Un modèle diphasique self-consistant pour la propagation du son dans des solutions concentrées de particules rigides.

Un modèle diphasique self-consistant est proposé pour modéliser la propagation du son dans des suspensions de particules rigides concentrées (en régime grande longueur d'onde) et ainsi tenir compte des effets de diffusion multiple. A partir des équations locales, des équations moyennes sont écrites pour chaque phase et la fermeture est obtenue à l'aide d'un shéma self-consistant initialement développé par Buyevich & Shchelchkova [Prog. Aerospace Sci., 1978] pour des écoulements incompressibles. Ainsi, les interactions entre les particules sont prises en compte à tous les ordres. De plus, les corrélations de position, c'est à dire la modification de la répartition des particules induite par leur non-recouvrement, ont également été incluses dans la modélisation de manière simplifiée. Au final, l'introduction de ces effets permet d'obtenir des courbes d'atténuation et de dispersion très proches des courbes expérimentales obtenues par Hipp et al. [Langmuir, 2002] pour des nanoparticules de silice dans de l'eau, avec des fractions volumiques allant jusqu'à 30 % et une gamme de fréquence comprise entre 1 et 100 MHz

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

Impact of reduced sonic boom exposure on psychophysical and cognitive performance for simulated booms presented in a realistic indoor environment

This study aimed to quantify, in situations representative of the daily life of European citizens, the effects of sonic boom exposure on human responses, in the case of a new generation of supersonic commercial aircraft that should emit a reduced (compared to the past generation like Concorde) but perceivable boom while flying overland. Two reduced boom simulators were affixed to the bedrooms’ windows of a house located on our university campus. The simulators were used to study indoor the participants’ responses to realistic “outdoor” booms. Testing took place in both the living room and kitchen because the booms caused different intensities of rattle noise in those two rooms. Participants performed various tasks (communication, working memory, drawing, valence evaluation), took three mandatory rests and filled in various questionnaires about the annoyance caused by the booms and their mood. This paper focuses on the psychophysical and cognitive performance results. The booms resulted in delayed responses in the working memory task and in the valence evaluation task, and in a momentary slowing down in the drawing task. There was no significant effect in the communication task, even though a trend for a worsening of communication efficiency was observed. Taken together, the results suggest that reduced booms can interfere with cognitive and motor tasks by capturing attention, which can momentarily divert cognitive resources away from the task at hand. These results suggest future research directions and may lead to recommendations for future sonic boom regulations

Bulk probing of shock wave spatial distribution in opaque solids by ultrasonic interaction

We present a method to investigate the bulk propagation of a shock wave in a thick, opaque metallic plate. The shock wave is generated by laser-loading. An elastic plane probe wave, contra-propagative with respect to the shock, is emitted by means of a phase-array device. Shock propagation monitoring is performed by analyzing on the phase-array detection the acoustic elastic plane wave after its interaction with the shock. The time-space detection of the probe wave allows to evaluate the spatial distribution of the shock wave all along its propagation in the opaque structure, from near to far field. Applications range from fundamental wave science to laser-loading material science

Propagation of laser-generated shock waves in metals: 3D axisymmetric simulations compared to experiments

This work aims at demonstrating the ability of an acoustic linear code to model the propagation of a shock wave created by a laser impact over a metallic surface. In this process, a high pressure surface level is reached using a ns laser pulse that heats the surface of the material and generates a dense plasma expansion. The pressure reaches few GPa so shock waves are generated and propagate into the bulk of the material. Currently, shock wave propagation is modeled using continuity equations and an ad hoc equation of state for the illuminated mate-rial, very limiting because it is numerically intensive. Here, we propose to model the shock wave bulk propagation using a linear acoustic code. A nonlinear surface pressure term, resulting from the laser–matter interaction, is used as a boundary condition. The applied numerical scheme is based on the Virieux scheme, including a fourth order finite difference discretization of the linearized elastomechanical equations. The role of longitudinal and transverse waves and their origins are highlighted. The importance of considering 3D geometries is pointed out. Simulations are finally confronted with experimental results obtained with the Hephaistos Laserlab facility (energy up to 14 J at 532 nm wavelength laser; pulse duration: 7 ns). Illuminations up to the optical breakdown in water are easily achieved with laser focal spots of 5 mm width. Excellent agreement between experiments and simulations is observed for several sets of experimental parameters for titanium, a material of high elastic limit, while limitations are founded for aluminum. The code is available in the MetaData

Sources and propagation of atmospherical acoustic shock waves

19th International Symposium on Nonlinear Acoustics (ISNA), Waseda Univ, Tokyo, JAPAN, MAY 21-24, 2012International audienceSources of aerial shock waves are numerous and produce acoustical signals that propagate in the atmosphere over long ranges, with a wide frequency spectrum ranging from infrasonic to audible, and with a complex human response. They can be of natural origin, like meteors, lightning or volcanoes, or human-made as for explosions, so-called ``buzz-saw noise'' (BSN) from aircraft engines or sonic booms. Their description, modeling and data analysis within the viewpoint of nonlinear acoustics will be the topic of the present lecture, with focus on two main points: the challenges of the source description, and the main features of nonlinear atmospheric propagation. Inter-disciplinary aspects, with links to atmospheric and geo-sciences will be outlined. Detailed description of the source is very dependent on its nature. Mobile supersonic sources can be rotating (fan blades of aircraft engines) or in translation (meteors, sonic boom). Mach numbers range from transonic to hypersonic. Detailed knowledge of geometry is critical for the processes of boom minimization and audible frequency spectrum of BSN. Sources of geophysical nature are poorly known, and various mechanisms for explaining infrasound recorded from meteors or thunderstorms have been proposed. Comparison between recorded data and modeling may be one way to discriminate between them. Moreover, the nearfield of these sources is frequently beyond the limits of acoustical approximation, or too complex for simple modeling. A proper numerical description hence requires specific matching procedures between nearfield behavior and farfield propagation. Nonlinear propagation in the atmosphere is dominated by temperature and wind stratification. Ray theory is an efficient way to analyze observations, but is invalid in various situations. Nonlinear effects are enhanced locally at caustics, or in case of grazing propagation over a rigid surface. Absorption, which controls mostly the high frequency part of the spectrum contained within shocks, is controlled by humidity, cloudiness or surface properties. Variability is large at all scales, and depends simultaneously on climate, daily meteorology, and local turbulent state, especially near the ground in the planetary boundary layer. Numerous features of outdoor propagation remain to be explored in the nonlinear case, such as complex 3D atmospheric description (role of turbulence, partial reflections, gravity waves) or topography

Parabolic approximation in ray coordinates for high-frequency nonlinear waves in a inhomogeneous and high speed moving fluid

International audienc

A quasi-analytical shock solution for general nonlinear progressive waves

International audienc

Ondes de choc acoustiques en milieu hétérogène, des ultrasons au bang sonique

PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF