Chronic liver diseases are the eighth leading cause of death in Brazil and a major public health problem in the world. Liver biopsy is the best available reference standard for evaluating and classifying stages of liver diseases, but it presents limitations and complications that are common in invasive methods. In recent years, elasticity imaging methods have been the focus of intense research activity with the ability to measure mechanical properties of soft tissues in a non-invasive way. Shear wave elastography is one of the most promising methods because it enables to quantitatively assess tissue elasticity. However, the current depth range of shear wave elastography impedes its application in obese patients, which have a great risk of developing liver disease. The aim of this study is to investigate the use of shear wave elastography in deeper tissues using a two-dimensional ultrasound transducer array. An efficient transducer array arrangement was simulated, fabricated and characterized. The results show that the proposed transducer configuration presents enhanced transmitting capabilities for generating tissue displacement in deeper tissues. In addition, numerical simulations were performed in order to track the tissue deformation and reconstruct its elastic properties. / Doenças crônicas do fígado são a oitava causa de morte no Brasil e um dos principais problemas de saúde pública do mundo. A biópsia do fígado é o melhor padrão de referência disponível para avaliação e classificação dos estágios das doenças hepáticas, mas apresenta limitações e complicações que são comuns nos métodos invasivos. Nos últimos anos, métodos de imagem por elasticidade têm sido o foco de intensa atividade de pesquisa, pois têm a capacidade de medir propriedades mecânicas dos tecidos moles de maneira não invasiva. A elastografia por ondas de cisalhamento é um dos métodos mais promissores, pois permite avaliar quantitativamente a elasticidade do tecido. No entanto, a atual faixa de profundidade da elastografia por ondas de cisalhamento impede sua aplicação em pacientes obesos, que apresentam grande risco de desenvolver doença hepática. O objetivo deste estudo é investigar o uso da elastografia por onda de cisalhamento em tecidos mais profundos usando um transdutor de ultrassom bidimensional. Uma configuração eficiente de transdutores matriciais foi simulada, fabricada e caracterizada. Os resultados mostram que o transdutor proposto possui capacidade de transmissão melhorada para gerar deslocamento em tecidos profundos. Além disso, simulações numéricas foram realizadas para monitorar a deformação do tecido e reconstruir suas propriedades elásticas.

Les constructeurs aéronautiques envisagent les systèmes de propulsion à hélices contra rotatives comme une alternative aux turboréacteurs, afin de réduire la consommation de carburant et les émissions des gaz à effet de serre. En raison de l’absence de carénage, la réduction du bruit engendrée par de tels systèmes représente un enjeu majeur pour les industriels. En particulier, le bruit de raies dû à l’impact des sillages de l’hélice amont sur l’hélice aval constitue une part significative de l’émission acoustique. Le travail présenté dans cette thèse a abouti à une méthode semi-analytique de prédiction de ce bruit d’interaction, intégrant de façon relativement réaliste les effets tridimensionnels des sillages de l’hélice amont et de la géométrie des pales de l’hélice aval. L’espace balayé par une pale est décomposé en tranches annulaires, déroulées pour décrire localement l’interaction en coordonnées cartésiennes. Le segment de pale obtenu est approché par un trapèze plat de forme et d’orientation quelconques. Une double stratégie est proposée pour la description du sillage. Premièrement, il peut être décrit par un modèle analytique tenant compte du vrillage et de l’expansion avec la distance au bord de fuite. Deuxièmement, il peut être post-traité à partir des calculs numériques. Ensuite, dans chaque tranche le déficit de vitesse ressenti par le segment de pale fait l’objet d’une décomposition de Fourier à deux nombres d’onde. Le calcul de la réponse aérodynamique instationnaire du segment est fait dans le domaine fréquentiel. Il étend des solutions analytiques existantes valables pour un segment rectangulaire, et prend en compte la compressibilité du fluide et la non-compacité des pales. On restitue ainsi les effets de la flèche, du vrillage et de la variation de la corde en envergure. Les fluctuations de portance induites sur les différents segments, obtenues par le calcul, sont utilisées pour construire une répartition de sources acoustiques équivalentes sur la surface réelle des pales, au sens de l’analogie acoustique. Le bruit en champ lointain est alors calculé en utilisant le formalisme de Ffowcs Williams & Hawkings, adapté au cas d’un dipôle tournant dans un écoulement uniforme. La méthodologie proposée a été implémentée dans l’outil ORION et évaluée avec des résultats numériques et des mesures en soufflerie. / Counter-rotating open rotors are seen as a possible alternative to turbofan engines for future subsonic aircraft propulsion, essentially for their higher fuel-efficiency. This technology leads to fuel saving sand to reduced green-house gas emissions. However, these benefits are balanced by some inherent draw-backs, as the increased noise radiation. Particularly, the tonal noise produced by the impingement of the wakes issuing from the front rotor onto the rear-rotor blades is recognized as a major contributor to the emitted noise. The research presented in this thesis led to a semi-analytical methodology to predict the rotor-rotor interaction tonal noise, including three-dimensional features of both rear-rotor blades and front-rotor wakes. The space is cut into annular regions, subsequently unwrapped for formulating the problem in equivalent Cartesian coordinates. Also, the obtained blade segments are assimilated as a set of flat trapezoids with arbitrary orientation, accounting for blade sweep and chord variations in the span wise direction. A double strategy is proposed for the description of front-rotor wakes. First, an analytical model is proposed in which wake direction and diffusion are deduced from the blade stagger angle and axial distance between the rotors. Secondly, a strategy for post-processing numerical wakes is presented. In both cases, the oncoming excitation is expanded in a series of sinusoidal gusts with two aerodynamic wavenumber components. Using this information the unsteady loading on the rear-rotor blades is obtained, in the frequency domain, from an extension of Amiet’s theory for gust-air foil interaction to account for air foil sweep and chord variations, flow compressibility and source non-compactness. The obtained noise source is back-projected on the blade mean-camber surface. An extended far-field formulation is then used to predict the noise. This theory is derived in detail from Ffowcs Williams &Hawkings’ formalism adapted for acoustic dipoles rotating in a uniformly moving atmosphere. The pro-posed methodology has been implemented in the tool ORION and assessed by comparing its results with numerical simulations and wind-tunnel measurements.

<p>Accurate and reliable prediction of laminar-turbulent boundary layer transition at hypersonic velocities is important for the development of a variety of practical high-speed flight systems currently under development. Boundary layer transition can cause up to an order of magnitude increase in skin friction and heat flux on a flight vehicle, meaning that understanding boundary layer behavior is critical to the design of weight-efficient thermal protection systems. Despite the importance of the topic, significant gaps remain in the community's current understanding of boundary layer transition and control. </p> <p>One of the biggest areas of concern in the field of high-speed boundary layer transition is the effect of facility noise on wind tunnel measurements. Conventional hypersonic wind tunnels are contaminated by freestream fluctuations which can be as much as two orders of magnitude higher than free-flight atmospheric conditions. These disturbances are typically produced by turbulent boundary layers on the tunnel walls; they are acoustic in nature and consist of pressure waves which radiate into the test section. This facility noise plays a leading role in high-speed transition phenomena in conventional hypersonic tunnels.</p> <p><br></p> <p>The current work studies the effects of facility noise on hypersonic transition using both linear stability theory and direct numerical simulation. A model for the freestream disturbance environment of the von Karman Facility's Tunnel B based on experimental measurements of the disturbance spectra present in the tunnel is created and used to study a past experiment performed in the same wind tunnel using a sharp cone and hollow cylinder. The results show that while linear stability theory accurately captures the behavior of second-mode instability growth, it fails to predict the growth of low-frequency instabilities recorded in the experiments. The stability theory analysis also suggests that very fine scale variation in nose tip geometry can play an outsize role in the development of boundary layer instabilities significantly farther downstream.</p> <p><br></p> <p>The direct numerical simulation demonstrates that, using an artificial body forcing term to implement the constructed tunnel noise model, the experimental effects of facility noise can be adequately captured with a sufficiently dense computational grid. For the conical geometry used in the experiments, calculations of surface heat flux indicate good experimental agreement with in prediction of transition location, and total temperature spectra extracted from the flow compare favorably with the experimental data as well. Visualizations of the flowfield confirm the onset of turbulence as a result of the freestream forcing. The computations also suggest that nonlinear interactions may be present in the turbulent breakdown region, leading to the production of streamwise streaks along the cone's surface. Transition on the hollow cylinder was not achieved due to suspected resolution issues, so detailed physical comparison of the two cases was not possible.</p> <p><br></p> <p>Overall, the results of this work suggest that direct numerical simulation is a capable tool for studying the effects of facility noise on hypersonic transition for simple geometries, albeit one which can be difficult to practically realize considering the required computational cost. Computational results indicate that two phenomena may play a role in the development of boundary layer instabilities for a sharp cone --- the fine-scale shape of the tip, which may change the behavior of the entropy layer near the nose; and the interactions between low- and high-frequency waveforms, which seems to cause nonlinear breakdown in line with current experimental understanding.</p>

In both, cell secretome analysis and bacteria evolution, controlled handling of particles with a few to sub-micrometers in size and media exchange are inevitable in order to investigate body fluid’s proteins or change the surrounding culture conditions for pivoted evolution. Typically, nanofiltration and ultra-centrifugation are employed which can lead to cell damage, need large sample volumes and have a high sample loss. Using contactless and label-free acoustic cell manipulation, disadvantages of other magnetic, dielectric or hydrodynamic methods can be avoided. Here, a novel design using acoustic forces for small particle trapping and media exchange is thoroughly numerically investigated including first- and second-order acoustic effects. The device comprises parallel aligned medium and air channels separated by a thin wall. Particle trapping occurs at this thin wall. The medium channel dimensions (height and width) and thin wall thickness are optimized with respect to trapping forces. Thinnest walls are preferable and an aspect ratio of 0.8. First preliminary experimental variation with polystyrene particles showed good agreement with the simulations. Thereby the particle trapping efficiency is evaluated under quiescent flow conditions. For particle trapping, a device with a channel height of 290μm and an aspect ratio of 0.7 is superior which supports the numerical results. Finally, medium exchange of E. coli bacteria is demonstrated with best results for a device with a channel height of 450μm and an aspect ratio of 0.8 showing that 13.4% of the initial bacteria were released after medium exchange which can be used for further processing.

Ultrasound directed self-assembly (DSA) utilizes the acoustic radiation force associated with a standing ultrasound wave field to organize particles dispersed in a fluid medium into specific patterns. The ability to tailor the organization and packing density of spherical particles using ultrasound DSA in a viscous fluid medium is crucial in the context of (additive) manufacturing of engineered materials with tailored properties. However, the fundamental physics of the ultrasound DSA process in a viscous fluid medium, and the relationship between the ultrasound DSA process parameters and the specific patterns of particles that result from it, are not well-understood. Researchers have theoretically described the acoustic radiation force and the acoustic interaction force that act on spherical particles in a standing ultrasound wave field in both inviscid and viscous media. In addition, they have solved the forward and inverse ultrasound DSA problem in an inviscid medium, in which they relate the patterns of particles and the ultrasound DSA operating parameters. However, no theoretical model exists that allows simulating the steady-state and transient local particle packing density in a viscous medium during ultrasound DSA. Thus, in this dissertation, we (i) theoretically derive and experimentally validate a model to determine the steady-state locations where spherical particles assemble during ultrasound DSA as a function of medium viscosity and particle volume fraction. (ii) We also theoretically derive and experimentally validate a model to quantify the steady-state and transient local packing density of spherical particles within the pattern features that result from ultrasound DSA. Using these models, we quantify and predict the locations where spherical particles assemble during ultrasound DSA in a viscous medium, considering the effects of medium viscosity and particle volume fraction. We demonstrate that the deviation between locations where particles assemble in viscous and inviscid media first increases and then decreases with increasing particle volume fraction and medium viscosity, which we explain by means of the sound propagation velocity of the mixture. In addition, we quantify and predict the steady-state and transient local packing density of spherical particles within the pattern features, using ultrasound DSA in combination with vat photopolymerization (VP). We show that the steady-state local particle packing density increases with increasing particle volume fraction and increases with decreasing particle size. We also show that the transient local particle packing density increases with increasing particle volume fraction, decreasing particle size, and decreasing fluid medium viscosity. Increasing particle size and decreasing fluid medium viscosity decreases the time to reach steady-state. Finally, we implement single and multiple scattering in the calculation of the acoustic radiation force for spherical particles in a viscous medium and quantify their relative contributions to the calculation of the acoustic radiation force as a function of ultrasound DSA operating parameters and material properties. We demonstrate that the deviation between considering single and multiple scattering may reach up to 100%, depending on the ultrasound DSA process parameters and material properties. Also, increasing the particle volume fraction increases the need to account for multiple scattering. Quantifying and predicting the local packing density of spherical particles during ultrasound DSA in a viscous medium, as a function of ultrasound DSA process parameters is crucial towards using ultrasound DSA in engineering applications, in particular (additive) manufacturing of engineered polymer matrix composite materials with tailored properties whose properties depend on the spatial organization and packing density of particles in the matrix material. / Doctor of Philosophy / Ultrasound directed self-assembly (DSA) is a technique that uses ultrasound waves to arrange small particles submerged in a fluid into specific patterns. When combined with other manufacturing techniques, ultrasound DSA can be used to fabricate composite materials that derive their properties from the spatial organization of particles in a matrix material. However, ultrasound DSA in viscous fluids is not well-understood. Researchers have studied the forces associated with ultrasound waves that move small spherical particles in an inviscid fluid medium (fluids that experience little to no internal resistance to flow), and they have demonstrated intricate control of the patterns of particles that form using ultrasound DSA. However, that knowledge is not currently available for ultrasound DSA in viscous media. In this dissertation, we develop and evaluate theoretical models to understand ultrasound DSA of small spherical particles in a viscous fluid medium. We simulate where particles organize and how densely they pack together. We also determine the difference of the time-dependent motion of particles in a viscous fluid compared to that in an inviscid fluid medium and relate the difference to the number of particles submerged in the fluid and the viscosity of the fluid. Additionally, we examine the effect of particle size and fluid viscosity on the speed by which the particles reach their final location. We also study how ultrasound waves interact with multiple small particles in a viscous fluid, focusing on the forces that move these particles. We explore two models that account for single and multiple ultrasound wave scattering. Scattering is the process by which ultrasound waves deflect in different directions when they encounter a particle. The results show that the difference between single and multiple scattering models can be significant, depending on the ultrasound DSA process parameters and the properties of the fluid and particles. In general, the importance of accounting for multiple scattering increases with the number of particles submerged in the fluid. Understanding particle packing density when using ultrasound DSA in a viscous fluid is essential in many engineering applications, in particular manufacturing of composite materials that derive their properties from the spatial arrangement of particles in a matrix material.

This dissertation advances the Vibration-Based Sound Power (VBSP) method for measuring the sound power of vibrating structures, expanding its applicability to a wider range of geometries and acoustic environments. The research addresses limitations of traditional sound power measurement techniques by developing an alternative method that achieves near Precision (Grade 1) accuracy while maintaining feasibility for in situ testing under uncontrolled acoustic conditions. After reviewing the current VBSP method in Unit 1, Unit 2 introduces stitching techniques for Scanning Laser Doppler Vibrometer (SLDV) measurements, enabling accurate 3D scans and extending the method to complex geometries. Experimental validation is provided for baffled simply curved plates and arbitrarily curved plates. The method also estimates sound power in uncontrolled acoustic environments, where traditional approaches are less effective. Initial work on thin unbaffled flat plates is presented, with a practical demonstration using pickleball paddles as a representative unbaffled configuration. Unit 3 addresses the computational demand of constructing radiation resistance (R) matrices, a key limitation of the VBSP method. Symmetry-based techniques leveraging acoustic reciprocity and geometric symmetries are applied to reduce computational demands by up to 75% for unbaffled structures. For baffled configurations, translational symmetry of acoustic reciprocity between elements results in the R matrix having Toeplitz symmetry, reducing the computational complexity from n^2 to n, where n is the number of mesh elements. Unit 4 introduces an indirect VBSP (I-VBSP) method to estimate sound power from encased sources, achieving near Precision (Grade 1) accuracy relative to the ISO 3741 standard using only a single surface scan. Validated on a Bluetooth speaker, this approach provides a simplified alternative to conventional methods, offering a practical solution for sound power measurement in structures with encased noise sources. Overall, this dissertation demonstrates that the VBSP method serves as a viable alternative to conventional sound power techniques, effectively applied across various geometries and scenarios. While the current VBSP method does not accommodate structures with multiple vibrating surfaces in contact, the I-VBSP method can theoretically achieve this by enclosing a structure and scanning one vibrating side. This research lays the foundation for future studies through the development of a generalized R matrix and application of foundational symmetries, enhancing the understanding of acoustic radiation from vibrating structures. Ultimately, this work aims to reduce noise pollution in consumer products through improved acoustic design and measurement strategies.

Ce travail de thèse présente la formalisation du problème de couplage d'une plaque en vibration de flexion avec le sol. La notion d'impédance intermodale de rayonnement vibratoire est définie de façon analogue à son équivalent acoustique. A partir de cette définition, la notion de masse, raideur et amortissement modal ajoutée sur la structure par le sol est introduite. L'effet sur le niveau vibratoire de la structure est présenté, notamment l'effet très amortissant du sol sur la structure. Une comparaison avec le modèle équivalent acoustique est présentée avec une attention particulière portée sur les différences entre les impédances intermodales. L'influence de la stratification sur le niveau vibratoire de la structure fait apparaitre des phénomènes nouveaux sur la partie imaginaire de l'impédance intermodale. Une comparaison théorie-expérience a été effectuée dans le cas d'une dalle de tramway couplée au sol. On présente également une comparaison avec un code numérique, MEFISSTO développé par P. Jean au sein du CSTB. On présente également une extension du modèle d'une plaque couplée au sol au cas de couplage de deux plaques avec le sol. On montre notamment que l'écriture du problème reste très similaire au problème d'une plaque couplée au sol. Les impédances intermodales peuvent encore être définies avec la prise en compte du couplage des modes d'une plaque sur les modes de l'autre plaque. On présentera trois applications de ce modèle. La première concerne l'utilisation d'une Barrière Vibratoire Horizontale à la surface du sol pour atténuer les vibrations issues d'une première plaque modélisant la dalle de tramway. Finalement une ouverture du problème de couplage d'une plaque avec le sol par l'utilisation de ce modèle dans des problématiques inverses est présentée. On montre qu'il est possible par un problème inverse de remonter aux efforts injectés sur une dalle de tramway au passage de celui-ci. / This thesis is concerned with the coupling between a fexural vibrating plate and a stratifed ground. A semi-analytical solution is introduced similar to the equivalent acoustical problem. The ground cross modal impedance is defined in a similar way as the equivalent acoustical impedance. From this definition, the ground added mass, stiffness and damping to the plate are presented. Similarities and discrepancies between the acoustical and the ground cross modal impedance are introduced. Influence of the ground stratification on the plate vibration shows new phenomena especially on the imaginary part of the ground cross modal impedance. A comparison between the model developed in this thesis and an experiment made on a tramway slab has been done as well as a comparison with a numerical model, MEFISSTO developed by P. jean at CSTB. One introduces an extension of the modeling developed and is concerned with modeling two flexural plates to the ground. It can be pointed out that problem formulation is still close to the problem formulation of one plate coupled to the ground. Three different fields of application of such modeling is presented. The first field of application is concerned with ground mitigation due to the passing tramway on. The first plate is the excited plate by the tramway and the second plate, called Horizontal Wave Barrier, is acting at the top surface as a ground attenuator. The second field of application is concerned with the modeling of building foundation. It is shown that the vibration received by the foundation of a building can be an input data for modeling an entire building vibration. The third field of application is concerned with different cases of tramway slab for reduction of ground vibration. Finally one presents an introduction of the use of this ground structure modeling in the case of inverse problem. It is shown that it is possible to identify injected force to the plate by the tramway. Furthermore the ground allows a regularization of the problem in the inversion which is not the case in the acoustical case.

