Phononic crystals are structures composed of periodically arranged scatterers in a background medium that affect the transmission of elastic waves. They have garnered much interest in recent years for their macro-scale properties that can be modulated by the micro-scale components. The elastic properties of the composite materials, the contrast in the elastic properties of the composite materials, and the material arrangement all directly affect how an elastic wave will behave as it propagates through the sonic structure. The behavior of an elastic wave in a periodic structure is revealed in its transmission bandstructure, and modification of any the elastic parameters will result in tuning of the band structure. In this dissertation, a phononic crystal with properties that can be modulated using electromagnetic radiation, and more specifically, radio-frequency (RF) light will be presented.

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No description available.

The perfectly matched layer (PML) is a novel technique to simulate the absorption of waves in unbounded domains. The underlying equations are often a system of second order hyperbolic partial differential equations. In the numerical treatment, second order systems are often rewritten and solved as first order systems. There are several benefits with solving the equations in second order formulation, though. However, while the theory and numerical methods for first order hyperbolic systems are well developed, numerical techniques to solve second order hyperbolic systems are less complete. We construct a strongly well-posed PML for second order systems in two space dimensions, focusing on the equations of linear elasto-dynamics. In the continuous setting, the stability of both first order and second order formulations are linearly equivalent. We have found that if the so-called geometric stability condition is violated, approximating the first order PML with standard central differences leads to a high frequency instability at most resolutions. In the second order setting growth occurs only if growing modes are well resolved. We determine the number of grid points that can be used in the PML to ensure a discretely stable PML, for several anisotropic elastic materials. We study the stability of the PML for problems where physical boundaries are important. First, we consider the PML in a waveguide governed by the scalar wave equation. To ensure the accuracy and the stability of the discrete PML, we derived a set of equivalent boundary conditions. Second, we consider the PML for second order symmetric hyperbolic systems on a half-plane. For a class of stable boundary conditions, we derive transformed boundary conditions and prove the stability of the corresponding half-plane problem. Third, we extend the stability analysis to rectangular elastic waveguides, and demonstrate the stability of the discrete PML. Building on high order summation-by-parts operators, we derive high order accurate and strictly stable finite difference approximations for second order time-dependent hyperbolic systems on bounded domains. Natural and mixed boundary conditions are imposed weakly using the simultaneous approximation term method. Dirichlet boundary conditions are imposed strongly by injection. By constructing continuous strict energy estimates and analogous discrete strict energy estimates, we prove strict stability.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 160-166).

La turbulence d'onde faible (TTF) est une théorie statistique appliquée à un ensemble d'ondes aléatoires non cohérentes et dispersives. En supposant un domaine infini et une nonlinéarité infinitésimale, une prédiction sur la cascade d'énergie entre échelles par le biais d'interactions résonantes des échelles d'injection aux échelles dissipatives est alors possible. La théorie semble souvent mise en défaut par la confrontation expérimentale pour les ondes de surface. Une explication potentielle de cette divergence entre expérience et théorie est l'aspect fortement restrictif des hypothèses nécessaires à la validité de la théorie. Nous proposons dans cette thèse d'explorer l'impact du non-respect de certaines de ces hypothèses sur les propriétés statistiques de la turbulence. Des expériences à l'interface de deux liquides non-miscibles ont été entreprises afin d'étudier l'impact de l'augmentation de la dissipation visqueuse et donc de la réduction du temps dissipatif sur la mise en place de la cascade d'énergie. Une expérience à la surface de l'eau avec un confinement progressif de la largeur de la cuve a été effectuée afin d'observer une potentielle coexistence de la turbulence discrète, dans la direction confinée, et continue, dans la direction non confinée. Une analyse expérimentale des ondes gravito-capillaires où la dispersion a été réduite a permis de mettre en lumière une transition d'un régime de TTF vers un régime contenant des structures cohérentes localisées que sont les solitons. Afin de vérifier si une telle transition peut être visible sur un système physique différent, une étude expérimentale et numérique ont été conduites sur les ondes dans une plaque élastique précontrainte. Dans ce milieu l'effet de dispersion des ondes de flexion et en compétition avec le caractère non-dispersif des ondes de tension. Nous nous intéresserons par ailleurs numériquement aux régimes faiblement et fortement non-linéaires des ondes purement non-dispersives dans la membrane. / Weak wave turbulence (WTT) is a statistical theory applied to a large number of incoherent and dispersive waves. Based on the hypothesis of small non-linearity and infinite domain the theory predicts an energy cascade from the forcing scales to the dissipative scales. The confrontation of WTT to experiment for surface waves raises many inconsistencies. The strong hypotheses on which is developed the WWT may be the explanation of such disparity between experiment and theory. The aim of this Thesis is to investigate the impact of the invalidation of some of these conditions on the statistical properties of turbulence. Experiments of interfacial waves between two non-miscible fluids with different viscosities have been carried out to characterize the effect of the increase of viscous dissipation on the energy cascade. An experiment at the surface of water with an increasing confinement of the width of the vessel has been done in order to possibly observe a co-existence between discrete turbulence and classical turbulence. An experimental study of gravity-capillary waves with a decrease of dispersion led us to the observation of a transition to a solitonic regime. In order to verify whether such a transition can be observed in a different physical system, an experimental and numerical study were conducted on the waves in a prestressed elastic plate. In this medium, the effect of dispersion of bending waves is competing with the non-dispersive aspect of stretching waves. We also studied weakly and strongly non-linear regimes of purely stretching waves in a membrane.

Orientador: José Mario De Martino / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T22:55:53Z (GMT). No. of bitstreams: 1 Santos_RodrigoMologniGoncalvesdos_M.pdf: 13617752 bytes, checksum: 7a0f3cc2f97bbc5f0bb170014d19861b (MD5) Previous issue date: 2011 / Resumo: Nas últimas décadas, o estudo dos fenômenos de propagação de ondas mecânicas e de suas conseqüências tem recebido crescente atenção de grupos de pesquisa de variados ramos da engenharia, sobretudo daqueles dedicados ao desenvolvimento de métodos computacionais para resolução de problemas complexos na área da Mecânica dos Meios Contínuos (MMC). Os métodos computacionais desenvolvidos por estes grupos geralmente são constituídos de modelagem matemática e simulação computacional de problemas físicos, que substituem a necessidade do uso de protótipos ou infraestrutura de laboratórios, mas que em contrapartida produzem uma volumosa quantidade de dados numéricos que pode dificultar ou inviabilizar uma análise mais eficiente dos resultados sem o suporte de técnicas específicas para o mapeamento destes dados em representações visuais. Esta dissertação apresenta um trabalho científico-tecnológico na área de Visualização Científica, cujas técnicas foram empregadas em MMC para a visualização dos fenômenos de propagação de ondas mecânicas, especificamente em meios materiais sólidos. Os objetivos principais do trabalho foram possibilitar que os especialistas pudessem validar mais rapidamente os seus métodos computacionais voltados ao estudo dos fenômenos de propagação de ondas mecânicas e, principalmente, que eles pudessem entender com mais facilidade os resultados gerados pela simulação computacional, ampliando assim a eficiência da análise de problemas complexos. Os estudos de casos realizados e apresentados no trabalho permitem afirmar que estes objetivos foram alcançados e os resultados foram satisfatórios. As principais contribuições deste trabalho são: identificação de um conjunto de informações derivadas dos dados brutos gerados pela simulação computacional que podem ser empregados para análise dos fenômenos de propagação de ondas mecânicas; metodologias e respectivas formulações matemáticas para cálculo destas informações; desenvolvimento de um protótipo de ambiente de visualização dos dados que descrevem o comportamento das ondas mecânicas; e estudo e definição de diretrizes de como as técnicas de visualização de dados escalares e vetoriais podem ser aplicadas para favorecer a análise das informações disponíveis. É importante observar que o trabalho é limitado à visualização de ondas mecânicas bi ou tridimensionais geradas sobre grades de dimensão bidimensional / Abstract: In recent decades, the study of the mechanical wave propagation phenomena and their consequences has been receiving increasing attention from research groups in engineering, principally those dedicated to the development of computational methods for solving complex problems in the area of Continuum Mechanics (CM). The computational methods developed by these groups usually consist of mathematical modeling and computer simulation of physical problems, which replace the need for prototypes or laboratory infrastructure. But in opposition, produces a large amount of numerical data that can hinder a more efficient analysis of the results without the support of specific techniques for mapping these data into visual representations. This master's dissertation presents a scientific-technological work in the area of Scientific Visualization, whose techniques were applied in the area of CM for visualization of the mechanical wave propagation phenomena, specifically in solid material media. The main objectives of the work were to allow MCM experts to validate more quickly their computational methods for the study of the mechanical wave propagation phenomena and, especially, that they could more easily understand the results generated by computer simulation, increasing the efficiency of analysis of complex problems. The case studies analyzed and presented in the dissertation allow to state that these objectives were attained and the results were satisfactory. The main contributions of the work are: identification of a set of implicit information, derived from raw data generated by computer simulation, that can be used to analyze the mechanical wave propagation phenomena; methodologies and their mathematical formulations to calculate these information; development of a visualization environment prototype of the data that describe the behavior of mechanical waves; and study and guideline definition of how to apply the visualization techniques of scalar and vector data for expand the analysis the available information. It is important to mention that the work is limited to visualization of two or three-dimensional mechanical waves generated on two-dimensional grids / Mestrado / Engenharia de Computação / Mestre em Engenharia Elétrica

Orientador: Joerg Dietrich Wilhelm Schleicher / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-20T00:32:10Z (GMT). No. of bitstreams: 1 Figueiredo_JoseJadsomSampaiode_D.pdf: 25764128 bytes, checksum: 358c6580d480aca067e19d0095ab844b (MD5) Previous issue date: 2012 / Resumo: Meios anisotrópicos fissurados ou fraturados têm sido amplamente investigados em muitos estudos teóricos e experimentais. Neste trabalho, realizamos uma série de medidas ultrassônicas objetivando investigar o comportamento de diferentes meios artificialmente anisotrópicos. Três questões foram abordadas: (1) estudo da birrefringência da onda S em função da frequência da fonte, (2) estimativa das direções de fraturas através de ondas elásticas e (3) o estudo do excesso de complacência em meio transversalmente isotrópico com a inclusão de fissuras. No primeiro caso, o efeito da frequência da fonte na estimativa dos parâmetros elásticos (o parâmetro de Thomsen e a atenuação de ondas cisalhantes) foi estudado em três modelos anisotrópicos contendo inclusões (pequenos discos de borrachas) em uma matriz sólida de resina epóxi e densidade de fissuras variando de 0 para 6,2 %. Dois dos três modelos fissurados tem 10 camadas enquanto o outro tem 17. Medidas de birrefringência das onda S têm mostrado que efeitos de dispersão são mais proeminentes em modelos em que a razão entre o comprimento de onda sísmica e a abertura da fissura é 1,6 - 1,64 do que para outros modelos em que essa razão está variando entre 2,72 - 2,85. O modelo com grandes fissuras deu uma magnitude de atenuação três vezes maior em comparação com outro modelo que tinha pequenas inclusões. Os resultados para estes modelos indicam que o espalhamento elástico, as atenuações intrínseca e de espalhamento ...Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital / Abstract: Anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we have performed ultrasonic surveys to investigate the behavior of different artificially anisotropic media. Three questions were addressed here: (1) study of the S-wave splitting as a function of source frequency, (2) estimation of the fracture directions using elastic waves and (3) investigation of compliance excess in transversally isotropic media with crack inclusions. Firstly, we studied the effect of source frequency on the estimation of elastic parameters (the Thomsen parameter and shear-wave attenuation) in four anisotropic models containing cracks simulated by penny-shaped rubber inclusions in a solid epoxy resin matrix with crack density that ranges from 0 to 6.2 %. Two of the three cracked models have 10 layers and the last one has 17 layers. Our S-wave splitting measurements have shown that scattering e_ects are more prominent in models where the ratio of seismic wavelength to crack aperture ranges from 1.6 to 1.64 than in other models where this ratio varies from 2.72 to 2.85. The model with large cracks gave a magnitude of attenuation three times higher as compared with another model that had small inclusions. The results for these models indicate that elastic scattering, intrinsic and scattering attenuation ...Note: The complete abstract is available with the full electronic document / Doutorado / Reservatórios e Gestão / Doutor em Ciências e Engenharia de Petróleo

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Liang-Wu Cai / A computational system is built for conducting deterministic simulations of three-dimensional multiple scattering of elastic waves by spherical inclusions. Based on expansion expression of elastic wave fields in terms of scalar and vector spherical harmonics, analytically exact solutions of single scattering and multiple scattering are obtained, implemented and verified. The verification is done by using continuities of displacement and surface traction at the interface between an inclusion and host medium, energy conservation and published results. The scatterer polymerization methodology is extended to three-dimensional multiple scattering solution. By using this methodology, an assemblage of actual scatterers can be treated as an abstract scatterer. This methodology is verified by using different approaches, with or without scatterer polymerization, to solve a physically the same multiple scattering problem. As an application example, band gap formation process for elastic wave propagation in cubic lattice arrangements of spherical scatterers is observed through a series of numerical simulations. Along the direction of the incident wave, scatterer arrangements are viewed as comprising layers of scatterers, within which scatterers form a square grid. Starting from one layer and by increasing the number of layers, near-field forward wave propagation spectra are computed as the number of layers increases. These simulations also demonstrates that the computational system has the capability to simulate multiple scattering solutions of elastic waves in three-dimension.

Orientador: Auteliano Antunes dos Santos Júnior / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T07:24:11Z (GMT). No. of bitstreams: 1 Buenos_AlexandreAparecido_D.pdf: 36097019 bytes, checksum: d270fa6d123f9a141621191306944498 (MD5) Previous issue date: 2014 / Resumo: Um método alternativo para a medição das tensões em componentes em serviço emprega o ultrassom, utilizando ondas longitudinais criticamente refratadas (LCR) e a teoria acustoelástica. Este método é influenciado por diversos fatores, dentre os quais os ligados à microestrutura do material, ainda não modelados. Este trabalho avalia a influência da microestrutura do material na velocidade de propagação das ondas LCR. Foram estudados os efeitos do tamanho dos grãos e da orientação preferencial dos grãos (textura) do material. Para isso, foram ensaiadas amostras de aço carbono de média resistência ASTM A36, laminadas, utilizadas em componentes estruturais. Parte das amostras foi tratada termicamente para crescimento dos grãos em temperaturas variadas, o que permitiu obter diferentes tamanhos de grão. Outras amostras foram utilizadas como recebidas para estudo do efeito da textura do material. O trabalho mostra que ambos, o tamanho dos grãos e a textura, têm efeito sobre a propagação das ondas LCR. Os resultados mostraram um aumento na variação do tempo de percurso médio (?TOF) das ondas LCR com o aumento do diâmetro dos grãos austeníticos médios (DGAM). Como consequência, houve uma diminuição na variação da velocidade da onda LCR média (?VLCR) devido ao aumento do DGAM. Os resultados mostraram também o efeito da direção de laminação (DL) na propagação das ondas LCR, mostrando que o tempo de percurso (TOF) é maior na direção de laminação (DL) do que na direção transversal à laminação (DT). Isso é atribuído ao alongamento dos grãos devido ao processo de laminação. O efeito da textura do material foi associado ao desvio padrão (DP) encontrado e ainda representa um desafio para o emprego do método em aços com orientação cristalográfica pouco definida. Tais resultados permitem direcionar as pesquisas atuais sobre o assunto para o desenvolvimento de técnicas que minimizem os efeitos dos fatores de influência estudados / Abstract: Critically refracted longitudinal waves (LCR) and the acoustoelastic theory can be an interesting alternative for measuring stress in components in service. This method is influenced by several factors, among which the ones linked to the material microstructure, not modeled yet. This work evaluates the influence of material microstructure on the LCR waves speed. The effects of grain size and preferred grain orientation (texture) of the material were studied. We tested samples of carbon steel ASTM A36 of medium strength, made from rolled plates, used in structural components. Part of the samples was heat treated for grain growth at various temperatures, generating different grain sizes. Other samples were used as received to study the effect of the material¿s texture. The work shows that both the grain size and texture affects the propagation of LCR waves. The results showed that the increase in variation of the mean time-of-flight (?TOF) of the LCR waves can be related to the increase of the mean austenitic grain diameter (DGAM). As consequence a decrease in the variation of the mean LCR wave speed (?VLCR) is linked to the increase in DGAM. The results also reveals the effect of the rolling direction (DL) in the propagation of LCR waves, showing that the time-of-flight (TOF) is greater in the DL direction than in the transverse direction to rolling (DT). This is attributed to the grain elongation due to the rolling process. The effect of texture was associated with the standard deviation (DP) found. This effect still represents a challenge to the employment of the method in steels with poorly defined crystallographic orientation. The results allow directing the current research on the subject to develop techniques that minimize the effects of influence factors studied / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica