made between the conventional and proposed approaches using microphone array measurements of a compact source in a closed section wind tunnel. Results show that the new de-reverberation method can give improvements in accuracy even if the wind tunnel geometry is not modelled accurately, provided that the number of image sources is chosen correctly. The results also highlight the significant challenges associated with Green's functions measurements in highly-reverberant environments.
BibTeX:
@inproceedings{FenechTakeda2007,
  author = {Fenech, B. and Takeda, K},
  title = {Towards more Accurate Beamforming Levels in Closed-Section Wind Tunnels via De-Reverberation},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), Rome, Italy, 21 - 23 May 2007},
  year = {2007}
}
Fine N and Kring D (2005), "Opto-Acoustic Tracking of Aircraft Wake Vortices", In 11th AIAA/CEAS Aeroacoustics Conference., AIAA-2005-2965., May, 2005.
Abstract: Flight Safety Technologies, Inc. is developing an opto-acoustic sensor array called SOCRATES™ to detect and track the sound generated by the trailing wake vortices created by aircraft. Tracking these aircraft wake vortices during arrival and departure will allow for safer and more efficient airport operations. The sensor array, in essence a type of sonar, employs infrared lasers that act as microphones. This paper describes the sensor array and its ongoing field testing.
BibTeX:
@inproceedings{FineKring2005,
  author = {Fine, N. and Kring, D.},
  title = {Opto-Acoustic Tracking of Aircraft Wake Vortices},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference},
  year = {2005},
  doi = {10.2514/6.2005-2965}
}
Fisher MJ, Harper-Bourne M and Glegg SAL (1977), "Jet engine noise source location: The polar correlation technique", J. Sound Vib.., March, 1977. Vol. 51(1), pp. 23-54.
Abstract: The objective of this paper is to introduce a new method of source location for use in aero-engine noise research. The technique, termed “polar correlation”, employs an array of far field microphones which are normally located on a polar arc centred on the jet nozzle. It is demonstrated that measurements of the cross power spectral density of signals from such an array can be employed to obtain both the location and relative strengths of an axially distributed array of sound sources, for any frequency of interest. For the modern generation of high by-pass ratio engine this might include a measurement of the relative contribution to the far field noise emanating from the fan inlet, by-pass duct and hot core exhaust as well as indicating that portion of the jet flow which is the principal contributor to the frequency considered. The potential of this method is illustrated by examples of test results for full size jet engines and model jets. Certain fundamental and philosophical difficulties involved in the general use of this and other far field source location methods are also reviewed is some detail.
BibTeX:
@article{Fisher_etal1977,
  author = {Fisher, M. J. and Harper-Bourne, M. and Glegg, S. A. L.},
  title = {Jet engine noise source location: The polar correlation technique},
  journal = {J. Sound Vib.},
  year = {1977},
  volume = {51},
  number = {1},
  pages = {23--54},
  doi = {10.1016/S0022-460X(77)80111-9}
}
Fisher MJ and Holland KR (1997), "Measuring the Relative Strengths of a Set of Partially Coherent Acoustic Sources", J. Sound Vib.., March, 1997. Vol. 201(1), pp. 103-125.
Abstract: The measurement of the relative contributions to the acoustic field made by a set of sources, which by necessity must operate simultaneously, is of importance in many areas of noise control technology. A partial solution to this problem, proposed in the 1970s, was the Polar Correlation Technique. This recognized, initially, the Fourier transform relationship between cross-spectra, measured in the acoustic far field, and the distribution of source strength of a line array of sources, typical of an aero-engine, for example. In a second development (1981) a parametric method was developed. Essentially, the position of the contributing sources was assumed to be known and a least squares error procedure was employed to establish an optimum fit between the source strength distribution and the cross-spectral data. A major restriction, however, was the necessary assumption of mutually incoherent sources. In the present work it is demonstrated that this restriction is unnecessary, albeit at the expense of some extra data processing. Specifically, we show that by employing several reference microphones, as opposed to one for incoherent sources, both the amplitude of and coherence between an array of sources may be determined. The potential capability of the method is established both analytically and through extensive numerical simulation.
BibTeX:
@article{FisherHolland1997,
  author = {Fisher, M. J. and Holland, K. R.},
  title = {Measuring the Relative Strengths of a Set of Partially Coherent Acoustic Sources},
  journal = {J. Sound Vib.},
  year = {1997},
  volume = {201},
  number = {1},
  pages = {103--125},
  doi = {10.1006/jsvi.1996.0743}
}
Fisher MJ and Holland KR (1994), "Near field noise prediction requirements" (ISVR-TR-234)
BibTeX:
@techreport{FisherHolland94,
  author = {Fisher, M. J. and Holland, K. R.},
  title = {Near field noise prediction requirements},
  year = {1994},
  number = {ISVR-TR-234}
}
Fleischer H, Sassaroli A and Zillmann J (2010), "Aeroacoustic Investigation of Free Turbulent Jet Flow - A Combined Experimental Approach", In 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010., AIAA-2010-3961., June, 2010.
Abstract: The aerodynamic and acoustic aspects of classical single turbulent jets have long been a matter of interest, because of their relation with the nozzle efflux of turbo jet engines. Hence the analysis of the jet’s turbulence behavior and the localization and the understanding of the corresponding acoustic noise sources can be directly transferred to the practical environmental problem of engine jet noise. This study introduces the experimental examination of the jet’s aerodynamic and acoustic properties by means of hot-wire measurements to map the flow field combined with phased array measurements to describe the acoustic features. The analysis is carried out at high subsonic speeds for two different nozzle shapes to follow divers’ cases of jet noise appearance.
BibTeX:
@inproceedings{Fleischer_etal2010,
  author = {Fleischer, H. and Sassaroli, A. and Zillmann, J.},
  title = {Aeroacoustic Investigation of Free Turbulent Jet Flow - A Combined Experimental Approach},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010},
  year = {2010}
}
Fleury V and Bulte J (2009), "Extension of Beamforming Algorithms to Analysis Moving Sources", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3280., May, 2009.
BibTeX:
@inproceedings{FleuryBulte2009,
  author = {Fleury, V. and Bulte, J.},
  title = {Extension of Beamforming Algorithms to Analysis Moving Sources},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009},
  doi = {10.2514/6.2009-3280}
}
Fleury V and Chélius A (2013), "Analysis of contra rotating open rotors flyover noise data by beamforming techniques", In Proceedings of Meetings on Acoustics / Volume 19., BeBeC-2012-02., June, 2013. Vol. 19, pp. POMA Volume 19, pp. 030123 (June 2013); (7 pages).
Abstract: For the preparation of forthcoming flyover CROR noise tests, CROR noise data are first simulated by a hybrid CFD/CAA solver and are then analyzed by a beamforming technique. The CROR is a realistic full-size CROR flying over a ground microphone array in take-off conditions. For the blade passage frequency of each rotor, the de-Dopplerized spectral density is well recovered by the beamforming technique from the microphone array data. However, the spectral density at the interaction frequencies is wrongly estimated. In this case, the beamforming technique, based on an acoustic model consisting of uncorrelated monopoles, should be modified in order to take into account the strong correlation of the acoustic sources between each rotor.
BibTeX:
@inproceedings{FleuryChelius2013,
  author = {Fleury, V. and Chélius, A.},
  title = {Analysis of contra rotating open rotors flyover noise data by beamforming techniques},
  booktitle = {Proceedings of Meetings on Acoustics / Volume 19},
  year = {2013},
  volume = {19},
  pages = {POMA Volume 19, pp. 030123 (June 2013); (7 pages)},
  note = {ICA 2013 Montreal, Canada, 2 - 7 June 2013},
  doi = {10.1121/1.4799312}
}
Fleury V, Coste L, Davy R, Mignosi A, Cariou C and Prosper J-M (2012), "Optimization of Microphone Array Wall Mountings in Closed-Section Wind Tunnels", AIAA Journal. Vol. 50(11), pp. 2325-2335.
BibTeX:
@article{Fleury_etal2012,
  author = {Fleury, V. and Coste, L. and Davy, R. and Mignosi, A. and Cariou, C. and Prosper, J.-M.},
  title = {Optimization of Microphone Array Wall Mountings in Closed-Section Wind Tunnels},
  journal = {AIAA Journal},
  year = {2012},
  volume = {50},
  number = {11},
  pages = {2325--2335},
  doi = {10.2514/1.J051336}
}
Fleury V, Coste L, Davy R, Mignosi A, Prosper J-M and Cariou C (2010), "Optimization of Microphone Array Wall-Mountings in Closed-Section Wind Tunnels", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3738., June, 2010.
Abstract: The objective of the present paper is to improve the implementation of microphone arrays on the wall of closed-section wind tunnels. A test campaign has been conducted in the ONERA F2 1.4 m × 1.8 m wind tunnel to investigate the performance of thin and smooth metallic clothes to protect the microphones from the hydrodynamic fluctuations in the turbulent boundary-layer flow and, still, to preserve the transmitted acoustic signal. Three microphone mountings have been considered : individually recessed microphones in (i) cylindrical and (ii) conical apertures and (iii) a recessed, screened, large-scale micro-phone mounting plate (microphones flush with the plate). It was found that by covering the top of the cylindrical and conical microphone apertures with a wire-mesh, the strong self-noise due to the interaction of the boundary-layer flow with the cavities can be suppressed. The most significant noise reduction is obtained when the large-scale microphone mounting plate is recessed behind the metallic wire-mesh. A reduction by up to 20 dB is then obtained with respect to a flush-mounted, unscreened, microphone. This microphone mounting out-performs the cone-nose-protected and Kevlar-protected microphone mountings, two conventional low-noise devices. Thanks to an original calibration technique, the acoustic response of the tested microphone mountings could be evaluated in presence of flow (≤ 80 m/s). The recessed, screened, microphone mounting plate has an oscillating acoustic response (in function of the frequency) by less than 5 dB deviation. This attenuation can be post-corrected by using a very simple acoustic model.
BibTeX:
@inproceedings{Fleury_etal2010,
  author = {Fleury, V. and Coste, L. and Davy, R. and Mignosi, A. and Prosper, J.-M. and Cariou, C.},
  title = {Optimization of Microphone Array Wall-Mountings in Closed-Section Wind Tunnels},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Fleury V and Davy R (2012), "Beamforming-Based Noise Level Measurements in Hard-Wall Closed-Section Wind Tunnels", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)., AIAA-2012-2226., June, 2012.
BibTeX:
@inproceedings{FleuryDavy2012,
  author = {Fleury, V. and Davy, R.},
  title = {Beamforming-Based Noise Level Measurements in Hard-Wall Closed-Section Wind Tunnels},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)},
  year = {2012},
  doi = {10.2514/6.2012-2226}
}
Fleury V and Malbequi P (2012), "Slat noise assessment from A340 flyover measurements with phased-array microphones", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-02., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: To predict and optimize the noise impact of aircraft traffic around airports, airframe noise needs to be described by simple but reliable acoustic models. Semiempirical and analytical models for high-lift and landing-gear noise are found in the literature for instance. The present work is focused on the assessment of slat noise from real aircraft flyover noise measurements. The aircraft is an Airbus A340 during approach. The originality of the approach is that it uses a recent beamforming-based deconvolution technique. The main interest of the method is to spatially separate the various airframe noise sources and to provide their individual de-Dopplerized acoustic levels over a range of more than 10 dB. Slat noise spectra and directivity patterns are computed for two flight velocities, 150 kts and 175 kts. The obtained results are in good agreement with the prediction from the slat noise model of Dobrzynski & Pott-Pollenske [AIAA paper 2001-2158]. Beamforming-based deconvolution techniques prove to be efficient tools to analyze real aircraft flyover noise.
BibTeX:
@inproceedings{FleuryMalbequi2012,
  author = {Fleury, V. and Malbequi, P.},
  title = {Slat noise assessment from A340 flyover measurements with phased-array microphones},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-02.pdf}
}
Flynn OE and Kinns R (1976), "Multiplicative signal processing for sound source location on jet engines", J. Sound Vib.., May, 1976. Vol. 46, pp. 137-150.
Abstract: It is known that multiplicative processing of signals from receiver arrays can be used to obtain increased resolution for target identification where the target signal is strong in relation to extraneous noise. Sound source location in jet engines requires resolution of the order of a wavelength where the source region may have high directionality and several types of sound sources may interact. There is an analogy between target identification and the location of sound sources in jet engines where the extent of sources is not great on a wavelength scale. A theory for multiplicative processing of signals from two sub-arrays is developed for the case of a line source of generally correlated sound radiators which share the measurable far-field properties of a real jet engine. The real part of the cross-spectrum of the sub-array signals is used as an estimator of frequency dependent sound source intensity and results are compared with their equivalents for additive processing. The method has been implemented on a mini-computer and used for studies on full-size jet engines. Some typical results are presented.
BibTeX:
@article{FlynnKinns1976,
  author = {Flynn, O. E. and Kinns, R.},
  title = {Multiplicative signal processing for sound source location on jet engines},
  journal = {J. Sound Vib.},
  year = {1976},
  volume = {46},
  pages = {137--150},
  doi = {10.1016/0022-460X(76)90823-3}
}
Fonseca WD, Gerges SNY and Dougherty RP (2008), "Pass-By Noise Measurements Using Beamforming Technique", In Proceedings of COBEM 2009., October, 2008.
BibTeX:
@inproceedings{Fonseca_etal2008,
  author = {Fonseca, W. D. and Gerges, S. N. Y. and Dougherty, R. P.},
  title = {Pass-By Noise Measurements Using Beamforming Technique},
  booktitle = {Proceedings of COBEM 2009},
  year = {2008},
  note = {37th International Congress and Exposition on Noise Control Engineering - Internoise 2008, Shanghai, China, October 2008}
}
Fournier G, Élias G, Piet JF, Putcrabey S, Betrand P and Jacques A (1993), "Localisation de sources de bruit d'ecoulement sur maquette en soufflerie (Localization of flow noise sources in wind tunnel models)"
BibTeX:
@techreport{Fournieretal93,
  author = {Fournier, G. and Élias, G. and Piet, J. F. and Putcrabey, S. and Betrand, P. and Jacques, A.},
  title = {Localisation de sources de bruit d'ecoulement sur maquette en soufflerie (Localization of flow noise sources in wind tunnel models)},
  year = {1993}
}
Fritzsche C, Sarradj E and Geyer T (2009), "Silent owl flight: setup for flyover noise measurements", In Fortschritte der Akustik - NAG / DAGA.
BibTeX:
@inproceedings{Fritzsche2009,
  author = {Fritzsche, C. and Sarradj, E. and Geyer, T.},
  title = {Silent owl flight: setup for flyover noise measurements},
  booktitle = {Fortschritte der Akustik - NAG / DAGA},
  year = {2009}
}
Fuchs HV (1978), "On the application of acoustic “mirror”, “telescope” and “polar correlation” techniques to jet noise source location", J. Sound Vib.., May, 1978. Vol. 58(1), pp. 117-126.
Abstract: Jet noise source identification and location is still an important issue since no really conclusive or generally accepted description of the noise generation processes in turbulent jets has been achieved to data. While there is a definite need for a better understanding of jet mixing noise, one may question if far field approaches via acoustic mirror, telescope, or polar correlation techniques can provide the missing information. There are not only limitations in the spatial resolution which restrict these techniques to jet noise at the higher Strouhal and Mach numbers but also more fundamental difficulties in the interpretation of measured “equivalent source strength density distributions”. In particular, if large scale coherent turbulence structures participate in jet noise generation the assumption of a uniform amplitude and phase of the pressure field radiated from compact elements of this distribution is questionable. It is shown that various acoustic interference mechanisms due to mere source coherence and specific source structure effects may cause “mislocation” of sources in a jet. Some of these objections are less valid at the lower Helmholtz numbers but for these, unfortunately, the spatial resolution of all three techniques becomes poor. Since interpretation of source location results depends on a specific model of the jet noise sources it appears to be very difficult to gain from these three techniques a new insight into the problem for the relevant jet flow parameters.
BibTeX:
@article{Fuchs1978,
  author = {Fuchs, H. V.},
  title = {On the application of acoustic “mirror”, “telescope” and “polar correlation” techniques to jet noise source location},
  journal = {J. Sound Vib.},
  year = {1978},
  volume = {58},
  number = {1},
  pages = {117--126},
  doi = {10.1016/S0022-460X(78)80065-0}
}
Funke S, Dougherty RP and Michel U (2014), "SODIX in Comparison with Various Deconvolution Methods", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-11., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: SODIX is a method for the localization of sound sources including the quantification of their directivities. Other source localization methods commonly assume point monopole sources with uniform directivity. The performance of SODIX is compared in this paper with previously published results [9] of conventional delay-and-sum beamforming and the advanced deconvolution methods DAMAS, DAMAS2, CLEAN-SC, TIDY, and LPD by using the same set of array data. The results show that the resolution of SODIX is only slightly inferior to those of the best advanced beamforming methods.
BibTeX:
@inproceedings{FunkeDoughertyMichel2014,
  author = {Funke, S and Dougherty, R. P. and Michel, U.},
  title = {SODIX in Comparison with Various Deconvolution Methods},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-11.pdf}
}
Funke S, Skorpel A and Michel U (2012), "An extended formulation of the SODIX method with application to aeroengine broadband noise.", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), June 4 -6, 2012, Colorado Springs, Colorado, USA.
Abstract: An improved version of the inverse source location method SODIX is presented. SODIX models broadband noise sources with a set of directive point sources by minimizing the difference between a measured and a simulated cross-spectral matrix of microphone signals. One big advantage of the method in comparison to other source location methods is, that it calculates a directive source strength from each point source towards each microphone. The new version of SODIX includes an implicit consideration of the constraint of positive source strengths in the iteration process. This improvement made the optimization process more stable and in addition independent of the initially assume source distribution. The method is also extended for applications with multidimensional source and microphone arrangements. Further, it is shown that the main diagonal of the cross-spectral matrix can be removed from the calculations without any mathematical violations and that the absolute strengths of the dominating sources are preserved. The improvements of the method are shown with exemplary results using measured data from a static aeroengine freefield test.
BibTeX:
@inproceedings{Funke_etal2012,
  author = {Funke, S and Skorpel, A. and Michel, U.},
  title = {An extended formulation of the SODIX method with application to aeroengine broadband noise.},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), June 4 -6, 2012, Colorado Springs, Colorado, USA},
  year = {2012},
  doi = {10.2514/6.2012-2276}
}
Garcia-Pedroche M (2011), "Aeroacoustic Noise Source Identification Using Irregularly Sampled LDV Measurements Coupled with Beamforming", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2719., June, 2011.
Abstract: This paper develops a technique which relates dynamic pressure measurements taken outside the hydrodynamic field of a low speed jet to single point, one component velocity measurements taken within the jet using a Laser Doppler Velocimetry (LDV) system. To improve the signal to noise ratio of the pressure measurement, a coherence based acoustic beamforming technique is applied and focussed on the LDV measurement volume in order to evaluate its contribution to the measured sound. As the pressure samples are acquired at regular time steps whereas the velocity at irregular time intervals dependent on the particle seeding, the calculation of the auto- and cross-spectra of the pressure and velocity measurements require special treatment. The signal processing procedures required to calculate these are described and implemented in the paper. To validate the proposed technique real experimental data was analysed. Laser Doppler Velocimetry measured velocity fluctuations created by rods placed in a jet. Synchronously, a planar random array focused on the same plane as the LDV measurement, measured pressure fluctuation outside the hydrodynamic field. The same set of data was then analysed using conventional and coherence based beamforming algorithms. The results from both techniques were compared. While conventional beamforming identified the contribution from the main sources within the flow, the coherence based method was able to single out the source related to the local measurement. The results shown demonstrated how coherence based beamforming, combined with LDV, can be a useful tool for aeroacoustic noise source investigations.
BibTeX:
@inproceedings{Garcia-Pedroche2011,
  author = {Garcia-Pedroche, Miguel},
  title = {Aeroacoustic Noise Source Identification Using Irregularly Sampled LDV Measurements Coupled with Beamforming},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Gauthier P-A, Gérard A, Camier C and A. Berry A (2014), "Acoustical inverse problems regularization: Direct definition of filter factors using Signal-to-Noise Ratio", Journal of Sound and Vibration. Vol. 333, pp. 761-773.
Abstract: Acoustic imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for acoustic imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement noise. The thresholding operation is achieved using modified filter functions. The originality of the approach is to propose the definition of a filter factor which provides more damping to the singular components dominated by noise than that given by the Tikhonov filter. This has the advantage of potentially simplifying the selection of the best regularization amount in inverse problems. Theoretical results show that this method is comparatively more accurate than Tikhonov regularization and truncated singular value decomposition.
BibTeX:
@article{Gauthier_etal2014,
  author = {Gauthier, P.-A. and Gérard, A. and Camier, C. and A. Berry, A.},
  title = {Acoustical inverse problems regularization: Direct definition of filter factors using Signal-to-Noise Ratio},
  journal = {Journal of Sound and Vibration},
  year = {2014},
  volume = {333},
  pages = {761--773},
  doi = {10.1016/j.jsv.2013.10.011}
}
Genescà M, Romeu J, Pàmies T and Sánchez A (2009), "Real time aircraft fly-over noise discrimination", J. Sound Vib.. Vol. 323(1-2), pp. 112-129.
Abstract: A method for measuring aircraft noise time history with automatic elimination of simultaneous urban noise is presented in this paper. A 3 m-long 12-microphone sparse array has been proven to give good performance in a wide range of urban placements. Nowadays, urban placements have to be avoided because their background noise has a great influence on the measurements made by sound level meters or single microphones. Because of the small device size and low number of microphones (that make it so easy to set up), the resolution of the device is not high enough to provide a clean aircraft noise time history by only applying frequency domain beamforming to the spatial cross-correlations of the microphones’ signals. Therefore, a new step to the processing algorithm has been added to eliminate this handicap.
BibTeX:
@article{Genesca_etal2009,
  author = {Genescà, M. and Romeu, J. and Pàmies, T. and Sánchez, A.},
  title = {Real time aircraft fly-over noise discrimination},
  journal = {J. Sound Vib.},
  year = {2009},
  volume = {323},
  number = {1--2},
  pages = {112--129},
  doi = {10.1016/j.jsv.2008.12.030}
}
Gerges SNY, Fonseca WD and Dougherty RP (2009), "State of the Art Beamforming Software and Hardware for Applications", In 16th International Congress on Sound and Vibration, 5-9 July 2009, Kraków , Poland., Proceedings of 16th International Congress on Sound and Vibration, 5-9 July 2009, Kraków , Poland., July, 2009.
Abstract: Hybrid cars have become more important due to increasing fuel costs and the goal of reducing CO2 emissions. In this talk, the noise producing mechanisms of a Honda Civic Hybrid will be studied using a phased array and a range of beamforming techniques. The importance of multiple propagation paths, incoherent and coherent source distributions, tone and broadband noise, and array focus distance will be illustrated. Frequencies to be considered run from 100 Hz to 30 kHz. Methods to be discussed and compared include classical beamforming in 2D and 3D, beamforming with enhanced resolution, CLEAN-SC, and DAMAS2. Emphasis will be given to exterior sounds, with some treatment of the interior case. The goal of the presentation will be to give a basic understanding of beamforming techniques including software and hardware and to illustrate their wide applicability to common noise control problems and the implications of the choice of method for different types of noise sources.
BibTeX:
@inproceedings{Gerges_etal2009a,
  author = {Gerges, S. N. Y. and Fonseca, W. D. and Dougherty, R. P.},
  title = {State of the Art Beamforming Software and Hardware for Applications},
  booktitle = {16th International Congress on Sound and Vibration, 5-9 July 2009, Kraków , Poland},
  year = {2009},
  note = {Keynote lecture 2}
}
Gerges SNY, Fonseca WD and Dougherty RP (2009), "Beamforming technique applied to the study of acoustic effect in damping treatment", In Proceedings of COBEM 2009., Proceedings of COBEM 2009., November, 2009.
Abstract: Damping materials such as Asphalt Melt Sheet and LASD material (Liquid Applied Sprayable Damper) are used to reduce vibration levels within passenger vehicles. The performance of the acoustic package depends on the position of application and the thickness of the material. These parameters must be optimized to ensure the best performance with lower cost and weight. However, the effect of this positioning on sound radiation has not been evaluated. This article presents a study ofsound radiation behavior in an ideal prototype passenger vehicle with optimized damping treatmentusing beamforming techniques. Beamforming was applied before and after application of damping material. This aims to elucidate the regions of higher sound radiation and the noise reduction after damping treatment.
BibTeX:
@inproceedings{Gerges_etal2009b,
  author = {Gerges, S. N. Y. and Fonseca, W. D. and Dougherty, R. P.},
  title = {Beamforming technique applied to the study of acoustic effect in damping treatment},
  booktitle = {Proceedings of COBEM 2009},
  year = {2009},
  note = {20th International Congress of Mechanical Engineering, 15-20 November 2009, Gramado, RS, Brazil}
}
Gerold CH and Wiese MR (1990), "Application of beamform to sound propagation in the atmoshere", In 13th AIAA Aeroacoustics Conference, Talahassee, Fl, Oct. 22-24, 1990., AIAA-1990-3990., October, 1990.
Abstract: Beamforming is a signal processing technique that uses the combined signal from an array of sensors as a spatial filter to locate sound sources. The method is established both in underwater acoustics and in seismological applications. The current project is intended to determine the feasibility of beamformer technology in atmospheric acoustics. The microphone array, data collection, and signal processing technologies are discussed. The signal processing method is the maximum-likelihood estimate algorithm in conjunction with eigenvalue decomposition. Input data are block averaged and filtered adaptively to reduce the effect of noise. Analysis is performed in the frequency domain. Field data have been obtained for stationary, as well as moving sound sources. Work to date indicates that stationary sources can be located and single moving sources can be tracked with adequate resolution using the beamformer. Multiple targets at the same frequency are misidentified as one source located at a position amid the sources. This may be due to the excessive
beamwidth that results when microphone spacing is small in comparison to the sound wavelength. At the other extreme, as the microphone spacing becomes large compared to the wavelenglh, spatial aliasing occurs. Thus, it is necessary to size the sensor array according to the expected range of frequencies of the source. Block averaging and adaptive filtering in the signal processing eliminate many false source indications. Current research concentrates on implementing further improvements in the signal processing to enhance resolution. and reduce the effects of noise.
BibTeX:
@inproceedings{GeroldWiese1990,
  author = {Gerold, Carl H. and Wiese, Michael R.},
  title = {Application of beamform to sound propagation in the atmoshere},
  booktitle = {13th AIAA Aeroacoustics Conference, Talahassee, Fl, Oct. 22-24, 1990},
  year = {1990}
}
Geyer T, Sarradj E and Fritzsche C (2012), "Nature-Inspired Porous Airfoils for Sound Reduction", In Nature-Inspired Fluid Mechanics. Springer.
BibTeX:
@incollection{Geyer2012b,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  editor = {Tropea, C. and Bleckmann, H.},
  title = {Nature-Inspired Porous Airfoils for Sound Reduction},
  booktitle = {Nature-Inspired Fluid Mechanics},
  publisher = {Springer},
  year = {2012}
}
Geyer T, Sarradj E and Fritzsche C (2013), "Silent Owl Flight: Comparative Acoustic Wind Tunnel Measurements on Prepared Wings", Acta Acustica united with Acustica. Vol. 99(1), pp. 139-153. S. Hirzel Verlag.
BibTeX:
@article{Geyer2013,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Silent Owl Flight: Comparative Acoustic Wind Tunnel Measurements on Prepared Wings},
  journal = {Acta Acustica united with Acustica},
  publisher = {S. Hirzel Verlag},
  year = {2013},
  volume = {99},
  number = {1},
  pages = {139--153}
}
Geyer T, Sarradj E and Fritzsche C (2012), "Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings.", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference). AIAA-Paper 2012-2230.
BibTeX:
@inproceedings{Geyer2012c,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Silent Owl Flight: Acoustic Wind Tunnel Measurements on Prepared Wings.},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference). AIAA-Paper 2012-2230},
  year = {2012}
}
Geyer T, Sarradj E and Fritzsche C (2010), "Measurement of the noise generation at the trailing edge of porous airfoils", Experiments in Fluids. Vol. 48(2), pp. 291-308.
Abstract: Owls are commonly known for their quiet flight, enabled by three adaptions of their wings and plumage: leading edge serrations, trailing edge fringes and a soft and elastic downy upper surface of the feathers. In order to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air, an experimental survey on a set of airfoils made of different porous materials was carried out. Several airfoils with the same shape and size but made of different porous materials characterized by their flow resistivities and one non-porous reference airfoil were subject to the flow in an aeroacoustic open jet wind tunnel. The flow speed has been varied between approximately 25 and 50 m/s. The geometric angle of attack ranged from −16° to 20° in 4°-steps. The results of the aeroacoustic measurements, made with a 56-microphone array positioned out of flow, and of the measurements of lift and drag are given and discussed.
BibTeX:
@article{Geyer_etal2010,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Measurement of the noise generation at the trailing edge of porous airfoils},
  journal = {Experiments in Fluids},
  year = {2010},
  volume = {48},
  number = {2},
  pages = {291--308},
  doi = {10.1007/s00348-009-0739-x}
}
Geyer T, Sarradj E and Fritzsche C (2010), "Porous Airfoils: Noise Reduction and Boundary Layer Effects", Int. J. Aeroacoustics., AIAA-2009-3329. Vol. 9(6), pp. 787-820.
Abstract: The present paper describes acoustic and hot-wire measurements that were done in the aeroacoustic wind tunnel at the Brandenburg Technical University of Cottbus on various SD7003-type airfoils made of different porous (fl ow permeable) materials. The objective of the research is the analysis of the turbulent boundary layer properties of porous airfoils and, subsequently, of the noise generated at the trailing edge. The in fluence of the porous materials, characterized by their air flow resistivity, is discussed. The acoustic measurements were performed using a planar 56-channel microphone array and the boundary layer properties were measured using constant temperature anemometry. The recorded acoustic data underwent further processing by application of an advanced beamforming algorithm. A noticeable reduction of the emitted trailing edge noise was measured for the porous airfoils, especially at low and medium frequencies. At high frequencies, some of the porous airfoils were found to generate more noise than the reference airfoil which might be due to the surface roughness noise contribution. It is found that the turbulent boundary layer thickness and the boundary layer displacement thickness of the airfoils increase with decreasing flow resistivities for both suction and pressure side. Both boundary layer thickness and displacement thickness of the non-porous airfoil are below those of the porous airfoils.
BibTeX:
@article{Geyer_etal2010b,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Porous Airfoils: Noise Reduction and Boundary Layer Effects},
  journal = {Int. J. Aeroacoustics},
  year = {2010},
  volume = {9},
  number = {6},
  pages = {787--820},
  note = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3392.pdf}
}
Geyer T, Sarradj E and Fritzsche C (2010), "Porous Airfoils: Noise Reduction and Boundary Layer Effects", International Journal of Aeroacoustics. Vol. 9(6), pp. 787-820.
BibTeX:
@article{Geyer2010b,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Porous Airfoils: Noise Reduction and Boundary Layer Effects},
  journal = {International Journal of Aeroacoustics},
  year = {2010},
  volume = {9},
  number = {6},
  pages = {787-820}
}
Geyer T, Sarradj E and Fritzsche C (2009), "Porous Airfoils: Noise Reduction and Boundary Layer Effects", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3329.
Abstract: The present paper describes acoustic and hot-wire measurements that were done in the aeroacoustic wind tunnel at the Brandenburg Technical University of Cottbus on various SD7003-type airfoils made of different porous (fl ow permeable) materials. The objective of the research is the analysis of the turbulent boundary layer properties of porous airfoils and, subsequently, of the noise generated at the trailing edge. The in fluence of the porous materials, characterized by their air flow resistivity, is discussed. The acoustic measurements were performed using a planar 56-channel microphone array and the boundary layer properties were measured using constant temperature anemometry. The recorded acoustic data underwent further processing by application of an advanced beamforming algorithm. A noticeable reduction of the emitted trailing edge noise was measured for the porous airfoils, especially at low and medium frequencies. At high frequencies, some of the porous airfoils were found to generate more noise than the reference airfoil which might be due to the surface roughness noise contribution. It is found that the turbulent boundary layer thickness and the boundary layer displacement thickness of the airfoils increase with decreasing flow resistivities for both suction and pressure side. Both boundary layer thickness and displacement thickness of the non-porous airfoil are below those of the porous airfoils.
BibTeX:
@inproceedings{Geyer_etal2009,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Porous Airfoils: Noise Reduction and Boundary Layer Effects},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3392.pdf}
}
Geyer T, Sarradj E and Fritzsche C (2009), "Silent owl flight: experiments in the aeroacoustic wind tunnel", In Fortschritte der Akustik - NAG / DAGA.
BibTeX:
@inproceedings{Geyer_etal2009a,
  author = {Geyer, T. and Sarradj, E. and Fritzsche, C.},
  title = {Silent owl flight: experiments in the aeroacoustic wind tunnel},
  booktitle = {Fortschritte der Akustik - NAG / DAGA},
  year = {2009}
}
Geyer T, Sarradj E and Giesler J (2012), "Application of a Beamforming Technique to the Measurement of Airfoil Leading Edge Noise", Advances in Acoustics and Vibration. Vol. 2012(905461), pp. 1-16.
BibTeX:
@article{Geyer2012,
  author = {Geyer, T. and Sarradj, E. and Giesler, J.},
  title = {Application of a Beamforming Technique to the Measurement of Airfoil Leading Edge Noise},
  journal = {Advances in Acoustics and Vibration},
  year = {2012},
  volume = {2012},
  number = {905461},
  pages = {1-16},
  doi = {10.1155/2012/905461}
}
Geyer T, Sarradj E, Giesler J and Hobracht M (2011), "Experimental assessment of the noise generated at the leading edge of porous airfoils using microphone array techniques", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)., AIAA-2011-2713., June, 2011.
BibTeX:
@inproceedings{Geyer_etal2011,
  author = {Geyer, T. and Sarradj,E. and Giesler,J. and Hobracht, .M},
  title = {Experimental assessment of the noise generated at the leading edge of porous airfoils using microphone array techniques},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference)},
  year = {2011},
  doi = {0.2514/6.2011-2713}
}
Giesler J and Sarradj E (2011), "Vorderkantenschall - Modelle und Versuch", In Fortschritte der Akustik - DAGA.
BibTeX:
@inproceedings{Giesler2011a,
  author = {Giesler, J. and Sarradj, E.},
  title = {Vorderkantenschall - Modelle und Versuch},
  booktitle = {Fortschritte der Akustik - DAGA},
  year = {2011}
}
Giesler J and Sarradj E (2010), "Experimentelle Analyse der aeroakustischen Schallentstehung an Zylinder-Profil-Anordnungen", In Fortschritte der Akustik - DAGA. , pp. 307-308.
BibTeX:
@inproceedings{Giesler2010,
  author = {Giesler, J. and Sarradj, E.},
  title = {Experimentelle Analyse der aeroakustischen Schallentstehung an Zylinder-Profil-Anordnungen},
  booktitle = {Fortschritte der Akustik - DAGA},
  year = {2010},
  pages = {307-308}
}
Giesler J and Sarradj E (2009), "Broadband noise investigation on rod-airfoil-configurations", In NAG/DAGA 2009 International Conference on Acoustics. , pp. 731-733. Deutsche Gesellschaft für Akustik e.V., Voltastraße 5, Gebäude 10-6, 13355 Berlin.
BibTeX:
@inproceedings{GieslerSarradj2009,
  author = {Giesler, J. and Sarradj, E.},
  title = {Broadband noise investigation on rod-airfoil-configurations},
  booktitle = {NAG/DAGA 2009 International Conference on Acoustics},
  publisher = {Deutsche Gesellschaft für Akustik e.V., Voltastraße 5, Gebäude 10-6, 13355 Berlin},
  year = {2009},
  pages = {731-733},
  note = {NAG/DAGA 2009 International Conference on Acoustics, Rotterdam, 23 - 26 March 2009, including the 35th German Annual Conference on Acoustics (DAGA)}
}
Ginn B, Gomes J and Hald J (2013), "Recent advances in Rail Vehicle Moving Source Beamforming", In Internoise 2013.
Abstract: A measurement technique is described for the localization and visualization of noise sources on moving rail vehicles using beamforming. The Delay-And-Sum (DAS) beamforming, is often used on stationary (fixed) sources. However the method can also be applied to moving sources such as rail vehicles, road vehicles and aircraft fly-overs, as well as rotating blades on wind turbines. Recently, deconvolution techniques have been introduced as post-processing after DAS to improve the spatial resolution and reduce the level of ghost sources in the calculated noise maps. This paper describes a commercially available system which includes DAS and deconvolution techniques, dedicated to the rail vehicle industry. Special consideration is paid to the configuration of the test site and its influence on the measurement results. The advantages of various microphone array designs for measurements on bogies, rails and pantographs are discussed. Guidelines are given for the selection of an appropriate array (half-wheel, logarithmic wheel) for the source of interest and illustrated with practical results from noise emission measurements on regional trains.
BibTeX:
@inproceedings{Ginn_etal2013,
  author = {Ginn, B. and Gomes, J. and Hald, J.},
  title = {Recent advances in Rail Vehicle Moving Source Beamforming},
  booktitle = {Internoise 2013},
  year = {2013},
  note = {Innsbruck, Austria, 15-18 September 2013, Innsbruck,Austria}
}
Ginn B and Hald J (2010), "Aerodynamic noise source identification in wind tunnels using acoustical array techniques", In 8th MIRA International Vehicle Aerodynamics Conference - 'Low Carbon Vehicles' (2010).
BibTeX:
@inproceedings{Ginn-Hald-2010,
  author = {Ginn, B. and Hald, J.},
  title = {Aerodynamic noise source identification in wind tunnels using acoustical array techniques},
  booktitle = {8th MIRA International Vehicle Aerodynamics Conference - 'Low Carbon Vehicles' (2010)},
  year = {2010}
}
Glegg SAL (1982), "The accuracy of source distributions measured by using polar correlation", J. Sound Vib.. Vol. 80, pp. 31-40.
Abstract: The paper is concerned with the jet noise measurement errors associated with the polar correlation technique of source location. Two areas are examined in detail: the limitation of the line source model used to describe the source along a jet engine, and the time averaging required to estimate the spectral level of the sources at each location. Criteria are developed for the accuracy of source location data in terms of the measurement parameters.
BibTeX:
@article{Glegg1982,
  author = {Glegg, S. A. L.},
  title = {The accuracy of source distributions measured by using polar correlation},
  journal = {J. Sound Vib.},
  year = {1982},
  volume = {80},
  pages = {31--40},
  doi = {10.1016/0022-460X(82)90389-3}
}
Gomes J (2012), "Noise Source Identification with Blade Tracking on a Wind Turbine", In Internoise 2012.
Abstract: Manufacturers of wind turbines often use simulation techniques such as Computational Fluid Dynamics to analyse noise radiation from the blades. Although simulations are very attractive during the design phase, they do not take all mechanisms from the real life into account, and therefore real measurements will also be necessary for validation during development. Beamforming is a measurement technique for decomposing the sound into directions of incidence. Measurements are performed with an array of microphones and the output is typically visualized as a contour plot showing the noise contribution on the surface of interest. In this paper a tracking beamforming approach is applied on an operating wind turbine. Knowing the position of the turbine and measuring the blade(s) azimuth angle, the focus points can follow the movement of the blades, and the noise map can be visualized on the blade(s) for each azimuth angle step. The array used for the measurements consists of 9 lines of microphones lying on the ground (flush mounted in rigid plates) with 12 microphones per line. On one of the blades there was a set of known source locations (whooshing sound from accelerometers mounted on the blade), and the results confirmed their locations.
BibTeX:
@inproceedings{Gomes2012,
  author = {Gomes, J.},
  title = {Noise Source Identification with Blade Tracking on a Wind Turbine},
  booktitle = {Internoise 2012},
  year = {2012},
  note = {Internoise 2012, August 19-22, New York City, NY, USA}
}
Gomes J, Hald J and Ginn B (2013), "Localising noise sources on a rail vehicle during pass-by", In IWRN13, International Workshop on Railway Noise (2013).
BibTeX:
@inproceedings{GUomes_etal2013,
  author = {Gomes, J. and Hald, J. and Ginn, B.},
  title = {Localising noise sources on a rail vehicle during pass-by},
  booktitle = {IWRN13, International Workshop on Railway Noise (2013)},
  year = {2013}
}
van der Goot R, Hendriks J, . SK, Hermans G.and van der Wal W and Simons DG (2012), "A low cost, high resolution acoustic camera with a flexible microphone configuration", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-08., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The need for aircraft noise reduction is acknowledged worldwide. Acoustic cameras play an important role to identify aircraft noise sources. An acoustic camera tailored for aircraft noise was designed, built and tested by students of the Faculty of Aerospace Engineering of Delft University of Technology. The camera uses only 32 microphones, while still maintaining a high angular resolution. The design resulted in an acoustic camera tailored for measuring aircraft noise with a flexible array configuration and array aperture due to a clever mechanical construction. The system is easily transportable and has a short set up time (less than half an hour). The specifications of the acoustic camera are comparable to existing commercial ones. Various beamforming methods were implemented: conventional least-squares-based beamforming, Capon beamforming, the MUSIC algorithm and so-called CLEAN-PSF and CLEAN-SC. Due to its versatility, the camera can also be used for other applications, such as abatement of traffic and industrial noise and architectural and room acoustics. The developed acoustic camera was tested by measuring fly-over noise of landing aircraft. Despite its low cost design, the cameraproved to have the required angular resolution to clearly distinguish between engine and airframe noise
BibTeX:
@inproceedings{vanderGoot2012,
  author = {van der Goot, R. and Hendriks, J. and Scheper K . and Hermans, G.and van der Wal, W. and Simons, D. G.},
  title = {A low cost, high resolution acoustic camera with a flexible microphone configuration},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-08.pdf}
}
Gramann RA and Mocio J (1995), "Aeroacoustic measurements in wind tunnels using adaptive beamforming methods", J. Acoust. Soc. Am.. Vol. 97, pp. 3694-3701.
BibTeX:
@article{GramannMocio1995,
  author = {Gramann, Robert A. and Mocio, James},
  title = {Aeroacoustic measurements in wind tunnels using adaptive beamforming methods},
  journal = {J. Acoust. Soc. Am.},
  year = {1995},
  volume = {97},
  pages = {3694--3701}
}
Gramann RA and Mocio J (1993), "Aeroacoustic measurements in wind tunnels using conventional and adaptive beamforming methods", In 15th AIAA Aeroacoustics Conference, Long Beach, Ca, Oct. 25-27, 1993., AIAA-1993-4341.
BibTeX:
@inproceedings{GramannMocio1993,
  author = {Gramann, Robert A. and Mocio, James},
  title = {Aeroacoustic measurements in wind tunnels using conventional and adaptive beamforming methods},
  booktitle = {15th AIAA Aeroacoustics Conference, Long Beach, Ca, Oct. 25-27, 1993},
  year = {1993}
}
Graurock C and Sesterhenn J (2014), "Acoustic Array Measurements of Vulcano Jet Eruptions", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-26., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper presents an array measurement on the volcano Stromboli in the area of Sicilia in Italy. Eruptions of one of the calderas are characterized by a turbulent jet. So far volcanologists often use seismological equipment, but lately other technologies find their way into the volcanology and were used to describe the state of the volcano. As it is shown by numerical CFD-LES-simulations the distance of the shock-cells of supersonic jets vary with the Mach-number. The sound sources are shown by applying a beamforming algorithm and deconvolution methods (DAMAS2) with synthetic generated microphone data from the simulation. With the knowledge of the main source positions of the jet it is possible to identify the inner pressure beyond the nozzle. This paper presents the experimental setup and preliminary work to lay out the array. As the array setup is very much dependent on the local conditions which are found at the volcano, it is necessary to locate the microphone positions of the array ad-hoc at the caldera. Also first results of the measurements are presented. With further knowledge about the gas composition and the temperature of the jet it is possible to determine the Mach-number of the jet. The main aim of the measurement is to obtain more state information about the volcano.
BibTeX:
@inproceedings{GraurockSesterhenn2014,
  author = {Graurock, C. and Sesterhenn, J.},
  title = {Acoustic Array Measurements of Vulcano Jet Eruptions},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-26.pdf}
}
Grosser T, Elsafadi A, Hübner D, Böck R and Wendemuth A (2010), "Adaptive beamforming in speaker diarization", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-18., February, 2010. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In this paper we outline the developement of a system for speaker diarization within group meetings to prepare those for automatic speech recognition. Since the acceptance of headsets for group meeting recordings is very limited a more comfortable approach is to use beamforming and to steer an adaptive beamformer towards the person who is speaking. In our setup we used 5 room microphones plus 4 headsets providing reference signals for performance evaluations. Recordings of virtual group meetings with limited vocabulary were done. Choosing from a vocabulary of only 1700 words, multiple sentences were constructed which were then spontaneously used within the group meeting recordings. Our goal is to capture the dynamics of group meetings but with limited vocabulary to make robust automatic speech recognition feasible. We plan to combine two methods to prepare for speaker diarization, blind source separation and adaptive beamforming in combination with direction of arrival estimation for each speaker. In speaker diarization the goal is to find the segments of time in which each meeting attendee is speaking. Time segments in which two or more speakers are speaking are especially challenging. We plan to use blind source separation in conjunction with an adaptive beamformer to steer towards all speakers simultaneously and achieve one audio recording per speaker.
BibTeX:
@inproceedings{Grosser_2010,
  author = {Grosser, T. and Elsafadi, A. and Hübner, D. and Böck, R. and Wendemuth, A.},
  title = {Adaptive beamforming in speaker diarization},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-18.pdf}
}
Guérin S and Michel U (2006), "Aero-Engine Noise Investigated from Flight Tests", In 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 8-10 June 2006., AIAA-2006-2463.
Abstract: Over one hundred acoustic flyover tests were performed with an Airbus A319 in 2004 with the objective to improve some existing aircraft noise prediction tools developed by DLR to investigate noise abatement procedures. The present paper deals with the noise emission of the two CFM56-5A5 engines and some installation effects. The analysis is based on acoustic dedopplerized spectra and localization maps calculated with the pressure signals of a phased array of 168 microphones. This study shows that the prediction of jet mixing noise collapses reasonably well with the measurements, a modal analysis of buzz-saw tones based on the farfield directivity gives results in agreement with the theory of buzz-saw tone generation, the amplitude of the blade passing frequency tone depends on the slat/flap settings and airspeed but not on the landing gear position. As outlook some preliminary results calculated with a source amplitude assessment method are presented.
BibTeX:
@inproceedings{GuerinMichel2006,
  author = {Guérin, S. and Michel, U.},
  title = {Aero-Engine Noise Investigated from Flight Tests},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 8-10 June 2006},
  year = {2006}
}
Guérin S and Siller H (2008), "A Hybrid Time-Frequency Approach for the Source Localization Analysis of Acoustic Fly-over Tests", In 14th CEAS/AIAA Aeroacoustics Conference, Vancouver, British Columbia, Canada, 5-7 May 2008., AIAA-2008-2955.
