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Dissertations / Theses on the topic 'Transient wave propagation'
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Bluck, Michael John. "Integral equation methods for transient wave propagation." Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/7973.
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Guddati, Murthy Narasimha. "Efficient methods for modeling transient wave propagation in unbounded domains /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Ordovas, Miquel Roland. "Covariant projection finite elements for transient wave propagation." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342285.
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Podo, Smardie D. "Comparison of layering effects in the propagation of transient planar stress waves." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/18378.
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Boston, Ian Edward. "Transient stress analysis by the transmission line method." Thesis, University of Hull, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259799.
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Gerasik, Vladimir. "Consolidation and wave propagation in a porous medium." Thesis, University of Waterloo, 2006. http://hdl.handle.net/10012/2950.
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Basic diffusion analytical solutions of one-dimensional consolidation are presented for the case of a semi-infinite domain. Typical tractions considered include instantaneous loads of the medium with a free boundary pressure, as well as the case of a permeable membrane located at the forced boundary. Two-dimensional boundary value problems for a porous half-space, described by the widely recognized Biot's equations of poroelasticity, including inertia effects is discussed. In this poroelastic version of Lamb's problem in the classical theory of linear elastic waves, the surface of a porous half-space is subjected to a prescribed line traction. The following two broadly applicable cases are considered: 1) A steady state harmonic load, 2) An impulsive load (Dirac delta function time dependence). A general analytical solution of the problem in the Fourier -- Laplace space was obtained by the application of the standard Helmholtz potential decomposition, which reduces the problem to a system of wave equations for three unknown potentials, which correspond to three types of motion: P1, slow P2 wave, and the shear wave S. The possibilities of, and procedure for, obtaining analytic solutions in the physical space subsequently are discussed in detail. When viscous dissipation effects are taken into account, a steady-state harmonic line traction solution can be represented in the form of well convergent integrals, while for the case when viscous dissipation is ignored, closed form analytic solutions can be obtained for impulsive forcing with the application of the Cagniard -- de Hoop inversion technique. Numerical studies of the dispersion relation of the Rayleigh, or surface, wave for cases in which the dissipation is not negligible are presented.
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Kowalski, Benjamin John. "Transient SH-Wave Interaction with a Cohesive Interface." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417706326.
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Le, Guennec Yves. "Transient dynamics of beam trusses under impulse loads." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2013. http://www.theses.fr/2013ECAP0016/document.
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Ce travail de recherche est dédié à la simulation de la réponse transitoire des assemblages de poutres soumis à des chocs. De tels chargements entraînent la propagation d’ondes haute fréquence dans l’ensemble de la structure. L’énergie qu’elles transportent peut être dommageable pour son fonctionnement ou celui des équipements embarqués. Dans des études précédentes, il a été observé sur des structures expérimentales qu’un régime vibratoire diffusif tend à s’installer pour des temps longs. Le but de cette étude est donc de développer un modèle robuste de la réponse transitoire des assemblages de poutres soumis à des chocs permettant de simuler, entre autres, cet état diffusif. Les champs de déplacement étant très oscillants et la densité modale élevée, la simulation numérique de la réponse transitoire à des chocs peut difficilement être menée par une méthode d’éléments finis classique. Une approche utilisant un estimateur de la densité d’énergie de chaque mode de propagation a donc été mise en œuvre. Elle permet d’accéder à des informations locales sur les états vibratoires, et de contourner certaines limitations intrinsèques aux longueurs d’onde courtes. Après avoir comparé plusieurs modèles de réduction cinématique de poutre à un modèle de Lamb de propagation dans un guide d’ondes circulaire, la cinématique de Timoshenko a été retenue afin de modéliser le comportement mécanique haute fréquence des poutres. En utilisant ce modèle dans le cadre de l’approche énergétique évoquée plus haut, deux groupes de modes de propagation de la densité d’énergie vibratoire dans une poutre ont été isolés : des modes longitudinaux regroupant un mode de compression et des modes de flexion, et des modes transversaux regroupant des modes de cisaillement et un mode de torsion. Il peut être également montré que l’´evolution en temps des densités d’énergie associées obéit à des lois de transport. Pour des assemblages de poutres, les phénomènes de réflexion/transmission aux jonctions ont du être pris en compte. Les opérateurs permettant de les décrire en termes de flux d’´energie ont été obtenus grâce aux équations de continuité des déplacements et des efforts aux jonctions. Quelques caractéristiques typiques d’un régime haute fréquence ont été mises en évidence, tel que le découplage entre les modes de rotation et les modes de translation. En revanche, les champs de densité d’énergie sont quant à eux discontinus aux jonctions. Une méthode d’éléments finis discontinus a donc été développée afin de les simuler numériquement comme solutions d’´equations de transport. Si l’on souhaite atteindre le régime diffusif aux temps longs, le schéma numérique doit être peu dissipatif et peu dispersif. La discrétisation spatiale a été faite avec des fonctions d’approximation de type spectrales, et l’intégration temporelle avec des schémas de Runge-Kutta d’ordre élevé du type ”strong stability preserving”. Les simulations numériques ont donné des résultats concluants car elles permettent d’exhiber le régime de diffusion. Il a été remarqué qu’il existait en fait deux limites diffusives différentes : (i) la diffusion spatiale de l’´energie sur l’ensemble de la structure, et (ii) l’équirépartition des densités d’énergie entre les différents modes de propagation. Enfin, une technique de renversement temporel a été développée. Elle pourra être utile dans de futurs travaux sur le contrôle non destructif des assemblages complexes et de grandes taillesThis research is dedicated to the simulation of the transient response of beam trusses under impulse loads. The latter lead to the propagation of high-frequency waves in such built up structures. In the aerospace industry, that phenomenon may penalize the functioning of the structures or the equipments attached to them on account of the vibrational energy carried by the waves. It is also observed experimentally that high-frequency wave propagation evolves into a diffusive vibrational state at late times. The goal of this study is then to develop a robust model of high-frequency wave propagation within three-dimensional beam trusses in order to be able to recover, for example, this diffusion regime. On account of the small wavelengths and the high modal density, the modelling of high-frequency wave propagation is hardly feasible by classical finite elements or other methods describing the displacement fields directly. Thus, an approach dealing with the evolution of an estimator of the energy density of each propagating mode in a Timoshenko beam has been used. It provides information on the local behavior of the structures while avoiding some limitations related to the small wavelengths of high-frequency waves. After a comparison between some reduced-order beam kinematics and the Lamb model of wave propagation in a circular waveguide, the Timoshenko kinematics has been selected for the mechanical modelling of the beams. It may be shown that the energy densities of the propagating modes in a Timoshenko beam obey transport equations. Two groups of energy modes have been isolated: the longitudinal group that gathers the compressional and the bending energetic modes, and the transverse group that gathers the shear and torsional energetic modes. The reflection/transmission phenomena taking place at the junctions between beams have also been investigated. For this purpose, the power flow reflection/transmission operators have been derived from the continuity of the displacements and efforts at the junctions. Some characteristic features of a high-frequency behavior at beam junctions have been highlighted such as the decoupling between the rotational and translational motions. It is also observed that the energy densities are discontinuous at the junctions on account of the power flow reflection/transmission phenomena. Thus a discontinuous finite element method has been implemented, in order to solve the transport equations they satisfy. The numerical scheme has to be weakly dissipative and dispersive in order to exhibit the aforementioned diffusive regime arising at late times. That is the reason why spectral-like approximation functions for spatial discretization, and strong-stability preserving Runge-Kutta schemes for time integration have been used. Numerical simulations give satisfactory results because they indeed highlight the outbreak of such a diffusion state. The latter is characterized by the following: (i) the spatial spread of the energy over the truss, and (ii) the equipartition of the energy between the different modes. The last part of the thesis has been devoted to the development of a time reversal processing, that could be useful for future works on structural health monitoring of complex, multi-bay trusses
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Wang, Hui. "Boundary integral modelling of transient wave propagation with application to acoustic radiation from loudspeakers." Thesis, University of Brighton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404067.
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Lednik, Dusan. "The application of Transient Statistical Energy Analysis and wave propagation approach to coupled structures." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239300.
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Kim, Jeong-Han. "Optical display of the Airy function and transient wave propagation in a dispersive medium." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-02132009-172038/.
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Tengelsen, Daniel Ross. "Acoustical Analysis of a Horn-Loaded Compression Drivers Using Numerical Analysis." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2448.
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Two numerical techniques, the boundary-element method (BEM) and the finite-difference method (FDM), are used for simulating the radiation from horn-loaded compression drivers and from an infinitely-baffled, finite-length pipe. While computations of the horn-loaded compression driver are in steady state, transient analysis of the finite-length pipe is studied as a precursor to transient analysis within the horn-loaded compression driver. BEM numerical simulations show promise for the development of new designs. Numerical simulations serve as a good tool for time and cost-effective prototyping as poor designs are detected before they are built.
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Markendahl, Anders. "Finite volume simulation of fast transients in a pipe system." Thesis, Uppsala University, Division of Scientific Computing, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-120205.
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The MUSCL-Hancock finite volume method with different slope limiters has been analyzed in the context of a fast transient flow problem. A derivation and analysis of the axial forces inside a pipe system due to a flow transient is also performed.
The following slope limiters were implemented and compared: MC, van Leer, van Albada, Minmod and Superbee. The comparison was based on the method's ability to calculate the forces due to a flow transient inside a pipe system.
The tests and comparisons in this thesis show that the MC, van Leer, van Albada and Minmod limiters behave very much the same for the flow transient problem. If one would rank these four limiters with respect to the numerical error, the order would be the one presented above, the MC limiter being the most accurate. The error the four limiters produce is mainly of diffusive nature and it is just the magnitude of the diffusion that seems to differ between the methods. One should also note that the workload rank of the four limiters is the same as the order presented above. The MC limiter being the least efficient of the four and the Minmod limiter the most efficient.
In most of the tests performed the Superbee limiter display a rather negative unpredictable behavior. For some relatively simple cases this particular approach shows big difficulties maintaining the dynamical properties of the force. However, the upside of the Superbee limiter is its remarkable ability to maintain the maximum value of the forces present in the pipe system, preventing underestimation of the maximum magnitude of the force.
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Aichele, Johannes. "Elastic waves in complex conditions : from the onset of rupture to viscous dispersion in foams." Electronic Thesis or Diss., Lyon, 2019. http://www.theses.fr/2019LYSE1217.
