Design and implementation of a multi-octave-band audio camera for realtime diagnosis

Noise pollution investigation takes advantage of two common methods of diagnosis: measurement using a Sound Level Meter and acoustical imaging. The former enables a detailed analysis of the surrounding noise spectrum whereas the latter is rather used for source localization. Both approaches complete each other, and merging them into a unique system, working in realtime, would offer new possibilities of dynamic diagnosis. This paper describes the design of a complete system for this purpose: imaging in realtime the acoustic field at different octave bands, with a convenient device. The acoustic field is sampled in time and space using an array of MEMS microphones. This recent technology enables a compact and fully digital design of the system. However, performing realtime imaging with resource-intensive algorithm on a large amount of measured data confronts with a technical challenge. This is overcome by executing the whole process on a Graphic Processing Unit, which has recently become an attractive device for parallel computing

Influence of the microstructure of 2D-random heterogeneous media on the propagation of acoustic coherent waves

International audienceMultiple scattering of waves arises in all fields of physics either in periodic or random media. For random media the organization of the microstructure (uniform or non-uniform statistical distribution of scatterers) has effects on the propagation of coherent waves. Using a recent exact resolution method and different homogenization theories, the effects of the microstructure on the effective wavenumber are investigated over a large frequency range (ka between 0.1 and 13.4) and high concentrations. For uniform random media, increasing the configurational constraint makes the media more transparent for low frequencies and less for high frequencies. As a side but important result, we show that two of the homogenization models considered here appear to be very efficient at high frequency up to a concentration of 60%, in the case of uniform media. For non-uniform media, for which clustered and periodic aggregates appear, the main effect is to reduce the magnitude of resonances and to make network effects appear. In this case, homogenization theories are not relevant to make a detailed analysis

Simulation numérique et expérimentale de la propagation non linéaire des ondes acoustiques en milieu hétérogène

La propagation à grande distance du bang sonique est sensible aux caractéristiques de l'atmosphère terrestre, notamment dans la couche turbulente située entre 0 et environ 1 km d'altitude. Nous avons réalisé des expériences à l'échelle 1 : 100 000 dans l'eau ainsi que des simulations numériques pour étudier l'interaction entre une onde de choc et un milieu hétérogène. Les expériences nous permettent de comprendre le lien entre le repliement du front d'onde (« wave front folding ») et l'augmentation du temps de montée ainsi que la distorsion des formes d'ondes. L'influence de la taille des hétérogénéités est aussi étudier expérimentalement. Ensuite, un modèle théorique et numérique est validé grâce au caractère déterministe de nos expériences. Les simulations numériques démontrent l'influence de la propagation non-linéaire et son effet sur la perception auditive du bang sonique

Statistical analysis of storm electrical discharges reconstituted from a lightning mapping system, a lightning location system, and an acoustic array

International audienceIn the framework of the European Hydrological Cycle in the Mediterranean Experiment project, a field campaign devoted to the study of electrical activity during storms took place in the south of France in 2012. An acoustic station composed of four microphones and four microbarometers was deployed within the coverage of a Lightning Mapping Array network. On the 26 October 2012, a thunderstorm passed just over the acoustic station. Fifty-six natural thunder events, due to cloud-to-ground and intracloud flashes, were recorded. This paper studies the acoustic reconstruction, in the low frequency range from 1 to 40 Hz, of the recorded flashes and their comparison with detections from electromagnetic networks. Concurrent detections from the European Cooperation for Lightning Detection lightning location system were also used. Some case studies show clearly that acoustic signal from thunder comes from the return stroke but also from the horizontal discharges which occur inside the clouds. The huge amount of observation data leads to a statistical analysis of lightning discharges acoustically recorded. Especially, the distributions of altitudes of reconstructed acoustic detections are explored in detail. The impact of the distance to the source on these distributions is established. The capacity of the acoustic method to describe precisely the lower part of nearby cloud-to-ground discharges, where the Lightning Mapping Array network is not effective, is also highlighted

Singularités d'amplitude et de phase en acoustique non linéaire (application au bang sonique)

PARIS-BIUSJ-Thèses (751052125) / SudocSudocFranceF

Theoretical and numerical studies of the streaming generated by a vortex beam

International audienc

Localization of aeroacoustic sound sources in viscous flows by a time reversal method

International audienceA time reversal procedure used previously for aeroacoustic source localization is extended to the viscous flows case. Successive flow configurations including steady flows and unsteady ones have been performed to test and validate the proposed procedure. It is demonstrated that it provides a useful methodology for the detection and the localization of aeroacoustic sources, not only in presence of a dissipative medium but also in unsteady flow configurations. When dealing with dissipative media, the application of time-reversal procedure allows for the recovery of both the shape and the location of the source of sound even if the source amplitude is damped due to the viscous energy loss. For unsteady flows (in presence or not of a dissipative medium), the aeroacoustic source detection method remains always effective even if some theoretical assumptions are not fully satisfied

Analyse statistique de la propagation des ondes de souffle en environnement complexe

La propagation acoustique des ondes de souffle est affectée par la topographie, la végétation et les conditions météorologiques. Ces effets comportent une part importante d'incertitudes du fait de la méconnaissance et de la nature aléatoire du milieu de propagation. Afin de quantifier ces incertitudes, des enregistrements acoustiques ont été réalisés autour d'un site pyrotechnique industriel jusqu'à 20 km pour environ 600 explosions d'énergies comprises entre 300 et 500 kg d'équivalent TNT. Ces mesures sont classifiées en fonction des conditions de propagation puis comparées à des simulations numériques. Les incertitudes associées à la source explosive sont analysées par des méthodes de clustering. Les incertitudes dues à la méconnaissance des grandes échelles de l'atmosphère sont analysées à l'aide d'un modèle de propagation unidirectionnel couplé avec des polynômes de chaos. Les résultats préliminaires montrent que l'incertitude associée à l'atmosphère est dominante et que son amplitude est en partie retrouvée par les modèles

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

International audienc