Orientador: Paulo Roberto Gardel Kurka / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-22T16:15:39Z (GMT). No. of bitstreams: 1 GonzalezRamos_Paola_M.pdf: 2350436 bytes, checksum: 0bb7c5bf390b9cfd31a3794e71412581 (MD5) Previous issue date: 2013 / Resumo: O uso de manipuladores longos e flexíveis em veículos de exploração autônoma, ao contrário dos braços curtos e rígidos, pode ser uma forma de obter dados de um ambiente específico de longo alcance, como encostas de terreno e penhascos. A desvantagem de se utilizar uma estrutura flexível é a dificuldade de controlar os seus movimentos de vibração durante a operação. Este trabalho, portanto, tem como objetivo principal projetar um controle de vibração ativa para uma viga flexível longa, deformável pela ação de um cabo fixado em sua extremidade. O controle pretende minimizar os movimentos oscilatórios da ponta da viga decorrentes de perturbações externas. A projeção do controle baseia-se no modelo matemático em tempo continua da viga, realizado pelo método de elementos finitos. A estratégia de controle é calculada com um modelo reduzido do sistema, no qual estão contidos os modos dominantes do mesmo. Mostra-se que uma resposta desejada de controle é obtida aplicando-se o método de alocação de pólos / Abstract: The use of long manipulators in autonomous exploration vehicles, as opposed to short and rigid arms, may be an attractive way to collect data in specific long range environments such as terrain slopes and cliff sides. The drawback of employing such a flexible structure is the fact that its vibrations cannot be easily controlled in real time operation. This work has the principal objective to project an active vibration control of a long flexible beam which is deformed by action of a pulling cable, fixed to its extremity. The control aims to minimize the oscillatory movements of the bean's tip caused by external disturbances. The control strategy is based on the continuous time mathematical model of the beam, using the finite element method. The control strategy is calculated in a reduced model system which contains the dominant modes of the same. It is shown that an adequate control response is obtained using the method of allocation of poles / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestra em Engenharia Mecânica

Orientador: Alberto Luiz Serpa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T00:36:50Z (GMT). No. of bitstreams: 1 Pereira_DanielAugusto_D.pdf: 10049171 bytes, checksum: 63439cd1c1df78b669ff99ba303ad488 (MD5) Previous issue date: 2013 / Resumo: Partindo-se do princípio de que detectar falhas em sistemas realimentados pode ser considerada tarefa difícil, nessa tese é proposto um método para detecção de falhas de sensores em estruturas flexíveis sujeitas a controle ativo de vibração. O método é baseado num esquema com banco de estimadores para geração de resíduos e no uso de indicadores para a análise quantitativa desses resíduos. O esquema de banco de estimadores permite o isolamento das falhas. Os estimadores utilizados são observadores de saída, filtros de Kalman e filtros H-infinito. Já os indicadores propostos são versões modificadas da diferença entre os valores RMS das saídas medidas e estimadas, a soma do módulo do erro de estimativa, a soma quadrática do erro de estimativa e o modal assurance criterion. É proposto um reescalamento dos indicadores e também um novo indicador, definido pelo produto das versões modificadas e reescaladas dos indicadores clássicos. Inicialmente a técnica foi validada em simulações, primeiro com um modelo de elementos finitos de uma estrutura de placa e posteriormente com um modelo de placa identificado experimentalmente, ambos sob controle ativo de vibração. Experimentos com a estrutura de placa também foram realizados e comprovaram a eficácia da técnica / Abstract: Assuming that fault detection in feedback systems can be considered a hard task, it is proposed in this thesis a method for sensor fault detection in flexible structures subjected to active vibration control. The method is based on a scheme with bank of estimators for residual generation and indicators for quantitative analysis of residues. The bank estimators scheme allows the fault isolation. The estimators used are output observers, Kalman filters and H-infinity filters. The proposed indicators are modified versions of the difference between RMS values of measured and estimated outputs, the sum of the modulus of the estimation error, the quadratic sum of the estimation error and the modal assurance criterion. It is proposed a rescaling of the indicators and also a new indicator, defined by the product of the modified and rescaled versions of classical indicators. Initially the technique is validated in simulations, first with a finite element model of a plate structure and latter with an experimentally identified plate model, both under active vibration control. Experiments with the plate were also performed and proved the effectiveness of the technique / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutor em Engenharia Mecânica

Orientador: Alberto Luiz Serpa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-23T23:04:02Z (GMT). No. of bitstreams: 1 ArizaZambrano_WilliamCamilo_M.pdf: 5789145 bytes, checksum: 151f5e3ef1780d5448a7073b85b4715f (MD5) Previous issue date: 2013 / Resumo: Este trabalho tem como objetivo principal o estudo de um método de controle baseado no uso de redes neurais artificiais aplicado ao problema de controle de vibrações em estruturas flexíveis. Este trabalho centra-se no estudo do esquema de controle inverso-direto, que consiste em identificar a dinâmica inversa da planta através de uma rede neural artificial para ser usada como controlador. Três exemplos de aplicação foram resolvidos utilizando-se controladores projetados com o método inverso-direto. A primeira aplicação é o controle de vibrações em uma estrutura mecânica de parâmetros concentrados. O segundo exemplo de aplicação é o controle de vibrações de uma placa engastada em uma de suas extremidades. Neste caso, a placa engastada foi modelada utilizando-se o método de elementos finitos. No seguinte exemplo, o modelo da placa usado no exemplo anterior foi reduzido, deixando apenas os primeiros modos de vibração. No último exemplo tratou-se o problema de controle não colocado das vibrações em uma placa engastada. Os resultados foram analisados a partir da resposta temporal e da resposta em frequência do sistema em malha fechada. Para comparar os resultados obtidos utilizando-se o método de controle baseado em redes neurais artificiais, os exemplos citados anteriormente foram também resolvidos utilizando-se o método de controle ??. Os resultados obtidos demonstram que o método de controle baseado em modelo inverso usando redes neurais foi eficaz na resolução deste tipo de problema / Abstract: The goal of this work is to study a control method based on artificial neural networks applied to the vibration control of flexible structures problem. This work focuses in the direct-inverse control scheme which consists of identifing the inverse dynamics of the plant through an artificial neural network to be used as the controller. Three application examples using the direct-inverse method were solved. The first application is the vibration control in a mechanical structure of concentrated parameters. The second application example is the vibration control of a cantilever plate. The cantilever plate was modeled using the finite elements method. In the third example, a reduction of the cantilever plate model was made. In the last example a non-collocated control problem of vibration in a cantilever plate was treated. The results of the scheme were evaluated according to the temporal response and the frequency response of the closed-loop system. In order to compare the results obtained using the control method based on artificial neural networks, the previous examples were also solved using the ?? control method. The obtained results show that the control method based on inverse model using neural networks was effective in solving this kind of problem / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Shape memory alloys (SMAs) are materials that show reversible, thermo-elastic, diffusionless, displacive (solid to solid) phase transformation, due to the application of temperature and/ or stress (/strain). Among different SMAs, NiTi is a popular one. NiTi shows reversible phase transformation, the shape memory effect (SME), where irreversible deformations are recovered upon heating, and superelasticity (SE), where large strains imposed at high enough temperatures are fully recovered. Phase transformation process in NiTi SMA is a very complex process that involves the competition between developed internal strain and phonon dispersion instability. In NiTi SMA, phase transformation occurs over a wide range of temperature and/ or stress (strain) which involves, evolution of different crystalline phases (cubic austenite i.e. B2, different monoclinic variant of martensite i.e. B19', and orthorhombic B19 or BCO structures). Further, it is observed from experimental and computational studies that the evolution kinetics and growth rate of different phases in NiTi SMA vary significantly over a wide spectrum of spatio-temporal scales, especially with length scales. At nano-meter length scale, phase transformation temperatures, critical transformation stress (or strain) and phase fraction evolution change significantly with sample or simulation cell size and grain size. Even, below a critical length scale, the phase transformation process stops. All these aspects make NiTi SMA very interesting to the science and engineering research community and in this context, the present focuses on the following aspects. At first this study address the stability, evolution and growth kinetics of different phases (B2 and variants of B19'), at different length scales, starting from the atomic level and ending at the continuum macroscopic level. The effects of simulation cell size, grain size, and presence of free surface and grain boundary on the phase transformation process (transformation temperature, phase fraction evolution kinetics due to temperature) are also demonstrated herein. Next, to couple and transfer the statistical information of length scale dependent phase transformation process, multiscale/ multiphysics methods are used. Here, the computational difficulty from the fact that the representative governing equations (i.e. different sub-methods such as molecular dynamics simulations, phase field simulations and continuum level constitutive/ material models) are only valid or can be implemented over a range of spatiotemporal scales. Therefore, in the present study, a wavelet based multiscale coupling method is used, where simulation results (phase fraction evolution kinetics) from different sub-methods are linked via concurrent multiscale coupling fashion. Finally, these multiscale/ multiphysics simulation results are used to develop/ modify the macro/ continuum scale thermo-mechanical constitutive relations for NiTi SMA. Finally, the improved material model is used to model new devices, such as thermal diodes and smart dampers.

Vibration-based energy harvesting using piezoelectric materials have been investigated by several research groups with the aim of harvesting maximum energy and providing power to low-powered wireless electronic systems for their entire operational life. The electromechanical coupling effect introduced by the piezoelectric vibration energy harvesting (PVEH) mechanism presents modelling challenges. For this reason, there has been a continuous effort to develop different modelling techniques to describe the PVEH mechanism and its effects on the dynamics of the system. The overall aims of this thesis are twofold: (1) a thorough theoretical and experimental analysis of a PVEH beam or assembly of beams; (2) an in-depth analytical and experimental investigation of the novel concept of a dual function piezoelectric vibration energy harvester beam/tuned vibration absorber (PVEH/TVA) or 'electromechanical TVA' and its potential application to vibration control. The salient novel contributions of this thesis can be summarised as follows: (i) An in-depth experimental validation of a PVEH beam model based on the analytical modal analysis method (AMAM), with the investigations conducted over a wider frequency range than previously tested. (ii) The precise identification of the electrical loads that harvest maximum power and that induce maximum electrical damping. (iii) A thorough investigation of the influence of mechanical damping on PVEH beams. (iv) A procedure for the exact modelling of PVEH beams, and assemblies of such beams, using the dynamic stiffness matrix (DSM) method. (v) A procedure to enhance the power output from a PVEH beam through the application of a tip rotational restraint and the use of segmented electrodes. (vi) The theoretical basis for the novel concept of a dual function PVEH beam/TVA, and its realisation and experimental validation for a prototype device. A thorough experimental validation of a cantilever piezoelectric bimorph energy harvester without a tip mass is presented under random excitation. The study provided a deep insight into the effect of PVEH on the dynamics of the system for variations in electrical load. An alternative modelling technique to AMAM, based on the DSM, is introduced for PVEH beams. Unlike AMAM, the DSM is exact, since it is based on the exact solution to the bending wave equation. It also readily lends itself to the modelling of beams with different boundary conditions or assemblies of beams of different crosssections. AMAM is shown to converge to DSM if a sufficiency of modes is used. Finally, an in-depth theoretical and experimental investigation of a prototype PVEHbeam/TVA device is presented. This device comprises a pair of bimorphs shunted by R-L-C circuitry and can be used as a tuned mass damper (TMD) to attenuate a vibration mode of a generic structure. The optimal damping required by this TMD is generated by the PVEH effect of the bimorphs. Such a device combines the advantages of conventional mechanical and electrical TVAs, overcoming their relative disadvantages. The results demonstrate that the ideal degree of attenuation can be achieved by the proposed device through appropriate tuning of the circuitry, thereby presenting the prospect of a novel class of 'electromechanical' tuned vibration absorbers.

Orientador: Alberto Luiz Serpa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T04:19:56Z (GMT). No. of bitstreams: 1 HuamanOrtiz_RonaldRichard_M.pdf: 3700691 bytes, checksum: e0c35e9a16c6fd36ae433ab9a61c6cbb (MD5) Previous issue date: 2015 / Resumo: O projeto de sistemas de controle ativo de vibrações para estruturas flexíveis envolve a síntese de controladores que, geralmente, reduzem certos picos da resposta em frequência do sistema em malha fechada. Em alguns casos é requerido controlar unicamente um modo de vibrar específico do sistema em análise que pode estar associado a uma faixa de baixa, média ou alta frequência, o que demanda de um controle modal de vibrações. Neste trabalho, propõem-se três métodos alternativos para sintetizar controladores modais utilizando a teoria de controle H-infinito em uma configuração de controle por realimentação de saída. O primeiro método é implementado utilizando funções de ponderação as quais são introduzidas no problema de controle H-infinito para definir as características do controlador de maneira que este atenue a vibração do sistema na região em frequência correspondente ao modo que se deseja controlar (modo de interesse). O segundo método procura sintetizar controladores modais de menor ordem, utilizando uma planta reduzida. Essa planta reduzida contém unicamente a informação dinâmica do modo que se deseja controlar e é obtida através de uma transformação modal. O terceiro método procura melhorar o desempenho do controlador modal (conseguir uma maior redução da vibração do modo de interesse). Este método propõe sintetizar o controlador modal formulando um problema de otimização não linear onde as variáveis do controlador modal são as variáveis de otimização e a função objetivo é definida com valores específicos da resposta em frequência do sistema dinâmico. A solução deste problema de otimização é obtida utilizando o algoritmo de programação quadrática sequencial (SQP). Os três métodos são verificados utilizando o modelo de uma viga flexível engastada que é modelada através do método dos elementos finitos. Finalmente, os resultados obtidos são discutidos analisando as vantagens e desvantagens dos métodos propostos / Abstract: The design of active vibration control systems for flexible structures involves the tuning of controllers that reduce, generally, certain frequency resonance peaks of the close loop system. In some cases it is required to control a specific vibration mode of the system from a low, middle or high frequency range, demanding a modal vibration control. In this study it is proposed three alternative modal control methods using the H-infinity control theory in an output feedback control configuration. The first method is implemented using weighting functions which are introduced into the H-infinity control problem to define the characteristics of the controller so that it mitigates the system vibration in the frequency region that corresponds to a specific vibration mode (mode of interest). The second method attempts to synthesize lower order modal controllers, using a reduced plant. This reduced plant contains only the dynamic information of the vibration mode you want to control and is obtained through a modal transformation. The third method aims to improve the performance of the modal controller (to achieve a further reduction of the vibration mode of interest). This method proposes to synthesize the modal controller formulating a non-linear optimization problem where the variables of the modal controller are defined as the optimization variables and the objective function is defined with specific values of the frequency response of the dynamic system. The solution to this optimization problem is obtained using the sequential quadratic programming (SQP) algorithm. The three methods are verified using the model of a cantilever flexible beam that is modeled by the finite element method. Finally, the results are discussed considering the advantages and disadvantages of the proposed methods / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

This thesis concerns the control of an adaptive passive vibration neutralizer and the feasibility of miniaturizing this type of tunable vibration neutralizer for small-scale applications. An analytical model for the adaptive passive vibration neutralizer is derived and compared to experimental results. A tuning algorithm is derived from a curve-fit of experimental tests on the specific neutralizer. A more generic tuning algorithm is also developed, which does not require testing of the neutralizer for optimal control. Both tuning algorithms are tested using a chirp forcing function to simulate drift in the excitation frequency of a host structure. Computer simulation and experimental results are given for these tests. A novel low-cost, small-scale vibration neutralizer is constructed from packing bubble-wrap. Analytical models for the stiffness are calculated, and experimental data is used to derive a damped mass-spring model. Miniaturization of vibration neutralizers is described, and many of the pitfalls in design are discussed. Theoretical tuning frequencies of possible adaptive passive vibration neutralizers at different scales are included. The goal for these miniaturized vibration neutralizers is vibration control in computer hard drives. A hard drive is analyzed for vibration problems. Included are plots of the velocities of the read-write head and spindle. Limitations of the measurement equipment are discussed, and directions for future work on small-scale tunable vibration neutralizers are outlined. / Master of Science

<p> Nonlinear flexural vibrations of simply supported rectangular plates with thermal coupling  are studied for the case when the plate is harmonically excited by the force acting normal to the  midplane of the plate. The coupled thermo-mechanical equations are derived by applying the  Galerkin procedure on the von-Karman equation and the energy equation for an element of the  plate. The thermo-mechanical equations are second order in transverse displacement and first order  in thermal dynamics. In our first study, we represent the transverse displacement, bending moment  and membrane force due to temperature by one mode approximation, and study the response of  thermoelastic plate in time and frequency domain. The analysis of forced vibration to a transverse  harmonic excitation is carried out using harmonic balance as well as direct time integration coupled  to a Fourier analysis for a range of excitation frequencies. The effects of thermal coupling, material  nonlinearity and different amplitudes of excitation on the thermoelastic plate’s transverse  displacement and thermoelastic variables are investigated. The method of averaging is applied to the one mode case to transform the nonlinear modal  equations into sets of two-dimensional dynamical systems which govern the amplitudes and phases  of the two modes. The averaged system is studied in detail by using pseudo arc-length continuation  schemes implemented in MATCONT. The physical phenomena of interest in this study arise when a plate exhibits two distinct  linear modes of vibration with nearly the same natural frequency. To analyze the dynamics of the  thermoelastic plate in this scenario, we utilize a two-mode approximation. The response of the  plate, as a function of excitation frequency, is determined for the two-mode model using  MATCONT, and several bifurcation points are identified. Our analysis reveals two types of  solutions: single-mode and coupled-mode solutions. We find that stable single-mode and coupled mode solutions can coexist over a wide range of amplitudes and excitation frequencies. Under the influence of thermal coupling, our analysis using MATCONT reveals the  identification of Neimark-Sacker bifurcation points. After a detailed study of the Neimark-Sacker  region using Fourier spectrum and Poincare section, we conclude that a pitchfork bifurcation  occurs, resulting in stable asymmetric solutions. We further investigate the effect of in-plane forces  or mechanical precompression on the thermoelastic plate, using MATCONT for a fixed value of  force, damping, and excitation frequency. We find that the in-plane forces lead to buckling, which  12 is identified as a branch point cycle (pitchfork bifurcation) in MATCONT. Consequently, the  bifurcation diagram of transverse displacement as a function of in-plane forces can be divided into  prebuckling and post buckling regions, with multistable solutions in each region. To validate our one mode model, we use ANSYS software to verify the transverse  displacement and temperature results. We validate the frequency and time domain results for both  the linear and nonlinear cases, and plot contours using ANSYS to observe the variation of  displacement and temperature over the surface of the plate. Our one mode model results closely  match with the ANSYS results, leading us to conclude that our one mode approximation is accurate  and that the coupled thermo-mechanical equations we derived are correct.  </p>

No description available.

Piezoelectric-based energy harvesting devices provide an attractive approach to powering remote devices as ambient mechanical energy from vibrations is converted to electrical energy. These devices have numerous potential applications, including actuation, sensing, structural health monitoring, and vibration control -- the latter of which is of particular interest here. This work seeks to develop an understanding of energy harvesting behavior within the framework of a semi-active technique for reducing turbomachinery blade vibrations, namely resonance frequency detuning. In contrast with the bulk of energy harvesting research, this effort is not focused on maximizing the power output of the system, but rather providing the low power levels required by resonance frequency detuning. The demands of this technique dictate that harvesting conditions will be far from optimal, requiring that many common assumptions in conventional energy harvesting research be relaxed. Resonance frequency detuning has been proposed as a result of recent advances in turbomachinery blade design that have, while improving their overall efficiency, led to significantly reduced damping and thus large vibratory stresses. This technique uses piezoelectric materials to control the stiffness, and thus resonance frequency, of a blade as the excitation frequency sweeps through resonance. By detuning a structure*s resonance frequency from that of the excitation, the overall peak response can be reduced, delaying high cycle fatigue and extending the lifetime of a blade. Additional benefits include reduced weight, drag, and noise levels as reduced vibratory stresses allow for increasingly light blade construction. As resonance frequency detuning is most effective when the stiffness states are well separated, it is necessary to harvested at nominally open- and short-circuit states, corresponding to the largest separation in stiffness states. This presents a problem from a harvesting standpoint however, as open- and short-circuit correspond to zero charge displacement and zero voltage, respectively, and thus there is no energy flow. It is, then, desirable to operate as near these conditions as possible while still harvesting sufficient energy to provide the power for state-switching. In this research a metric is developed to study the relationship between harvested power and structural stiffness, and a key result is that appreciable energy can be harvested far from the usual optimal conditions in a typical energy harvesting approach. Indeed, sufficient energy is available to power the on-blade control while essentially maintaining the desired stiffness states for detuning. Furthermore, it is shown that the optimal switch in the control law for resonance frequency detuning may be triggered by a threshold harvested power, requiring minimal on-blade processing. This is an attractive idea for implementing a vibration control system on-blade, as size limitations encourage removing the need for additional sensing and signal processing hardware.