Dans le cadre de la lutte contre les nuisances sonores et vibratoires, cette thèse porte sur la modélisation numérique des structures amorties par dispositifs piézoélectriques shuntés. La première partie du travail concerne la modélisation par éléments finis de structures en vibrations avec des pastilles piézoélectriques shuntées. Dans un premier temps, une formulation éléments finis originale, qui utilise des variables électriques globales (différence de potentiel et charge dans chaque pastille piézoélectrique), est analysée et validée. Dans un second temps, différentes stratégies de réduction de modèle basées sur la méthode de projection modale sont proposées pour résoudre le problème électromécanique discrétisé par éléments finis à moindre coût. La convergence de ces modèles d’ordre réduits est ensuite analysée pour les cas de shunts résistif et résonant. La deuxième partie du travail est consacrée à l’optimisation du système électromécanique, dans le but de maximiser l’amortissement apporté par les dispositifs piézoélectriques shuntés. Pour cela, une procédure d’optimisation topologique, basée sur la méthode SIMP (Solid Isotropic Material with Penalization method), est développée pour déterminer les géométries et les emplacements optimaux des pastilles piézoélectriques. Cette procédure permet de maximiser le coefficient de couplage électromécanique modal entre les éléments piézoélectriques et la structure hôte, ceci de façon indépendante du choix des composants du circuit électrique. Les avantages de l’approche proposée sont mis en avant à travers un exemple de validation et un cas d'application industrielle. Enfin, la dernière partie du travail propose une approche numérique pour modéliser et optimiser la réduction du rayonnement acoustique de plaques minces dans le domaine des basses fréquences avec des éléments piézoélectriques shuntés. Cette approche est valable pour n’importe quelle plaque mince bafflée et non trouée, indépendamment des conditions aux limites. Un exemple d’application concernant l’atténuation du rayonnent acoustique d’une plaque avec renforts est présenté et analysé. / Passive structural vibration and noise reduction by means of shunted piezoelectric patches is addressed in this thesis. The first part of the work concerns the finite element modeling of shunted piezoelectric systems. Firstly, an original finite element formulation, with only a couple of electric variables per piezoelectric patch (the global charge/ voltage), is analyzed and validated. Secondly, several reduced order models based on a normal mode expansion are proposed to solve the electromechanical problem. The convergence of these reduced order models is then analyzed for a resistive and a resonant shunt circuits. In the second part of the work, the concept of topology optimization, based on the Solid Isotropic Material with Penalization method (SIMP), is employed to optimize, in terms of damping efficiency, the geometry of piezoelectric patches as well as their placement on the host elastic structure. The proposed optimization procedure consists of distributing the piezoelectric material in such a way as to maximize the modal electromechanical coupling factor of the mechanical vibration mode to which the shunt is tuned, independently of the choice of electric circuit components. Numerical examples validate and demonstrate the potential of the proposed approach for the design of piezoelectric shunt devices. Finally, the last part of the work concerns the numerical modeling of noise and vibration reduction of thin structures in the low frequency range by using shunted piezoelectric elements. An efficient approach that can be applied to any thin continuous plates in an infinite baffle, independently of the boundary conditions, is proposed. An application example of a thin plate with reinforcements is presented and analyzed.

