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Dissertations / Theses on the topic 'Wave Propagation Analysis'
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Yildirim, Baran. "Acoustic Wave Analysis Using Different Wave Propagation Models." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609527/index.pdf.
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In this study in order to simulate the acoustic waves, Ray Theory and Normal Mode models are used. These methods are analyzed using MATLAB simulation tool<br>differences between two models are examined and a region with a known bottom profile and sound velocity profiles is investigated. The Ray Theory is used in acoustic systems which is the one of the applications of wave modeling. Ray theory is solved with standard Ordinary Differential Equation solvers and normal mode with finite element method. Different bottom profiles and sound velocity profiles previously taken are interpolated to form an environment and examined in the case study.
in the case study.
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Casadei, Filippo. "Multiscale analysis of wave propagation in heterogeneous structures." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44889.
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The analysis of wave propagation in solids with complex microstructures, and local heterogeneities finds extensive applications in areas such as material characterization, structural health monitoring (SHM), and metamaterial design. Within continuum mechanics, sources of heterogeneities are typically associated to localized defects in structural components, or to periodic microstructures in phononic crystals and acoustic metamaterials. Numerical analysis often requires computational meshes which are refined enough to resolve the wavelengths of deformation and to properly capture the fine geometrical features of the heterogeneities. It is common for the size of the microstructure to be small compared to the dimensions of the structural component under investigation, which suggests multiscale analysis as an effective approach to minimize computational costs while retaining predictive accuracy.
This research proposes a multiscale framework for the efficient analysis of the dynamic behavior of heterogeneous solids. The developed methodology, called Geometric Multiscale Finite Element Method (GMsFEM), is based on the formulation of multi-node elements with numerically computed shape functions. Such shape functions are capable to explicitly model the geometry of heterogeneities at sub-elemental length scales, and are computed to automatically satisfy compatibility of the solution across the boundaries of adjacent elements. Numerical examples illustrate the approach and validate it through comparison with available analytical and numerical solutions. The developed methodology is then applied to the analysis of periodic media, structural lattices, and phononic crystal structures. Finally, GMsFEM is exploited to study the interaction of guided elastic waves and defects in plate structures.
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Feng, Jiling. "Wave propagation in flexible tubes." Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/5367.
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Wave dissipation was previously investigated intensively in the frequency domain, in which the dissipation of waves is described as attenuation of pressure pulse decay with respect to the frequency or harmonics. In this thesis, wave dissipation, including decay of pressure pulse, peak of wave intensity and wave energy, is investigated in the time domain using wave intensity analysis (WIA). Wave intensity analysis benefits to this research in several aspects including: 1) WIA allows for wave dissipation investigated in the time domain; 2) WIA does not make any assumptions about the tube's wall non-linearity and the analysis takes into account the effects of the vessel's wall viscoelastic properties, convective, frictional effects and fluid viscosity; 3) WIA offers a technique (separation) to study wave dissipation in one direction whilst taking into account the effect of reflections from the opposite direction; 4) The physical meaning of wave intensity provides a convenient method to study the dissipation of energy carried by the waves along flexible tubes. In this research, it is found that the degree of dissipation in flexible tube were not only affected by the mechanical properties of the wall property and viscosity of liquid but also by the other factors including initial pressure and pumping speed of piston as well as direction of wave in relation to direction of flow. Also an new technique to separate waves into forward and backward directions only using diameter and velocity might potentially be used to separate the waves in both directions non-invasively based on the non-invasive measurement of diameter (wall movement) available.
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Guardasoni, C. "Wave propagation analysis with boundary element method." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/148439.
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Time-dependent problems, that are frequently modelled by hyperbolic partial differential equations, can be dealt with the boundary integral equations (BIEs) method. The ideal situation is when the partial differential equation is homogeneous with constant coefficients, the initial conditions vanish and the data are given only on the boundary of a domain independent of time. In this situation the transformation of the differential problem to a BIE follows the same well-known method for elliptic boundary value problems. In fact the starting point for a BIE method is the representation of the differential problem solution in terms of single layer and double layer potentials using the fundamental solution of the hyperbolic partial differential operator.
(Pubblicata - vedi http://hdl.handle.net/2434/148419)
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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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Hammerton, Paul William. "Nonlinear wave propagation with diffusion and relaxation." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358650.
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Qing, Li. "GIS Aided Radio Wave Propagation Modeling and Analysis." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33287.
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The analysis of radio wave propagation is a crucial part in designing an efficient wireless communication system. The Geographic Information System (GIS) can be incorporated into this procedure because most of the factors in radio wave propagation are geographic features.
In this research, a commercial wireless planning software is tested in a field driving test carried out in Montgomery County, VA. The performance of current wireless planning software is evaluated based on field measurement. The received signal strength data collected during this driving test are then analyzed in a GIS environment in a statistical approach. The effects of local geographic features are modeled in GIS by appropriate spatial analyses.<br>Master of Science
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Motamed, Mohammad. "Topics in Analysis and Computation of Linear Wave Propagation." Doctoral thesis, Stockhollm : Numerical Analysis, Kungliga tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4715.
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Bashir, Hussam. "Calculation of Wave Propagation for Statistical Energy Analysis Models." Thesis, Uppsala universitet, Tillämpad mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267928.
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This thesis investigates the problems of applying Statistical Energy Analysis (SEA) tomodels that include solid volumes. Three wave types (Rayleigh waves, Pressure wavesand Shear waves) are important to SEA and the mathematics behind them is explainedhere. The transmission coefficients between the wave types are needed for energytransfer in SEA analysis and different approaches to solving the properties of wavepropagation on a solid volume are discussed. For one of the propagation problems, asolution, found in Momoi [6] is discussed, while the other problem remains unsolveddue to the analytical difficulties involved.
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Arshad, Kamran. "Modelling of radio wave propagation using Finite Element Analysis." Thesis, Middlesex University, 2007. http://eprints.mdx.ac.uk/9768/.
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Fourth generation (4G) wireless communication systems are intended to support high data rates which requires careful and accurate modelling of the radio environment. In this thesis, for the first time finite clement based accurate and computationally efficient models of wave propagation in different outdoor and indoor environments has been developed. Three different environments were considered: the troposphere, vegetation and tunnels and wave propagation in these environments were modelled using finite element analysis. Use of finite elements in wave propagation modelling is a novel idea although many propagation models and approaches were used in past. Coverage diagrams, path loss contours and power levels were calculated using developed models in the troposphere, vegetation and tunnels. Results obtained were compared with commercially available software Advanced Refractive Effects Prediction Software (AREPS) to validate the accuracy of the developed approach and it is shown that results were accurate with an accuracy of 3dB. The developed models were very flexible in handling complex geometries and similar analysis can be easily extended to other environments. A fully vectored finite element base propagation model was developed for straight and curved tunnels. An optimum range of values of different electrical parameters for tunnels of different shapes has been derived. The thesis delivered a novel approach to modelling radio channels that provided a fast and accurate solution of radio wave propagation in realistic environments. The results of this thesis will have a great impact in modelling and characterisation of future wireless communication systems.
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Sholtes, Joel Doyle Martin W. "Hydraulic analysis of stream restoration on flood wave propagation." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2009. http://dc.lib.unc.edu/u?/etd,2523.
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Thesis (M.A.)--University of North Carolina at Chapel Hill, 2009.<br>Title from electronic title page (viewed Oct. 5, 2009). "... in partial fulfillment of the requirements for the degree of Master of Arts in the Department of Geography." Discipline: Geography; Department/School: Geography.
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Holst, Henrik. "Multi-scale methods for wave propagation in heterogeneous media." Licentiate thesis, Stockholm : Datavetenskap och kommunikation, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10511.
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Häggblad, Jon. "Boundary and Interface Conditions for Electromagnetic Wave Propagation using FDTD." Licentiate thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25744.
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Simulating electromagnetic waves is of increasing importance, for example, due to the rapidly growing demand of wireless communication in the fields of antenna design, photonics and electromagnetic compatibility (EMC). Many numerical and asymptotic techniques have been developed and one of the most common is the Finite-Difference Time-Domain (FDTD) method, also known as the Yee scheme. This centered difference scheme was introduced by Yee in 1966. The success of the Yee scheme is based on its relatively high accuracy, energy conservation and superior memory efficiency from the staggered form of defining unknowns. The scheme uses a structured Cartesian grid, which is excellent for implementations on modern computer architectures. However, the structured grid results in loss of accuracy due to general geometry of boundaries and material interfaces. A natural challenge is thus to keep the overall structure of Yee scheme while modifying the coefficients in the algorithm near boundaries and interfaces in order to improve the overall accuracy. Initial results in this direction have been presented by Engquist, Gustafsson, Tornberg and Wahlund in a series of papers. Our contributions are new formulations and extensions to higher dimensions. These new formulations give improved stability properties, suitable for longer simulation times. The development of the algorithmsis supported by rigorous stability analysis. We also tackle the problem of controlling the divergence free property of the solution—which is of extra importance in three dimensions—and present results of a number of numerical tests.<br>QC 20101101
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Hartmann, Axel [Verfasser]. "Experimental Analysis of Wave Propagation at Buffet Flows / Axel Hartmann." Aachen : Shaker, 2012. http://d-nb.info/106904623X/34.
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Salisbury, Christopher. "Spectral Analysis of Wave Propagation Through a Polymeric Hopkinson Bar." Thesis, University of Waterloo, 2001. http://hdl.handle.net/10012/799.
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The importance of understanding non-metallic material behaviour at high strain rates is becoming ever more important as new materials are being developed and used in shock loading applications. Applying conventional methods for high strain rate testing to non-metallic materials proved ineffective due to impedance mismatch between the specimen and apparatus and so a new test method was developed. A polymeric Hopkinson bar was developed enabling non-metallic materials, such as polycarbonate and rubber, to be tested at strain rates from 500 s^-1 to 4000 s^-1. Conventional Hopkinson bar analysis is invalid due to the viscoelastic nature of the polymeric bar material. As waves propagate along the bar length, the inherent material behaviour causes the waves to undergo a degree of attenuation and dispersion. Through the use of spectral analysis, a comparison of the dispersive relationships for 6061 T-6 aluminium, extruded acrylic and low density polyethylene is presented. The application of spectral methods to viscoelastic wave analysis was validated by three separate methods. A comparison of predicted and measured waves along the bar length allowed the dispersive relationship to be substantiated. The use of an enhanced laser velocity system further verified the predicted wave magnitude. A comparison of results for polycarbonate and ballistic gelatin to published results showed good agreement.
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Guo, Shiyan. "Asymptotic Analysis of Wave Propagation through Periodic Arrays and Layers." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8886.
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In this thesis, we use asymptotic methods to solve problems of wave propagation through infinite and finite (only consider those that are finite in one direction) arrays of scatterers. Both two- and three-dimensional arrays are considered. We always assume the scatterer size is much smaller than both the wavelength and array periodicity. Therefore a small parameter is involved and then the method of matched asymptotic expansions is applicable. When the array is infinite, the elastic wave scattering in doubly-periodic arrays of cavity cylinders and acoustic wave scattering in triply-periodic arrays of arbitrary shape rigid scatterers are considered. In both cases, eigenvalue problems are obtained to give perturbed dispersion approximations explicitly. With the help of the computer-algebra package Mathematica, examples of explicit approximations to the dispersion relation for perturbed waves are given. In the case of finite arrays, we consider the multiple resonant wave scattering problems for both acoustic and elastic waves. We use the methods of multiple scales and matched asymptotic expansions to obtain envelope equations for infinite arrays and then apply them to a strip of doubly or triply periodic arrays of scatterers. Numerical results are given to compare the transmission wave intensity for different shape scatterers for acoustic case. For elastic case, where the strip is an elastic medium with arrays of cavity cylinders bounded by acoustic media on both sides, we first give numerical results when there is one dilatational and one shear wave in the array and then compare the transmission coefficients when one dilatational wave is resonated in the array for normal incidence. Key words: matched asymptotic expansions, multiple scales, acoustic scattering, elastic scattering, periodic structures, dispersion relation.
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Otsubo, Masahide. "Particle scale analysis of soil stiffness and elastic wave propagation." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/44380.
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Soils are granular materials consisting of many particles, and the overall response of a soil can be considered to be a complex accumulation of the inter-particle responses. Small-strain soil stiffness is important to predict the ground deformation in situ and in practice and is often deduced from elastic wave velocity in laboratory experiments. The dynamic properties of soils are also important for dynamic analyses including site response analysis. Stress waves propagate through soil via the grain contact network, thus the actual particle-scale mechanics differ from those assumed in continuum mechanics which is often used to simulate and analyse stress wave propagation. Thus the particle properties including surface characteristics should have a direct impact on the overall response of soil to stress wave disturbances. Surface roughness effects on the inter-particle response have previously been considered in the experimental work of Cavarretta (2009) and in the dynamic analyses using the discrete element method (DEM) described by O'Donovan (2013). This research aims to develop understanding of the extent of the sensitivity of soil stiffness to the contact rheology by adopting theoretical, numerical (DEM) and experimental approaches. The theoretical approach follows Yimsiri & Soga (2000) who combined micromechanical effective medium theory and a rough surface contact model; their approach is revisited here considering more recent UK-based tribology studies. The contact laws considered in the DEM analyses presented here include particle surface roughness, partial slip at tangential contacts, and spin resistance based on these developments by the work of O'Donovan (2013). The experimental approach used two types of dynamic tests: bender element tests in a cubical cell apparatus, and shear plate tests in a triaxial apparatus. For both test types, smooth and rough surface spherical ballotini are used to study the surface roughness effects on the sample shear modulus. Shear plates are not commonly used in soil mechanics dynamic testing and so the study also included an assessment of this technology. The data generated show that the small-strain stiffness of granular materials is measurably reduced sensitively with the surface roughness especially at a low stress level. This explains partially a higher exponent n value in the relationship between the shear modulus and the confining stress (n > 0.5). As the stress level increases the shear modulus of the assembly of rough particles approach the smooth equivalent.
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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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Kieri, Emil. "Numerical Methods for Wave Propagation : Analysis and Applications in Quantum Dynamics." Doctoral thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-268625.
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We study numerical methods for time-dependent partial differential equations describing wave propagation, primarily applied to problems in quantum dynamics governed by the time-dependent Schrödinger equation (TDSE). We consider both methods for spatial approximation and for time stepping. In most settings, numerical solution of the TDSE is more challenging than solving a hyperbolic wave equation. This is mainly because the dispersion relation of the TDSE makes it very sensitive to dispersion error, and infers a stringent time step restriction for standard explicit time stepping schemes. The TDSE is also often posed in high dimensions, where standard methods are intractable. The sensitivity to dispersion error makes spectral methods advantageous for the TDSE. We use spectral or pseudospectral methods in all except one of the included papers. In Paper III we improve and analyse the accuracy of the Fourier pseudospectral method applied to a problem with limited regularity, and in Paper V we construct a matrix-free spectral method for problems with non-trivial boundary conditions. Due to its stiffness, the TDSE is most often solved using exponential time integration. In this thesis we use exponential operator splitting and Krylov subspace methods. We rigorously prove convergence for force-gradient operator splitting methods in Paper IV. One way of making high-dimensional problems computationally tractable is low-rank approximation. In Paper VI we prove that a splitting method for dynamical low-rank approximation is robust to singular values in the approximation approaching zero, a situation which is difficult to handle since it implies strong curvature of the approximation space.<br>eSSENCE
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Andrén, Erik. "Simulation and Analysis of Ultrasonic Wave Propagation in Pre-stressed Screws." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75570.
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The use of ultrasound to measure preload in screws and bolts has been studied quite frequently the last decades. The technique is based on establishing a relationship between preload and change in time of flight (TOF) for an ultrasonic pulse propagating back and forth through a screw. This technique has huge advantages compared to other methods such as torque and angle tightening, mainly because of its independence of friction. This is of great interest for Atlas Copco since it increases the accuracy and precision of their assembly tools. The purpose of this thesis was to investigate ultrasonic wave propagation in pre-stressed screws using a simulation software, ANSYS, and to analyse the results using signal processing. The simulations were conducted in order to get an understanding about the wavefront distortion effects that arise. Further, an impulse response of the system was estimated with the purpose of dividing the multiple echoes that occur from secondary propagation paths from one other. The results strengthen the hypothesis that the received echoes are superpositions of reflections taking different propagation paths through the screw. An analytical estimation of the wavefront curvature also shows that the wavefront distortion due to a higher stress near the screw boundaries can be neglected. Additionally, a compressed sensing technique has been used to estimate the impulse response of the screw. The estimated impulse response models the echoes as superpositions of secondary echoes, with significant taps corresponding to the TOF of the shortest path and a mode-converted echo. The method is also shown to be stable in noisy environments. The simulation model gives rise to a slower speed of sound than expected, which most likely is due to the fact that finite element analysis in general overestimates the stiffness of the model.
