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Made available in DSpace on 2014-06-11T19:34:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-09Bitstream added on 2014-06-13T21:06:53Z : No. of bitstreams: 1 barros_e_dr_guara.pdf: 1499137 bytes, checksum: 5a94296d58a74230125376ce4552f941 (MD5) / Universidade Estadual Paulista (UNESP) / Na presença de não linearidades, a resposta forçada de estruturas exibe diversos fenômenos físicos que não podem ser descritos através de modelos lineares. Estes fenômenos incluem ressonâncias sub-harmônicas, ressonâncias super-harmônicas, jumps , movimentos quasi-periódicos, movimentos de período múltiplo, caos e interações modais. Recentes estudos experimentais indicam que um novo tipo de interação modal pode ocorrer através de mecanismos não ressonantes, decorrente da transferência de energia de modos de alta freqüência e baixa amplitude para modos de baixa freqüência e alta amplitude. Neste trabalho, interações modais não ressonantes são investigadas na resposta planar não linear de vigas cantilever flexíveis sujeitas a excitações externas e paramétricas. As equações diferenciais e as condições de contorno associadas que governam o movimento flexional-flexional não linear de uma viga assumida inextensível, metálica e isotrópica, são apresentadas. O estudo experimental conduzido revelou que a transferência de energia entre modos de alta freqüência para modos de baixa freqüência ocorre via modulação, sendo função do valor da amplitude de excitação e da proximidade entre os valores da freqüência de modulação e da freqüência dos modos ativados. O estudo revelou também que a ativação de modos de baixa freqüência pode ocorrer sob uma variedade de condições de entrada. Em adição, outros fenômenos dinâmicos não lineares classificados como rotas para o movimento caótico são também observados. Em determinadas condições, movimentos quasi-periódicos com amplitudes moduladas caoticamente e moduladas periodicamente são exibidos. Um movimento de resposta de período dois é também observado. / Interesting physical phenomena occur in the forced response of structures in the presence of nonlinearities, which cannot be explained by linear models. These phenomena include subharmonic resonances, superharmonic resonances, jumps, period-multiplying motions, quasiperiodic motions, chaos and modal interactions. Recent studies suggest that another type of modal interaction may occur through nonresonant mechanisms, due to the energy transfer from the low-amplitude highfrequency modes to high-amplitude low-frequency modes. In this work, nonresonant modal interactions in the nonlinear planar motions of flexible cantilever beams subjected to transverse and parametric harmonic excitations are investigated. The governing equations of the nonlinear bending-bending motions and the associated boundary conditions for an isotropic metallic inextensional beam are presented. An experimental study revealed that the transfer of energy from high-frequency to lowfrequency modes occurs via modulation and is found to be function of the excitation amplitude and the closeness of the modulation frequency to the frequencies of the low modes activated. The experimental study also revealed that the energy transfer from high-frequency modes to low-frequency modes occurs for a variety of conditions. In addition, others nonlinear dynamic phenomenas routes to the chaotic motions, are also observed. Under certain conditions, quasiperiodic motion with periodically and chaotically modulated amplitudes are exhibited. Period-doubling motion is also observed.

Resumo: Na presença de não linearidades, a resposta forçada de estruturas exibe diversos fenômenos físicos que não podem ser descritos através de modelos lineares. Estes fenômenos incluem ressonâncias sub-harmônicas, ressonâncias super-harmônicas, “jumps”, movimentos quasi-periódicos, movimentos de período múltiplo, caos e interações modais. Recentes estudos experimentais indicam que um novo tipo de interação modal pode ocorrer através de mecanismos não ressonantes, decorrente da transferência de energia de modos de alta freqüência e baixa amplitude para modos de baixa freqüência e alta amplitude. Neste trabalho, interações modais não ressonantes são investigadas na resposta planar não linear de vigas cantilever flexíveis sujeitas a excitações externas e paramétricas. As equações diferenciais e as condições de contorno associadas que governam o movimento flexional-flexional não linear de uma viga assumida inextensível, metálica e isotrópica, são apresentadas. O estudo experimental conduzido revelou que a transferência de energia entre modos de alta freqüência para modos de baixa freqüência ocorre via modulação, sendo função do valor da amplitude de excitação e da proximidade entre os valores da freqüência de modulação e da freqüência dos modos ativados. O estudo revelou também que a ativação de modos de baixa freqüência pode ocorrer sob uma variedade de condições de entrada. Em adição, outros fenômenos dinâmicos não lineares classificados como rotas para o movimento caótico são também observados. Em determinadas condições, movimentos quasi-periódicos com amplitudes moduladas caoticamente e moduladas periodicamente são exibidos. Um movimento de resposta de período dois é também observado. / Abstract: Interesting physical phenomena occur in the forced response of structures in the presence of nonlinearities, which cannot be explained by linear models. These phenomena include subharmonic resonances, superharmonic resonances, jumps, period-multiplying motions, quasiperiodic motions, chaos and modal interactions. Recent studies suggest that another type of modal interaction may occur through nonresonant mechanisms, due to the energy transfer from the low-amplitude highfrequency modes to high-amplitude low-frequency modes. In this work, nonresonant modal interactions in the nonlinear planar motions of flexible cantilever beams subjected to transverse and parametric harmonic excitations are investigated. The governing equations of the nonlinear bending-bending motions and the associated boundary conditions for an isotropic metallic inextensional beam are presented. An experimental study revealed that the transfer of energy from high-frequency to lowfrequency modes occurs via modulation and is found to be function of the excitation amplitude and the closeness of the modulation frequency to the frequencies of the low modes activated. The experimental study also revealed that the energy transfer from high-frequency modes to low-frequency modes occurs for a variety of conditions. In addition, others nonlinear dynamic phenomenas routes to the chaotic motions, are also observed. Under certain conditions, quasiperiodic motion with periodically and chaotically modulated amplitudes are exhibited. Period-doubling motion is also observed. / Orientador: Fernando de Azevedo Silva / Coorientador: Mauro Hugo Mathias / Banca: Othon Cabo Winter / Banca: Victor Orlando Gamarra Rosado / Banca: José Juliano de Lima Júnior / Banca: Olivério Moreira de Macedo Silva / Doutor

The objective of this dissertation is to develop a mechanical model of a nonlinear piezoelectric energy harvesting system induced by Duffing oscillator and predict the periodic motions of such a nonlinear dynamical system under different excitation frequency. In this dissertation, analytical distributed-parameter electromechanical modeling of a piezoelectric energy harvester will be presented. The electromechanically coupled circuit equation excited by infinitely many vibration modes is derived. The governing electromechanical equations are reduced to ordinary differential equations in modal coordinates and eventually an infinite set of algebraic equations is obtained for the complex modal vibration response and the complex voltage response of the energy harvester beam. One single vibration mode is chosen and discussed. The periodic motions are obtained through an implicit mapping method with high accuracy, stability and bifurcations of periodic motions are determined by the eigenvalue analysis. Frequency-amplitude characteristics of periodic motions are achieved by the Fourier transform

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This thesis investigates the torsional performance of steel structures with and without rigid diaphragm constraints through numerical simulations and evaluates the appropriateness of relevant design provisions in current seismic design codes. In the first part of the work, six theme structures with different (1) in-plane stiffness of diaphragm, and (2) horizontal configurations of vertical braced frames were designed and their performance evaluated through both nonlinear static and dynamic analyses. Comparisons of the analytical results between the structures with and without rigid diaphragm constraints indicate that the in-plane rigidity of the diaphragms affects the efficiency of in-plane force transfer mechanisms, resulting in different global ductility and strength demands. Rigid diaphragm structures exhibit higher global strengths as well as higher torsional rotation capacity because of the infinite in-plane stiffness of the diaphragm. Semi-rigid diaphragm structures have higher ductility demands due to the finite in-plane diaphragm stiffness. The inclusion of bi-axial forces in the analyses reduces the structural strength and increases the ductility demands on the peripheral frames. The axial forces in the collectors and chords that make up the diaphragm depend on (1) the sequence of brace buckling and (2) vertical configuration of the braced frames. The results show higher axial forces in collectors in the roof diaphragms, and higher chord axial forces in the third floor diaphragms. The shear connections in the beams that make up both the collectors and chords are susceptible to failure due to the significant increment of axial forces in those members. The conventional beam analogy used in design can severely underestimate the axial forces in chords and collectors when the structures step into the inelastic stage. / Ph. D.

This thesis is concerned with volatility estimation using financial panels and bias-reduction in non-linear dynamic panels in the presence of dependence. Traditional GARCH-type volatility models require large time-series for accurate estimation. This makes it impossible to analyse some interesting datasets which do not have a large enough history of observations. This study contributes to the literature by introducing the GARCH Panel model, which exploits both time-series and cross-section information, in order to make up for this lack of time-series variation. It is shown that this approach leads to gains both in- and out-of-sample, but suffers from the well-known incidental parameter issue and therefore, cannot deal with short data either. As a response, a bias-correction approach valid for a general variety of models beyond GARCH is proposed. This extends the analytical bias-reduction literature to cross-section dependence and is a theoretical contribution to the panel data literature. In the final chapter, these two contributions are combined in order to develop a new approach to volatility estimation in short panels. Simulation analysis reveals that this approach is capable of removing a substantial portion of the bias even when only 150-200 observations are available. This is in stark contrast with the standard methods which require 1,000-1,500 observations for accurate estimation. This approach is used to model monthly hedge fund volatility, which is another novel contribution, as it has hitherto been impossible to analyse hedge fund volatility, due to their typically short histories. The analysis reveals that hedge funds exhibit variation in their volatility characteristics both across and within investment strategies. Moreover, the sample distributions of fund volatilities are asymmetric, have large right tails and react to major economic events such as the recent credit crunch episode.

Nous étudions l’influence d’une rétroaction optique à conjugaison de phase dans une diode laser. Ce type de rétroaction a été peu étudié et nous montrons ici qu’il donne des résultats intéressants, permettant de débloquer du contenu à haute fréquence. Cela pourrait mener à de meilleures performances dans des systèmes de génération de nombres aléatoires utilisant du chaos optique. / We study the influence of phase-conjugate feedback in a laser diode. This type of feedback has not been studied a lot and yet we show here that it can give interesting results. It unlocks oscillations at high frequencies. This could lead to an improvement in the performance of random number generators based on optical chaos.

The research aims at modeling and analyzing the interactions among functional process variables (FPVs) for process control in semiconductor manufacturing. Interaction is a universal phenomenon and different interaction patterns among system components might characterize the system conditions. To monitor and control the system, process variables are normally collected for observation which could vary with time and present in a functional form. These FPVs interact with each other and contain rich information regarding the process conditions. As an example in one of the semiconductor manufacturing processes, changes of interactions among FPVs like temperature and coefficient of friction (COF) might characterize different process conditions. This dissertation systematically developed a methodology to study interaction among FPVs through statistical and physical modeling. Three main topics are discussed in this dissertation: (1) Interaction patterns of FPVs under varying process conditions are studied both through experiments and statistical approaches. A method based on functional canonical correlation analysis (FCCA) is employed to extract the interaction patterns between FPVs and experiments of wafer polishing processes are conducted to verify the patterns of FPVs under varying process conditions. (2) Interaction among FPVs is further studied based on physics for process condition diagnosis. A mathematical model based on nonlinear dynamics is developed to study the strength of interaction and their directionalities, and advanced statistical control charts followed by this nonlinear dynamics model are established for process monitoring. (3) Complex interaction structures among multiple FPVs are analyzed based on nonlinear dynamics for a better understanding of process mechanism. An approach with extended nonlinear dynamics model is proposed to characterize process conditions, and combined engineering knowledge, complex interaction structure patterns are concluded accordingly for interpretation of process mechanism. The main contribution of this dissertation is to propose a novel methodology based on nonlinear dynamics, which could investigate interactions between components of systems and provide physical understanding of process mechanism for process monitoring and diagnosis. Through studies on interaction among FPVs in semiconductor manufacturing, this research provides guidance for improvement of manufacturing processes. Not limited to manufacturing, the developed methodology can be applied to other areas such as healthcare delivery.

In this work, we introduce several novel approaches to feedback controller design, known collectively as the “Robust Bode” methods, which adapt classical control principles to a modern robust control (H∞) framework. These methods, based on specially modified Bode diagrams extend familiar frequency-domain controller design techniques to linear and nonlinear, single–input/single– output (SISO) and multi–input/multi–output (MIMO) systems with parametric and/or unstructured uncertainties. In particular, we introduce the Contoured Robust Controller Bode (CRCBode) plots which show contours (level-sets) of a robust metric on the Bode magnitude and phase plots of the controller. An iterative loop shaping design procedure is then employed in an attempt to eliminate all intersections of the controller frequency response with certain forbidden regions indicating that a robust stability and performance criteria is satisfied. For SISO systems a robust stability and performance criterion is derived using Nyquist arguments leading to the robust metric used in the construction of the CRCBode plots. For open-loop unstable systems and for non-minimum phase systems the Youla parametrization of all internally stabilizing controllers is used to develop an alternative Robust Bode method (QBode). The Youla parametrization requires the introduction of state-space methods for coprime factorization, and these methods lead naturally to an elegant connection between linear-quadratic Gaussian (LQG) optimal control theory and Robust Bode loop-shaping controller design. Finally, the Robust Bode approach is extended to MIMO systems. Utilizing a matrix norm based robustness metric on the MIMO CRCBode plots allows cross-coupling between all input/output channels to be immediately assessed and accounted for during the design process, making sequential MIMO loop-shaping controller design feasible.