Robert Dougherty

Robert Dougherty
University of Washington Seattle | UW · Department of Aeronautics and Astronautics

PhD

About

88
Publications
34,339
Reads
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3,894
Citations
Citations since 2016
17 Research Items
2573 Citations
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Introduction
Robert Dougherty currently works at the Department of Aeronautics and Astronautics, University of Washington Seattle, and OptiNav, Inc. Robert does research in Acoustic Engineering, Aeronautical Engineering and Acoustics.

Publications

Publications (88)
Conference Paper
Functional Beamforming is a new method that promises to replace Frequency Domain Beamforming as the standard microphone array processing technique in aeroacoustics. It offers the same speed as FDBF with dramatically improved dynamic range and slightly improved resolution. It is not a deconvolution technique and is not compatible with standard decon...
Preprint
Full-text available
Ambient wet-bulb temperature, T_wb, is proposed as a unifying parameter for predicting the environmental risk of SARS-CoV-2. This is explored from two directions. A crowd-sourced database of SARS-CoV-2 superspreading events is analyzed. Also, a simplified, 2D, finite difference code is developed and used to estimate the temperature of the nasal muc...
Article
Full-text available
How do Great Gray Owls (Strix nebulosa) capture voles (Cricetidae) through a layer of snow? As snow is a visual barrier, the owls locate voles by ear alone. To test how snow absorbs and refracts vole sound, we inserted a loudspeaker under the snowpack and analysed sound from the loudspeaker, first buried, then unburied. Snow attenuation coefficient...
Conference Paper
It is important to be able to determine spectral noise components from aeroacoustic phased array tests. Despite decades of effort, this a tricky, time-consuming, and error-prone process. A method is presented here that may improve the situation, at least for broadband sources typical of airframe noise. The approach combines two methods introduced p...
Conference Paper
Full-text available
Functional Beamforming (FB) offers excellent dynamic range, giving very small results, instead of the usual sidelobes, when the computed steering vectors match the normalized Green’s functions of the actual acoustic sources. It can be proven that FB result will not be less than the correct result if the steering vector is accurate. Unfortunately, s...
Conference Paper
Full-text available
Beamforming deconvolution is modified to use the output of Functional Beamforming as the dirty map and to change the elements of the point spread function, raising them to the power ν. The first change increases the dynamic range of the method. The second improves the condition of the system of equations to be solved, possibly speeding convergence....
Presentation
Update July 18, 2021. I wrote this document in late 2020 in an effort to publicize and expand upon a message from a paper by Moriyama et al in Annual Reviews of Virology that influenza and COVID-19 respond to indoor humidity. Since then, several things have changed. The humidity mechanism seems clearer now and I am pursuing that in a scientific tra...
Conference Paper
Full-text available
Functional Projection Beamforming (FPB) is a method proposed by Dougherty in 2019, based on functional beamforming. It yields the integrated sound spectrum for a given region of integration (ROI) within the functional beamforming source map. FPB does not suffer from the loss of level that can affect functional beamforming, especially for coarse sca...
Conference Paper
Full-text available
Engineering results from a microphone phased array should ideally include component spectra reflecting the sound radiated from Regions of Interest within the field of view. A new processing method for producing component spectra, Functional Projection Beamforming, was introduced in 2019. It offers high dynamic range and consistent integration of co...
Conference Paper
A new method for measuring component spectra from microphone array data is presented. It is offered as a replacement for the earlier concepts of integrating the conventional beamform map or a deconvolved beamform map over Regions of Interest (ROI). It is based on characterizing an ROI as a subspace in array steering vector space, projecting the arr...
Conference Paper
Full-text available
The adaptive beamforming formula gives the source power estimate as the reciprocal of an expression similar to the classical frequency domain beamforming formula with the cross spectral matrix (CSM) replaced by an inverse of the CSM. The adaptive formula, also known as Capon and by other names, offers superior resolution, though it can be unstable....
Conference Paper
Aim of this course is to improve the knowledge for the practical application of microphone array measurements in wind tunnels, including the post-processing and the interpretation of the achieved results. Test engineers can participate to obtain the necessary knowledge to improve the quality of aeroacoustic measurements with microphone arrays and p...
Article
The synthetic array technique has previously been used to provide insight for developing improved microphone array data processing techniques. In recent work, however, it has also been successfully applied to diagnose the source of unexpected (and nonphysical) tones which arose in unsteady computational fluid dynamics (CFD) simulations of hot super...
Conference Paper
Frequency domain beamforming relies on the array Cross Spectral Matrix (CSM). In many cases, typified by windy aeroacoustics tests, the CSM is contaminated by interfering noise on the diagonal. The noise in these matrix elements be can excluded from the beamforming results by not using those values, with or without compensating by adjusting the alg...
Conference Paper
Aim of this course is to improve the knowledge for the practical application of microphone array measurements in wind tunnels, including the post-processing and the interpretation of the achieved results. Test engineers can participate to obtain the necessary knowledge to improve the quality of aeroacoustic measurements with microphone arrays and p...
Conference Paper
A research project to improve phased array beamforming techniques for gaining insight into the generation and radiation of high speed jet noise has been conducted. The work was led by the Innovative Technology Applications Company with contributions from Philip Morris and Kenneth Brentner at the Pennsylvania State University and Robert Dougherty at...
Conference Paper
To mitigate noise impact to residents around airports in the US, the Federal Aviation Administration has a Residential Sound Insulation Program. An aspect of this program is the estimation of the building Noise Level Reduction. A commonly used method of measuring Noise Level Reduction uses a loudspeaker outside the house and microphones inside. Thi...
Article
This paper experimentally investigates the noise from a large wind turbine (GE 1.5 MW) with a compact microphone array (OptiNav 24) using advanced deconvolution based beamforming methods, such as DAMAS and CLEAN-SC beamforming algorithms, for data reduction. Our study focuses on the ability of a compact microphone array to successfully locate both...
Article
A review of modern experimental methods in aeroacoustics is provided along with sample applications. Specific emphasis has been placed on four advanced experimental techniques: (i) beamforming, (ii) acoustic holography, (iii) phase averaging and simultaneous flow/acoustic measurements and (iv) higher order spectral analysis. Through a description a...
Conference Paper
Full-text available
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 adv...
Conference Paper
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 appli...
Article
Phased arrays of microphones have proved themselves to be a powerful tool for aeroacoustic investigations. There are many different algorithms for processing the resulting data, including classical beamforming, its modern derivatives, Linear Programming, and Generalized Inverse Methods. The current work stems from a recognition that, for configurat...
Conference Paper
Full-text available
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 TID...
Conference Paper
Full-text available
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-WOPW...
Article
Locating the dominant noise sources on a wind turbine is an important problem in designing and developing low noise wind turbines. Previously very large microphone arrays were used to locate these sources. The primary focus of this paper is to show that using a compact and mobile microphone array with advanced beamforming algorithms, the noise sour...
Article
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 sho...
Conference Paper
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 measuremen...
Conference Paper
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 o...
Conference Paper
Full-text available
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 tunn...
Conference Paper
Full-text available
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 th...
Conference Paper
Full-text available
The use of phased array for acoustics measurement in wind tunnels is known to suffer degradation in integrated SPL and acoustic image dynamic range due to decorrelation between each pair of microphones after the acoustic ray has crossed the wind tunnel boundary layer. Based in the extensive works of radio propagation, underwater acoustic and atmosp...
Conference Paper
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 t...
Article
Full-text available
Bone geometry is commonly measured on computed tomographic (CT) and X-ray microtomographic (μCT) images. We obtained hundreds of CT, μCT and synchrotron μCT images of bones from diverse species that needed to be analysed remote from scanning hardware, but found that available software solutions were expensive, inflexible or methodologically opaque....
Conference Paper
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 o...
Conference Paper
Full-text available
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 mi...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
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 su...
Conference Paper
