Numerical and Experimental Modal Control of Flexible Rotor Using Electromagnetic Actuator

The present work is dedicated to active modal control applied to flexible rotors. The effectiveness of the corresponding techniques for controlling a flexible rotor is tested numerically and experimentally. Two different approaches are used to determine the appropriate controllers. The first uses the linear quadratic regulator and the second approach is the fuzzy modal control. This paper is focused on the electromagnetic actuator, which in this case is part of a hybrid bearing. Due to numerical reasons it was necessary to reduce the size of the model of the rotating system so that the design of the controllers and estimator could be performed. The role of the Kalman estimator in the present contribution is to estimate the modal states of the system and to determine the displacement of the rotor at the position of the hybrid bearing. Finally, numerical and experimental results demonstrate the success of the methodology conveyed

Monitoramento da Integridade Estrutural de uma laje de concreto utilizando transformadas de wavelet

This paper describes the methodology to locate the damage area on the concrete slab structure. The damaged structure is numerically simulated using the Finite Element Method (FEM). The vertical displacement signal has obtained is using for location of the damage area position employing the Discrete Wavelet Transform (DWT). The mother wavelets studied were: Daubechies, Symlets and ReverseBior. The damage on the slab is numerically simulated as one stiffness reduction in the concrete and the displacement signal obtained from the static analysis is interpolated and then amplified by means of the Tikhonov regularization. The finite element is quadrilateral with corner nodes only and each node has six degrees of freedom per node, i.e. three translations and three rotations. The calibration of Tikhonov regularization parameters bj is important to amplify and smooth the perturbations of wavelet coefficients graphs. In addition, all the mother wavelets available in this paper have being able to identify the damage. Results suggest when the damage reduces the concrete modulus of elasticity more than 20% it is only necessary the knowledge of signal of damage structure to detect the damaged area position. For the smaller damage values it is required to know the different between the displacement signals about the undamaged and damaged structure.A presente contribuição utiliza uma metodologia para localizar danos em um sistema estrutural do tipo laje de concreto empregando transformadas de Wavelet. Esse sistema estrutural é modelado numericamente empregando o Método dos Elementos Finitos (MEF). O sinal da deflexão vertical da laje danificada é utilizado na localização da posição do dano empregando a transformada discreta de wavelet (TDW). As wavelets mães estudadas foram a: Daubechies, Symlets e ReverseBior. O tipo de dano implementado é dado sob a forma de perda localizada da rigidez do concreto da laje utilizando uma variável escalar de dano D. O sinal da deflexão, obtido na análise estática da laje, é interpolado e depois ampliado empregando a regularização de Tikhonov antes de ser transformado. O elemento finito utilizado na modelagem da laje apresenta quatro nós e seis graus de liberdade por nó, sendo três translações e três rotações. A calibração dos parâmetros bj da regularização de Tikhonov mostrou-se fundamental para amplificar e suavizar as perturbações nos gráficos dos coeficientes de wavelet. Além disso, todas as wavelets mães avaliadas foram capazes de identificar o dano proposto. Entretanto, quando a variável escalar de dano é maior ou igual a 0,20, somente o sinal da estrutura na condição danificada foi necessário para detectar a posição do dano. Já, para valores de dano menores que 0,20, foi necessário o emprego do sinal da diferença, obtido entre as condições da estrutura sem e com dano

Vibration control of rotating machines using electromagnetic actuators

The aim of the present work is the study of active vibration control of flexible rotors using electromagnetic actuators. For this purpose, a flexible rotor was considered and modeled by using the Finite Element Method. As the original rotor model presents a high number of degrees of freedom, the Pseudo-Modal Method was used for reducing the size of the model. The design of the controllers used two different approaches. The architecture of the first one is based on the H∞ norm and Optimal Control, so that both methods were developed by using Linear Matrix Inequalities. The advantage of the LMIs is that they are able to take into account parameter uncertainties. In the second approach, the architecture of the controllers was developed by using Fuzzy Logic techniques. In these two approaches the controllers were designed in the modal domain. The advantage of the modal contol is that the controllers can be designed using small number vibration modes of the system, thus contributing to reduce the computational cost. In the modal control, the modal states are not directly accessible from the experiment. For determining the mode estimates, the Kalman estimation technique (Kalman Filter) was employed. The advantage of this estimator is its ability in determining the modes from noisy signals. Regarding the electromagnetic actuators, they have nonlinear behavior; the corresponding nonlinear problem is solved by using the inverse model of the actuators. The developed methodology was analyzed both numerically and experimentally.The performance of the controllers was tested under several conditions for the operation of the rotor. The obtained results, both numerical and experimental, demonstrate the success of the methodology conveyed and its great potential for the active vibration control of flexible rotors, in the context of the so-called smart rotors.Fundação de Amparo a Pesquisa do Estado de Minas GeraisDoutor em Engenharia MecânicaO presente trabalho tem por objetivo o estudo de controle ativo de vibrações em rotores flexíveis utilizando atuadores eletromagnéticos. Dentro deste contexto, foi estudado um rotor flexível que foi modelado empregando o Método dos Elementos Finitos. Como o modelo original do rotor possui um elevado número de graus de liberdade, foi necessário reduzir tal modelo, sendo utilizado para isto o Método Pseudo-Modal. O projeto dos controladores foi realizado utilizando duas diferentes abordagens. A primeira abordagem envolve controladores projetados via norma H∞ e Controle Ótimo, sendo que ambos os casos foram desenvolvidos utilizando desigualdades matriciais, técnica que facilita a inclusão de incertezas no projeto do controlador. Na segunda abordagem, os controladores foram desenvolvidos utilizando a Lógica Nebulosa (Fuzzy). Nestas duas abordagens os controladores foram projetados no domínio modal. A vantagem de se utilizar a metodologia de controle modal é que os controladores são projetados com base apenas em poucos modos de vibração do sistema, aspecto que, dentre suas vantagens, contribui para a redução do custo computacional. Neste tipo de controle, nem sempre os estados modais são acessíveis experimentalmente, exigindo, portanto, sua estimação. Com este propósito foram utilizados estimadores de Kalman (Filtro de Kalman), os quais apresentam como ponto positivo sua capacidade de estimação a partir de um sinal contendo ruído. Com relação aos atuadores eletromagnéticos, que são não lineares, o problema da não linearidade é resolvido a partir do emprego do modelo inverso dos atuadores. A metodologia desenvolvida foi analisada tanto no âmbito numérico como no experimental. O desempenho dos controladores foi testado para diversas condições de funcionamento do rotor. Os resultados obtidos, tanto numéricos como experimentais, mostram o sucesso da metodologia empregada e as potencialidades do uso do tipo de atuador aqui empregado no campo do controle ativo de vibração de rotores, considerando os chamados rotores inteligentes

Diagnose de falhas em sistemas rotativos com excitações desconhecidas, através da metodologia dos observadores de estado

Neste trabalho desenvolveu-se uma metodologia de detecção e localização de falhas via observadores de estado projetados via LQR (Regulador Linear Quadrático) e LMIs (Desigualdades Matriciais Lineares) em sistema rotativo considerando-se suas fundações e excitações desconhecidas. A necessidade de desenvolver novas técnicas de prevenção de falhas vem da preocupação das indústrias com o bom funcionamento de seus equipamentos a fim de evitar paradas repentinas no processo produtivo. A metodologia dos observadores de estado consiste em utilizar sua capacidade de estimar estados não medidos. Assim, projeta-se um banco de observadores de estado, sendo que cada um é robusto a um determinado parâmetro sujeito a falha. Quanto à identificação de forças de excitação, durante os últimos anos, vários métodos têm sido propostos, embora nenhum deles possa ser considerado como sendo universalmente adequado a todas as situações. Neste trabalho foram utilizadas metodologias utilizando funções ortogonais de Fourier, Legendre e Chebyshev para a identificação das excitações desconhecidas. Para verificar a validade da metodologia desenvolvida tanto para a identificação de forças como detecção e localização de falhas foram simulados dois sistemas mecânicos: sistema massa-mola-amortecedor de 4 gdl (graus de liberdade) e sistema rotativo considerando-se suas fundações. Por fim, foi realizada a comprovação experimental, utilizando para isto um sistema rotativo pertencente ao laboratório de vibrações mecânicas do Departamento de Engenharia Mecânica da Faculdade de Engenharia, Campus de Ilha SolteiraIn this work a methodology for faults detection and location in rotative system considering its foundation and unknown inputs was developed using state observers designed by LQR (Linear Quadratic Regulator) and LMIs (Linear Matrix Inequalities). The necessity of design new techniques of faults prevention proceeds from concerns of industries with the good worked of its equipments in order to avoid suddenly stopped in the productive process. The methodology of state observers consists to use its capacity to esteem the states not measured. So, it projects a bank of state observes, being that everyone is robust a parameter subject a fault. As at excitation forces identification, during last years, many methods have been proposed, however no one of them can be considered as universally adequate for every situation, being that in this work the methodologies using orthogonal functions of Fourier, Legendre and Chebyshev were used for unknown inputs identification. To validate the methodology two mechanicals systems were simulated: system mass-spring-damper of 4 dof (degree of freedom) and rotative system considering its foundations. At the end, the experimental proof was realized, using for this a rotative system in the mechanical vibrations laboratory at Ilha Solteira’s Mechanical Engineering DepartmentFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Structure-control optimal design of 6-DOF fully parallel robot

International audienceThis contribution aims at introducing an optimal design methodology for the Stewart Platform robot that considers structure and control design variables simultaneously. This methodology intends to maximize the positioning accuracy in order to optimize the overall performance of the robot for a specific task. The structure design variables of the mechanism combined with the gains of the controller are the structure-control design variables, this global set is considered simultaneously in the optimal design methodology. A position control scheme, based on a PD controller, and the complete dynamics of the robot are considered to compute the overall tracking position as function of the structure-control design variables. A sensitivity analysis is performed to evaluate the effect of the structure-control design variables on the tracking position accuracy of the robot. The associated optimization problem is solved by using metaheuristic optimization methods. Simulation results demonstrate that the proposed design procedure is effective to increase the positioning accuracy, as well as to improve the closed loop dynamics performance of the robot

Design of a state observer using decay rate LMI constraints for fault detection in mechanical systems

Nowadays, one of the most important concerns for many companies is to maintain the operation of their systems without sudden equipment break down. Because of this, new techniques for fault detection and location in mechanical systems subject to dynamic loads have been developed. This paper studies of the influence of the decay rate in the design of state observers using LMI for fault detection in mechanical systems. This influence is analyzed by the performance index proposed by Huh and Stein for the condition of a state observer. An example is presented to illustrate the methodology discussed

Uncertainty analysis of flexible rotors considering fuzzy parameters and fuzzy-random parameters

Abstract The components of flexible rotors are subjected to uncertainties. The main sources of uncertainties include the variation of mechanical properties. This contribution aims at analyzing the dynamics of flexible rotors under uncertain parameters modeled as fuzzy and fuzzy random variables. The uncertainty analysis encompasses the modeling of uncertain parameters and the numerical simulation of the corresponding flexible rotor model by using an approach based on fuzzy dynamic analysis. The numerical simulation is accomplished by mapping the fuzzy parameters of the deterministic flexible rotor model. Thereby, the flexible rotor is modeled by using both the Fuzzy Finite Element Method and the Fuzzy Stochastic Finite Element Method. Numerical simulations illustrate the methodology conveyed in terms of orbits and frequency response functions subject to uncertain parameters

Vibration Attenuation in Rotating Machines Using Smart Spring Mechanism

This paper proposes a semiactive vibration control technique dedicated to a rotating machine passing by its critical speed during the transient rotation, by using a Smart Spring Mechanism (SSM). SSM is a patented concept that, using an indirect piezoelectric (PZT) stack actuation, changes the stiffness characteristics of one or more rotating machine bearings to suppress high vibration amplitudes. A Genetic Algorithm (GA) optimization technique is used to determine the best design of the SSM parameters with respect to performance indexes associated with the control efficiency. Additionally, the concept of ecologically correct systems is incorporated to this work including the PZT stack energy consumption in the indexes considered for the optimization process. Simulation carried out on Finite Element Method (FEM) model suggested the feasibility of the SSM for vibration attenuation of rotors for different operating conditions and demonstrated the possibility of incorporating SSM devices to develop high-performance ecologic control systems.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Optimization of parameters of a modal active control in a beam of composite material

The present work proposes the active vibration control in a beam of composite material, using electromagnetic actuators, in order to obtain a reduction in the response of the displacement of the system associated to a reduction in energy consumption. The control theory used was the linear quadratic regulator solved by linear matrix inequalities. The electromagnetic actuator was then linearized using a methodology similar to that used in magnetic bearings. The work also proposes to study the optimization of parameters applied in this active control, by means of the heuristic optimization methods. From numerical simulations, the system´s response was obtained in the time domain that demonstrated the efficiency of the proposed technique in the active control of vibrations