Thesis (Ph. D.)--University of Wisconsin--Madison, 1949. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains x, 138 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 125-129).

Thesis (M.S.)--Ohio University, August, 1995. / Title from PDF t.p.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed May 23, 2007). PDF text: v, 326 p. : ill. (some col.) ; 3.85Mb UMI publication number: AAT 3237557. Includes bibliographical references. Also available in microfilm and microfiche formats.

Energy dissipation in systems with linear viscoelastic damping is examined. It is shown that in such viscoelastically damped systems the use of additional dissipation mechanisms (such as boundary velocity feedback or thermal coupling) may not improve the rate of energy decay. The situation where the viscoelastic stress relaxation modulus decreases to its (positive) equilibrium modulus at a subexponential rate, e.g., like (1 + t)^-x + E, where α > 0, E > 0 is examined. In this case, the nonoscillatory modes (the so-called creep modes) dominate the energy decay rate. The results are in two parts. In the first part, a linear viscoelastic wave equation with infinite memory is examined. It is shown that under appropriate conditions on the kernel and initial history, the total energy is integrable against a particular weight if the kinetic energy component of the total energy is integrable against the same weight. The proof uses energy methods in an induction argument. Precise energy decay rates have recently been obtained using boundary velocity feedback. It is shown that the same decay rates hold for history value problems with conservative boundary conditions provided that an <i>a priori</i> knowledge of the decay rate of the kinetic energy term is assumed. In the second part, a simple linear thermo-viscoelastic system, namely, a viscoelastic wave equation coupled to a heat equation, is examined. Using Laplace transform methods, an integral representation formula for <i>W(x,s</i>), the transform of the displacement <i>w(x, t)</i>, is obtained. After analyzing the location of the zeros of the appropriate characteristic equation, an asymptotic expansion for the displacement <i>w(O,t)</i> is obtained which is valid for large <i>t</i> and the specific kernel <i>g(t) = g</i>(–) + δtη-1 [over]Î (η), 0 < η < 1. With this expansion it is shown that the coupled system tends to its equilibrium at a slower rate than that of the uncoupled system. / Ph. D.

Orientador: José Maria Campos dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T14:11:06Z (GMT). No. of bitstreams: 1 Nobrega_EdilsonDantas_M.pdf: 12912450 bytes, checksum: 790ec696a10ed45d5c22747b666dea61 (MD5) Previous issue date: 2015 / Resumo: A fim de superar as limitações atuais na análise dinâmica de estruturas em médias e altas frequências e tirando proveito da natureza periódica de muitas destas estruturas, nos últimos anos, foram desenvolvidos métodos de guia de ondas. São modelos obtidos a partir de fatias das guia de ondas e modeladas pelo Método dos Elementos Finitos (MEF) e pelo Método do Elemento Espectral (SEM), também conhecidos como Método de Propagação de Ondas por Elementos Finitos (Wave Finite Element Method - WFEM) e Método de Propagação de Ondas por Elementos Espectrais (Wave Spectral Element Method - WSEM), respectivamente. Exemplos de guia de ondas podem ser encontrados em diferentes tipos de estruturas tais como, os trilhos de trem, tubulações e até mesmo em estruturas complexas tipo a fuselagem de um avião e outras. Este trabalho apresenta uma extensão destes métodos de guias de ondas para a modelagem com elementos de barra de alta ordem. Os métodos foram implementados computacionalmente em códigos Matlab e os resultados são comparados com os do Método do Elemento Espectral (Spectral Element Method - SEM), do Método dos Elementos Finitos e com os do modelo analítico da Placa de Rayleigh-Lamb. Três elementos de barra de alta ordem são formulados: o modelo de Love (ou de Um modo), o modelo de Mindlin-Herrmann (ou de Dois modos) e o modelo de Doyle (ou de Três modos). O método é avaliado através de exemplos simulados computacionalmente e os resultados são analisados e comparados com aqueles da literatura / Abstract: In order to overcome the current limitations in the dynamic analysis of structures at middle and high frequencies and taking advantage of the periodic nature of many of these structures, in recent years, waveguide methods were developed. Models are obtained from slices of patterned waveguides, were developed by Finite Element Method (FEM) and Spectral Element Method, also known as Wave Finite Element Method - WFEM and Wave Spectral Element Method - WSEM. Examples of waveguides can be found in different types of structures such as the railroad tracks, pipelines and even complex structures like the fuselage of an airplane and others. This work presents an extension of these waveguides methods to model high order rod elements. The methods were implemented in Matlab codes and the results are compared with Spectral Element Method - SEM, Finite Element Method and the analytical Rayleigh-Lamb plate model. Three high order bar elements are formulated: the Love's model (or one mode), the Mindlin-Herrmann's model (or two modes) and the Doyle's model (or three modes). The method is evaluated through computationally simulated examples and the results are analyzed and compared with those of the literature / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica