On the difference-to-sum power ratio of speech and wind noise based on the Corcos model

The difference-to-sum power ratio was proposed and used to suppress wind noise under specific acoustic conditions. In this contribution, a general formulation of the difference-to-sum power ratio associated with a mixture of speech and wind noise is proposed and analyzed. In particular, it is assumed that the complex coherence of convective turbulence can be modelled by the Corcos model. In contrast to the work in which the power ratio was first presented, the employed Corcos model holds for every possible air stream direction and takes into account the lateral coherence decay rate. The obtained expression is subsequently validated with real data for a dual microphone set-up. Finally, the difference-to- sum power ratio is exploited as a spatial feature to indicate the frame-wise presence of wind noise, obtaining improved detection performance when compared to an existing multi-channel wind noise detection approach.Comment: 5 pages, 3 figures, IEEE-ICSEE Eilat-Israel conference (special session

Simulating Multi-channel Wind Noise Based on the Corcos Model

A novel multi-channel artificial wind noise generator based on a fluid dynamics model, namely the Corcos model, is proposed. In particular, the model is used to approximate the complex coherence function of wind noise signals measured with closely-spaced microphones in the free-field and for time-invariant wind stream direction and speed. Preliminary experiments focus on a spatial analysis of recorded wind noise signals and the validation of the Corcos model for diverse measurement set-ups. Subsequently, the Corcos model is used to synthetically generate wind noise signals exhibiting the desired complex coherence. The multi-channel generator is designed extending an existing single-channel generator to create N mutually uncorrelated signals, while the predefined complex coherence function is obtained exploiting an algorithm developed to generate multi-channel non-stationary noise signals under a complex coherence constraint. Temporal, spectral and spatial characteristics of synthetic signals match with those observed in measured wind noise. The artificial generation overcomes the time-consuming challenge of collecting pure wind noise samples for noise reduction evaluations and provides flexibility in the number of generated signals used in the simulations.Comment: 5 pages, 2 figures, IWAENC 201

Spectra and space-time correlations of the fluctuating pressures at a wall beneath a supersonic turbulent boundary layer perturbed by steps and shock waves

Spectra and space-time correlations of fluctuating pressures at wall beneath supersonic turbulent boundary layer perturbed by steps and shock wave

Techniques and errors in measuring cross- correlation and cross-spectral density functions

Techniques and errors in measuring cross spectral density and cross correlation functions of stationary dynamic pressure dat

Holographic Detection and Reduction of Wind Noise

Many devices that include built-in microphone(s) are used in windy situations. Wind noise degrades the quality of audio detected by the microphone(s), causes microphone signal saturation at high wind speeds, causes nonlinear acoustic echo, and reduces the performance of acoustic echo cancellation (AEC). Applications such as voice‐trigger, automatic speech recognition (ASR), and voice over internet protocol (VoIP) communication are negatively impacted by such degradation. This disclosure describes cost‐effective and robust techniques to detect and reduce wind noise. The described techniques deliver optimum removal and detection results by processing the audio signal in a holographic way by dealing with all related domains including time, frequency, and 3D space. This approach can improve the audio detection performance of any device that incorporates the techniques and can thereby improve the user experience of various applications such as voice-trigger, speech recognition, voice communication, event detection, etc. even on devices that have limited computational capability

Boundary Layer Flows

Written by experts in the field, this book, "Boundary Layer Flows - Theory, Applications, and Numerical Methods" provides readers with the opportunity to explore its theoretical and experimental studies and their importance to the nonlinear theory of boundary layer flows, the theory of heat and mass transfer, and the dynamics of fluid. With the theory's importance for a wide variety of applications, applied mathematicians, scientists, and engineers - especially those in fluid dynamics - along with engineers of aeronautics, will undoubtedly welcome this authoritative, up-to-date book

Statistical Scaling of Turbulent Surface Pressure in the Atmospheric Boundary Layer

Turbulence in the atmosphere produces fluctuations in static pressure through a variety of mechanisms. These fluctuations are of interest both to atmospheric scientists, as a fluid dynamic property, and to acousticians, as a source of wind noise. At the ground surface, previous work has found the dominant source of pressure fluctuations to be an interaction of the turbulent vertical velocity with the shear rate in the mean wind. In this work, the existing theoretical framework was extended to investigate the effects of atmospheric stability, shear anisotropy, and different turbulence models. A rapid-distortion model was introduced and compared with the existing mirror-flow model. Solutions for the surface pressure spectra from each model were derived, and a method for estimating the model parameters from average elevation-dependent flow properties was developed. In order to validate and compare these spectral models, an experiment was conducted in Laramie, Wyoming to obtain measurements of low-frequency surface pressure simultaneous with the boundary-layer meteorology over a wide range of atmospheric conditions. The velocity data were then used to fit the turbulence model parameters, and predictions of the surface pressure spectra were made. These predictions were compared with the spectra of the surface pressure measurements over half-hour intervals, converted to wavenumber space by introducing a convection velocity. In stable conditions, a low-wavenumber amplification of the spectrum was observed, in accordance with predictions. In convection conditions, the rapid-distortion model performed best, and the shear anisotropy contained in this model was found to be relevant to fitting nearly-neutral cases. The modification of the spectral structure by the shear-anisotropic model suggests a possible unifying mechanism for discrepancies between engineering and atmospheric boundary-layer pressure statistics

Un modèle numérique de l’excitation couche limite turbulente pour prédire le bruit à l’intérieur d’une automobile

L’objectif principal de la thèse est de développer une approche numérique basée sur la dynamique computationnelle des fluides (CFD) pour modéliser une excitation produite par une couche limite turbulente (TBL) et, par la suite, prédire le bruit à l’intérieur de l’automobile. A cet égard, deux corps non profilés (bluff) ont été considérés : a) Un obstacle représentatif du pilier A et b) un rétroviseur générique. Ces deux corps non profilès sont placés sur un système plaque-cavité qui représente la cabine intérieure et la vitre latérale d’une automobile. Les fluctuations de la pression pariétale (WPF) sont finement résolues en utilisant une analyse CFD. Par la suite, elles sont quantifiées en termes de spectre de puissance, de spectre croisé, de cohérence et de spectre de fréquence d’onde en utilisant le code k-omega développé dans cette thèse. Grâce à la longue durée calculée par CFD, et de la finesse du maillage, les zones acoustiques et aérodynamiques sont correctement capturées pour une analyse vibro-acoustique poussée. Trois stratégies numériques sont proposées pour calculer la puissance injectée à la plaque : 1) Identification des paramètres empiriques du modèle Corcos à partir de la WPF, 2) Calcul de la puissance injectée dans le domaine du nombre d’ondes, et 3) Échantillonnage aléatoire de l’excitation TBL. Ces différentes approches ont été comparées et discutées pour proposer une approche optimale du point de vue computationnel. En d’autres termes, la véritable réalisation a consisté à trouver une méthode efficace en terme du temps de calcul pour coupler le modèle CFD de la WPF aux modes propres de la plaque afin d’obtenir la puissance injectée. Le couplage entre la structure spatiale de l’excitation et les modes propres de la structure est donnée par la “joint-acceptance”. Les indicateurs vibro-acoustiques du système plaque-cavité, comme la puissance injectée, la vitesse quadratique et la pression quadratique, sont calculés à l’aide de l’approche d’analyse énergétique modale et statistique (SEA). La procédure numérique CFD/SEA appliquée à un système plaque-cavité est validée par des expériences menées dans la soufflerie de Purdue University. Parmi les trois approches numériques, le modèle Corcos dérivé de CFD semble très prometteur en termes d’efficacité en temp de calcul, car il est basé sur une méthode analytique. La meilleure approche en termes de calcul et précision est la seconde, qui résout complètement le WPF de la TBL en utilisant une CFD transitoire et calcule la puissance injectée dans le domaine de nombre d’ondes. L’originalité de cette thèse est l’estimation des paramètres du modèle de Corcos à partir d’un calcul CFD statistiquement convergé de la pression pariétale. Une autre contribution originale est de réduire le temps de calcul au niveau de l’intégration dans l’espace du nombre d’onde de la joint acceptance en proposant un nouveau critère pour les limites supérieure d’intégration.Abstract: The main objective is to develop a Computational Fluid Dynamics(CFD) based numerical approach to model the turbulent boundary layer (TBL) excitation and later predict the interior noise. In this regard, two automobile bluff bodies were considered a) flat fence representative of A-pillar and b) generic side mirror. These two bluff bodies are placed over a plate-cavity system as a representation of side window-interior cabin of an automobile. Turbulent Wall-Pressure Fluctuations (WPF) are finely resolved using unsteady CFD analysis and later quantified in terms of power spectrum, cross-spectrum, coherence and wavenumber-frequency spectrum using the k-omega code developed as a part of this work. Due to a lengthy CFD run and finely resolved CFD mesh, both acoustic and aerodynamic zones were properly captured for further vibro-acoustic analysis. Three numerical strategies are proposed to calculate the TBL power input to the plate. 1) Identification of empirical Corcos model parameters from unsteady CFD WPF through curve fitting; 2) TBL power input calculation in wavenumber domain; 3) Random sampling of TBL excitation. Different approaches have been compared and discussed to propose a computationally optimal approach. In simple words, the real task at hand is to find a computationally efficient approach to couple the CFD WPF with plate modeshapes to obtain the TBL power input. The coupling strength between excitation and structural modeshapes is given by “joint-acceptance”. The vibro-acoustics indicators of plate-cavity system like input power, quadratic velocity, quadratic pressure are calculated using Modal and Statistical Energy Analysis (SEA) approach. The numerical CFD/SEA procedure applied for a plate-cavity system is validated with experiments conducted at Purdue University wind tunnel. Among the three numerical approaches, CFD derived Corcos model looks very promising in terms of computational efficiency as its based on analytical method. The best approach in terms of accuracy and computation is the second one, which fully resolves the TBL WPF using unsteady CFD and calculate the TBL power input to plate in wavenumber domain. The originality of thesis is due to the estimation of Corcos parameters from a statistically converged CFD wall-pressure. Another original contribution is to minimize the computational effort in the wavenumber integration of joint acceptance by proposing a new criterion for upper limits

Acoustic Modeling Of A Uas For Use In A Hostile Fire Detection System

Unmanned Aerial System (UAS) usage has continually increased in recent years for both recreational and military applications. One particular military application being researched is utilizing a UAS as a host platform for Hostile Fire Detection Systems (HFDS), with particular interest being focused on multi-rotor drone platforms. The type of HFDS considered in this work is based upon acoustic sensors. An acoustic based HFDS utilizes an array of microphones to measure acoustic data and then applies signal processing algorithms to determine if a transient signal is present and if present then estimates the direction from which the sound arrived. The main issue with employing an acoustic based HFDS on a multi-rotor drone is the high level of background noise due to motors, propellers, and flow noise. In this thesis a study of the acoustic near field, particularly relevant to microphones located on the drone, was performed to understand the noise produced by the UAS. More specifically, the causes and characteristics of the sources of noise were identified. The noise characteristics were then used to model the noise sources for multiple motor assemblies based upon position of the microphone and revolutions per minute (RPM) of the motors. Lastly, signal processing techniques were implemented to identify if transient signals are present and if present estimate the direction from which the sound arrives