Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-10-31Bitstream added on 2014-06-13T19:55:36Z : No. of bitstreams: 1 carvalhal_r_me_ilha.pdf: 892699 bytes, checksum: 6654a8de1bfad0655527d3268f00f2f1 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho apresenta o desenvolvimento analítico da modelagem de estruturas flexíveis do tipo treliça com o objetivo de atenuação de vibrações através do uso de técnicas de controle ativo. Atuadores de pilha piezelétricos são usados para exercer as forças de controle na estrutura, os quais substituem barras inteiras ou somente uma parte delas. Estes tipos de atuadores, também, satisfazem a necessidade de obtenção de estruturas leves. O posicionamento ótimo desses atuadores e de sensores é encontrado através da norma Hx, que é usada como função objetivo. Como técnica de controle é aplicado o Controle no Espaço Modal Independente (IMSC), no qual os estados são estimados por um estimador modal e são realimentados de acordo com a teoria de controle ótimo, o Regulador Linear Quadrático (LQR). O IMSC é eficiente computacionalmente mesmo aplicado a sistemas de alta ordem e também reduz os efeitos de spillover. Uma melhoria do IMSC, o Controle Modal Eficiente (EMC) também é apresentado com o propósito de reduzir as amplitudes das forças de controle. O modelo matemático da estrutura inteligente é obtido a partir do Método dos Elementos Finitos (MEF) considerando o acoplamento eletromecânico entre os atuadores de pilhas piezelétricos e a estrutura base. O projeto de uma treliça espacial, o posicionamento ótimo dos atuadores e sensores e o controle ativo de vibração são apresentados em simulações numéricas. Os resultados mostram que ambos os controladores aumentam o amortecimento da estrutura e, ainda, o EMC reduz as amplitudes das forças de controle. / This work presents the analytic development of the modeling of flexible truss structures with the aim to suppress the mechanical vibration using active control techniques. Piezoelectric stack actuators are used to produce control force in the structure, which can replace an entire bar or can be coupled to structural members. They also satisfy the necessity to obtain lighter structures. The optimal placement of actuators and sensors is found through the Hã norm as objective function. As control technique is presented the Independent Modal Space Control (IMSC), in which a modal estimator is used and the Linear Quadratic Regulator (LQR) feedback the estimated states according the optimal control theory. IMSC is computationally efficient also applied in high order system and reduces the negative effects of the control and observer spillover. An improvement in the IMSC is the Efficient Modal Control (EMC) that is proposed to reduce the amplitudes of control forces. The mathematical model of the intelligent structure is obtained from Finite Elements Method (FEM) considering the electromechanical coupling between the piezoelectric stack actuators and the base structure. The design of a space truss structure, the optimal placement of active members and the active damping vibration control is numerically implemented. Two control techniques are tested and compared: IMSC and EMC. Results show that the controllers increase the damping of the structure noticeably. The EMC controller provides better performance, reducing the amplitudes of control forces.

Nas últimas décadas, intensas pesquisas estão sendo desenvolvidas na área de controle ativo de vibrações utilizando estruturas flexíveis e transdutores piezoelétricos distribuídos em sua superfície. Este trabalho possui como objetivo a implementação, identificação e a aplicação do controle ativo de vibrações em barras engastadas. Os transdutores piezoelétricos são fixados próximos à extremidade fixa da barra. Um sistema de aquisição de sinais e de controle é utilizado para gravar os dados experimentais e implementar os projetos dos controladores de vibrações. Para a implementação computacional foi utilizado o software Matlab operando em conjunto com uma placa dSpace DS1104. A identificação do sistema, efetuada a partir da resposta em frequência das barras, é realizada considerando apenas os três primeiros modos de vibração das barras. Um modelo teórico que representa a dinâmica do sistema é apresentado e seus parâmetros são ajustados de acordo com dados experimentais, obtidos em ensaios, com a estrutura flexível. Para o problema de rejeição a perturbações e regulação de posição, são aplicados os métodos de controle conhecidos como Positive Position Feedback (PPF) e de Alocação de Pólos. Resultados experimentais são apresentados para demonstrar a eficácia do controle ativo de vibrações, utilizando transdutores piezoelétricos. / In recent decades, intensive researches have been developed in the area of active vibration control making use of flexible structures and piezoelectric transducers distributed on its surface. This work aims to identify, implement and apply the active control of vibrations in cantilevers beams. The piezoelectric transducers are surface-bonded near the fixed end of cantilever beam. A data acquisition and control system is used to record experimental data and to implement the design of a vibration controller. The software Matlab operating in conjunction with a board dSpace DS1104 was used for the computational implementation. The identification system, made from the frequency response of the cantilevers beams, is performed by considering only the first three modes of vibration of the cantilevers beams. A theoretical model representing the system dynamics is presented and its parameters are adjusted according to experimental data, obtained in tests, with the flexible structure. As for the problem of disturbance rejection and regulation position, control methods known as Positive Position Feedback (PPF) and Pole Placement are applied. Experimental results are presented to demonstrate the effectiveness of active control of vibration using piezoelectric transducers.

Nas últimas décadas, intensas pesquisas estão sendo desenvolvidas na área de controle ativo de vibrações utilizando estruturas flexíveis e transdutores piezoelétricos distribuídos em sua superfície. Este trabalho possui como objetivo a implementação, identificação e a aplicação do controle ativo de vibrações em barras engastadas. Os transdutores piezoelétricos são fixados próximos à extremidade fixa da barra. Um sistema de aquisição de sinais e de controle é utilizado para gravar os dados experimentais e implementar os projetos dos controladores de vibrações. Para a implementação computacional foi utilizado o software Matlab operando em conjunto com uma placa dSpace DS1104. A identificação do sistema, efetuada a partir da resposta em frequência das barras, é realizada considerando apenas os três primeiros modos de vibração das barras. Um modelo teórico que representa a dinâmica do sistema é apresentado e seus parâmetros são ajustados de acordo com dados experimentais, obtidos em ensaios, com a estrutura flexível. Para o problema de rejeição a perturbações e regulação de posição, são aplicados os métodos de controle conhecidos como Positive Position Feedback (PPF) e de Alocação de Pólos. Resultados experimentais são apresentados para demonstrar a eficácia do controle ativo de vibrações, utilizando transdutores piezoelétricos. / In recent decades, intensive researches have been developed in the area of active vibration control making use of flexible structures and piezoelectric transducers distributed on its surface. This work aims to identify, implement and apply the active control of vibrations in cantilevers beams. The piezoelectric transducers are surface-bonded near the fixed end of cantilever beam. A data acquisition and control system is used to record experimental data and to implement the design of a vibration controller. The software Matlab operating in conjunction with a board dSpace DS1104 was used for the computational implementation. The identification system, made from the frequency response of the cantilevers beams, is performed by considering only the first three modes of vibration of the cantilevers beams. A theoretical model representing the system dynamics is presented and its parameters are adjusted according to experimental data, obtained in tests, with the flexible structure. As for the problem of disturbance rejection and regulation position, control methods known as Positive Position Feedback (PPF) and Pole Placement are applied. Experimental results are presented to demonstrate the effectiveness of active control of vibration using piezoelectric transducers.

This research thesis aims to achieve the structural analysis and active vibration damping of the Tetraform machining structure. The Tetraform is a space frame made up of four equilateral triangles with spherical masses at the four vertices. This frame was originally developed for grinding of optical lenses and is now being adapted for use in micro-precision milling. The Tetraform is beneficial to the milling process due to its exceptionally high dynamic stiffness characteristics, which increases the machining stability and allows for higher material removal rates and accuracy. However, there are still some modes of vibration that are critical to the milling process and need to be dampened out. Under operating conditions of many structures, resonant modes of vibration can easily be excited which often lead to structural failure or significant reduction in operating performance. For the milling application, resonant frequencies of the machining structure can severely limit the milling process. The goal of the presented research is to increase surface and subsurface integrity with optimal material removal rate and least possible machining vibration, while maintaining accurate precision and surface finish. The vibrations from the machine tool not only affect the quality of the machined part but also the machine tool itself, since the cutting tool is susceptible to break or wear quickly when operating at high vibration modes, thus inevitably decreasing tool life. Vibration control has gained considerable attention in many areas including aerospace, automotive, structural, and manufacturing. Positive Position Feedback (PPF) is a vibration control scheme that is commonly used for its robust stability properties. A PPF controller works as a low pass filter, eliminating instability from unmodeled higher-frequency modes. The PPF controller concept is used in developing an active vibration control scheme to target the critical frequencies of the Tetraform. The controller is implemented with use of piezoelectric actuators and sensors, where the sensors are bonded to the opposing sides of the beams as the actuators, allowing for the assumption of collocation. The sensor/actuator pairs are placed at an optimal location on the Tetraform with high modal displacements for all the critical frequencies. Multiple finite element models are developed in order to analyze the structural dynamics and allow for controller design. A model is developed in the finite element software ANSYS and is used to obtain the Tetraform's dynamic characteristics, which include natural frequencies and mode shapes. This model is also used to visualize the changes in mode shapes due to structural modifications or different material selections. Other models are also developed in Matlab and Simulink. This consists of the creation of a finite element model which is then converted to state space. The piezoelectric transducers are included in this model for the input and output of the state space model. This model can be used for controller design where the goal is to create maximum decibel reduction at critical frequencies while attempting to minimize controller effort.

No / Although computer architectures incorporate fast processing hardware resources, high performance real-time implementation of a complex control algorithm requires an efficient design and software coding of the algorithm so as to exploit special features of the hardware and avoid associated architecture shortcomings. This paper presents an investigation into the analysis and design mechanisms that will lead to reduction in the execution time in implementing real-time control algorithms. The proposed mechanisms are exemplified by means of one algorithm, which demonstrates their applicability to real-time applications. An active vibration control (AVC) algorithm for a flexible beam system simulated using the finite difference (FD) method is considered to demonstrate the effectiveness of the proposed methods. A comparative performance evaluation of the proposed design mechanisms is presented and discussed through a set of experiments.

No description available.

No / This paper presents an investigation into the impact of data dependencies in real-time high performance sequential and parallel processing. An adaptive active vibration control algorithm is considered to demonstrate the impact of data dependencies in real-time computing. The algorithm is analysed in detail to explore the inherent data dependencies. To minimize the impact of data dependencies, an investigation into reducing memory access in sequential computing is provided. The impact of data dependencies with various interconnections is also explored and demonstrated in real-time parallel processing through a set of experiments.

This paper presents an investigation into the impact of algorithm design for real-time active control systems. An active vibration control (AVC) algorithm for flexible beam systems is employed to demonstrate the critical design impact for real-time control applications. The AVC algorithm is analyzed, designed in various forms and implemented to explore the impact. Finally, a comparative real-time computing performance of the algorithms is presented and discussed to demonstrate the merits of different design mechanisms through a set of experiments.

A novel control method called orthogonal eigenstructure control is developed for active vibration cancellation in structures. Orthogonal eigenstructure control is a feedback control method applicable to multi-input multi-output linear systems. While the available control design methodologies offer a large and complex design space of options that can often overwhelm a designer, this control method offers a significant simplification of the design task while still allowing some experience-based design freedom. For example, eigenstructure assignment methods need definition of a desired eigenvector for the closed-loop system. The controller designer may also be required to do pole placement. Considering the fact that there are no one-to-one relationships between the elements of the closed-loop eigenvectors of a model and the states of the system, this effort could be inefficient for many practical systems. Moreover, for large-scale systems, defining or shaping the eigenstructures become a relatively difficult task. Orthogonal eigenstructure control is a state feedback-like control law that is relatively easy to design and implement to multiple-input multiple-output systems. It allows control engineers to achieve good performing designs even with little design experience, while the existing methods are highly dependent on designer experience. Orthogonal eigenstructure control is introduced and extended to be applicable to linear systems regardless of the number and location of the actuators and sensors. Also, the concept of progressive application of the proposed control method for increasing robustness is described. Finally, the result of application of the control method for vibration cancellation of a test plate is investigated through experiments for tonal and wideband disturbances. The results show a significant reduction of vibrations using the orthogonal eigenstructure control with relative ease in finding the control gain matrix. / Ph. D.

Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-05-26Bitstream added on 2014-06-13T19:55:33Z : No. of bitstreams: 1 galavotti_tv_me_ilha.pdf: 4073080 bytes, checksum: 0605ef5edb68c7bc2b71f8c976c0fe09 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nos últimos anos, as indústrias têm mostrado bastante interesse no desenvolvimento de novas técnicas para o controle de vibrações. O objetivo principal é atribuir valores aceitáveis das amplitudes de vibrações nos sistemas, garantindo um bom funcionamento dos mesmos e evitando falhas que provoquem paradas abruptas, mostrando-se uma área científica muito importante e que aproxima vários campos da engenharia moderna. Atualmente essa tecnologia é crescente e grande investimento tem sido aplicado no seu desenvolvimento. Este trabalho apresenta resultados obtidos para técnicas ativas e semi-ativas de controle de vibrações, considerando que as modificações estruturais são provenientes da alteração da rigidez e amortecimento. Utiliza-se para essa análise, Amortecedores Ativos Controlados por Atuadores Piezelétricos, denominados em inglês por Piezoelectric Friction Damper (PFD). A aplicação da metodologia é realizada em máquinas rotativas modeladas pelo Método dos Elementos Finitos e em um protótipo projetado e construído em laboratório. Os resultados procuram atenuar os níveis de vibrações e demonstram a viabilidade da aplicação de PFDs em estruturas. / Nowadays industries have shown great interest in developing new techniques for vibration control. The target is getting acceptable values of the amplitudes of vibrations in systems, ensuring proper working order avoiding failures. This is a scientific area of very important and approach fields of modern engineering. Currently this technology is growing and large investments has been applied in its development. This paper presents results obtained for active and semi-active techniques vibration control, where the structural changes are from the modification of stiffness and damping. It is used for this analysis a system known by Piezoelectric Friction Damper (PFD). The methodology was applied in rotating machines modeled by finite element method and in a prototype designed and built in the laboratory. The results try to mitigate the vibration levels and demonstrate the feasibility of applying PFDs in rotating machine.