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Appelö, Daniel. "Absorbing Layers and Non-Reflecting Boundary Conditions for Wave Propagation Problems." Doctoral thesis, KTH, Numerisk Analys och Datalogi, NADA, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-448.
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The presence of wave motion is the defining feature in many fields of application,such as electro-magnetics, seismics, acoustics, aerodynamics,oceanography and optics. In these fields, accurate numerical simulation of wave phenomena is important for the enhanced understanding of basic phenomenon, but also in design and development of various engineering applications. In general, numerical simulations must be confined to truncated domains, much smaller than the physical space were the wave phenomena takes place. To truncate the physical space, artificial boundaries, and corresponding boundary conditions, are introduced. There are four main classes of methods that can be used to truncate problems on unbounded or large domains: boundary integral methods, infinite element methods, non-reflecting boundary condition methods and absorbing layer methods. In this thesis, we consider different aspects of non-reflecting boundary conditions and absorbing layers. In paper I, we construct discretely non-reflecting boundary conditions for a high order centered finite difference scheme. This is done by separating the numerical solution into spurious and physical waves, using the discrete dispersion relation. In paper II-IV, we focus on the perfectly matched layer method, which is a particular absorbing layer method. An open issue is whether stable perfectly matched layers can be constructed for a general hyperbolic system. In paper II, we present a stable perfectly matched layer formulation for 2 x 2 symmetric hyperbolic systems in (2 + 1) dimensions. We also show how to choose the layer parameters as functions of the coefficient matrices to guarantee stability. In paper III, we construct a new perfectly matched layer for the simulation of elastic waves in an anisotropic media. We present theoretical and numerical results, showing that the stability properties of the present layer are better than previously suggested layers. In paper IV, we develop general tools for constructing PMLs for first order hyperbolic systems. We present a model with many parameters which is applicable to all hyperbolic systems, and which we prove is well-posed and perfectly matched. We also use an automatic method, derived in paper V, for analyzing the stability of the model and establishing energy inequalities. We illustrate our techniques with applications to Maxwell s equations, the linearized Euler equations, as well as arbitrary 2 x 2 systems in (2 + 1) dimensions. In paper V, we use the method of Sturm sequences for bounding the real parts of roots of polynomials, to construct an automatic method for checking Petrowsky well-posedness of a general Cauchy problem. We prove that this method can be adapted to automatically symmetrize any well-posed problem, producing an energy estimate involving only local quantities.<br>QC 20100830
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アシャ, シインダゲ, and Asha Shendge. "Wave propagation on covered /cabtyre cables and modeling for inverter surge analysis." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12614641/?lang=0, 2013. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB12614641/?lang=0.
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Zhu, Guang. "Wave propagation analysis in complex medium based on second strain gradient theory." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC045.
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Dans ce travail, deux modèles enrichis décrivant respectivement un mouvement longitudinal non classique dans des tiges et un mouvement de flexion et de cisaillement non classique dans des poutres sont établis basés sur la théorie du second gradient de contrainte de Mindlin. Ce dernier peut décrire l’hétérogénéité provoquée par les interactions micro-structure dans le cadre de la mécanique des milieux continus. La modélisation multi-échelle commence par exprimer l'énergie de déformation, l'énergie cinétique et le travail virtuel effectué par des forces externes basés sur la théorie SSG. Les équations du mouvement et les conditions aux limites associées sont ensuite dérivées en utilisant le principe de Hamilton. Un modèle en cristalline pour modèle enrichi de tige est proposé pour que les interactions à longue distance correspondent à des constantes d'ordre supérieur de matériau dans la théorie de la SSG.La relation de dispersion de l'onde longitudinale non classique ainsi que les deux ondes supplémentaires apparaissant exclusivement dans le modèle de tige basé sur la théorie de la SSG est étudiée. Ensuite, on étudie également les ondes de flexion et les ondes de cisaillement non classiques, ainsi que les quatre ondes supplémentaires dans le modèle de poutre de Timoshenko basé sur la théorie de la SSG. Les recherches sont basées à la fois sur la densité modale des ondes propagées, le flux d'énergie concernant des paramètres cinétiques d'ordre supérieur, la mobilité des structures enrichies, le transfert de puissance dans l'espace et l'analyse de la réponse en fréquence pour une tige enrichie ainsi qu’une poutre enrichie à excitation forcée ponctuelle. Les résultats de réponse en fréquence sont validés par les résultats de la méthode MEF dans COMSOL.En utilisant le modèle de tige enrichie et le modèle de poutre proposés, les caractéristiques de transmission et de réflexion des vibrations via une interface plane entre deux milieux basés sur la théorie de la SSG sont étudiées. Les coefficients de transmission et de réflexion de l'onde longitudinale dans une tige enrichie et de l'onde de flexion dans une tige enrichie sont calculés. Basé sur ces coefficients, la distribution et l'atténuation de l'énergie dans les ondes réfléchies et dans les ondes transmises sont discutées. La transmission et la réflexion des ondes à travers une certaine longueur de tige basée sur la théorie SSG sont ensuite étudiées.En utilisant le modèle de poutre enrichie, le rayonnement d'onde provenant d'une surface vibrante infinie d’une poutre enrichie basée sur la théorie SSG est étudié. Les caractéristiques enrichies, y compris la vitesse carrée de la surface vibrante, l'impédance de rayonnement et le champ de pression rayonné, sont calculées et interprétées en se combinant au caractère de propagation des ondes dans une structure de poutre enrichie. Ensuite, le rayonnement d'onde provenant d'une poutre simplement supportée est étudié en utilisant la formulation intégrale à limite directe basée sur le théorème d'intégrale de Kirchhoff-Helmholtz. Les influences des effets de micro-structure locale sont discutées et bien interprétées sur la base des résultats du modèle SSG et du modèle classique<br>In this work, two enriched models respectively describing non-classical longitudinal motion in bars, and non-classical bending and shear motion in beams, are established based on Mindlin's Second Strain Gradient (SSG) theory. The latter can describe heterogeneity caused by complex micro-structure interaction in the frame of continuum mechanics. The multi-scale modelling starts with expressing the SSG theory based strain energy, kinetic energy and virtual work done by external forces, then the governing equations and the associated boundary conditions are derived with the utilization of Hamilton principle. Lattice model corresponding to 1D longitudinal motion is proposed to map the long range interactions to higher order material constants in SSG theory.Due to the local behavior of underlying micro-structures, Wave propagation features in SSG theory continua are significantly different. With the formulated SSG theory based rod model, dispersion relation of non-classical longitudinal wave accompanying with two evanescent waves are investigated. Meanwhile, non-classical bending wave and shear wave together with four evanescent waves are also investigated with the SSG theory based Timoshenko beam model. The investigations are based on the modal density of the propagating waves, energy flow involving higher order kinetic parameters, mobility of the non-classical structures, vibrating power transfer in spatial position, and forced response analysis of enriched rod as well as enriched beam. The frequency response results are validated by FEM approach resulting from COMSOL.With employing the proposed enriched rod model and beam model, vibration transmission and reflection characteristics through planar interface between two SSG theory based mediums are studied. The study is conducted on transmission and reflection coefficients of longitudinal wave in non-classical rod, and bending wave in non-classical beam, based on which energy distribution and attenuation in reflected waves and in transmitted waves are discussed. Wave transmission and reflection through a certain length of SSG theory based rod is also investigated.With utilization of the derived enriched beam model, wave radiation from infinite vibrating surface is studied. Radiation characteristics including square velocity of the vibrating surface, radiation impedance and radiated pressure field are achieved, and these enriched characteristics are interpreted combining with wave propagation characters in non-classical beam structure. Wave radiation from baffled finite beam is investigated with employing the direct boundary integral formulation based on the Kirchhoff-Helmholtz integral theorem.The influences of local behavior caused by complex micro-structure interactions are discussed and well interpreted based on results of SSG model and classical model
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Mazzaro, Gregory. "Analysis and simulation of the effects of atmospheric turbulence on optical wave propagation." Diss., Online access via UMI:, 2006.
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Shatalov, MY, AC Every, and AS Yenwong-Fai. "Analysis of non-axisymmetric wave propagation in a homogeneous piezoelectric solid circular cylinder of transversely isotropic material." Elsevier, 2008. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001768.
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a b s t r a c t
A study concerning the propagation of free non-axisymmetric waves in a homogeneous
piezoelectric cylinder of transversely isotropic material with axial polarization is carried
out on the basis of the linear theory of elasticity and linear electro-mechanical coupling.
The solution of the three dimensional equations of motion and quasi-electrostatic equation
is given in terms of seven mechanical and three electric potentials. The characteristic equations
are obtained by the application of the mechanical and two types of electric boundary
conditions at the surface of the piezoelectric cylinder. A novel method of displaying dispersion
curves is described in the paper and the resulting dispersion curves are presented for
propagating and evanescent waves for PZT-4 and PZT-7A piezoelectric ceramics for circumferential
wave numbers m = 1, 2, and 3. It is observed that the dispersion curves are sensitive
to the type of the imposed boundary conditions as well as to the measure of the
electro-mechanical coupling of the material.
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Li, Ye. "Propagation and reflection of pulse waves in flexible tubes and relation to wall properties." Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/6554.
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The wall properties of the arteries play an important role in cardiovascular function. Stiffness of large artery is predictive of cardiovascular events. To understand the function of the cardiovascular system, special attention should be paid to the understanding of pulse wave propagation, because pulse waves carry information of the cardiovascular function, and provide information which can be useful for the prevention and diagnosis of diseases. This thesis presents a series of in vitro experimental studies of wave propagation, wave reflection and determination of mechanical properties of flexible vessels. In this thesis, several studies have been included: 1) applied and compared foot-to-foot, PU-loop and lnDU-loop methods for determination of wave speed in flexible tubes and calf aortas; 2) investigated the variation of local wave speed determined by PU-loop with proximity to the reflection site; 3) investigated using wave intensity analysis (WIA) as the analytical technique to determine the reflection coefficient; 4) developed a new technique which based on one-point simultaneous measurements of diameter and velocity to determine the mechanical properties of flexible tubes and calf aortas. In the first study, it is found wave speeds determined by PU-loop and lnDU-loop methods are very similar, and smaller than those determined by foot-to-foot method. The timing of arrival time of reflected wave based on diameter and velocity technique highly agreed with the corresponding timing based on pressure and velocity technique. The shapes of forward and backward non-invasive wave intensities based on diameter and velocity are very similar with the corresponding shapes based on pressure and velocity. Although the density term is not part of the equation, the lnDU-loop method for determining local wave speed is sensitive to the fluid density. In the second study, it is found wave speed measured by PU-loop is varied with proximity to the reflection site. The closer the measurement site to the reflection site, the greater the effect upon measured wave speed; a positive reflection caused an increase in measured wave speed; a negative reflection caused a decrease in measured wave speed. Correction iteration process was also considered to correct the affected measured wave speed. In the third study, it is found, reflection coefficient determined by pressure, square roots of wave intensity and wave energy are very close, but they are different from reflection coefficient determined by wave intensity and wave energy. Due to wave dissipation, the closer the measurement site to the reflection site, the greater is the value of the local reflection coefficient. The local reflection coefficient near the reflection site determined by wave intensity and wave energy are very close to the theoretical value of reflection coefficient. In the last study I found that distensibility determined by the new technique which utilising lnDU-loop is in agreement with that determined from the pressure and area which obtained from tensile test in flexible tubes; distensibility determined by the new technique is similar to those determined in the static and dynamic distensibility tests in calf aortas; Young’s modulus determined by the new technique are in agreement with that those determined by tensile tests in both flexible tubes and calf aortas. In conclusion, wave speed determined by PU-loop and lnDU-loop methods are very similar, the new technique lnDU-loop provides an integrated noninvasive system for studying wave propagation; wave speed determined by PU-loop is affected by the reflection, the closer the measurement site to the reflection site, the greater the change in measured wave speed; WIA could be used to determine local reflection coefficient when the measurement site is close to the reflection site; the new technique using measurements of diameter and velocity at one point for determination of mechanical properties of arterial wall could potentially be non-invasive and hence may have advantage in the clinical setting.
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Ratan, Naren. "Complex phase space representation of plasma waves : theory and applications." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:af5654e3-3137-4d9a-b41d-574cd72103b2.
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This thesis presents results on the description of plasma waves in terms of wavepackets. The wave field is decomposed into a distribution of wavepackets in a space of position, wavevector, time, and frequency. A complex structure joining each pair of Fourier conjugate variables into a single complex coordinate allows the efficient derivation of equations of motion for the phase space distribution by exploiting its analytic properties. The Wick symbol calculus, a mathematical tool generalizing many convenient properties of the Fourier transform to a local setting, is used to derive new exact phase space equations which maintain full information on the phase of the waves and include effects nonlocal in phase space such as harmonic generation. A general purpose asymptotic expansion of the Wick symbol product formula is used to treat dispersion, refraction, photon acceleration, and ponderomotive forces. Examples studied include the nonlinear Schrödinger equation, mode conversion, and the Vlasov equation. The structure of partially coherent wave fields is understood in terms of zeros in the phase space distribution caused by dislocations in its complex phase which are shown to be correlated with the field entropy. Simulations of plasma heating by crossing electron beams are understood by representing the resulting plasma waves in phase space. The local coherence properties of the beam driven Langmuir waves are studied numerically.
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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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Ängskog, Per. "Measurement and Analysis of Radio Wave Coverage in Industrial Environments." Thesis, Högskolan i Gävle, Avdelningen för elektronik, matematik och naturvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-13615.
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Several studies have characterized the path loss properties in industrial environments. However most of them have focused on one frequency, and some two or maximum three frequencies, usually cellular telephone frequencies or the unlicensed ISM bands that are commonly used in various industries. Few, if any, have characterized a larger part of the useable frequency range.This thesis is taking that challenge and investigates the path loss characteristics over a large frequency range, 300 MHz – 3 GHz, in industrial environments. First a measurement system suitable for the harsh environments found in industries is designed and verified. The measurement system is designed as two asynchronous stand-alone units that can be positioned at an arbitrary position to measure the path loss characteristics in any environment without interfering with the normal activities at the location. After that a measurement campaign involving three different types of environments is carried out. The environment types are: first, one highly absorbing – a paper warehouse at a paper mill; second, one highly reflective – a furnace building filled with metal objects and constructions and third, a mine tunnel – located 1 km below the surface of earth which is neither highly reflective nor absorbing but exhibits somewhat wave-guide like characteristics. The environments are shown to have very different behavior when it comes to propagation characteristics. Observations in the first environment reveal an environment that almost cancels out certain frequency bands and only line-of-sight communication is possible, hence no improvement will be achieved if installing systems that take multipath propagation into account, like MIMO. In the second environment reflections are legion; there are so many reflecting surfaces at different angles so any polarization of the signal is almost completely eliminated. Large fading variations were observed.The third environment is the underground mine where signals propagate inside the tunnels like in waveguides. It is shown that there are regions in the spectrum where the path loss dips and that these dips at least partly can be modeled with a simple two-beam propagation model normally used for outdoor propagation over infinite fields. The overall conclusion is that industrial environments are more heterogeneous regarding propagation characteristics than commonly assumed when selecting communication solutions. And that the only way to really know if a radio system will work at a certain location is to measure and characterize the environment.
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De, Larquier Sebastien. "The mid-latitude ionosphere under quiet geomagnetic conditions: propagation analysis of SuperDARN radar observations from large ionospheric perturbations." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24770.
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The Earth's ionosphere is a dynamic environment strongly coupled to the neutral atmosphere, magnetosphere and solar activity. In the context of this research, we restrict our interest to the mid-latitude (a.k.a., sub-auroral) ionosphere during quiet geomagnetic conditions. The Super Dual Auroral Radar Network (SuperDARN) is composed of more than 30 low-power High Frequency (HF, from 8-18 MHz) Doppler radars covering the sub-auroral, auroral and polar ionosphere in both hemispheres. SuperDARN radars rely on the dispersive properties of the ionosphere at HF to monitor dynamic features of the ionosphere. Though originally designed to follow auroral expansion during active periods, mid-latitude SuperDARN radars have observed ground and ionospheric scatter revealing several interesting features of the mid-latitude ionosphere during periods of moderate to low geomagnetic activity. The past 7 years' expansion of SuperDARN to mid-latitudes, combined with the recent extended solar minimum, provides large-scale continuous views of the sub-auroral ionosphere for the first time. We have leveraged these circumstances to study prominent and recurring features of the mid-latitude ionosphere under quiet geomagnetic conditions.
First, we seek to establish a better model of HF propagation effects on SuperDARN observations. To do so, we developed a ray-tracing model coupled with the International Reference Ionosphere (IRI). This model is tested against another well established ray-tracing model, then optimized to be compared to SuperDARN observations (Chapter 2).
The first prominent ionospheric feature studied is an anomaly in the standard ionospheric model of photo-ionization and recombination. This type of event provides an ideal candidate for testing the ray-tracing model and analyzing propagation effects in SuperDARN observations. The anomaly was first observed in ground backscatter occurring around sunset for the Blackstone, VA SuperDARN radar. We established that it is related to an unexpected enhancement in electron densities that leads to increased refraction of the HF signals. Using the ray-tracing, IRI model, and measurements from the Millstone Hill Incoherent Scatter Radar (ISR), we showed that this enhancement is part of a global phenomenon in the Northern Hemisphere, and is possibly related to the Southern Hemisphere's Weddell Sea Anomaly. We also tested a potential mechanism involving thermospheric winds and geomagnetic field configuration which showed promising results and will require further modeling to confirm (Chapter 3).
The second ionospheric feature was a type of decameter-scale irregularity associated with very low drift velocities. Previous work had established that these irregularities occur throughout the year, during nighttime, and equatorward of both the auroral regions and the plasmapause boundary. An initial analysis suggested that the Temperature Gradient Instability (TGI) was responsible for the growth of such irregularities. We first used our ray-tracing model to distinguish between HF propagation effects and irregularity occurrence in SuperDARN observations. This revealed the irregularities to be widespread within the mid-latitude ionosphere and located in the bottom-side F-region (Chapter 4). A second study using measurements from the Millstone Hill ISR revealed that TGI driven growth was possible but only in the top-side F-region ionosphere. We found that initial growth may occur primarily at larger wavelengths, with subsequent cascade to decameter-scale with coupling throughout the F-region (Chapter 5).
In summary, the research conducted during this PhD program has established a robust method to analyze quiet-time SuperDARN observations. It also furthered our physical understanding of some prominent features of the mid-latitude ionosphere. It leaves behind a flexible ray-tracing model, multiple online tools to browse SuperDARN data, and a thorough and growing Space Science API providing access to multiple datasets, models and visualization tools.<br>Ph. D.
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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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Arjmand, Doghonay. "Analysis and Applications of Heterogeneous Multiscale Methods for Multiscale Partial Differential Equations." Doctoral thesis, KTH, Numerisk analys, NA, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160122.
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This thesis centers on the development and analysis of numerical multiscale methods for multiscale problems arising in steady heat conduction, heat transfer and wave propagation in heterogeneous media. In a multiscale problem several scales interact with each other to form a system which has variations over a wide range of scales. A direct numerical simulation of such problems requires resolving the small scales over a computational domain, typically much larger than the microscopic scales. This demands a tremendous computational cost. We develop and analyse multiscale methods based on the heterogeneous multiscale methods (HMM) framework, which captures the macroscopic variations in the solution at a cost much lower than traditional numerical recipes. HMM assumes that there is a macro and a micro model which describes the problem. The micro model is accurate but computationally expensive to solve. The macro model is inexpensive but incomplete as it lacks certain parameter values. These are upscaled by solving the micro model locally in small parts of the domain. The accuracy of the method is then linked to how accurately this upscaling procedure captures the right macroscopic effects. In this thesis we analyse the upscaling error of existing multiscale methods and also propose a micro model which significantly reduces the upscaling error invarious settings. In papers I and IV we give an analysis of a finite difference HMM (FD-HMM) for approximating the effective solutions of multiscale wave equations over long time scales. In particular, we consider time scales T^ε = O(ε−k ), k =1, 2, where ε represents the size of the microstructures in the medium. In this setting, waves exhibit non-trivial behaviour which do not appear over short time scales. We use new analytical tools to prove that the FD-HMM accurately captures the long time effects. We first, in Paper I, consider T^ε =O(ε−2 ) and analyze the accuracy of FD-HMM in a one-dimensional periodicsetting. The core analytical ideas are quasi-polynomial solutions of periodic problems and local time averages of solutions of periodic wave equations.The analysis naturally reveals the role of consistency in HMM for high order approximation of effective quantities over long time scales. Next, in paperIV, we consider T^ε = O(ε−1 ) and use the tools in a multi-dimensional settingto analyze the accuracy of the FD-HMM in locally-periodic media where fast and slow variations are allowed at the same time. Moreover, in papers II and III we propose new multiscale methods which substantially improve the upscaling error in multiscale elliptic, parabolic and hyperbolic partial differential equations. In paper II we first propose a FD-HMM for solving elliptic homogenization problems. The strategy is to use the wave equation as the micro model even if the macro problem is of elliptic type. Next in paper III, we use this idea in a finite element HMM setting and generalize the approach to parabolic and hyperbolic problems. In a spatially fully discrete a priori error analysis we prove that the upscaling error can be made arbitrarily small for periodic media, even if we do not know the exact period of the oscillations in the media.<br><p>QC 20150216</p><br>Multiscale methods for wave propagation
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Mohamed, Ali N. "An analysis of wave propagation due to pile driving vibrations by the finite element method." Thesis, University of Strathclyde, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372108.
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Buchanan, William J. "Analysis of electromagnetic wave propagation using 3D finite-difference time-domain methods with parallel processing." Thesis, Edinburgh Napier University, 1996. http://researchrepository.napier.ac.uk/Output/4022.
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The 3D Finite-Difference Time-Domain (FDTD) method simulates structures in the time-domain using a direct form of Maxwell's curl equations. This method has the advantage over other simulation methods in that it does not use empirical approximations. Unfortunately, it requires large amounts of memory and long simulation times. This thesis applies parallel processing to the method so that simulation times are greatly reduced. Parallel processing, though, has the disadvantage in that simulation programs require to be segmented so that each processor processes a separate part of the simulation. Another disadvantage of parallel processing is that each processor communicates with neighbouring processors to report their conditions. For large processor arrays this can result in a large overhead in simulation time. Two main methods of parallel processing discussed: Transputer arrays and clustered workstations over a local area network (LAN). These have been chosen because of their relatively cheapness to use, and their widespread availability. The results presented apply to the simulation of a microstrip antenna and to propagation of electrical signals in a printed circuit board (PCB). Microstrip antennas are relatively difficult to simulate in the time-domain because they have resonant pulses. Methods that reduce this problem are discussed in the thesis. The thesis contains a novel analysis of the parallel processing showing, using equations, tables and graphs, the optimum array size for a given inter-processor communication speed and for a given iteration time. This can be easily applied to any processing system. Background material on the 3D FDTD method and microstrip antennas is also provided. From the work on the parallel processing of the 3D FDTD a novel technique for the simulation of the Finite-element (FE) method is also discussed.
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Cheng, Jiqi. "A Study of Wave Propagation and Limited-Diffraction Beams for Medical Imaging." University of Toledo / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1133820434.
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Arjmand, Doghonay. "Analysis and Applications of the Heterogeneous Multiscale Methods for Multiscale Elliptic and Hyperbolic Partial Differential Equations." Licentiate thesis, KTH, Numerisk analys, NA, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129237.
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This thesis concerns the applications and analysis of the Heterogeneous Multiscale methods (HMM) for Multiscale Elliptic and Hyperbolic Partial Differential Equations. We have gathered the main contributions in two papers. The first paper deals with the cell-boundary error which is present in multi-scale algorithms for elliptic homogenization problems. Typical multi-scale methods have two essential components: a macro and a micro model. The micro model is used to upscale parameter values which are missing in the macro model. Solving the micro model requires, on the other hand, imposing boundary conditions on the boundary of the microscopic domain. Imposing a naive boundary condition leads to $O(\varepsilon/\eta)$ error in the computation, where $\varepsilon$ is the size of the microscopic variations in the media and $\eta$ is the size of the micro-domain. Until now, strategies were proposed to improve the convergence rate up to fourth-order in $\varepsilon/\eta$ at best. However, the removal of this error in multi-scale algorithms still remains an important open problem. In this paper, we present an approach with a time-dependent model which is general in terms of dimension. With this approach we are able to obtain $O((\varepsilon/\eta)^q)$ and $O((\varepsilon/\eta)^q + \eta^p)$ convergence rates in periodic and locally-periodic media respectively, where $p,q$ can be chosen arbitrarily large. In the second paper, we analyze a multi-scale method developed under the Heterogeneous Multi-Scale Methods (HMM) framework for numerical approximation of wave propagation problems in periodic media. In particular, we are interested in the long time $O(\varepsilon^{-2})$ wave propagation. In the method, the microscopic model uses the macro solutions as initial data. In short-time wave propagation problems a linear interpolant of the macro variables can be used as the initial data for the micro-model. However, in long-time multi-scale wave problems the linear data does not suffice and one has to use a third-degree interpolant of the coarse data to capture the $O(1)$ dispersive effects apperaing in the long time. In this paper, we prove that through using an initial data consistent with the current macro state, HMM captures this dispersive effects up to any desired order of accuracy in terms of $\varepsilon/\eta$. We use two new ideas, namely quasi-polynomial solutions of periodic problems and local time averages of solutions of periodic hyperbolic PDEs. As a byproduct, these ideas naturally reveal the role of consistency for high accuracy approximation of homogenized quantities.<br><p>QC 20130926</p>
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Albers, Bettina [Verfasser]. "Modeling and Numerical Analysis of Wave Propagation in Saturated and Partially Saturated Porous Media / Bettina Albers." Aachen : Shaker, 2010. http://d-nb.info/1124364218/34.
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BARBOSA, JOSÉ MARIA ANDRADE. "ANALYSIS OF THE INFLUENCE OF THERMOMECHANICAL COUPLING IN WAVE PROPAGATION IN ELASTIC-VISCOPLÁSTICAS BARS WITH DAMAGE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1998. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=26522@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>É considerado neste trabalho um modelo mecânico para simulação do comportamento anisotérmico de materiais inelásticos submetidos a carregamentos dinâmicos. O trabalho tem como motivação o estudo, através de simulações numéricas, dos efeitos da propagação da onda de tensão no meio, e de fenômenos como o aquecimento e a degradação local induzida pelas deformações inelásticas. A equação da energia com seus termos de acoplamentos entre os efeitos térmico e mecânico é incluída na modelagem. A teoria constitutiva utilizada baseia-se na mecânica do dano contínuo no contexto de variáveis internas sendo particularizada para materiais elastoviscoplásticos e aplicado ao caso de uma barra solicitada axialmente. O sistema não linear de equações diferenciais parciais resultante do modelo é resolvido através do uso uma técnica de decomposição do operador que permite a aplicação de procedimentos numéricos clássicos de solução. Dentre estes procedimentos, foi usado no trabalho, o método de Glimm. Exemplos numéricos retratando a evolução do dano e da temperatura induzida pela deformação plástica devido a carregamentos de impacto e de alta frequência, são apresentados e analisados. Comparações entre simulações com os modelos isotérmico e anisotérmico permitem caracterizar as influências da equação da energia e do dano.<br>This work presents a mechanical model for simulating the anisothermal behavior of damageable inelastic solids under dynamical loadings. The main motivation of this study is to investigate, by means of numerical simulations, the thermomechanical coupling in a simple one-dimensional problem involving the wave propagation phenomenon in a damageable non-isothermal solid. To achieve this goal, the equation of energy is taken into account in the modeling with the coupling terms between the thermal and mechanical effects. The damageable inelastic mechanical behavior is describe by means of an internal variable constitutive theory and the analysis is restricted to elastoviscoplastic solids. The resulting system of non linear partial differential equations is solved by using an operator splitting technique, along with classical numerical procedures such as the Glimm s method. Numerical examples which illustrate the damage and temperature evolution induced by the plastic deformation process due to impact and cyclic loadings are presented and analyzed. A suitable comparative analysis between simulations with and without the thermomechanical couplings shows the situations under which these terms are relevant.
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BARBOSA, JOSÉ MARIA ANDRADE. "ANALYSIS OF THE INFLUENCE OF THERMOMECHANICAL COUPLING IN WAVE PROPAGATION IN ELASTIC-VISCOPLÁSTICAS BARS WITH DAMAGE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1993. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=33261@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>Este trabalho apresenta uma técnica numérica. baseada no Método de Decomposição do Operador (Operator Splitting Method) e algorítimos sequenciais associados (product formula algorithm) para simular o fenômeno de propagação de ondas em barras elasto-viscoplásticas. Este método tem boas propriedades de estabilidade e preciaão mesmo quando um esquema explícito de baixa ordem é utilizado na integração temporal. Esta técnica numérica é usada para simular carregamentos cíclicos de alta frequência em barras de aço austenítico a altas temperaturas.<br>The present work presents a numerical technique ( based on the Operator Split Method associated with product formula algorithm ) for simulating the wave propagation phenomenon in bars with any kind of elastic-viecoplastic oonstitutive equations. This method has very good properties of stability and precision even if explicit time evolution schemes are used. This numerical technique is used to simulate high frequency cyclic loadings in austenitic steel bars at high temperatures.
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Manktelow, Kevin Lee. "Dispersion analysis of nonlinear periodic structures." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51936.
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The present research is concerned with developing analysis methods for analyzing and exploring finite-amplitude elastic wave propagation through periodic media. Periodic arrangements of materials with high acoustic impedance contrasts can be employed to control wave propagation. These systems are often termed phononic crystals or metamaterials, depending on the specific design and purpose. Design of these systems usually relies on computation and analysis of dispersion band structures which contain information about wave propagation speed and direction. The location and influence of complete (and partial) band gaps is a particularly interesting characteristic. Wave propagation is prohibited for frequencies that correspond to band gaps; thus, periodic systems behave as filters, wave guides, and lenses at certain frequencies. Controlling these behaviors has typically been limited to the manufacturing stage or the application of external stimuli to distort material configurations. The inclusion of nonlinear elements in periodic unit cells offers an option for passive tuning of the dispersion band structure through amplitude-dependence. Hence, dispersion analysis methods which may be utilized in the design of nonlinear phononic crystals and metamaterials are required. The approach taken herein utilizes Bloch wave-based perturbation analysis methods for obtaining closed-form expressions for dispersion amplitude-dependence. The influence of material and geometric nonlinearities on the dispersion relationship is investigated. It is shown that dispersion shifts result from both self-action (monochromatic excitation) and wave-interaction (multi-frequency excitation), the latter enabling dynamic anisotropy in periodic media. A particularly novel aspect of this work is the ease with which band structures of discretized systems may be analyzed. This connection enables topology optimization of unit cells with nonlinear elements. Several important periodic systems are considered including monoatomic lattices, multilayer materials, and plane stress matrix-inclusion configurations. The analysis methods are further developed into a procedure which can be implemented numerically with existing finite-element analysis software for analyzing geometrically-complex materials.
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Pereira, Flavio Nunes. "Propagação de ondas e detecção de danos com modelos de barra de alta ordem pelo metodo do elemento espectral." [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265411.
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Orientador: Jose Maria Campos dos Santos<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica<br>Made available in DSpace on 2018-08-12T16:32:14Z (GMT). No. of bitstreams: 1
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Previous issue date: 2009<br>Resumo: Este trabalho investiga o problema de propagação de ondas em estruturas do tipo barra com modelos de alta ordem. O enforque principal do trabalho concentra-se na implementação de modelos numéricos que representem o fenômeno da propagação de ondas em barras saudáveis e danificadas por uma trinca. Para a investigação do problema utilizou-se o Método do Elemento Espectral, o qual consiste em uma solução analítica das equações diferenciais da onda no domínio da freqüência utilizando-se técnicas matriciais similares ao Método dos Elementos Finitos. Quatro modelos de barra, com diferentes modos de propagação foram implementados computacionalmente em linguagem Matlab®: o modelo elementar; modelo de Love ou do primeiro modo; o modelo de Mindlin-Herrmann ou de dois modos; e o modelo de Mindlin-McNiven ou dos três modos. Para cada modelo de barra foram implementados os elementos espectrais: saudável finito, saudável semi-finito e trincado. Para avaliar o comportamento da onda durante sua propagação nas estruturas analisadas, diferentes exemplos numéricos foram feitos e validados através de comparações com resultados similares encontrados na literatura. As estruturas são excitadas por forças impulsivas construídas por uma onda senoidal modulada com uma janela triangular. Os resultados confirmam que os modelos de elemento espectral representam muito bem o fenômeno da propagação de onda em uma estrutura e também podem ser usados como uma ferramenta eficiente para a localização de trincas.<br>Abstract: This work investigates the wave propagation problem in high order rod type structures. The main approach is the implementation of numerical models that represent the phenomenon of wave propagation in healthy and cracked rods. The investigation uses the Spectral Element Method, which consists of an analytical solution of wave deferential equations in the frequency domain using matrix techniques similar to the Finite Element Method. Four rod models with diferent propaga- tion modes were implemented computationally in Matlab® language: the elementary model; Love's model or the first model, Mindlin-Herrmann's model or the two model, and Mindlin- McNiven's model or the three-model. For each type of rod spectral elements were implemented: finite he-althy, throw-o® healthy and cracked. To evaluate the wave propagation behavior in the analyzed structures, diferent numerical examples were made and validated through comparisons with si-milar results from the literature. The structures are excited by impulsive forces built by a sine wave modulated with a triangular window. The results confirm that the Spectral Element Method represent the phenomenon of the wave propagation very well in a structure and they can also be used as an efficient tool for the location of crack.<br>Mestrado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Mestre em Engenharia Mecânica
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Anyintuo, Thomas Becket. "Seepage-Coupled Finite Element Analysis of Stress Driven Rock Slope Failures for BothNatural and Induced Failures." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7731.
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Rock slope failures leading to rock falls and rock slides are caused by a multitude of factors, including seismic activity, weathering, frost wedging, groundwater and thermal stressing. Although these causes are generally attributed as separate causes, some of them will often act together to cause rock slope failures. In this work, two of the above factors, seepage of water through cracks and crack propagation due to the after effects of blasting are considered. Their combined impact on the development of rock falls and rock slides is modeled on ANSYS workbench using the Bingham Canyon mine slope failure of 2013 as a case study. Crack path modeling and slope stability analysis are used to show how a combination of crack propagation and seepage of water can lead to weakening of rock slopes and ultimate failure. Based on the work presented here, a simple approach for modeling the development of rock falls and rock slides due to crack propagation and seepage forces is proposed. It is shown how the information from remote sensing images can be used to develop crack propagation paths. The complete scope of this method involves demonstrating the combination of basic remote sensing techniques combined with numerical modeling on ANSYS workbench.
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Tran, Quang Huy. "Résolution et étude numériques de quelques problèmes de propagation d'ondes acoustiques en géophysique." Paris, ENMP, 1994. http://www.theses.fr/1994ENMP0494.
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Cette these est composee de quatre travaux differents qui se rapportent tous a un meme sujet: la simulation numerique de la propagation d'onde en geophysique. 1. Propagation des ondes acoustiques en milieu aleatoire: etudes numeriques en 1-d et 3-d. Il s'agit d'etablir experimentalement les proprietes de cette propagation, sachant que de nombreux travaux theoriques, bases sur l'hypothese de linearisation, existent deja. 2. Optimisation sous contrainte en tomographie de reflexion: la methode du lagrangien augmente. On relate ici la recherche d'une methode d'optimisation efficace pour resoudre un probleme inverse concret mais difficile. 3. Decomposition de domaines appliquee a l'equation des ondes acoustiques. On presente une nouvelle methode de simulation qui permet d'adapter le pas du maillage aux caracteristiques de chaque sous-domaine. Une analyse de convergence est fournie. 4. Analyse de dispersion et du cout des schemas aux differences finies en 3-d. A une precision imposee sur l'erreur de groupe relative et une taille donnee du modele geologique, on compare les schemas 2-4 et 2-8 du point de vue du nombre d'operations flottantes necessaires
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Zhou, Changwei. "Approche couplée propagative et modale pour l'analyse multi-échelle des structures périodiques." Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0040/document.
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La dynamique d’une structure peut être vue aussi bien en termes de modes (ondes stationnaires) qu’en termes d’ondes élastiques libres. Les approches modales sont largement utilisées en mécanique et de nombreuses techniques de réduction de modèles (Model Order Reduction - MOR) ont été développées dans ce cadre. Quant à la dynamique des structures périodiques, les approches propagatives sont majoritairement utilisées, où la périodicité est exploitée en utilisant la théorie de Bloch. Pour les structures périodiques complexes, plusieurs techniques MOR sur la base d’onde ont été proposées dans la littérature. Dans ce travail, une approche couplée propagative et modale a été développée pour étudier la propagation des ondes dans les structures périodiques. Cette approche commence par la description modale d’une cellule unitaire (échelle mésoscopique) en utilisant la synthèse modale (Component Mode Synthesis - CMS). Par la suite, la méthode propagative - Wave Finite Element Method (WFEM) est appliquée sur la structure (échelle macroscopique). Cette méthode est nommée “CWFEM” pour CondensedWave Finite Element Method. Elle combine les avantages de la CMS et WFEM. La CMS permet d’analyser le comportement local d’en extraire une base réduite. La WFEM exploite la périodicité de la structure d’en extraire les paramètres de propagation. Ainsi, l’analyse de la propagation des ondes dans la structure à l’échelle macroscopique peut être réalisée en prenant en compte l’échelle mésoscopique. L’efficacité de la CWFEM est illustrée par de nombreuse applications aux structures périodiques monodimensionnelle (1D) et bidimensionnelle (2D). Le critère de réduction optimale assurant la convergence est discuté. Les caractéristiques de propagation dans les structures périodiques sont identifiées: bande passante, bande interdite, la directivité marquée (wave beaming effects), courbe de dispersion, band structure, surface des lenteurs... Ces propriétés peuvent répondre au besoin de conception des barrières vibroacoustiques, pièges à ondes. La CWFEM est ensuite appliquée pour étudier la propagation des ondes dans des plaques perforées et plaques raidies. Une méthode d’homogénéisation pour déterminer le modèle équivalent de la plaque perforée est proposée. Les comportements à haute fréquence tels que la directivité marquée sont également prédits par CWFEM. Trois modèles de plaques avec perforations différentes sont étudiées dans ce travail. Une validation expérimentale est effectuée sur deux plaques. Pour la plaque raidie, l’influence des modes internes sur la propagation globale est discutée. La densité modale est estimée, en moyenne et haute fréquences, pour une plaque raidie finie, où une bonne corrélation est obtenue en comparant les résultats à l’issue des analyses modales<br>Structural dynamics can be described in terms of structural modes as well as elastic wave motions. The mode-based methods are widely applied in mechanical engineering and numerous model order reduction (MOR) techniques have been developed. When it comes to the study of periodic structures, wave description is mostly adopted where periodicity is fully exploited based on the Bloch theory. For complex periodic structures, several MOR techniques conducted on wave basis have been proposed in the literature. In this work, a wave and modal coupled approach is developed to study the wave propagation in periodic structures. The approach begins with the modal description of a unit cell (mesoscopic scale) using Component Mode Synthesis (CMS). Subsequently, the wave-based method -Wave Finite Element Method (WFEM) is applied to the structure (macroscopic scale). The method is referred as “CWFEM” for Condensed Wave Finite Element Method. It combines the advantages of CMS and WFEM. CMS enables to analyse the local behaviour of the unit cell using a reduced modal basis. On the other hand, WFEM exploits fully the periodic propriety of the structure and extracts directly the propagation parameters. Thus the analysis of the wave propagation in the macroscopic scale waveguides can be carried out considering the mesoscopic scale behaviour. The effectiveness of CWFEM is illustrated via several one-dimensional (1D) periodic structures and two-dimensional (2D) periodic structures. The criterion of the optimal reduction to ensure the convergence is discussed. Typical wave propagation characteristics in periodic structures are identified, such as pass bands, stop bands, wave beaming effects, dispersion relation, band structure and slowness surfaces...Their proprieties can be applied as vibroacoustics barriers, wave filters. CWFEM is subsequently applied to study wave propagation characteristics in perforated plates and stiffened plate. A homogenization method to find the equivalent model of perforated plate is proposed. The high frequency behaviours such as wave beaming effect are also predicted by CWFEM. Three plate models with different perforations are studied. Experimental validation is conducted on two plates. For the stiffened plate, the influence of internal modes on propagation is discussed. The modal density in the mid- and high- frequency range is estimated for a finite stiffened plate, where good correlation is obtained compared to the mode count from modal analysis
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Pipkins, Daniel Scott. "Non-linear analysis of (i) wave propagation using transform methods and (ii) plates and shells using integral equations." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/20052.
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Eisenträger, Sascha [Verfasser], and Ulrich [Akademischer Betreuer] Gabbert. "Higher order finite elements and the fictitious domain concept for wave propagation analysis / Sascha Duczek. Betreuer: Ulrich Gabbert." Magdeburg : Universitätsbibliothek, 2014. http://d-nb.info/1063503302/34.
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Kessler, Ellis Carl. "A Physically Informed Data-Driven Approach to Analyze Human Induced Vibration in Civil Structures." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104020.
Full textAbstract:
With the rise of the Internet of Things (IoT) and smart buildings, new algorithms are being developed to understand how occupants are interacting with buildings via structural vibration measurements. These vibration-based occupant inference algorithms (VBOI) have been developed to localize footsteps within a building, to classify occupants, and to monitor occupant health. This dissertation will present a three-stage journey proposing a path forward for VBOI research based on physically informed data-driven models of structural dynamical systems.
The first part of this dissertation presents a method for extracting temporal gait parameters via underfloor accelerometers. The time between an occupant's consecutive steps can be measured with only structural vibration measurements with a similar accuracy to current gait analysis tools such as force plates and in-shoe pressure sensors. The benefit of this, and other VBOI gait analysis algorithms, is in their ease of use. Gait analysis is currently limited to a clinical setting with specialized measurement systems, however VBOI gait analysis provides the ability to bring gait analysis to any building.
VBOI algorithms often make some simplifying assumptions about the dynamics of the building in which they operate. Through a calibration procedure, many VBOI algorithms can learn some system parameters. However, as demonstrated in the second part of this dissertation, some commonly made assumptions oversimplify phenomena present in civil structures such as: attenuation, reflections, and dispersion. A series of experimental and theoretical investigations show that three common assumptions made in VBOI algorithms are unable to account for at least one of these phenomena, leading to algorithms which are more accurate under certain conditions.
The final part of this dissertation introduces a physically informed data-driven modelling technique which could be used in VBOI to create a more complete model of a building. Continuous residue interpolation (CRI) takes FRF measurements at a discrete number of testing locations, and creates a predictive model with continuous spatial resolution. The fitted CRI model can be used to simulate the response at any location to an input at any other location. An example of using CRI for VBOI localization is shown.<br>Doctor of Philosophy<br>Vibration-based occupant inference (VBOI) algorithms are an emerging area of research in smart buildings instrumented with vibration sensors. These algorithms use vibration measurements of the building's structure to learn something about the occupants inside the building. For example the vibration of a floor in response to a person's footstep could be used to estimate where that person is without the need for any line-of-sight sensors like cameras or motion sensors. The storyline of this dissertation will make three stops:
The first is the demonstration of a VBOI algorithm for monitoring occupant health.
The second is an investigation of some assumptions commonly made while developing VBOI algorithms, seeking to shed light on when they lead to accurate results and when they should be used with caution.
The third, and final, is the development of a data-driven modelling method which uses knowledge about how systems vibrate to build as detailed a model of the system as possible.
Current VBOI algorithms have demonstrated the ability to accurately infer a range of information about occupants through vibration measurements. This is shown with a varied literature of localization algorithms, as well as a growing number of algorithms for performing gait analysis. Gait analysis is the study of how people walk, and its correlation to their health. The vibration-based gait analysis procedure in this work demonstrates extracting distributions of temporal gait parameters, like the time between steps.
However, many current VBOI algorithms make significant simplifying assumptions about the dynamics of civil structures. Experimental and theoretical investigations of some of these assumptions show that while all assumptions are accurate in certain situations, the dynamics of civil structures are too complex to be completely captured by these simplified models.
The proposed path forward for VBOI algorithms is to employ more sophisticated data-drive modelling techniques. Data-driven models use measurements from the system to build a model of how the system would respond to new inputs. The final part of this dissertation is the development of a novel data-driven modelling technique that could be useful for VBOI. The new method, continuous residue interpolation (CRI) uses knowledge of how systems vibrate to build a model of a vibrating system, not only at the locations which were measured, but over the whole system. This allows a relatively small amount of testing to be used to create a model of the entire system, which can in turn be used for VBOI algorithms.
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Zhou, Youchuan. "Bandgap Characteristics And Dynamic Behaviours Of Mechanical Metamaterials." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29504.
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This study’s aim is to systemically demonstrate the bandgap characteristic and dynamic performance of mechanical metamaterials and attempt to evaluate the relationship between them, based on theoretical models, finite element analyses and experimental investigations. This study starts with the design and comprehensive investigation of a 1D metamaterial chain with a dual resonance system. The modified mass-spring analogy and the effective property theory successfully predict the bandgap characteristics and the wave attenuation capacity of the proposed metamaterial. Subsequently, by hybridizing the negative Poisson’s ratio property and the local resonant mechanism, a novel 2D mechanical metamaterial is proposed by embedding metal inclusions as resonators into a conventional reentrant frame, forming a hybrid metamaterial (HMM). By controlling the ratio of the bandgap width to the frequency band width of impact excitations, i.e., the bandgap overlap ratio, an attempt is made to quantify the relationship between the bandgap characteristics and the dynamic performance of HMM under impact load. With the aim of improving the impact mitigation performance and simultaneously reducing the total weight of the proposed HMM, two configurations, i.e., graded-type and dual-type metamaterials, are designed and developed to superpose the bandgap of each layer and induce the coupling effect in local resonant mechanisms, respectively. Additionally, the Continuous Wavelet Transform method is utilised to evaluate the dynamic performance of different local unit cells by determining time-frequency-locations details. Finally, the proposed HMM is extended to 3D structures, following the abovementioned design principles. With the help of vibration mode analyses near the edge frequency of bandgaps, a study on the design flexibility of 3D-HMM reveals the sensitivity of the key geometrical parameters on the material properties and the bandgap characteristics.
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Farzbod, Farhad. "Analysis of Bloch formalism in undamped and damped periodic structures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/42885.
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Bloch analysis was originally developed by Felix Bloch to solve Schrödinger's equation for the electron wave function in a periodic potential field, such as that found in a pristine crystalline solid. His method has since been adapted to study elastic wave propagation in periodic structures. The absence of a rigorous mathematical analysis of the approach, as applied to periodic structures, has resulted in mistreatment of internal forces and misapplication to nonlinear media. In this thesis, we detail a mathematical basis for Bloch analysis and thereby shed important light on the proper application of the technique. We show conclusively that translational invariance is not a proper justification for invoking the existence of a "propagation constant," and that in nonlinear media this results in a flawed analysis. Next, we propose a general framework for applying Bloch analysis in damped systems and investigate the effect of damping on dispersion curves. In the context of Schrödinger's equation, damping is absent and energy is conserved. In the damped setting, application of Bloch analysis is not straight-forward and requires additional considerations in order to obtain valid results. Results are presented in which the approach is applied to example structures. These results reveal that damping may introduce wavenumber band gaps and bending of dispersion curves such that two or more temporal frequencies exist for each dispersion curve and wavenumber. We close the thesis by deriving conditions which predict the number of wavevectors at each frequency in a dispersion relation. This has important implications for the number of nearest neighbor interactions that must be included in a model in order to obtain dispersion predictions which match experiment.
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Gonella, Stefano. "Homogenization and Bridging Multi-scale Methods for the Dynamic Analysis of Periodic Solids." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16144.
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This work investigates the application of homogenization
techniques to the dynamic analysis of periodic solids, with
emphasis on lattice structures. The presented analysis is
conducted both through a Fourier-based technique and through an
alternative approach involving Taylor series expansions directly
performed in the spatial domain in conjunction with a finite
element formulation of the lattice unit cell. The challenge of
increasing the accuracy and the range of applicability of the
existing homogenization methods is addressed with various
techniques. Among them, a multi-cell homogenization is introduced
to extend the region of good approximation of the methods to
include the short wavelength limit. The continuous partial
differential equations resulting from the homogenization process
are also used to estimate equivalent mechanical properties of
lattices with various internal configurations. In particular, a
detailed investigation is conducted on the in-plane behavior of
hexagonal and re-entrant honeycombs, for which both static
properties and wave propagation characteristics are retrieved by
applying the proposed techniques. The analysis of wave propagation
in homogenized media is furthermore investigated by means of the
bridging scales method to address the problem of modelling
travelling waves in homogenized media with localized
discontinuities. This multi-scale approach reduces the
computational cost associated with a detailed finite element
analysis conducted over the entire domain and yields considerable
savings in CPU time. The combined use of homogenization and
bridging method is suggested as a powerful tool for fast and
accurate wave simulation and its potentials for NDE applications
are discussed.