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 steerin...
Conference Paper
Full-text available
New techniques for the visualization of the sound field have enabled more precise mapping of sound sources, and this is the basic principle of the beamforming technique, that is, it can recognize the regions of prominent noise. The application of this technique to moving sources can provide an assessment of sound sources and also locate the sources...
Conference Paper
Full-text available
The evolution of techniques for evaluation of noise made it possible to map sound sources to determine more precisely the regions of prominent noise, this is the basic principle of the Beamforming technique. Extending the technique to moving sources is possible to do the same assessment and thus locate the sources that are generated by effects of t...
Conference Paper
Full-text available
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...
Article
Full-text available
Determining the health of muscle cells by in vivo imaging could impact the diagnosis and monitoring of a large number of congenital and acquired muscular or cardiac disorders. However, currently used technologies are hampered by insufficient resolution, lack of specificity, or invasiveness. We have combined intrinsic optical second-harmonic generat...
Conference Paper
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 steerin...
Article
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 freque...
Conference Paper
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 mic...
Conference Paper
Full-text available
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 cla...
Article
Full-text available
This study presents the development of an ImageJ plugin for surface characterization. Based on gradient analysis, parameters, such as the gradient magnitude, orientation, mean resultant vector and surface area are derived. A comparative study of supercalendered (SC) papers was performed to verify the surface representations yielded by a laser profi...
Conference Paper
Full-text available
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 amplifica...
Conference Paper
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 p...
Article
The ability to unambiguously identify the acoustic energy generated by airplane wake vortices using phased microphone‐array intensity distribution maps is hampered by the lack of knowledge of the associated non‐stationary spectrum throughout the wake’s duration. This ambiguity is especially pronounced when the low broadband signal to noise ratio re...
Article
Full-text available
From August to September 2003, NASA conducted an extensive measurement campaign to characterize the acoustic signal of wake vortices. A large, both spatially as well as in number of elements, phased microphone array was deployed at Denver International Airport for this effort. This paper will briefly describe the program background, the microphone...
Conference Paper
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 impleme...
Article
Full-text available
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 a...
Article
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 companie...
Conference Paper
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 re...
Chapter
Non-intrusive measurements of wind tunnel model noise can be made in non-acoustic, hardwall wind tunnels, as well as free jets and other challenging settings, by using beamforming techniques with sparse, wide-band phased arrays of microphones. The process, which was developed for this application at Boeing in the last few years, begins by measuring...
Article
Full-text available
Mr. Weir presented source location results obtained from an engine test as part of the Engine Validation of Noise Reduction Concepts program. Two types of microphone arrays were used in this program to determine the jet noise source distribution for the exhaust from a 4.3 bypass ratio turbofan engine. One was a linear array of 16 microphones locate...
Article
not available for EP0823547Abstract of corresponding document: US5702231Noise attenuating linings for a turbofan engine inlet are installed around the upper crown area and/or around the lower lip. The acoustical lining at the upper crown area attenuates those fan noise emissions which are normally reflected from the crown area downward toward the g...
Conference Paper
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 a...
Article
Turbulence spectra have been measured downstream of the gap between the leading-edge slat and the main airfoil of a generic transport aircraft wing model. The model consisted of a NACA 63_2-215 Mod. B main element with a half span Fowler flap and a full span LB-546 slat. Velocity-pressure coherence spectra were determined using signals from a hot-w...
Article
Full-text available
A wind tunnel test was conducted to determine the effects of inlet shape on fan radiated noise. Four inlet geometries, which included a long standard flight type inlet, a short, aggressive flight inlet a scarf inlet, and an elliptical inlet were investigated in the study. The fan model used in the study was a 0.1 scale of the Pratt and Whitney Adva...