Abstract: A hybrid time-frequency approach based on acoustic beamforming has been successfully developed in order to determine the absolute contribution of the aircraft noise components measured during fly-overs. The method, derived from DAMAS accounts for the fact that the sources move relative to the microphones. Indeed, the motion is responsible for a frequency shift of the sidelobes and a strong modification of the point-spread functions compared to the static case. The method developed is hybrid in the sense that the beamforming algorithm is applied in the time domain while the point-spread functions are approximated in the frequency domain. When the sound sources are characterized by broadband spectra, it becomes possible to discard the frequency coupling between the sources and the sidelobes. This enables to reduce the computing time considerably. In the present publication, the method is applied to AIRBUS A340 fly-overs with the high-lift devices deployed, landing gear up, and the engines running at idle. The study is focused
on the influence of some processing parameters (grid spacing, number of iterations, cut of the focusing grid, and frequency bandwidth) on the source breakdown. It turns out that the noise spectra of the aircraft components are almost independent of reasonable variations of these parameters. This indicates that the method is relatively robust. A detailed investigation of the noise sources (flaps, slats, and engines) with respect to the variations of the airspeed, the ECAM position, the engine rating, etc. is not part of this work.
BibTeX:
@inproceedings{GuerinSiller2008,
  author = {Guérin, S. and Siller, H.},
  title = {A Hybrid Time-Frequency Approach for the Source Localization Analysis of Acoustic Fly-over Tests},
  booktitle = {14th CEAS/AIAA Aeroacoustics Conference, Vancouver, British Columbia, Canada, 5-7 May 2008},
  year = {2008}
}
Guérin S and Weckmüller C (2008), "Frequency-domain reconstruction of the point-spread function for moving sources", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-14. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In beamforming applications where the acoustic source is moving relative to the microphone array, the sidelobes are frequency shifted with respect to the frequency of the source. Furthermore the shape of the beamforming pattern is modified compared to that of the static case at the same position. Provided these two effects are predicted, the DAMAS deconvolution method developed for wind tunnel tests can be modified and applied to aircraft flyovers. While beamforming gives a qualitative information about the noise emission, the deconvolution method enables to quantify separately the level of the sources. In the present paper a solution is given which approximates the point-spread function in the frequency domain. The agreement with simulations is very good for the prediction of the frequency shift and reasonably good for the pattern shape.
BibTeX:
@inproceedings{GuerinWeckmueller2008,
  author = {Guérin, S. and Weckmüller, C.},
  title = {Frequency-domain reconstruction of the point-spread function for moving sources},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://www.bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-14_Guerin_Weckmueller.pdf}
}
Guérin S, Weckmüller C and Michel U (2006), "Beamforming and deconvolution for aerodynamic sound sources in motion", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22--23 November, 2006., BeBeC-2008-16. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Acoustic beamforming with microphone phased-arrays is a powerful method to investigate the noise emission of vehicles (aircraft, trains, cars, etc.). Per definition, the aerodynamic sound sources appear when these vehicles are in motion. Some of the sources, like the highlift devices of aircraft, are distributed in space. The beamforming patterns are the result of a convolution between the sources and point spread functions, which depend on the array geometry and source position. The performance of a phased array is characterised by two parameters: i) the beamwidth on which depends the capacity to separate two sources close to each other, and ii) the level of the side-lobes which describes the dynamic range. In static applications (the source positions are fixed with respect to the microphone array) the source strength of distributed sources can be determined by deconvoluting the beamforming solution. Some issues arise when a deconvolution is applied to moving sources because the frequencies of the side-lobes are shifted with respect to the main lobe. An approximate method for the deconvolution of the beampattern of moving broadband sources is derived and it is shown with simulated data that solutions can be obtained with a reasonable accuracy and computing time.
BibTeX:
@inproceedings{Guerin_etal2006,
  author = {Guérin, S. and Weckmüller, C. and Michel, U.},
  title = {Beamforming and deconvolution for aerodynamic sound sources in motion},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22--23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://www.bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-16_Guerin_Weckmueller_Michel.pdf}
}
Guidati S (2010), "Advanced beamfoming techniques in vehicle acoustics", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-04., February, 2010. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: A problem for the classic beamforming approach is the limited dynamic range of the acoustic mapping. Louder sources are masking quieter sources. This limitation is valid for sources in the same frequency range. With multi band beamforming sources in different frequency ranges can be visualized with the only limitation being the dynamic range of the measurement system. Coherence filtering techniques allow for the distinction between incoherent sources and the detection of mirror sources. Here, the coherence between an additional sensor placed as reference close to the main source is used to filter the array signals increasing the overall dynamic of the acoustic source mapping. The real sensor can be replaced by a virtual sensor signal as result of the beamforming calculation allowing for a wider range of applications. Recent advantages in computer technologies allow for a real time processing of the microphone array data resulting in an online visualization of the sound sources.
BibTeX:
@inproceedings{Guidati2010,
  author = {Guidati, S.},
  title = {Advanced beamfoming techniques in vehicle acoustics},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-04.pdf}
}
Guidati S, Brauer C and Wagner S (2002), "The reflection canceller - Phased array measurements in a reverberating environment", In 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2462.
Abstract: Wind tunnels are used in combination with phased array techniques or elliptic mirrors to localize and quantify the aerodynamic noise coming e.g. from an airfoil or a high-lift device. Wind tunnels with a closed test section deliver good aerodynamic conditions but have often poor acoustic conditions due to reflections caused by the test section walls which decrease the resolution of phased arrays at low frequencies. In previous paper the authors presented an algorithm called reflection canceller (RC) which integrates the reflections in the beamforming process. In simulations and measurements without flow this algorithm showed a good spatial resolution that exspecially in the low frequencies was higher than using the classical beamforming algorithms under anechoic conditions. In this paper measurements in a closed test section wind tunnel are presented. With a point source integrated in a NACA-0020 profile the Green´s functions characterising the reverberating environment have been measured for different wind speeds. These functions are used to optimize the RC. In measurements with aerodynamic point sources the RC shows again an increased spatial resolution .
BibTeX:
@inproceedings{Guidati_etal2002,
  author = {Guidati, S. and Brauer, C. and Wagner, S.},
  title = {The reflection canceller - Phased array measurements in a reverberating environment},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Guidati S, Guidati G and Wagner S (2001), "Beamforming in a reverberating environment with the use of measured steering vectors", In AIAA/CEAS Aeroacoustics Conference and Exhibit, Maastricht, Netherlands, May 28-30, 2001., AIAA-2001-2166., May, 2001.
Abstract: The paper tackles the problem of aerodynamic noise measurements in wind tunnels with an acoustically hard closed test section. Data processing based on phased array techniques like the Classical Beamformer often fails due to the reflections caused by the test section walls. In a previous paper the authors proposed a modification of the Classical Beamformer called Reflection Canceller. This algorithm incorporates the reflections caused by rectangular test section walls by expanding the steering vectors with mirror sources. This algorithm performed well in simulations and measurements in a reverberating chamber and showed even an increased spatial resolution compared to the anechoic environment. Before the Reflection Canceller is used in real wind tunnel measurements the algorithm, foremost its basic quantity, the steering vector, has to be validated with some basic experiments. For this the steering vector was measured using a monopole point source. This was done in two steps, (1) in a closed test section wind tunnel without flow to confirm the effect of increased spatial resolution and (2) in a nonreflecting environment wind tunnel with flow to compare the measured steering vectors with the modeled ones. This paper shows results from both experiments. The first one, performed in the Laminar Wind Tunnel at the University of Stuttgart, shows the predicted increased spatial resolution. The second one, performed in the Acoustic Wind Tunnel at the Technical University of Dresden, shows good agreement between measured and modeled steering vectors. Finally an algorithm is presented which allows to increase the performance of multiplexing DAQ-Cards for steady state sound fields.
BibTeX:
@inproceedings{Guidatei_etal2001,
  author = {Guidati, S. and Guidati, G. and Wagner, S.},
  title = {Beamforming in a reverberating environment with the use of measured steering vectors},
  booktitle = {AIAA/CEAS Aeroacoustics Conference and Exhibit, Maastricht, Netherlands, May 28-30, 2001},
  year = {2001}
}
Gurovich YA, Plotkin KJ, Robinson DH, Blake WK and Donavan PR (2009), "Acoustic Beamforming: Mapping Sources of Truck Noise" 500 Fifth Street, NW, Washington, DC 20001 USA, Nov., 2009. (635)
Abstract: This report documents the use of the acoustic beamforming technique to pinpoint and measure noise levels from heavy truck traffic. The system uses an elliptical array of more than 70 microphones and data acquisition software to measure noise levels from a variety of noise sources on large trucks—including the engine, tires, mufflers, and exhaust pipes. The results validate the feasibility of beamforming technology, offer new insight into the distribution of truck noise sources, and provide valuable input to the design and testing of quieter pavements and noise barrier systems. This report will be of interest to anyone concerned with understanding and mitigating highway noise levels.
BibTeX:
@techreport{Gurovich_etal2009,
  author = {Gurovich, Y. A. and Plotkin, K. J. and Robinson, D. H. and Blake, W. K. and Donavan, P. R.},
  title = {Acoustic Beamforming: Mapping Sources of Truck Noise},
  year = {2009},
  number = {635},
  url = {http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_635.pdf}
}
Hald J (1995), "Use of spatial transformation of sound fields (STFS) techniques in the automotive industry", Brüel \& Kjær, Technical Review 1-1995.
BibTeX:
@misc{Hald1995,
  author = {Hald, J.},
  title = {Use of spatial transformation of sound fields (STFS) techniques in the automotive industry},
  howpublished = {Brüel \& Kjær, Technical Review 1-1995},
  year = {1995}
}
Hald J (1989), "STFS - A unique technique for scan based near-field acoustic holography without restrictions on coherence", Brüel \& Kjær, Technical Review 1-1989.
BibTeX:
@misc{Hald1989,
  author = {Hald, J.},
  title = {STFS - A unique technique for scan based near-field acoustic holography without restrictions on coherence},
  howpublished = {Brüel \& Kjær, Technical Review 1-1989},
  year = {1989}
}
Hald J, Ishii Y, Ishii T, Oinuma H, Nagai K, Yokokawa Y and Yamamoto K (2012), "High-resolution Fly-over Beamforming Using a Small Practical Array", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), June 2012, Colorado Springs, CO.
Abstract: The paper describes a commercially available fly-over beamforming system based on methodologies already published, but using an array that was designed for quick and precise deployment on a concrete runway rather than for minimum sidelobe level. Time domain tracking Delay And Sum (DAS) beamforming is the first processing step, followed by Deconvolution in the frequency domain to reduce sidelobes, enhance resolution, and get absolute scaling of the source maps. The system has been used for a series of fly-over measurements on a Business Jet type MU300 from Mitsubishi Heavy Industries. Results from a couple of these measurements are presented: Contribution spectra from selected areas on the aircraft to the sound pressure level at the array are compared against the total sound pressure spectrum measured by the array. One major aim of the paper is to verify that the system performs well although the array was designed with quick deployment as a main criterion. The results are very encouraging. A second aim is to elaborate on the handling of the array shading function in connection with the calculation of the Point Spread Function (PSF) used in deconvolution. Recent publications have used a simple formula to compensate for Doppler effects for the case of flat broadband spectra. A more correct formula is derived in the present paper, covering also a Doppler correction to be made in the shading function, when that function is used in the PSF calculation.
BibTeX:
@inproceedings{Hald_etal2012,
  author = {Hald, J. and Ishii, Y. and Ishii,T. and Oinuma, H. and Nagai, K. and Yokokawa, Y. and Yamamoto, K.},
  title = {High-resolution Fly-over Beamforming Using a Small Practical Array},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), June 2012, Colorado Springs, CO},
  year = {2012}
}
Hanson C and Barsikow B (2000), "Noise sources on Amtrak's high-speed train", In Proc. InterNoise 2000, Nizza. (Paper IN2000/64)
BibTeX:
@inproceedings{HansonBarsikow2000,
  author = {Hanson, C. and Barsikow, B.},
  title = {Noise sources on Amtrak's high-speed train},
  booktitle = {Proc. InterNoise 2000, Nizza},
  year = {2000},
  number = {Paper IN2000/64}
}
Harrington R (1961), "Sidelobe reduction by non-uniform element spacing", Inst. Radio Eng. Trans. Antennas and Propagation. Vol. 9, pp. 187-201.
BibTeX:
@article{Harrington1961,
  author = {Harrington, R.F.},
  title = {Sidelobe reduction by non-uniform element spacing},
  journal = {Inst. Radio Eng. Trans. Antennas and Propagation},
  year = {1961},
  volume = {9},
  pages = {187--201}
}
Haxter S and Spehr C (2014), "Infinite Beamforming: Wavenumber Decomposition of Surface Pressure Fluctuations", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-04., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The fluctuating pressure field underneath a turbulent boundary layer can lead to excitation of the surface structure of airplanes, trains and cars. At high flow speeds, this excitation becomes a major noise source in the vehicle interior. In the past, the characteristics of this excitation have been measured by the DLR in wind tunnels and in flight tests. A beam forming technique using planar waves was used as wavenumber decomposition in order to analyze the pressure fluctuations present over an installed microphone array. The information contained in the wavenumber spectrum resulting from the analysis is essential when empirically modeling the excitation behavior of a surface exposed to a pressure field. Speed, direction, and propagation mechanism (acoustic or hydrodynamic) of pressure waves can be determined from the position of sources in the wavenumber domain. This makes the wavenumber decomposition a helpful tool for the characterization of source mechanisms. In this paper, a summary of the test results is given. The attributes and potential of the wavenumber decomposition are emphasized in particular.
BibTeX:
@inproceedings{Haxter-Spehr2014,
  author = {Haxter, S. and Spehr,, C.},
  title = {Infinite Beamforming: Wavenumber Decomposition of Surface Pressure Fluctuations},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-04.pdf}
}
Hecht M and Zogg H (1995), "Lärmdesign moderner Triebfahrzeuge am Beispiel der Lok 2000-Familie, Anwendung von Telemetrie, Intensitäts- und Arraymeß technik", ZEV+DET Glasers Annalen. Vol. 119, pp. 463-472.
BibTeX:
@article{HechtZogg95,
  author = {Hecht, M. and Zogg, H.},
  title = {Lärmdesign moderner Triebfahrzeuge am Beispiel der Lok 2000-Familie, Anwendung von Telemetrie, Intensitäts- und Arraymeß technik},
  journal = {ZEV+DET Glasers Annalen},
  year = {1995},
  volume = {119},
  pages = {463--472}
}
Heilmann G and Döbler D (2008), "Applications of time-domain beam-forming using 3D microphone arrays", In IOA - AUTUMN CONFERENCE 2008, SEE IT HEAR! Demonstrating current & emerging techniques for sound, 21 - 22 October 2008., October, 2008.
Abstract: Acoustic measurements inside any cavity are mostly conducted with a view number of microphones. By this means it is possible to gain information about frequencies, orders, sound pressures. However, a space selective analysis is nearly impossible and it is not feasible to find multiple sound sources position in space in a practical way. Traditional beamforming systems with planar microphone arrays do not give comprehensive information about the sound sources inside a cavity such as car interior or an office room. Therefore, the constituents of the Acoustic Camera of the GFaI were extended by a spherical, acoustically transparent and omni directional array. A new option is to map onto a common 3D-CAD-models of the object of interest, for instance an office or class room, car, bus or plane interiors. First of all the advantages and disadvantages of 2D- and 3D-mappings will be discussed in the paper. Furthermore, the important issue of positioning an array at first in the coordinate system of the 3D-model and second in the actual cavity which is to be measured will be addressed. The paper discusses the geometric and acoustic properties of microphone arrays which are applicable for complete 3D-measurements and mappings of cavities. A practicable way of determining the array’s position and direction related to the measurement object will be proposed. Several practical experiments will be displayed to underline the methods capability and reliability.
BibTeX:
@inproceedings{Heilmann_etal2008b,
  author = {Heilmann, G. and Döbler, D.},
  title = {Applications of time-domain beam-forming using 3D microphone arrays},
  booktitle = {IOA - AUTUMN CONFERENCE 2008, SEE IT HEAR! Demonstrating current & emerging techniques for sound, 21 - 22 October 2008},
  year = {2008},
  url = {http://www.acoustic-camera.de/images/stories/_docs/paper/2008_IOA.pdf}
}
Heilmann G, Meyer A and Döbler D (2008), "Time-domain beamforming using 3D-microphone arrays", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-20., February, 2008. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Acoustic measurements inside any cavity are mostly conducted with a view number of microphones. By this means it is possible to gain information about frequencies, orders, sound pressures. However, a space selective analysis is nearly impossible and it is not feasible to find multiple sound sources position in space in a practical way. Traditional beam forming systems with planar microphone arrays do not give comprehensive information about the sound sources inside a cavity such as car interior or an office room. Therefore, the constituents of the Acoustic Camera of the GFaI were extended by a spherical, acoustically transparent and omni directional array. A new option is to map onto a common 3D-CAD-models of the object of interest, for instance an office or class room. First of all the advantages and disadvantages of 2D- and 3D-mappings will be discussed in the paper. Furthermore, the important issue of positioning an array at first in the coordinate system of the 3D-model and second in the actual cavity which is to be measured will be addressed. The paper discusses the geometric and acoustic properties of microphone arrays which are applicable for complete 3D-measurements and mappings of cavities. A practicable way of determining the array’s position and direction related to the measurement object will be proposed. Several practical experiments will be displayed to underline the methods capability and reliability.
BibTeX:
@inproceedings{Heilmann_etal2008a,
  author = {Heilmann, G. and Meyer, A. and Döbler, D.},
  title = {Time-domain beamforming using 3D-microphone arrays},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-20_Heilmann_Meyer_Doebler.pdf}
}
Heinz G, Nguyen T and Doebler D (1999), "Acoustic photo- and cinematography based on interference transformation", Acta Acustica. Vol. 85, Supplement 1, Book of Abstracts, pp. S363.
BibTeX:
@article{Heinz99,
  author = {Heinz, G. and Nguyen, T. and Doebler, D.},
  title = {Acoustic photo- and cinematography based on interference transformation},
  journal = {Acta Acustica},
  year = {1999},
  volume = {85, Supplement 1, Book of Abstracts},
  pages = {S363},
  note = {EEIG/ASA/DEGA Conference Forum Acusticum 1999, TU Berlin, March 14-19,1999}
}
Henning A, Ehrenfried K and Koop L (2010), "Causality correlation in aeroacoustic experiments by means of simultaneous PIV and microphone-array", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-02., February, 2010. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In this paper we present applications of the causality correlation technique by means of simultaneous PIV measurements in a turbulent flow and microphone-array measurements in the aeroacoustic far field. Both measurements are conducted in a synchronized manner so as to enable the calculation of the cross-correlation between the acoustic pressure and flow quantities derived from the measured velocity fluctuations. The main idea of the concept presented here is to use the therewith obtained coefficient matrix to identify regularities in the flow that are related to the radiated sound field. Here we show a comparative study of the results for measurements on different flow-configurations with strong tonal components as well as with broadband spectra in the acoustic far-field.
BibTeX:
@inproceedings{Henning_etal2010,
  author = {Henning, A. and Ehrenfried, K. and Koop, L.},
  title = {Causality correlation in aeroacoustic experiments by means of simultaneous PIV and microphone-array},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-01.pdf}
}
Henning A, Koop L, Ehrenfried K and Lauterbach A. Kröber S (2009), "Simultaneous Multiplane PIV and Microphone Array Measurements on a Rod-Airfoil Configuration", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3184., May, 2009.
Abstract: The aeroacoustic sound generation process on a rod-airfoil configuration has been investigated by means of simultaneous Particle-Image-Velocimetry (PIV) in the near-field and phased-microphone-array measurements in the far-field. Up to 20 000 PIV snapshots per field of view have been recorded. A coplanar multiplane PIV system has been used, providing statistically independent samples of the temporal derivative of the velocity field. Both measurements were conducted in a synchronized manner so as to enable the calculation of the cross-correlation between the acoustic pressure and flow quantities derived from the measured velocity fluctuations. The main idea of the concept used in the study presented here was to use the coefficient matrix obtained from the aforementioned correlation to identify regularities in the near-field fluctuations that are related to the radiated sound field. Additionally a technique to localize flow structures responsible for the far-field sound by means of the calculation of the near-field intensity has been tested.
BibTeX:
@inproceedings{Henning_etal2009,
  author = {Henning, A. and Koop, L. and Ehrenfried, K. and Lauterbach, A. Kröber, S.},
  title = {Simultaneous Multiplane PIV and Microphone Array Measurements on a Rod-Airfoil Configuration},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3184.pdf}
}
Herkes WH and Strout FG (1985), "Evaluation of a correction for sound propagation through free-jet shear layers", Journal of Aircraft. Vol. 22, pp. 1065-1071.
BibTeX:
@article{HerkesStrout85,
  author = {Herkes, W. H. and Strout, F. G.},
  title = {Evaluation of a correction for sound propagation through free-jet shear layers},
  journal = {Journal of Aircraft},
  year = {1985},
  volume = {22},
  pages = {1065--1071}
}
Herkes WH and Strout FG (1983), "Evaluation of a correction for sound propagation through free-jet shear layers", In 8th AIAA Aeroacoustics Conference, Atlanta, Ga, Apr. 11-13, 1983., AIAA Paper 83-0757.
BibTeX:
@inproceedings{HerkesStrout83,
  author = {Herkes, W. H. and Strout, F. G.},
  title = {Evaluation of a correction for sound propagation through free-jet shear layers},
  booktitle = {8th AIAA Aeroacoustics Conference, Atlanta, Ga, Apr. 11-13, 1983},
  year = {1983}
}
Herold G and Sarradj E (2014), "Preliminary Benchmarking of Microphone Array Methods", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-10., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Microphone-array-based methods have become a common tool for the characterization of acoustic sources. One of the main objectives when using these methods is determining the exact magnitude of the noise radiated by each separate sound source, which can be described by the sound pressure level at a certain distance and direction from the source. In this contribution, simulated as well as measured data of known source configurations are being evaluated using array-based methods like DAMAS, CLEAN, CLEAN-SC, Orthogonal Beamforming, and Covariance Matrix Fitting. The results obtained using these methods and varying several of their parameters will be compared. It will be shown that, in part, these results differ considerably in terms of calculated position and magnitude of the sound sources. This underlines the need for defining criteria to assess the reliability of microphone array methods under different boundary conditions.
BibTeX:
@inproceedings{HeroldSarradj2014,
  author = {Herold, G. and Sarradj, E.},
  title = {Preliminary Benchmarking of Microphone Array Methods},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-10.pdf}
}
Herold G, Sarradj E and Geyer T (2013), "Covariance Matrix Fitting for Aeroacoustic Application", In Fortschritte der Akustik - DAGA.
BibTeX:
@inproceedings{Herold2013,
  author = {Herold, G. and Sarradj, E. and Geyer, T.},
  title = {Covariance Matrix Fitting for Aeroacoustic Application},
  booktitle = {Fortschritte der Akustik - DAGA},
  year = {2013}
}
Hileman J and Samimy M (2003), "Effects of vortex generating tabs on noise sources in an ideally expanded mach 1.3 jet", Int. J. Aeroacoustics., January, 2003. Vol. 2(1), pp. 35-63.
Abstract: The flow and acoustic fields of an ideally expanded Mach 1.3 axisymmetric jet with delta tabs were examined to explore the effects of the tabs on noise sources. This work continues research that was performed on a baseline (no-tab) jet. Noise measurements were made at an angle of 30° to the downstream jet axis to allow a direct comparison to previous work, and to relate the sound generation mechanisms to the large structures that were visualized with temporally resolved flow visualization. Additional acoustic measurements were made at 60˚ and 90˚ locations. Three cases were examined: a baseline jet, a single delta tab jet, and a dual delta tab jet. Both tab jets were operated at the same pressure ratio as the baseline jet, which was ideally expanded. Power spectra and average acoustic waveform measurements were made for a variety of azimuthal locations; apparent noise origins were estimated with a 3-D microphone array; and temporally resolved flow visualization was used to examine the dynamic flow structure of the jet's mixinglayer. The results confirm that the tabs generate strong streamwise vortices that have a significant effect on both the flow and acoustic fields of the jet. The tabs cause significant deformation in the cross-stream plane of the mixing-layer, as well as regulating the formation and roll-up of vortices due to Kelvin Helmholtz instability. With the addition of tabs, the noise field becomes azimuthally dependent and the region of noise generation moves dramatically upstream. It appears that the tabs are directly responsible for an increase in noise over a range of Strouhal numbers between 0.8 and 2.5 through generated streamwise vortices and they are indirectly responsible for the modification of the noise generating mechanisms at Strouhal numbers below 0.6 through the induced spanwise vortex roll-ups.
BibTeX:
@article{HilemanSamimy2003,
  author = {Hileman, J. and Samimy, M.},
  title = {Effects of vortex generating tabs on noise sources in an ideally expanded mach 1.3 jet},
  journal = {Int. J. Aeroacoustics},
  year = {2003},
  volume = {2},
  number = {1},
  pages = {35--63},
  doi = {10.1260/147547203322436935}
}
Hogbom JA (1974), "Aperture synthesis with a non-regular distribution of interferometer baselines", Astron. Astrophys. Suppl.. Vol. 15, pp. 417-426.
BibTeX:
@article{Hogbom1974,
  author = {Hogbom, J. A.},
  title = {Aperture synthesis with a non-regular distribution of interferometer baselines},
  journal = {Astron. Astrophys. Suppl.},
  year = {1974},
  volume = {15},
  pages = {417--426}
}
Holland KR and Nelson PA (2013), "The application of inverse methods to spatially distributed acoustic sources", J. Sound Vib.. Vol. 332, pp. 5727-5747.
Abstract: Acoustic inverse methods, based on the output of an array of microphones, can be readily applied to the characterisation of acoustic sources that can be adequately modelled as a number of discrete monopoles. However, there are many situations, particularly in the fields of vibroacoustics and aeroacoustics, where the sources are distributed continuously in space over a finite area (or volume). This paper is concerned with the practical problem of applying inverse methods to such distributed source regions via the process of spatial sampling. The problem is first tackled using computer simulations of the errors associated with the application of spatial sampling to a wide range of source distributions. It is found that the spatial sampling criterion for minimising the errors in the radiated far-field reconstructed from the discretised source distributions is strongly dependent on acoustic wavelength but is only weakly dependent on the details of the source field itself. The results of the computer simulations are verified experimentally through the application of the inverse method to the sound field radiated by a ducted fan. The un-baffled fan source with the associated flow field is modelled as a set of equivalent monopole sources positioned on the baffled duct exit along with a matrix of complimentary non-flow Green functions. Successful application of the spatial sampling criterion involves careful frequency-dependent selection of source spacing, and results in the accurate reconstruction of the radiated sound field. Discussions of the conditioning of the Green function matrix which is inverted are included and it is shown that the spatial sampling criterion may be relaxed if conditioning techniques, such as regularisation, are applied to this matrix prior to inversion.
BibTeX:
@article{HollandNelson2013,
  author = {Holland, K. R. and Nelson, P. A..},
  title = {The application of inverse methods to spatially distributed acoustic sources},
  journal = {J. Sound Vib.},
  year = {2013},
  volume = {332},
  pages = {5727--5747},
  doi = {10.1016/j.jsv.2013.06.009}
}
Holm S (1998), "The coarray of sparse arrays with minimum sidelobe level", In in Proc. IEEE NORSIG-98, (Vigs). , pp. 137-140.
BibTeX:
@inproceedings{Holm1998,
  author = {Holm, S.},
  title = {The coarray of sparse arrays with minimum sidelobe level},
  booktitle = {in Proc. IEEE NORSIG-98, (Vigs)},
  year = {1998},
  pages = {137--140}
}
Hölzl G, Fodiman P, Schmitz K-P, Pallas MA and Barsikow B (1994), "DeuFraKo-2: Localized sound sources on the high-speed vehicles ICE, TGV-A, and TR 07.", In Proc. Inter-Noise '94, Yokohama. , pp. 193-198.
BibTeX:
@inproceedings{Hoelzl_etal1994,
  author = {Hölzl, G. and Fodiman, P. and Schmitz, K.-P. and Pallas, M. A. and Barsikow, B.},
  title = {DeuFraKo-2: Localized sound sources on the high-speed vehicles ICE, TGV-A, and TR 07.},
  booktitle = {Proc. Inter-Noise '94, Yokohama},
  year = {1994},
  pages = {193--198}
}
Horne C, Hayes J. A., Jaeger SM and Jovic S (2000), "Effects of distributed source coherence on the response of phased acoustic arrays", In AIAA/CEAS, Aeroacoustics Conference and Exhibit, 6th (21st AIAA Aeroacoustics Conference), Lahaina, HI, June 12-14, 2000., AIAA-2000-1935., June, 2000.
BibTeX:
@inproceedings{Horne_etal2000,
  author = {Horne, C. and Hayes, J. A., and Jaeger, S. M. and Jovic, S.},
  title = {Effects of distributed source coherence on the response of phased acoustic arrays},
  booktitle = {AIAA/CEAS, Aeroacoustics Conference and Exhibit, 6th (21st AIAA Aeroacoustics Conference), Lahaina, HI, June 12-14, 2000},
  year = {2000},
  url = {http://pdf.aiaa.org/preview/2000/PV20:00_1935.pdf}
}
Horne WC, James KD, Arledge TK, Soderman PT, Burnside N and Jaeger SM (2005), "Measurements of 26%-scale 777 Airframe Noise in the NASA Ames 40- by 80 Foot Wind Tunnel", In 11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference) 23 - 25 May 2005, Monterey, California., AIAA-2005-2810., May, 2005.
Abstract: An aeroacoustic investigation of a 26% Boeing 777 semi-span wing was conducted in the NASA Ames 40-by 80- Foot Wind Tunnel. For landing and approach configurations and conditions, the acoustic field was surveyed with a 40 in. (1meter) diameter traversing phased microphone array and a fixed 96 in. (2.43-meter) diameter array. Prominent acoustic sources were located for each configuration, and a spatial integration method was used to compare the relative strengths of the various sources, and to assess the effectiveness of a variety of noise reduction treatments for flap, slat and gear noise. Selected results are presented and discussed for the landing configuration at M = 0.21, α = 6°.
BibTeX:
@inproceedings{Horne_etal2005,
  author = {Horne, W. C. and James, K. D. and Arledge, T. K. and Soderman, P. T. and Burnside, N. and Jaeger, S. M.},
  title = {Measurements of 26%-scale 777 Airframe Noise in the NASA Ames 40- by 80 Foot Wind Tunnel},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference (26th AIAA Aeroacoustics Conference) 23 - 25 May 2005, Monterey, California},
  year = {2005},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO05_1140/PV2005_2810.pdf}
}
Horvath C (2014), "Investigating Counter-Rotating Open Rotor Noise Sources From a Broadband Point of View", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-13., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In an attempt to lower the noise level of counter-rotating open rotors, phased array microphone measurements and state-of-the-art beamforming technology have recently been implemented in their investigation. The results are very useful, though initially misleading and difficult to comprehend. Recent publications have helped explain beamforming results of rotating coherent noise sources, typical tonal noise sources for counter-rotating open rotors. Building on the former results, the present beamforming investigation provides a novel approach for identifying broadband noise sources of counter-rotating open rotors. The method pinpoints dominant broadband noise sources to given areas of the rotor surface, and also helps separate out a noise source associated with shaft orders which result from blade nonuniformities, such as measurement instrumentation mounted on the rotor surface, which could otherwise be mistakenly associated with the tonal or broadband noise sources.
BibTeX:
@inproceedings{Horvath2014,
  author = {Horvath, C.},
  title = {Investigating Counter-Rotating Open Rotor Noise Sources From a Broadband Point of View},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-13.pdf}
}
Horvath C, Envia E and Podboy GG (2013), "Limitations of Phased Array Beamforming in Open Rotor Noise Source Imaging", In 19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany,May 27-29, 2013., May, 2013. AIAA.
Abstract: Phased array beamforming results of the F31/A31 historical baseline counter-rotating open rotor blade set were investigated for measurement daa aken on the NASA Counter-Rotating Open Rotor Propulsion Rig in the 9’ x 15’ Low Speed Wind Tunnel of NASA Glenn Research Center as well as data produced using the LINPROP open rotor tone noise code. The planar microphone array was positioned broadside and parallel to the axis of the open rotor, roughly 2.3 rotor diameters away. The results provide insight as to why the apparent noise sources of the blade passing frequency tones and interaction tones appear at their nominal Mach radii instead of at the actual noise sources, even if those locations are not on the blades. Contour maps corresponding to the sound fields produced by the radiating sound waves, taken from the simulations, are used to illustrate how the interaction patterns of circumferential spinning modes of rotating coherent noise sources interact with the phased array, often giving misleading results, as the apparent sources do not always show where the actual noise sources are located. This suggests that a more sophisticated source model would be required to accurately locate the sources of each tone. The results of this study also have implications with regard to the shielding of open rotor sources by airframe empennages.
BibTeX:
@inproceedings{Horvath_Envia_Podboy2013,
  author = {Horvath, C. and Envia, E. and Podboy, G. G.},
  title = {Limitations of Phased Array Beamforming in Open Rotor Noise Source Imaging},
  booktitle = {19th AIAA/CEAS Aeroacoustics Conference, Berlin, Germany,May 27-29, 2013},
  publisher = {AIAA},
  year = {2013},
  note = {AIAA-2013-2098}
}
Howell GP, Bradley MA, McCormick MA and Brown JD (1986), "De-Dopplerization and acoustic imaging of aircraft Flyover noise measurements", J. Sound Vib.., Feb, 1986. Vol. 105(1), pp. 151-167.
BibTeX:
@article{Howell_etal1986,
  author = {Howell, G. P. and Bradley, M. A. and McCormick, M. A. and Brown, J. D.},
  title = {De-Dopplerization and acoustic imaging of aircraft Flyover noise measurements},
  journal = {J. Sound Vib.},
  year = {1986},
  volume = {105},
  number = {1},
  pages = {151--167},
  doi = {10.1016/0022-460X(86)90227-0}
}
Huang X (2009), "Real-time algorithm for acoustic imaging with a microphone array", J. Acoust. Soc. Am.., May, 2009. Vol. 125(5), pp. EL190-EL195.
Abstract: Acoustic phased array has become an important testing tool in aeroacoustic research, where the conventional beamforming algorithm has been adopted as a classical processing technique. The computation however has to be performed off-line due to the expensive cost. An innovative algorithm with real-time capability is proposed in this work. The algorithm is similar to a classical observer in the time domain while extended for the array processing to the frequency domain. The observer-based algorithm is beneficial mainly for its capability of operating over sampling blocks recursively. The expensive experimental time can therefore be reduced extensively since any defect in a testing can be corrected instantaneously.
BibTeX:
@article{Huang2009,
  author = {Huang, X.},
  title = {Real-time algorithm for acoustic imaging with a microphone array},
  journal = {J. Acoust. Soc. Am.},
  year = {2009},
  volume = {125},
  number = {5},
  pages = {EL190--EL195},
  note = {JASA EXPRESS LETTERS},
  doi = {10.1121/1.3100641}
}
Huang X, Vinogradov I, Bai L and Ji J (2010), "Observer for Phased Microphone Array Signal Processing with Nonlinear Output", AIAA J.., November, 2010. Vol. 48(11), pp. 2702-2705.
BibTeX:
@article{Huang_etal2010,
  author = {Huang, Xun and Vinogradov, I. and Bai, Long and Ji, Jianchao},
  title = {Observer for Phased Microphone Array Signal Processing with Nonlinear Output},
  journal = {AIAA J.},
  year = {2010},
  volume = {48},
  number = {11},
  pages = {2702--2705},
  doi = {10.2514/1.52439}
}
Humphreys Jr WM and Brooks TF (2009), "Noise spectra and directivity for a scale-model landing gear", Int. J. Aeroacoustics., July, 2009. Vol. 8(5), pp. 409-444.
Abstract: An extensive experimental study has been conducted to acquire detailed noise spectra and directivity data for a high-fidelity, 6.3%-scale, Boeing 777 main landing gear. The measurements were conducted in the NASA Langley Quiet Flow Facility using a 41-microphone directional array system positioned at a range of polar and azimuthal observer angles with respect to the model. DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) array processing as well as straightforward individual microphone processing were employed to compile unique flyover and sideline directivity databases for a range of freestream Mach numbers (0.11 – 0.17) covering typical approach conditions. Comprehensive corrections were applied to the test data to account for shear layer ray path and amplitude variations. This allowed proper beamforming at different measurement orientations, as well as directivity presentation in free-field emission coordinates. Four different configurations of the landing gear were tested: a baseline configuration with and without an attached side door, and a noise reduction concept “toboggan” truck fairing with and without side door. Spectral analyses demonstrated that individual microphones could establish model spectra. This finding permitted the determination of unique, spatially-detailed directivity contours of spectral band levels over a hemispherical surface. Spectral scaling for the baseline model confirmed that the acoustic intensity scaled with the expected sixth-power of the Mach number. A comparison of spectra and directivity between the baseline gear and the gear with
an attached toboggan indicated that the toboggan fairing may be of some value in reducing gear noise over particular frequency ranges. Finally, spectrum results were scaled quantitatively to data obtained from flyover tests of a full-scale 777 aircraft. The comparison showed good agreement in frequency and level, suggesting the general applicability of the model-scale noise results.
BibTeX:
@article{HumphreysBrooks2009,
  author = {Humphreys, Jr, W. M. and Brooks, T. F.},
  title = {Noise spectra and directivity for a scale-model landing gear},
  journal = {Int. J. Aeroacoustics},
  year = {2009},
  volume = {8},
  number = {5},
  pages = {409--444},
  doi = {10.1260/147547209788549316}
}
Humphreys Jr WM and Brooks TF (2007), "Noise Spectra and Directivity for a Scale-Model Landing Gear", In 13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007., AIAA-2007-3458., May, 2007.
BibTeX:
@inproceedings{HumphreysBrooks2007,
  author = {Humphreys, Jr, W. M. and Brooks, T. F.},
  title = {Noise Spectra and Directivity for a Scale-Model Landing Gear},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007},
  year = {2007},
  url = {http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070021690_2007019794.pdf}
}
Humphreys Jr WM, Brooks TF, Hunter WW and Meadows KR (1998), "Design and Use of Microphone Directional Arrays for Aeroacoustics Measurements", In 36 st Aerospace Sciences Meeting & Exhibit, Reno NV., AIAA-1998-0471. (AIAA Paper 98-0471)
Abstract: An overview of the development of two microphone directional arrays for aeroacoustic testing is presented. These arrays were specifically developed to measure airframe noise in the NASA Langley Quiet Flow Facility. A large aperture directional array using 35 flush-mounted microphones was constructed to obtain high resolution noise localization maps around airframe models. This array possesses a maximum diagonal aperture size of 34 inches. A unique logarithmic spiral layout design was chosen for the targeted frequency range of 2-30 kHz. Complementing the large array is a small aperture directional array, constructed to obtain spectra and directivity information from regions on the model. This array, possessing 33 microphones with a maximum diagonal aperture size of 7.76 inches, is easily moved about the model in elevation and azimuth. Custom microphone shading algorithms have been developed to provide a frequency- and position-invariant sensing area from 10-40 kHz with an overall targeted frequency range for the array of 5-60 kHz. Both arrays are employed in acoustic measurements of a 6 percent of full scale airframe model consisting of a main element NACA 632-215 wing section with a 30 percent chord half-span flap. Representative data obtained from these measurements is presented, along with details of the array calibration and data post-processing procedures.
BibTeX:
@inproceedings{Humphreys_etal1998,
  author = {Humphreys, Jr, W. M. and Brooks, T. F. and Hunter, W. W. and Meadows, K. R.},
  title = {Design and Use of Microphone Directional Arrays for Aeroacoustics Measurements},
  booktitle = {36 st Aerospace Sciences Meeting & Exhibit, Reno NV},
  year = {1998},
  number = {AIAA Paper 98-0471}
}
Humphreys Jr WM, Gerhold CH, Zuckerwar AJ, Herring GC and M. BS (2003), "Performance Analysis of a Cost-Effective Electret Condenser Microphone Directional Array", In 9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003., AIAA-2003-3195., May, 2003.
Abstract: Microphone directional array technology continues to be a critical part of the overall instrumentation suite for experimental aeroacoustics. Unfortunately, high sensor cost remains one of the limiting factors in the construction of very high-density arrays (i.e., arrays containing several hundred channels or more) which could be used to implement advanced beamforming algorithms. In an effort to reduce the implementation cost of such arrays, the authors have undertaken a systematic performance analysis of a prototype 35-microphone array populated with commercial electret condenser microphones. An ensemble of microphones coupling commercially available electret cartridges with passive signal conditioning circuitry was fabricated for use with the Langley Large Aperture Directional Array (LADA). A performance analysis consisting of three phases was then performed: (1) characterize the acoustic response of the microphones via laboratory testing and calibration, (2) evaluate the beamforming capability of the electret-based LADA using a series of independently controlled point sources in an anechoic environment, and (3) demonstrate the utility of an electret-based directional array in a real-world application, in this case a cold flow jet operating at high subsonic velocities. The results of the investigation revealed a microphone frequency response suitable for directional array use over a range of 250 Hz - 40 kHz, a successful beamforming evaluation using the electret-populated LADA to measure simple point sources at frequencies up to 20 kHz, and a successful demonstration using the array to measure noise generated by the cold flow jet. This paper presents an overview of the tests conducted along with sample data obtained from those tests.
BibTeX:
@inproceedings{Humphreys_etal2003,
  author = {Humphreys, Jr, W. M. and Gerhold, C. H. and Zuckerwar, A. J. and Herring, G. C. and Bartram S. M.},
  title = {Performance Analysis of a Cost-Effective Electret Condenser Microphone Directional Array},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO03_772/PV2003_3195.pdf}
}
Humphreys Jr WM, Shams QA, Graves SS, Sealey BS, Bartram SM and Comeaux T (2005), "Application of MEMS Micrphone Array Technology to Airframe Noise Measurements", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-3004., May, 2005.
Abstract: Current generation microphone directional array instrumentation is capable of extracting accurate noise source location and directivity data on a variety of aircraft components, resulting in significant gains in test productivity. However, with this gain in productivity has come the desire to install larger and more complex arrays in a variety of ground test facilities, creating new challenges for the designers of array systems. To overcome these challenges, a research study was initiated to identify and develop hardware and fabrication technologies which could be used to construct an array system exhibiting acceptable measurement performance but at much lower cost and with much simpler installation requirements. This paper describes an effort to fabricate a 128-sensor array using commercially available Micro-Electro-Mechanical System (MEMS) microphones. The MEMS array was used to acquire noise data for an isolated 26%-scale high-fidelity Boeing 777 landing gear in the Virginia Polytechnic Institute and State University Stability Tunnel across a range of Mach numbers. The overall performance of the array was excellent, and major noise sources were successfully identified from the measurements.
BibTeX:
@inproceedings{Humphreys_etal2005,
  author = {Humphreys, Jr, W. M. and Shams, Q. A. and Graves, S. S. and Sealey, B. S. and Bartram, S. M. and Comeaux, T.},
  title = {Application of MEMS Micrphone Array Technology to Airframe Noise Measurements},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Hutcheson FV and Brooks TF (2004), "Effects of Angle of Attack and Velocity on Trailing Edge Noise", In 42nd AIAA Aerospace Sciences Meeting and Exhibit, 5 - 8 January 2004, Reno, Nevada., AIAA-2004-1031., January, 2004.
Abstract: Trailing edge (TE) noise measurements for a NACA 63-215 airfoil model are presented, providing benchmark experimental data for a cambered airfoil. The effects of flow Mach number and angle of attack of the airfoil model with different TE bluntnesses are shown. Far-field noise spectra and directivity are obtained using a directional microphone array. Standard and diagonal removal beamforming techniques are evaluated employing tailored weighting functions for quantitatively accounting for the distributed line character of TE noise. Diagonal removal processing is
used for the primary database as it successfully removes noise contaminates. Some TE noise predictions are reported to help interpret the data, with respect to flow speed, angle of attack, and TE bluntness on spectral shape and peak levels. Important findings include the validation of a TE noise directivity function for different airfoil angles of attack and the demonstration of the importance of the directivity function’s convective amplification terms.
BibTeX:
@inproceedings{HutchesonBrooks2004,
  author = {Hutcheson, Florence V. and Brooks, Thomas F.},
  title = {Effects of Angle of Attack and Velocity on Trailing Edge Noise},
  booktitle = {42nd AIAA Aerospace Sciences Meeting and Exhibit, 5 - 8 January 2004, Reno, Nevada},
  year = {2004}
}
Hutcheson FV and Brooks TF (2001), "Measurement of trailing edge noise using directional array and coherent output power methods", Int. J. Aeroacoustics., October, 2001. Vol. 1(4), pp. 329-353.
Abstract: The use of a directional array of microphones for the measurement of trailing edge (TE) noise is described. The capabilities of this method are evaluated via measurements of TE noise from a NACA 63-215 airfoil model and from a cylindrical rod. This TE noise measurement approach is compared to one that is based on the cross spectral analysis of output signals from a pair of microphones (COP method). Advantages and limitations of both methods are examined. It is shown that the microphone array can accurately measures TE noise and captures its two-dimensional characteristic over a large frequency range for any TE configuration as long as noise contamination from extraneous sources is within bounds. The COP method is shown to also accurately measure TE noise but over a more limited frequency range that narrows for increased TE thickness. Finally, the applicability and generality of an airfoil self-noise prediction method was evaluated via comparison to the experimental data obtained using the COP and array measurement methods. The predicted and experimental results are shown to agree over large frequency ranges.
BibTeX:
@article{HutchesonBrooks2002,
  author = {Florence V. Hutcheson and Thomas F. Brooks},
  title = {Measurement of trailing edge noise using directional array and coherent output power methods},
  journal = {Int. J. Aeroacoustics},
  year = {2001},
  volume = {1},
  number = {4},
  pages = {329--353},
  doi = {10.1260/147547202765275952}
}
Imran M and Jeon J (2014), "Spatial and Temporal Estimation od Sound Field Duíffuseness in Concert Halls Employing Spherical Microphone Array by Using Beamforming", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-28., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
BibTeX:
@inproceedings{ImranJeon2014,
  author = {Imran, M. and Jeon, J.Y.},
  title = {Spatial and Temporal Estimation od Sound Field Duíffuseness in Concert Halls Employing Spherical Microphone Array by Using Beamforming},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-28.pdf}
}
Ishii Y, Hald J, Ishii T, Oinuma H, Nagai K, Yokokawa Y and Yamamoto K (2014), "High-Resolution Fly-Over Beamforming Using a Practical Array", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-16., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In a previous paper presented at the AIAA 1012 Aeroacoustics Conference, the authors described a commercially available fly-over beamforming system based on a small practical 108-element array with 12 metre diameter designed for quick deployment on a concrete runway. However, the resolution at frequencies below 700 Hz was not sufficient to provide useful noise source identification and quantification. The present paper describes an extended 135-element array with 29 metre diameter, designed for frequencies down to 300 Hz, while still supporting quick deployment on a runway, and it analyzes the results from a series of measurements taken in November 2011 at Taiki Aerospace Research Field, Taiki, Hokkaido, Japan. As in the previous paper, the aircraft under test was a business jet type MU300 from Mitsubishi Heavy Industries. For comparison with engine sound power estimates from fly-over measurements, a set of array measurements was performed on the
right engine with the aircraft fixed on the ground. Sound power spectra show good agreement between fly-over and ground-based measurements with comparable engine load conditions.
BibTeX:
@inproceedings{Ishii_etal2014,
  author = {Ishii, Y. and Hald, J. and Ishii, T. and Oinuma, H. and Nagai, K. and Yokokawa, Y. and Yamamoto, K.},
  title = {High-Resolution Fly-Over Beamforming Using a Practical Array},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-16.pdf}
}
Jacquet B and Gely D (1992), "Etude de bruit engendre par l'impact d'un jet supersonique chaud sur un obstacle (Study of noise generated by the impingement of a hot supersonic jet on an obstacle)", In 2nd Congres Francais d'Acoustique, Arcachon, France, Apr. 14-16, 1992., ONERA, TP No. 1992-33, 1992.
BibTeX:
@inproceedings{JacquetGely1992,
  author = {Jacquet, B. and Gely, D.},
  title = {Etude de bruit engendre par l'impact d'un jet supersonique chaud sur un obstacle (Study of noise generated by the impingement of a hot supersonic jet on an obstacle)},
  booktitle = {2nd Congres Francais d'Acoustique, Arcachon, France, Apr. 14-16, 1992},
  year = {1992}
}
Jaeckel O (2006), "Strengths and weaknesses of calculating beamforming in the time domain", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-02. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Most of the present beamforming systems in commercial and academic applications are performing their calculations solely in the frequency domain. While the early historical beamformers actually have been implemented in the time domain by inclusion of simple analog hardware delay lines, this principle was not applied anymore due to the availability of digital signal processors which allowed the calculation of fast Fourier transforms already within the data acquisition hardware frontends. Nowadays, modern computers offer the feasibility to process huge amounts of multichannel data in the frequency domain as well as in the time domain, so computational effort is not the only concern anymore. The paper compares the benefits and the disadvantages of both domains, focusing on the time domain because the latter is neglected or at least heavily underrepresented throughout the classical array signal processing textbooks and most of the current papers dealing with the beamforming method. Therefore, it is not the purpose of this paper to present a new theory or any advanced algorithms, but rather to give a general overview which is motivated from an application-oriented and practical standpoint of view. It is pointed out that a high signal bandwidth and a sampling rate much higher than twice the Nyquist frequency necessary for the channel data are especially important when working in the time domain. Application examples from technical and nontechnical fields will be given.
BibTeX:
@inproceedings{Jaeckel2006,
  author = {Jaeckel, O.},
  title = {Strengths and weaknesses of calculating beamforming in the time domain},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-02_Jaeckel.pdf}
}
Jaeger S, Burnside N, Soderman P, Horne W and James K (2002), "Microphone Array Assessment of an Isolated, 26%-scale, High-fidelity Landing Gear", In 8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2410., June, 2002.
Abstract: An aeroacoustic study of a 26%-scale landing gear model was conducted in the NASA Ames 7- by 10-Foot Wind Tunnel using a phased microphone array. The incorporation of complex parts via stereo lithography produced a model that can mimic full-scale details down to 3 mm. These details include the contours, brake cylinders, bolt holes, and wheel hubs that appear on the real landing gear. Major noise sources were identified and ranked. From the sideline view, the noise levels of the cable harness and torque link were each at least 8 dB above that of a clean configuration. Sources from the more ambiguous fly-over view, such as the front axle, center axle and rear axle regions, were 11 dB above the clean configuration for frequencies below 2000 Hz full-scale. This increment in noise likely included other sources situated behind the truck. Referenced to the clean configuration, the braces and links contributed as much as 8 dB. Tests with a fully sealed fairing on the landing gear suggest, through careful design of major components, a noise reduction of up to 15 dB can be achieved although 2 to 6 dB of noise reduction is probably a more realistic goal.
BibTeX:
@inproceedings{Jaeger_etal2002,
  author = {Jaeger, S. and Burnside, N. and Soderman, P. and Horne, W. and James, K.},
  title = {Microphone Array Assessment of an Isolated, 26%-scale, High-fidelity Landing Gear},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Jiang M, Li XD and Tong WM (2014), "Identification and Localization of Airfoil Noise Sources at Low Angles of Attack", In AIAA SciTech, 52nd Aerospace Sciences Meetingm 13-17 January 2014, National Harbor, Maryland., Jan, 2014.
Abstract: Phased microphone array technique has received much attention for the localization of sound sources. In this paper, this technique is applied to investigate the airfoil self-noise based on a Computational Aeroacoustics (CAA) database. Two-dimensional Direct Numerical Simulation (DNS) is conducted of flow over NACA0012 airfoil at low angles of attack and a moderate Reynolds number. Both the mean flow and acoustics results agree well with previous experimental and numerical data. The numerical data then served as an input for the noise identification and localization process. Three beamfoming algorithms are considered. The results of the phased array calculations show that the tonal noise is the dominant source for NACA0012 airfoil operating at low angles of attack and a moderate Reynolds number. With angle of attack increasing, the tonal sources move upstream and the noise strength is enhanced.
BibTeX:
@inproceedings{JiangLiTong2014,
  author = {Jiang, M. and Li, X. D. and Tong, W. M.},
  title = {Identification and Localization of Airfoil Noise Sources at Low Angles of Attack},
  booktitle = {AIAA SciTech, 52nd Aerospace Sciences Meetingm 13-17 January 2014, National Harbor, Maryland},
  year = {2014}
}
Johnson DH and Dudgeon DE (1993), "Array Signal Processing, Concepts and Techniques" P T R Prentice Hall, Englewood Cliffs .
BibTeX:
@book{JohnsonDudgeon1993,
  author = {Johnson, Don H. and Dudgeon, Dan E.},
  title = {Array Signal Processing, Concepts and Techniques},
  publisher = {P T R Prentice Hall, Englewood Cliffs },
  year = {1993}
}
Jordan P, Fitzpatrick JA and Meskell C (2003), "Beampattern control of a microphone array to minimize secondary source contamination", J. Acoust. Soc. Am.., October, 2003. Vol. 114(4), pp. 1920-1925.
Abstract: A null-steering technique is adapted and applied to a linear delay-and-sum beamformer in order to measure the noise generated by one of the propellers of a (1/8) scale twin propeller aircraft model. The technique involves shading the linear array using a set of weights, which are calculated according to the locations onto which the nulls need to be steered (in this case onto the second propeller). The technique is based on an established microwave antenna theory, and uses a plane-wave, or far field formulation in order to represent the response of the array by an nth-order polynomial, where n is the number of array elements. The roots of this polynomial correspond to the minima of the array response, and so by an appropriate choice of roots, a polynomial can be generated, the coefficients of which are the weights needed to achieve the prespecified set of null positions. It is shown that, for the technique to work with actual data, the cross-spectral matrix must be conditioned before array shading is implemented. This ensures that the shading function is not distorted by the intrinsic element weighting which can occur as a result of the directional nature of aeroacoustic systems. A difference of 6 dB between measurements before and after null steering shows the technique to have been effective in eliminating the contribution from one of the propellers, thus providing a quantitative measure of the acoustic energy from the other.
BibTeX:
@article{Jordan_etal2003,
  author = {Jordan, P. and Fitzpatrick, J. A. and Meskell, C.},
  title = {Beampattern control of a microphone array to minimize secondary source contamination},
  journal = {J. Acoust. Soc. Am.},
  year = {2003},
  volume = {114},
  number = {4},
  pages = {1920--1925},
  doi = {10.1121/1.1568755}
}
Jordan P, Fitzpatrick JA and Valière J-C (2002), "Measurement of an aeroacoustic dipole using a linear microphone array", J. Acoust. Soc. Am.., March, 2002. Vol. 111(3), pp. 1267-1273.
Abstract: It is shown that the standard beamformer technique is inadequate for both the source location and the measurement of a simple dipole and that this is due to the assumption of monopole propagation in the calculation of the phase weights used to steer the focus of the array. A numerical simulation is used to illustrate the problem and to develop a correction to the signal processing algorithm to account for the dipole propagation characteristic. This is then applied to array measurements for an aeroacoustic dipole produced by a cylinder in a cross flow. The resulting source map and the beamformed spectrum are shown to give a true representation of the source energy and frequency content. A secondary effect of this correction is that the array becomes insensitive to other source types so that in addition to acting as a spatial filter, the array can perform as a source filter. This work also demonstrates how an array measurement can be misinterpreted if applied without consideration of the source mechanism.
BibTeX:
@article{Jordan_etal2002,
  author = {Jordan, P. and Fitzpatrick, J. A. and Valière, J.-C.},
  title = {Measurement of an aeroacoustic dipole using a linear microphone array},
  journal = {J. Acoust. Soc. Am.},
  year = {2002},
  volume = {111},
  number = {3},
  pages = {1267--1273},
  doi = {10.1121/1.1446052}
}
Kagami S, Mizoguchi H, Tamai Y and Kanade T (2006), "Microphone Array for 2D Sound Localization and Capture" Vol. 21, pp. 45-54. Springer Berlin / Heidelberg.
Abstract: This paper describes two circular microphone arrays and a square microphone array which can be used for sound localization and sound capture. Sound capture by microphone array is achieved by Sum and Delay Beam Former (SDBF). Simulation of sound pressure distribution of 32 & 128ch circular microphone array and 128ch square microphone array are shown. According to simulation results, dedicated PCI 128-channel simultaneous input board and Firewire (IEEE1394) 32-channel board are developed with maximum sampling rate of 44.1kHz and 11.025kHz sample respectively. Then a 32ch circular microphone array and a 128ch square microphone array have been developed. The 32ch circular microphone array can capture sound from an arbitrary direction. The 128ch square microphone array can capture sound from a specific point. Both systems are evaluated by using frequency components of the sound. The circular type system will be used on a mobile robot including humanoid robot, and square type will be extend towards room coverage type application.
BibTeX:
@inbook{Kagamai_etal2006,
  author = {Kagami, S. and Mizoguchi, H. and Tamai, Y. and Kanade, T.},
  editor = {B. Siciliano, O. Khatib, and F. Groen},
  title = {Microphone Array for 2D Sound Localization and Capture},
  publisher = {Springer Berlin / Heidelberg},
  year = {2006},
  volume = {21},
  pages = {45--54},
  doi = {10.1007/11552246_5}
}
Kastner J, Kim J-H and Samimy M (2009), "A study of the correlation of large-scale structure dynamics and far-field radiated noise in an excited Mach 0.9 jet", Int. J. Aeroacoustics. Vol. 8(3), pp. 231-259.
Abstract: The main goal of the present work is to excite various instabilities of an axisymmetric Mach 0.9 jet with a ReD of 0.76 × 106, track the ensuing large-scale structures/instability waves, and investigate relations between the dynamics of these structures and the far-field sound. The jet was excited over a large range of Strouhal numbers and several azimuthal modes by eight localized arc filament plasma actuators, equally spaced around the circumference of the nozzle, near the nozzle exit. The flow field and far-field noise were investigated using particle image velocimetry and a three-dimensional array of 12 microphones at 30° polar angle to the downstream jet axis. The microphone array results show that the high amplitude noise radiated to 30° polar angle is originated just downstream of the end of the potential core, in agreement with our previous results and the results in the literature. The streamwise noise source distribution was only sensitive to azimuthal modes around the jet preferred mode. Otherwise, the general trend was that forcing the jet at low Strouhal numbers moves the distribution upstream compared to the baseline jet, and at high Strouhal numbers results in a source distribution similar to the baseline jet. Conditionallyaveraged
PIV data were used to relate the flow dynamics and noise sources. The growth, saturation, and decay of the conditionally-averaged velocity fluctuations along the jet centerline correlate well with the far-field noise and the noise source distribution estimated using the microphone array. For m = 0 mode excitation around the jet column Strouhal number, the conditionally-averaged streamwise velocity fluctuations correlate well with the noise source distribution. While for m = 1, the correlation is best with the conditionally-averaged cross-stream fluctuations.
BibTeX:
@article{Kastner_etal2009,
  author = {Kastner, J. and Kim, Jin-Hwa and Samimy, M.},
  title = {A study of the correlation of large-scale structure dynamics and far-field radiated noise in an excited Mach 0.9 jet},
  journal = {Int. J. Aeroacoustics},
  year = {2009},
  volume = {8},
  number = {3},
  pages = {231--259},
  doi = {10.1260/147547208786940008}
}
Kern M and Opfer H (2008), "Enhancement of the dynamic range in acoustic photos by modified time domain beamforming", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-16. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The fast identification of acoustic (noise-)sources is an important discipline in the process of automotive engineering. Based on time domain beamforming in the far-field, the Acoustic Camera [2] is capable of localizing sound sources by detecting the direction of incidence. The interpretation of measurement results is sometimes complicated because of inherent drawbacks of the system and the method itself, and moreover by bad acoustic conditions. In this context self noise of the microphones can affect the acoustic image. By means of the well-known diagonal deletion in the cross-spectral matrix this effect can be reduced in the frequency domain. In this study the diagonal deletion technique is applied for time domain beamforming, suggested by Dougherty in [1]. The results are compared to the pure delay-and-sum algorithm and are discussed in terms of an extended applicability of the Acoustic Camera.
BibTeX:
@inproceedings{KernOpfer2008,
  author = {Kern, M. and Opfer, H.},
  title = {Enhancement of the dynamic range in acoustic photos by modified time domain beamforming},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-16_Kern_Opfer.pdf}
}
Kern M and Opfer H (2006), "Extension of the beamforming-method by synchronized multiple measurements", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-15., November, 2006. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The fast identification of acoustic (noise-)sources becomes more and more important in the process of automotive engineering. Beamforming as a far-field method is capable of localizing sound sources by detecting the direction of incidence. The interpretation of measurement results is sometimes complicated because of inherent drawbacks of the system and the method itself, and moreover by bad acoustic conditions. The finite number of sensors and the final size of the arrangement of sensors limits the dynamic range and the spatial resolution. In this study synchronized multiple measurements were used to create a virtual larger array, that is, to improve the spatial resolution especially at lower frequencies. In terms of an extended applicability of the Acoustic Camera method first results are discussed.
BibTeX:
@inproceedings{KernOpfer2006,
  author = {Kern, M. and Opfer, H.},
  title = {Extension of the beamforming-method by synchronized multiple measurements},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-15_Kern_Opfer.pdf}
}
Kim Y and Nelson PA (2003), "Spatial resolution limits for the reconstruction of acoustic source strength by inverse methods", J. Sound Vib.. Vol. 265, pp. 583-608.
BibTeX:
@article{KimNelson2003,
  author = {Kim, Y. and Nelson, P. A.},
  title = {Spatial resolution limits for the reconstruction of acoustic source strength by inverse methods},
  journal = {J. Sound Vib.},
  year = {2003},
  volume = {265},
  pages = {583--608}
}
King III WF (1996), "A précis of developments in the aeroacoustics of fast trains", J. Sound Vib.., May, 1996. Vol. 193(1), pp. 349-358.
Abstract: After briefly reviewing the important mechanisms by which aerodynamic sound sources are generated on high speed tracked vehicles, two characteristic train speeds that quantify the significance of this noise are defined. The results of microphone array measurements are used to illustrate sound levels by flow interactions with a pantograph. Recent developments in measurement technology, analysis and hardware are then surveyed.
BibTeX:
@article{King1996,
  author = {King III, W. F.},
  title = {A précis of developments in the aeroacoustics of fast trains},
  journal = {J. Sound Vib.},
  year = {1996},
  volume = {193},
  number = {1},
  pages = {349--358},
  doi = {10.1006/jsvi.1996.0275}
}
King III WF and Bechert D (1979), "On the Sources of Wayside Noise Generated by High-Speed Trains", J. Sound Vib.. Vol. 66, pp. 311-332.
Abstract: A linear array of 14 microphones was used to measure radiated noise generated by a four-carriage electric train travelling at speeds between 160 and 250 km/h. Most of the results given in this paper pertain to apparent source locations of wheel/rail interaction noise, although preliminary data collected in a concurrent study of railway aerodynamic noise are briefly mentioned. An analysis of the measurements suggests that apparent sources of wheel/rail interaction noise are located (i) in the rail or substructure at low frequencies, (ii) on the wheel rim just below the axle at intermediate or peak frequencies, and (iii) on the lower part of the wheel and possibly in the rail at high frequencies.
BibTeX:
@article{KingBechert1979,
  author = {King III, W. F. and Bechert, D.},
  title = {On the Sources of Wayside Noise Generated by High-Speed Trains},
  journal = {J. Sound Vib.},
  year = {1979},
  volume = {66},
  pages = {311--332},
  doi = {10.1016/0022-460X(79)90848-4}
}
Koop L and Ehrenfried K (2008), "Microphone-array processing for wind-tunnel measurements with strong background noise", In 14th AIAA/CEAS Aeroacoustics Conference, Vancouver, BC, Canada, May 5-7, 2008., AIAA-2008-2907., May, 2008.
Abstract: Acoustic array measurements have been carried out in a wind tunnel with a closed test-section on a swept constant-chord half-model. The experiments show that strong background noise present in the test section disturbs the array measurements and causes artefacts in source maps obtained with conventional beamforming (CB). By analyzing the components of the wavenumber spectrum in the array plane using the delay-and-sum beamforming with an infinite focal distance it is shown that this noise consists mainly of upstream propagating spurious waves. They can be reduced either by modifications to the wind tunnel test-section or by the BiCLean algorithm, a more advanced array processing technique. In a second step the robustness of deconvolution algorithms is investigated with respect to the noisy data obtained from the closed test-section measurements. The new deconvolution algorithms E-DAMAS2 proposed by Ehrenfried and Koop and the CLEAN-SC algorithm introduced by Sijtsma are applied to the present experimental data. The results show that the spatial resolution can be increased considerably by applying these algorithms and that side lobes are successful suppressed. The integrated spectra obtained from the deconvolution source-powers agree very well with standard source-power integration results based on CB. The background noise which is present in the CB results is detected also with the deconvolution algorithms. But no instabilities have been observed in the deconvolution process due to this noise.
BibTeX:
@inproceedings{KoopEhrenfried2008,
  author = {Koop, L. and Ehrenfried, K.},
  title = {Microphone-array processing for wind-tunnel measurements with strong background noise},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference, Vancouver, BC, Canada, May 5-7, 2008},
  year = {2008}
}
Koop L, Ehrenfried K and Dillmann A (2004), "Reduction of Flap Side-Edge Noise: Passive and Active Flow Control", In 10th AIAA/CEAS Aeroacoustics Conference., AIAA-2004-2803.
Abstract: Microphone array and particle image velocimetry measurements have been performed to investigate the potential of passive and active flow control methods for flap noise reduction. The extended wing flap of the swept constant chord half-model was equipped with either a blowing facility as an active flow control device or with other flap side-edge modifications such as wing tip fences, microtabs and winglets. The flap side edge noise is reduced with the blowing configuration between 2 kHz and 5 kHz. The maximum noise reduction of 15:9 dB is achieved at 2:9 kHz. Varying the diameter of the blowing orifices shows that the noise reduction is governed by the momentum rather than the flow rate of the blowing. The winglets and the suction side fence are most effective in reducing the flap side-edge noise. The reduced level with these configurations is even lower than with the active blowing. The vortex generators and the pressure side fence turn out to be the least effective flow control devices. PIV-measurements at an isolated unswept flap model show that the main vortex on the suction side exhibits a very inhomogeneous vorticity distribution which can be attributed to the unstable shear layer that separates at the lower corner of the flap side-edge and to the negative vorticity production on the suction surface. With blowing the vorticity of the shear layer is concentrated in several small vortices. The distance between those vortices and the solid surface increases with higher blowing momentum and because of this the negative vorticity production due to recirculation is disappears. These distinct modifications of the side-edge flow field explain the noise reduction shown in the aeroacoustic measurements.
BibTeX:
@inproceedings{Koop_etal2004,
  author = {Koop, L. and Ehrenfried, K. and Dillmann, A.},
  title = {Reduction of Flap Side-Edge Noise: Passive and Active Flow Control},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference},
  year = {2004}
}
Koop L, Ehrenfried K, Dillmann A and Michel U (2002), "Reduction of flap side edge noise by active flow control", In 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2469.
Abstract: One dominant airframe noise source is situated at the side edge of the extended wing flap. The objective of the present study is to reduce this noise by blowing air into the flap side-edge vortex to displace or destroy the vortical structure and thus reduce the emission of sound. PIV measurements without blowing yield a rather complicated unsteady vortical structure at the flap side-edge which confirms the assumption of a noise source. This is verified by microphone array measurements. They show that the flap side-edge noise, besides other noise sources, is present over a broad frequency range. The flight parameters such as angle of incidence and slat and flap angles, however, determine which noise source is dominant. PIV measurements with blowing show that the vortical structure can be almost completely dispersed and that the maximum vorticity in the vortex core is reduced. Consequently, a reduction of the flap side–edge noise can be seen in the microphone array measurement. In addition, the sound pressure level in the acoustic far field is reduced by 3 to 4 dB above 1.25 kHz.
BibTeX:
@inproceedings{Koop2002,
  author = {Koop, L. and Ehrenfried, K. and Dillmann, A. and Michel, U.},
  title = {Reduction of flap side edge noise by active flow control},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Koop L, Ehrenfried K and Kröber S (2005), "Investigation of the systematic phase mismatch in microphone-array analysis", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, May 23--25, 2005., AIAA-2005-2962., May, 2005.
Abstract: The paper investigates phase deviations as they occur in aeroacoustic array measurements in open jet wind tunnels. The accuracy of an approximative zero-thickness shear layer model, which is used in practice to predict the phase shift between source and microphones, is investigated numerically. The exact wave propagation through a generic shear layer is calculated by solving the full linearized Euler equations using a finite element method and by means of geometrical acoustics. The results are taken to determine the phase deviations between the simplified model and the exact case. It is demonstrated that the position of the zero-thickness shear layer is important for the accuracy at high frequencies. Additionally measurements are made to analyze the phase fluctuations which are generated by the scattering at turbulent structures in the open-jet shear layer. A procedure is proposed to compensate these phase fluctuations and to improve the array efficiency.
BibTeX:
@inproceedings{Koop2005,
  author = {Koop, L. and Ehrenfried, K. and Kröber, S.},
  title = {Investigation of the systematic phase mismatch in microphone-array analysis},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, CA, May 23--25, 2005},
  year = {2005}
}
Kopiev V and Zaytsev M (2014), "Application of Beamforming to Jet/Flap Interaction Noise", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-24., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The article is devoted to experimental study of additional noise source which arises due to interaction of deflecting wing flap and dual flow jet modeling the exhaust of modern high-bypass ratio aircraft engines. The study was conducted in TsAGI’s free jet aerodynamic tunnel with anechoic test section with small-scale models by the use of 42-channel microphone array and far field microphones. The different test cases were investigated with different nozzle pressure ratios and co-flow velocities corresponding to aircraft take-off and landing conditions. The comparison of source localization obtained by delay and sum postprocessing technique with refined postprocessing is presented.
BibTeX:
@inproceedings{Kopiev_Zaytsev2014,
  author = {Kopiev, V. and Zaytsev, M.},
  title = {Application of Beamforming to Jet/Flap Interaction Noise},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-24.pdf}
}
Kröber S, Ehrenfried K and Koop L (2008), "Design and testing of sound sources for phased microphone array calibration", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-02., February, 2008. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The phased array technique is a powerful tool for the localisation and quantification of sound sources in aeroacoustic testing. The accuracy of the results is limited due to phase and sensitivity errors of the microphones. A reliable calibration procedure for the microphone array would enhance the applicability of the measurement technique. Currently, appropriate sound sources are lacking, especially for in-flow calibration. An ideal calibration sound source exhibits monopole characteristics and covers a frequency range up to 70 kHz. The present study reviews concepts for omni-directional sound sources and evaluates their capability for microphone array calibration. Two concepts of calibration sources with aerodynamic fairings for the use in wind tunnels have been developed. The radiated sound field of both probes was examined in experiments in an anechoic facility. The presented results comprise the spatial amplitude characteristics of the designed sound sources. In addition, beamforming with a synthetic microphone array was performed to analyse the phase characteristics.
BibTeX:
@inproceedings{Kroeber_etal2008,
  author = {Kröber, S. and Ehrenfried, K. and Koop, L.},
  title = {Design and testing of sound sources for phased microphone array calibration},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-02_Kroeber_Ehrenfried_Koop.pdf}
}
Kröber S, Ehrenfried K, Koop L and Lauterbach A (2010), "In-flow calibration approach for improving beamforming accuracy", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-11., February, 2010.
Abstract: The phased microphone array technique is a well established tool in aeroacoustic testing for the localisation and quantification of sound sources. The measurements are often carried out in closed or open wind tunnels using scaled models. In both types of wind tunnels flow effects derogate the accuracy of beamforming results. In the open test-section the sound waves have to pass through the wind tunnel shear layer before reaching the microphone. That results in a spatial coherence loss due to turbulent scattering and refraction and potentially leads to degraded source maps and under-estimated source levels. The present study addresses this matter and proposes a calibration approach for an open wind tunnel using an in-flow calibration source. This source employs a ribbon loudspeaker which can provide sufficiently high sound pressure levels in a broad frequency range and its properties are known. The presented results comprise details of the applied in-flow calibration sound source, the calibration procedure and its evaluation with respect to the achieved beamforming accuracy.
BibTeX:
@inproceedings{Kroeber_etal2010,
  author = {Kröber, S. and Ehrenfried, K. and Koop, L. and Lauterbach, A.},
  title = {In-flow calibration approach for improving beamforming accuracy},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-11.pdf}
}
Kröber S, Ehrenfried K, Koop L, Lauterbach A and Henning A (2010), "Systematic Comparison of Microphone Array Measurements in Open and Closed Wind Tunnels", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3734., June, 2010.
Abstract: A systematic comparison between microphone array measurements in closed and open test sections of a wind tunnel is presented. The study focuses on the beamforming accuracy in both wind tunnel types with respect to source position, relative and absolute levels of beamforming results and integrated spectra using two different sound sources. At first, an in-flow calibration sound source incorporated in an electromechanic driver and with known characteristics is used. This kind of source allows to investigate the influence of the different flow conditions on the sound propagation and their influence on beamforming results. In the second part of the test a plate with various cavities serves as an aeroacoustic sound source. In both wind tunnels the same phased microphone array is used for the measurements, whereby the aim is to keep the experimental setup and conditions as identical as possible in both cases in order to be able to examine the test section-dependent effects. The beamforming results of the two different sources, obtained from measurements in both test sections, show a high qualitative and quantitative agreement provided that the SNR is sufficiently high enough. The wind tunnel dependent deviations of the integrated source spectra do not exceed 4.7 dB.
BibTeX:
@inproceedings{Kroeber_etal2010b,
  author = {Kröber, S. and Ehrenfried, K. and Koop, L. and Lauterbach, A. and Henning, A.},
  title = {Systematic Comparison of Microphone Array Measurements in Open and Closed Wind Tunnels},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Kroeber S and Koop L (2011), "Comparison of Microphone Array Measurements of an Airfoil with High-Lift Devices in Open and Closed Wind Tunnels", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2721., June, 2011.
Abstract: A comparison between microphone array measurements in closed and open test sections of wind tunnels using a generic 3-element high-lift system is presented. Aeroacoustic and aerodynamic measurements were performed simultaneously in order to be able to examine their respective test section-dependent characteristics and their influences on aeroacoustic sound generation and propagation. The study focuses on the beamforming results in both wind tunnel types with respect to source maps, relative and absolute levels of beamforming results and integrated spectra by considering the aerodynamic performance in terms of the resulting lift and static pressure distribution along the model. In both wind tunnels the same phased microphone array is used for the measurements, whereby the aim is to keep the experimental setup and conditions as close to identical as possible in both cases in order to be able to examine the test section-dependent effects. In addition, an in-flow calibration sound source incorporated in an electromechanic driver and with known characteristics is used for characterizing the influence of the different flow conditions in the different test sections on the sound propagation and their influence on beamforming results.
BibTeX:
@inproceedings{KroeberKoop2011,
  author = {Kroeber, Stefan and Koop,Lars},
  title = {Comparison of Microphone Array Measurements of an Airfoil with High-Lift Devices in Open and Closed Wind Tunnels},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Lan J, Premo J, Zlavog G, Breard C, Callender B and Martinez M (2007), "Phased Array Measurements of Full-Scale Engine Inlet Noise", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007., AIAA-2007-3434., May, 2007.
Abstract: During the Quiet Technology Demonstrator 2 program, a GE90-115B engine was tested statically which provided the opportunity to demonstrate several advanced phased array systems for measuring inlet noise. In order of increasing complexity, these included a 10 element microphone arc array located in the acoustic near-field, a 100 element Kulite array mounted on the aeroacoustic bellmouth, and a 275 element Kulite array mounted on the turbulence control structure (TCS). This paper discusses the design objectives, mplementation, and sample results from these arrays. The source localization capability of the relatively simple microphone arc array was demonstrated. The inlet noise was also decomposed into its modal content by both the bellmouth array and TCS array for a subsonic and a transonic fan tip relative Mach number. These phased array systems were successfully deployed to demonstrate the capabilities of the advanced measurements and provide useful insights into inlet radiated fan and compressor noise.
BibTeX:
@inproceedings{Lan_etal2007,
  author = {Lan, J. and Premo, J. and Zlavog, G. and Breard, C. and Callender, B. and Martinez, M.},
  title = {Phased Array Measurements of Full-Scale Engine Inlet Noise},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007},
  year = {2007},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO07_1493/PV2007_3434.pdf}
}
Lardies J (1989), "Acoustic ring array with constant beamwidth over a very wide frequency range", Acoustics letters. Vol. 13(5), pp. 77-81.
Abstract: A simple technique is presented for maintaining the beamwidth of a transducer constant over a very wide frequency range (over N octaves). A acoustical ring array of six sensors is used to produce a radiation pattern at frequency F1. A half-scale model is implemented to give the same directivity pattern at frequency 2F1. Two compensation filters, whose frequency responses are derived by imposing the constant beamwidth constraints, are used in the respective array outputs, to produce a constant beamwidth over the octave. The design process is repeated N times, to obtain an acoustical array with constant beamwidth over a very wide frequency range (over N octaves)
BibTeX:
@article{Lardies1989,
  author = {Lardies, J.},
  title = {Acoustic ring array with constant beamwidth over a very wide frequency range},
  journal = {Acoustics letters},
  year = {1989},
  volume = {13},
  number = {5},
  pages = {77--81}
}
Lasdon LS, Plummer J, Buehler B and Waren AD (1987), "Optimal design of efficient acoustic antenna arrays", Mathematical Programming., June, 1987. Vol. 39(2), pp. 131-155.
Abstract: Minimax optimal design of sonar transducer arrays can be formulated as a nonlinear program with many convex quadratic constraints and a nonconvex quadratic efficiency constraint. The variables of this problem are a scaling and phase shift applied to the output of each sensor. This problem is solved by applying Lagrangian relaxation to the convex quadratic constraints. Extensive computational experience shows that this approach can efficiently find near-optimal solutions of problems with up to 391 variables and 579 constraints.
BibTeX:
@article{Lasdon_etal1987,
  author = {Lasdon, L. S. and Plummer, J. and Buehler, B. and Waren, A. D.},
  title = {Optimal design of efficient acoustic antenna arrays},
  journal = {Mathematical Programming},
  year = {1987},
  volume = {39},
  number = {2},
  pages = {131--155},
  doi = {10.1007/BF02592949}
}
Lauterbach A and Ehrenfried K (2009), "Procedure for the Accurate Phase Calibration of a Microphone Array", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3122., May, 2009.
Abstract: The “delay and sum beamformer” algorithm (“DSB”) is a powerful tool for the localisation and quantification of acoustic sources with microphone arrays. For the calculation of beamforming maps the DSB algorithm requires the following input data: time series of all microphones, a grid of focus points which includes the region of interest, paramater of the flow for boundary layer or shear layer corrections and the accurate position of all microphones. The present paper is focused on the last item: the accurate estimation of the microphone positions. Especially for aeroacoustic applications the number of microphones should be large enough in order to obtain good beamforming results. The estimation of the accurate microphone positions can mean a huge time consuming effort. The method which will be presented in this paper is similar to the well known global positioning system: distances to satellites provide information about the position of a receiver. Here, several monopole-like acoustical point sources with known positions and a reference microphone which is installed close to the sound sources are used to compute the position of the microphones of a microphone array in the three-dimensional space. After pointing out the basic concepts and algorithms a practical implementation of the test sources is described. Eight test sources and the reference microphone are integrated in a so-called calibration unit. Afterwards a calibration of a microphone array with known microphone positions is presented to verify the method and to assess the accuracy that can be achieved. Furthermore the problem is addressed how many test sources are necessary to achieve accurate results. Finally, the procedure is used to calibrate an out-of-flow microphone array with a layout of microphones where the positions are only known with some uncertainty. Investigations concerning the frequency dependence of the calibration are presented. Beamforming on a loudspeaker is performed to show in how far more accurately known microphone positions can improve beamforming results, particularly in the higher frequency range.
BibTeX:
@inproceedings{LauterbachEhrenfried2009,
  author = {Lauterbach, A. and Ehrenfried, K.},
  title = {Procedure for the Accurate Phase Calibration of a Microphone Array},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3122.pdf},
  doi = {10.2514/6.2009-3122}
}
Lauterbach A, Ehrenfried K and Koop L (2008), "Array measurements in wind tunnels with open test sections", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-09. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Acoustically optimized wind tunnels usually have an anechoic chamber around an open test section. For array measurements in this type of tunnels the acoustic array is typically placed outside the flow field - beside or above the test section. The sound emitted from sources in the flow has to propagate through a turbulent shear layer to reach the microphones. During their passage through the shear layer the sound waves interact with turbulent structures. The higher the frequency of the wave, the more significant the effect of the shear layer is. In the present paper these interaction of sound waves with a turbulent shear layer is investigated. It is analyzed which effects can occur when sound waves propagate through a turbulent shear layer and how these effects can influence the results of array measurements. Experiments with a test source in a wind tunnel with open test section are performed. It is shown that turbulent structures in the shear layer lead to systematic phase fluctuations. These phase fluctuations have a certain spectrum and a distinct spatial correlation. Beside these effects the spectral broadening of tones due to the propagation trough the shear layer is investigated.
BibTeX:
@inproceedings{Lauterbach_etal2008,
  author = {Lauterbach, A. and Ehrenfried, K. and Koop, L.},
  title = {Array measurements in wind tunnels with open test sections},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-09_Lauterbach_Ehrenfried_Koop.pdf}
}
Lauterbach A, Ehrenfried K, Kröber S, Ahlefeldt T and Loose S (2010), "Microphone array measurements on high-speed trains in wind tunnels", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-01., February, 2010.
Abstract: The present study evaluates the capabilities of the phased microphone array technique for the localisation and quantification of aeroacoustic sound sources of high-speed trains in wind tunnels. The major challenge is to obtain a sufficient resolution of the sources with low source strength. The experiments were carried out using 1:25 models in the Aeroacoustic Wind Tunnel Brunswick (AWB) of the German Aerospace Center (DLR). This Göttingen – type wind tunnel has an open test secttion which is surrounded by an anechoic chamber. The microphone array consists of 143 microphones and is positioned outside the flow. In order to achieve reasonable results a shear layer correction is applied. Performing a phase-calibration can increase the signal-to-noise ratio, especially for higher frequencies. This procedure will be presented als well.
BibTeX:
@inproceedings{Lauterbach_etal2010,
  author = {Lauterbach, A. and Ehrenfried, K. and Kröber, S. and Ahlefeldt, T. and Loose, S.},
  title = {Microphone array measurements on high-speed trains in wind tunnels},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-01.pdf}
}
Leclère Q (2009), "Acoustic imaging using under-determined inverse approaches: Frequency limitations and optimal regularization", J. Sound Vib.. Vol. 321, pp. 605-619.
Abstract: This paper presents an acoustic imaging technique based on an under-determined inverse approach. The principle is to quantify an elementary source distribution on a source surface from acoustic pressure measurements. The acoustic transfer system between elementary sources and microphone positions, very under-determined, is then reduced to a square system using singular value decomposition. The high frequency limitation of this method is studied, as well as the regularization techniques that have to be used at low frequency. A Monte-Carlo simulation is carried out to compare the efficiency of generalized cross validation and L-curve validation to choose the Tikhonov regularization parameter. A combined validation criterion is finally proposed to take advantage of both approaches.
BibTeX:
@article{Leclere2009,
  author = {Leclère, Q.},
  title = {Acoustic imaging using under-determined inverse approaches: Frequency limitations and optimal regularization},
  journal = {J. Sound Vib.},
  year = {2009},
  volume = {321},
  pages = {605--619},
  doi = {10.1016/j.jsv.2008.10.022}
}
Lee M and Bolton J (2007), "Source characterization of a subsonic jet by using near-field acoustic holography", J. Acoust. Soc. Am.. Vol. 121, pp. 967-977.
Abstract: In the present study, patch near-field acoustical holography was used in conjunction with a multireference, cross-spectral sound pressuremeasurement to visualize the sound field emitted by a subsonic jet and to predict its farfield radiation pattern. A strategy for microphone array design is described that accounts for the low spatial coherence of aeroacoustic sources and for microphone self-noise resulting from entrained flow near the jet. In the experiments, a 0.8-cm-diameter burner was used to produce a subsonic, turbulent jet with a Mach number of 0.26. Six fixed, linear arrays holding eight reference microphones apiece were disposed circumferentially around the jet, and a circular array holding sixteen, equally spaced field microphones was traversed along the jet axis to measure the sound field on a 30-cm-diameter cylindrical surface enclosing the jet. The results revealed that the jet could be modeled as a combination of eleven uncorrelated dipole-, quadrupole-, and octupole-like sources, and the contribution of each source type to the total radiated sound power could be identified. Both the total sound field reconstructed in a three-dimensional space and the farfield radiation directivity obtained by using the latter model were successfully validated by comparisons to directly measured results.
BibTeX:
@article{Lee_Bolton-2007,
  author = {Lee, M. and Bolton, J.S.},
  title = {Source characterization of a subsonic jet by using near-field acoustic holography},
  journal = {J. Acoust. Soc. Am.},
  year = {2007},
  volume = {121},
  pages = {967--977},
  doi = {10.1121/1.2404626}
}
Lee SS (2006), "Phased-Array Measurement of Modern Regional Aircraft Turbofan Engine Noise", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2653., May, 2006.
Abstract: The phased-array system has been applied to identify the noise source distributions for a static engine test. The noise source distribution along the engine centerline was investigated the 39-microphone arc array. The 39-microphone arc array system whose microphones were located between 70 and 160 degrees successfully identify the relative importance between the jet noise and the other internal noise sources, that include inlet, fan and core noises. The relative strength between the fan noise and the core noise was investigated by using the system of 13 microphones between 75 and 105 degrees. The 6 microphones from 70 to 90 degrees are used for the upstream angle noise characteristics. The ratios of the beamforming levels of the baseline configuration to those of the treated core are used to investigate the effectiveness of a core treatment. It is shown that the treated core reduced the internal core noise for the frequencies between 300 and 550 Hz. The phased-array analysis identified the reduced core noise even at high speed condition where the narrowband spectra were almost identical. The beamforming analysis from the 32-microphone spiral array shows the same result.
BibTeX:
@inproceedings{Lee2006,
  author = {Lee, S. S.},
  title = {Phased-Array Measurement of Modern Regional Aircraft Turbofan Engine Noise},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006}
}
Lee SS and Bridges J (2006), "Phased-Array Study of Dual-Flow Jet Noise: Effect of Nozzles and Mixers", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2647., May, 2006.
Abstract: A 16-microphone linear phased-array installed parallel to the jet axis and a 32-microphone azimuthal phased-array installed in the nozzle exit plane have been applied to identify the noise source distributions of nozzle exhaust systems with various internal mixers (lobed and axisymmetric) and nozzles (three different lengths). Measurements of velocity were also obtained using cross-stream stereo particle image velocimetry (PIV). Among the three nozzle lengths tested, the medium length nozzle was the quietest for all mixers at high frequency on the highest speed flow condition. Large differences in source strength distributions between nozzles and mixers occurred at or near the nozzle exit for this flow condition. The beamforming analyses from the azimuthal array for the 12-lobed mixer on the highest flow condition showed that the core flow and the lobe area were strong noise sources for the long and short nozzles. The 12 noisy spots associated with the lobe locations of the 12-lobed mixer with the long nozzle were very well detected for the frequencies 5 KHz and higher. Meanwhile, maps of the source strength of the axisymmetric splitter show that the outer shear layer was the most important noise source at most flow conditions. In
general, there was a good correlation between the high turbulence regions from the PIV tests and the high noise source regions from the phased-array measurements.
BibTeX:
@inproceedings{LeeBridges2006,
  author = {Lee, S. S. and Bridges, J.},
  title = {Phased-Array Study of Dual-Flow Jet Noise: Effect of Nozzles and Mixers},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006}
}
Lee SS and Bridges J (2005), "Phased-Array Measurements of Single Flow Hot Jets", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-2842., May, 2005.
Abstract: A 16 microphone phased-array system has been successfully applied to measure jet noise source distributions. In this study, a round convergent nozzle was tested at various hot and cold flow conditions: acoustic Mach numbers are between 0.35 and 1.6 and static temperature ratios are varied from cold to 2.7. The classical beamforming method was applied on narrowband frequencies. From the measured source distributions locations of peak strength were tracked and found to be very consistent between adjacent narrowband frequencies. In low speed heated and unheated jets, the peak source locations vary smoothly from the nozzle exit to downstream as the frequency is decreased. When the static temperature ratio was kept constant, the peak source position moved downstream with increasing acoustic Mach number for the Strouhal numbers smaller than about 1.5. It was also noted that the peak source locations of low frequencies occurs farther downstream than the end of potential core.
BibTeX:
@inproceedings{LeeBridges2005,
  author = {Lee, S. S. and Bridges, J.},
  title = {Phased-Array Measurements of Single Flow Hot Jets},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Legg M and Bradley S (2012), "Comparison of CLEAN-SC for 2D and 3D scanning surfaces", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-06., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: We present experimental data comparing the accuracy obtained for 2D and 3D scanning surfaces using CLEAN-SC deconvolution of beamformed acoustic maps. A spherical array is used to obtain recordings from a dense point cloud of sound source locations. Beamforming and CLEAN-SC acoustic maps are generated using traditional 2D scanning surfaces and 3D scanning surfaces corresponding to the surface geometry of an object being acoustically imaged. Results for the 3D method show improved accuracy of measured positions and magnitudes of sound sources under a range of circumstances. The most benefit, in regard to position error, is for frequencies above 5kHz and sound sources located less than a metre from the array. In these circumstances, the three-dimensionality is more dominant.
BibTeX:
@inproceedings{LeggBradley2012,
  author = {Legg, M. and Bradley, St.},
  title = {Comparison of CLEAN-SC for 2D and 3D scanning surfaces},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-06.pdf}
}
Li X, Tong W and Jiang M (2014), "Sound Source Localization via Elastic Net Regularization", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-02., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Most phased microphone array algorithms solve liner equations to localize sound sources. Since only a small portion of the source scanning region is expected to possess strong sources, the solutions of these equations would be sparse. In this paper, the elastic net regularization technique is proposed to solve the linear equations for sound source localization. Numerical validation results show that the elastic net regularization technique could improve both the resolution and accuracy compared with DAS (Delay-and-Sum) beamforming and DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) algorithm, particularly for cases under low signal-to-noise ratios. To demonstrate the advantage of the elastic net regularization, the NACA0012 airfoil self-noise sources are localized based on a direct numerical simulation database. Results also show that methods based on elastic net regularization have better performance than DAS beamforming and DAMAS algorithm.
BibTeX:
@inproceedings{Li-Tong-Jiang2014,
  author = {Li, X. and Tong, W. and Jiang, M.},
  title = {Sound Source Localization via Elastic Net Regularization},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-02.pdf}
}
Li Y, Smith M and X. Z (2010), "Identification and Attenuation of a Tonal-Noise Source on an Aircraft's Landing Gear", Journal of Aircraft. Vol. 47(3), pp. 796-804.
Abstract: Aircraft landing gear noise is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. Fairings covering geometrically complex areas of the gears have proved to be very effective in noise reduction. However, in tests on an A340’s main landing gear, the overall benefit of the fairings was offset by both a slight increase in low-frequency broadband noise and a strong tonal noise. In this study, the identification and attenuation of the tonal-noise source has been carried out using a one-quarter-scale A340 main-landing-gear model. Aeroacoustic and aerodynamic tests were conducted in a closed-section wind tunnel, using a phased microphone array on the ceiling of the test section, flush-mounted pressure transducers on the model surface, and the particleimage- velocimetry technique. Far-field noise tests were then taken in an open jet aeroacoustic facility, using far-field microphones to verify the wind-tunnel test results. The experiments demonstrated the tonal-noise mechanism and a number of different control methods.
BibTeX:
@article{Li_etal2010,
  author = {Li, Yong and Smith, M. and Zhang X.},
  title = {Identification and Attenuation of a Tonal-Noise Source on an Aircraft's Landing Gear},
  journal = {Journal of Aircraft},
  year = {2010},
  volume = {47},
  number = {3},
  pages = {796--804},
  doi = {10.2514/1.43183}
}
Liu Y, Dowling A, Shin Ho-Chul and Quale A (2007), "Experimental Study of Surface Roughness Noise", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007., AIAA-2007-3449., May, 2007.
Abstract: A turbulent boundary-layer flow over a rough wall generates a dipole sound field as the near-field ydrodynamic disturbances in the turbulent boundary-layer scatter into radiated sound at small surface irregularities. In this paper, phased microphone arrays are applied to the experimental study of surface roughness noise. The radiated sound from two rough plates and one smooth plate in an open jet is measured at three streamwise locations, and the beamforming source maps demonstrate the dipole directivity. Higher source strengths can be observed in the rough plates than the smooth plate, and the rough plates also enhance the trailing-edge noise. A prediction scheme in previous theoretical work is used to describe the strength of a distribution of incoherent dipoles over the rigid plate and to simulate the sound detected by the microphone array. Source maps of measurement and simulation exhibit encouraging similarities in both source pattern and source strength, which confirms the dipole nature and the predicted magnitude of roughness noise. The simulations underestimate the streamwise gradient of the source strengths and overestimate the source strengths at the highest frequency.
BibTeX:
@inproceedings{Liu_etal2007,
  author = {Liu, Yu and Dowling, A. and Shin, Ho-Chul, and Quale, A.},
  title = {Experimental Study of Surface Roughness Noise},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007},
  year = {2007}
}
Liu Y, Dowling AP and Quayle A (2008), "Numerical Simulation of Beamforming Correction for Dipole Source Identification", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-05. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In this paper, a beamforming correction for dipole source identification by means of phased microphone array measurements is proposed and validated by numerical simulation. Conventional beamforming algorithms are normally based on the monopole source assumption, and can result in significant misinterpretation when applied directly to array measurements of dipole sources. A previous correction technique aims to realign the phases of microphone signals, and has been proved effective to retrieve dipole locations. However, this technique is only applicable to a single source with a linear microphone array and thus its applications are limited in practice. This work extends the signal correction technique to account for both source location and source power for 2-D microphone arrays. A dipole characteristic term is obtained based on theoretical analysis and used for the correction of both signal phase and amplitude. Numerical simulations are performed for a ideal dipole source and a reference monopole to validate the improved beamforming correction. Simulation results have shown that the proposed correction technique is capable of reconstructing dipole sources in both location and amplitude. It is therefore suggested to carefully consider the source mechanisms of aeroacoustic systems before applying array measurements.