Dans le cadre de la lutte contre les nuisances sonores et vibratoires, cette thèse porte sur la modélisation numérique des structures amorties par dispositifs piézoélectriques shuntés. La première partie du travail concerne la modélisation par éléments finis de structures en vibrations avec des pastilles piézoélectriques shuntées. Dans un premier temps, une formulation éléments finis originale, qui utilise des variables électriques globales (différence de potentiel et charge dans chaque pastille piézoélectrique), est analysée et validée. Dans un second temps, différentes stratégies de réduction de modèle basées sur la méthode de projection modale sont proposées pour résoudre le problème électromécanique discrétisé par éléments finis à moindre coût. La convergence de ces modèles d’ordre réduits est ensuite analysée pour les cas de shunts résistif et résonant. La deuxième partie du travail est consacrée à l’optimisation du système électromécanique, dans le but de maximiser l’amortissement apporté par les dispositifs piézoélectriques shuntés. Pour cela, une procédure d’optimisation topologique, basée sur la méthode SIMP (Solid Isotropic Material with Penalization method), est développée pour déterminer les géométries et les emplacements optimaux des pastilles piézoélectriques. Cette procédure permet de maximiser le coefficient de couplage électromécanique modal entre les éléments piézoélectriques et la structure hôte, ceci de façon indépendante du choix des composants du circuit électrique. Les avantages de l’approche proposée sont mis en avant à travers un exemple de validation et un cas d'application industrielle. Enfin, la dernière partie du travail propose une approche numérique pour modéliser et optimiser la réduction du rayonnement acoustique de plaques minces dans le domaine des basses fréquences avec des éléments piézoélectriques shuntés. Cette approche est valable pour n’importe quelle plaque mince bafflée et non trouée, indépendamment des conditions aux limites. Un exemple d’application concernant l’atténuation du rayonnent acoustique d’une plaque avec renforts est présenté et analysé. / Passive structural vibration and noise reduction by means of shunted piezoelectric patches is addressed in this thesis. The first part of the work concerns the finite element modeling of shunted piezoelectric systems. Firstly, an original finite element formulation, with only a couple of electric variables per piezoelectric patch (the global charge/ voltage), is analyzed and validated. Secondly, several reduced order models based on a normal mode expansion are proposed to solve the electromechanical problem. The convergence of these reduced order models is then analyzed for a resistive and a resonant shunt circuits. In the second part of the work, the concept of topology optimization, based on the Solid Isotropic Material with Penalization method (SIMP), is employed to optimize, in terms of damping efficiency, the geometry of piezoelectric patches as well as their placement on the host elastic structure. The proposed optimization procedure consists of distributing the piezoelectric material in such a way as to maximize the modal electromechanical coupling factor of the mechanical vibration mode to which the shunt is tuned, independently of the choice of electric circuit components. Numerical examples validate and demonstrate the potential of the proposed approach for the design of piezoelectric shunt devices. Finally, the last part of the work concerns the numerical modeling of noise and vibration reduction of thin structures in the low frequency range by using shunted piezoelectric elements. An efficient approach that can be applied to any thin continuous plates in an infinite baffle, independently of the boundary conditions, is proposed. An application example of a thin plate with reinforcements is presented and analyzed.

