No description available.

Les infrasons sont des ondes acoustiques de fréquence inférieure à environ 20 Hz qui sont produits par une grande variété de sources naturelles (éruptions volcaniques, séismes, etc.) ou artificielles (explosions chimiques, avions, tirs de mine, etc.). Ils peuvent se propager dans l’atmosphère terrestre jusqu’à de très grandes distances, de quelques centaines à plusieurs milliers de kilomètres, et transportent des informations importantes concernant leur source. Pour cette raison, la mesure des ondes infrasonores représente aujourd’hui une des principales techniques utilisées dans le cadre du Traité d’interdiction complète des essais nucléaires (TICE) pour la détection, la localisation et l’identification de sources. La modélisation de la propagation atmosphérique des infrasons a été classiquement réalisée par des approximations géométriques, comme le tracé de rayons, ou par la résolution d’équations paraboliques. Grâce à un coût de calcul raisonnable, allant de quelques secondes à une heure, ces approches sont largement employées dans le domaine opérationnel. Leur efficience est néanmoins obtenue au détriment de la complexité physique de la propagation atmosphérique. Les avancées récentes de la simulation numérique directe en aéroacoustique rendent cependant envisageable la résolution directe des équations de Navier-Stokes instationnaires et compressibles, permettant ainsi de décrire sans approximation la propagation infrasonore. Dans la présente thèse, trois objectifs principaux ont été poursuivis. En utilisant une méthode de tracé de rayons, une caractérisation des effets non linéaires, visqueux, thermiques et de relaxation sur les ondes infrasonores produites par des sources explosives a été d’abord effectuée. La propagation non linéaire des signaux infrasonores dans l’atmosphère terrestre a été ensuite examinée à l’aide de simulations tridimensionnelles directes des équations de Navier-Stokes instationnaires et compressibles. Des sources de très grande amplitude et de fréquence de l’ordre de 0.1 Hz ont été considérées. Les calculs ont été menés jusqu’à des distances de propagation de plusieurs centaines de kilomètres et jusqu’à des altitudes de l’ordre de 140 km. Une étude détaillée de la diffusion par les petites échelles de l’atmosphère a été effectuée. Une première analyse de la pénétration en zone d’ombre provoquée par des phénomènes de diffraction au niveau des caustiques a été également réalisée. Des cas test bidimensionnels ont été enfin formulés et des solutions de référence ont été déterminées afin de permettre la validation numérique de codes de calcul et l’évaluation des erreurs commises par les approximations usuelles. / Infrasounds are acoustic signals of frequency lower than about 20 Hz. They are generated by a large variety of natural events, such as volcanic eruptions or earthquakes, and by artificial sources, like nuclear or chemical explosions and supersonic booms. Infrasonic waves can propagate through the different atmospheric layers up to very large distances, from few hundreds to thousands of kilometres, and can potentially carry relevant information about their source. For this reason, within the framework of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), infrasound recordings are widely employed to monitor clandestine nuclear tests. Infrasound modelling has classically been based on simplified equations. Ray tracing and parabolic models have been the most commonly used techniques. Their efficiency in terms of computational cost is however obtained at the expense of generality and some of the main phenomena affecting infrasound propagation are inherently excluded by these methods. Over the past decade, progress has been made towards the simulation of acoustic propagation by directly solving the fluid dynamics equations. Understandably, this approach is expected to allow a finer description of atmospheric propagation and to lead to a better interpretation of experimental observations. In the present thesis, three main objectives have been achieved. First of all, using ray theory, a characterization of nonlinear effects and absorption induced by thermo-viscous and vibrational relaxation phenomena on the propagation of infrasonic signals generated by explosive sources has been carried out. Direct numerical simulations of the three-dimensional unsteady compressible Navier-Stokes equations have been then performed to calculate the sound field generated by an infrasonic source in a realistic atmosphere. Computations have been carried out using a low-dispersive and low-dissipative finite-difference time-domain method, for very large source amplitudes and for source frequencies of order of 0.1 Hz, up to altitudes of 140 km and ranges of few hundreds of kilometres. The scattering from small-scale inhomogeneities, of characteristic dimension of the same order as the wavelength of the infrasonic wave, has been investigated. The penetration in the shadow zone induced by diffraction phenomena at the thermospheric caustic has also been studied. Two-dimensional benchmarks specific to infrasound atmospheric propagation have been finally formulated and reference solutions have been computed. They aim to allow the assessment of the accuracy of numerical solvers as well as the evaluation of the range of validity of the classical approaches.

Many problems in shallow water acoustics require accurate predictions of the acoustic field in space and time. The accuracy of the predicted acoustic field depends heavily on the accuracy of the inputs to the propagation model. Oceanographic internal waves are known to introduce considerable temporo-spatial variability to the water column, subsequently affecting the propagation of acoustic waves. As a result, when internal waves are present, errors in model inputs can significantly degrade the accuracy of the predicted acoustic field. Accurate temporo-spatial predictions of the acoustic field in the presence of internal waves therefore depend largely on one's ability to accurately prescribe the water column properties for the acoustic model. This work introduces a data-driven oceanographic model, named the evolutionary propagated thermistor string (EPTS) model, that captures the temporo-spatial evolution of the internal wave field along a fixed track, thereby permitting prediction of temporal fluctuations in the acoustic field. Simultaneously-measured oceanographic and acoustic data from the Office of Naval Research Shallow Water 2006 experiment are utilized in this work. Thermistor measurements, recorded on four oceanographic moorings spaced along the continental shelf, provide the data from which the EPTS model constructs the internal wave field over a 30 km track. The acoustic data were acquired from propagation measurements over a co-located path between a moored source and a vertical line array. Acoustic quantities computed in the model space, such as received level, depth-integrated intensity, and scintillation index are directly compared to measured acoustic quantities to evaluate the fidelity of the oceanographic model. In addition, a strong correlation is observed between the amplitude of the internal wave field and acoustic intensity statistics at a distant receiving array. It is found that the EPTS model possessed sufficient fidelity to permit the prediction of acoustic intensity distributions in the presence of nonlinear internal waves. / text

No description available.

In June 2003, the Littoral Acoustic Demonstration Center conducted an acoustic characterization experiment for a standard seismic exploration array. Two moorings with Environmental Acoustic Recording Systems (EARS) were deployed in the northern part of the Gulf of Mexico to measure ambient noise and collect shot information. A 21-element seismic airgun array was towed along five parallel linear tracks with horizontal closest approach points to the EARS buoy position of 63, 500, 1000, 2000, and 5000 m. Calibrated acoustic pressure measurements collected during the experiment were analyzed to obtain zero-to-peak sound pressures, sound exposure levels, and pressure levels in 1/3-octave frequency bands. In addition, the experimental data were modeled by using a modified underwater acoustic propagation model to fill in missing data measurements. The resulting modeling procedure showed good agreement between measured and modeled data in absolute pressure amplitudes and frequency interference patterns for frequencies up to 1000 Hz. The analysis is important for investigating the potential impact on marine mammals and fish and predicting the exposure levels for newly planned seismic surveys in other geographic areas. Based on results of the experiment conducted and data analysis performed, a new experimental design was proposed to maximize the amount of collected data using the available equipment while minimizing the time needed for the source ship. The design used three patches, one with 3º angular spacing between the lines at a reference depth. Embedded is a smaller patch with 1º spacing and within that a still smaller patch with one half degree spacing. This arrangement gives a reasonably uniform distribution of shots versus solid angle with a large variety of emission and azimuthal angles for different ranges. Due to the uncertainty of positioning systems, the angular space is divided into solid angle bins. Simulations predicted more than 200 shots per bin for emission angles greater than 13 degrees. Statistical analysis of collected data will be performed on the proposed bin basis. An experiment based on the proposed design was conducted in Fall 2007. The data measurements collected during the experiment are currently being analyzed and will be reported in the near future.

L’étude de la propagation sonore dans un milieu confiné nécessite une connaissance précise des caractéristiques acoustiques et géométriques des parois qui le délimitent. En effet, le relief géométrique des parois d’un local engendre des phénomènes acoustiques complexes pouvant impacter significativement la propagation sonore : diffusion, diffraction ou encore résonance si le relief présente une géométrie particulière. L’objectif de cette étude est de développer un modèle numérique simulant la propagation sonore dans un espace confiné délimité par des parois à relief géométrique. Dans un premier temps, la méthode de décomposition rectangulaire adaptative (ARD) est utilisée pour simuler la propagation en milieu confiné. Cette méthode est ensuite couplée à la méthode de différences finies dans le domaine temporel (FDTD) et l’utilisation de filtres d’impédance numériques (DIF) pour simuler des parois à relief géométrique possédant une impédance dépendante de la fréquence. L’intégration de la méthode FDTD dans la méthode ARD est rendue possible par l’utilisation de couches absorbantes parfaitement adaptées (PML). Le modèle numérique est validé par comparaison aux méthodes Kobayashi Potential (KP) et sources images ainsi qu’à des résultats expérimentaux. Enfin, le modèle est utilisé pour étudier la diffusion acoustique causée par plusieurs parois à relief expérimentales. Un coefficient d’absorption acoustique apparent est ainsi estimé pour caractériser chacune de ces parois / The study of sound propagation in an enclosed space requires a precise knowledge of the acoustic and geometrical characteristics of its boundaries. Indeed, the geometric relief on the walls of a room causes complex acoustic phenomena that can significantly impact the sound propagation: scattering, diffraction or even resonance if the relief has a particular geometry. The objective of this study is to develop a numerical model of sound propagation in an enclosed space bounded by walls with geometric relief. First, the Adaptive Rectangular Decomposition (ARD) method is used to simulate the propagation in a room. Then, this method is coupled with the Finite Difference in Time Domaine (FDTD) method and the use of digital impedance filters (DIF) to include boundaries with geometric relief and frequency-dependent impedance. The integration of the FDTD method into the ARD method is made possible by the use of perfectly matched layers (PML). The numerical model is validated by comparison with the Kobayashi Potential (KP) and image source methods as well as experimental results. Finally, the model is used to study the sound scattering caused by several experimental relief walls. An apparent sound absorption coefficient is thus estimated to characterize each of these different walls

Este trabalho tem como objetivo global contribuir para o desenvolvimento do estudo da propagação de ondas em dutos de transporte de fluidos, especialmente oleodutos e gasodutos, através da análise da atenuação acústica e da velocidade de propagação da onda. Para isso, foram feitos ensaios experimentais, tanto em escoamento mono quanto bifásico, variando-se a vazão do escoamento em uma linha de testes de 1500 metros e 50 mm de diâmetro, para aquisição de sinais gerados a partir do fechamento de válvulas de simulação de vazamentos em pontos ao longo da tubulação. Para análise da atenuação acústica foi proposta uma metodologia baseada na medição do coeficiente de amortecimento temporal das ondas de pressão como subsídio para o cálculo do coeficiente de atenuação, através da utilização de um único sensor de pressão. Esta metodologia foi validada pela medição direta do coeficiente de atenuação e os resultados mostram uma excelente concordância em escoamentos monofásicos. Para os testes em escoamento bifásico não foi possível aplicar esta metodologia devido ao forte amortecimento das ondas de pressão, sendo feitas apenas medições diretas da atenuação com resultados fenomenologicamente coerentes. A velocidade de propagação acústica para escoamento monofásico foi influenciada pela presença de gás dissolvido e bolhas de cavitação, apresentando valores próximos aos da literatura para baixas vazões de escoamento. Para altas vazões, as velocidades foram compatíveis com o escoamento bifásico a bolhas finamente dispersas. Para o escoamento bifásico o regime de escoamento variou de bolhas a pistonado. As velocidades de propagação obtidas são compatíveis com aquelas obtidas por modelos teóricos. / This work aims to contribute to the development of the study of wave propagation in fluid transport pipelines, through the analysis of acoustic attenuation and propagation speed. For this reason, experimental tests were made in single and two-phase flow, varying the flow rate in a test line of 1500 meters and 50 mm in diameter, for the acquisition of signals generated from the closing of leak simulation valves at known points along the pipeline. To analyze the acoustic attenuation it was proposed a methodology based on measurement of temporal damping coefficient of pressure waves as input for calculating the attenuation coefficient, by using a single pressure sensor. This methodology was validated by direct measurement of attenuation coefficient and the results show an excellent agreement in single-phase flow. For the tests in two-phase flow it was not possible to apply this methodology due to the strong damping of pressure waves, which only made direct measurements of attenuation results phenomenologically consistent. Acoustic propagation velocity for single phase flow was influenced by the presence of dissolved gas and cavitation bubbles, having values close to the literature for low flow rates. For high flows rates, the velocities were consistent with a two-phase flow at finely dispersed bubbles. For the two-phase flow the regime varied from slug to bubbles. The propagation velocities obtained are consistent with those obtained by theoretical models.

Depuis plus de deux décennies, I'enregistrement des signaux hydroacoustiques par des hydrophones dans le canal SOFAR (SOund Fixing And Ranging) a permis la détection et la localisation de nombreux séismes de faible magnitude dans I'océan. Cependant, I'interprétation de ces signaux est actuellement incomplète. La complexité de la conversion des ondes sismiques en ondes acoustiques, appelées « ondes T », au niveau du plancher océanique, et de leur propagation dans la tranche d'eau n'est pas intégralement comprise et ne permet pas d'extraire beaucoup d'informations sur les séismes à leur origine. Une simulation numérique de ces signaux est proposée pour identifier et comprendre les paramètres environnementaux et les phénomènes majeurs entrant en jeu dans la génération des ondes T. L'approche proposée est la méthode des éléments spectraux, mise en œuvre dans le code SPECFEM2D. Cette approche s'avère adaptée à cet usage car elle permet d'aborder le phénomène de la génération et la propagation des ondes T dans son ensemble en tenant compte ses principales caractéristiques : le couplage fluide/solide (propagation sismique, conversion, et propagation acoustique), les profils de vitesse d'onde dans I'eau et dans la croute, et le tenseur des moments sismiques donnant le diagramme de radiation de la source. Les signaux simulés présentent des formes, des durées, des temps d'arrivée, et des amplitudes relatives tout à fait comparables aux enregistrements réels. Les différences observées proviennent sans doute du traitement 2D du problème et d'une représentation trop simpliste des environnements et de la source sismique. / For more than 2 decades, recording of hydroacoustic signals in the sopen channel (Sound Fixing And Ranging) has allowed the detection and localization of many low-magnitude earthquakes in the ocean. However the interpretation of these signals is still incomplete.The generation of acoustic waves, known as T-waves, resulting from the conversion of seismic waves into acoustic waves at the sea-bottom, and their propagation in the water column are not yet fully understood, which prevents to extract more information about the earthquakes they originate from. Here, we use numerical modelling to identify and understand the main environmental parameters and phenomena that control the generation and propagation of acoustic T-waves in the ocean. The proposed approach is a spectral element method, implemented in the code SPECFEM2D, which allows to address the problem in a comprehensive way taking into account the solid/fluid coupling (seismic propagation, conversion, acoustic propagation), velocity profiles of the waves in the crust and the ocean, and the moment tensor of the earthquake that defines the radiation pattern of the seismic source. Simulated acoustic signals present many similarities in the shape, duration, arrival times and amplitudes of the predicted T-waves with observed T-waves. Differences are likely due to the 2D representation of the problem and to the simplistic representation of the environment and of the seismic source.

Complex structures and multiple interfaces of modern microelectronic packages complicate the interpretation of acoustic data. This study has four novel contributions. 1) Contributions to the finite element method. 2) Novel approaches to reduce computational cost. 3) New post processing technologies to interpret the simulation data. 4) Formation of theoretical guidance for acoustic image interpretation. The impact of simulation resolution on the numerical dispersion error and the exploration of quadrilateral infinite boundaries make up the first part of this thesis's contributions. The former focuses on establishing the convergence score of varying resolution densities in the time and spatial domain against a very high fidelity numerical solution. The latter evaluates the configuration of quadrilateral infinite boundaries in comparison against traditional circular infinite boundaries and quadrilateral Perfectly Matched Layers. The second part of this study features the modelling of a flip chip with a 140µm solder bump assembly, which is implemented with a 230MHz virtual raster scanning transducer with a spot size of 17µm. The Virtual Transducer was designed to reduce the total numerical elements from hundreds of millions to hundreds of thousands. Thirdly, two techniques are invented to analyze and evaluate simulated acoustic data: 1) The C-Line plot is a 2D max plot of specific gate interfaces that allows quantitative characterization of acoustic phenomena. 2) The Acoustic Propagation Map, contour maps an overall summary of intra sample wave propagation across the time domain in one image. Lastly, combining all the developments. The physical mechanics of edge effects was studied and verified against experimental data. A direct relationship between transducer spot size and edge effect severity was established. At regions with edge effect, the acoustic pulse interfacing with the solder bump edge is scattered mainly along the horizontal axis. The edge effect did not manifest in solder bump models without Under Bump Metallization (UBM). Measurements found acoustic penetration improvements of up to 44% with the removal of (UBM). Other acoustic mechanisms were also discovered and explored. Defect detection mechanism was investigated by modelling crack propagation in the solder bump assembly. Gradual progression of the crack was found have a predictable influence on the edge effect profile. By exploiting this feature, the progress of crack propagation from experimental data can be interpreted by evaluating the C-Scan image.

Este trabalho tem como objetivo global contribuir para o desenvolvimento do estudo da propagação de ondas em dutos de transporte de fluidos, especialmente oleodutos e gasodutos, através da análise da atenuação acústica e da velocidade de propagação da onda. Para isso, foram feitos ensaios experimentais, tanto em escoamento mono quanto bifásico, variando-se a vazão do escoamento em uma linha de testes de 1500 metros e 50 mm de diâmetro, para aquisição de sinais gerados a partir do fechamento de válvulas de simulação de vazamentos em pontos ao longo da tubulação. Para análise da atenuação acústica foi proposta uma metodologia baseada na medição do coeficiente de amortecimento temporal das ondas de pressão como subsídio para o cálculo do coeficiente de atenuação, através da utilização de um único sensor de pressão. Esta metodologia foi validada pela medição direta do coeficiente de atenuação e os resultados mostram uma excelente concordância em escoamentos monofásicos. Para os testes em escoamento bifásico não foi possível aplicar esta metodologia devido ao forte amortecimento das ondas de pressão, sendo feitas apenas medições diretas da atenuação com resultados fenomenologicamente coerentes. A velocidade de propagação acústica para escoamento monofásico foi influenciada pela presença de gás dissolvido e bolhas de cavitação, apresentando valores próximos aos da literatura para baixas vazões de escoamento. Para altas vazões, as velocidades foram compatíveis com o escoamento bifásico a bolhas finamente dispersas. Para o escoamento bifásico o regime de escoamento variou de bolhas a pistonado. As velocidades de propagação obtidas são compatíveis com aquelas obtidas por modelos teóricos. / This work aims to contribute to the development of the study of wave propagation in fluid transport pipelines, through the analysis of acoustic attenuation and propagation speed. For this reason, experimental tests were made in single and two-phase flow, varying the flow rate in a test line of 1500 meters and 50 mm in diameter, for the acquisition of signals generated from the closing of leak simulation valves at known points along the pipeline. To analyze the acoustic attenuation it was proposed a methodology based on measurement of temporal damping coefficient of pressure waves as input for calculating the attenuation coefficient, by using a single pressure sensor. This methodology was validated by direct measurement of attenuation coefficient and the results show an excellent agreement in single-phase flow. For the tests in two-phase flow it was not possible to apply this methodology due to the strong damping of pressure waves, which only made direct measurements of attenuation results phenomenologically consistent. Acoustic propagation velocity for single phase flow was influenced by the presence of dissolved gas and cavitation bubbles, having values close to the literature for low flow rates. For high flows rates, the velocities were consistent with a two-phase flow at finely dispersed bubbles. For the two-phase flow the regime varied from slug to bubbles. The propagation velocities obtained are consistent with those obtained by theoretical models.