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Ces travaux s'inscrivent dans la continuité des recherches académiques du Labtau (Laboratory of therapeutic applications of ultrasound) et de l’ ISTerre (Institut des sciences de la terre) à l'interface entre imagerie médicale et sismologie, deux disciplines reposant sur la propagation des ondes élastiques. La nature de la propagation des ondes élastiques dans des milieux complexes est étudiée à travers l'imagerie ultrasonore ultrarapide - également connue sous le nom d'imagerie d’ondes de cisaillement. Cette technique d'imagerie médicale permet de récupérer un champ d'onde de cisaillement se propageant dans un milieu élastique mou. Elle est habituellement utilisée comme modalité d’imagerie cartographiant les élasticités d’organes tels que le foie ou le sein. La première partie se penche sur le comportement des ondes dans des milieux poreux. La dispersion de l'onde de cisaillement et de l'onde de compression secondaire dans des matériaux imitant le poumon est analysées expérimentalement, puis comparées à la théorie de poro-élasticité de Biot. Les résultats quant à l'onde de cisaillement sont conformes à la théorie, et ceux de l’onde de compression y correspondent qualitativement. Pour conclure, dans le cas des milieux mous, poreux et élastiques, la dispersion des ondes élastiques est gouvernée par les propriétés du fluide visqueux. Ainsi, les résultats présentés au cours de cette thèse pourraient consolider la théorie nécessaire à une imagerie de l’élasticité pulmonaire. Potentiellement d’autres organes pourraient en bénéficier : en effet, le foie et la rate sont constitués d'un pourcentage élevé de sang. Ce fluide non-Newtonien présente une forte variabilité de la viscosité. Celle-ci implique la nécessité d’étudier le rôle du sang vis-à-vis de l'élastographie du foie, pas encore expliquée par les modèles visco-élastique. En outre, la preuve expérimentale de l'onde de compression secondaire est utile dan l’étude de la propagation d'ondes poro-élastiques. Il est important de noter que l’onde de compression secondaire a été objet principal d’études approfondies en géophysique et n’a été observée que dans quelques rares cas. La partie suivante s’intéresse à une problématique de la géophysique explorée au moyen de l’imagerie de l’onde de cisaillement : Que pourrait révéler sur la nature de la rupture dynamique d’une instabilité de friction l’étude du champs d’onde élastique ? Comment la rupture, le processus responsable des tremblements de terre, est générée? En observant la carte du champ d’onde de cisaillement pendant la rupture d’une aspérité granulaire au point source et dans le milieu, il est possible d’acquérir une meilleure compréhension de la propagation de la rupture. L’expérience qui se base sur l’utilisation de fantômes mous et élastiques montre une multitude de phénomènes qui sont aussi présents dans la friction des roches en laboratoire, ainsi que dans la Terre. Par exemple, les ruptures supershear, sub-Rayleigh, une phase de nucléation et la friction du type stick-slip ont été observés. Toutefois, ni un mécanisme de source d’une force unique, ni un double-couple n’arrivent à expliquer l’ensemble des ruptures observées. De plus, pour analyser la complexité spatio-temporelle des ruptures de cette expérience, un workflow semi-automatique intègrant la segmentation d’image et la vision numérique est suggéréThis thesis is part of the research at Labtau (Laboratory of therapeutic applications of ultrasound) and ISTerre (Institut des sciences de la terre - earth science institute) at the interface of medical imaging and seismology, two research disciplines that are based on the propagation of elastic waves. It investigates the nature of elastic wave propagation in complex conditions by ultrafast ultrasound imaging, also known as transient elastography or shear wave imaging. This medical imaging technique allows for retrieval of the dynamic shear wave field inside a soft elastic material and is commonly applied in hospitals for elasticity mapping in, e.g., the liver and breast. In the present manuscript, two research questions of interest for bio- and geophysics are tackled. The first part treats elastic wave propagation in porous materials. The dispersion of the shear and secondary compression wave in lung-mimicking materials is analyzed experimentally and compared to Biot's theory of poro-elasticity. The results show a good agreement for the shear wave and qualitative agreement for the secondary compression wave. This has direct implications for elasticity imaging: the properties of the viscous fluid govern the shear wave dispersion in highly porous soft elastic materials. The thesis thus contributes to the emerging branch of lung elasticity imaging. The results could have clinical implications for other organs as well. The liver and spleen contain a high percentage of blood, a non-Newtonian fluid which exposes a highly varying viscosity. The conclusions drawn from the comparison of the experimental results and poro-elastic theory imply, that the role of the pore-filling fluid should be investigated in liver elastography: The clinically observed dispersion of shear waves in the liver remains partly unexplained by purely visco-elastic models. Furthermore, the experimental proof of the secondary compression wave is of general interest for poroelasticity. Originally, this wave has been the object of geophysical studies and has scarcely been shown experimentally. In the second part, the ultrafast ultrasound shear wave imaging technique is applied to a geophysical research question. What does the elastic wavefield, which is emitted by a frictional instability, reveal about the nature of dynamic rupture propagation? How does rupture, the process behind earthquakes, nucleate? By mapping the shear wave-field during rupture of a granular asperity at the source point and in the medium, unique insights into rupture nucleation are gained. The experimental setup, which relies on soft elastic phantoms, is shown to reproduce many characteristics of sliding friction that have been show for real rocks in the earth and the laboratory. These include supershear and sub-Rayleigh rupture propagation, a nucleation phase and stick-slip friction. Neither a singular-force nor a double-couple source mechanism explain the entirety of observed rupture modes. Finally, in order to statistically analyze the complex spatio-temporal evolution of the presented experiment, a semi-automated data analysis workflow, taking advantage of image segmentation and computer vision, is suggested
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Kriščiūnas, Andrius. "Vamzdyno trūkio vietos nustatymo algoritmo sukūrimas pagal fizikine elgsena grįstą slėgio bangos sklidimo modelį." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2012~D_20131104_110942-69578.
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Darbo metu apžvelgiami metodai pereinamiesiems procesams vamzdyne realizuoti. Aprašyta vamzdyno tėkmės pereinamųjų procesų dinamika matematinės lygtys ir sudarytas baigtinių elementų modelis skaitiniam vamzdynų pereinamųjų procesų modeliavimui. Panaudojant atgalinį slėgio bangos modeliavimą esant idealizuotam slėgio bangos sklidimo modeliui, sudaromas slėgio impulso vietos nustatymo algoritmas ir įvertinamos atsirandančios paklaidos. Realizuota programine įranga patikrinamas sudarytų modelių ir algoritmo teisingumas, bei pateikiami pasiūlymai, atsiradusioms paklaidoms mažinti.During this research, the methods to realize the transient processes in piping systems are overviewed, also finite element method and idealized wave propagation of pressure mathematical models are set up. Using the backward pressure wave modelling at idealized pressure wave propagation model, piping system rupture location algorithm and the assessment of estimated errors are set up. With released software, the developed models and correctness of the algorithm are verified, and suggestions to reduce the resulting errors are presented.
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Foteinopoulou, Stavroula. "Electromagnetic Wave Propagation in Two-Dimensional Photonic Crystals." Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/822058-9BqHHS/native/.
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Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 12 Dec 2003.Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2048" Stavroula Foteinopoulou. 12/12/2003. Report is also available in paper and microfiche from NTIS.
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Methenni, Hajer. "Modélisation mathématique et méthode numérique pour la simulation du contrôle santé intégré par ultrasons de plaques composites stratifiées." Electronic Thesis or Diss., Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAE002.
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Ce sujet de thèse s’inscrit dans le contexte du contrôle intégré des structures, ou « Structural Health Monitoring » (SHM). Cette technique de contrôle non-destructif vise à utiliser un ou plusieurs capteurs, installés dans ou sur la structure d’intérêt. Le contrôle se fait in-situ et de façon périodique, afin d’obtenir des informations sur l’éventuelle apparition de défauts, tels que les défauts de corrosion pour les matériaux métalliques ou les défauts de délaminage pour les matériaux composites. Les données recueillies par les capteurs alimentent une analyse statistique dont le but est d’évaluer la santé de la structure au moment du contrôle, d’estimer son temps de vie restant et de faciliter la prise de décision quant à sa maintenance. Le SHM est de plus en plus présent dans de nombreux domaines industriels, en particulier dans le secteur aéronautique. Aussi le développement de modèles numériques pertinents comme performants constitue un atout majeur dans la conception de ces systèmes. Grâce à leur capacité à se propager sur de très grande distance, l’utilisation de capteurs ultrasonores générant des ondes guidées élastiques est une solution attirante. En pratique, des capteurs piézo-électriques fins, disposés à la surface de la structure, ou éventuellement enfouis pendant le procédé de fabrication, sont utilisés. Ils permettent l’émission et la réception des perturbations ultrasonores. Cependant, la nature dispersive des ondes guidées, combinée avec l’anisotropie inhérente aux matériaux composites rend difficile l’analyse des signaux obtenus lors du contrôle. De plus, proposer une modélisation fine de la propagation de ce type d’onde dans des configurations industrielles faisant intervenir des géométries complexes est une tâche difficile. Ces deux points constituent des obstacles non négligeables au développement de la méthodologie SHM, et l’objectif de cette thèse est de constituer l’ensemble des outils numériques qui permettront de proposer des solutions concrètes à ces problèmesThis thesis is embedded in the context of « Structural Health Monitoring ». This method of non-destructive testing aiming at monitoring in-situ an engineered structure is increasingly used in numerous industrial fields, e.g. the aeronautics industry. It is based upon elastic guided waves propagating over large distances. The interactions between incident wave fields and structural defects are gathered through a network of receiving sensors. The dispersive nature of guided waves, combined with the inherent anisotropy of some industrial materials, such as composites, makes the interpretation of the output signals difficult. The goal of this thesis is to provide meaningful numerical tools enhancing the understanding and analysis of propagation and interaction phenomena, appearing during the control experiment. The thesis lies between the physical and mathematical modelling of elastic waves and the construction of relevant numerical schemes, altogether in an innovating industrial context involving complex geometries and materials
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Li, Sijia. "Couches absorbantes pour la propagation d'ondes dans les sols non bornés à l’aide de la décomposition en sous-domaines et l'intégration temporelle hybride asynchrone." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI042.
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Le travail de thèse a pour objet de proposer de nouvelles formulations de couches absorbantes artificielles aux frontières des maillages éléments finis pour la simulation numérique de la propagation d’ondes dans des milieux infinis 2D et 3D, afin de traiter des problèmes complexes d’interaction sol-structure en dynamique transitoire. Trois couches absorbantes sont développées : les couches absorbantes basées sur les amortissements de Rayleigh ou de Kosloff et les PML (Perfectly Matched Layers). En étudiant analytiquement la forme forte de la propagation des ondes dans chaque milieu, il est montré que les amortissements de Kosloff et ceux provenant de PML sont indépendants de la fréquence, ce qui n’est pas le cas de l'amortissement de Rayleigh. Le problème de propagation des ondes à l’interface entre un milieu élastique non dissipatif et un milieu dissipatif est aussi étudié, afin de dégager des conditions optimales permettant de calibrer les caractéristiques mécaniques des couches absorbantes. La discrétisation spatiale des couches absorbantes est conduite à l’aide de la méthode des éléments finis, tandis que la discrétisation temporelle s’appuie sur le cadre performant et flexible des méthodes dites HATI (Heterogeneous Asynchronous Time Integrator), permettant de sélectionner, selon les caractéristiques des sous-domaines du problème et les phénomènes physiques qui s’y déroulent, les schémas d’intégration temporelle et les pas de temps les mieux adaptés. L’efficacité des trois couches absorbantes hybrides asynchrones pour la modélisation de domaines non bornés a été illustrée dans diverses applications numériques, 2D et 3D, telles que le test de Lamb dans des milieux hétérogènes stratifiés ou des problèmes d’interaction sol-structure comportant des barrières d’ondes. Finalement, des versions implicite ou explicite de PML asynchrone sont mises en place et testées pour des problèmes avec un nombre important de degrés de liberté. Elles s’avèrent être plus précises et performantes que les couches absorbantes basées sur des amortissements de Rayleigh et KosloffThe purpose of this thesis is to propose novel designs and formulations of different absorbing layers at the boundaries of finite element meshes for the numerical simulation of wave propagation in unbounded 2D and 3D media, in order to deal with complex soil-structure interaction problems in transient dynamics. Three absorbing layers are developed: Rayleigh Absorbing Layer, Kosloff Absorbing Layer and Perfectly Matched Layer (PML). By studying analytically the strong form of elastic wave propagation in each medium, the frequency-independent absorbing ability of Kosloff damping and PML is derived, whereas the attenuation due to Rayleigh damping turns out be frequency-dependent. The interface problem between a non-dissipative elastic medium and a dissipative medium has been investigated by considering the wave propagation in the continuous setting, in order to establish optimal conditions to further reduce the spurious waves reflected at the interface. The three absorbing layers are discretized in space by the finite element method, while the time discretization is based on the powerful and flexible HATI framework (Heterogeneous Asynchronous Time Integrator), enabling adopt the most suitable time integration schemes and time steps, depending on the characteristics and physical phenomena occurring in the different subdomains. The efficiency of three asynchronous hybrid absorbing layers for modeling unbounded domains has been illustrated in various 2D and 3D numerical applications, such as Lamb’s test in stratified heterogeneous media or soil-structure interaction problems involving wave barriers. Finally, implicit and explicit versions of asynchronous PML are implemented and tested in problems with a large number of degrees of freedom. It is proved to be more accurate and efficient than the absorbing layers based on Rayleigh and Kosloff damping
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Barnwell, Ellis. "One and two-dimensional propagation of waves in periodic heterogeneous media : transient effects and band gap tuning." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/one-and-twodimensional-propagation-of-waves-in-periodic-heterogeneous-media-transient-effects-and-band-gap-tuning(9a5bd9d7-09da-46a8-ae57-b63d9d815f10).html.
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In this thesis, the propagation of transient waves in heterogeneous media and the tuning of periodic elastic materials are studied. The behaviour of time harmonic waves in complex media is a well understood phenomenon. The primary aim of this text is to gain a deeper understanding into the propagation of transient waves in periodic media. The secondary aim is to explore the time harmonic behaviour of two dimensional pre-stressed elastic media and investigate the plausibility of band gap tuning. We begin this text by investigating the reflection of pulses from a semi-infinite set of point masses (we call 'beads') on a string. The reflected pulse is formulated using Fourier transforms which involve the harmonic reflection coefficient. We find that the reflected amplitude of a harmonic wave depends on its frequency. We then ask whether it is possible to find an effective reflection coefficient by assuming the beaded portion of the string is given by some effective homogeneous medium. An effective reflection coefficient is found by assuming the homogeneous medium has the wavenumber given by the infinite beaded string. This effective reflection coefficient is compared to the exact reflection coefficient found using the Wiener-Hopf technique. The results from studying the reflection problem gave inspiration to chapter 4, which focuses on the time dependent forcing of an infinite beaded string that is initially at rest. We again use the Fourier transform to find a time dependent solution. The z-transform is then used, after sampling the solution at the bead positions. We impose a sinusoidal loading which is switched on at a specified time. In doing this we are able to explore how the system behaves differently when excited in a stop band, a pass band and at a frequency on the edge between the two. An exact solution for the infinite beaded string is found at any point in time by expanding the branch points of the solution as a series of poles. We compare this exact solution to the long time asymptotics. The energy input into the system is studied with the results from the exact solution and long time approximation showing agreement. Interesting behaviour is discovered on the two edges between stop and pass bands. In chapter 5 the effect of a nonlinear elastic pre-stress on the wave band structure of a two dimensional phononic crystal is investigated. In this chapter we restrict ourselves to incompressible materials with the strain energy functions used being the neo-Hookean, Mooney-Rivlin and Fung. The method of small-on-large is used to derive the equation for incremental elastic waves and then the plane wave expansion method is used to find the band structure. Finally, chapter 6 focuses on the same geometry with a compressible elastic material. The strain energy function used is the one suggested by Levinson and Burgess. We use the theory of small-on-large to derive the incremental equations for coupled small amplitude pressure and shear waves in this material. In both compressible and incompressible materials we show how it is possible to control the stop bands in a material by applying a large elastic pre-stress.
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May, Daniel. "Transiente Methoden der Infrarot-Thermografie zur zerstörungsfreien Fehleranalytik in der mikroelektronischen Aufbau- und Verbindungstechnik." Doctoral thesis, Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-163082.
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In dieser Arbeit wurde eine neue fehleranalytische Methode zur industriellen Anwendung an neuen Technologien der Aufbau- und Verbindungstechnik entwickelt. Das Verfahren basiert auf der Wechselwirkung von thermischen Wellen und Defekten. Die Besonderheit ist dabei die Zerstörungsfreiheit, die Geschwindigkeit, das Auflösungsvermögen und die durch neueste IR-Detektoren erreichte Temperaturempfindlichkeit. Es wurden grundlegende Studien bezüglich Auflösung und parasitären Effekten bei der Anwendung unter industriellen Randbedingungen durchgeführt. Dabei wurde eine systematische Vorgehensweise bezüglich der Komplexität gewählt. Dies ermöglicht nun u.a. eine Vorhersage der zu erwartenden Prüfdauer zur Auflösung vergrabener Defekte, der Begrenzung der maximalen Anregungsimpulsbreite (bei gegebener Defekttiefe) und die quantitative Ermittlung des Einflusses einer Lackschicht. Methodisch kamen grundsätzlich Simulationen und vergleichende Experimente zum Einsatz. Es wurden spezielle Proben zur Isolierung und Klärung parasitärer Effekte verwendet. Letztlich konnte das Messsystem erfolgreich an industriellen Problemstellung demonstriert werden. Das entwickelte Messsystem zeichnet sich durch hohe Flexibilität aus. Verschiedene problemangepasste Anregungsquellen (interne und externe Anregung durch zahlreiche physikalische Effekte) kommen zum Einsatz. Das Messsystem besteht aus vier Hauptmodulen, der Differenzbild-Methode, der Impulsthermografie, und zwei Varianten der LockIn-Thermografie. Zusammen ist das System in der Lage, Voids, Delaminationen und Risse in verschiedenen Bereichen auch der modernen AVT sicher zu erkennen. Es werden dabei Temperaturauflösugnen bis zu 5 mK und laterale Auflösungen bis 17 µm erreicht. Diese Arbeit legt einen Grundstein für die Anwendung der thermischen Fehleranalytik in der Industrie, indem hier die Grenzen der IR-Messtechnik aufgezeigt und charakterisiert werdenIn this work a new failure analytical method for the industrial application of new technologies in electronic packaging has been developed. The developed method is based on the interaction of the thermal waves and defects. The special fature is non-destructive, speed, resolution and high temperature sensitivity due to latest IR-detectors. It fundamental studies regarding resolution and parasitic effects in the application were carried out cinsidering industrial conditions. Here, a systematic approach regarding the complexity has been selected. This now enables a prediction of the expected test period for detecting buried defects, limits for excitation pulse width (for a given defect depth) and the quantitative determination of the influence of parasitic paints. Methodically always simulations and comparative experiments were used. Simple samples for the isolation and purification of parasitic effects has been used. Finally, the measurement system has been successfully demonstrated on an industrial applications. The developed measurement system is characterized by high flexibility. Different problem-adapted excitation sources (internal and external excitation by numerous physical effects) are used. The measurement system currently consists of four main modules, the difference image method, the pulse thermography, and two variants of LockIn-thermography. Together, the system is capable of detecting voids, delaminations and cracks in various fields of electronic packageing. It will reach temperature resolutions up to 5 mK and lateral resolutions down to 17 µm. This work stes a foundation for the application of thermal failure analysis for industry by showing and charcterization the limits of IR imaging
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Theethayi, Nelson. "Electromagnetic Interference in Distributed Outdoor Electrical Systems, with an Emphasis on Lightning Interaction with Electrified Railway Network." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5889.
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Bremner, Sherry. "Analysing transient effects in the ionosphere using narrowband VLF data." Thesis, 2009. http://hdl.handle.net/10413/8323.
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Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere
waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation
conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere,
such as the presence of the D-region during the day, or the precipitation of energetic particles,
are the main causes of this modification. Using narrowband receivers monitoring remote VLF
transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis
technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters
such as seasonal and diurnal changes which affect the variation of these signals. Data was
then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and
solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric
propagation.Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.
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Chang, Chun-Kai, and 張鈞凱. "Experimental Measurement, Theoretical Analysis and Numerical Calculation of Transient Wave Propagation of Displacement and Strain." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/16245636584723214868.
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碩士國立臺灣大學
機械工程學研究所
99
Recently, piezoelectric film(PVDF) and fiber Bragg grating(FBG) are usually investigated by researcher. We use the FBG with power modulated sensing method to measure strain and displacement of the structure, and compared the sensing results with other sensors. Also, we investigate and discuss the dynamic measurement ability of the three-dimensional FBG measurement system. Then, PVDF can be used to measure pressure and dynamic external force history and has many advantages such as light, thin, excellent dynamic measurement ability and easy to adhesive on the object surface. In this thesis, we establish a measurement method to measure the dynamic force history on thin plate structures. We can use the force history to conduct theoretical analysis and numerical calculation of finite element method(ABAQUS) then obtain the results of transient wave propagation within the structure. In theoretical analysis, we use the normal mode method and the Laplace transform method to calculate the results of transient wave propagation within the structure. For the Laplace transform method, it’s difficult to derive the inversion in transform domain. Therefore, we use the Durbin numerical inversion method to inverse the solution in transform domain and the inversion can be easier and more efficient. Besides, we use the exact solution determined by normal mode method to compare with the solution determined by Laplace method. It’s not easy to obtain the theoretical solution of transient wave propagation within the structure in most of engineering structure issue, thus, we can use the finite element method to estimate it. Finally, we compare the transient response of theoretical analysis, finite element method and experimental measurement to verify the accuracy of experimental measurement.
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Xi-Hong, Chen. "Theoretical Transient Analyses of Stress Wave Propagation and Dynamic Fracture for Interfacial Crack in Elastic-Piezoelectric Bi-materials." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1308200612442000.
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Chen, Xi-Hong, and 陳熙洪. "Theoretical Transient Analyses of Stress Wave Propagation and Dynamic Fracture for Interfacial Crack in Elastic-Piezoelectric Bi-materials." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/97486724804187589218.
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博士國立臺灣大學
機械工程學研究所
94
In transversely isotropic elastic solids, there is no surface wave for anti-plane deformation. However, for certain orientations of piezoelectric materials, a surface wave propagating along the free surface (interface) will occur and is called the Bleustein-Gulyaev (Maerfeld-Tournois) surface wave. The existence of the surface wave strongly influences the crack propagation event. Hence the existence condition and velocity of the interfacial surface wave between two piezoelectric materials are analyzed. The nature of anti-plane dynamic fracture in piezoelectric materials is fundamentally different from that in purely elastic solids. Piezoelectric surface wave phenomena are clearly seen to be critical to the behavior of the moving crack. In this study, the problem has characteristic lengths and a direct attempt towards solving this problem by transform and Wiener-Hopf techniques is not applicable. A new fundamental solution for propagating interfacial crack between elastic-piezoelectric bi-materials is proposed and the transient response of the propagating crack is determined by superposition of the fundamental solution in the Laplace transform domain. The fundamental solution to be used is the responses of applying exponentially distributed traction in the Laplace transform domain on the propagating crack surface. Four situations for different combination of shear wave velocity and the existence of MT surface wave are discussed to completely analyze this problem. Exact analytical transient solutions are obtained by using the Cagniard-de Hoop method of Laplace inversion and are expressed in explicit forms. Finally, numerical results for the transient solutions are evaluated and discussed in detail.
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Kuo-Chih, Chuang, and 莊國志. "Development of Multidimensional, High Resolution Fiber Bragg Grating Dynamic Displacement and Strain Sensing System for Measurement of Transient Wave Propagation." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/68408836337703912482.
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博士國立臺灣大學
機械工程學研究所
96
A method for setting up a fiber Bragg grating (FBG) sensor which can measure the point-wise, out-of-plane or in-plane dynamic displacement is proposed. A multiplexing demodulation system based on a single long-period fiber grating (LPFG) or an FBG filter is used in this study. First, the FBG displacement sensor is employed as a feedback sensor in a multilayer piezoceramic actuator tracking control system. The dynamic measurement ability of the proposed FBG sensor is demonstrated by the system identification experiment and various control strategies. The experimental results compared with a laser Doppler vibrometer (LDV) simultaneously show that the proposed sensor system can serve as a feedback control sensor which has a displacement sensitivity of 5 mV/nm. We further measure the dynamic response of a cantilever beam or a cantilever plate subjected to impact loadings. An optical amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) technique and FEM numerical calculations are used to provide full-field vibration mode shapes and resonant frequencies of the cantilever structures. The amplitudes of the frequency spectrums are emphasized from the mode shapes and impact locations. Finally, we employ three orthogonal FBG displacement sensors to measure the three-dimensional displacements for transient wave propagation in a solid. The experimental results also indicate the excellent dynamic measurement ability of the proposed in-plane FBG strain sensor.
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Lin, Bo-Ruei, and 林柏睿. "The development of high sensitive fiber grating filter and sensor in the applications of displacement measurement for transient wave propagation." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/15081268519750610950.
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碩士國立臺灣大學
機械工程學研究所
94
In the measurement of strain field and temperature variation, fiber grating sensor detection technique has been widely used. It has many advantages, such as high sensitivity, low insertion loss, electromagnetic immunity and potentially low cost. The characteristics of fiber grating sensor in sensing static and low frequency response have been frequently reported in the literature. However, in the capability of sensing dynamic response for fiber grating sensor may need for further investigations. The main objective of this thesis is to establish the experimental measurement system based on the grating based fiber sensors to obtain the dynamic transient response of structures subjected to dynamic impact loadings. In this thesis, the tilted fiber Bragg grating (TFBG) and normal fiber Bragg grating (FBG) are proposed as new filter to increase the sensitivity of the fiber grating sensor measuring system. We also provide a new gluing method, it can be used to perform the measurement of out-of-plane motion . The fiber grating sensing-system is used as a displacement sensor and measurement sensitivity is in the order of submicrometer. The etched fiber grating sensor is developed to analyze the in-plane and out-plane coupling effect in transient wave propagation. All the transient responses are simutaneously measured by Laser Doppler vibrometer (LDV), and the results are in excellent agreement with that obtained by fiber grating sensing system.
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Chuang, Kuo-Chih. "Development of Multidimensional, High Resolution Fiber Bragg Grating Dynamic Displacement and Strain Sensing System for Measurement of Transient Wave Propagation." 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-3107200813354400.
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Liao, Chan-Yi, and 廖展誼. "Theoretical Analysis, Numerical Calculation and Experimental Measurement on Vibration Characteristic and Transient Wave Propagation of Rectangular Plate Coupled with Fluid." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/wp23sf.
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博士國立臺灣大學
機械工程學研究所
106
This study investigates the dynamic characteristics of a thin rectangular plate in air and coupled with fluid by theoretical analysis, experimental measurements, and finite element calculation. The dynamic characteristics involve the vibration properties and the transient behaviors of plate. In this study, the resonant frequencies and mode shapes of the rectangular plate is determined by the superposition method. The results are compared with the results obtained by the Rayleigh-Ritz method. It is shown that the superposition method can fully satisfy the governing equation and the free edge boundary conditions, and give even more accurate result than Rayleigh-Ritz method. The mode shapes of plate in air obtained by superposition method can then be used as the fundamental function to construct the mode shapes of the plate coupled with fluid. The behavior of the compressible fluid induced by the deformation of the plate is obtained from a three-dimensional acoustic equation. The frequency response equation is derived from the hydrostatic equilibrium between the fluid and plate. Solving the frequency response equation makes it possible to obtain the vibrational properties of the fluid-plate system, such as resonant frequencies, wet mode shapes, and pressure of the fluid. Two experimental methods were employed to measure the vibration characteristics of the thin plate immersed in water. Polyvinylidene difluoride (PVDF) measures resonant frequencies of the fluid-plate system. Amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) was used to measure clear mode shapes of the plate in the fluid. Comparison of the results from theoretical analysis, finite element method, and experimental measurements confirmed the accuracy of our theoretical analysis. This study employed theoretical analysis and experimental measurements in an exploration of the transient behavior of a cantilever plate subjected to impact loading. Theoretical derivation has established that displacement is a product of the time and space functions (mode shapes). The superposition method was used to obtain the mode shapes and resonant frequencies of free vibrations, while the orthogonality of the mode function was used to solve the time function. The variation of the applied external force with regard to time, i.e. force history, was measured experimentally by attaching PVDF sensors. More importantly, it was taken into consideration in our theoretical analysis to determine the transient responses, including displacement and strain. Our results obtained in the theoretical analysis are highly consistent with experimental measurements. This is a clear demonstration of the effectiveness of pairing theoretical analysis with experimentally measured force histories in the representation of transient behavior of a cantilever plate. Based on the vibrational characteristics of a fluid-plate system, a theoretical method is developed to investigate its transient behavior. The simultaneous equations are constructed by the normal-mode expansion. The transient displacement and velocity of the plate coupled with water can be obtained by solving the simultaneous equations.
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Lee, Kuan-Te, and 李冠德. "Application of the Fiber Bragg Grating Sensor on Measuring and Analyzing Dynamic Characteristics and Transient Wave Propagation of Solid-liquid Structures." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/80239714741726366275.
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碩士國立臺灣大學
機械工程學研究所
104
In recent years, the optical fiber sensors, especially Fiber Bragg Grating (FBG) sensors, have been developed very rapidly due to its excellent mechanical properties, electromagnetics immunity and high sensitivity. FBG can be used to monitor the static problems by using I-MON system. It also can be used to measure the transient response of mechanical structures by using power modulating method. Both of them can be used to measure mutiple points simultaneously with wavelength division multiplexer. Digital image correlation (DIC) is a full field and non-contact measurement technique and can be widely used to measure displacement and strain. PVDF has some excellent properties, such as flexibility, piezoelectricity and can be made for any size. It is widely used as a sensor or a transducer. All of them were developed in our laboratory and will be used in this thesis. The main object of this research is to use the advantages of FBG to perform the measurement under water to show it has the ability to measure the transient response of cylinder and cantilever plate structure in both air and water. Not only use FS sensor to measure displacement, velocity, acceleration field to enhance the credibility of experiment, but also use DIC to measure the dynamic displacement along the length of the plate. The transient displacement obtained by DIC can be filtered to construct the mode shape of plate. On the other hand, the boundary condition of the plate in the water can be checked by frequency annlysis of I-MON system. The last part of this research is focused on the prediction of the length and location of the defect in a beam structure from measured frequencies.
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Huang, Kuo-Shu, and 黃國書. "Transient Elastic Waves Propagating in a Two-Layered Piezoelectric Medium Subjected to the Mechanical and Electrical Concentrated Loadings." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/66176725181073204278.
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碩士淡江大學
航空太空工程學系碩士班
99
In this study, transient elastic waves propagating in a two-layered piezoelectric medium subjected to anti-plane concentrated loading and in-plane electric displacement loading on the upper and lower free surfaces are investigated. The double-layer composite is constructed of two layers of piezoelectric materials with different thicknesses. The one-sided and the two-sided Laplace transforms are applied to obtain the shear stresses and the electric displacements in the transform domain. And then, the Durbin’s method for one-sided Laplace transform inversion and the extended Durbin’s method for two-sided Laplace transform inversion are used to carry out the numerical inversions. The numerical results for different field points, different ratios of thicknesses and different loading types are evaluated and discussed in detail.