This thesis investigates the implementation of a passive isolator with a pressurized air cushion for spacecraft payloads in mission architectures implementing in-space assembly technologies. A pressurized air bed capable of briefly surviving the space environment for cargo delivery was prototyped and experimentally evaluated for launch vehicle vibration dynamics resulting in a 72%, 93%, and 88% reduction in experienced GRMS loads for the X-Axis, Y-Axis, and Z-Axis, respectively. A preliminary Total Mass Loss evaluation of the Low-Density Polyethylene Film utilized for the air bed resulted in a mass loss of 0.7%, indicating that commercial off-the-shelf films might require minimal modification for flight readiness. An analytical model of a planar rectangular payload experiencing free vibrations with a Winkler foundation is generated and compared to the experimental results, showing a potential way for characterizing and designing such a foundation to reduce experienced vibrations. These preliminary results show a potential path for a non-cost-prohibitive method for space payloads to reduce loads experienced during launch as inspired by the successful hosted payloads program aboard the International Space Station.

The thesis consists of general characteristics, list of notations, introduction, four main chapters, general conclusions, 56 pictures, 2 tables and list of references. The total scope of the dissertation is 106 pages.

Orientador: Douglas Domingues Bueno / Resumo: A redução de vibração estrutural tem sido um importante tópico para muitas aplicações de engenharia. Nos projetos tradicionais, diferentes técnicas de controle passivo envolvendo mate- riais visco-elásticos e absorvedores dinâmicos e, mais recentemente, metodologias de controle ativo incluindo atuadores e sensores têm sido empregado com sucesso. Diferentes pesquisas tem demostrado que redução de vibração pode ser obtida usando o conceito de periodicidade. As estruturas periódicas envolvem elementos idênticos ou partes conectadas repetidamente. O projeto de estruturas periódicas pode ser empregado para conseguir bandas de frequências em que não há propagação de ondas elásticas, denominadas de "stop bands", introduzindo um efeito similar ao de um filtro. Neste contexto, o presente trabalho apresenta uma abordagem alterna- tiva para o projeto de barras periódicas. Esta alternativa envolve a modelagem de uma barra periódica do tipo híbrida infinita na qual uma estrutura periódica finita é conectada entre duas barras semi-infinitas. Para isto, é utilizada uma metodologia que relaciona vetor de estados e amplitude de ondas. A principal proposta deste trabalho é desenvolver uma relação entre as amplitudes de ondas longitudinais transmitidas e incidentes em termos das propriedades físi- cas e geométricas de uma genérica estrutura periódica para simplificar o processo do projeto. Usando esta formulação mostra-se que uma barra periódica pode ser projetada para satisfazer os requisitos de um... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The reduction of structural vibration has been an important topic for many engineering applica- tions. In traditional projects different passive control techniques involving viscoelastic materials and dynamic absorbers and, more recently, active control methodologies including actuators and sensors have been successfully employed. Different researches have demonstrated that vibra- tion reduction can be obtained using the concept of periodicity. The periodic structures involve identical elements or parts connected repeatedly. The design of periodic structures can be em- ployed to get frequency band without elastic waves propagation, i.e., stop bands, introducing an effect similar to the filter. In this context, the present work introduces an alternative approach for designing periodic rods. This alternative involves the modeling of an infinite hybrid type periodic rod in which a finite periodic structure is connected between two semi-infinite rods. It is used a methodology that relates state vector and wave amplitudes. The main proposal of this work is to develop a relation between the transmitted and incident longitudinal waves amplitudes in terms of physical and geometrical properties of a generic candidate structure to simplify the process of designing. Based on this approach is shown that a periodic rod can be designed to satisfy requirements of a vibration suppression. A hypothetical problem is proposed and numerical and experimental results show the stop bands obtained to so... (Complete abstract click electronic access below) / Doutor

Submitted by RODRIGO BORGES SANTOS null (rbsantos10@hotmail.com) on 2018-03-21T18:00:25Z No. of bitstreams: 1 TeseDR_Rodrigo - FinalABNT_.pdf: 6767187 bytes, checksum: d2b448466fef19bb7263d3902afe9b0a (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-03-21T18:19:42Z (GMT) No. of bitstreams: 1 santos_rb_dr_ilha.pdf: 6767187 bytes, checksum: d2b448466fef19bb7263d3902afe9b0a (MD5) / Made available in DSpace on 2018-03-21T18:19:42Z (GMT). No. of bitstreams: 1 santos_rb_dr_ilha.pdf: 6767187 bytes, checksum: d2b448466fef19bb7263d3902afe9b0a (MD5) Previous issue date: 2018-03-06 / A redução de vibração estrutural tem sido um importante tópico para muitas aplicações de engenharia. Nos projetos tradicionais, diferentes técnicas de controle passivo envolvendo mate- riais visco-elásticos e absorvedores dinâmicos e, mais recentemente, metodologias de controle ativo incluindo atuadores e sensores têm sido empregado com sucesso. Diferentes pesquisas tem demostrado que redução de vibração pode ser obtida usando o conceito de periodicidade. As estruturas periódicas envolvem elementos idênticos ou partes conectadas repetidamente. O projeto de estruturas periódicas pode ser empregado para conseguir bandas de frequências em que não há propagação de ondas elásticas, denominadas de "stop bands", introduzindo um efeito similar ao de um filtro. Neste contexto, o presente trabalho apresenta uma abordagem alterna- tiva para o projeto de barras periódicas. Esta alternativa envolve a modelagem de uma barra periódica do tipo híbrida infinita na qual uma estrutura periódica finita é conectada entre duas barras semi-infinitas. Para isto, é utilizada uma metodologia que relaciona vetor de estados e amplitude de ondas. A principal proposta deste trabalho é desenvolver uma relação entre as amplitudes de ondas longitudinais transmitidas e incidentes em termos das propriedades físi- cas e geométricas de uma genérica estrutura periódica para simplificar o processo do projeto. Usando esta formulação mostra-se que uma barra periódica pode ser projetada para satisfazer os requisitos de uma supressão de vibração. Um problema hipotético é proposto e resultados numéricos e experimentais mostram os "stop bands" obtidos para resolver o problema. Isto mostra que esta abordagem é uma importante ferramenta para o projeto deste tipo de estruturas. / The reduction of structural vibration has been an important topic for many engineering applica- tions. In traditional projects different passive control techniques involving viscoelastic materials and dynamic absorbers and, more recently, active control methodologies including actuators and sensors have been successfully employed. Different researches have demonstrated that vibra- tion reduction can be obtained using the concept of periodicity. The periodic structures involve identical elements or parts connected repeatedly. The design of periodic structures can be em- ployed to get frequency band without elastic waves propagation, i.e., stop bands, introducing an effect similar to the filter. In this context, the present work introduces an alternative approach for designing periodic rods. This alternative involves the modeling of an infinite hybrid type periodic rod in which a finite periodic structure is connected between two semi-infinite rods. It is used a methodology that relates state vector and wave amplitudes. The main proposal of this work is to develop a relation between the transmitted and incident longitudinal waves amplitudes in terms of physical and geometrical properties of a generic candidate structure to simplify the process of designing. Based on this approach is shown that a periodic rod can be designed to satisfy requirements of a vibration suppression. A hypothetical problem is proposed and numerical and experimental results show the stop bands obtained to solve the problem. It shows that this approach is an important tool for designing this type of structures.

Orientador: Marcos Silveira / Resumo: O objetivo deste trabalho é explorar a atenuação da vibração de uma metaestrutura por meio da adição de absorvedores de forma periódica. Além disso é explorada a atenuação da vibração de uma metaestrutura quando um absorvedor com rigidez cúbica não linear é incluído sem aumentar a massa total. As metaestruturas, e especificamente as estruturas periódicas, apresentam características interessantes para atenuação da vibração que não são encontradas em estruturas clássicas. Estas características foram exploradas para aplicações automotivas e aeroespaciais, entre outras, pois estruturas com baixa massa são fundamentais para essas indústrias. Também é desejável manter baixos níveis de vibração em uma ampla faixa de frequência. Foi demonstrado que a adição de absorvedores de vibração em um arranjo periódico pode fornecer atenuação da vibração para entrada de choque sem aumentar a massa total de uma estrutura. Neste trabalho, a resposta dinâmica do sistema proposto é comparada a uma metaestrutura base sem absorvedores e uma metaestrutura com absorvedores lineares para entrada harmônica através da avaliação da norma H2 da resposta em frequência. Um procedimento de otimização é mostrado para encontrar a posição ideal e os coeficientes de rigidez do absorvedor não linear. A resposta dinâmica do sistema ideal é obtida numericamente e mostra que a adição de um absorvedor não linear pode melhorar a atenuação da vibração. / Abstract: The objective of this work is to explore the vibration attenuation of a metastructure by periodically adding absorbers, and the vibration attenuation of a metastructure is explored when a nonlinear cubic stiffness absorber is included without increasing the total mass. Metastructures, and specifically periodic structures, present interesting characteristics for vibration attenuation that are not found in classical structures. These characteristics have been explored for automotive and aerospace applications, among others, as structures with low mass are paramount for these industries, and keeping low vibration levels in wide frequency range is also desirable. It has been shown that the addition of vibration absorbers in a periodic arrangement can provide vibration attenuation for shock input without increasing the total mass of a structure. In this work, the dynamical response of the proposed system is compared to a base metastructure without absorbers and a metastructure with linear absorbers for harmonic input via the evaluation of the H2 norm of the frequency response. An optimisation procedure is shown to find the optimal position and stiffness coefficients of the nonlinear absorber. The dynamical response of the optimal system are obtained numerically, and shows that the addition of one nonlinear absorber can improve vibration attenuation. / Mestre

Employing the Finite Element Method (FEM), we numerically study three problems involving free and forced vibrations of linearly and nonlinearly elastic plates with a third order shear and normal deformable theory (TSNDT) and the three dimensional (3D) elasticity theory. We used the commercial software ABAQUS for analyzing 3D deformations, and an in-house developed and verified software for solving the plate theory equations. In the first problem, we consider trapezoidal load-time pulses with linearly increasing and affinely decreasing loads of total durations equal to integer multiples of the time period of the first bending mode of vibration of a plate. For arbitrary spatial distributions of loads applied to monolithic and laminated orthotropic plates, we show that plates' vibrations become miniscule after the load is removed. We call this phenomenon as vibration attenuation. It is independent of the dwell time during which the load is a constant. We hypothesize that plates exhibit this phenomenon because nearly all of plate's strain energy is due to deformations corresponding to the fundamental bending mode of vibration. Thus taking the 1st bending mode shape of the plate vibration as the basis function, we reduce the problem to that of solving a single second-order ordinary differential equation. We show that this reduced-order model gives excellent results for monolithic and composite plates subjected to different loads. Rectangular plates studied in the 2nd problem have points on either one or two normals to their midsurface constrained from translating in all three directions. We find that deformations corresponding to several modes of vibration are annulled in a region of the plate divided by a plane through the constraining points; this phenomenon is termed mode localization. New results include: (i) the localization of both in-plane and out-of-plane modes of vibration, (ii) increase in the mode localization intensity with an increase in the length/width ratio of a rectangular plate, (iii) change in the mode localization characteristics with the fiber orientation angle in unidirectional fiber- reinforced laminae, (iv) mode localization due to points on two normals constrained, and (iv) the exchange of energy during forced harmonic vibrations between two regions separated by the line of nearly stationary points that results in a beating-like phenomenon in a sub-region of the plate. This technique can help design a structure with vibrations limited to its small sub-region, and harvesting energy of vibrations of the sub-region. In the third problem, we study finite transient deformations of rectangular plates using the TSNDT. The mathematical model includes all geometric and material nonlinearities. We compare the results of linear and nonlinear TSNDT FEM with the corresponding 3D FEM results from ABAQUS and note that the TSNDT is capable of predicting reasonably accurate results of displacements and in-plane stresses. However, the errors in computing transverse stresses are larger and the use of a two point stress recovery scheme improves their accuracy. We delineate the effects of nonlinearities by comparing results from the linear and the nonlinear theories. We observe that the linear theory over-predicts the deformations of a plate as compared to those obtained with the inclusion of geometric and material nonlinearities. We hypothesize that this is an effect of stiffening of the material due to the nonlinearity, analogous to the strain hardening phenomenon in plasticity. Based on this observation, we propose that the consideration of nonlinearities is essential in modeling plates undergoing large deformations as linear model over-predicts the deformation resulting in conservative design criteria. We also notice that unlike linear elastic plate bending, the neutral surface of a nonlinearly elastic bending plate, defined as the plane unstretched after the deformation, does not coincide with the mid-surface of the plate. Due to this effect, use of nonlinear models may be of useful in design of sandwich structures where a soft core near the mid-surface will be subjected to large in-plane stresses. / Doctor of Philosophy / Plates and shells are defined as structures which have thickness much smaller as compared to their length and width. These structures are extensively used in many fields of engineering such as, designing ship hulls, airplane wings and fuselage, bodies of automobile, etc. Depending on the complexity of a plate/shell deformation problem, deriving analytical solutions is not always viable and one relies on computational methods to obtain numerical solutions of the problem. However, obtaining 3-dimensional (3D) numerical solutions of deforming plates/shells often require high computational effort. To avoid this, plate/shell theories are used for modeling these structures, which, based on certain assumptions, reduce the 3D problem into an equivalent 2-dimensional (2D) problem. However, quality of the solution obtained from such a theory depends on how suitable the assumptions are for the specific problem being studied. In this work, one such plate theory called as the Third Order Shear and Normal Deformable Theory (TSNDT) is used to model the mechanics of deforming rectangular plates under different boundary conditions (constraint conditions for the boundaries of the plate) and loading conditions (conditions of applied loads on the plate). We develop the TSNDT mathematical model of plate deformations and solve it using a computational technique called as the Finite Element Method (FEM) to analyze three different problems of mechanics of rectangular plates. These problems are briefly described below. vi In the first problem, we study vibrations of rectangular plates under time dependent (dynamic) loads. When a dynamic load acts on a plate, due to the effects of inertia, the plate continues to vibrate after the removal of the load. This is analogous to ringing of a bell long after the strike of the hammer on the bell. In this study we show that such vibrations of a rectangular plate can be varied by changing time dependencies of the applied load. We observe that under certain particular loading conditions, vibrations of the plate becomes miniscule after the load removal. We call this phenomenon as Vibration Attenuation and investigate this computationally in different problems of plate deformation using FEM solutions. In the second problem, we computationally investigate the effects of presence of internal fixed points (points within the volume of the plate restricted of motion) on the vibration characteristics of rectangular plate using TSNDT FEM solutions. We observe that when one or more points at locations inside a rectangular plate are fixed, vibration behavior of the plate significantly changes and the deformations are localized in certain regions of the plate. This phenomenon is called as Mode Localization. We study mode localization in rectangular plates under different boundary and loading conditions and analyze the effects of plate dimensions, locations of the internal fixed points and dynamic load characteristics on mode localization. In the third problem, we investigate the effects of introduction of nonlinearities into the TSNDT mathematical model of plate deformations. Simple models in mechanics consider materials to be linearly elastic, which means that the deformations of a body are proportional to the applied loads in a linear relation. However, most materials in nature undergoing large deformations (human tissues, rubbers, and polymers, for example) do not behave in this fashion and their deformation depends nonlinearly to applied loads. To investigate the effects of such nonlinearities, we study the behavior of nonlinearly elastic plates under different boundary and loading conditions and delineate the differences in the results of linearly elastic and nonlinearly elastic plates using the TSNDT FEM solutions. Findings of this study establishes that linear models overestimate the plate deformation under given boundary and loading conditions as compared to nonlinear models. This understanding may help in developing better design criteria for plates undergoing large deformations.

En raison de leurs grandes longueurs d'onde, les vibrations mécaniques en basses fréquences ne peuvent être facilement réduites dans les structures par l'utilisation de matériaux dissipatifs. Malgré ces difficultés, l'atténuation des vibrations en basses fréquences reste un enjeu important. Pour résoudre ce problème, différents axes de recherche ont été étudiés et ont été mis en application pour stocker et dissiper l'énergie vibratoire comme l'utilisation d'oscillateurs linéaires, composés d'une masse, d'un ressort et d'un amortisseur. Leur fréquence de résonance doit coïncider avec la fréquence de résonance de la structure que l'on veut atténuer. L'utilisation d'absorbeurs se comportant comme des oscillateurs ayant un comportement non linéaire est une alternative intéressante. En effet, grâce à un étalement fréquentiel de la réponse de l'oscillateur, celui-ci permet d'atténuer les vibrations de la structure sur une plus large bande de fréquence que ceux ayant un comportement linéaire, sans avoir de dédoublement de la résonance de la réponse en deux pics. Les travaux présentés ici se placent dans le cadre de la réduction vibratoire, à l'échelle macroscopique, en basses fréquences, pour lesquelles les premiers modes structuraux sont excités. Un absorbeur non linéaire a été conçu, réalisé et analysé expérimentalement, modélisé et identifié expérimentalement pour mettre en évidence le phénomène d'élargissement de la bande de fréquence de la réponse. Les effets de cet absorbeur sur le comportement dynamique d'une poutre console ont ensuite été numériquement étudiés, à partir d'un modèle de poutre couplée à des absorbeurs non linéaires. Un modèle réduit et son solveur stochastique ont été développés dans ce cadre. Les résultats ont exposé le fait que l'absorbeur non linéaire permet une atténuation de la réponse de la poutre, sans le dédoublement de la résonance / Due to their long wavelengths, mechanical vibrations at low frequencies cannot easily be reduced in structures by using dissipative materials. Despite these difficulties, the attenuation of vibration at low frequencies remains an important concern. To solve this problem, several ways of research have been explored and have been applied to vibration energy pumping such as linear oscillators, composed of a mass, a spring, and a damper. Their resonance frequency must coincide with the resonant frequency of the structure that has to be attenuated. The absorbers that are oscillators with a nonlinear behavior constitute an interesting alternative. The response of the nonlinear oscillator allows for obtaining an attenuation of vibration over a broader frequency band than the response of linear oscillator, without splitting the resonance that has to be attenuated into two resonances. The work presented here is in the frame of the vibratory reduction, on a macro-scale, at low frequencies, for which the first structural modes are excited. A nonlinear absorber has been designed, experimentally realized and analyzed, modeled and experimentally identified to highlight the phenomenon of broadening the frequency band of the response. The effects of this absorber on the dynamic behavior of a cantilever beam have been numerically studied, using a model of the beam coupled to nonlinear absorbers. A reduced-model and its stochastic solver have also been developed. The results obtained show that the nonlinear absorber allows for obtaining an attenuation on the beam response, without splitting of the resonance that has to be attenuated

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2016-09-27T13:23:56Z No. of bitstreams: 2 Dissertação - Gustavo Henrique Jesus Mesquita - 2016.pdf: 1893414 bytes, checksum: b18598c3179586967bc12f642386c3f1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2016-09-27T13:24:18Z (GMT) No. of bitstreams: 2 Dissertação - Gustavo Henrique Jesus Mesquita - 2016.pdf: 1893414 bytes, checksum: b18598c3179586967bc12f642386c3f1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2016-09-27T13:24:18Z (GMT). No. of bitstreams: 2 Dissertação - Gustavo Henrique Jesus Mesquita - 2016.pdf: 1893414 bytes, checksum: b18598c3179586967bc12f642386c3f1 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2016-08-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The aim of this work is to propose a methodology of application of the FEM and topology optimization technique as tools of analysis and optimal design of mechanical systems subject to natural and forced vibrations in order to reach the optimal geometry of a dynamic absorbing of vibrations. It presents the mathematical reasoning and develop a program in Matlab® that implements the topology optimization technique will be employed to generate the optimal material distribution ( layout ) continuous mechanical systems without external excitation and subject to harmonic forces with preset frequency. / Propõe-se uma metodologia de aplicação do MEF (Método dos Elementos Finitos), juntamente com uma técnica de otimização topológica como ferramenta de análise e projeto ótimo de sistemas mecânicos sujeitos a vibração forçada. Em particular, chega-se à geometria ótima de um absorvedor dinâmico de vibrações contínuo. Apresenta-se a modelagem matemática, além de se desenvolver um código em Matlab® que implementa a técnica de otimização topológica por distribuição de material aplicado a sistemas mecânicos contínuos com excitação externa e harmônica de tal forma que a menor frequência natural seja predefinida.

Orientador: Gustavo Luiz Chagas Manhães de Abreu / Resumo: Diversos estudos relacionados à atenuação de vibrações utilizando materiais inteligentes vem sendo amplamente explorados no meio acadêmico. Neste âmbito, as Ligas de Memória de Forma (LMF) se destacam por apresentarem dissipação de energia vibratória devido ao seu comportamento histerético promovido pelo efeito pseudoelástico. No presente trabalho, dois sistemas com um e dois graus de liberdade, contendo mola helicoidal de LMF como elemento resiliente, são implementados numericamente para demonstrar a atenuação de vibrações ocasionada pelas transformações de fase presentes no material. Para cada um dos sistemas mecânicos investigados, dois modelos termomecânicos são confrontados numericamente visando a obtenção das características de cada modelo em representar a atenuação de vibrações dos sistemas submetidos à carregamentos termo-mecânicos. O trabalho termina comentando as potencialidades da proposta apresentada, discutindo as facilidades e dificuldades encontradas na sua implementação e apontando para o desenvolvimento de futuros estudos. / Mestre

Submitted by RAFAEL DE OLIVEIRA SILVA null (rafa_engemec@hotmail.com) on 2017-04-24T14:27:25Z No. of bitstreams: 1 dissertacao_final.pdf: 3521819 bytes, checksum: b08a60dcaa91691a2bf36a0cc59992e6 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-04-26T13:27:52Z (GMT) No. of bitstreams: 1 silva_ro_me_ilha.pdf: 3521819 bytes, checksum: b08a60dcaa91691a2bf36a0cc59992e6 (MD5) / Made available in DSpace on 2017-04-26T13:27:52Z (GMT). No. of bitstreams: 1 silva_ro_me_ilha.pdf: 3521819 bytes, checksum: b08a60dcaa91691a2bf36a0cc59992e6 (MD5) Previous issue date: 2017-03-31 / Diversos estudos relacionados à atenuação de vibrações utilizando materiais inteligentes vem sendo amplamente explorados no meio acadêmico. Neste âmbito, as Ligas de Memória de Forma (LMF) se destacam por apresentarem dissipação de energia vibratória devido ao seu comportamento histerético promovido pelo efeito pseudoelástico. No presente trabalho, dois sistemas com um e dois graus de liberdade, contendo mola helicoidal de LMF como elemento resiliente, são implementados numericamente para demonstrar a atenuação de vibrações ocasionada pelas transformações de fase presentes no material. Para cada um dos sistemas mecânicos investigados, dois modelos termomecânicos são confrontados numericamente visando a obtenção das características de cada modelo em representar a atenuação de vibrações dos sistemas submetidos à carregamentos termo-mecânicos. O trabalho termina comentando as potencialidades da proposta apresentada, discutindo as facilidades e dificuldades encontradas na sua implementação e apontando para o desenvolvimento de futuros estudos. / Several studies regarding the vibration attenuation using intelligent materials have been widely explored in the academic world in engineering. In this context, the shape memory alloys (SMAs) exhibit vibratory energy dissipation due to their hysteretic behavior caused by the pseudoelastic effect. In the present work, two systems with one and two degrees of freedom, containing a SMA helical spring as a resilient element, are numerically implemented to demonstrate the vibration attenuation of the system caused by the phase transformations present in the SMA spring. For each considered mechanical systems, two thermomechanical models are numerically confronted in order to obtain the characteristics of each model in representing the vibration attenuation of the systems submitted to thermo-mechanical loads. This work is concluded presenting the potentialities of the design methodology proposed and future developments to be implemented.