BibTeX:
@inproceedings{Liu_etal2008a,
  author = {Liu, Yu and Dowling, A. P. and Quayle, A.R.},
  title = {Numerical Simulation of Beamforming Correction for Dipole Source Identification},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-05_Liu_Dowling_Quayle.pdf}
}
Liu Y, Dowling AP and Shin H-C (2006), "Application of phased arrays in the study of roughness noise", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-09. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The generation of sound by turbulent boundary-layer flow over a rough wall has been investigated theoretically and numerically. The roughness elements were speculated to behave like point dipoles with the dipole strength due to scattering of the near turbulent pressure fluctuations by a roughness element. The roughness-generated noise was shown to be comparable to the trailing-edge noise on an aircraft. Experiments were also performed and the results confirmed that roughness noise is not a negligible sound source. In this study, phased arrays were applied to localize the possible dipole sound sources due to roughness elements on a flat plate. The radiated sound from two rough and one smooth plates in an open jet was measured by 48-channel phased arrays at three locations. The rough regions were manufactured by a square distribution of rigid, hemispherical bosses on a rigid plate. The beamforming source maps obtained at different locations have displayed some features of dipole sources, and the rough plates have shown higher source strengths than the smooth plate. Simulated source maps were obtained for a distribution of incoherent dipoles with source strengths predicted by theory and distributed over the rigid plate. They exhibited encouraging similarities to the measured source maps.
BibTeX:
@inproceedings{Liu_etal2006,
  author = {Liu, Yu and Dowling, A. P. and Shin, Ho-Chul},
  title = {Application of phased arrays in the study of roughness noise},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-09_Liu_Dowling_Shin.pdf}
}
Liu Y, Quayle AR, Dowling AP and Sijtsma P (2008), "Beamforming correction for dipole measurement using two-dimensional microphone arrays", J. Acoust. Soc. Am.., July, 2008. Vol. 124, pp. 182-191.
Abstract: In this paper, a beamforming correction for identifying dipole sources by means of phased microphone array measurements is presented and implemented numerically and experimentally. Conventional beamforming techniques, which are developed for monopole sources, can lead to significant errors when applied to reconstruct dipole sources. A previous correction technique to microphone signals is extended to account for both source location and source power for two-dimensional microphone arrays. The new dipole-beamforming algorithm is developed by modifying the basic source definition used for beamforming. This technique improves the previous signal correction method and yields a beamformer applicable to sources which are suspected to be dipole in nature. Numerical simulations are performed, which validate the capability of this beamformer to recover ideal dipole sources. The beamforming correction is applied to the identification of realistic aeolian-tone dipoles and shows an improvement of array performance on estimating dipole source powers.
BibTeX:
@article{Liu_etal2008,
  author = {Liu, Yu and Quayle, A. R. and Dowling, A. P. and Sijtsma, P.},
  title = {Beamforming correction for dipole measurement using two-dimensional microphone arrays},
  journal = {J. Acoust. Soc. Am.},
  year = {2008},
  volume = {124},
  pages = {182--191},
  doi = {10.1121/1.2931950}
}
Long D (2003), "Acoustic Source Location in Wind Tunnel Tests via Subspace Beamforming", In 41st Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan. 6-9, 2003., AIAA-2003-0369., Jan, 2003.
Abstract: Beamforming is presented as a general tool for the analysis of a fluctuating pressure field in the presence of high speed turbulent flow. These fluctuations can be either hydrodynamic, which convect with the mean flow turbulence, or acoustic fluctuations that propagate at the local speed of sound. The present study focuses on the pressure fluctuations created by models installed in a transonic wind tunnel. Subspace Beamforming is used to isolate the structural features of the turbulent and/or the acoustic field using data collected on a multi-element microphone array. Results for two test cases are presented following development of the analytical procedures.
BibTeX:
@inproceedings{Long2003,
  author = {Long, D.},
  title = {Acoustic Source Location in Wind Tunnel Tests via Subspace Beamforming},
  booktitle = {41st Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan. 6-9, 2003},
  year = {2003}
}
Lowis C and Joseph P (2006), "A Focused Beamformer Technique for Separating Rotor and Stator-Based Broadband Sources", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference)., AIAA-2006-2710., May, 2006.
BibTeX:
@inproceedings{LowisJoseph2006,
  author = {Lowis, C. and Joseph, P.},
  title = {A Focused Beamformer Technique for Separating Rotor and Stator-Based Broadband Sources},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference)},
  year = {2006},
  doi = {10.2514/6.2006-2710}
}
Lurati M, Cigada A, Ripamonti F and Vanali M (2008), "Beamforming method: suppression of spatial aliasing using moving arrays", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-19. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In the scientific and industrial community a growing interest is nowadays devoted to sound source localization techniques. Among all the existing methods, the use of the beamforming algorithm in sound source localization problems is increasing, thanks to its many advantages if compared to the other available methods (Nearfield Acoustic Holography and Helmholtz Equation Least Square Method). The beamforming limits are well known and deeply investigated in literature and the study of possible solutions to overcome these limitations is a key point. The present paper deals with the spatial aliasing problem and proposes an innovative approach to improve the method performances. The spatial aliasing phenomenon causes the appearance of “ghost sources” in the reconstructed images. An innovative solution based on the use of moving microphone arrays is here proposed. The array motion, multiplying the measurement points, allows to reduce the aliasing errors. This paper presents the theoretical background of the innovative method and the results obtained with numerical simulations, in comparison with the traditional “Delay & Sum” method. The influence of some parameters, such as the array speed, and the geometry are investigated and a first experimental validation is given.
BibTeX:
@inproceedings{Lurati_etal2008,
  author = {Lurati, M and Cigada, A. and Ripamonti, F. and Vanali, M.},
  title = {Beamforming method: suppression of spatial aliasing using moving arrays},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-19_Cigada_Lurati_etal.pdf}
}
Möser M (1988), "Analyse und Synthese akustischer Spektren" Springer-Verlag.
BibTeX:
@book{Moeser1988,
  author = {Möser, M.},
  title = {Analyse und Synthese akustischer Spektren},
  publisher = {Springer-Verlag},
  year = {1988}
}
Marcolini MA and Brooks TF (1992), "Rotor Noise Measurement Using a Directional Microphone Array", Journal of the American Helicopter Society. Vol. 37, pp. 11-22.
BibTeX:
@article{MarcoliniBrooks1992,
  author = {Marcolini, M. A. and Brooks, T. F.},
  title = {Rotor Noise Measurement Using a Directional Microphone Array},
  journal = {Journal of the American Helicopter Society},
  year = {1992},
  volume = {37},
  pages = {11--22}
}
Martinez M (2007), "Microphone Polar Arc Phased Array for Locating Turbofan Source Noise Components", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)., AIAA-2007-3445., May, 2007.
Abstract: GE Aviation has implemented phased array processing techniques using its standard 150ft polar arc static engine microphone array. The 150ft polar arc array is the standard array used to obtain engineering and certification spectral data. Using phased array processing techniques, this array is used to locate turbofan engine noise sources. The advanced processing techniques allow GE to obtain at minimal additional cost valuable additional information from existing data. This paper explores the phased array attributes of polar arc microphone array. The paper begins by examining the properties of the continuous polar arc sensor and how it relates to a continuous disk sensor. It then examines the discrete sensor array and compares the continuous sensor array. The paper also explores the use of sub-arrays of the polar arc array and shows various examples of turbofan engine noise analyzed using the phased array.
BibTeX:
@inproceedings{Michael2007,
  author = {Martinez, M.},
  title = {Microphone Polar Arc Phased Array for Locating Turbofan Source Noise Components},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)},
  year = {2007}
}
Maynard JD, Williams EG and Lee Y (1985), "Nearfield acoustic holography: I. Theory of generalized holography and development of NAH", J. Acoust. Soc. Am.. Vol. 78, pp. 1395-1412.
BibTeX:
@article{Maynard_etal1985,
  author = {Maynard, J. D. and Williams, E. G. and Lee, Y.},
  title = {Nearfield acoustic holography: I. Theory of generalized holography and development of NAH},
  journal = {J. Acoust. Soc. Am.},
  year = {1985},
  volume = {78},
  pages = {1395--1412}
}
Mellet C, Létourneaux F, Poisson F and Talotte C (2006), "High speed train noise emission: Latest investigation of the aerodynamic/rolling noise contribution", J. Sound Vib.., June, 2006. Vol. 293(3-5), pp. 535-546.
Abstract: The aim of this paper is to discuss the quantification of aeroacoustic and rolling noise sources emitted by high-speed trains externally. This work relies on the comparison of experimental data obtained in the DEUFRAKO Annex K and K2 projects and those produced more recently. These are firstly measurements obtained within the NOEMIE project dedicated to the High Speed Technical Specifications for Interoperability involving the measurement of the acoustic emission of different rolling stock travelling at 250, 300 and 320 km/h (TGV-Duplex, ICE3, Thalys). Additionally, measurements are considered that are obtained in the framework of an SNCF acoustic test campaign performed on a TGV-Duplex at speeds up to 350 km/h. These comprise source localisation using two-dimensional acoustic array measurements and assessment of the wayside noise increase as a function of the speed. The conclusions drawn in the DEUFRAKO K project are compared with the new set of data. A detailed analysis of the results is also provided, supported by complementary measurements (wheel and rail measurements) and simulations (TWINS calculations).
BibTeX:
@article{Melleta_etal2006,
  author = {Mellet, C. and Létourneaux, F. and Poisson, F. and Talotte, C.},
  title = {High speed train noise emission: Latest investigation of the aerodynamic/rolling noise contribution},
  journal = {J. Sound Vib.},
  year = {2006},
  volume = {293},
  number = {3-5},
  pages = {535--546},
  note = {Proceedings of the Eigth International Workshop on Railway Noise},
  doi = {10.1016/j.jsv.2005.08.069}
}
Mendoza J, Brooks T and Humphreys W (2002), "Aeroacoustic Measurements of a Wing/Slat Model", In 8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2604., June, 2002.
Abstract: Aeroacoustic evaluations of high-lift devices have been carried out in the Quiet Flow Facility of the NASA Langley Research Center. The present paper deals with detailed flow and acoustic measurements that have been made to understand, and to possibly predict and reduce, the noise from a wing leading edge slat configuration. The acoustic database is obtained by a moveable Small Aperture Directional Array of microphones designed to electronically steer to different portions of models under study. The slat is shown to be a uniform distributed noise source. The data was processed such that spectra and directivity were determined with respect to a one-foot span of slat. The spectra are normalized in various fashions to demonstrate slat noise character. In order to equate portions of the spectra to different slat noise components, trailing edge noise predictions using measured slat boundary layer parameters as inputs are compared to the measured slat noise spectra.
BibTeX:
@inproceedings{Mendoza_etal2002,
  author = {Mendoza, J. and Brooks, T. and Humphreys, W.},
  title = {Aeroacoustic Measurements of a Wing/Slat Model},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Mendoza JM, Brooks TF and Humphreys Jr. WM (2002), "An aeroacoustic study of a leading edge slat configuration", Int. J. Aeroacoustics., September, 2002. Vol. 1(3), pp. 241-274.
Abstract: Aeroacoustic evaluations of high-lift devices have been carried out in the Quiet Flow Facility of the NASA Langley Research Center. The present paper describes detailed flow and acoustic measurements that have been made in order to better understand the noise generated from airflow over a wing leading edge slat configuration, and to possibly predict and reduce this noise source. The acoustic database is obtained by a moveable Small Aperture Directional Array of microphones designed to electronically steer to different portions of models under study. The slat is shown to be a uniform distributed noise source. The data was processed such that spectra and directivity were determined with respect to a one-foot span of slat. The spectra are normalized in various fashions to demonstrate slat noise character. In order to equate portions of the spectra to different slat noise components, trailing edge noise predictions using measured slat boundary layer parameters as inputs are compared to the measured slat noise spectra.
BibTeX:
@article{Mendoza_etal2002b,
  author = {Mendoza, J. M. and Brooks, T. F. and Humphreys, Jr., W. M.},
  title = {An aeroacoustic study of a leading edge slat configuration},
  journal = {Int. J. Aeroacoustics},
  year = {2002},
  volume = {1},
  number = {3},
  pages = {241-274},
  doi = {10.1260/147547202320962583}
}
Messer H (1992), "Source localization performance and the array beampattern", Signal Processing., August, 1992. Vol. 28(2), pp. 163-181.
Abstract: Passive localization of sources in space is done using data collected by an array of sensors. The performance of all source location estimation (SLE) algorithms depends on the source-array geometry. In this paper we study this dependence and we show that array localization ability is uniquely determined by a single scalar function — the array beampattern. By analyzing absolute lower bounds on the mean-square-error (mse) of the source location estimates in different scenarios we exploit the relation between features of the array beampattern and the best achievable array localization performance. The beampattern is characterized by its sidelobes level and smoothness, its beamwidth and its mainlobe curvature. We study the effect of these features on source localization properties such as sensitivity to the presence of other sources, resolution ability, sensitivity to ambiguous estimates, etc.
BibTeX:
@article{Messer1992,
  author = {Messer, H.},
  title = {Source localization performance and the array beampattern},
  journal = {Signal Processing},
  year = {1992},
  volume = {28},
  number = {2},
  pages = {163--181},
  doi = {10.1016/0165-1684(92)90033-S}
}
Meyer A and Döbler D (2006), "Noise source localization within car interior using 3D-microphone arrays", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-17. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The „Acoustic Camera“ is a measurement tool which joined the field of acoustics a few years ago also in industrial applications. Simple mapping of a virtual plane at a fixed distance is sufficient if the interesting object has a planar surface and we can arrange array and surface orthogonally. In contrast, the surface of many real objects shows complex three dimensional structures. In these cases, the approximation of three dimensional structures onto a plane implements errors in calculating the focus of the beamformer. A correct calculation is possible if we replace the mapping of a virtual plane at a fixed distance by different measurement distances to individual points at a 3D-model surface. The paper discusses advantages and disadvantages of 2D- and 3D-mapping. In interior spaces the mapping of a plane is not practicable. A car interior for example is composed by many different flat and round subareas. In addition to mapping of three dimensional surfaces we need an omni-directional, non-planar array for complete 3Dmapping. A second problem is how to determine the position and direction of an array in the interior room. The paper discusses the geometry and acoustic properties of microphone arrays which are applicable for a complete 3D-mapping of interior rooms and offers a practicable way of determining the array position and direction related to the measurement object.
BibTeX:
@inproceedings{MeyerDoebler2006,
  author = {Meyer, A. and Döbler, D.},
  title = {Noise source localization within car interior using 3D-microphone arrays},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-17_Meyer_Doebler.pdf}
}
Meyer A, Döbler D and Gräser M (2014), "Efficient Methods for the Analysis of Moving Sound Sources with High Channel Microphone Arrays", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-19., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The localization of stationary and transient sound sources on moving or static objects by multichannel arrays is State of the art for several years. In many industrial sectors (e.g. automotive industry, aircraft industry...) this method is indispensable for the noise reduction, noise analysis and error detection. Analysing moving sound sources increased requirements of hardware and software components. With the aid of light barriers or GPS in combination with inertial navigation systems (INS), it is possible to determine the mostly unknown average speed, or to estimate the speed as a function of time. Also entry and exit times of the moving objects can be determined. For smaller measurement campaigns, this method is not efficient.
For fast moving, long objects (e.g. rail vehicle, truck) often it is not possible to take a photo of the entire object with the built-in optical camera during the measurement. Hence, usually a draft is overlaid with the acoustical image manually, which, however, often does not match the actual object completely and therefore the exact localization of the acoustic sources proves difficult. Furthermore, a frequency shift due to the Doppler effect is present in the sound signals affecting the runtime and phase information which are essential to Beamforming. This leads to significant spatial and spectral blurring of sound sources in the acoustical image. Efficient methods are presented in this paper which allow the solution of solving the complex tasks of generating optical photos of the entire object, overlaying the images automatically and determining the velocity profile as well as enter and exit times using a microphone array with an integrated camera. Another section deals with the algorithm for the determination of the source position under consideration of the Doppler effect.
BibTeX:
@inproceedings{Meyer_etal2014,
  author = {Meyer, A. and Döbler, D. and Gräser, M.},
  title = {Efficient Methods for the Analysis of Moving Sound Sources with High Channel Microphone Arrays},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-19.pdf}
}
Michel U (2006), "History of acoustic beamforming", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-01. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The development of the beamforming method (also called microphone antenna, phased array of microphones, acoustic telescope, or acoustic camera) is reviewed in this paper. The microphone antenna was invented by Billingsley (1974) and has since seen dramatic improvements due to the availability of better data acquisition and computing hardware. Recent mathematical and software developments invert the beamforming process and allow a quantitative determination of the sources. Beamforming is indispensable for the localization of sound sources on moving objects, on flying aircraft, on high-speed trains, on motor cars in motion, on open rotors like helicopter and wind turbine rotors. In these applications, the ability to follow the motion of the sources is important. The second important applications are source localization tests in the test sections of open and closed wind tunnels. The background noise suppression capability of the beamforming method is required here. The various applications are discussed with a long list of references.
BibTeX:
@inproceedings{Michel2006a,
  author = {Michel, U.},
  title = {History of acoustic beamforming},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://www.bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-01_Michel.pdf}
}
Michel U (1997), "On the Usability of Signal Processing in the Frequency Domain for the Mapping of Moving Sound Sources with Planar Microphone Arrays", DLR-IB 92517-97/B3. (DLR-IB 92517-97/B3)
BibTeX:
@techreport{Michel1997ab,
  author = {Michel, U.},
  title = {On the Usability of Signal Processing in the Frequency Domain for the Mapping of Moving Sound Sources with Planar Microphone Arrays},
  year = {1997},
  number = {DLR-IB 92517-97/B3}
}
Michel U and Barsikow B (2003), "Localisation of sound sources on moving vehicles with microphone arrays.", In Proc. EuroNoise 2003, Neapel, 19.-21.05.2003., Paper ID 537., May, 2003. (paper ID 537)
BibTeX:
@inproceedings{MichelBarsikow2003,
  author = {Michel, U. and Barsikow, B.},
  title = {Localisation of sound sources on moving vehicles with microphone arrays.},
  booktitle = {Proc. EuroNoise 2003, Neapel, 19.-21.05.2003},
  year = {2003},
  number = {paper ID 537}
}
Michel U, Barsikow B, Böhning P and Hellmig M (2004), "Localisation of moving sound sources with phased microphone arrays", Proceedings Inter-Noise 2004., In Inter-Noise 2004, Prague, Czech Republic, 22.- 25 August 2004.
Abstract: The phased microphone array is becoming a standard method for the investigation of the sound emission of railways, aircraft, and road vehicles. It is the only method that allows an
identification of the noise sources when the vehicle is in motion. Wheel-rail noise and aerodynamic noise of railways, airframe noise and installed engine noise of aircraft, tyre-road noise of automobiles are typical examples. The method has improved in the past years with the appearance of data acquisition systems capable of sampling a large number of signals and the use of relatively cheap electret microphones. In addition, the data reduction computing times have decreased substantially with modern fast personal computers. The requirements for source localisation on aircraft are especially high. The large flyover altitudes require large array dimensions and large number of microphones. The system that has been developed by DLR for this application will be presented. The spatial resolution and the requirements for the data acquisition are derived. The limits and possibilities for obtaining quantitative results are also demonstrated. Various examples for the distribution of noise sources on aircraft and motor vehicles will be shown and discussed.
BibTeX:
@conference{Michel_etal2004a,
  author = {Michel, U. and Barsikow, B. and Böhning, P. and Hellmig, M.},
  title = {Localisation of moving sound sources with phased microphone arrays},
  booktitle = {Inter-Noise 2004, Prague, Czech Republic, 22.- 25 August 2004},
  journal = {Proceedings Inter-Noise 2004},
  year = {2004},
  url = {http://www.bebec.eu/Downloads/Beamforming_Repository/Internoise-2004_Michel_etal.pdf}
}
Michel U, Barsikow B, Haverich B and Schüttpelz M (1997), "Investigation of airframe and jet noise in high-speed flight with a microphone array", In 3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997., AIAA Paper 97-1596.
BibTeX:
@inproceedings{Micheletal97,
  author = {Michel, U. and Barsikow, B. and Haverich, B. and Schüttpelz, M.},
  title = {Investigation of airframe and jet noise in high-speed flight with a microphone array},
  booktitle = {3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997},
  year = {1997}
}
Michel U, Barsikow B, Haverich B and Schüttpelz M (1997), "Investigation of airframe and jet noise in high-speed flight with a microphone array", In 3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997., AIAA-1997-1596., May, 1997.
Abstract: A Panavia Tornado aircraft was flown to investigate airframe and jet noise in high-speed flight. The locations of the noise sources were examined with a line array consisting of 29 microphones. The flights were performed in an altitude of about 35 m above ground. The influences of various parameters were studied by flying with three different airspeeds (220, 250, 275 m/s) in unaccelerated flight and three different engine power settings (flight idle; normal; max dry) with identical airspeeds (250 m/s) over the measuring position. The influence of external stores on airframe noise was studied by flying with stores first and repeating all tests with an operationally clean aircraft. Two surprising results were found, (i) airframe noise is louder with the aircraft in the operationally clean configuration, and (ii) a strong noise source exists close to the nozzle exit plane that dominates the noise radiation toward the side and into the forward arc.
BibTeX:
@inproceedings{Michel_etal1997,
  author = {Michel, U. and Barsikow, B. and Haverich, B. and Schüttpelz, M.},
  title = {Investigation of airframe and jet noise in high-speed flight with a microphone array},
  booktitle = {3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997},
  year = {1997},
  url = {http://bebec.eu/Downloads/Beamforming_Repository/AIAA-1997-1596_Michel_etal.pdf}
}
Michel U, Barsikow B, Helbig J, Hellmig M and Schüttpelz M (1998), "Flyover noise measurements on landing aircraft with a microphone array", In 4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, June 2-4, 1998., AIAA-1998-2336., June, 1998.
Abstract: The noise sources of landing commercial aircraft were examined with planar arrays consisting of 96 or 111 microphones mounted on an 8 m by 8 m plate under the glide path on the ground. It is shown that important airframe noise sources can be identified in spite of the presence of engine noise, i.e., landing-gear noise, flap side-edge noise, flap-gap noise, jet-flap interaction noise, slat-horn noise, slat-track noise. A surprising finding is a noise source near the wing tips of some aircraft which is tentatively called wake-vortex wing interaction noise. It is shown to be the by far strongest noise source (6 dB(A) louder than the engines) on a regional jet aircraft. (Remark by the authors: the latter source was soon after identified as a cavity noise source.)
BibTeX:
@inproceedings{Michel_etal1998,
  author = {Michel, U. and Barsikow, B. and Helbig, J. and Hellmig, M. and Schüttpelz, M.},
  title = {Flyover noise measurements on landing aircraft with a microphone array},
  booktitle = {4th AIAA/CEAS Aeroacoustics Conference, Toulouse, France, June 2-4, 1998},
  year = {1998},
  url = {http://bebec.eu/Downloads/Beamforming_Repository/AIAA-1998-2336_Michel_etal.pdf}
}
Michel U and Böhning P (2002), "Investigation of aircraft wake vortices with phased microphone arrays", In 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002., AIAA-2002-2501.
Abstract: Wake vortices of landing aircraft emit a faint noise that is audible when wind speed is low and might be related to aerodynamic parameters of the vortices. Results from a test of the capability of phased microphone arrays for the investigation of wake vortices are presented. It is shown that it is possible to estimate the frequency spectrum of wake-vortex noise, its spatial sound source distribution and even the trajectory of the two counter-rotating vortices. The paper presents vortex-noise frequency spectra and sound source distributions of the wake vortices measured behind a Boeing 737, Boeing 757 and an Airbus A320. The phased microphone array technique is shown to be an appropriate tool for wake vortex investigations.
BibTeX:
@inproceedings{MichelBoehning2002,
  author = {Michel, U. and Böhning, P.},
  title = {Investigation of aircraft wake vortices with phased microphone arrays},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002},
  year = {2002}
}
Michel U and Funke S (2008), "Inverse method for the acoustic source analysis of an aeroengine", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-12., Feb, 2008. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: It is demonstrated that the source strengths and directivities of all sound sources of a high bypass ratio aeroengine can be determined from measurements in an open air test bed with a line array of microphones, which is laid out parallel to the engine axis in the geometric near field of the engine. The method is based on modelling the matrix of the cross-spectra of the microphones with a set of contributions from point monopoles assumed in positions along the engine axis and by solving the resulting set of linear equations for the unknown source strengths. The directivities of the sources are estimated by performing the analysis with a subarray of microphones, sliding from the front to the rear of the engine. The set of linear equations is solved with the side condition that the source strengths must be non-negative. The results demonstrate that the various sources of an aeroengine have a highly non-uniform directivity. The source positions are resolved with a separation of 0.4 wave lengths.
BibTeX:
@inproceedings{MichelFunke2008a,
  author = {Michel, U. and Funke, S.},
  title = {Inverse method for the acoustic source analysis of an aeroengine},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-12_Michel_Funke.pdf}
}
Michel U and Funke S (2008), "Noise Source Analysis of an Aeroengine with a New Inverse Method SODIX", In 14th AIAA/CEAS Aeroacoustics Conference, Vancouver, BC, Canada, May 5-7, 2008., AIAA-2008-2860., May, 2008.
Abstract: The directivities of all broadband sound sources of an aeroengine can be determined from measurements with a line array of microphones. A new data analysis method SODIX (SOurce DIrectivity modelling in cross-spectral matriX) was developed for this purpose and applied to the experimental data obtained with a high-bypass ratio turbofan engine in an open air test bed. The method is based on modelling the matrix of the cross-spectra of the microphone signals with a set of contributions from point sources with unknown directivities assumed in positions along the engine axis. The source positions are defined with a separation of typically 0.4 wave lengths. The analysis has to be performed in narrow frequency bands. The influences of tones are eliminated in the cross-spectral matrix of the microphone signals by interpolation in the frequency domain. The unknown directivities of the point sources are determined with the side conditions that the values must be non-negative and that the directivities and source distributions are smooth. The results of this non-linear optimisation problem confirm that the various sources of an aeroengine have highly non-uniform directivities. The far field can be predicted from the source distributions for positions over a large range of emission angles. The predictions on a 45.72 m radius around the engine agree within about 1 dB with experimental data. These far-field directivities can be separated into the contributions from inlet, casing, the two nozzles, and the jet.
BibTeX:
@inproceedings{MichelFunke2008b,
  author = {Michel, U. and Funke, S.},
  title = {Noise Source Analysis of an Aeroengine with a New Inverse Method SODIX},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference, Vancouver, BC, Canada, May 5-7, 2008},
  year = {2008}
}
Michel U and King M (1997), "Feasibility study on the use of two-dimensional microphone arrays in the DNW", DLR-IB 92517-97/B2. (DLR-IB 92517-97/B2)
BibTeX:
@techreport{Michel1997a,
  author = {Michel, U. and King, M.},
  title = {Feasibility study on the use of two-dimensional microphone arrays in the DNW},
  year = {1997},
  number = {DLR-IB 92517-97/B2}
}
Michel U and Qiao W (1999), "Directivity of landing gear noise based on flyover measurements", In 5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Wa, May 10-12, 1999., AIAA-1999-1956.
Abstract: The noise emission of the nose-landing gear of commercial aircraft is studied with a phased array of microphones. The results are found to vary considerably between different aircraft types. Tonal noise components are found in some cases. Seven single-aisle and seven twin-aisle aircraft types are compared. A-weighted one-third octave spectra and the directivities of the A-weighted sound-pressure levels are reported. The investigation is based on recordings made on the airport of Frankfurt/Main with a sparse array of 111 microphones distributed over a plate sized 8 m by 8 m. The average altitude of the aircraft above the array was 31 m.
BibTeX:
@inproceedings{Michel_etal1999,
  author = {Michel, U. and Qiao, W.},
  title = {Directivity of landing gear noise based on flyover measurements},
  booktitle = {5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Wa, May 10-12, 1999},
  year = {1999}
}
Miles J (2011), "Identification of Indirect Combustion Noise at the Exit of a Gas Turbine", In 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011., AIAA-2011-844., January, 2011.
Abstract: Currently, low frequency noise generated in the turbofan engine core may make a significant contribution to the overall noise signature in the aft direction at the low power settings which are used on an airport flight approach trajectory. The presence of low frequency indirect combustion noise may be a problem for future aircraft. This paper discusses the development of identification techniques. Magnitude squared coherence function and cross-spectral density phase angle measurement made in a turbofan engine at the combustor and turbine exit are used to show the presence of indirect combustion noise over the frequency range of 0-400 Hz. The coherence is above 0.4 from 0-100 Hz. In addition, a four parameter low frequency turbine transfer function is discussed. It provides a means to relate measurements of the pressure cross-spectral density and the autospectral density at the turbine exit to measurements of the pressure autospectral density in the combustor for the particular turbofan engine studied over a range of operating conditions. An estimate of the contribution of the combustion noise to the total noise at the turbine exit would be useful. The linear system transfer function approach has limited success in the indirect combustion noise source region from 0-50 Hz. However, the coherence and time delay measurements indicate that the indirect combustion noise dominates in this frequency range so this has little consequence as far as source identification. It is in better agreement in the 50-100 Hz linear system region. The results show indirect combustion noise is important in the 0-100 Hz region and at higher frequencies this contribution falls to levels far below that of the measured turbine exit autospectral density. Current combustion noise prediction capability does not include indirect combustion noise and thus applies over a very narrow design space. The underlying physics discussed herein is not included. Consequently, new turbofan engine core configurations might be outside the current combustion noise prediction capability.
BibTeX:
@inproceedings{Miles2011,
  author = {Miles, J.},
  title = {Identification of Indirect Combustion Noise at the Exit of a Gas Turbine},
  booktitle = {49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011},
  year = {2011}
}
Mohammad-Djafari A (2012), "Bayesian inference methods for source separation", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-32., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The main aim of this paper is first to present the Bayesian inference approach for sources separation where we want to infer on the mixing matrix, the sources and all the hyper-parameters associated to probabilistic modeling (likelihood and priors). For this purpose, the sources separation problem is considered in four steps: i) Estimation of the sources when the mixing matrix is known; ii) Estimation of the mixing matrix when the sources are known; iii) Joint estimation of sources and the mixing matrix; and finally, iv) Joint estimation of sources and the mixing matrix, hidden variables and hyper-parameters. In all cases, one of the main steps is modeling of sources and the mixing matrix prior laws. We propose to use sparsity enforcing probability laws (such as Generalized Gaussian, Student-t and mixture models) both for the sources and the mixing matrix. For algorithmic and computational aspects, we consider either Joint MAP, MCMC Gibbs sampling or Variational Bayesian Approximation tools. For each class of methods we discuss about their relative costs and performances
BibTeX:
@inproceedings{Mohammad-Djafari2012,
  author = {Mohammad-Djafari, A.},
  title = {Bayesian inference methods for source separation},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-32.pdf}
}
Morfey CL and Joseph PF (2001), "Shear Layer Refraction Corrections for off-axis Sources in a Jet Flow", J. Sound Vib.. Vol. 239, pp. 819-848.
BibTeX:
@article{MorfeyJoseph2001,
  author = {Morfey, C. L. and Joseph, P. F.},
  title = {Shear Layer Refraction Corrections for off-axis Sources in a Jet Flow},
  journal = {J. Sound Vib.},
  year = {2001},
  volume = {239},
  pages = {819--848}
}
Morfey CL and Tester BJ (1977), "Noise Measurements in a Free Jet Flight Simulation Facility: Shear Layer Refraction Correction and Facility-to-Flight Corrections", J. Sound Vib.. Vol. 54, pp. 83-106.
BibTeX:
@article{MorfeyTester1977,
  author = {Morfey, C. L. and Tester, B. J.},
  title = {Noise Measurements in a Free Jet Flight Simulation Facility: Shear Layer Refraction Correction and Facility-to-Flight Corrections},
  journal = {J. Sound Vib.},
  year = {1977},
  volume = {54},
  pages = {83--106}
}
Moritoh Y, Zenda Y and Nagakura K (1996), "Noise control of high speed Shinkansen", J. Sound Vib.. Vol. 193, pp. 319-334.
BibTeX:
@article{Moritoh_etal1996,
  author = {Moritoh, Y. and Zenda, Y. and Nagakura, K.},
  title = {Noise control of high speed Shinkansen},
  journal = {J. Sound Vib.},
  year = {1996},
  volume = {193},
  pages = {319--334}
}
Morris S, Shannon D and Silver J (2009), "Acoustics of a Dual-jet Circulation Control Elliptical Airfoil", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA 2009-3346., May, 2009.
BibTeX:
@inproceedings{Morris_etal2009,
  author = {Morris, S.C. and Shannon, D.W. and Silver, J.},
  title = {Acoustics of a Dual-jet Circulation Control Elliptical Airfoil},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009},
  doi = {10.2514/6.2009-3346}
}
Mosher M (1996), "Phased Arrays for Aerocoustic Testing: Theoretical Development", In 2nd AIAA/CEAS Aeroacoustics Conference, State College, Pa, May 6-8, 1996., AIAA-1996-1713., May, 1996.
Abstract: Until very recently, researchers made most acoustic measurements with a single microphone or possibly a pair of microphones. A single microphone provides an acoustic time history or a pressure spectrum from the acoustic signal received at one spatial location. A pair of microphones adds the ability to measure coherence and acoustic intensity. With the improved performance to cost ratio of electronic equipment and computers, it is now practical for researchers to make acoustic measurements with phased arrays containing many microphones. Measurements made with phased arrays offer the significant benefits of locating sources and making accurate acoustic measurements in adverse environments that contain high background noise levels and/or reflections. This paper describes the basics of array processing, special considerations for aeroacoustic testing in wind tunnels, the current methods used in Ames' 40- by 80- Foot Wind Tunnel and developments needed to expand the range and usefulness of arrays in aeroacoustic testing.
BibTeX:
@inproceedings{Mosher1996,
  author = {Mosher, M.},
  title = {Phased Arrays for Aerocoustic Testing: Theoretical Development},
  booktitle = {2nd AIAA/CEAS Aeroacoustics Conference, State College, Pa, May 6-8, 1996},
  year = {1996},
  url = {http://pdf.aiaa.org/preview/1996/PV1996_1713.pdf}
}
Mosher M, Watts ME, Jovic S and Jaeger SM (1997), "Calibration of microphone arrays for phased array processing", In 3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, GA, May 12-14, 1997., AIAA-1997-1678.
Abstract: An array of microphones was calibrated so that it could be used to make accurate measurements of point sources. This paper describes the analysis and procedures that differ from calibrating a single microphone for accurate measurements. Calibration involves the phase of all microphones and electronic instrumentation and the amplitude and directivity response of the entire array. Procedures include measuring the phase response of the instrumentation, phase checking with a point source, calibrating a source in an anechoic chamber and using the calibration source to calibrate the array for amplitude and for directivity. Results show good phase fidelity, a frequency dependent amplitude deviation from a simple free-field microphone and fairly smooth directivity characteristics that can be corrected with a non-linear neural net model.
BibTeX:
@inproceedings{Mosher_etal1997,
  author = {Mosher, M. and Watts, M. E. and Jovic, S. and Jaeger, S. M.},
  title = {Calibration of microphone arrays for phased array processing},
  booktitle = {3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, GA, May 12-14, 1997},
  year = {1997},
  url = {http://pdf.aiaa.org/preview/1997/PV1997_1678.pdf}
}
Nagy AB and Fiala P (2012), "Using mirror image sources to increase performance of beamforming in closed enclosures", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-14., Feb, 2012.
Abstract: Performance of the basic delay and sum beamforming is influenced by the reflections of sound from surfaces in the environment. In closed spaces this effect is even more significant, where signals from the high number of close secondary mirror image sources interfere with the primary signal. However, one can also make use of the presence of these image sources. If the geometry of the surrounding surfaces is known, one can also focus on the closest secondary image sources, create secondary sound maps (images) and combine them with the primary ones. The advantage of focusing on the secondary sources is that they are seen under independent direction characteristics, which allows the elimination of real interferences, obstructing objects. In this paper we present the results of our investigations of employing room acoustical considerations to increase efficiency and performance of a random-placed microphone array used in a closed enclosure. A simple case of a shoebox shaped room is used for the simulations. The effect, advantages and limits of using sound maps created by second and higher order image sources is discussed.
BibTeX:
@inproceedings{NagyFiala2012,
  author = {Nagy, A. B. and Fiala, P.},
  title = {Using mirror image sources to increase performance of beamforming in closed enclosures},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-14.pdf}
}
Nau C, Moll W, Pollow M and Vorländer M (2014), "Extension of Traditional Measurement Methods in Vehicle Acoustics to the Method of Source Localization in the Vehicle Interior", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-15., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Growing demands on the acoustic comfort of a vehicle and the increase of the importance of lightweight design represent a new challenge in acoustic development tools of an automobile manufacturer. Traditional acoustic measurement techniques offer the opportunity to make statements about structure-borne noise and airborne sound radiation by a vehicle component using accelerometers and microphones. Structure-borne noise and airborne sound sensors thus provide direct information on the accelerations and the sound pressure in the near field. However, single channel methods reach their limits there, where it is important to determine the complex radiation patterns and their superposition into directional radiation. But especially in the interior of the vehicle the direction information of the airborne noise radiation to the occupants is of superior importance. In airborne sound this possibility is given by the microphone array technology (Beamforming). Beyond usual body and airborne sound information, beamforming can thus provide important additional information on the influence of acoustic phenomena on the sound field and the places of occurrence in the vehicle interior. To make the extension to the beamforming suitable and efficient, the evaluation of the results is carried out in multiple stages. The represented work based on a practical example illustrates the methodology of such an advanced, multi-stage approach in the acoustic development of a car manufacturer and will show the potential to improve the sound source localization in the vehicle interior.
BibTeX:
@inproceedings{Nau_etal2014,
  author = {Nau, C. and Moll, W. and Pollow, M. and Vorländer, M.},
  title = {Extension of Traditional Measurement Methods in Vehicle Acoustics to the Method of Source Localization in the Vehicle Interior},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-15.pdf}
}
Navvab M, Bisegna F, Heilmann G and Böck M (2014), "Capturing Historical Buildings Space Sound Signature Using Beamforming", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-27., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Historical buildings and ancient theaters are used for live performances for a variety of venues, and there is a demand for detail information relating to sound field within these remarkable historical architectural buildings. The objective method used to examine these types of spaces for their room acoustic characteristics is onsite sound measurement using beamforming at their current status. Computer simulation incorporating the past archeological records for their architectural detail that relate to material and surface characteristics are also used for parametric design studies. The objectives of this study are to demonstrate the ability to visualize sound fields and to capture a sound signature that significantly represents the room acoustics characteristics of all architectural elements toward their historical preservation. The results are used to represent these acoustic conditions for the general public to experience using virtual environment.
BibTeX:
@inproceedings{Navvab_etal2014a,
  author = {Navvab, M. and Bisegna, F. and Heilmann, G. and Böck, M.},
  title = {Capturing Historical Buildings Space Sound Signature Using Beamforming},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-27.pdf}
}
Navvab M, Bisegna F, Heilmann G and Böck M (2012), "Variations of direct and reflected sound pressure levels in Rome Coliseum using beamforming", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-28., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Ancient theaters are used for live performances for a variety of venues, and there is a demand for detail information relating to sound field within these remarkable historical architectural buildings. The objectives methods used to examine these types of spaces for their room acoustic characteristics are on site measurement at their current status and structural integrity, computer simulation and or scale models incorporating the past archeological records for their architectural details that relate to material and surface characteristics. The objective of this study is to demonstrate the ability to visualize sound fields of real and simulated spaces. Research objectives are to capture a space sound signature that significantly represents the characteristics of all architectural elements with their contributions to the room acoustics toward their historical preservation, and to visualize the audible impact of these elements, and represent these acoustic conditions within a virtual environment for the general public to experience. This paper describes a new approach in measuring the contribution of various frequency ranges for evaluation of the existing condition of the Rome Coliseum. Data were measured using Acoustic Camera spherical array, 120 channel data recorders, and utilizing various acoustic software for data reduction, computer modelling, simulation and analysis. The measured and simulated results based on these parametric studies are compared against selected well-known studies of Greek and Roman theatres. As part of the new historical preservation effort, and given the historical records on the use of materials with their unique surface characteristic, the frequency domain and spectral analysis are used as input to the computer modelling, simulation and analysis of the space. Newly developed room acoustic indicators provide a new approach in estimating the impact of the direct and reflected sound contribution to the sound level available within the current space. The results show a new research approach in room acoustics evaluation utilizing current standards and techniques.
BibTeX:
@inproceedings{Navvab_etal2012b,
  author = {Navvab, M. and Bisegna, F. and Heilmann, G. and Böck, M.},
  title = {Variations of direct and reflected sound pressure levels in Rome Coliseum using beamforming},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-28.pdf}
}
Navvab M, Farrehi P, Shahbazi F and Meyer A (2014), "Application of Beamforming Techniques to Localize and Reduce Hospital Noises within Acute Care Patient Environment", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-29., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
BibTeX:
@inproceedings{Navvab_etal2014b,
  author = {Navvab, M. and Farrehi, P. and Shahbazi, F. and Meyer, A.},
  title = {Application of Beamforming Techniques to Localize and Reduce Hospital Noises within Acute Care Patient Environment},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-29.pdf}
}
Navvab M, Heilmann G and Meyer A (2012), "Visualization, simulation and perception of sound in a virtual environment using beamforming", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-15., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper describes a method to visualize and localiize the sound that is simulated within a virtual environment using beamforming. The use of an acoustic camera along with noise image software as a short introduction to beamforming method is demonstrated. Furthermore, the transition from the three-dimensional sound recording to the three-dimensional virtual acoustic mapping, visualization and sound perception for its directionality by real subjects within the virtual environment is described. Prerequisite for this is a 3D-model which can be created quickly within this computer aided virtual environment. The results show that the subjects were able to navigate and locate a real and virtual sound source in a dynamic virtual acoustic environment. The findings from these simulations, auditory navigation experiments via visualization technique within this virtual environment demonstrate the beamforming method combined with human subject data provide opportunities to study sound localization and fine tune the current Head Related Transfer Function (HRTF) for various room acoustic design applications.
BibTeX:
@inproceedings{Navvab_etal2012a,
  author = {Navvab, M. and Heilmann, G. and Meyer, A.},
  title = {Visualization, simulation and perception of sound in a virtual environment using beamforming},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-15.pdf}
}
Navvab M, Heilmann G and Sulisz D (2008), "Crowd noise measurement and simulation in large stadium using beamforming", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-22., February, 2008.
Abstract: The noise generated by the crowds and organized fans during sporting events has created a challenge for the sport facility management. The new demand for full compliance to National Football League rules on crowd noise, and cities' regulations on noise ordinance require new methods or approaches in measuring such environmental conditions. Given their dynamic range and possible classification, noise levels generated by large crowds has impacted the outcome of games, and recent analysis of the available data shows an increase in noise related penalties. This situation has provided more excitement for the spectators and greater participation in the events, however sound intensity of 95 to 110dBA is now the typically reported range of recorded noise levels within various sport arenas. This paper describes a new approach in measuring crowd noise, and estimating the contribution of various frequency ranges for evaluation of the existing, and in this case, the proposed University of Michigan newly designed addition of sky boxes to the football stadium. Data was measured using Acoustic Camera spherical array, 120 channel data recorder, and utilizing various acoustic software for data reduction, computer modeling, simulation and analysis. The measured and simulated results based on these parametric studies are compared against selected well known stadiums for their crowd noise conditions. The frequency domain and spectral analysis are used as input to the computer modeling, simulation and analysis of the space. Using newly developed room acoustic indicators provide a new approach in estimating the impact of the reflected sound contribution to the crowd noise; given the sky boxes as part of the new addition with their unique facade and window geometry.
BibTeX:
@inproceedings{Navvab_etal2008,
  author = {Navvab, M. and Heilmann, G. and Sulisz, D.},
  title = {Crowd noise measurement and simulation in large stadium using beamforming},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-22_Navvab_Heilmann_Sulisz.pdf}
}
Navvab M, Meyer A and Heilmann G (2010), "Application of head transfer function in room acoustic design using beamforming", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-08., February, 2010.
Abstract: Head Related Transfer Function (HRTF) describes how a given sound wave input is filtered by the diffraction and reflection properties of the body, before the sound reaches the
eardrum. HRTF measurements of a population of US - American troops in the 1960s provided the data and knowledge of the measurement technology for various acoustic application including artificial head. The use of Acoustic camera allows to perform very complex functions in room acoustic evaluation in real timeand examine the room acoustic characteristics under different sound sources and room acoustic conditions. The real time data provides the designers and audio engineer to fine tune or calibrate their sound system for a given standard associated to architectural design. The data obtain through this system also provides the fundamentals to validate the latest software in acoustic design and or audio engineering. The process establishes new room acoustic indexes for pre and post design evaluations. This paper describes the process in obtaining the HRTF and its conversion to Spatial Frequency Response Surfaces through the format used by MATLAB data files of compensated Head-Related Impulse Response (HRIR) measurements. The measurements were made using Acoustic Camera with its' various settings and capabilities under real room acoustic conditions. Hearing with both ears is defined as binaural hearing. It provides the ability in hearing the sound naturally and accurately. The sound that is received from both ears allows to locate the direction and true spatial perception of sounds. The geometrical parameters of the human body have a major impact on binaural hearing. The application and the analysis of the latest room acoustic measurements by Acoustic Camera allows to examine this concept and new development in the creation of a possible new room acoustic index. This approach will include an improved representation of the current indexes used in architectural design. and contributes to the upgrading of the current standards for room acoustics.
BibTeX:
@inproceedings{Navvab_etal2010,
  author = {Navvab, M. and Meyer, A. and Heilmann, G.},
  title = {Application of head transfer function in room acoustic design using beamforming},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Presentations/BeBeC-2010-08.pdf}
}
Nelson C, Cain AB, Dougherty RP, Brentner KS and Morris PJ (2013), "Application of Synthetic Phased Array Techniques to Hot Supersonic Jet Noise", In 51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition., AIAA-2013-0327.
Abstract: he use of an unsteady CFD simulation to provide data for a full acoustic analysis of a hot supersonic jet flow has been demonstrated in a preliminary study. The CHOPA solver was used to predict the near-field flow solution. The data from the CFD simulation was sampled to provide the input for the PSU-WOPWOP Ffowcs Williams-Hawkings solver. PSU-WOPWOP was used to predict the farfield acoustic conditions at locations that correspond to a virtual phased array of microphones. The pressure "measurements" from the virtual array were then processed using the Beamform Interactive software package using the same techniques used for physical microphone array measurements. All the stages of this process have been demonstrated to show how the process is able to predict the expected dominant noise sources in the flow from a military-style faceted nozzle. When fully realized, this technology offers the possibility of providing the insight needed to develop improved beamforming methods as well as allowing the screening of nozzle designs and experimental configurations for acoustical qualities prior to fabrication and operational testing.
BibTeX:
@inproceedings{Nelson_etal2013,
  author = {Nelson, C. and Cain, A. B. and Dougherty, R. P. and Brentner, K. S. and Morris, P. J.},
  title = {Application of Synthetic Phased Array Techniques to Hot Supersonic Jet Noise},
  booktitle = {51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition},
  year = {2013}
}
Nelson CC, Cain AB, Raman G, Chan T, Saunders M, Noble J, Engeln R, Dougherty RP, Brentner KS and Morris PJ (2012), "Numerical Studies of Wind Turbine Acoustics", In 50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 09 - 12 January 2012, Nashville, Tennessee., AIAA-2012-0006., Jan, 2012.
Abstract: The use of an unsteady CFD simulation to provide data for a full acoustic analysis of a wind turbine has been demonstrated. The OVERFLOW solver was employed to predict the near-field conditions. The data from the CFD simulation was sampled to provide the input for the PSU-WOPWOP Ffowcs Williams-Hawkings solver. PSU-WOPWOP was employed to predict the farfield acoustic conditions at locations that correspond to a virtual phased array of microphones. The pressure “measurements” from the virtual array were then processed using the Beamform Interactive software package using the same techniques employed for physical microphone array measurements. All the stages of this process have now been demonstrated, and the process is able to predict the expected broadband noise sources focused near the rotor tips. When fully realized, this technology offers the possibility of screening wind turbine designs for acoustical qualities prior to building and operational testing.
BibTeX:
@inproceedings{Nelson_etal2012,
  author = {Nelson, C. C. and Cain, A. B. and Raman, G. and Chan, T. and Saunders, M. and Noble, J. and Engeln, R. and Dougherty, R. P. and Brentner, K. S. and Morris, P. J.},
  title = {Numerical Studies of Wind Turbine Acoustics},
  booktitle = {50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 09 - 12 January 2012, Nashville, Tennessee},
  year = {2012}
}
Nelson P and Yoon S (2000), "Estimation of Acoustic Source Strength by Inverse Methods: Part I, Conditioning of the Invese Problem", J. Sound Vib.. Vol. 233, pp. 639-664.
Abstract: This paper deals with the discrete inverse problem in acoustics. It is assumed that a number of acoustic sources are located at known spatial positions and that the acoustic pressure is measured at a number of spatial positions in the radiated field. The transfer functions relating the strengths of the acoustic sources to the radiated pressures are also assumed known. In principle, the strengths of the acoustic sources can be deduced from the measured acoustic pressures by inversion of this matrix of transfer functions. The accuracy of source strength reconstruction (in the presence of noise which contaminates the measured pressures) is crucially dependent on the conditioning of the matrix to be inverted. This paper examines the conditioning of this inverse problem, particularly with regard to the geometry and number of sources and measurement positions and the non-dimensional frequency. A preliminary investigation is also presented of methods such as Tikhonov regularization and singular value discarding which can improve the accuracy of source strength reconstruction in poorly conditioned cases. Results are also presented which enable the solution of the inverse problem when the time histories of the acoustic sources are time-stationary random processes and the spectra and cross-spectra are measured at a number of positions in the radiated field. The paper illustrates the possibilities and limitations of the use of inverse methods in the deduction of acoustic source strength from radiated field measurements.
BibTeX:
@article{NelsonYoon2000a,
  author = {Nelson, P.A. and Yoon, S.H.},
  title = {Estimation of Acoustic Source Strength by Inverse Methods: Part I, Conditioning of the Invese Problem},
  journal = {J. Sound Vib.},
  year = {2000},
  volume = {233},
  pages = {639--664}
}
Nelson P and Yoon S (2000), "Estimation of Acoustic Source Strength by Inverse Methods: Part II, Experimental Investigation of Methods for Choosing Regularization Parameters", J. Sound Vib.. Vol. 233, pp. 665-701.
Abstract: Two regularization methods, Tikhonov regularization and singular value discarding, are used to improve the accuracy of reconstruction of acoustic source strength by inverse techniques. In this paper, some methods are investigated for choosing the Tikhonov regularization parameter and the singular values to be discarded. Of these, we concentrate on the use of ordinary cross-validation and generalized cross-validation. These methods can provide an appropriate regularization parameter without prior knowledge of either the acoustic source strength or the contaminating measurement noise. Some experimental results obtained using a randomly vibrating simply supported plate mounted in a baffle are presented to illustrate the performance of the methods for choosing the regularization parameters.
BibTeX:
@article{NelsonYoon2000b,
  author = {Nelson, P.A. and Yoon, S.H.},
  title = {Estimation of Acoustic Source Strength by Inverse Methods: Part II, Experimental Investigation of Methods for Choosing Regularization Parameters},
  journal = {J. Sound Vib.},
  year = {2000},
  volume = {233},
  pages = {665--701}
}
Neugebauer S, Barré S and Döbler D (2014), "Application of Correlation Analyses in 2D and 3D Beamforming", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-06., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: This article presents an application of beamforming technique using a 3D microphone array and transfer functions measurement with sine sweeps. The calculated room impulse responses (RIRs) can be decomposed into their components with a high time and spatial resolution. Linear spectral deconvolution is used to calculate impulse responses for every channel of a 48-channel spherical microphone array. As an example a conference room was scanned and the reference source and early and late reflections of 1st and 2nd order with 1 ms time resolution were found. The reflections could be precisely located in a 3D model giving completely new insights in sound propagation using a highly reproducible and strictly defined excitation signal.
BibTeX:
@inproceedings{Neugebauer_etal2014,
  author = {Neugebauer, S. and Barré, S. and Döbler, D.},
  title = {Application of Correlation Analyses in 2D and 3D Beamforming},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-06.pdf}
}
Nordborg A, Wedemann J and Willenbrink L (2000), "Optimum array microphone configuration", In Proceedings of Internoise, Nice, France, 27–30 August 2000. Vol. 4, pp. 2474–-2478.
BibTeX:
@inproceedings{NordborgWedemannWillenbrink2000,
  author = {Nordborg, A. and Wedemann, J. and Willenbrink, L.},
  title = {Optimum array microphone configuration},
  booktitle = {Proceedings of Internoise, Nice, France, 27–30 August 2000},
  year = {2000},
  volume = {4},
  pages = {2474–-2478},
  note = {Paper IN2000/974}
}
Oakley K (2012), "4D time domain beamforming on waveform timeslices identifies separate sources of aeroacoustic noise on a hovercraft", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-31., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Earlier studies have shown that hovercraft noise is dominated by 2 tonal noises – the engine firing frequency and the blade passing frequency. 3D narrowband beamforming analysis of the latter on a particular test craft shows there are at least 2 major sources apparent within each bladepass period. But standard time domain beamforming using the whole bladepass Fourier waveform gives a noisepicture which is an average of the two sources. By gating in timeslot slices of the total bladepass Fourier waveform and time domain beamforming only on that slice it's possible to see clearly how each source develops and decays during the bladepass period. By splitting the total bandpass waveform into 32 such time slices a short ‘movie’ is produced. A downside of this partial waveform technique is that the sound sources appear to move over time towards the centre of the microphone array, due largely to the way the beamformer works. However the volume peaks within this movie do indicate accurately the position of the sources of noise and their phase relationship with the position of the fan blades. In the case of our test craft this partial waveform technique showed 2 noise sources within the lift air distribution ducting behind the fan, where the air is poorly ducted and thus air turbulence is likely to occur. One particular source correlated well with a regular dirty patch deposited in the same position on a similar craft, which was cured by improving the ducting.
BibTeX:
@inproceedings{Oakley2012,
  author = {Oakley, K.},
  title = {4D time domain beamforming on waveform timeslices identifies separate sources of aeroacoustic noise on a hovercraft},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-31.pdf}
}
Oakley K (2010), "NoiseCam – Using 3D Beamforming to better localise noise sources on Hovercraft", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-22., February, 2010.
Abstract: Light Hovercraft are fun but with high revving engines and fans they can be noisy. NoiseCam, a homebrew 2D beamforming system, has been used on over 130 amateur craft worldwide to identify the loudest noise sources, resulting in several craft being reduced by up to 10 dBA. It localises and quantifies individual tonal sources such as engine exhausts, air intakes and fan turbulence in the range 40 Hz to 800 Hz, typically within about 100 mm and about 5 Hz. A number of improvements have been made to the system. It now incorporates a ring of far-field dba meters to provide direct traceability from regulatory dba measurements, through frequency analysis and then beamforming to locate the key sources. The problem of large spot size and positional displacement of low frequency sources has been addressed by a technique for adding spikes to the beamformer waveforms. A 3D microphone array with 24 mics is being developed to reduce astigmatism and better identify fan turbulence sources. Turbulent areas identified by the system have been confirmed by probing with pressure sensors. An air horn audio marker beacon now provides better alignment between the noisepics and conventional pictures.
BibTeX:
@inproceedings{Oakley2010,
  author = {Oakley, K.},
  title = {NoiseCam – Using 3D Beamforming to better localise noise sources on Hovercraft},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-22.pdf}
}
Oakley K (2008), "NoiseCam - Using Beamforming to identify noise sources on Hovercraft", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-23.
Abstract: Racing single seat hovercraft may be a fun thing to drive but with a 2 stroke engine and a high revving industrial cooling fan they can be noisy. Identifying the loudest sources on each craft quickly and easily is challenging because of the variety of noise sources, and because each craft is different and mostly homemade. A low cost, homebrew, beamforming system has been built and successfully used to identify around 95% of sources on 100 hovercraft from across Europe during the 2007 season. The system uses a highly portable 2 metre radius semicircular array of 16 microphones with comb filter software to focus on tonal noise, a delay and multiply algorithm to improve ‘noise picture’ definition and a simple inverse technique to estimate the db elimination value of individual frequencies. It pinpoints sources in the range 30hz to 800hz, typically within about 100mm and about 5hz, even though several similarly loud sources are present within the space of about a 1.5 metre cube. The common sources are engine air intakes, exhaust silencers, and various fan obstructions such as pulleys, radiators, stators, engine covers etc causing airflow turbulence and thus noise. It has also provided early warnings of bearing and crankshaft failure.
BibTeX:
@inproceedings{Oakley2008,
  author = {Oakley, K.},
  title = {NoiseCam - Using Beamforming to identify noise sources on Hovercraft},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  year = {2008},
  url = {http://www.bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-23_Oakley.pdf}
}
Oerlemans S (2009), "Detection of aeroacoustic sound sources on aircraft and wind turbines". Thesis at: University of Twente, Enschede.
Abstract: This thesis deals with the detection of aeroacoustic sound sources on aircraft and wind turbines using phased microphone arrays. First, the reliability of the array technique is assessed using airframe noise measurements in open and closed wind tunnels. It is demonstrated that quantitative acoustic measurements are possible in both wind tunnels. Then, the array technique is applied to characterize the noise sources on two modern large wind turbines. It is shown that practically all noise emitted to the ground is produced by the outer part of the blades during their downward movement. This asymmetric source pattern, which causes the typical swishing noise during the passage of the blades, can be explained by trailing edge noise directivity and convective amplification. Next, a semi-empirical prediction method is developed for the noise from large wind turbines. The prediction code is successfully validated against the experimental results, not only with regard to sound levels, spectra, and directivity, but also with regard to the noise source distribution in the rotor plane and the temporal variation in sound level (swish). The validated prediction method is then applied to calculate wind turbine noise footprints, which show that large swish amplitudes can occur even at large distance. The influence of airfoil shape on blade noise is investigated through acoustic wind tunnel tests on a series of wind turbine airfoils. Measurements are carried out at various wind speeds and angles of attack, with and without upstream turbulence and boundary layer tripping. The speed dependence, directivity, and tonal behaviour are determined for both trailing edge noise and inflow turbulence noise. Finally, two noise reduction concepts are tested on a large wind turbine: acoustically optimized airfoils and trailing edge serrations. Both blade modifications yield a significant trailing edge noise reduction at low frequencies, but also cause increased tip noise at high frequencies. Nevertheless, it is demonstrated that using trailing edge serrations wind turbine noise can be halved without adverse effects on the aerodynamic performance.
BibTeX:
@phdthesis{Oerlemans2009,
  author = {Oerlemans, S.},
  title = {Detection of aeroacoustic sound sources on aircraft and wind turbines},
  school = {University of Twente, Enschede},
  year = {2009},
  url = {http://doc.utwente.nl/67363/1/thesis_S_Oerlemans.pdf}
}
Oerlemans S, Broersma L and Sijtsma P (2007), "Quantification of Airframe Noise Using Microphone Arrays in Open and Closed Wind Tunnels", Int. J. Aeroacoustics. Vol. 6(4), pp. 309-333.
BibTeX:
@article{Oerlemans_etal2007b,
  author = {Oerlemans, S. and Broersma, L. and Sijtsma, P.},
  title = {Quantification of Airframe Noise Using Microphone Arrays in Open and Closed Wind Tunnels},
  journal = {Int. J. Aeroacoustics},
  year = {2007},
  volume = {6},
  number = {4},
  pages = {309--333}
}
Oerlemans S, Fisher M, Maeder T and Kögler K (2009), "Reduction of Wind Turbine Noise Using Optimized Airfoils and Trailing-Edge Serrations", AIAA Journal. Vol. 47(6), pp. 1470-1481.
BibTeX:
@article{Oerlemans_etal2009,
  author = {Oerlemans, S. and Fisher, M. and Maeder, T. and Kögler, K.},
  title = {Reduction of Wind Turbine Noise Using Optimized Airfoils and Trailing-Edge Serrations},
  journal = {AIAA Journal},
  year = {2009},
  volume = {47},
  number = {6},
  pages = {1470--1481}
}
Oerlemans S and Méndez López B (2005), "Acoustic Array Measurements on a Full Scale Wind Turbine", In 11th AIAA/CEAS Aeroacoustics Conference., AIAA-2005-2963.
BibTeX:
@inproceedings{OelrmensMendes-Lopez2005,
  author = {Oerlemans, S. and Méndez López, B.},
  title = {Acoustic Array Measurements on a Full Scale Wind Turbine},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference},
  year = {2005},
  doi = {10.2514/6.2005-2963}
}
Oerlemans S, Méndez López B and Eólica G (2005), "Acoustic Array Measurements on a Full Scale Wind Turbine", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-2963., May, 2005.
Abstract: Acoustic array measurements were performed on a three-bladed GAMESA G58 wind turbine with a rotor diameter of 58 m and a tower height of 53.5 m. The goal was to characterize the noise sources on this turbine, and to verify whether aerodynamic noise from the blades is dominant. In order to assess the effect of blade roughness, one blade was cleaned, one blade was tripped, and one blade was left untreated. The acoustic array consisted of 152 microphones mounted on a horizontal wooden platform (15 by 18 m2), which was positioned about 58 m upwind from the rotor. In parallel to the acoustic measurements, a number of turbine parameters were monitored, such as wind speed, power, turbine orientation, RPM, and blade pitch angle. In total more than 100 measurements were taken at wind speeds between 6 and 10 m/s. Two array processing methods were used to characterise the noise from the turbine. First, the noise sources in the rotor plane were localised using conventional beamforming. These results clearly show that, besides a minor source at the rotor hub, practically all noise (radiated to the ground) is produced during the downward movement of the blades. The noise is produced by the outer part of the blades (but not by the very tip), and blade noise levels scale with the 5th power of the local flow speed. The second processing method employed rotating scan planes to localise the noise sources on the individual blades. It turns out that the tripped blade is significantly noisier than the clean and untreated blades, which is a strong indication of trailing edge noise (rather than inflow turbulence noise). The similar noise levels for the clean and untreated blades suggest that the untreated blade was aerodynamically clean.
BibTeX:
@inproceedings{Oerlemans_etal2005,
  author = {Oerlemans, S. and Méndez López, B. and Eólica, G.},
  title = {Acoustic Array Measurements on a Full Scale Wind Turbine},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Oerlemans S and Sijtsma P (2004), "Acoustic Array Measurements of a 1:10.6 Scaled Airbus A340 Model", In 10th AIAA/CEAS Aeroacoustics Conference , Manchester, GREAT BRITAIN, May 10-12, 2004., AIAA-2004-2924., May, 2004.
Abstract: Acoustic array measurements were carried out on a 1:10.6 scaled Airbus A340 model. Tests were done in both the open jet and a closed test section of the DNW-LLF wind tunnel. The purpose of these measurements was to investigate several noise reduction concepts for high-lift devices (slats and flaps) in landing configuration. The possibilities and limitations of arrays for the determination of quantitative results are discussed. Besides the identification of dominant noise source regions with conventional beamforming, local source spectra were determined using a power integration method. For the open jet results, the integration method was applied with and without the 'diagonal removal' (DR) technique, in which the main diagonal of the cross-power matrix is discarded. It is shown that application of DR results in meaningful local spectra, whereas without DR the results are obscured by the influence of the main diagonal. On the other hand, by comparing integrated spectra with absolute sound levels on farfield microphones, it is shown that the application of DR, in combination with coherence loss, results in significantly reduced absolute levels. However, while the absolute sound levels can be too low, level differences between configurations can be accurately determined under certain conditions. From the closed test section array results, dominant source regions are identified as a function of frequency and angle-ofattack. These results are quantified by application of the integration method to several source areas on the wing. The local and overall effect of noise reduction devices is assessed. The effect of coherence loss on the absolute levels is investigated by varying the effective array size.
BibTeX:
@inproceedings{OerlemansSijtsma2005,
  author = {Oerlemans, S. and Sijtsma, P.},
  title = {Acoustic Array Measurements of a 1:10.6 Scaled Airbus A340 Model},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference , Manchester, GREAT BRITAIN, May 10-12, 2004},
  year = {2004}
}
Oerlemans S and Sijtsma P (2002), "Determination of Absolute Levels from Phased Array Measurements Using Spatial Source Coherence", In 8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002., AIAA-2002-2464., June, 2002.
Abstract: The phased array technique is a valuable tool in acoustic testing for its capability to distinguish between different source locations. However, the interpretation of phased array measurements is still difficult due to the simultaneous occurrence of several effects: the size and level of a spot in a conventional acoustic 'source plot' may be affected by a combination of (1) the limited resolution of the array (2) coherence loss during propagation to the array (3) the spatial extent of the source region. This ambiguity complicates the determination of absolute source levels from phased array measurements. The current paper addresses this problem for a noise source that is extended mainly in one direction, i.e. trailing-edge noise. Simulations are done for a line source, and the influence of array resolution and source coherence length on the array output is investigated. Furthermore, an array processing technique is presented which determines the coherence level between different sources in the scan plane. As a first application, the technique is used to identify
mirror sources in a closed wind tunnel. The new method is then applied to trailing-edge noise measurements in NLR's Small Anechoic Wind Tunnel, in order to estimate the spanwise coherence length. In conjunction with the simulations this enables an improved determination of absolute trailing-edge noise from phased array measurements.
BibTeX:
@inproceedings{OerlemansSijtsma2002,
  author = {Oerlemans, S. and Sijtsma, P.},
  title = {Determination of Absolute Levels from Phased Array Measurements Using Spatial Source Coherence},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference and Exhibit, Breckenridge, Colorado, June 17-19, 2002},
  year = {2002}
}
Oerlemans S and Sijtsma P (2000), "Effects of wind tunnel side-plates on airframe noise measurements with phased arrays", In 6th AIAA/CEAS Aeroacoustics Conference, Lahaina, HI, June 12-14, 2000., AIAA-2000-1938., June, 2000.
BibTeX:
@inproceedings{Oerlemans_Sijtsma2000,
  author = {Oerlemans, S. and Sijtsma, P.},
  title = {Effects of wind tunnel side-plates on airframe noise measurements with phased arrays},
  booktitle = {6th AIAA/CEAS Aeroacoustics Conference, Lahaina, HI, June 12-14, 2000},
  year = {2000}
}
Oerlemans S and Sijtsma P (2000), "Effects of wind tunnel side-plates on airframe noise measurements with phased arrays"
Abstract: A convenient method for airframe noise measurements in an open jet acoustic wind tunnel is the combination of an out-of-flow phased array with a semi-open test section consisting of two sideplates between which a model can be mounted. In this paper the effects of these side-plates on acoustic measurements with a phased array are investigated both experimentally and theoretically. First, a set-up with hard wooden side-plates and a cross-shaped array was tested. Calibration measurements with a monopole source placed between the plates showed errors in source strength up to 10 dB, with strong dependence on frequency and source location. A theoretical study identified acoustic interference (standing waves) between the hard plates as the cause of this inaccuracy. Theory predicted much better results when the cross-shaped array was replaced by a sparse array and the hard plates by acoustically lined plates. After application of these modifications in the test set-up, new calibration measurements indeed showed impressive improvement in the ability to determine absolute levels with a phased array. True monopole source levels were recovered within 2 dB for frequencies up to 8 kHz and a tunnel flow speed up to M = 0.22. Moreover, the measured source level was practically independent on the source location.
BibTeX:
@techreport{OerlemansSijtsma2000,
  author = {Oerlemans, S. and and Sijtsma, P.},
  title = {Effects of wind tunnel side-plates on airframe noise measurements with phased arrays},
  year = {2000},
  url = {http://www.nlr.nl/id~4283/l~en.pdf}
}
Oerlemans S, Sijtsma P and Méndez López B (2007), "Location and Quantification of Noise Sources on a Wind Turbine", J. Sound Vib.. Vol. 299, pp. 869-883.
Abstract: Acoustic field measurements were carried out on a three-bladed wind turbine with a rotor diameter of 58 m, in order to characterize the noise sources and to verify whether trailing edge noise from the blades was dominant. To assess the effect of blade roughness, one blade was cleaned, one blade was tripped, and one blade remained untreated. A large horizontal microphone array, positioned about one rotor diameter upwind from the turbine, was used to measure the distribution of the noise sources in the rotor plane and on the individual blades. The operation parameters of the turbine were recorded in parallel to the acoustic tests. In total more than 100 measurements were performed at wind speeds between 6 and 10 m/s. The array results reveal that besides a minor source at the rotor hub, practically all noise (emitted to the ground) is produced during the downward movement of the blades. This strongly asymmetric source pattern can be explained by convective amplification and trailing edge noise directivity. The blade noise is produced at the outer part of the blades (but not at the very tip), and the level scales with the fifth power of the local flow speed. Comparison of the noise from the individual blades shows that the tripped blade is significantly noisier than the other two. Narrowband analysis of the de-dopplerized blade noise spectra indicates that trailing edge bluntness noise is not important. All in all, the test results convincingly show that broadband trailing edge noise is the dominant noise source for this wind turbine.
BibTeX:
@article{Oerlemans_etal2007,
  author = {Oerlemans, S. and Sijtsma, P. and Méndez López,B.},
  title = {Location and Quantification of Noise Sources on a Wind Turbine},
  journal = {J. Sound Vib.},
  year = {2007},
  volume = {299},
  pages = {869--883},
  doi = {10.1016/j.jsv.2006.07.032}
}
Orlando S, Bale A and Johnson D (2010), "Design and preliminary testing of a MEMS microphone phased array", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-21., February, 2010.
Abstract: In recent years, electret and MEMS (micro-electrical mechanical systems) microphones have been used as low-cost alternatives to more costly condenser microphones for use in phased arrays. In aeroacoustic testing, phased arrays are ideal for their ability to locate and quantify noise sources. Research into the design, fabrication, and implementation of a low-cost, electronically simple phased array will increase its potential as a common research tool. This paper discusses the design and preliminary testing of a simplified MEMS microphone array for use in aeroacoustic testing. The primary intent of the array design was to improve the signal-to-noise ratio of aeroacoustic sources as opposed to locating them accurately, particularly in a wind tunnel with a square cross section of 152.4 mm x 152.4 mm. Using a number of beamforming algorithms, the design of the phased array was modeled numerically. The phased array was constructed on a single, two-layer PCB (printed circuit board) and composed of 27 MEMS microphones each with built-in amplification and RF protection. The Underbrink equal area aperture array layout was used in the design with 9 spirals each consisting of 3 microphones. Further design and manufacturing details are presented. The array was calibrated and used successfully in preliminary testing using the conventional beamforming technique to locate noise sources within the expected margin of error.
BibTeX:
@inproceedings{Orlando_etal2010,
  author = {Orlando, S. and Bale, A. and Johnson, D.},
  title = {Design and preliminary testing of a MEMS microphone phased array},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-21.pdf}
}
Oudompheng B, Pereira A, Picard C, Leclère Q and Nicolas B (2014), "A Theoretical and Experimental Comparison of the Iterative Equivalent Source Method and the Generalized Inverse Beamforming", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-12., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Many acoustic source mapping methods exist to perform noise source localization and quantification and appear to be powerful tools for acoustic diagnosis in industrial applications. Two classes of methods have known many developments in the last few decades: deconvolution algorithms combined with beamforming (CLEAN, DAMAS, etc) and inverse methods such as the Equivalent Source Method (ESM) and the Generalized Inverse Beamforming (GIB). In this paper, a special attention will be paid to the use of inverse methods in complex acoustic environments. Recently, Suzuki has demonstrated the applicability of the GIB to the study of aerodynamic sound sources [25], highlighting comparable performances to the existing deconvolution techniques. On the other hand, an iterative version of the ESM has been proposed in the context of acoustic imaging in closed spaces, at INSA Lyon [22]. This paper provides a theoretical and experimental comparison between two inverse methods: the iterative ESM and the GIB using various benchmark problems and aeroacoustic experimental data. The experimental set-up consists of a steel rod placed in the potential core of a rectangular jet inside an open-jet anechoic wind tunnel. It will be shown that both methods are based on similar mathematical formulations although they were developed for different application fields. Reconstruction performances of the algorithms in terms of localization and quantification will be discussed as well as their computational efficiency.
BibTeX:
@inproceedings{Oudompheng_etal2014,
  author = {Oudompheng, B. and Pereira, A. and Picard, C. and Leclère, Q and Nicolas, B.},
  title = {A Theoretical and Experimental Comparison of the Iterative Equivalent Source Method and the Generalized Inverse Beamforming},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-12.pdf}
}
Padois T and Valeau V (2010), "Potentiality of time-reversed array processing for localizing acoustic sources in flows: a numerical study", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-09., February, 2010.
Abstract: The present study aims at assessing the potentiality of the time-reversal (TR) technique to localize sound sources in flows, in the context of wind-tunnel measurements. The proposed method is a two-step procedure : the pressure fluctuations are recorded on a linear array of microphones located outside the flow; then the back-propagation of the acoustic waves is simulated by using the time-reversed Linearized Euler Equations (LEE), with the experimental signals as input data, in order to estimate virtually the position of the sound source from which the waves were radiated. The advantage of the proposed method is that the use of the LEE permits an exact description of the convection and refraction of the radiated waves during their propagation to the array. An experiment in a wind-tunnel has been set up, in which a monopolar sine-wave source is located in the flow. The TR results indicate that the source position can be estimated only if the source-array distance is known. However, further simulations of the experiment show that realistic experimental configurations are possible, for which the source position can be accurately estimated without this knowledge.
BibTeX:
@inproceedings{Padois_etal2010,
  author = {Padois, T. and Valeau, V.},
  title = {Potentiality of time-reversed array processing for localizing acoustic sources in flows: a numerical study},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-09.pdf}
}
Pallas MA, Schmitz K-P, Barsikow B, Fodiman P and Hölzl G (1994), "DeuFraKo: Localized sound sources on the high-speed verhicles ICE, TGV-A, and TR 07", In Proc. World Congress on Railway Research (WCRR '94), Paris, 1994. , pp. 377-383.
BibTeX:
@inproceedings{Pallas_etal1994,
  author = {Pallas, M. A. and Schmitz, K.-P. and Barsikow, B. and Fodiman, P. and Hölzl, G.},
  title = {DeuFraKo: Localized sound sources on the high-speed verhicles ICE, TGV-A, and TR 07},
  booktitle = {Proc. World Congress on Railway Research (WCRR '94), Paris, 1994},
  year = {1994},
  pages = {377--383}
}
Panda J and Mosher M (2011), "Use of a Microphone Phased Array to Determine Noise Sources in Rocket Plumes", In 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011., AIAA-2011-974., January, 2011.
Abstract: A 70-element microphone phased array was used to identify noise sources in the plume of a solid rocket motor. A weather-resistant case was built and other precautions were taken to protect the sensitive condenser microphones from rain, thunderstorms and other environmental elements during prolonged stay in the outdoor test stand. A camera mounted at the center of the array was used to photograph the plume. In the first phase of the study the array was placed in an anechoic chamber for calibration and validation of the indigenous Matlab® based beamform software. It was found that the “advanced” beamform methods, such as CLEAN-SC were partially successful in indentifying speaker sources placed closer than the Rayleigh criterion. To participate in the field test, all of the equipment was shipped to NASA Marshal Space Flight Center, where the array hardware was rebuilt around the test stand. The sensitive amplifiers and the data acquisition hardware were placed in a safe basement, and 50m long cables were used to connect the microphones, Kulites and the camera. The array case and the microphones were found to withstand the environmental elements as well as the shaking from the rocket plume generated noise. The beamform map was superimposed on a photo of the rocket plume to readily identify the source distribution. It was found that the plume made an exceptionally long, greater than 30 diameter, noise source over a large frequency range. The shock pattern created spatial modulation of the noise source. Interestingly, the concrete pad of the horizontal test stand was found to be a good acoustic reflector: the beamform map showed two distinct source distributions- the plume and its reflection on the pad. The array was found to be most effective in the frequency range of 2 kHz to 10 kHz. As expected, the classical beamform method excessively smeared the noise sources at lower frequencies and produced excessive side-lobes at higher frequencies. The “advanced” beamform routine CLEAN-SC created a series of lumped sources which may be unphysical. We believe that the present effort is the first-ever attempt to directly measure noise source distribution in a rocket plume.
BibTeX:
@inproceedings{PandaMosher2011,
  author = {Panda, J. and Mosher, M.},
  title = {Use of a Microphone Phased Array to Determine Noise Sources in Rocket Plumes},
  booktitle = {49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011},
  year = {2011}
}
Papamoschou D (2011), "Imaging of Directional Distributed Noise Sources", J. Sound Vib.., AIAA-2008-2885., May, 2011. Vol. 330, pp. 2265-2280.
Abstract: This study relates to the acoustic imaging of noise sources that are distributed and strongly directional such as in turbulent jets.The goal is to generate high-resolution noise source maps with self-consistency, i.e., their integration over the extent of the noise source region gives the far-field pressure auto-spectrum for a particular emission direction. Self-consistency is possible by including a directivity factor in the formulation of the source cross-spectral density. The resulting source distribution is based on the complex coherence, rather than the cross-spectrum, of the measured acoustic field. For jet noise, whose spectral nature changes with emission angle, it is necessary to conduct the measurements with a narrow-aperture array. Three coherence-based imaging methods were applied to a Mach 0.9 turbulent jet: delay-and-sum beamforming; deconvolution of the beamformer output; and direct spectral estimation that relies on minimizing the difference between the measured and modeled coherences of the acoustic field. The delay-and-sumbeamforming generates noise source maps with strong spatial distortions and sidelobes. Deconvolution leads to a five-fold improvement in spatial resolution and
significantly reduces the intensity of the sidelobes. The direct spectral estimation produces maps very similar to those obtained by deconvolution. The coherence-based noise source maps, obtained by deconvolution or direc tspectral estimation, are similar at small and large observation angles relative to the jet axis.
BibTeX:
@article{Papamoschou2011,
  author = {Papamoschou,, D.},
  title = {Imaging of Directional Distributed Noise Sources},
  journal = {J. Sound Vib.},
  year = {2011},
  volume = {330},
  pages = {2265--2280}
}
Papamoschou D (2008), "Imaging of Directional Distributed Noise Sources", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)., AIAA-2008-2885., May, 2008.
BibTeX:
@inproceedings{Papamoschou2008,
  author = {Papamoschou,, D.},
  title = {Imaging of Directional Distributed Noise Sources},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)},
  year = {2008}
}
Papamoschou D, Morris P and McLaughlin D (2010), "Beamformed Flow-Acoustic Correlations in a Supersonic Jet", AIAA Journal 2010. Vol. 48(10), pp. 2445-2453.
Abstract: An experimental study of simultaneous multipoint measurements in the flowfield and acoustic field of a Mach 1.75 cold-air jet is presented. A series of four optical-deflectometer probes measured turbulent fluctuations in or near the jet flow, and eight microphones recorded the far-field pressure in the direction of peak emission. The correlation methodology involves the coherence between the delay-and-sum beamformer outputs of the optical-deflectometer probes and the microphones. This procedure yields results with greater fidelity and higher coherence levels than obtained with individual optical-deflectometer-to-microphone correlations. With the optical-deflectometer probes in the jet shear layer, there is a significant correlation, on the order of 0.1, between the turbulent fluctuations and farfield noise. As the optical-deflectometer probe moves transversely away from the jet, its correlation with the microphone beamformer first drops and then increases. This trend signifies the transition from hydrodynamic to acoustic pressure fields. In the vicinity of the nozzle exit, the peak coherence between the beamformed optical deflectometer and microphone signals coincides with the physical location of the optical-deflectometer probe. However, as the shear layer thickens downstream, the peak coherence generally lags the probe location, which is a probable result of acoustic refraction by the mean flow.
BibTeX:
@article{Papamoshou_etal2010,
  author = {Papamoschou, D. and Morris, P. and McLaughlin, D.},
  title = {Beamformed Flow-Acoustic Correlations in a Supersonic Jet},
  journal = {AIAA Journal 2010},
  year = {2010},
  volume = {48},
  number = {10},
  pages = {2445-2453},
  doi = {10.2514/1.51650}
}
Papamoschou D, Morris PJ and McLaughlin D (2009), "Beamformed Flow-Acoustic Correlations in High-Speed Jets", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3212., May, 2009.
BibTeX:
@inproceedings{Papamochou2009,
  author = {Papamoschou, D. and Morris, P. J. and McLaughlin, D.},
  title = {Beamformed Flow-Acoustic Correlations in High-Speed Jets},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009}
}
Papamoschou D, Morris PJ and McLaughlin D (2009), "Beamformed Flow-Acoustic Correlations in High-Speed Jets", AIAA Journal., May, 2009. Vol. 48(10), pp. 2445-2453.
BibTeX:
@article{Papamoschou2009,
  author = {Papamoschou, D. and Morris, P. J. and McLaughlin, D.},
  title = {Beamformed Flow-Acoustic Correlations in High-Speed Jets},
  journal = {AIAA Journal},
  year = {2009},
  volume = {48},
  number = {10},
  pages = {2445--2453},
  doi = {10.2514/1.J050325}
}
Papamoschou D and Rostamimonjezi S (2010), "Effect of Velocity Ratio on Noise Source Distribution of Coaxial Jet", AIAA J.. Vol. 48(7), pp. 1504-1512.
Abstract: The noise source distribution of coaxial jets with a diameter ratio of 1.6 and variable velocity ratio is investigated with a small-aperture microphone phased array. The array design enables differentiation of noise emitted by largescale and fine-scale turbulence structures, which have different directivities. The acoustic data are complemented by pitot surveys of the mean flow, which yield measurements of the primary and secondary cores of the jet. For zero velocity ratio (single-stream jet), the region near the nozzle emits strong high-frequency noise. Increasing the secondary-to-primary velocity ratio suppresses the near-nozzle noise and extends the location of the peak noise downstream, which increases moderately. The axial location of peak noise is approximately situated at the end of the primary core. The suppression of high-frequency noise is explained by the creation and elongation of the secondary core as the velocity ratio increases. The acoustic trends with velocity ratio are similar for small and large array observation angles from which large-scale and fine-scale turbulence noise, respectively, have been shown to radiate. However, the increase in peak noise is more pronounced for the large-scale noise.
BibTeX:
@article{PapamoschouRostamimonjezi2010,
  author = {Papamoschou, D. and Rostamimonjezi, S.},
  title = {Effect of Velocity Ratio on Noise Source Distribution of Coaxial Jet},
  journal = {AIAA J.},
  year = {2010},
  volume = {48},
  number = {7},
  pages = {1504--1512},
  doi = {10.2514/1.50857}
}
Paschereit CO and Barsikow B (1994), "The microphone array: a tool on the path towards reducing railway noise", In Proc. World Congress on Railway Research (WCRR '94). , pp. 371-376.
BibTeX:
@inproceedings{PaschereitBarsikow1994,
  author = {Paschereit, C. O. and Barsikow, B.},
  title = {The microphone array: a tool on the path towards reducing railway noise},
  booktitle = {Proc. World Congress on Railway Research (WCRR '94)},
  year = {1994},
  pages = {371--376},
  note = {Proc. World Congress on Railway Research (WCRR '94), Paris, 1994}
}
Pavic G (2001), "Acoustic source characterisation using an inverse procedure.", In Proceedings
of the 8th International Congress on Sound and Vibration, Hong Kong, 2001. , pp. 1623-1628.
BibTeX:
@inproceedings{Pavic2001,
  author = {Pavic, G.},
  title = {Acoustic source characterisation using an inverse procedure.},
  booktitle = {Proceedings
of the 8th International Congress on Sound and Vibration, Hong Kong, 2001}, year = {2001}, pages = {1623--1628} }
Pereira A, Leclère Q and Antoni J (2012), "A theoretical and experimentalcomparison of the equivalent source method and a Bayesian approach to noise source identification", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-21., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Noise source identification and quantification based on field measurements performed by a microphone array is an usual task in many fields of acoustical engineering. Several approaches have been developed in order to tackle this problem, for example, beamforming, near-field acoustic holography (NAH), inverse methods such as equivalent source method (ESM) and the inverse boundary element method (IBEM), to cite only a few. Depending on the problem configuration (nature of the source field, frequency range of interest and the operational conditions) one method is often preferred over the others. Recently, a Bayesian approach combining physical and probabilistic information was proposed to solve acoustic source reconstruction problems. The deduction of a particular regularization mechanism and a criterion to select the regularization parameter depending on the probabilistic assumptions about the source field is a significant feature of this approach. The aim of this paper is to provide a theoretical and experimental comparison between Bayesian approach and the ESM to deal with a noise source identification problem
BibTeX:
@inproceedings{Pereira_etal2012,
  author = {Pereira, A. and Leclère, Q and Antoni, J.},
  title = {A theoretical and experimentalcomparison of the equivalent source method and a Bayesian approach to noise source identification},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-21.pdf}
}
Piet J-F and Élias G (1997), "Airframe noise source localization using a microphone array", In 3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997., AIAA Paper 97-1643.
BibTeX:
@inproceedings{PietElias97,
  author = {Piet, J.-F. and Élias, G.},
  title = {Airframe noise source localization using a microphone array},
  booktitle = {3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997},
  year = {1997}
}
Piet J-F, Élias G and Lebigit P (1999), "Localization of acousitc source from a landing aircraft with a microphone array", In 5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Washington, USA, May 10-12, 1999., AIAA Paper 99-1811.
BibTeX:
@inproceedings{Pietetal99,
  author = {Piet, J.-F. and Élias, G. and Lebigit, P.},
  title = {Localization of acousitc source from a landing aircraft with a microphone array},
  booktitle = {5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Washington, USA, May 10-12, 1999},
  year = {1999}
}
Piet J-F and Élias G (1997), "Airframe noise source localization using a microphone array", In 3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997., AIAA-1997-1643.
Abstract: A new phased-array processing method has been developed to achieve accurate two-dimensional localization of acoustic sources. While conventional processing requires a full 2D array with an excessive number of microphones, the present method is designed for sparse arrays, and uses many fewer microphones. A cross-shaped array of 39 microphones was built for wind tunnel testing. The near real-time processing is based on the above method. This is applied to an airframe noise source study on an Airbus aircraft model in the French CEPRA-19 anechoic wind tunnel. The localization maps give an idea of the array's performance.
BibTeX:
@inproceedings{PietElias1997,
  author = {Piet, J.-F. and Élias, G.},
  title = {Airframe noise source localization using a microphone array},
  booktitle = {3rd AIAA/CEAS Aeroacoustics Conference, Atlanta, Ga, May 12-14, 1997},
  year = {1997},
  url = {http://pdf.aiaa.org/preview/1997/PV1997_1643.pdf}
}
Piet J-F, Élias G and Lebigot P (1999), "Localization of acoustic source from a landing aircraft with a microphone array", In 5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Washington, USA, May 10-12, 1999., AIAA-1999-1811., May, 1999.
Abstract: Acoustic source two-dimensional localization was performed during flyover tests with an Airbus A340 in Tarbes, France, in 1997. The method combined a cross-shaped array of 29 microphones developed by ONERA to a D-GPS tracking system operated by Aerospatiale. These tests aimed to validate the method and evaluate its precision and performance. The signal processing used a 32-channel digital tape recorder, where both D-GPS synchronization tops and the acoustic signals were recorded on the ground while D-GPS information was recorded on board. The aircraft performed flyovers above the array at altitudes between 40 and 180 meters and for different flight configurations. An acoustic emitter producing tone noise placed on the aircraft nose has helped for the method calibration. The source is clearly localized with a bias on position that can be lower than 50 cm. The method interest for extended and multiple sources is also confirmed : a few examples of airframe noise source maps are presented for configurations with landing gears and high-lift devices extended.
BibTeX:
@inproceedings{Piet_etal1999,
  author = {Piet, J.-F. and Élias, G. and Lebigot, P.},
  title = {Localization of acoustic source from a landing aircraft with a microphone array},
  booktitle = {5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Washington, USA, May 10-12, 1999},
  year = {1999},
  url = {http://pdf.aiaa.org/preview/1999/PV1999_1811.pdf}
}
Piet J-F and Michel U (2000), "Localisation of the acoustic sources of the A320 during flight tests", FR30/6189 DSNA/Y/DMAE and DLR-IB 92517-2000/B2. (FR30/6189 DSNA/Y/DMAE and DLR-IB 92517-2000/B2)
BibTeX:
@techreport{PietMichel2000,
  author = {Piet, J.-F. and Michel, U.},
  title = {Localisation of the acoustic sources of the A320 during flight tests},
  year = {2000},
  number = {FR30/6189 DSNA/Y/DMAE and DLR-IB 92517-2000/B2}
}
Piet J-F and Michel U (1999), "Acoustic sources localisation during A340 flight tests in Tarbes", FR12/6189 DSNA/Y/DMAE and DLR-IB 92517/B1. (FR12/6189 DSNA/Y/DMAE and DLR-IB 92517/B1)
BibTeX:
@techreport{PietMichel1999,
  author = {Piet, J.-F. and Michel, U.},
  title = {Acoustic sources localisation during A340 flight tests in Tarbes},
  year = {1999},
  number = {FR12/6189 DSNA/Y/DMAE and DLR-IB 92517/B1}
}
Piet J-F, Michel U and Böhning P (2002), "Localization of the acoustic sources of the A340 with a large phased microphone array during flight tests", In 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002., AIAA-2002-2506.
Abstract: Flyover measurements with a phased array of microphones extending over an area of 16 m by 16 m are reported. The 161 microphone array was made possible by combining hardware from ONERA and DLR. In this investigation of the airframe noise of an Airbus A340, the yover altitudes were between 90 m and 165 m. The data reduction methods for moving objects of DLR and ONERA are compared. Some source maps are shown and discussed. It is demonstrated that nested arrays must be used for a study over a wide frequency range, and that comparisons of the noise maps between di erent arrays provide valuable information about the noise sources. The ONERA method is shown to be a powerful data reduction method based on a small number of microphones while the DLR method results in alias-free maps at the expense of a much larger number of microphones.
BibTeX:
@inproceedings{Piet_etal2002,
  author = {Piet, J.-F. and Michel, U. and Böhning, P.},
  title = {Localization of the acoustic sources of the A340 with a large phased microphone array during flight tests},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002},
  year = {2002},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO02_554/PV2002_2506.pdf}
}
Plotkin KJ, Gurovich Y, Blake W and Donovan P (2008), "Noise source mapping for trucks, part 1: development and design", In Proceedings of Euronoise, Acoustics'08, Paris.
BibTeX:
@inproceedings{Plotkin_etal2008a,
  author = {Plotkin, K. J. and Gurovich, Y. and Blake, W. and Donovan, P.},
  title = {Noise source mapping for trucks, part 1: development and design},
  booktitle = {Proceedings of Euronoise, Acoustics'08, Paris},
  year = {2008},
  url = {http://intellagence.eu.com/acoustics2008/acoustics2008/cd1/data/articles/000362.pdf}
}
Plotkin KJ, Gurovich Y, Blake W and Donovan P (2008), "Noise source mapping for trucks, part 2: experimental results", In Proceedinsg of Euronoise, Acoustics'08, Paris 2008.
BibTeX:
@inproceedings{Plotkin_etal2008b,
  author = {Plotkin, K. J. and Gurovich, Y. and Blake, W. and Donovan, P.},
  title = {Noise source mapping for trucks, part 2: experimental results},
  booktitle = {Proceedinsg of Euronoise, Acoustics'08, Paris 2008},
  year = {2008},
  url = {http://intellagence.eu.com/acoustics2008/acoustics2008/cd1/data/articles/003300.pdf}
}
Podboy G and Horvath C (2009), "Phased Array Noise Source Localization Measurements Made on a Williams International FJ44 Engine", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference).., AIAA-2009-3183., May, 2009. (AIAA-2009-3183)
Abstract: A 48-microphone planar phased array system was used to acquire noise source localization data on a full-scale Williams International FJ44 turbofan engine. Data were acquired with the array at three different locations relative to the engine, two on the side and one in front of the engine. At the two side locations the planar microphone array was parallel to the engine centerline; at the front location the array was perpendicular to the engine centerline. At each of the three locations, data were acquired at eleven different engine operating conditions ranging from engine idle to maximum (take off) speed. Data obtained with the array off to the side of the engine were spatially filtered to separate the inlet and nozzle noise. Tones occurring in the inlet and nozzle spectra were traced to the low and high speed spools within the engine. The phased array data indicate that the Inflow Control Device (ICD) used during this test was not acoustically transparent; instead, some of the noise emanating from the inlet reflected off of the inlet lip of the ICD. This reflection is a source of error for far field noise measurements made during the test. The data also indicate that a total temperature rake in the inlet of the engine is a source of fan noise.
BibTeX:
@inproceedings{PodboyHorwath2009,
  author = {Podboy, G. and Horvath, C.},
  title = {Phased Array Noise Source Localization Measurements Made on a Williams International FJ44 Engine},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference).},
  year = {2009},
  number = {AIAA-2009-3183}
}
Podboy G. G., Bridges J. E. and Henderson BS (2010), "Phased Array Noise Source Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale" (NASA/TM-2010-216366)
Abstract: A 48-microphone planar phased array system was used to acquire jet noise source localization data on both a full-scale F404-GE-F400 engine and on a 1/4th scale model of a F400 series nozzle. The full-scale engine test data show the location of the dominant noise sources in the jet plume as a function of frequency for the engine in both baseline (no chevron) and chevron configurations. Data are presented for the engine operating both with and without afterburners. Based on lessons learned during this test, a set of recommendations are provided regarding how the phased array measurement system could be modified in order to obtain more useful acoustic source localization data on high-performance military engines in the future. The data obtained on the 1/4th scale F400
series nozzle provide useful insights regarding the full-scale engine jet noise source mechanisms, and document some of the differences associated with testing at model-scale versus fullscale.
BibTeX:
@techreport{Podboy_Bridges_Henderson2010,
  author = {Podboy, G. G., and Bridges, J. E., and Henderson, B. S},
  title = {Phased Array Noise Source Localization Measurements of an F404 Nozzle Plume at Both Full and Model Scale},
  year = {2010},
  number = {NASA/TM-2010-216366},
  url = {http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100033097_2010036415.pdf}
}
Qiao W, Ji L, Tong W, Xu K and Chen W (2014), "Application of Phased Array in the Study of Linear Cascade Noise Reduction on the Indoor Test Bed", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-22., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: A measurement technique with microphone array conventional beamforming for indoor linear cascade noise test is developing in NPU (Northwestern Polytechnical University of China) to quantify differences of sound source levels of linear cascade as a result of blade trailing edge modifications. The useful practical experience has been gained during this test. The special indoor microphones placement to avoid introducing ambiguities into sound source localization measurements in the hard-walled room test is firstly described in the paper. The reverberation time of test room is measured and is used to determine the range of direct-field of noise source acoustic radiation. A special microphones indoor placement method is used in the study to reduce the reflection from wall and to increase signal-to-noise ratio of the microphone array. The noise reduction potential of trailing edge serrations in NPU turbine linear cascade with 6 high-loaded LPT turbine blades is investigated experimentally with low cascade outlet Mach number. It is shown that turbulent boundary layer trailing edge noise is reduced in the low- to mid- frequency range and the largest noise reduction is about ~2 dB. This magnitude of cascade blade trailing edge noise reduction is obviously smaller than that of the isolated airfoil with using of serrated trailing edge.
BibTeX:
@inproceedings{Qiao_etal2014,
  author = {Qiao, W. and Ji, L. and Tong, W. and Xu, K. and Chen, W.},
  title = {Application of Phased Array in the Study of Linear Cascade Noise Reduction on the Indoor Test Bed},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-22.pdf}
}
Quayle A, Ann Dowling A, Babinsky H, Graham W and Yu Liu Y (2007), "Phased Array Measurements from Landing Gear Models", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007., AIAA-2007-3463., May, 2007.
Abstract: Landing gear is now well known to be a major source of aircraft noise. Several studies have also identified the importance of surface details in the noise generated by landing gears at high frequencies. However, the basic mechanisms of noise generation at lower frequencies are less well understood. In this study, we examine the effect of changes to the overall gear layout on the noise produced. 1/12th scale models containing only the wheels, axles and main struts have been studied using two nested, 48-microphone arrays in the closed-section Markham wind tunnel at Cambridge University. Local fairings have also been added to isolate and identify individual noise sources. Results indicate that shape and placement of the wheels can affect the overall noise level by at least 6dB on simplified four wheel models. Changes in geometry were also found to substantially affect high frequency sources close to the main oleo, suggesting that noise sources from conventional, fully dressed gears might be equally susceptible to small changes in the overall design.
BibTeX:
@inproceedings{Quayle_etal2007,
  author = {Quayle, A. and Ann Dowling, A. and Babinsky, H. and Graham, W. and Yu Liu, Yu},
  title = {Phased Array Measurements from Landing Gear Models},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference) , Rome, Italy, May 21-23, 2007},
  year = {2007},
  url = {http://silentaircraft.org/object/download/2163/doc/AIAA-2007-3463-394.pdf}
}
Quayle AR, Dowling A, Graham WRG and Babinsky H (2006), "Comparison of source estimation algorithms / Methods in closed tunel noise measurements.", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-08. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The Markham aerodynamic wind tunnel at Cambridge University has been modified to include two nested, 48 microphone arrays. The setup has been designed by the Nationaal Lucht- en Ruimtevaartlaboratorium in the Netherlands (NLR) and has been used to support the design of landing gear fairings for the Silent Aircraft Initiative. Source power estimates have been computed using a power integration method (POWINT) and verified using the CLEAN source identification method. These are included as part of the NLR beamforming suite. POWINT computes the integrated source power over a specified grid containing the model. The CLEAN algorithm identifies the maximum source on the plot and removes it together with appropriate side lobes. It continues to compute and remove successive maximum sources which can later be added together to give an overall noise measure. In the case where there are background sources or side-lobes visible on source plots, the use of the CLEAN algorithm to estimate source levels allows the user to choose which sources to integrate. The effect of background noise or sources exterior to the model can therefore be rejected. This technique may be of particular interest for array measurements in aerodynamic tunnels which are typically of higher background noise.
BibTeX:
@inproceedings{Quayle_etal2006,
  author = {Quayle, A. R. and Dowling, A.P. and Graham, W. R. Graham and Babinsky, H.},
  title = {Comparison of source estimation algorithms / Methods in closed tunel noise measurements.},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-08_Quayle_Dowling_etal.pdf}
}
Quayle AR, Graham W, Dowling AP, Babinsky H and Liu Y (2008), "Mitigation of beamforming interference from closed wind tunnels using CLEAN-SC", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-10. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The Markham aerodynamic wind tunnel at Cambridge has been used for a series of aeroacoustic investigations into noise from landing gears and wing slats. This tunnel uses a pair of nested arrays to determine source strength across a range of frequencies. In the course of experiments it has been found that measurements from the smaller, high frequency array can under-estimate source strength at frequencies where the two arrays are expected to overlap. The effect on the spectrum was to mask lower level sources. As a result, the noise reduction available from a particular configuration could appear significantly larger than is actually the case. In this paper we present a discussion of measurements from the tunnel and mechanisms for interference from wind tunnel sources. We confirm the existence of the effect using sources in an anechoic chamber. We also present a method for mitigating interference using the ‘CLEAN-SC’ algorithm with appropriately reshaped scanning grids for beamforming. Results show that more consistent measurements are obtained from the two acoustic arrays, providing some validation of the method. This analysis has the potential to be significant in a variety of closed wind tunnel testing.
BibTeX:
@inproceedings{Quayle_etal2008,
  author = {Quayle, A. R. and Graham, W. and Dowling, A. P. and Babinsky, H. and Liu, Yu},
  title = {Mitigation of beamforming interference from closed wind tunnels using CLEAN-SC},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-10_Quayle_Graham_etal.pdf}
}
Rafaely B, Peled Y, Agmon M, Khaykin D and Fisher E (2010), "Spherical Microphone Array Beamforming" , pp. 281-305. Springer Berlin / Heidelberg.
Abstract: Spherical microphone arrays have been recently studied for spatial sound recording, speech communication, and sound field analysis for room acoustics and noise control. Complementary studies presented progress in beamforming methods. This chapter reviews beamforming methods recently developed for spherical arrays, from the widely used delay-and-sum and Dolph-Chebyshev, to the more advanced optimal methods, typically performed in the spherical harmonics domain.
BibTeX:
@inbook{Rafaely_etal2010,
  author = {Rafaely, B. and Peled, Y. and Agmon, M. and Khaykin, D. and Fisher, E.},
  editor = {Israel Cohen, Jacob Benesty and Sharon Gannot},
  title = {Spherical Microphone Array Beamforming},
  publisher = {Springer Berlin / Heidelberg},
  year = {2010},
  pages = {281--305},
  doi = {10.1007/978-3-642-11130-3_11}
}
Ramachandran R, Patel H and Raman G (2012), "Localization of wind turbine noise sources using a compact microphone array with advanced beamforming algorithms", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-25., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: One of the challenges that one faces when developing and designing low noise wind turbines is knowledge of components that radiate the most noise. Typical measurement techniques using a single microphone will result only in the overall sound pressure level radiated by the wind turbines. When it comes to locating sources of noise on a wind turbine, advanced techniques such as the microphone array in conjunction with beamforming algorithms are required. Earlier work has examined wind turbine noise using a microphone array with 148 microphones. These microphones were spread out on the ground over an area of 270 m² near the wind turbine and were not mobile and compact. This paper focuses on using a compact mobile microphone array with advanced beamforming algorithms to measure the noise radiated from wind turbines and identify them with their corresponding sources. Our initial experimental observation on locating the components on a wind turbine radiating noise suggests that it is indeed possible to locate these sources using a compact 24 microphone array with advanced beamforming algorithms such as DAMAS2, CLEAN-SC and TIDY. The qualification experiments performed on the array in laboratory using synthetic noise sources showed the differences between the various advanced beamforming algorithms. In locating the noise sources at desired narrowband frequencies CLEAN-SC was found to perform the best followed by DAMAS2 and conventional frequency domain beamforming. At desired broadband frequencies TIDY performed better in locating the source followed by delay-and-sum. It was also observed that the knowledge of Rayleigh criterion played an important role in locating the sources at the lower frequencies. The experimental results on a full scale wind turbine reveal that most noise radiated were due to aerodynamic noise from the blade tip and mechanical noise from nacelle. Additionally, we were able to measure and locate the noise radiated due to the yaw motors in particular. The initial results presented here offer strong evidence of the potential of compact microphone arrays in measuring and locating the noise sources on wind turbines.
BibTeX:
@inproceedings{Ramachandran_etal2012,
  author = {Ramachandran, R.C. and Patel, H. and Raman, G.},
  title = {Localization of wind turbine noise sources using a compact microphone array with advanced beamforming algorithms},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-25.pdf}
}
Ramachandran RC and Raman G (2011), "Evaluation of Various Beamforming Algorithms for Wind Turbine Noise Measurement", In 49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011., AIAA-2011-722., January, 2011.
Abstract: Wind energy is one of the oldest and cleanest forms of energy and the most developed of the renewable energy sources. Noise made by wind turbines is of key interest for many reasons. The noise made by a machine is a measure of its inefficiency. Wind turbine that are associated with excessive noise and vibrations are wasting energy and are prone to structural damage. In addition, one of the major factors in certification of wind turbines and obtaining a site license is wind turbine noise. It is important to locate the source of wind turbine noise in order to study the noise generation mechanism in wind turbines. One of the emerging methods for acoustic source localization is the acoustic array beamformer. There are various beamforming algorithms that were developed for aeroacoustic measurements. This paper presents a comparison of four such beamforming algorithms namely; Frequency domain beamforming (FDBF), DAMAS2 (DMS2), CLEAN-SC (CLSC) and TIDY. The behavior of these algorithms when exposed to single source, multiple incoherent and coherent sources and an oscillating source are systematically studied to evaluate suitable beamforming algorithms for wind turbine applications.
BibTeX:
@inproceedings{RamachandranRaman2011,
  author = {Ramachandran, R. C. and Raman, G.},
  title = {Evaluation of Various Beamforming Algorithms for Wind Turbine Noise Measurement},
  booktitle = {49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011},
  year = {2011}
}
Ramachandran RC, Raman G and Dougherty RP (2012), "Wind Turbine Field Measurements With Compact Microphone Array Using Advanced Beamforming Methods", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference) 04 - 06 June 2012, Colorado Springs, CO., AIAA-2012-2274., June, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The knowledge of noise source locations on a wind turbine is crucial for designing low noise wind turbines. It is also important to monitor the noise from the wind turbine, be it mechanical or aerodynamic noise, to monitor the health of the wind turbine. Currently compliance standards for wind turbine noise are based on single microphone measurements at various designated locations around a wind turbine. This only provides amplitude and frequency data of the overall wind turbine noise. It is however impossible to locate noise sources with a single microphone. A sophisticated method, namely the use of a microphone phased array with advanced beamforming is necessary. Typical microphone arrays that have been used in the past for monitoring aircraft noise and wind turbine noise are very large ranging up to 300 m^2 in area with about 150 microphones. The setup is xed for a particular wind turbine and takes considerable amount of time. Our idea is to use a compact microphone array to locate and separate wind turbine noise sources successfully with the use of advanced beamforming methods such as DAMAS2, CLSC and TIDY. Such a compact tool could be used to measure multiple wind turbines as the apparatus is not xed and will be much faster and easier to make measurements. A GE 1.5 MW full scale production wind turbine was used in our study with an Optinav 24 microphone array (of area 1.5 m^2). A wind screen was used to cover the microphone array to eliminate ambient air interaction with the microphones. On site calibration was performed to account for the loss in amplitude due to the wind screen. The frequency spectrum of the wind turbine was studied to identify the contribution of various noise sources on the wind turbine such as mechanical noise from the nacelle and tower and aerodynamic noise from the blades. The low frequency noise component was found to be due to ampli cation of noise from the nacelle through the tower of the wind turbine. Mid and high frequency noise components were attributed to trailing edge noise and blade tip vortex noise from the blade. The cooling fan in the nacelle was also observed to radiate high frequency noise. It was also observed that during the yaw motor operation the structural noise was ampli ed considerably. Detailed discussions and the results of the experiments are presented in this paper
BibTeX:
@inproceedings{Ramachandran_etal2012b,
  author = {Ramachandran, R. C. and Raman, G. and Dougherty, R. P.},
  title = {Wind Turbine Field Measurements With Compact Microphone Array Using Advanced Beamforming Methods},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference) 04 - 06 June 2012, Colorado Springs, CO},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012}
}
Raman G, Perschke R and Ramachandran R (2012), "Detection of flow separation using microphone arrays", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-19., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The role of microphone phased arrays as a tool to detect flow separation is investigated. A backward-facing step is used to create a separated flow, thereby inducing a region of elevated free-stream turbulence downstream of the step. Velocity measurements and a flow visualization technique are used to complement microphone measurements. It is shown that flow separation can be distinguished from flow-edge interaction noise due to their different dependencies on Mach number and observation angle. Flow separation noise is produced several centimeters downstream of the flow-edge interaction noise and is more dominant at high Mach numbers. The performance of the beamforming algorithms TIDY, DAMAS2, and CLEAN-SC are evaluated. It is observed that all the beamforming algorithms provide good separation of free-stream noise and flow-edge interaction noise at the relatively high frequencies considered although CLEAN-SC tends to yield output powers that are typically 3 dB lower.
BibTeX:
@inproceedings{Raman_etal2012,
  author = {Raman, G. and Perschke, R. and Ramachandran, R.C.},
  title = {Detection of flow separation using microphone arrays},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-19.pdf}
}
Raman G, Prakash M, Ramachandran R, Patel H and Chelliah H (2014), "Remote Detection of Building Air Infiltration Using a Compact Microphone Array and Advanced Beamforming Methods", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-14., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In the United States excess air infiltration is estimated to account for approximately 23% and 14% of the total amount of energy used for heating and cooling in all residential and commercial buildings, respectively. The overall goal is to use a non-intrusive acoustic phased array with beamforming techniques to remotely detect specific envelope leaks in buildings. Pressure fluctuations associated with the leakage flow can be localized by using a compact, noninvasive microphone array with advanced beamforming algorithms.
BibTeX:
@inproceedings{Raman_etal2014,
  author = {Raman, G. and Prakash, M. and Ramachandran, R. and Patel, H. and Chelliah, H.},
  title = {Remote Detection of Building Air Infiltration Using a Compact Microphone Array and Advanced Beamforming Methods},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-14.pdf}
}
Ravetta PA, Burdisso RA and Ng WF (2004), "Wind Tunnel Aeroacoustic Measurements of a 26%-scale 777 Main Landing Gear", In 10th AIAA/CEAS Aeroacoustics Conference and Exhibit, May 2004, Manchester, United Kingdom., AIAA-2004-2885., May, 2004. (AIAA-2004-2885)
BibTeX:
@inproceedings{Ravetta_etal2004,
  author = {Ravetta, P. A. and Burdisso, R. A. and Ng, W. F.},
  title = {Wind Tunnel Aeroacoustic Measurements of a 26%-scale 777 Main Landing Gear},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference and Exhibit, May 2004, Manchester, United Kingdom},
  year = {2004},
  number = {AIAA-2004-2885}
}
Ravetta P and Burdisso R (2006), "Noise Source Localization and Optimization of Phased Array Results", In 12th AIAA/CEAS Aeroacoustics Conference., AIAA-2006-2713., May, 2006. (AIAA-2006-2713)
BibTeX:
@inproceedings{RavettaBurdisso2006,
  author = {Ravetta, P. and Burdisso , R.},
  title = {Noise Source Localization and Optimization of Phased Array Results},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference},
  year = {2006},
  number = {AIAA-2006-2713}
}
Ravetta P, Burdisso R and Ng W (2009), "Noise Source Localization and Optimization of Phased-Array Results", AIAA Journal. Vol. 47(11), pp. 2520-2533.
Abstract: A new approach to the deconvolution of acoustic sources has been developed and is presented in this work. The goal of this postprocessing is to simplify the beamforming output by suppressing the side lobes and reducing the sources’ main lobes to single (or a small number of) points that accurately identify the noise sources’ positions and their actual levels. In this work, a new modeling technique for the beamforming output is proposed. The idea is to use an image-processing-like approach to identify the noise sources from the beamforming maps: that is, recognizing lobe patterns in the beamformed output and relating them to the noise sources that would produce that map. For incoherent sources, the beamforming output is modeled as a superposition of point-spread functions and a linear system is posted. For coherent sources, the beamforming output is modeled as a superposition of complex pointspread functions and a nonlinear system of equations in terms of the sources’ amplitudes is posted. As a first approach to solving this difficult problem, the system is solved using a new two-step procedure. In the first step, an approximated linear problem is solved. In the second step, an optimization is performed over the nonzero values obtained in the previous step. The solution to this system of equations renders the sources’ positions and amplitudes. In the case of coherent sources, their relative phase can also be recovered. The technique is referred as noise source localization and optimization of phased-array results. A detailed analytical formulation, numerical simulations, and sample experimental results are shown for the proposed postprocessing.
BibTeX:
@article{Ravetta_etal2009,
  author = {Ravetta, P. and Burdisso, R. and Ng, Wing},
  title = {Noise Source Localization and Optimization of Phased-Array Results},
  journal = {AIAA Journal},
  year = {2009},
  volume = {47},
  number = {11},
  pages = {2520--2533},
  doi = {10.2514/1.38073}
}
Ravetta P, Burdisso R, Ng W, Khorrami M and Stoker R (2007), "Screening of Potential Noise Control Devices at Virginia Tech for QTD II Flight Test", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 21 - 23 May 2007 Rome., AIAA-2007-3455., May, 2007.
BibTeX:
@inproceedings{Ravetta_etal2007,
  author = {Ravetta, P. and Burdisso, R. and Ng, W. and Khorrami, M. and Stoker, R.},
  title = {Screening of Potential Noise Control Devices at Virginia Tech for QTD II Flight Test},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference), 21 - 23 May 2007 Rome},
  year = {2007}
}
Rechenberg I (1973), "Evolutionsstrategie" Frommann Verlag Stuttgart.
BibTeX:
@book{Rechenberg73,
  author = {Rechenberg, I.},
  title = {Evolutionsstrategie},
  publisher = {Frommann Verlag Stuttgart},
  year = {1973}
}
Remillieux M, Camargo H, Burdisso R. and Ng W (2007), "Aeroacoustic Study of a 26%-Scale, High-Fidelity, Boeing 777 Main Landing Gear in a Semi-Anechoic-Wind-Tunnel Test Section", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)., AIAA-2007-3453., May, 2007.
BibTeX:
@inproceedings{Remillieux_etal2007,
  author = {Remillieux, M. and Camargo, H. and Burdisso, R., and Ng, W.},
  title = {Aeroacoustic Study of a 26%-Scale, High-Fidelity, Boeing 777 Main Landing Gear in a Semi-Anechoic-Wind-Tunnel Test Section},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)},
  year = {2007},
  doi = {10.2514/6.2007-3453}
}
Romenskiy I and Jaeckel O (2008), "Improvement of source separation for phased microphone array measurements", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-17. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: The paper presents a new method for the improvement of microphone array measurement results using an unconventional, relatively simple and very fast iterative post processing algorithm suitable for 2D-beamforming acoustic maps. This procedure is based on the mathematical model of a time reversed diffusion process which is numerically stabilized by means of a spatial low pass filter as well as by an additional amplitude renormalization step. The method allows the reduction of the mainlobe width of acoustic point sources in the map and can thus be applied for the improvement of the usually very bad image contrast in the lower frequency range and also for a better separation of closely lying sources which can not be clearly resolved by simple delay-and-sum beamforming. An outstanding property of the proposed algorithm is that it does not rely on the knowledge of the point spread function which is needed in complete deconvolution approaches. The iteration procedure merely utilizes the local curvature information that is already hidden within the acoustic beamforming map to sharpen the individual sources while simultaneously smoothing out disturbing high frequency components that otherwise would lead to numerical instability and unlimited amplification of unwanted small false signal and noise components.
BibTeX:
@inproceedings{RomenskiyJaeckel2008,
  author = {Romenskiy, I. and Jaeckel, O.},
  title = {Improvement of source separation for phased microphone array measurements},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-17_Romenskiy_Jaeckel.pdf}
}
Ross M, Shannon D, Blake W and Morris S (2008), "Unsteady Lift and Radiated Sound Generated by a 2-D Airfoil in a Single Stream Shear Layer", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)., AIAA-2008-2963., May, 2008.
BibTeX:
@inproceedings{Ross_etal2008,
  author = {Ross, M. and Shannon, D. and Blake, W. and Morris, S.},
  title = {Unsteady Lift and Radiated Sound Generated by a 2-D Airfoil in a Single Stream Shear Layer},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)},
  year = {2008},
  doi = {10.2514/6.2008-2963}
}
Ross R, van Nunen JWG, Young KJ, Allen RM and van Ditshuizen JCA (1983), "Aeroacoustic calibration of the German-Dutch Wind Tunnel (DNW) open jet"
BibTeX:
@techreport{Rossetal83,
  author = {Ross, R. and van Nunen, J. W. G. and Young, K. J. and Allen, R. M. and van Ditshuizen, J. C. A.},
  title = {Aeroacoustic calibration of the German-Dutch Wind Tunnel (DNW) open jet},
  year = {1983}
}
Sarradj E (2012), "Three-Dimensional Acoustic Source Mapping with Different Beamforming Steering Vector Formulations", Advances in Acoustics and Vibration. Vol. 2012(292695), pp. 1-12.
BibTeX:
@article{Sarradj2012,
  author = {Sarradj, E.},
  title = {Three-Dimensional Acoustic Source Mapping with Different Beamforming Steering Vector Formulations},
  journal = {Advances in Acoustics and Vibration},
  year = {2012},
  volume = {2012},
  number = {292695},
  pages = {1-12},
  doi = {10.1155/2012/292695}
}
Sarradj E (2012), "Three-Dimensional Acoustic Source Mapping", In Fourth Berlin Beamforming Conference.
BibTeX:
@inproceedings{Sarradj2012c,
  author = {Sarradj, E.},
  title = {Three-Dimensional Acoustic Source Mapping},
  booktitle = {Fourth Berlin Beamforming Conference},
  year = {2012}
}
Sarradj E (2011), "Charakterisierung von aeroakustischen Schallquellen mit Mikrofonarrays", In Vorkolloquium Strömungsakustik, Fortschritte der Akustik - DAGA.
BibTeX:
@inproceedings{Sarradj2011b,
  author = {Sarradj, E.},
  title = {Charakterisierung von aeroakustischen Schallquellen mit Mikrofonarrays},
  booktitle = {Vorkolloquium Strömungsakustik, Fortschritte der Akustik - DAGA},
  year = {2011}
}
Sarradj E (2010), "A fast signal subspace approach for the determination of absolute levels from phased microphone array measurements", J. Sound Vib.., April, 2010. Vol. 329(9), pp. 1553-1569.
Abstract: Phased microphone arrays are used in a variety of applications for the estimation of acoustic source location and spectra. The popular conventional delay-and-sum beamforming methods used with such arrays suffer from inaccurate estimations of absolute source levels and in some cases also from low resolution. Deconvolution approaches such as DAMAS have better performance, but require high computational effort. A fast beamforming method is proposed that can be used in conjunction with a phased microphone array in applications with focus on the correct quantitative estimation of acoustic source spectra. This method bases on an eigenvalue decomposition of the cross spectral matrix of microphone signals and uses the eigenvalues from the signal subspace to estimate absolute source levels. The theoretical basis of the method is discussed together with an assessment of the quality of the estimation. Experimental tests using a loudspeaker setup and an airfoil trailing edge noise setup in an aeroacoustic wind tunnel show that the proposed method is robust and leads to reliable quantitative results.
BibTeX:
@article{Sarradj2010,
  author = {Sarradj, E.},
  title = {A fast signal subspace approach for the determination of absolute levels from phased microphone array measurements},
  journal = {J. Sound Vib.},
  year = {2010},
  volume = {329},
  number = {9},
  pages = {1553--1569},
  doi = {10.1016/j.jsv.2009.11.009}
}
Sarradj E (2010), "Modulares Mess- und Auswertesystem für Mikrofonarraymessungen", In Fortschritte der Akustik - DAGA. , pp. 325-326.
BibTeX:
@inproceedings{Sarradj2010b,
  author = {Sarradj, E.},
  title = {Modulares Mess- und Auswertesystem für Mikrofonarraymessungen},
  booktitle = {Fortschritte der Akustik - DAGA},
  year = {2010},
  pages = {325-326}
}
Sarradj E (2009), "Aeroacoustic source characterisation using subspace and deconvolution techniques", In Noise and Vibration: Emerging Methods.
BibTeX:
@inproceedings{Sarradj2009b,
  author = {Sarradj, E.},
  title = {Aeroacoustic source characterisation using subspace and deconvolution techniques},
  booktitle = {Noise and Vibration: Emerging Methods},
  year = {2009}
}
Sarradj E (2008), "Quantitative source spectra from acoustic array measurements", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-03. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: While phased microphone arrays are often applied with the focus on acoustic source localization, in many cases quantitative source information is also needed. The estimation of quantitative source spectra from array measurements is not straightforward and a number of methods exist that either use integration of the beamforming map or solve inverse problems for source estimation. An alternative, computationally efficient method is proposed that is based on a signal subspace approach. A short overview of the theory is given and the method is demonstrated using two examples, a four loudspeaker set-up and trailing edge noise measurement.
BibTeX:
@inproceedings{Sarradj2008,
  author = {Sarradj, E.},
  title = {Quantitative source spectra from acoustic array measurements},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://www.bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-03_Sarradj.pdf}
}
Sarradj E, Fritzsche C and Geyer T (2011), "Silent Owl Flight: Bird Flyover Noise Measurements", AIAA J.., AIAA Journal 2011. Vol. 49(4), pp. 769-779.
Abstract: Most genera of owls (Strigiformes) have the ability to fly silently. The mechanisms of the silent flight of the owl have been the subject of scientific interest for many decades. The results from studies in the past are discussed in detail in this paper and the rationale for the present research is given, which included flyover noise measurements on different species of birds. Successful acoustic measurements were made on a Common Kestrel, a Harris Hawk, and a Barn Owl. Measurements on three other birds did not lead to reliable results. The setup and procedure used for the outdoor measurements are discussed. These include the estimation of the trajectory from dual video camera recordings and microphone-array measurements with a moving-focus beamforming technique. The main result from the 50 successful flyovers is that the owl flight produces aerodynamic noise that is indeed a few decibels below that of other birds, even if flying at the same speed. This noise reduction is significant at frequencies above 1.6 kHz. At frequencies above 6.3 kHz the noise from the owl remains too quiet to be measured.
BibTeX:
@article{Sarradj_etal2011,
  author = {Sarradj, E. and Fritzsche, Christoph and Geyer, T.},
  title = {Silent Owl Flight: Bird Flyover Noise Measurements},
  journal = {AIAA J.},
  year = {2011},
  volume = {49},
  number = {4},
  pages = {769--779},
  doi = {10.2514/1.53992}
}
Sarradj E, Fritzsche C and Geyer T (2010), "Silent Owl Flight: Bird Flyover Noise Measurements", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3991., June, 2010.
Abstract: Most genera of owls (Strigiformes) have the ability to fly silently. The mechanisms of the silent flight of the owl have been the subject of scientific interest for many decades. The results from studies in the past are discussed in detail in the paper and the rationale for the present research is given, that included flyover noise measurements on different species of birds. Successful acoustic measurements were made on a Common Kestrel, a Harris Hawk and a Barn Owl. Measurements on three other birds did not lead to reliable results. The setup and procedure used for the outdoor measurements is discussed. This includes the estimation of the trajectory from dual video camera recordings as well as microphone array measurements with a moving focus beamforming technique. The main result from the 50 sucessful flyovers is that the owl flight produces aerodynamic noise which is indeed a few decibels below that of other birds, even if flying at the same speed. This noise reduction is significant at frequencies above 1.6 kHz. At frequencies above 6.3 kHz the noise from the owl remains to quiet to be measured.
BibTeX:
@inproceedings{Sarradj_etal2010b,
  author = {Sarradj, E. and Fritzsche, C. and Geyer, T.},
  title = {Silent Owl Flight: Bird Flyover Noise Measurements},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Sarradj E, Fritzsche C and Geyer T (2010), "Silent Owl Flight: Bird Flyover Noise Measurements", In 16th AIAA/CEAS Aeroacoustics Conference (31th AIAA Aeroacoustics Conference), AIAA paper 2010-3991.
BibTeX:
@inproceedings{Sarradj2010c,
  author = {Sarradj, E. and Fritzsche, C. and Geyer, T.},
  title = {Silent Owl Flight: Bird Flyover Noise Measurements},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference (31th AIAA Aeroacoustics Conference), AIAA paper 2010-3991},
  year = {2010}
}
Sarradj E and Geyer T (2007), "Noise Generation by Porous Airfoils", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)., AIAA-2007-3719.
Abstract: The noise generated by the flow around airfoils continues to be one of the important aeroacoustic noise sources. Innovative techniques for airfoil noise reduction are, therefore, of great importance. The present experimental study deals with the use of porous material for the construction of airfoils and the subsequent noise reduction. The use of such material controls the flow around the airfoil and has an influence on the sound generation. The analysis focuses on the characterization of the influence of the porous material parameters, especially the flow resistivity and the porosity, on the noise generation. Results of aeroacoustic wind tunnel tests on several porous and non-porous SD 7003 model scale airfoils are compared. Using microphone array measurements, it was found that not only the overall sound pressure level, but also the spectral characteristics depend on the parameters of the porous material. While the overall sound pressure level decreases in the order of a few decibel, at lower frequencies the reduction is considerable larger and extends 10 dB in some cases. Additionally, the influence of the material parameters on drag and lift is discussed. The aerodynamic performance of the porous airfoils is in general inferior to that of non-porous airfoils. However, there appear to be sets of material parameters that provide a considerable decrease in sound generation and only a minor degradation of aerodynamic effciency.
BibTeX:
@inproceedings{SarradjGeyer2007,
  author = {Sarradj, E. and Geyer, T.},
  title = {Noise Generation by Porous Airfoils},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)},
  year = {2007},
  url = {http://www.tu-cottbus.de/fakultaet3/fileadmin/uploads/aeroakustik/files/AIAA-2007-3719.pdf}
}
Sarradj E, Geyer T, Brick H, Kirchner K-R and Kohrs T (2012), "Application of Beamforming and Deconvolution Techniques to Aeroacoustic Sources at Highspeed Trains", In NOVEM - Noise and Vibration: Emerging Methods, Sorrento.
BibTeX:
@inproceedings{Sarradj2012b,
  author = {Sarradj, E. and Geyer, T. and Brick, H. and Kirchner, K.-R. and Kohrs, T.},
  title = {Application of Beamforming and Deconvolution Techniques to Aeroacoustic Sources at Highspeed Trains},
  booktitle = {NOVEM - Noise and Vibration: Emerging Methods, Sorrento},
  year = {2012}
}
Sarradj E and Schulze C (2006), "Practical Application of Orthogonal Beamforming", In Proceedings Euronoise 2006.
BibTeX:
@inproceedings{Sarradj2006c,
  author = {Sarradj, E. and Schulze, C.},
  title = {Practical Application of Orthogonal Beamforming},
  booktitle = {Proceedings Euronoise 2006},
  year = {2006}
}
Sarradj E and Schulze C (2006), "Practical Application of Orthogonal Beamforming", EURONOISE 2006., In EURONOISE 2006.
BibTeX:
@conference{SarradjSchulze2006,
  author = {Sarradj, E. and Schulze, C.},
  title = {Practical Application of Orthogonal Beamforming},
  booktitle = {EURONOISE 2006},
  journal = {EURONOISE 2006},
  year = {2006},
  note = {2006-05-30 - 2006-06-01}
}
Sarradj E, Schulze C and Zeibig A (2006), "Aspects of source separation in beamforming", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-03., November, 2006. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: One of the most important elements to consider in the application of beamforming is the identification of sources from the beamforming result. This result is often given in form of a map of sound pressure contributions from a number of locations. While on first look the dominating sources may be easily identified, a number of problems arise during practical application: (a) sources closely spaced cannot be separated due to the width of the directional beam, (b) minor sources cannot be detected at all due to the limited signal-to-noise ratio, (c) it is not possible to separate sound pressure contributions from different source mechanisms. Some signal processing methods to deal with these problems are explained in short. The implications of each this methods are discussed. Practical examples using a 32-microphone array are given.
BibTeX:
@inproceedings{Sarradj_etal2006,
  author = {Sarradj, E. and Schulze, C. and Zeibig, A.},
  title = {Aspects of source separation in beamforming},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://www.bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-03_Sarradj_Schulze_Zeibig.pdf}
}
Sarradj E, Schulze C and Zeibig A (2005), "Identification of Noise Source Mechanisms using Orthogonal Beamforming", In Noise and Vibration: Emerging Methods.
BibTeX:
@inproceedings{Sarradj2005a,
  author = {Sarradj, E. and Schulze, C. and Zeibig, A.},
  title = {Identification of Noise Source Mechanisms using Orthogonal Beamforming},
  booktitle = {Noise and Vibration: Emerging Methods},
  year = {2005}
}
Schlinker RH and Amiet RK (1980), "Refraction and scattering of sound by a shear layer" (3371)
BibTeX:
@techreport{SchlinkerAmiet1980a,
  author = {Schlinker, R. H. and Amiet, R. K.},
  title = {Refraction and scattering of sound by a shear layer},
  year = {1980},
  number = {3371}
}
Schlinker RH and Amiet RK (1980), "Shear Layer Refraction and Scattering of Sound", In 6th AIAA Aeroacoustics Conference, Hartford, Ct, June 4-6, 1980., AIAA Paper 80-0973.
BibTeX:
@inproceedings{SchlinkerAmiet1980b,
  author = {Schlinker, R. H. and Amiet, R. K.},
  title = {Shear Layer Refraction and Scattering of Sound},
  booktitle = {6th AIAA Aeroacoustics Conference, Hartford, Ct, June 4-6, 1980},
  year = {1980}
}
Schmidt R (1986), "Multiple emitter location and signal parameter estimation", IEEE Transactions on Antennas and Propagation. Vol. 34, pp. 276-280.
BibTeX:
@article{Schmidt1986,
  author = {Schmidt, R.},
  title = {Multiple emitter location and signal parameter estimation},
  journal = {IEEE Transactions on Antennas and Propagation},
  year = {1986},
  volume = {34},
  pages = {276--280}
}
Schmidt RO (1982), "A signal subspace approach to multiple emitter location and spectral estimation", SCHMIDT, R.O.: , PhD Thesis, Stanford University (USA), 1982... Thesis at: Stanford University (USA).
BibTeX:
@phdthesis{Schmidt1982,
  author = {Schmidt, R. O.},
  title = {A signal subspace approach to multiple emitter location and spectral estimation},
  journal = {SCHMIDT, R.O.: , PhD Thesis, Stanford University (USA), 1982.},
  school = {Stanford University (USA)},
  year = {1982}
}
Schmidt S (2014), "Reducing Beamforming Calculation Time with GPU Accelerated Algorithms", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-08., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Beamforming algorithms make high demands on the computer hardware and the computation time is an important factor for the assessment of this method. This paper describes techniques for optimizing the implementation of beamforming algorithms in regard to calculation time. The main focus is on using the Graphic Processing Unit for accelerating beamforming. After a brief introduction to general purpose GPU computing, the realization of time-domain, frequency-domain and order-domain beamforming on the GPU is explained. Several benchmarks have been run and the results show that all three algorithms can gain shorter calculation time on the GPU. The tests also examine the differences in performance of the two main development toolkits, CUDA and OpenCL. Furthermore, the impact of the GPU hardware is analysed regarding computational power and scalability.
BibTeX:
@inproceedings{Schmidt2014,
  author = {Schmidt, S.},
  title = {Reducing Beamforming Calculation Time with GPU Accelerated Algorithms},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-08.pdf}
}
Schmitt A and Lamotte L (2010), "Source identification inside cabin using inverse methods", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-05., February, 2010.
Abstract: The presented sound source localization technique is based on the analysis of microphones array measurements. Here, the microphone array is a rigid sphere, which is well adapted to inside cabin acoustic fields (eg. vehicle, industry room…). Calculation points are located on a three dimensional mesh surrounding the measurement array. The method, which extends beamforming’s algorithm capabilities, consists in reconstructing an equivalent source power distribution using a Green’s function transfer matrix and an adapted inversion procedure. Generally speaking, propagation transfer function inversion is an important point when using inverse methods to identify sound sources. It is, for example, responsible for the efficiency of the method and must be adapted to the measured acoustic field. This paper compares two inversion methods, the first being based on a singular value decomposition operation and the second on an iterative algorithm.
BibTeX:
@inproceedings{SchmittLamotte2010,
  author = {Schmitt, A. and Lamotte, L.},
  title = {Source identification inside cabin using inverse methods},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-05.pdf}
}
Schmitz K-P (1993), "Sound Measurements on TRANSRAPID 07 - Methods and Results", In The International Conference on Speedup Technology for Railway and Maglev Vehicles. Vol. 2, pp. 33-38. The Japan Society of Mechanical Engineers.
BibTeX:
@inproceedings{Schmitz1993,
  author = {Schmitz, K.-P.},
  title = {Sound Measurements on TRANSRAPID 07 - Methods and Results},
  booktitle = {The International Conference on Speedup Technology for Railway and Maglev Vehicles},
  publisher = {The Japan Society of Mechanical Engineers},
  year = {1993},
  volume = {2},
  pages = {33--38}
}
Schröder R and Jaeckel O (2012), "Evaluation of beamforming systems", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-26., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The growing number of commercially available beamforming systems and the quite large number of end users and application fields confronts all potential customers with the task of comparing the systems of different suppliers as well as with the problem of evaluating the quality of beamforming solutions in general. This article will point out some of the main problems connected to this practically often difficult task and it also develops some proposals for a more systematic evaluation of acoustic array beamforming systems. Some useful quantities and evaluation methods which seem appropriate for a possible classification of beamforming systems will be proposed and discussed in detail. This discussion shall serve as a first contribution for a future standardisation and hence for the further qualification of acoustic beamforming as a measurement method.
BibTeX:
@inproceedings{SchroederJaeckel2012,
  author = {Schröder, R. and Jaeckel, O.},
  title = {Evaluation of beamforming systems},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-26.pdf}
}
Schröder R, Romenskiy I and Jäckel O (2010), "Alternative methods for the improvement of 2D/3D -microphone array measurements", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-20., February, 2010.
Abstract: Conventional Beamforming maps frequently show a low contrast and an unsatisfying spatial resolution especially at lower frequencies. This paper presents a new method for the improvement of phased array results using a Multi-Modal-Beamforming approach. The method allows the reduction of the main lobe width as well as the suppression of the side lobes of acoustic sources in the map and can thus be applied for the improvement of the usually very bad image contrast in the lower frequency range and also for a better separation of closely lying sources which can not be clearly resolved by simple delay-and-sum Beamforming. An outstanding property of the proposed algorithm is that it yields the possibility of synthesizing nearly arbitrary acoustic maps using a low number of phase mode excitations. The presented method is applicable even for the separation of correlated sources, which is impossible using the conventional Beamforming method.
BibTeX:
@inproceedings{Schroeder_etal2010,
  author = {Schröder, R. and Romenskiy, I. and Jäckel, O.},
  title = {Alternative methods for the improvement of 2D/3D -microphone array measurements},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-20.pdf}
}
Schulte-Werning B, Jäger K, Strube R and L. Willenbrink L (2003), "Recent developments in noise research at Deutsche Bahn (noise asessment, noise source localization and specially monitored track)", J. Sound Vib.. Vol. 267(3), pp. 689-699.
Abstract: To strengthen the environmental friendliness of railway traffic in Germany, Deutsche Bahn (DB) is in the process of performing a major research programme concerning noise reduction. To realize this, the DB ‘Low Noise Railway’ programme deals simultaneously with the noise treatment of trains and the wheel/rail system as well as other topics. The assessment of a particular sound experience as annoying noise is a very personal judgement and cannot be dealt with by physical quantities alone. To permit a better understanding of this phenomenon and to support the legislative authorities, the assessment of noise quality is being investigated in detail. To reduce railway noise, the exact location and the magnitude of the different sound sources have to be known. This can be analyzed with an array of many microphones which has been developed by DB in the last few years. Most recently, DB has developed the acoustic concept of the ‘Specially Monitored Track (SMT)’ into a practical application and is now starting to upgrade SMT to increased performance and at a lower cost.
BibTeX:
@article{Schulte-Werning_etal2003,
  author = {Schulte-Werning, B. and Jäger, K. and Strube, R. and L. Willenbrink, L.},
  title = {Recent developments in noise research at Deutsche Bahn (noise asessment, noise source localization and specially monitored track)},
  journal = {J. Sound Vib.},
  year = {2003},
  volume = {267},
  number = {3},
  pages = {689--699},
  note = {Proceedings of the Seventh International Workshop on Railway Noise},
  doi = {10.1016/S0022-460X(03)00733-8}
}
Schulze C, Sarradj E and Zeibig A (2004), "Characteristics of microphone arrays", In Inter-Noise.
BibTeX:
@inproceedings{Schulze2004,
  author = {Schulze, C. and Sarradj, E. and Zeibig, A.},
  title = {Characteristics of microphone arrays},
  booktitle = {Inter-Noise},
  year = {2004}
}
Schuster B (2009), "Generation of Spurious Modes in Rotated Circular Microphone Array Measurements", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3119., May, 2009.
Abstract: Circular arrays of wall mounted microphones are often used to deduce the circumferential mode content of acoustic fields propagating inside circular or annular ducts. When microphone availability is limited, circular arrays of equally spaced microphones can be rotated to multiple circumferential clocking positions, and the data from multiple clocking positions of the array can be combined together using a reference timing signal to increase the modal analysis resolution when analyzing shaft synchronous signals such as fan tone noise. However, when the data sets from different clocking positions are combined, phase errors are introduced due to the inability to precisely align the time history sequences. These phase errors can result in the generation of spurious modes in the modal decomposition analysis. The mode orders and amplitudes of these modes can be deduced from theoretical considerations. These results can help identify the presence of spurious modes in fan rig modal measurements.
BibTeX:
@inproceedings{Schuster2009,
  author = {Schuster, B.},
  title = {Generation of Spurious Modes in Rotated Circular Microphone Array Measurements},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  year = {2009},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO09_2131/PV2009_3119.pdf}
}
Shanno DF and Phua KH (1980), "Remark on ``Algorithm 500: Minimization of Unconstrained i Multivariate Functions [E4]''", ACM Trans. Math. Softw.. New York, NY, USA Vol. 6(4), pp. 618-622. ACM.
BibTeX:
@article{ShannoPhua1980,
  author = {D. F. Shanno and K. H. Phua},
  title = {Remark on ``Algorithm 500: Minimization of Unconstrained i Multivariate Functions [E4]''},
  journal = {ACM Trans. Math. Softw.},
  publisher = {ACM},
  year = {1980},
  volume = {6},
  number = {4},
  pages = {618--622},
  doi = {10.1145/355921.355933}
}
Shanno DF and Phua KH (1976), "Algorithm 500: Minimization of Unconstrained Multivariate Functions [E4]", ACM Trans. Math. Softw.. New York, NY, USA Vol. 2(1), pp. 87-94. ACM.
BibTeX:
@article{ShannoPhua1976,
  author = {D. F. Shanno and K. H. Phua},
  title = {Algorithm 500: Minimization of Unconstrained Multivariate Functions [E4]},
  journal = {ACM Trans. Math. Softw.},
  publisher = {ACM},
  year = {1976},
  volume = {2},
  number = {1},
  pages = {87--94},
  doi = {10.1145/355666.355673}
}
Shannon D (2008), "Experimental Investigation of Slotted Circulation Control Airfoil Acoustics", In 14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)., AIAA-2008-2815., May, 2008.
Abstract: The objective of this study was to complete an experimental investigation of the noise generated by a dual-slotted Circulation Control (CC) airfoil. It has been well documented that the introduction of fluid at relatively small mass flow rates through a slot at the trailing edge of elliptical airfoils can be advantageous to the lift and drag characteristics of these control surfaces. The noise generation mechanisms associated with such devices, however, are not well understood. The sound generated by a CC model was measured utilizing a microphone array for relatively high Reynolds numbers ( ~ 700,000) and low free stream Mach number ( < 0.1). Sound measurements suggest that the noise generated by the slot-jet flow (with and without external flow) contains distinct spectral features which occur at specific frequencies that do not scale with the slot-jet velocity. When both the external and slot-jet flows were activated a power law velocity scaling of the noise levels was not apparent. The internal cavity resonances associated with the slot-jet plenum were not observed to affect the sound generated by the CC model.
BibTeX:
@inproceedings{Shannon2008,
  author = {Shannon, D.},
  title = {Experimental Investigation of Slotted Circulation Control Airfoil Acoustics},
  booktitle = {14th AIAA/CEAS Aeroacoustics Conference (29th AIAA Aeroacoustics Conference)},
  year = {2008},
  doi = {10.2514/6.2008-2815}
}
Shannon D, Morris S and Mueller T (2005), "Trailing Edge Flow Physics and Acoustics", In 11th AIAA/CEAS Aeroacoustics Conference., AIAA-2005-2957., May, 2005.
BibTeX:
@inproceedings{Shannon_etal2005,
  author = {Shannon, D. and Morris, S. and Mueller, T.},
  title = {Trailing Edge Flow Physics and Acoustics},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference},
  year = {2005},
  doi = {10.2514/6.2005-2957}
}
Sheplak M, Nishida T, Cattafesta III LN and Arnold DP (2002), "MEMS-based acoustic array technology", In AIAA Aerospace Sciences Meeting and Exhibit, 40th, Reno, NV, Jan. 14-17, 2002., AIAA-2002-0253., Jan, 2002.
Abstract: A novel micro-electromechanical system (MEMS)-based directional acoustic array is presented to demonstrate key scaling technologies that can reduce cost, improve speed, and increase mobility over conventional array technologies. The system uses 16 hybrid-packaged piezoresistive silicon microphones mounted to a printed-circuit-board and a high-speed signal processing system to generate the array response over 2400 scan location in under 20 sec. Material construction costs for the array were reduced by two orders of magnitude over conventional array systems. The hybrid microphone packages show an average sensitivity of 831 mV/Pa with matched magnitude (±0.6 dB) and phase (± 1 degree) responses between devices. The measured array response matches the theoretical response over the frequency range of 3 kHz to 8 kHz with a localization error of ± 0.3 in. The array has a minimum detectable signal of 43.5 dB SPL for a 1 Hz bin at 6 kHz and a maximum pressure input of at least 160 dB SPL. These results represent a proof-of-concept
demonstration of a high speed, low cost directional acoustic array system.
BibTeX:
@inproceedings{Sheplak_etal2002,
  author = {Sheplak, M. and Nishida, T. and Cattafesta III, L. N. and Arnold, D. P.},
  title = {MEMS-based acoustic array technology},
  booktitle = {AIAA Aerospace Sciences Meeting and Exhibit, 40th, Reno, NV, Jan. 14-17, 2002},
  year = {2002}
}
Shin H-C, Graham W, Sijtsma P and Andreou C (2006), "Design and Implementation of a Phased Microphone Array in a Closed-Section Wind Tunnel", In 12th AIAA/CEAS Aeracoustics Conference 2006., AIAA-2006-2651., May, 2006.
BibTeX:
@inproceedings{Shin_etal2006,
  author = {Shin, H.-C. and Graham, W. and Sijtsma, P. and Andreou, C.},
  title = {Design and Implementation of a Phased Microphone Array in a Closed-Section Wind Tunnel},
  booktitle = {12th AIAA/CEAS Aeracoustics Conference 2006},
  year = {2006}
}
Sibul LH (1995), "Array processing and generalized inverses", In 29th Asilomar Conference on Signals, Systems and Computers (2-Volume Set). Vol. 1, pp. 438-443.
Abstract: A basic function of array processing is to estimate the spatial location of disturbed or discrete radiating and scattering sources. We show that classical beamformers, optimum array processors, matched field and matched mode processors can be cast into the unified framework of generalized inverse theory.
BibTeX:
@inproceedings{Sibul1995,
  author = {Sibul, L. H.},
  title = {Array processing and generalized inverses},
  booktitle = {29th Asilomar Conference on Signals, Systems and Computers (2-Volume Set)},
  year = {1995},
  volume = {1},
  pages = {438--443},
  doi = {10.1109/ACSSC.1995.540587}
}
Sijtsma P (2012), "Green's Functions for In-Duct Beamforming Applications", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)., AIAA-2012-2248., Jun, 2012.
BibTeX:
@inproceedings{Sitsma2012,
  author = {Sijtsma, P.},
  title = {Green's Functions for In-Duct Beamforming Applications},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)},
  year = {2012},
  doi = {10.2514/6.2012-2248}
}
Sijtsma P (2012), "Circular Harmonics Beamforming with Multiple Rings of Microphones", In 18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)., AIAA-2012-2224., Jun, 2012.
BibTeX:
@inproceedings{Sitsma2012b,
  author = {Sijtsma, P.},
  title = {Circular Harmonics Beamforming with Multiple Rings of Microphones},
  booktitle = {18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference)},
  year = {2012},
  doi = {10.2514/6.2012-2224}
}
Sijtsma P (2010), "AARC Benchmark1 revisited", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-06., February, 2010.
Abstract: In this paper, the first benchmark problem of the 2006 AARC Phased Array Workshop is reconsidered. The challenge was the determination of the spectra emitted by two acoustic
sources from synthetic time data of a small array of microphones. With this benchmark problem, the merits of two new advanced array processing methods are demonstrated. These
methods are CSEM (Cross-Spectral Estimation Method) and CLEAN-SC (CLEAN based on spatial Source Coherence). It was found that both methods are well able to estimate the source spectra. For CSEM it was necessary to use a full CSM (Cross-Spectral Matrix). CLEAN-SC was able to recover the source spectra also when the CSM diagonal was removed.
BibTeX:
@inproceedings{Sijtsma2010,
  author = {Sijtsma, P.},
  title = {AARC Benchmark1 revisited},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-06.pdf}
}
Sijtsma P (2008), "Tutorial: Improving resolution with CLEAN-SC", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008.
BibTeX:
@inproceedings{Sijtsma2008,
  author = {Sijtsma, P.},
  title = {Tutorial: Improving resolution with CLEAN-SC},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  year = {2008},
  url = {http://bebec.eu/Downloads/BeBeC2008/Presentations/BeBeC-2008_Sijtsma_CLEAN_SC.pdf}
}
Sijtsma P (2008), "Acoustic array corrections for coherence loss due to the wind tunnel shear layer", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-15. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: Out-of-flow acoustic array measurements in open jet wind tunnels are hampered by the presence of the turbulent shear layer. Signal coherence between pairs of microphones in the array is reduced because sound from a wind tunnel model passes through the shear layer. As a result, the spatial resolution of the beamforming images is significantly lower than without wind, and integrated sound levels are too low. In this paper, a method is discussed to counteract the effects of this shear layer induced coherence loss. This method features the use of one or more miniature loudspeakers, mounted non-intrusively on a wind tunnel model. By instantaneously measuring the unsteady time delay between such a speaker and each of the microphones, corrections can be made to counteract the coherence loss. Such a method for improving phased array results is already applied successfully in the field of radio astronomy, where a well-known bright star is used to define corrections for the turbulence in the atmosphere. This paper presents an implementation of this “Guide Star” method for acoustic arrays. An application to measurements on an A320 model in the open jet of the DNW-LLF is presented. Provided that a number of conditions are fulfilled, the method proves to work well.
BibTeX:
@inproceedings{Sijtsma2008a,
  author = {Sijtsma, P.},
  title = {Acoustic array corrections for coherence loss due to the wind tunnel shear layer},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://www.bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-15_Sijtsma.pdf}
}
Sijtsma P (2007), "Feasibility of In-Duct Beamforming", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)., AIAA-2007-3696., May, 2007.
Abstract: This paper discusses the possibility of source location by phased array beamforming on fan and stator of turbofan engines using an intake wall-mounted microphone array. To demonstrate the feasibility, beamforming techniques were applied to existing measured data of a circular microphone array in the intake of a fan rig. This array is normally used for azimuthal mode detection. From the measured data set a test case was selected with low engine speed, and with an intake liner between the fan and the array. Beamforming methods with both stationary and rotating focus are applied, and the contributions of tonal noise and broadband noise were separated. Thus, tonal and broadband noise sources can be identified on both fan and stator. The free-field Green’s function is used for the definition of the steering vectors, thereby ignoring duct wall reflections. By a simulation study it is shown that the presence of an intake liner is a necessary condition for obtaining meaningful beamforming results. Further simulations showed that significantly improved beamforming results can be obtained with an in-duct “cage” array consisting of a number of parallel microphone rings.
BibTeX:
@inproceedings{Sijtsma2007,
  author = {Sijtsma, P.},
  title = {Feasibility of In-Duct Beamforming},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)},
  year = {2007}
}
Sijtsma P (2007), "CLEAN Based on Spatial Source Coherence", In 13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007., AIAA Paper 2007-3436. , pp. AIAA-2007-3436.
BibTeX:
@inproceedings{Sijtsma2007a,
  author = {Sijtsma, P.},
  title = {CLEAN Based on Spatial Source Coherence},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference, Rome, Italy, May 21-23, 2007},
  year = {2007},
  pages = {AIAA-2007-3436}
}
Sijtsma P (2007), "CLEAN based on spatial source coherence", International Journal of Aeroacoustics. Vol. 6, pp. 357-374.
BibTeX:
@article{Sijtsma2007b,
  author = {Sijtsma, P.},
  title = {CLEAN based on spatial source coherence},
  journal = {International Journal of Aeroacoustics},
  year = {2007},
  volume = {6},
  pages = {357--374}
}
Sijtsma P (2007), "Feasibility of In-Duct Beamforming", In 13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)., May, 2007.
BibTeX:
@inproceedings{Sijtsma2007c,
  author = {Sijtsma, P.},
  title = {Feasibility of In-Duct Beamforming},
  booktitle = {13th AIAA/CEAS Aeroacoustics Conference (28th AIAA Aeroacoustics Conference)},
  year = {2007},
  doi = {10.2514/6.2007-3696}
}
Sijtsma P and Holthusen H (2003), "Level Estimation of Extended Acoustic Sources Using an Array of Microphones", In 9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003., AIAA Paper 2003-3196.
BibTeX:
@inproceedings{Sijtsma2003,
  author = {Sijtsma, P. and Holthusen, H.},
  title = {Level Estimation of Extended Acoustic Sources Using an Array of Microphones},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003}
}
Sijtsma P and Holthusen H (2003), "Corrections for mirror sources in phased array processing techniques", In 9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003., AIAA-2003-3196., May, 2003.
Abstract: When an aero-acoustic source is close to a reflecting wall, results from conventional phased array beamforming techniques are disturbed by the nearby mirror source, which is coherent with the original source. The recalculated source spectrum tends to deviate from the spectrum of the same source obtained in an anechoic environment. A periodic modulation of the spectrum occurs, which is most prominent at low frequencies. In this paper, a number of non-conventional beamforming techniques to correct for this spectral modulation is investigated. First, a technique is discussed which adds the mirror source to the transmission model. It was found that this technique is not very suitable because of its lack of robustness. Then, a more robust beamforming technique is proposed that minimises the influence of a given mirror source. By this technique, much better results were found. Nevertheless, at low frequencies the method still suffers from lack of robustness. Finally, a modification to this minimisation technique is proposed which preserves the robustness. Using this “controlled minimisation” technique, the best agreement was found between the recalculated spectra of a source close to a wall and the same source in anechoic conditions. The beamforming techniques were applied to array measurements on a calibration source in the DNW Low Speed Wind Tunnel LST.
BibTeX:
@inproceedings{SijtsmaHolthusen2003,
  author = {Sijtsma, P. and Holthusen ,H.},
  title = {Corrections for mirror sources in phased array processing techniques},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003},
  url = {http://www.nlr.nl/smartsite.dws?id=2862}
}
Sijtsma P and Holthusen H (1999), "Source location by phased array measurements in closed wind tunnel test sections", In 5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Wa, May 10-12, 1999., AIAA-1999-1814., May, 1999.
Abstract: The feasibility of high frequency phased array measurements on aircraft scale models in a closed wind tunnel test section was investigated. For that purpose, 100 microphones were built in a 0.6x0.5 m^2 plate. which was installed in a floor panel of the 8x6 m^2 test section of the Large Low-speed Facility of the German Dutch Wind tunnel (DNW-LLF). For the microphone positions a sparse array design was used that minimises side lobes in the beamforming process. To suppress boundary layer noise, the array could optionally be covered with a 0.5 cm thick layer of acoustic foam and a 5% open perforated plate. To assess the effect of wall reflections, tests without wind were performed with a loudspeaker at several positions in the tunnel section. Furthermore, wind tunnel tests were carried out on an Airbus transport aircraft model. It is shown that location of acoustic sources is indeed possible for frequencies between 2 and 30 kHz, but their levels may differ from those measured in an anechoic environment. For the lower frequencies, application of the layer of foam and the perforated plate is beneficial. Finally, it is shown that filtering out the most dominant source can extend the array potential.
BibTeX:
@inproceedings{SijtsmaHolthusen1999,
  author = {Sijtsma, P. and Holthusen, H.},
  title = {Source location by phased array measurements in closed wind tunnel test sections},
  booktitle = {5th AIAA/CEAS Aeroacoustics Conference, Bellevue, Wa, May 10-12, 1999},
  year = {1999}
}
Sijtsma P and Holthusen H (1999), "Source location by phased array measurements in closed wind tunnel test sections" (NLR-TP-99108)
Abstract: The feasibility of high frequency phased array measurements on aircraft scale models in a closed wind tunnel test section was investigated. For that purpose, 100 microphones were built in a 0.6 x 0.5 m2 plate, which was installed in a floor panel of the 8x6 m2 test section of the Large Low-speed Facility of the German Dutch Wind tunnel (DNW-LLF). For the microphone positions a sparse array design was used that minimises side lobes in the beamforming process. To suppress boundary layer noise, the array could optionally be covered with a 0.5 cm thick layer of acoustic foam and a 5% open perforated plate. To assess the effect of wall reflections, tests without wind were performed with a loudspeaker at several positions in the tunnel section. Furthermore, wind tunnel tests were carried out on an Airbus transport aircraft model. It is shown that location of acoustic sources is indeed possible for frequencies between 2 and 30 kHz, but their levels may differ from those measured in an anechoic environment. For the lower frequencies, application of the layer of foam and the perforated plate is beneficial. Finally, it is shown that filtering out the most dominant source can extend the array potential.
BibTeX:
@techreport{SijtsmaHolthusen1999b,
  author = {Sijtsma, P. and Holthusen, H.},
  title = {Source location by phased array measurements in closed wind tunnel test sections},
  year = {1999},
  number = {NLR-TP-99108},
  url = {http://www.nlr.nl/id~4445/l~en.pdf}
}
Sijtsma P, Oerlemans S and Holthusen H (2001), "Location of Rotating Sources by Phased Array Measurements", In 7th AIAA/CEAS Aeroacoustics Conference 28-30 May 2001 Maastricht, Netherlands., AIAA-2001-2167., May, 2001.
Abstract: A method is described for the location of moving sources by a microphone array. This method can be applied to out-of-flow measurements in an open jet wind tunnel. For that purpose, an expression is derived for the pressure Held of a moving monopole in a uniform flow. It is argued that the open jet shear layer does not form a serious obstacle. A technique is described for reconstruction of power spectra with high signal/noise ratio. The method was implemented for rotating sources, resulting in the computer program ROSI ("Rotating Source Identifier")* Applications of ROSI are given for rotating whistles, blades of a helicopter in hover and wind turbine blades. The test with the rotating whistles demonstrated convincingly the capability to reconstruct the emitted sound. On the helicopter blades, rotating broadband noise sources were made clearly visible. On the wind turbine blades, noise emitted from the leading and trailing edge could be distinguished well.
BibTeX:
@inproceedings{Sijtsma_etal2001,
  author = {Sijtsma, P. and Oerlemans, S. and Holthusen, H.},
  title = {Location of Rotating Sources by Phased Array Measurements},
  booktitle = {7th AIAA/CEAS Aeroacoustics Conference 28-30 May 2001 Maastricht, Netherlands},
  year = {2001}
}
Sijtsma P and Stoker R (2004), "Determination of Absolute Contributions of Aircraft Noise Components Using Fly-over Array Measurements", In 10th AIAA/CEAS Aeroacoustics Conference, Manchester, United Kingdom, 10-12 May 2004., AIAA-2004-2958.
Abstract: For wind tunnel array measurements, the source power integration technique has proved to be a valuable technique to determine absolute source levels. This paper describes the extension of the source power integration technique to moving sources, and the application to fly-over array measurements on landing aircraft at Amsterdam Airport Schiphol. The technique is applied in combination with a modified version of the Delay-and-Sum beamforming technique, which includes microphone- and frequency-dependent weight factors. These weight factors are used to correct for microphone spatial density and to account for the effects of coherence loss. This beamforming technique works well in combination with the array design, which consists of a number of concentric rings of microphones, with increasing density towards the center. In this paper, it is demonstrated that the extended source power integration technique is able to determine absolute levels from fly-over array measurements, when it is used in combination with the special beamforming technique and the Schiphol array design. Thus, absolute quantification of difference source regions on an aircraft is feasible. Microphone auto-correlations must be included in the beamforming process in order to obtain correct integrated levels, although acoustic images look better when beamforming is done without auto-correlations. The source power integration technique is applied to a Boeing 737-400, and to an Airbus A340.
BibTeX:
@inproceedings{SijtsmaStoker2004,
  author = {Sijtsma, P. and Stoker, R.},
  title = {Determination of Absolute Contributions of Aircraft Noise Components Using Fly-over Array Measurements},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference, Manchester, United Kingdom, 10-12 May 2004},
  year = {2004}
}
Siller H (2012), "Localisation of sound sources on aircraft in flight", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-01., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Sound sources on aircraft in flight can be localised and analysed using phased microphone arrays. The flight trajectory has to be known in order to reconstruct the signal at the source from the Doppler shifted microphone data and map the sound sources by applying time domain beamforming. Different array types can be used depending on the equipment available, other constraints of the experiment, and the desired spatial resolution and dynamic range of the sound source maps. In order to obtain quantitative results, a deconvolution of the maps with the point spread function of the array has to performed. This compensates the imaging properties of the microphone array. From the deconvoluted source maps, the acoustic power can be integrated over different source regions in order to obtain a ranking of the sources.
BibTeX:
@inproceedings{Siller2012,
  author = {Siller, H.},
  title = {Localisation of sound sources on aircraft in flight},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-01.pdf}
}
Siller HA, Arnold F and Michel U (2001), "Investigation of aero-engine core-noise using a phased microphone array", In 7th AIAA/CEAS Aeroacoustics Conference and Exhibit, Maastricht, Netherlands, May 28-30, 2001, Collection of Technical Papers. Vol. 2 (A01-30800 07-71)., AIAA-2001-2269.
Abstract: The sound radiation from the nozzle, i.e. the core noise, of a BR700 aero-engine is studied with the aid of a phased line array of microphones. The engine was mounted on a noise-test pylon, and the microphone array consisted of 64 microphones laid out on the ground along a line parallel with the jet. The microphone signals and the pressure fluctuations in the combustion chamber of the engine measured with a rumble probe were recorded simultaneously. The sound emitted from the nozzle is studied for emission angles ranging from 60 to 135 degrees relative to the forward direction with a sub-array of 25 microphones. The focused, time shifted signal of the sub-array is used to calculate the coherence with the signal of the rumble probe. The coherence between the microphone signal focused on the nozzle and the rumble probe was found to be surprisingly high for low engine power settings at frequencies below 300Hz. For higher power settings, coherence is considerably reduced. The coherent output power is compared with farfield microphone spectra in order to assess the contribution of the core noise to the total noise emitted by the engine. It may be concluded that at low power settings, where other sound sources are relatively weak, noise originating from the combustion chamber is a major contributor to the noise emitted from the nozzle. The combined array and correlation techniques are shown to be useful tools for core noise investigations.
BibTeX:
@inproceedings{Siller_etal2001,
  author = {Siller, H. A. and Arnold, F. and Michel, U.},
  title = {Investigation of aero-engine core-noise using a phased microphone array},
  booktitle = {7th AIAA/CEAS Aeroacoustics Conference and Exhibit, Maastricht, Netherlands, May 28-30, 2001, Collection of Technical Papers. Vol. 2 (A01-30800 07-71)},
  year = {2001}
}
Siller H, Bassetti A, Davies S and Funke S (2014), "Investigation of the noise emission of the V2500 engine of an
A320 aircraft during ground tests with a line array and SODIX"
, In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-18., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Within the framework of the DLR research project SAMURAI, the jet noise of a an Airbus A320 during ground tests was investigated with a linear microphone array. One of the objectives of SAMURAI was to perform parallel measurements with a microphone array and laser anemometry methods, which required the experiments to be performed in the noise-protection hangar for static engine tests of Lufthansa Technik at Hamburg airport. In order to assess the impact of the room acoustics on the sound field, reference measurements under free-field conditions were performed on the airfield in Cochstedt. The microphone array data was analysed using classical spectral methods. With the SODIX (Source Directivity in the Cross Spectral Matrix) method, equivalent source distributions for different freqency bands and emission directions were calculated from the Cochstedt and Hamburg data. They show sources at the engine inlet, nozzle and along the jet. The main result of a comparative analysis of the data is that the conditions in the hangar are suitable for jet-noise measurements of an aircraft during ground tests.
BibTeX:
@inproceedings{Siller_etal2014,
  author = {Siller, H. and Bassetti, A. and Davies, S. and Funke, S.},
  title = {Investigation of the noise emission of the V2500 engine of an
A320 aircraft during ground tests with a line array and SODIX}, booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014}, publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin}, year = {2014}, url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-18.pdf} }
Siller H, Drescher M, Saueressig G and Lange R (2010), "Fly-over source localisation on a Boeing 747-400", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-13., February, 2010.
Abstract: Fly-over measurements with several Boeing 747-400 aircraft of Lufthansa were performed on the airport of Parchim in September, 2008 in the framework of the German national research project FREQUENZ. The engine acoustics department of the DLR institute of propulsion technology performed array measurements using a microphone array with 238 microphones that were arranged in a multi-arm spiral. The array had an elliptical shape with the major axis in the direction of flight and covered an area of 42 by 35 m. The trajectory of the aircraft was measured with an array of laser distance meters on the ground and with a GPS system on board the aircraft. An extensive data set of over 80 flyovers in different flight configurations has been acquired during the three test days. The results of the beamforming analysis for one fly-over with extended landing gears will be presented together with a description of the experimental set-up and the methods employed during the data reduction.
BibTeX:
@inproceedings{Siller_etal2010,
  author = {Siller, H. and Drescher, M. and Saueressig, G. and Lange, R.},
  title = {Fly-over source localisation on a Boeing 747-400},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-13.pdf}
}
Siller H and Michel U (2002), "Buzz-Saw Noise Spectra and Directivity from Flyover Tests", In 8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002., AIAA-2002-2562.
Abstract: A fly-over noise test with an Airbus A319 was conducted jointly by DLR and Lufthansa with support from Airbus and Snecma. The signals of a large array of 238 electret microphones were recorded. In a first test, the noise emission of each engine was studied by running the other engine with flight-idle power. De-dopplerised narrow-band frequency spectra averaged over a large number of microphones were used. Alternatively, the noise emission from the inlet of each engine was evaluated with both engines at take-off power with the aid of a phased microphone array focused on each moving engine inlet. The results show as expected that buzz-saw noise is mainly radiated in the forward arc. The peaks at multiples of the shaft frequency can easily be identified in the de-dopplerised narrow-band spectra. The directivity of a number of frequency components is evaluated. The characteristics of buzz-saw noise are seen to vary between individual engines and even, for the same engine, between different fly-overs. The resulting directivities also indicate that mode scattering has a large influence on the radiated buzz-saw noise field.
BibTeX:
@inproceedings{SillerMichel2002,
  author = {Siller, H. and Michel, U.},
  title = {Buzz-Saw Noise Spectra and Directivity from Flyover Tests},
  booktitle = {8th AIAA/CEAS Aeroacoustics Conference, Breckenridge, Co, 17-19 June 2002},
  year = {2002},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO02_554/PV2002_2562.pdf}
}
Siller H, Michel U, Zwiener C and Saueressig G (2006), "Reduction of Approach Noise of the MD-11", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2464., May, 2006.
Abstract: The noise emission of the Boeing MD-11 with CF6-80C2 engines can be reduced substantially during the landing approach. This is the result of a flight-test campaign usinjg a phased microphone array, which was performed by Lufthansa and DLR in 2002. The landing noise is dominated by a strong tonal radiation at the blade-passing frequency. Operating the aircraft with the flaps set to 35 degrees rather than to 50 degrees reduces the tone level substantially. The tone vanishes completely, when the wing mounted engines are operated with a lower speed and the tail mounted engine with a higher speed while keeping the flap setting 35 degrees. Implementation of this differential thrust operation in daily routine would require a modification of the thrust schedule and its certification. A further strong tone is emitted from a position close to the main landing gear of the aircraft. Its precise origin is still unclear, but it is assumed that the tone is generated by a cavity in the landing gear and can be eliminated by small modifications. The broad-band noise at frequencies above 3 kHz in the rear arc is dominated by the noise emission from the primary nozzles of the engines. Installation of a hot-stream liner should yield a considerable noise reduction, which would also reduce the take-off noise. The study demonstrates the value of flyover noise testing with phased arrays of microphones, a method that makes it possible to localize the source positions of the dominating sources.
BibTeX:
@inproceedings{Siller_etal2006,
  author = {Siller, H. and Michel, U. and Zwiener, C. and Saueressig, G.},
  title = {Reduction of Approach Noise of the MD-11},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO06_1268/PV2006_2464.pdf}
}
Siller H, Schröder S, Saueressig G and Fröhlich S (2008), "Beamforming on a turbofan engine in an indoor test-facility", In Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008., BeBeC-2008-18. GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper describes the progress of an ongoing project with the ultimate goal to develop a method for acoustic indoor tests of aircraft engines. Measurements with a turbofan aircraft engine in the indoor test-stand of Lufthansa Technik are described. A linear microphone array has been set up using a special arrangement that has been patented by DLR that minimises the effect of reflected sound waves. It is demonstrated that with a beamforming algorithm that uses a small, ’sliding’ sub-array, it is possible to measure differences between the sound fields of different engine modifications.
BibTeX:
@inproceedings{Siller_etal2008,
  author = {Siller, H. and Schröder, S. and Saueressig, G. and Fröhlich, S.},
  title = {Beamforming on a turbofan engine in an indoor test-facility},
  booktitle = {Proceedings on CD of the 2nd Berlin Beamforming Conference, 19-20 February, 2008},
  publisher = {GFaI, Gesellschaft zur Förderung angewandter Informatik e.V., Berlin},
  year = {2008},
  url = {http://www.bebec.eu/Downloads/BeBeC2008/Papers/BeBeC-2008-18_Siller_Schroeder_etal.pdf}
}
Silverman H, Patterson III W and Flanagan J (1999), "The huge microphone array, part 2", IEEE Concurrency. Vol. 7, pp. 32-47.
BibTeX:
@article{Silverman_etal1999,
  author = {Silverman, H.F. and Patterson III, W.R. and Flanagan, J.L.},
  title = {The huge microphone array, part 2},
  journal = {IEEE Concurrency},
  year = {1999},
  volume = {7},
  pages = {32--47}
}
Silverman H, Patterson III W and Flanagan J (1998), "The huge microphone array", IEEE Concurrency. Vol. 6, pp. 36.
BibTeX:
@article{Silverman_etal1998,
  author = {Silverman, H.F. and Patterson III, W.R. and Flanagan, J.L.},
  title = {The huge microphone array},
  journal = {IEEE Concurrency},
  year = {1998},
  volume = {6},
  pages = {36}
}
Simley E, Moriarty P and Palo S (2010), "Aeroacoustic Noise Measurements of a Wind Turbine with BSDS Blades Using an Acoustic Array", In 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2010., AIAA-2010-642., January, 2010.
Abstract: Environmental noise restrictions play a role in the performance of wind turbines and the dominant source of noise on modern turbines is aeroacoustic noise produced by the blades. A 32 sensor acoustic array has been developed in cooperation between the National Renewable Energy Laboratory (NREL) and the University of Colorado to conduct measurements of aeroacoustic noise from a 100 kW wind turbine. The array is capable of broadband measurements from 125 Hz to 8 kHz and can locate noise sources with a spatial resolution of 2 meters. Successful noise measurements have been made on a 36.4 meter hub height wind turbine at the National Wind Technology Center (NWTC) in Colorado. Currently the array is deployed at the USDA Agricultural Research Service in Bushland, Texas. Sandia National Laboratories is field testing the BSDS blades on a 23 meter hub height turbine and the array is being used to study their noise signature. Trailing edge noise near the blade tip has traditionally been the focus of acoustic array field experiments, but a goal of this test campaign is to observe the inboard sections of the blades as well as the tip region. The many challenges in designing an array for broadband analysis of small wind turbines using a limited number of sensors are presented here along with an overview of the general design process. Initial results from the Bushland, TX field measurements are provided including analysis of low frequency inboard blade noise and higher frequency noise near the blade tip. Noise near the blade tip is strongest on the downward half cycle of rotation as expected, while the inboard noise is present at all rotor azimuth angles.
BibTeX:
@inproceedings{Simley_etal2010,
  author = {Simley, E. and Moriarty, P. and Palo, S.},
  title = {Aeroacoustic Noise Measurements of a Wind Turbine with BSDS Blades Using an Acoustic Array},
  booktitle = {48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2010},
  year = {2010},
  url = {http://pdf.aiaa.org/preview/2010/CDReadyMASM10_1812/PV2010_642.pdf}
}
Skofronick-Jackson GM and Gasiewski AJ (1995), "A CLEAN-based iterative nonlinear statistical rain rate retrieval algorithm", In Proceedings of the 1995 International Geosciences and Remote Sensing Symposium., Proceedings of the 1995 International Geosciences and Remote Sensing Symposium, pp. 1898--1900. , pp. 1898-1900.
BibTeX:
@inproceedings{SkofronickGasiewski95,
  author = {Skofronick-Jackson, G. M. and Gasiewski, A. J.},
  title = {A CLEAN-based iterative nonlinear statistical rain rate retrieval algorithm},
  booktitle = {Proceedings of the 1995 International Geosciences and Remote Sensing Symposium},
  year = {1995},
  pages = {1898--1900}
}
Snellen M, Domhof J, Koelewijn A and Smeur E (2012), "Phased array B737 fly over measurements for assessing noise level variations", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-03., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
BibTeX:
@inproceedings{Snellen_etal2012,
  author = {Snellen, M. and Domhof, J. and Koelewijn, A. and Smeur, E.},
  title = {Phased array B737 fly over measurements for assessing noise level variations},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-03.pdf}
}
Snellen M, Simons D and van Midden L (2014), "High-Resolution Fly-Over Beamforming Using a Practical Array", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-17., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: I
BibTeX:
@inproceedings{Snellen_etal2014,
  author = {Snellen, M. and Simons, D.G. and van Midden, L.},
  title = {High-Resolution Fly-Over Beamforming Using a Practical Array},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Presentations/BeBeC-2014-17.pdf}
}
Soderman P and Noble SC (1974), "A directional microphone array for acoustic studies of wind tunnel models", In 8th AIAA Aerodynamic Testing Conference, Bethesda, Md. July 8-10, 1974., AIAA-1974-0640., July, 1974.
BibTeX:
@inproceedings{SodermanNoble1974,
  author = {Soderman, P.T. and Noble, S. C.},
  title = {A directional microphone array for acoustic studies of wind tunnel models},
  booktitle = {8th AIAA Aerodynamic Testing Conference, Bethesda, Md. July 8-10, 1974},
  year = {1974}
}
Soderman PT and Allen CS (2002), "Microphone Measurements In and Out of Airstream", In Aeroacoustic Measurements. , pp. 1-61. Springer-Verlag.
BibTeX:
@incollection{SodermanAllen2002,
  author = {Soderman, P. T. and Allen, C. S.},
  editor = {Mueller, T. J.},
  title = {Microphone Measurements In and Out of Airstream},
  booktitle = {Aeroacoustic Measurements},
  publisher = {Springer-Verlag},
  year = {2002},
  pages = {1--61}
}
Soderman PT, Kafyeke F, Boudreau J, Burnside NJ, Jaeger SM and Chandrasekharan R (2004), "Airframe noise study of a Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-foot wind tunneJ", Int. J. Aeroacoustics., January, 2004. Vol. 3(1), pp. 1-42.
Abstract: An acoustic and aerodynamic experimental study was conducted of a 7%-scale unpowered Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-Foot Wind Tunnel for the purpose of identifying and attenuating airframe noise sources. Simulated landing, takeoff and approach configurations were evaluated at Mach 0.22 and 0.26. With a phased-microphone array mounted in the ceiling over the inverted model, various noise sources in the high-lift system, landing gear, fins, and other miscellaneous components were located and compared for sound level and frequency at one flyover location. Numerous model modifications and noise-alleviation devices were evaluated. Simultaneous with acoustic measurements, aerodynamic forces were recorded to document aircraft conditions and any performance changes caused by the geometric modifications. Such performance changes
were small and are not reported here. Ten airframe noise sources were identified that might be important to approach and landing noise of the full-scale aircraft The top five noise sources were: a) slat gap, b) main gear, c) flap tips at wing crank, d) flap inboard gap, and e) slat inboard tip. Relative strengths of these sources were documented along with their dependence on aircraft configuration and operating condition. Although the data were scaled to full-scale frequencies, no extrapolation to full-scale flyover was attempted.
BibTeX:
@article{Soerman_etal2004,
  author = {Soderman, P. T. and Kafyeke, F. and Boudreau, J. and Burnside, N. J. and Jaeger, S. M. and Chandrasekharan, R.},
  title = {Airframe noise study of a Bombardier CRJ-700 aircraft model in the NASA Ames 7- by 10-foot wind tunneJ},
  journal = {Int. J. Aeroacoustics},
  year = {2004},
  volume = {3},
  number = {1},
  pages = {1--42},
  doi = {10.1260/147547204323022248}
}
Soderman PT and Noble SC (1975), "Directional Microphone Array for Acoustic Studies of Wind Tunnel Models", Journal of Aircraft. Vol. 12, pp. 168-173.
Abstract: An end-fire microphone array that utilizes a digital time delay system has been designed, fabricated, and evaluated for measuring noise in wind tunnels. The directional response of both a four- and eight-element linear array of microphones has enabled substantial rejection of background noise and reverberations in the NASA Ames 40- by 80-ft Wind Tunnel. In addition, it is estimated that four- and eight-element arrays reject 6 and 9 dB, respectively, of microphone wind noise, as compared with a conventional omnidirectional microphone with nose cone. Array response to two types of jet engine models in the wind tunnel is presented. Comparisons are made of array response to loudspeakers in the wind tunnel and in freefield.
BibTeX:
@article{SodermanNoble1975,
  author = {Soderman, P. T. and Noble, S. C.},
  title = {Directional Microphone Array for Acoustic Studies of Wind Tunnel Models},
  journal = {Journal of Aircraft},
  year = {1975},
  volume = {12},
  pages = {168--173},
  doi = {10.2514/3.59813}
}
Spalt T, Fulelr C and Brooks T (2011), "A Background Noise Reduction Technique using Adaptive Noise Cancellation for Microphone Arrays", In 17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011., AIAA-2011-2715., June, 2011.
Abstract: Background noise in wind tunnel environments poses a challenge to acoustic measurements due to possible low or negative Signal to Noise Ratios (SNRs) present in the testing environment. This paper overviews the application of time domain Adaptive Noise Cancellation (ANC) to microphone array signals with an intended application of background noise reduction in wind tunnels. An experiment was conducted to simulate background noise from a wind tunnel circuit measured by an out-of-flow microphone array in the tunnel test section. A reference microphone was used to acquire a background noise signal which interfered with the desired primary noise source signal at the array. The technique’s efficacy was investigated using frequency spectra from the array microphones, array beamforming of the point source region, and subsequent deconvolution using the Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) algorithm. Comparisons were made with the conventional techniques for improving SNR of spectral and Cross-Spectral Matrix subtraction. The method was seen to recover the primary signal level in SNRs as low as -29 dB and outperform the conventional methods. A second processing approach using the center array microphone as the noise reference was investigated for more general applicability of the ANC technique. It outperformed the conventional methods at the -29 dB SNR but yielded less accurate results when coherence over the array dropped. This approach could possibly improve conventional testing methodology but must be investigated further under more realistic testing conditions.
BibTeX:
@inproceedings{Spalt_etal2011,
  author = {Spalt, Taylor and Fulelr,Christopher and Brooks,Thomas},
  title = {A Background Noise Reduction Technique using Adaptive Noise Cancellation for Microphone Arrays},
  booktitle = {17th AIAA/CEAS Aeroacoustics Conference (32nd AIAA Aeroacoustics Conference), Portland, Oregon, June 5-8, 2011},
  year = {2011}
}
Steinberg BD (1976), "Principles of Aperture and Array System Design" John Wiley & Sons, New York.
BibTeX:
@book{Steinberg1976,
  author = {Steinberg, B. D.},
  title = {Principles of Aperture and Array System Design},
  publisher = {John Wiley & Sons, New York},
  year = {1976}
}
Stier J and Beilschmidt M (2012), "Generating train side views from video sequences for microphone array pass-by measurements", In Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012., BeBeC-2012-27., February, 2012. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: A significant field of application for microphone arrays is the pass-by measurement of moving objects, mainly trains. In a former article, a special time-domain beamforming algorithm has been introduced which is able to evaluate whole pass-by measurements with respect to computational performance and memory. The evaluation results in a sound pressure level mapping of the train passing. But this mapping only shows the sound sources and their positions represented by coordinate values resulting in interpretation difficulties. A possible solution is the overlay of the sound pressure level mapping with a sketch or a picture of the whole train side view. Since this kind of picture is only available in very few cases or only for single parts of the train, an approach was developed which allows the picture generation of a train side view independently from its composition. In addition to the array measurements, the train’s passing is recorded with a video camera simultaneously. By analyzing the video frames with the SIFT algorithm and combining them based on the gained information, a side view picture of the whole train can be created. The approach presented, including its advantages and requirements, is described in detail. Additionally, further developments are exposed and the capabilities of this approach are demonstrated with an example taken from a variety of measurements completed so far.
BibTeX:
@inproceedings{StierBeischmmidt2012,
  author = {Stier, J. and Beilschmidt, M.},
  title = {Generating train side views from video sequences for microphone array pass-by measurements},
  booktitle = {Proceedings on CD of the 4th Berlin Beamforming Conference, 22-23 February 2012},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2012},
  url = {http://bebec.eu/Downloads/BeBeC2012/Papers/BeBeC-2012-27.pdf}
}
Stier J, Hahn C, Zechel G and Beitelschmidt M (2014), "Computational Optimization of a Time-Domain Beamforming Algorithm Using CPU and GPU", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-09., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: In 2010, a special time-domain beamforming algorithm was presented at the Berlin Beamforming Conference [3]. This algorithm is primarily designed for the sound source localization on moving objects with known velocity (e.g. freight trains). By determining the object trajectory, the acoustic map’s quality can be improved with respect to the Doppler effect. The bottleneck of the algorithm is the time-consuming computational evaluation. Although computational effiency was considered in the algorithm’s first implementation, it can take on hour or more to calculate an acoustic map for a passing train on a regular personal computer. There are several factors which affect the evaluation time, e.g. sampling rate, train speed or the train’s length.
This paper mainly focusses on the computational implementation of the time-domain beamforming algorithm using CPU (Central Processing Unit) and GPU (Graphics Processing Unit). In general, the implementation on a CPU is rather straight foward if common parallelization libraries are used (e.g. OpenMP), offering only a few variation opportunities. The realizable speed-up is proportional to the number of physical cores in a CPU, and can attain a factor of 8 on recent workstations. Implementing the beamforming algorithm on a GPU with CUDA (Compute Unified Device Architecture) is more complicated and requires substantial knowledge of the GPU’s processor architecture. Nevertheless, speed-ups of 30 times or even more compensate the high implementation effort. Additionally, a modification of the algorithm according to [3] is presented. Specific calculation coefficients called ”beamfactors” are introduced, which represent the shading factors in time-domain beamforming. Precomputing those factors before beamforming can reduce the evaluation time by a factor of 2, regardless of the computational implementation and the computer system used. Although the beamfactors-algorithm offers a sufficient reduction of computational costs, it has been parallelized on CPU and GPU as well.
BibTeX:
@inproceedings{Stier_etal2014,
  author = {Stier, J. and Hahn, C. and Zechel, G. and Beitelschmidt, M.},
  title = {Computational Optimization of a Time-Domain Beamforming Algorithm Using CPU and GPU},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-09.pdf}
}
Stoker R and Guo Y (2004), "Airframe Noise Source Locations of a 777 Aircraft in Flight and Comparison with Past Model-Scale Tests", In 10th AIAA/CEAS Aeroacoustics Conference, Manchester, United Kingdom, 10-12 May 2004., AIAA-2004-3232.
BibTeX:
@inproceedings{StokerGuo2004,
  author = {Stoker, R. and Guo, Y.},
  title = {Airframe Noise Source Locations of a 777 Aircraft in Flight and Comparison with Past Model-Scale Tests},
  booktitle = {10th AIAA/CEAS Aeroacoustics Conference, Manchester, United Kingdom, 10-12 May 2004},
  year = {2004}
}
Stoker RW, Guo Y, Streett C and Burnside N (2003), "Airframe Noise Source Locations of a 777 Aircraft in Flight and Comparisons with Past Model-Scale Tests", In 9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003., AIAA-2003-3232., May, 2003.
Abstract: In September 2001, Boeing performed a Noise Technology Flight Test in Glasgow, Montana. During this flight test, Boeing acquired data for several flights with the flaps deployed and the engines at idle to measure airframe noise. Data were acquired with both free-field microphones and with a microphone phased array. The flight test microphone phased array data have been compared with data from two past model-scale tests. One test, using a 6.3%-scale model, was performed in Boeing’s Low Speed Aeroacoustic Facility. The other test, using a 26%-scale model, was performed in NASA Ames’ 40ftx80ft wind tunnel. Results from the tests show many similarities, but at least one major discrepancy. Both model-scale tests show significant amounts of noise being generated from the leading edge slat. The full-scale flight test results show almost no noise being generated from the leading edge. The exact cause of this discrepancy is unknown, but could be caused by Reynolds number effects, detail modeling issues, or beamforming analysis issues.
BibTeX:
@inproceedings{Stoker_etal2003,
  author = {Stoker, R. W. and Guo, Y. and Streett, C. and Burnside, N.},
  title = {Airframe Noise Source Locations of a 777 Aircraft in Flight and Comparisons with Past Model-Scale Tests},
  booktitle = {9th AIAA/CEAS Aeroacoustics Conference and Exhibit, Hilton Head, South Carolina, May 12-14, 2003},
  year = {2003}
}
Stoker RW, Underbrink JR and Neubert GR (2001), "Investigations of airframe noise in pressurized wind tunnels", In AIAA/CEAS Aeroacoustics Conference and Exhibit, 7th, Maastricht, Netherlands, May 28-30, 2001; Collection of Technical Papers.. Vol. Vol. 1 (A01-30800 07-71)
Abstract: Phased arrays are increasingly being used to examine noise sources in closed-wall wind tunnels. With improved capabilities of phased arrays, it is now possible to acquire acoustic data at higher Reynolds numbers using pressurized wind tunnels. Over the last five years, Boeing has performed several airframe noise tests in pressurized wind tunnels. Results are presented from airframe noise investigations done in three different pressurized wind tunnels: a DC-10 configuration examined in NASA Ames' 12-ft wind tunnel; a simple landing gear model examined in the NASA Langley's Low Turbulence Pressure Tunnel; a 747-400 examined in DeRA's 5m pressure tunnel. The investigations show that airframe noise can be successfully measured in pressurized wind tunnels. The experimental results indicate that airframe noise sources can depend on Reynolds number.
BibTeX:
@inproceedings{Stoker_etal2001,
  author = {Stoker, R. W. and Underbrink, J. R. and Neubert, G. R.},
  title = {Investigations of airframe noise in pressurized wind tunnels},
  booktitle = {AIAA/CEAS Aeroacoustics Conference and Exhibit, 7th, Maastricht, Netherlands, May 28-30, 2001; Collection of Technical Papers.},
  year = {2001},
  volume = {Vol. 1 (A01-30800 07-71)},
  note = {AIAA-2001-2107}
}
Storms BL, Ross JC, Horne WC, Hayes JA, Dougherty RP, Underbrink JR, Scharpf DF and Moriarty PJ (1998), "An Aeroacoustic Study of an Unswept Wing With a Three-Dimensional High-Lift System" National Aeronautics and Space Administration, Ames Research Center, Moffett Field, California 93035-1000, February, 1998. (NASA/TM-1998-112222)
Abstract: Experimental and computational results are presented for the aerodynamics and acoustics of an upswept wing with a half-span flap and both a full- and three-quarter span slat. The wing spanned the wind tunnel test section with no exposed wing tip. Concurrent aerodynamic and acoustic measurements were obtained for high-lift riggings representative of landing-approach configurations. Phased microphone array measurements identified two noise sources at the mid-span flap tip that were approximately equal in intensity at 7 kHz. The noise source at the flap forward side edge is dominant at higher frequencies, while the source from the flap aft upper surface is dominant at lower frequencies. The resulting overall spectra generaily decay monotonically with a peak frequency less than 2 kHz, since no peak was evident in the measurement range from 2-38 kHz. Both flap lift and flap-tip noise increase with increasing flap deflection. Raking the flap tip relative to the freestream flow yielded significant changes in the flap-tip vortex formation and resulting noise level. A flap-tip noise model based on flap-tip velocities and flow angles accurately predicted the change in noise with flap deflection and rake-angle variation. A flap-tip fence and porous flap tip both yielded significant overall noise reduction of 3 dB and 4-8 dB, respectively. Two noise sources were identified for the slat. Slat-gap noise was dominant for a low slat loading while slat-tip noise was significant at a high slat loading. The slat-tip flow field is similar to that of the flap tip, and a slat-tip fence resulted in significant noise reduction of 3-6 dB. Slat-gap noise is apparently associated with a feedback mechanism between the recirculating flow in the slat cove and the high-velocity flow through the slat gap. Serration of the slat trailing edge yielded a peak noise reduction of 18 dB while serration of the slat cusp was significantly less effective. Unsteady-pressure and hot-wire measurements revealed important details of both the flap and slat flow structures. Component interactions were found to be small (less than 2 dB) between the flap and slat noise sources.
BibTeX:
@techreport{Storms_etal1998,
  author = {Storms, B. L. and Ross, J. C. and Horne, W. C. and Hayes, J. A. and Dougherty, R. P. and Underbrink, J. R. and Scharpf, D. F. and Moriarty, P. J.},
  title = {An Aeroacoustic Study of an Unswept Wing With a Three-Dimensional High-Lift System},
  year = {1998},
  number = {NASA/TM-1998-112222}
}
Strand ON (1971), "Numerical Study of the Gain Pattern of a Shielded Acoustic Antenna", J. Acoust. Soc. Am.., June, 1971. Vol. 49(6A), pp. 1698-1703.
Abstract: The farfield gain pattern of a shielded acoustic antenna is studied numerically by the use of Kirchhoff's integral. Circular symmetry and perfectly absorbing walls are assumed. Results are reported for a frequency of 2 kHz.
BibTeX:
@article{Strand1971,
  author = {Strand, O. N.},
  title = {Numerical Study of the Gain Pattern of a Shielded Acoustic Antenna},
  journal = {J. Acoust. Soc. Am.},
  year = {1971},
  volume = {49},
  number = {6A},
  pages = {1698--1703}
}
Sutcliff D, Dougherty RP and Walker B (2010), "Evaluating the Acoustic Effect of Over-the-Rotor Foam-Metal-Liner Installed on a Low Speed Fan Using Virtual Rotating Microphone Imaging", In 16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010., AIAA-2010-3800., June, 2010.
Abstract: An in-duct beam-forming technique for imaging rotating broadband fan sources has been used to evaluate the acoustic characteristics of a Foam-Metal Liner installed Over-the-Rotor of a low-
speed fan. The NASA Glenn Research Center’s Advanced Noise Control Fan was used as a test bed. A duct wall-mounted phased array consisting of several rings of microphones was employed. The data are mathematically re-sampled in the fan rotating reference frame and subsequently used in a conventional beam-forming technique. The steering vectors for the beamforming technique are derived from annular duct modes, so that effects of reflections from the duct walls are reduced.
BibTeX:
@inproceedings{Sutcliff_etal2010,
  author = {Sutcliff, D. and Dougherty , R. P. and Walker, B.},
  title = {Evaluating the Acoustic Effect of Over-the-Rotor Foam-Metal-Liner Installed on a Low Speed Fan Using Virtual Rotating Microphone Imaging},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, Stockholm, Sweden, June 7-9, 2010},
  year = {2010}
}
Suzuki T (2011), "L1 generalized inverse beam-forming algorithm resolving coherent/incoherent, distributed and multipole sources", J. Sound Vib.., August, 2011. Vol. 330, pp. 5835-5851.
Abstract: To resolve coherent/incoherent, distributed/compact, and multipole aerodynamic-sound sources with phased-array pressure data, a new source-detection algorithm is developed based on L1 generalized inverse techniques. To extract each coherent signal, a cross spectral matrix is decomposed into eigenmodes. Subsequently, the complex source-amplitude distribution that recovers each eigenmode is solved using generalized inverse techniques with reference solutions which include multipoles as well as a monopole. Namely, the source distribution consisting of pre-defined source types is solved as an L1 norm problem using iteratively re-weighted least squares (IRLS). The capabilities of the proposed algorithm are demonstrated using various benchmark problems to compare the results with several existing beam-forming algorithms, and it is found that distributed sources as well as dipoles with arbitrary orientation can be identified regardless of coherency with another source. The resolution is comparable to existing deconvolution techniques, such as DAMAS or CLEAN, and the computational cost is only several times more than that of DAMAS2. The proposed algorithm is also examined using previous model-scale test data taken in an open-jet wind-tunnel for a study on jet–flap interaction, and some indication of dipole radiation is discerned near the flap edge.
BibTeX:
@article{Suzuki2011,
  author = {Suzuki, Takao},
  title = {L1 generalized inverse beam-forming algorithm resolving coherent/incoherent, distributed and multipole sources},
  journal = {J. Sound Vib.},
  year = {2011},
  volume = {330},
  pages = {5835--5851},
  doi = {10.1016/j.jsv.2011.05.021}
}
Suzuki T (2010), "DAMAS2 Using a Point-Spread Function Weakly Varying in Space", AIAA J.. Vol. 48(9), pp. 2165-2169.
BibTeX:
@article{Susuki2010,
  author = {Suzuki, T.},
  title = {DAMAS2 Using a Point-Spread Function Weakly Varying in Space},
  journal = {AIAA J.},
  year = {2010},
  volume = {48},
  number = {9},
  pages = {2165--2169},
  doi = {10.2514/1.51674}
}
Suzuki T (2010), "A review of diagnostic studies on jet-noise sources and generation mechanisms of subsonically convecting jets", Fluid Dyn. Res.. Vol. 42(1), pp. 014001.
Abstract: Many efforts have been made to reveal the jet-noise generation mechanisms for more than half a century. Although jet-noise phenomena of some specific types have been well understood, the mechanism of the most fundamental one, i.e. mixing noise, has not been revealed, or at least none of the claims or hypotheses have been widely accepted. To overcome this hurdle, recent acoustic- and flow-diagnostic techniques have been applied to near- and far-field measurements, and the relation between large-scale flow structures and far-field sound as well as properties of jet-noise sources have been investigated in many studies. In this paper, these diagnostic studies are reviewed, particularly focusing on the multi-point measurements including phased-array techniques, and the studies on subsonically convecting round jets, i.e. jets whose phase velocity is less than the speed of sound, are summarized.
BibTeX:
@article{Suzuki2010,
  author = {Suzuki, T.},
  title = {A review of diagnostic studies on jet-noise sources and generation mechanisms of subsonically convecting jets},
  journal = {Fluid Dyn. Res.},
  year = {2010},
  volume = {42},
  number = {1},
  pages = {014001},
  doi = {10.1088/0169-5983/42/1/014001}
}
Suzuki T (2010), "Noise Sources of Subsonic Round Jets Investigated Using Phased Microphone Arrays", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3958., June, 2010.
Abstract: To investigate the noise-source properties of a subsonic round jet at low frequencies (0.25 ≤ St ≤ 0.8), two sets of phased-array data studied in the past, one from a mid-field acoustic array and the other from a near-field hydrodynamic array, are post-processed. The acoustic data are processed with a generalized-inverse beam-forming algorithm, capable of resolving multipole distributed sources with high resolution regardless of the coherency. The hydrodynamic data are used to construct disturbances associated with instability waves, and acoustic fields are calculated by imposing these disturbances as near-field boundary values. Source maps produced by L3/2 generalized-inverse beam-forming indicate that acoustic fields upstream of the peak angle are recoverable from detected source distributions, while downstream sound is not representable with superposition up to octupoles even if taking refraction into account. The boundary-value problem demonstrates that the jet-spreading effect, which is included via streamwise growth and decay of the eigenfunctions from linear stability analysis, is too weak to explain the downstream-sound generation. Direct projection from the hydrodynamic data indicates that the downstream sound is governed by disturbances beyond the potential-core end, whose decay rate is gentler and phase velocity is faster than the predictions based on linear stability analysis using PIV mean-flow data.
BibTeX:
@inproceedings{Suzuki2010b,
  author = {Suzuki, T.},
  title = {Noise Sources of Subsonic Round Jets Investigated Using Phased Microphone Arrays},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Suzuki T (2008), "Generalized Inverse Beam-forming Algorithm Resolving Coherent/Incoherent, Distributed and Multipole Sources", AIAA-2008-2954. May, 2008.
Abstract: To resolve coherent (or incoherent), distributed (or compact), and multipole aerodynamic-sound sources with phased-array pressure data, a new source-detection algorithm is developed based on generalized inverse techniques. To extract each coherent signal, a cross spectral matrix is decomposed into eigenmodes. Subsequently, the complex source-amplitude distribution that recovers an eigenmode is solved using generalized inverse techniques with reference solutions which include multipoles as well as a monopole. The source distribution consisting of pre-defined source types is first solved with a least square approach and then iteratively narrowed from an underdetermined to an overdetermined problem. The capabilities of the proposed algorithm are demonstrated using various model problems by comparing with several existing beam-forming algorithms, and it is found that distributed sources as well as dipoles with arbitrary orientation can be identified regardless of coherency with another source. The resolution is nearly comparable to DAMAS2, and the computational cost is only few times more than that of existing iterative approaches. The proposed algorithm is also examined using previous model-scale test data taken in an open-jet wind-tunnel from a study on jet-flap interaction, and some indication of dipole radiation is discerned near the flap edge.
BibTeX:
@misc{Suzuki2008,
  author = {Suzuki, T.},
  title = {Generalized Inverse Beam-forming Algorithm Resolving Coherent/Incoherent, Distributed and Multipole Sources},
  howpublished = {AIAA-2008-2954},
  year = {2008}
}
Suzuki T (2006), "Identification of multipole noise sources in low Mach number jets near the peak frequency", Journal of Acoustical Society of America. Vol. 119(6), pp. 3649-3659.
Review: A beam-forming algorithm is developed to identify noise source structures in low Mach number jets near the peak frequency. Pressure data from a conical phased microphone array are Fourier decomposed in the azimuthal direction, and the dominant eigenvectors of a cross-spectral matrix are extracted for each azimuthal mode; subsequently, a robust adaptive beam-forming technique is applied to a cross-spectral matrix reconstructed from the primary eigenmodes. The coherent sound signals are then decomposed into multipoles in spherical coordinates, and the primary mode and its axial position are identified for the axisymmetric and first two azimuthal modes. The proposed beam-forming algorithm is applied to an unheated round jet over a range of Mach numbers and frequencies. The result indicates that at low Mach numbers, the second zenithal mode (i.e., quadrupole) appears to be dominant for each azimuthal mode, and the source position slightly shifts downstream with increasing azimuthal mode number.
BibTeX:
@article{Suzuki2006,
  author = {Suzuki, Takao},
  title = {Identification of multipole noise sources in low Mach number jets near the peak frequency},
  journal = {Journal of Acoustical Society of America},
  year = {2006},
  volume = {119},
  number = {6},
  pages = {3649--3659}
}
Suzuki T and Day B (2013), "Comparative study on mode-identification algorithms using a phased-array system in a rectangular duct", J. Sound Vib..
Abstract: To identify multiple acoustic duct modes, conventional beam-forming, CLEAN as well as L2 (i.e. pseudo-inverse) and L1 generalized-inverse beam-forming are applied to phased-array pressure data. A tone signal of a prescribed mode or broadband signal is generated upstream of a curved rectangular duct, and acoustic fields formed in both upstream and downstream stations of the test section are measured with identical wall-mounted microphone arrays. Sound-power distributions of several horizontal and vertical modes including upstream- and downstream-propagating waves can be identified with phased-array techniques, and the results are compared among the four approaches. The comparisons using synthetic data demonstrate that the L2 generalized-inverse algorithm can sufficiently suppress undesirable noise levels and detect amplitude distributions accurately in over-determined cases (i.e. the number of microphones is more than the number of cut-on modes) with minimum computational cost. As the number of cut-on modes exceeds the number of microphones (i.e. under-determined problems), the L1 algorithm is necessary to retain better accuracy. The comparison using test data acquired in the curved duct test rig (CDTR) at NASA Langley Research Center suggests that the L1 / L2 generalized-inverse approach as well as CLEAN can improve the dynamic range of the detected mode by as much as 10 dB relative to conventional beam-forming even with mean flow of M=0.5.
BibTeX:
@article{Suzuki_Day_2013,
  author = {Suzuki, T. and Day, B.J.},
  title = {Comparative study on mode-identification algorithms using a phased-array system in a rectangular duct},
  journal = {J. Sound Vib.},
  year = {2013},
  doi = {10.1016/j.jsv.2013.06.027}
}
Suzuki Y, Imaizumi Y, Kawakami Y and Araki K (2002), "Beam forming for large-scale phased array antennas", In 20th AIAA International Communication Satellite Systems Conference and Exhibit, 12-15 May 2002, Montreal, Quebec, Canada., AIAA-2002-1987., May, 2002.
Abstract: For high-data-rate satellite communication systems, the satellite must need high performance onboard equipment. To improve the onboard antenna performance in higher frequency band, the circuits scale of active phased array antennas take a tendency to become large. This paper presents a novel beam forming technique for onboard large-scale active phased array antennas. The proposed technique uses fewer phase control circuits than the conventional technique. The proposed technique is validated by antenna pattern simulations. The design of an onboard large-scale phased-array-fed reflector antenna based on the proposed technique is described for high-data-rate satellite communication systems.
BibTeX:
@inproceedings{Suzuki_etal2002,
  author = {Suzuki, Y. and Imaizumi, Y. and Kawakami, Y. and Araki, K.},
  title = {Beam forming for large-scale phased array antennas},
  booktitle = {20th AIAA International Communication Satellite Systems Conference and Exhibit, 12-15 May 2002, Montreal, Quebec, Canada},
  year = {2002},
  url = {http://pdf.aiaa.org/preview/CDReadyMICSSC02_586/PV2002_1987.pdf}
}
Takano Y (1998), "X-shaped two-dimensional microphone array systems for measuring noise-source distribution on moving vehicles", JSME International Journal Series C - Mechanical Systems Machine Elements and Manufacturing. Vol. 41, pp. 46-50.
BibTeX:
@article{Takano1998,
  author = {Takano, Y.},
  title = {X-shaped two-dimensional microphone array systems for measuring noise-source distribution on moving vehicles},
  journal = {JSME International Journal Series C - Mechanical Systems Machine Elements and Manufacturing},
  year = {1998},
  volume = {41},
  pages = {46--50}
}
Takano Y, Horihata K, Kaneko R, Matsui Y and Fujita H (1996), "Analysis of sound characteristics of Shinkansen cars by means of x-shaped microphone arrays", In Proceedings of Internoise 96. , pp. 399-402.
BibTeX:
@inproceedings{Takano_etal1996,
  author = {Takano, Y. and Horihata, K. and Kaneko, R. and Matsui, Y. and Fujita, H.},
  title = {Analysis of sound characteristics of Shinkansen cars by means of x-shaped microphone arrays},
  booktitle = {Proceedings of Internoise 96},
  year = {1996},
  pages = {399--402}
}
Takano Y, Terada K, Aizawa E, Iida A and Fujita H (1992), "Development of a 2-Dimensional Microphone Array Measurement System for Noise Sources of Fast Moving Vehicles", In Proceedings of Internoise 92. , pp. 1175-1178.
BibTeX:
@inproceedings{Takano_etal1992,
  author = {Takano, Y. and Terada, K. and Aizawa, E. and Iida, A. and Fujita, H.},
  title = {Development of a 2-Dimensional Microphone Array Measurement System for Noise Sources of Fast Moving Vehicles},
  booktitle = {Proceedings of Internoise 92},
  year = {1992},
  pages = {1175--1178}
}
Taylor TT (1955), "Design of line source antennas for narrow beam width and low sidelobes,", IRE Transactions on Antennas and Propagation. Vol. AP-3, pp. 16-28.
BibTeX:
@article{Taylor1955,
  author = {Taylor, T. T.},
  title = {Design of line source antennas for narrow beam width and low sidelobes,},
  journal = {IRE Transactions on Antennas and Propagation},
  year = {1955},
  volume = {AP-3},
  pages = {16--28}
}
Tester BJ and Glegg SAL (2010), "Phased array transformation methods to estimate non-compact jet noise source characteristics", In 16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden., AIAA-2010-3739., June, 2010.
Abstract: This paper reviews the basis of the beam former (BF) and polar correlation (PC) phased array methods and shows that these provide different information about axially distributed noise sources. In principle, the BF method provides an image of the source CSD, whereas the PC method yields a ‘source strength’ which is an image of a more complex quantity namely the axial wavenumber transform of the source CSD. At first sight the BF method is therefore more useful for diagnostic purposes but the results presented here suggest that the combined effects of resolution and source convection place serious limitations on the source CSD image information and only the source PSD axial shape can be obtained with the BF method, not its absolute level. The PC method provides more limited diagnostic information but yields a source strength at each reference microphone which when integrated over the source length, yields the far-field PSD at that reference microphone. Therefore the PC source strength is arguably the more relevant quantity to measure when determining what proportion of the sound at a particular microphone position comes from each region of the jet axis.
BibTeX:
@inproceedings{TesterGlegg2010,
  author = {Tester, B. J. and Glegg, S. A. L.},
  title = {Phased array transformation methods to estimate non-compact jet noise source characteristics},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, 7-9 June 2010, Stockholm, Sweden},
  year = {2010}
}
Tiana-Roig E, Torras-Rosell A, Fernandes-Grande E, Jeong C-H and Agerkvist FT (2014), "Enhancing the Beamforming Map of Spherical Arrays at Low Frequencies Using Acoustic Holography", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-03., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Recent studies have shown that the localization of acoustic sources based on circular arrays can be improved at low frequencies by combining beamforming with acoustic holography. This paper extends this technique to the three dimensional case by making use of spherical arrays. The pressure captured by a rigid spherical array under free-field conditions is used to compute the expected pressure on a virtual and larger sphere by means of acoustic holography. Beamforming is then applied with the pressure predicted at the virtual array. Since the virtual array has a larger radius compared to the one of the physical array, the low frequencies (the ones with larger wavelength) are better captured by the virtual array, and therefore, the performance of the resulting beamforming system is expected to improve at these frequencies. The proposed method is examined with simulations based on delay-and-sum beamforming. In addition, the principle is validated with experiments.
BibTeX:
@inproceedings{Tiana-Roig_etal2014,
  author = {Tiana-Roig, E. and Torras-Rosell, A. and Fernandes-Grande, E. and Jeong, C.-H. and Agerkvist, F. T.},
  title = {Enhancing the Beamforming Map of Spherical Arrays at Low Frequencies Using Acoustic Holography},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-03.pdf}
}
Tiete J, Domínguez F, da Silva B, Segers L, Steenhaut K and Touhafi A (2014), "SoundCompass: A Distributed MEMS Microphone Array-Based Sensor for Sound Source Localization", Sensors. Vol. 14(2), pp. 1918-1949.
Abstract: Sound source localization is a well-researched subject with applications ranging from localizing sniper fire in urban battlefields to cataloging wildlife in rural areas. One critical application is the localization of noise pollution sources in urban environments, due to an increasing body of evidence linking noise pollution to adverse effects on human health. Current noise mapping techniques often fail to accurately identify noise pollution sources, because they rely on the interpolation of a limited number of scattered sound sensors. Aiming to produce accurate noise pollution maps, we developed the SoundCompass, a low-cost sound sensor capable of measuring local noise levels and sound field directionality. Our first prototype is composed of a sensor array of 52 Microelectromechanical systems (MEMS) microphones, an inertial measuring unit and a low-power field-programmable gate array (FPGA). This article presents the SoundCompass’s hardware and firmware design together with a data fusion technique that exploits the sensing capabilities of the SoundCompass in a wireless sensor network to localize noise pollution sources. Live tests produced a sound source localization accuracy of a few centimeters in a 25-m2 anechoic chamber, while simulation results accurately located up to five broadband sound sources in a 10,000-m2 open field.
BibTeX:
@article{Tiete_etal2014,
  author = {Tiete, J. and Domínguez, F. and da Silva, B. and Segers, L. and Steenhaut, K. and Touhafi, A.},
  title = {SoundCompass: A Distributed MEMS Microphone Array-Based Sensor for Sound Source Localization},
  journal = {Sensors},
  year = {2014},
  volume = {14},
  number = {2},
  pages = {1918--1949},
  doi = {10.3390/s140201918}
}
Underbrink JR (2002), "Aeroacoustic Phased Array Testing in Low Speed Wind Tunnels", In Aeroacoustic Measurements. , pp. 98-217. Springer-Verlag Berln Heidelberg New York.
BibTeX:
@incollection{Underbrink2002,
  author = {Underbrink, J. R.},
  editor = {Mueller, T. J.},
  title = {Aeroacoustic Phased Array Testing in Low Speed Wind Tunnels},
  booktitle = {Aeroacoustic Measurements},
  publisher = {Springer-Verlag Berln Heidelberg New York},
  year = {2002},
  pages = {98--217}
}
Ura H, Yokokawa Y and Ito T (2006), "Phased Array Measurement of High Lift Devices in Low Speed Wind Tunnel", In 12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006., AIAA-2006-2565., May, 2006.
Abstract: The aeroacoustic measurement using a half-span aircraft model equipped with high lift devices was carried out for the first time in JAXA 6.5m x 5.5m low speed wind tunnel. As the result of this test, the noise sources
BibTeX:
@inproceedings{Ura_etal2006,
  author = {Ura, H. and Yokokawa, Y. and Ito, T.},
  title = {Phased Array Measurement of High Lift Devices in Low Speed Wind Tunnel},
  booktitle = {12th AIAA/CEAS Aeroacoustics Conference (27th AIAA Aeroacoustics Conference), Cambridge, Massachusetts, May 8-10, 2006},
  year = {2006},
  url = {http://pdf.aiaa.org/preview/CDReadyMAERO06_1268/PV2006_2565.pdf}
}
Urick RJ (1983), "Principles of Underwater Sound 3rd Edition" Mc Graw-Hill Book Company.
BibTeX:
@book{Urick1983,
  author = {Urick, R. J.},
  title = {Principles of Underwater Sound 3rd Edition},
  publisher = {Mc Graw-Hill Book Company},
  year = {1983}
}
Van Trees HL (2002), "Detection, Estimation, and Modulation Theory, Part IV, Optimum Array Processing" John Wiley & Sons, New York.
BibTeX:
@book{VanTress2002,
  author = {Van Trees, H. L.},
  title = {Detection, Estimation, and Modulation Theory, Part IV, Optimum Array Processing},
  publisher = {John Wiley & Sons, New York},
  year = {2002}
}
Venkatesh SR, Polak DR and Narayanan S (2003), "Beamforming Algorithm for Distributed Source Localization and Its Application to Jet Noise", AIAA Journal. Vol. 7(7), pp. 1238-1246.
Abstract: A new algorithm for estimating noncompact, distributed sources by means of phased array microphone measurements is presented and experimentally implemented to determine the noise source distribution in a subscale jet flow. Conventional beamforming techniques, developed for spatially well-separated point sources, can lead to significant errors when applied to reconstruct continuous source distributions such as jet noise. A new beamforming approach is developed for estimating such continuous source distributions. The objective is to recover the average source strength over a small region around each focus position as opposed to seeking the exact source strength at each spatial location as in conventional approaches. This strategy overcomes the drawbacks of conventional methods and yields a beamformer with uniform spatial resolution and accuracy over a large frequency range. The measurement technique is applied to the localization of broadband noise sources in a high-subsonic, heated, turbulent jet flow and shows good comparisons with prior measurements using other techniques.
BibTeX:
@article{Venkatesh_etal2003,
  author = {Venkatesh, S. R. and Polak, D. R. and Narayanan, S.},
  title = {Beamforming Algorithm for Distributed Source Localization and Its Application to Jet Noise},
  journal = {AIAA Journal},
  year = {2003},
  volume = {7},
  number = {7},
  pages = {1238--1246},
  doi = {10.2514/2.2092}
}
Venkatesh SR, Polak DR and Narayanan S (2000), "Phased array design, validation, and application to jet noise source localization", In AIAA/CEAS, Aeroacoustics Conference and Exhibit, 6th (21st AIAA Aeroacoustics Conference), Lahaina, HI, June 12-14, 2000., AIAA-2000-1934., June, 2000.
BibTeX:
@inproceedings{Venkatesh_etal2000,
  author = {Venkatesh, S. R. and Polak, D. R. and Narayanan, S.},
  title = {Phased array design, validation, and application to jet noise source localization},
  booktitle = {AIAA/CEAS, Aeroacoustics Conference and Exhibit, 6th (21st AIAA Aeroacoustics Conference), Lahaina, HI, June 12-14, 2000},
  year = {2000}
}
Vold H, Shah P, Davis J, Bremner P, McLaughlin D, Morris P, Veltin J and McKinley R (2010), "High-Resolution Continuous Scan Acoustical Holography Applied to High-Speed Jet Noise", In 16th AIAA/CEAS Aeroacoustics Conference, 07-09 June 2010.
BibTeX:
@inproceedings{Vold_etal2010,
  author = {Vold, H. and Shah, P.N. and Davis, J. and Bremner, P. and McLaughlin, D. and Morris, PO. and Veltin, J. and McKinley, R.},
  title = {High-Resolution Continuous Scan Acoustical Holography Applied to High-Speed Jet Noise},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference, 07-09 June 2010},
  year = {2010},
  doi = {10.2514/6.2010-3754}
}
van der Wal H and Sijtsma P (2009), "Source Localization Techniques with Acoustic Arrays", In NAG/DAGA 2009 International Conference on Acoustics. , pp. 1043-1046. Deutsche Gesellschaft für Akustik e.V., Voltastraße 5, Gebäude 10-6, 13355 Berlin.
BibTeX:
@inproceedings{WalSiijtsma2009,
  author = {van der Wal, H. and Sijtsma, P.},
  title = {Source Localization Techniques with Acoustic Arrays},
  booktitle = {NAG/DAGA 2009 International Conference on Acoustics},
  publisher = {Deutsche Gesellschaft für Akustik e.V., Voltastraße 5, Gebäude 10-6, 13355 Berlin},
  year = {2009},
  pages = {1043-1046},
  note = {NAG/DAGA 2009 International Conference on Acoustics, Rotterdam, 23 - 26 March 2009, including the 35th German Annual Conference on Acoustics (DAGA)}
}
Wang Z, Li J, Stoica P, Nishida T and Sheplak M (2004), "Constant-beamwidth and constant-powerwidth wideband robust Capon beamformers for acoustic imaging", J. Acoust. Soc. Am.., September, 2004. Vol. 116(3), pp. 1621-1631.
Abstract: The standard Capon beamformer (SCB) is sensitive to the mismatch between the assumed and actual array steering vector, which occurs often in practice. Recently a robust Capon beamformer (RCB) was proposed by extending the SCB to the case of uncertain array steering vectors. In certain applications such as acoustic imaging, it is desirable that the beamwidth is constant across the frequency bins. This prevents future corrections for different frequencies and contributes to consistent sound pressure level ~SPL! estimation, which means that for an acoustic wideband monopole source with a flat spectrum the acoustic image for each frequency bin stays the same. However, the beamwidth of RCB decreases with frequency, which can lead to inconsistent imaging results across the frequencies. In this paper two beamformers are proposed, namely a constant-beamwidth robust Capon beamformer ~CBRCB! and a constant-powerwidth robust Capon beamformer (CPRCB), as extensions of RCB for consistent wideband acoustic imaging. Both CBRCB and CPRCB are more robust against array steering vector errors and finite sample size problems than SCB and have better resolution and interference suppression capability than data-independent beamformers. Moreover, they both can be efficiently implemented. The effectiveness of CBRCB and CPRCB is demonstrated via a number of simulated and experimental examples.
BibTeX:
@article{Wang_etal,
  author = {Wang, Zhisong and Li, Jian and Stoica, P. and Nishida, T. and Sheplak, M.},
  title = {Constant-beamwidth and constant-powerwidth wideband robust Capon beamformers for acoustic imaging},
  journal = {J. Acoust. Soc. Am.},
  year = {2004},
  volume = {116},
  number = {3},
  pages = {1621--1631},
  doi = {10.1121/1.1744751}
}
Washburn KB, Frazer T and Kunio J (2005), "Correlating Noise Sources Identified by Beamforming with Sound Power Measurements", In SAE 2005 Noise and Vivbration Conference and Exhibition.
Abstract: Farfield beamforming is a powerful tool for identifying spatially distributed noise sources. The technique yields an image of the relative sound levels within the measurement aperture. The latest version of the beamforming software is now able to estimate the total power within its measurement aperture. In this work, the noise sources on three types of construction equipment are imaged with a beamforming array, while simultaneously the radiated sound powers are determined by a six-microphone hemisphere per ISO 6393 or ISO 6395. Of particular interest are: noise induced by turbulent flow at the exit of an exhaust stack, the effect of a noise reduction package in the engine compartment, and crawler track noise during motion. The absolute levels of the mapped source regions are compared with the total radiated sound power.
BibTeX:
@inproceedings{Washburn_etal2005,
  author = {Washburn, K. B. and Frazer, T. and Kunio, J.},
  title = {Correlating Noise Sources Identified by Beamforming with Sound Power Measurements},
  booktitle = {SAE 2005 Noise and Vivbration Conference and Exhibition},
  year = {2005},
  note = {SAE Technical Paper 2005-01-2510},
  url = {http://www.sae.org/search/?content-type=(%22PAPER%22)&presentedin=(%22SAE+2005+Noise+and+Vibration+Conference+and+Exhibition%22)},
  doi = {10.4271/2005-01-2510}
}
Watts ME, Mosher M and Barnes M (1996), "The Microphone Array Phased Processing System (MAPPS)", In 2nd AIAA/CEAS Aeroacoustics Conference, State College, Pa, May 6-8, 1996., AIAA-1996-1714., May, 1996.
Abstract: A measurement system has been developed to meet increasing demands for detailed noise measurement of individual model components. The Microphone Array Phased Processing System (MAPPS) incorporates a heterogeneous network of computers with a 40 element acoustic array and produces noise maps for selected frequencies in a near real-time testing environment. This system has been used successfully on a model scale test in the NASA Ames 40- by 80-Foot Wind Tunnel.
BibTeX:
@inproceedings{Watts_etal1996,
  author = {Watts, M. E. and Mosher, M. and Barnes, M.},
  title = {The Microphone Array Phased Processing System (MAPPS)},
  booktitle = {2nd AIAA/CEAS Aeroacoustics Conference, State College, Pa, May 6-8, 1996},
  year = {1996}
}
Wei Q, Chen B and Huang X (2014), "Application of Compressive Sensing Based Beamforming in Aeroacoustic Experiment", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-07., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: Compressive sensing (CS) is a newly emerging method in information technology that could reduce sampling efforts extensively by conducting L1 optimization. In this work, CS is extended to array beamforming applications and two algorithms (CSB-I and CSB-II) are presented with the assumption of spatially sparse and incoherent sound sources. The two algorithms are examined using both simulation and aeroacoustic experiments. The simulation case clearly shows that the CSB-I algorithm is quite sensitive to the sensing noise. The CSB-II algorithm, on the other hand, is more robust to noisy measurements. In addition, aeroacoustic tests of an airplane model demonstrate the good performance in terms of resolution and sidelobe rejection of CSB-II algorithm.
BibTeX:
@inproceedings{WeiChenHuang2014,
  author = {Wei, Q. and Chen, B. and Huang, X.},
  title = {Application of Compressive Sensing Based Beamforming in Aeroacoustic Experiment},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-07.pdf}
}
Wei Q, Yu W and Huang X (2014), "Acoustic Wind Tunnel Measurements on a Live Level Flight Pigeon", In Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014., BeBeC-2014-25., February, 2014. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The flow-induced noise of the pigeon (Columba livia) during level flight is investigated with an exploratory method employed in an anechoic open-section wind tunnel. At the wind tunnel test flow of 15 m/s, a live pigeon was managed to maintain a steady level flight. A 63 channel planar microphone array parallel to the plane of pigeon wings was used to measure the sound pressure. Then, conventional beamforming method and CLEAN-SC method were adopted to yield the corresponding narrowband acoustic images and broadband sound pressure spectral results. The acoustic images show that the flight noise of the pigeon is mostly from the wing tips. In addition, the spectral waveform of the pigeon flight shows a slope of -20 dB/dec between 500 Hz and 5 kHz.
BibTeX:
@inproceedings{WeiYuHuang2014,
  author = {Wei, Q. and Yu, W. and Huang, X},
  title = {Acoustic Wind Tunnel Measurements on a Live Level Flight Pigeon},
  booktitle = {Proceedings on CD of the 5th Berlin Beamforming Conference, 19-20 February 2014},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2014},
  url = {http://bebec.eu/Downloads/BeBeC2014/Papers/BeBeC-2014-25.pdf}
}
Wettklo A (2006), "Tonic strains of a chamber orchestra", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-14. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: This paper deals with the acoustic behaviour of classical string instruments. The subject to be examined with the acoustic camera is a classical chamber orchestra including two violins, one viola and one cello. First each musician was asked to play the concert pitch. This note, the a’ corresponds to 440 Hz which is equivalent to a wavelength of 75cm. Then different tones, strains and different accents were played and measured. And now the questions are: What is the way of the tonic strains in the room ? Are there maybe any sensitive spots on the surface of the instruments ? Where does the strains come from ? Are there differences between the instruments ? What about the harmonic emission of notes? This paper should give an answer to these questions and should open the awareness for room acoustics.
BibTeX:
@inproceedings{Wettklo2006,
  author = {Wettklo, A.},
  title = {Tonic strains of a chamber orchestra},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-14_Wettklo.pdf}
}
Wetzel D, Liu F, Rosenberg B and Cattafesta L (2009), "Acoustic Characteristics of a Circulation Control Airfoil", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3103., May, 2009.
BibTeX:
@inproceedings{Wetzel_etal2009,
  author = {Wetzel, D. and Liu, F. and Rosenberg, B. and Cattafesta, L.},
  title = {Acoustic Characteristics of a Circulation Control Airfoil},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009},
  doi = {10.2514/6.2009-3103}
}
Williams EG, Maynard JD and Skudrzyk E (1980), "Sound source reconstructions using a microphone array", J. Acoust. Soc. Am.. Vol. 68, pp. 340-344.
BibTeX:
@article{Williams_etal1980,
  author = {Williams, E. G. and Maynard, J. D. and Skudrzyk, E.},
  title = {Sound source reconstructions using a microphone array},
  journal = {J. Acoust. Soc. Am.},
  year = {1980},
  volume = {68},
  pages = {340--344},
  doi = {10.1121/1.384602}
}
Yamazaki N, Nagakura K, Ikeda M and Sagawa A (2005), "Methods to Measure Acoustic Sources in a Closed Wind Tunnel Test Section", In 11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005., AIAA-2005-3003.
BibTeX:
@inproceedings{Yamazaki_etal2005,
  author = {Yamazaki, N. and Nagakura, K. and Ikeda, M. and Sagawa, A.},
  title = {Methods to Measure Acoustic Sources in a Closed Wind Tunnel Test Section},
  booktitle = {11th AIAA/CEAS Aeroacoustics Conference, Monterey, California, May 23-25, 2005},
  year = {2005}
}
Yamazaki N, Takaishi T, Toyooka M, Nagakura K, Sagawa A and Yano H (2008), "Wind Tunnel Tests on the Control of Aeroacoustic Noise from High Speed Train", In Noise and Vibration Mitigation for Rail Transportation Systems. (99), pp. 33-39. Springer-Verlag.
Abstract: In this study, we propose techniques for reducing the noise from gaps between Shinkansen cars based on the results of noise source localization in wind tunnel testing. In order to obtain the accurate noise source distributions, the microphone array is installed near the train model. The influence of the shear layer around the main flow on the directivity of the microphone array is clarified so that the microphone array should be set in the shear layer rather than the outside of the flow. Analysis of the noise source localization reveals the principal noise sources around the gap, which suggests efficient approaches to the noise reduction. Firstly, we found that the noise level of the gap section with rounded edge can be effectively reduced by approximately 7 dB compared with that of the case with current condition. We also confirmed qualitatively the effect of noise reduction techniques for the gap section by the field test.
BibTeX:
@incollection{Yamazaki_etal2008,
  author = {Yamazaki, N. and Takaishi, T. and Toyooka, M. and Nagakura, K. and Sagawa, A. and Yano, H.},
  editor = {Burkhard Schulte-Werning et al.},
  title = {Wind Tunnel Tests on the Control of Aeroacoustic Noise from High Speed Train},
  booktitle = {Noise and Vibration Mitigation for Rail Transportation Systems},
  publisher = {Springer-Verlag},
  year = {2008},
  number = {99},
  pages = {33-39},
  note = {Proceedings of the 9th International Workshop on Railway Noise, Munich, Germany, 4 - 8 September 2007},
  doi = {10.1007/978-3-540-74893-9_5}
}
Yardibi T, Bahr C, Zawodny N, Liu F, Cattafesta L and Li J (2009), "Uncertainty Analysis of the Standard Delay-and-Sum Beamformer and Array Calibration", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3120., May, 2009.
Abstract: Beamforming has become an ubiquitous task in aeroacoustic noise measurements for source localization and power estimation. The standard delay-and-sum (DAS) beamformer is the most commonly used beamforming algorithm due to its simplicity and robustness and also serves as the basis for more sophisticated algorithms, such as the deconvolution approach for the mapping of acoustic sources (DAMAS). The DAS data reduction equation is a function of many parameters including the microphone locations, microphone transfer functions, temperature and the cross spectral matrix (CSM), where each one of these parameters has a unique uncertainty associated with it. This paper provides a systematic uncertainty analysis of the DAS beamformer and Dougherty's widely used calibration procedure under the assumption that the underlying mathematical model of incoherent, monopole sources is correct. A Monte-Carlo uncertainty analysis is presented for calibration, and both a complex multivariate uncertainty analysis and a Monte-Carlo uncertainty analysis are presented for the DAS beamformer. The analytical multivariate method is based on a ¯rst-order Taylor series expansion, whereas the Monte-Carlo method is based on assumed uncertainty distributions for the input variables. It is shown that the multivariate uncertainty analysis method fails when the perturbations are relatively large and/or the output distribution is non-Gaussian, and therefore the Monte-Carlo analysis should be used in the general case. The calibration procedure is shown to greatly reduce the uncertainties in the DAS power estimates. In particular, 95% con¯dence intervals for the DAS power estimates are presented with simulated data for various scenarios. Moreover, the 95% confidence intervals for the integrated DAS levels at di®erent frequencies are computed using experimental data. It is shown that with experimental data, the 95% con¯dence intervals for the integrated power levels are within §1 dB of the mean levels when the component uncertainties are set at low but achievable values.
BibTeX:
@inproceedings{Yardibi_etal2009,
  author = {Yardibi, T. and Bahr, C. and Zawodny, N. and Liu, Fei and Cattafesta, L. and Li, Jian},
  title = {Uncertainty Analysis of the Standard Delay-and-Sum Beamformer and Array Calibration},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  year = {2009},
  doi = {10.2514/6.2009-3120}
}
Yardibi T, Bahr C, Zawodny N, Liu F and Cattafesta III L.N..and Li J (2010), "Uncertainty analysis of the standard delay-and-sum beamformer and array calibration", J. Sound Vib.., In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009., AIAA-2009-3120. Vol. 329, pp. 2654–2682.
Abstract: Beamforming has become an ubiquitous task in aeroacoustic noise measurements for source localization and power estimation. The standard delay-and-sum (DAS) beamformer is the most commonly used beamforming algorithm due to its simplicity
and robustness and also serves as the basis for more sophisticated algorithms, such as the deconvolution approach for the mapping of acoustic sources (DAMAS). The DAS data reduction equation is a function of many parameters including the microphone locations, microphone transfer functions, temperature and the cross-spectral matrix (CSM), where each one of these parameters has a unique uncertainty associated with it. This paper provides a systematic uncertainty analysis of the DAS beamformer and Dougherty’s widely used calibration procedure under the assumption that the underlying mathematical model of incoherent, monopole sources is correct. An analytical multivariate method based on a first-order Taylor series expansion and a numerical Monte-Carlo method based on assumed uncertainty distributions for the input variables are considered. The uncertainty of calibration is analyzed using the Monte-Carlo method, whereas the uncertainty of the DAS beamformer is analyzed using both the complex multivariate and the Monte-Carlo methods. It is shown that the multivariate uncertainty analysis method fails when the perturbations are relatively large and/or the output distribution is non-Gaussian, and therefore the Monte-Carlo
analysis should be used in the general case. The calibration procedure is shown to greatly reduce the uncertainties in the DAS power estimates. In particular, 95 percent confidence intervals for the DAS power estimates are presented with simulated data for various scenarios. Moreover, the 95 percent confidence intervals for the integrated DAS levels at different frequencies are computed using experimental data. It is shown that with experimental data, the 95 percent confidence intervals for the integrated power levels are within +-1dB of the mean levels when the component uncertainties are set at low but achievable values
BibTeX:
@article{Yardibi_etal2010,
  author = {Yardibi, T. and Bahr, C. and Zawodny, N. and Liu, F. and Cattafesta III, L.N..and Li, J.},
  title = {Uncertainty analysis of the standard delay-and-sum beamformer and array calibration},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), Miami, Florida, May 11-13, 2009},
  journal = {J. Sound Vib.},
  year = {2010},
  volume = {329},
  pages = {2654–2682}
}
Yardibi T, Li J, Stoica P and Cattafesta III LN (2008), "Sparsity constrained deconvolution approaches for acoustic source mapping", J. Acoust. Soc. Am.. Vol. 123(5), pp. 2631-2642.
Abstract: Using microphone arrays for estimating source locations and strengths has become common practice in aeroacoustic applications. The classical delay-and-sum approach suffers from low resolution and high sidelobes and the resulting beamforming maps are difficult to interpret. The deconvolution approach for the mapping of acoustic sources (DAMAS) deconvolution algorithm recovers the actual source levels from the contaminated delay-and-sum results by defining an inverse problem that can be represented as a linear system of equations. In this paper, the deconvolution problem is carried onto the sparse signal representation area and a sparsity constrained deconvolution approach (SC-DAMAS) is presented for solving the DAMAS inverse problem. A sparsity preserving covariance matrix fitting approach (CMF) is also presented to overcome the drawbacks of the DAMAS inverse problem. The proposed algorithms are convex optimization problems. Our simulations show that CMF and SC-DAMAS outperform DAMAS and as the noise in the measurements increases, CMF works better than both DAMAS and SC-DAMAS. It is observed that the proposed algorithms converge faster than DAMAS. A modification to SC-DAMAS is also provided which makes it significantly faster than DAMAS and CMF. For the correlated source case, the CMF-C algorithm is proposed and compared with DAMAS-C. Improvements in performance are obtained similar to the uncorrelated case.
BibTeX:
@article{Yardibi_atal2008,
  author = {Yardibi, T. and Li, J. and Stoica, P. and Cattafesta, III, L. N.},
  title = {Sparsity constrained deconvolution approaches for acoustic source mapping},
  journal = {J. Acoust. Soc. Am.},
  year = {2008},
  volume = {123},
  number = {5},
  pages = {2631--2642},
  doi = {10.1121/1.2896754}
}
Zavala PAG, De Roeck W, Janssens K, Arruda JRF, Sas P and Desmet W (2010), "Monopole and Dipole Identification Using Generalized Inverse Beamforming", In 16th AIAA/CEAS Aeroacoustics Conference., AIAA-2010-3740., June, 2010.
Abstract: Aeroacoustic problems pose some challenges to the conventional techniques normally used to source localization and identification. The main difficulties are that sources are normally distributed, with coherent and incoherent regions, and with simultaneous mono and multipole radiation patterns. Among the most recent ones, the Generalized Inverse Beamforming method has the promise to meet these challenges. In this paper, the potential for identification of compact sources in close vicinity, similar to a distributed source, and the potential to identify a dipole center and orientation, induced by two compact sources, are illustrated in two no-flow tests. Results obtained in semi-anechoic room are compared to numerical prediction, and the generalized inverse beamforming performance compared to the conventional beamforming results. This validation is a preparation for the application of the method to aeroacoustic problems.
BibTeX:
@inproceedings{Zavala_etal2010b,
  author = {Zavala, P. A. G. and De Roeck, W. and Janssens, K. and Arruda, J. R. F. and Sas, P. and Desmet, W.},
  title = {Monopole and Dipole Identification Using Generalized Inverse Beamforming},
  booktitle = {16th AIAA/CEAS Aeroacoustics Conference},
  year = {2010}
}
Zavala PAG, de Roeck W, Hanssens K, de Franca Arruda JR, Sas P and Desmet W (2010), "Generalized inverse beamforming investigation and hybrid estimation", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-10., February, 2010.
Abstract: Conventional beamforming, among the several techniques that can be used for noise source localization, has been widely used in complex problems, including aeroacoustics applications. The sound generated by flow turbulence can present a distributed coherent source region, which presents some challenges to the conventional beamforming localization accuracy. The Generalized Inverse Beamforming (GIB) is a recent method aiming at the identification of coherent or incoherent, distributed or compact, monopole or multipole sources. This method is based on the microphone array cross-spectral eigenstructure, resulting in a robust localization technique. In this work, the performance of the GIB method is investigated for two simple cases in comparison to conventional beamforming. The first test case, a simple monopole, illustrates the frequency range accuracy, and the second test case, two monopoles in coherent radiation, illustrates the different performance in coherent scenarios. Numerical investigation is used to define the test array aperture and distance to the target region. In order to improve the generalized inverse estimation on the coherent case, a new hybrid estimation is proposed. This consists in creating a source mapping that is comparable to the conventional mapping based on the generalized inverse mapping and the array Point Spread Function. The offsetting between the hybrid mapping and the conventional mapping indicates the quality of the generalized inverse estimation and the hybrid estimation points to the actual sources overall strength.
BibTeX:
@inproceedings{Zavala_etal2010,
  author = {Zavala, P. A. G. and de Roeck, W. and Hanssens, K. and de Franca Arruda, J. R. and Sas, P. and Desmet, W.},
  title = {Generalized inverse beamforming investigation and hybrid estimation},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-10.pdf}
}
Zawodny N, Liu F, Yardibi T, Cattafesta L, Khorrami M, Neuhart D and Van de Ven T (2009), "A Comparative Study of a 1/4-Scale Gulfstream G550 Aircraft Nose Gear Model", In 15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)., AIAA-2009-3153., May, 2009.
BibTeX:
@inproceedings{Zawodny_etal2009,
  author = {Zawodny, N. and Liu, F. and Yardibi, T. and Cattafesta, L. and Khorrami, M and Neuhart, D and Van de Ven, T.},
  title = {A Comparative Study of a 1/4-Scale Gulfstream G550 Aircraft Nose Gear Model},
  booktitle = {15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference)},
  year = {2009}
}
Zechel G, Zeibig A and Beitelschmidt M (2010), "Time-domain beamforming on moving objects with known trajectories", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-12., February, 2010.
Abstract: The application of beamforming algorithms to locate sound sources on fast-moving objects like trains or cars can be troublesome. Typically, very short signal frames have to be used to achieve an “acoustic still image” for the pinpointing of sound sources on the observed moving object. On the other hand, if the trajectory of the object is given or can be gathered by additional measurements, it can be used to computationally eliminate the object movement allowing large signal frames, to correct sound pressure levels assuming spherical wave propagation, and to remove frequency shifts caused by the Doppler effect. To achieve this, a simple time-domain beamforming algorithm has been developed that basically reconstructs and evaluates the source signals of hypothetical point monopoles on the objects surface. The algorithm itself and ways to optimize it to reduce memory usage and CPU time when processing measurements of very large objects are shown in detail. Results of measurements on trains that underline its capabilities are demonstrated.
BibTeX:
@inproceedings{Zechel_etal2010,
  author = {Zechel, G. and Zeibig, A. and Beitelschmidt, M.},
  title = {Time-domain beamforming on moving objects with known trajectories},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-12.pdf}
}
Zeibig A, Schulze C and Sarradj E (2005), "Microphone array measurements for aeroacoustic applications", In 12th International Congress on Acoustics.
BibTeX:
@inproceedings{Zeibig2005,
  author = {Zeibig, A. and Schulze, C. and Sarradj, E.},
  title = {Microphone array measurements for aeroacoustic applications},
  booktitle = {12th International Congress on Acoustics},
  year = {2005}
}
Zeibig A, Schulze C, Sarradj E and Beitelschmidt M (2006), "Microphone array measurements on aeroacoustic sources", In Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006., BeBeC-2006-13., November, 2006. GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin.
Abstract: The flow around obstacles is often very complex, leading to distributed aeroacoustic sources. In experimental investigations, microphone arrays can help to separate, analyze and quantify these partial sources. In order to do so, a microphone array with a high spatial resolution and a high dynamic range is essential. In this publication, the setup and application of a microphone array for aeroacoustic measurements in a model scale wind tunnel will be discussed. Initially, the development and optimization of the microphone array will be described. Preliminary considerations and the derivation of major quality criteria will be explained. Methods for the enhancement of the measurement results as well as for the source characterization will be presented. These methods include the variation of the measurement conditions as well as advanced signal processing. Results of measurements on various test structures will be presented. These structures do all possess aeroacoustic sources with dipole sound radiation but do also exhibit different frequency behaviour of narrowband (cylinder) and broadband (generic wing profile) radiation.
BibTeX:
@inproceedings{Zeibig_etal2006,
  author = {Zeibig, A. and Schulze, C. and Sarradj, E. and Beitelschmidt, M.},
  title = {Microphone array measurements on aeroacoustic sources},
  booktitle = {Proceedings on CD of the 1st Berlin Beamforming Conference, 22-23 November, 2006},
  publisher = {GFaI, Gesellschaft zu Förderung angewandter Informatik e.V., Berlin},
  year = {2006},
  url = {http://bebec.eu/Downloads/BeBeC2006/Papers/BeBeC-2006-13_Zeibig_Schulze_et_al.pdf}
}
Zheng YR, Goubrant R and El-Tananyt M (2003), "A Nested Sensor Array Focusing on Near Field Targets", In Sensors, 2003. Proceedings of IEEE. 22/11/2003; Vol.2.. , pp. 843-848.
BibTeX:
@inproceedings{Zheng_etal2003,
  author = {Zheng, Y. R. and Goubrant, R.A. and El-Tananyt, M.},
  title = {A Nested Sensor Array Focusing on Near Field Targets},
  booktitle = {Sensors, 2003. Proceedings of IEEE. 22/11/2003; Vol.2.},
  year = {2003},
  pages = {843--848},
  url = {http://scholarsmine.mst.edu/post_prints/pdf/01279062_09007dcc8030d146.pdf},
  doi = {10.1109/ICSENS.2003.1279062}
}
Zillmann J and C. Carou C (2010), "Array analysis for aircraft flyover measurements", In Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010., BeBeC-2010-14., February, 2010.
Abstract: Microphone Arrays installed on the ground are used to identify and to quantify noise sources at aircrafts. This is an important tool to assess novel treatments, to establish an empirical noise data base for noise prediction tools and to validate acoustic source models used by computational aero acoustics. An array can comprise several hundred microphones and is widely used for stationary applications in the automotive industry and in wind tunnel facilities. The focus of this presentation is on a specialised array methodology for moving objects, which are far away from the array, e.g. the altitude of an aircraft is about 200 meters for those measurements. The beam-forming map exhibits side lobes, which make the localisation and quantification of sources rather difficult. Therefore an Inverse Source Density Modelling is introduced to remove the side lobes. Care has to be taken to mitigate the frequency shift due to the Doppler effect and to be capable of processing badly conditioned matrices. The success of this approach is discussed based on measurement data.
BibTeX:
@inproceedings{ZillmannCarou2010,
  author = {Zillmann, J. and C. Carou, C.},
  title = {Array analysis for aircraft flyover measurements},
  booktitle = {Proceedings on CD of the 3rd Berlin Beamforming Conference, 24-25 February, 2010},
  year = {2010},
  url = {http://bebec.eu/Downloads/BeBeC2010/Papers/BeBeC-2010-14.pdf}
}
Ziomek LJ (1985), "Underwater Acoustics, A Linear System Approach" Academic Press, Inc..
BibTeX:
@book{Ziomek1985,
  author = {Ziomek, Lawrence J.},
  title = {Underwater Acoustics, A Linear System Approach},
  publisher = {Academic Press, Inc.},
  year = {1985}
}