Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 89-97). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 77-82). Also available on the World Wide Web.

In this paper consider the problem of controlling a thermoviscoelastic system. We present a semigroup setting for this system, and prove the well-posedness by applying a general theorem which is given in this paper. We also study the stability of the system. We give a finite element/averaging scheme to approximate the linear quadratic regulator problem governed by the system. We prove that yields faster convergence. We give a proof of convergence of the simulation problem for singular kernels and of the control problem for L2 kernels. We carry on the numerical computation to investigate the effect of heat transfer on damping and the closed-loop system. / Ph. D.

Viscoelastic polymer materials are being actively considered as a novel material for semiconductor packaging applications as a result of their ability to develop strong adhesive bonds at lower temperatures. Viscoelastic thermoset materials are impacted by the stresses generated during the curing process, which is also accompanied by a dissipation of thermal energy. There is a need to develop a generic modeling formulation that is applicable to any material of interest in order to enable the study of different bonding materials and develop optimized curing cycles. This study reports a numerical formulation to evaluate the stress generated and energy dissipated during the cure of viscoelastic polymers. A generalized method to define the transient variation of degree of cure was developed using a 4th order Runge Kutta approximation. The mathematical formulation was implemented using a novel evaluation methodology that helped reduce the computational power requirement. The commercially-available 3501-6 resin was simulated as a characteristic material in this study. The numerical model was validated against analytically derived solutions for both a single Maxwell model, and a Generalized Maxwell Model (GMM) for cases of constant-strain inputs, and subsequently for sinusoidal strain inputs, wherein, material properties were considered to be constant or varying linearly with degree of cure. A good agreement was obtained between the present model and analytical solutions.

O espalhamento de ondas de som tem por objetivo compreender a natureza de propagacao de ondas sonoras incidentes e espalhadas, para diferentes estruturas e geometrias dos centros espalha- dores que formam um meio desordenado. Na literatura, em geral, obtemos informacoes relativas ao espalhamento acustico em regioes distantes dos centros espalhadores (aproximacao de campo distante), para algumas formas de onda incidentes e de particulas espalhadoras. Buscando compre- ender o comportamento ondulatorio em regioes proximas ao centro espalhador e em seu interior, nosso estudo fornece uma descricao analitica dos campos de radiacao acustica nessas regioes. Ini- cialmente, considera-se o problema do espalhamento de uma onda plana acustica plana (viajando num fluido ideal newtoniano) por uma particula esferica fluida, com caracteristicas distintas das do fluido inicial. Ainda, calculamos a energia interna armazenada nesse centro espalhador como funcao do volume da esfera espalhadora, bem como do comprimento da onda em seu interior, de sua amplitude e da densidade do centro espalhador. Posteriormente, os materiais espalhadores sao considerados de natureza viscoelastica (que apresentam comportamentos viscosos e elasticos sob a acao de forcas externas), por serem viaveis na modelagem de celulas biologicas e polimeros, em geral. Para isso, tratamos formalmente da fisica de materiais elasticos, como deformacoes e tensoes, a fim de respaldar o tratamento do modelo viscoelastico de Kelvin-Voigt fracionario usado em nosso estudo. Obtivemos formulas fechadas para os coeficientes de espalhamento (bem como os coeficientes das ondas internas ao centro espalhador) desse problema em questao, a partir da solucao de um sistema linear de equacoes. Os resultados permitem a construcao de uma teoria de base para um estudo generalizado do espalhamento de ondas acusticas por materiais viscoelasticos, perspectiva a ser conduzida num futuro proximo. / The sound wave scattering aims to understand the propagation nature of scattered and incident sound waves, for different structures and geometries of the scattering centers that form a disordered environment. In the literature, in general, we obtain information regarding the acoustic scattering in regions distant from the scattering centers (far-field approximation), for some incident wave- forms and scattering particles. In order to understand the undulatory behavior in regions close to and within the scattering center, our study provides an analytical description of the acoustic radiation fields in these regions. First, the problem considered is the scattering of an acoustic plane wave (previously traveling through an ideal newtonian fluid) by a spherical fluid particle, with distinct acoustic characteristics from the initial fluid. Still, it is determined the internal acoustic energy stored in this scattering center, as a function of the scattering spheres volume, as well as the wavelength in its interior, its amplitude and the density of the scattering center. Later, the scattering materials are considered to be viscoelastic (which exhibit viscous and elas- tic behavior when subjected to external forces), as they are feasible in the modeling of biological cells and polymers in general. For such, we deal formally with elastic materials physics, such as deformations and tensions, in order to deal with the Kelvin-Voigt viscoelastic model used in this problem. Were determined closed formulas for the scattering coefficients for this problem (as well as the internal wave coefficients), from the solution of a linear system of equations. The results allow the construction of a fundamental theory for a generalized study of sound wave scattering by viscoelastic materials, which is a goal to be achieved in a near future.

Haptic simulation of medical procedures is an active area of research in engineering and medicine. Analogous to flight simulators for pilots, surgery simulators can allow medical students and doctors to practice procedures in a risk free and well monitored virtual environment. The quality of interaction that a surgery simulator can generate is dependent upon many components. In this thesis, careful attention is paid to the haptic display of viscous effects. / Viscous terms, defined here as terms that are dependent upon velocity, are typically computed 'using a discrete time backwards difference estimation of the velocity. It is well known that differentation has the tendency to amplify high frequency noise, and as a result, the backwards difference estimation generates considerable errors when applied to the quantized position readings from a digital encoder. Prior to this work, the only feasible method to improve velocity estimation was to use a variety of observation or filtering techniques, all of which inevitably add phase delay. In this thesis, the backwards difference operation was analyzed in detail. It was found that feedback viscosity simulation is very non-robust to noise, and oscillations exist in the presence of quantization noise regardless of the physical parameters of the plant. / A typical haptic interface for surgery simulation consists of a mechanical linkage driven by electric motors. These linkages are controlled with a computer using a discrete-time force update law that generates a prescribed force given the user's position in the medical virtual environment. It is clear from the literature that a haptic interface must have some level of physical dissipation to enable a passive rendering due to the inherent instability associated with time delayed systems. However, dissipation in typical haptic interfaces is a byproduct of their design, and is neither controllable nor easily identifiable. A prototype haptic interface is presented in this thesis that uses eddy current brakes to add high bandwidth programmable dissipation to an existing motor linkage. The new hardware has been optimized experimentally to maximize damping and minimize inertia given conventional machining and available material constraints. / A new paradigm in the control of haptic interfaces is time-domain passivity control. Passive systems are desirable in haptics because a passive system is globally stable, passivity theory applies to linear and nonlinear systems alike, and a user cannot extract energy from a passive system. Passivity controllers monitor the energy flow in the device and add virtual damping to remove any energy that violates the passivity constraint. Unfortunately, the amount of virtual damping available to a given device is limited by the physical dissipation that it exhibits. If the device is directly driven and light, such as the pantograph, the available virtual damping is insufficient to maintain the passivity constraint. The eddy current brakes allow programmable physical damping to be used in place of virtual damping which has been shown with experiments to improve the stable impedance range of a haptic interface. / It is clear from the literature that most tissues in a human body exhibit viscoelastic behavior. Simulation of viscoelastic objects requires that the velocity of interaction be known. Because typical haptic interfaces use digital encoders to sample position, the estimated velocity signal is noisy, delayed or both. Eddy current brakes are viscous actuators by nature, as they generate a resistive force proportional to the velocity. To take advantage of this fact, viscoelastic decomposition algorithms were developed that can output viscous components to the eddy current brakes and elastic components to the motors. This technique reduces or eliminates the use of a velocity estimation signal in the feedback loop which improves passivity, reduces motor saturation effects, and allows for a wider stable range of mechanical impedances than conventional haptic interfaces can achieve.

Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-07-19Bitstream added on 2014-06-13T20:18:21Z : No. of bitstreams: 1 santade_f_me_bauru.pdf: 1882891 bytes, checksum: 8a15967197afaf47ad9929eeb4946264 (MD5) / Neste trabalho foi proposto o estudo do amortecimento estrutural em vigas engastadas com adição de materiais viscoelásticos. As vigas foram montadas na condição engastada-livre e sujeitas de força na extremidade livre. Duas análises foram feitas. O primeiro modelo foi desenvolvido utilizando a Matriz de Impedância de Elemento Espectral (MEE) e o outro modelo foi desenvolvido utilizando Método dos Elementos finitos (MEF). Para validar os modelos numéricos foram realizados ensaios experimentais utilizando um acelerômetro e um martelo de impacto para obter a função de resposta em frequencia para as diferentes configurações de vigas idealizadas. Através dos resultados obtidos pode-se observar e comprovar o comportamento com frequencia de resposta do sistema e detectou-se redução de amplitude devido ao fator incremental de amortecimento viscoelástico proporcionado pelas camadas de fita (materiais viscoelásticos), comprovando assim, a importância da utilização de um material viscoelástico como atenuador de amplitudes no efeito da flexão do sistema. Os resultados experimentais foram comparados aos resultados dos modelos analíticos e numéricos de modo a se obter a validação experimental / This work proposes the study of structural damping in beams with added viscoelastic materials. The beams are mounted in a clamped-free condition and subject to force input at the free end. Two types analisis were made. The first model was developed using the Impedance Matrix of Spectral Element. The other model was developed using Finite Element Method (FEM). To validate the numerical models, experimental tests were performed using one accelerometer and a impact hammer to obtain frequency responce function of the diferente beams configurations. From the results we can observe and verify the variation in frequency response of the system and was detected amplitude reduction factor due to the incremental viscoelastic damping provided by the layers of tape (viscoelastic materials), thereby proving the importance of using a viscoelastic attenuator as possible amplitudes effect of the bending system. The results were compared to the results of analytical and numerical models in order to obtain experimental validation

Orientador: Edson Antônio Capello Souza / Coorientador: Paulo José Paupitz Gonçalves / Banca: Laercio Javarez Junior / Banca: Bento Rodrigues de Pontes Junior / Resumo: Neste trabalho foi proposto o estudo do amortecimento estrutural em vigas engastadas com adição de materiais viscoelásticos. As vigas foram montadas na condição engastada-livre e sujeitas de força na extremidade livre. Duas análises foram feitas. O primeiro modelo foi desenvolvido utilizando a Matriz de Impedância de Elemento Espectral (MEE) e o outro modelo foi desenvolvido utilizando Método dos Elementos finitos (MEF). Para validar os modelos numéricos foram realizados ensaios experimentais utilizando um acelerômetro e um martelo de impacto para obter a função de resposta em frequencia para as diferentes configurações de vigas idealizadas. Através dos resultados obtidos pode-se observar e comprovar o comportamento com frequencia de resposta do sistema e detectou-se redução de amplitude devido ao fator incremental de amortecimento viscoelástico proporcionado pelas camadas de fita (materiais viscoelásticos), comprovando assim, a importância da utilização de um material viscoelástico como atenuador de amplitudes no efeito da flexão do sistema. Os resultados experimentais foram comparados aos resultados dos modelos analíticos e numéricos de modo a se obter a validação experimental / Abstract: This work proposes the study of structural damping in beams with added viscoelastic materials. The beams are mounted in a clamped-free condition and subject to force input at the free end. Two types analisis were made. The first model was developed using the Impedance Matrix of Spectral Element. The other model was developed using Finite Element Method (FEM). To validate the numerical models, experimental tests were performed using one accelerometer and a impact hammer to obtain frequency responce function of the diferente beams configurations. From the results we can observe and verify the variation in frequency response of the system and was detected amplitude reduction factor due to the incremental viscoelastic damping provided by the layers of tape (viscoelastic materials), thereby proving the importance of using a viscoelastic attenuator as possible amplitudes effect of the bending system. The results were compared to the results of analytical and numerical models in order to obtain experimental validation / Mestre

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