Les joints de porte et de vitrage des voitures jouent un rôle très important dans la réduction du bruit d’origine aérodynamique, à la fois par transmission directe et de par son rôle en tant que condition limite ees autres éléments transmetteurs (portes et fenêtres). Par conséquent, sa conception est fondamentale pour l’optimisation du confort de passager. Néanmoins, la méthode traditionnelle pour sa conception, basée sur une approche par tâtonnement de tests en soufflerie, est très coûteuse et insuffisante. Une approche différente est envisagée dans ce manuscrit, par la création d’un modèle capable de prédire la transmission du bruit jusqu’`a la cavité du véhicule, qui puisse être appliqué ultérieurement dans une routine d’optimisation. La modélisation des joints de vitrage et des fenêtres fait face à plusieurs difficultés. La fermeture de la porte subie par le joint de porte avant d’être soumis à l’excitation acoustique, ainsi que le comportement hyperélastique du caoutchouc, mènent à des déformations non-linéaires. Ce comportement change les propriétés (telles que la rigidité) du joint comprimé lors qu’il est soumis à l’excitation acoustique. De plus, l’interaction du son transmis par les joints avec la cavité du véhicule doit être prise en compte. Néanmoins, la taille réduite et la géométrie complexe du joint appellent à une approche telle que la méthode EF, tandis que la grande taille de la cavité véhicule nécessite d’une approche plus grossière, pour ne pas aboutir sur un modèle trop lourd. La solution proposée dans ce manuscrit implique la création d’un modèle hybride capable de modéliser le joint et la cavité séparément, avec l’approche la plus adaptée `a chaque cas, et de les coupler dans un seul modèle. Les comportements hyperélastique et viscoélastique des joints, avant et durant l’excitation acoustique, sont modélisés à l’aide du code commercial ABAQUS, tandis qu’une méthode énergétique appelée Méthode Energétique Simplifiée est utilisée pour la propagation ´ du son depuis les joints jusqu’au reste de la cavité. Cette méthode, adaptée aux besoins de l’application souhaitée, et couplée aux résultats du modèle EF, permet l’obtention rapide et locale du niveau de pression acoustique en n’importe quel point de la cavité. Finalement, des campagnes expérimentales sont mises en œuvre pour la validation des modèles. Les mises en place et les résultats sont détaillés dans ce manuscrit. / Car door and window seals have been proven to be of utmost importance to reduce aerodynamic noise, both through direct transmission and through their role as boundary conditions of the other transmitting elements (car doors and windows). As consequence, their design has become of great relevance when it comes to passenger comfort optimization. However, the traditional method for their conception, based on a trial and error approach through wind-tunnel testing, has been found to be insufficient and costly. A different approach is contemplated in this dissertation, through the development of a model capable of predicting sound transmission through seals and into the vehicle cavity, for its subsequent application into an optimization procedure. Several difficulties arise from the modeling of car door and window seals. Indeed, the door closure imposed on the door seal before any acoustic excitation, as well as the hyperelasticity of the rubber lead to a non-linear deformation behavior. This behavior changes the seal properties (e.g. stiffness) which have to be modeled under acoustic excitation. Additionally, the interaction of the transmitted sound with the vehicle cavity must be taken into account. However, the small, precise geometry of the seal would call for an approach such as FE method, whereas the big dimensions of a vehicle cavity demand a much coarser approach so that the problem doesn’t become unmanageable in size. The solution that is proposed in this dissertation, implies the creation of an hybrid model capable of modeling the seal and the vehicle cavity separately, with the most adequate approach to each case, and coupling them afterward into a single model. As consequence, the hyperelastic and viscoelastic behaviors of the seals, prior to and during the acoustic excitation, are modeled through FE software ABAQUS, whereas an energy method called Méthode Energétique Simplifiée is used for the propagation ´ of the sound from the seal to the rest of the cavity. This method, improved to better suit the requirements of the discussed application, and coupled to the results of the FE model, allows a fast and local computation of the sound pressure level at any point inside the cavity. Finally, some experimental tests are put in place for the validation of the models. The different setups and results are detailed in this dissertation.