Made available in DSpace on 2014-06-11T19:27:13Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-07-26Bitstream added on 2014-06-13T20:16:17Z : No. of bitstreams: 1 paschoal_ef_me_ilha.pdf: 1666225 bytes, checksum: c8e0ac9ef47b75399e16b35077ba6dac (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O presente trabalho tem como objetivo a aplicação da tecnologia de controle semi-ativo em suspensões veiculares, empregando amortecedores magnetoreológicos e controladores nebulosos. O princípio de funcionamento dos amortecedores magnetoreológicos é evidenciado a partir de um procedimento de identificação numérica onde os resultados obtidos pela técnica de modelagem apresentada são confrontados com dados experimentais coletados. O grande avanço experimentado pelos controladores nebulosos nos últimos anos tem aberto novas possibilidades de aplicação prática de tais controladores. O comportamento não linear dos amortecedores magnetoreológicos associado às variações paramétricas e não- linearidades presentes em modelos de suspensões veiculares são características que corroboram para o uso dos controladores nebulosos. A formulação básica para a análise e projeto destes controladores é discutida e analisada através de um conjunto de simulações numéricas efetuado para a avaliação da robustez, estabilidade e desempenho dos mesmos. A bancada experimental, constituída de um sistema de dois graus de liberdade contendo um amortecedor magnetoreológico, é apresentada e tem seus parâmetros principais identificados. Tal bancada é usada para comparar os resultados numéricos simulados com aqueles obtidos experimentalmente. O trabalho termina comentando as potencialidades da metodologia apresentada, discutindo as facilidades e dificuldades encontradas na sua implementação e aponta propostas para a sua continuidade / This work focus on the investigation of semi-active vibration control technology in vehicle suspensions by using magneto-rheological dampers and fuzzy controllers. The operation principle of magneto-rheological dampers is verified by a numerical identification procedure and the results obtained by the presented modeling techniques are compared with the experimental collected data. The great progress tried by the fuzzy controllers in the last years has been opening new possibilities of practical application for these controllers. The non- linear behavior of the magnetorheological dampers associated to the parametric variations and non-linearities on vehicle suspension models corroborate to the use of the fuzzy controllers. The fundamental formulation of this controller is discussed and its robustness, stability and performance are shown through numeric simulations. An experimental apparatus representing a two degree-of-freedom system containing a magnetorheological damper is used to identify the main parameters and to compare the previous simulation results. This work is concluded presenting the potentialities of the design methodology proposed and future developments to be implemented

A utilização de sistemas semi-ativos no controle de movimento e vibração vem crescendo muito nos últimos anos, e está se firmando como a opção mais econômica em muitas aplicações. Os sistemas de controle semi-ativos baseados em fluidos magneto-reológicos (MR) já são empregados no controle de vibrações desde máquinas de lavar a grandes pontes suspensas, e até mesmo no controle de vibração de edifícios sujeitos a abalos sísmicos. No controle de movimento, eles têm sido aplicados em aparelhos de fisioterapia, próteses de joelho humano e embreagens. No setor automobilístico, os sistemas semi-ativos são empregados em sistemas de controle da suspensão e sistemas anti-rolagem, e também no controle de sistemas de torque e tração. Visto a crescente importância dos sistemas de controle semi-ativo, este trabalho aborda este assunto dividindo-o em duas partes: a primeira, apresentada no volume 1, trata do projeto de atuadores magneto-reológicos e do seu modelamento dinâmico voltado para projetos de controle; e a segunda parte, apresentada no volume 2, trata de projeto de controladores para sistemas semi-ativos, mais especificamente voltados para o controle de suspensão veicular semi-ativa, buscando a melhoria do desempenho em conforto, segurança e dirigibilidade do veículo. Na primeira parte, a maior contribuição deste trabalho está em preencher uma lacuna na literatura no que diz respeito a uma técnica sistemática de projeto de atuadores magneto-reológicos e da forma mais adequada de sua representação dinâmica para projetos de controle, que é feita a partir de dados experimentais. Na segunda parte deste trabalho buscou-se desenvolver um sistema de controle economicamente viável para veículos utilitários (caminhonetes principalmente). Estes são os veículos que mais carecem de sistemas de suspensão capazes de atender a uma grande variedade de situações (variação de pista, variação de carga), e cujo mercado exige uma relação custo/benefício melhor que aquela dos mercados de carros de luxo, onde estes sistemas são empregados atualmente. Como resultados mais importantes deste trabalho têmse: uma proposição para o uso da lei de controle LQG/LTR em sistemas não estritamente próprios; um modelo de um veículo utilitário completo com sete graus de liberdade e capaz de representar as situações mais importantes do comportamento dinâmico deste tipo de veículo; o desenvolvimento de uma estratégia de controle robusto baseado na técnica LQG/LTR, adequada para trabalhar com atuadores semi-ativos, e que utiliza sensores de custo compatível com a aplicação. O sistema de controle proposto foi capaz de melhorar o desempenho em conforto e segurança, evitando situações de perda de aderência dos pneus e comportamentos dinâmicos indesejáveis destes veículos, que foi verificado experimentalmente e através de simulações em computador. / The application of semi-active systems to motion and vibration control has significantly grown during the last years, and it is becoming an economically viable option for several applications. Semi-active systems based on magneto-rheological (MR) fluids were applied to vibration control ranging from washing machines to suspended bridges, and also in vibration control of buildings under seismic tremors. Regarding the movement control, they have been used in gym apparati, human knee prosthesis and clutches. More specifically in the automotive industry, semi-active systems have been applied in suspension and anti-roll systems, and also in torque and traction control systems. This work treats this subject dividing it into two parts: the first one, presented in volume 1, deals with the design of semi-active actuators based on magneto-rheological fluids and dynamic modeling; and the second one, presented in volume 2, deals with the design of semi-active control for vehicular suspension systems. The control main objective is the performance improvement in comfort, safety and handling features of a vehicle. In the first part, the main contribution of this work is to fulfill a literature gap regarding a systematic procedure for design of magneto-rheological actuators and to find a better representation for the dynamic behavior regarding the control system development, which is done based on experimental data analysis. The second part of this work leaded with the development of a vehicular suspension system for utility vehicles (for SUVs, and mainly for light trucks), which need suspension systems able to face a great number of situations (road variation, load variation, etc.), and which present stability problems due to its high gravity center height. Important results of this work are: the development of a robust control strategy based on LQG/LTR techniques for non-strictly proper systems, the development of a dynamic model for light trucks and SUVs with seven degrees of freedom; the development of a robust control strategy based on the LQG/LTR synthesis, suit to work with semi-active actuators, and using sensors with costs compatible to the application. The proposed control system was able to improve the performance of comfort and safety, avoiding the loss of adherence between tires and the ground and other undesirable dynamic behaviors of these vehicles, that was verified experimentally and through computer simulations.

Many devices are available on the market for the evaluation and rehabilitation of patients suffering from muscular disorders. Most of them are small, low-cost, passive devices based on the use of springs and resistive elements and exhibit very limited (or even not any) evaluation capabilities; extended muscular force evaluation is only possible on stationary, expensive, multi-purpose devices, available only in hospitals, which offer many exercise modes (e.g. isokinetic mode) that are not available on other devices.<p><p>The objective of this thesis is to make the functionalities currently only implemented on bulky multi-purpose devices available at a lower cost and in a portable fashion, enabling their use by a large number of independent practitioners and patients, even at home (tele-medecine applications).<p><p>In order to achieve this goal, a portable rehabilitation device, using a magneto-rheological fluid brake as actuator, has been designed. This particular technology was selected for its high level of compactness, simple mechanical design, high controllability, smooth and safe operation. The first part of this thesis is devoted to the design of MR-fluid brakes and their experimental validation. The second part is dedicated to the design of the rehabilitation device and the comparison of its performances with a commercial multi-purpose device (CYBEX). / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Magnetoactive elastomers (MAEs) are polymer composites containing magnetically soft or hard particles incorporated into an elastomer matrix during the crosslinking procedure. In the presence of a magnetic field, the induced magnetic interactions and the corresponding particle rearrangements significantly alter the mechanical properties in dependence on the initial particle distribution and sample shape. In addition, applying magnetic fields also changes the macroscopic shape of an MAE. This thesis investigates the magneto-mechanical coupled behaviour of MAEs by means of analytical and numerical methods. The effects of particle distribution and sample shape have been studied with the help of a physically motivated model of MAEs that considers dipole-dipole interactions between magnetizable particles. The presence of a magnetic field leads to a mechanical anisotropy in MAEs with isotropic particle distribution, and the induced anisotropy is directed along the orientation of the field. Thus, MAEs exhibit direction-dependent mechanical properties with distinct elastic moduli along and perpendicular to the field direction when the MAE sample is subjected to uniaxial deformation. A good agreement is reported between the physically motivated approach and conventional transversely isotropic material models. Furthermore, we investigate the important interplay between the particle distribution and the sample shape of MAEs, where a simple analytical expression is derived based on geometrical arguments to describe the particle distribution inside MAEs. We show that the enhancement of elastic moduli arises not only from the induced dipole-dipole interactions but also considerably from the change in the particle microstructure. Moreover, the magneto-mechanical behaviour of isotropic MAEs under shear deformations is studied. Three principal geometries of shear deformation are investigated with respect to the orientation of the applied magnetic field. We show that the Cauchy stress tensor of MAEs is not always symmetric due to the generation of a magnetic torque acting on an anisometric MAE sample under shear loadings. The theoretical study of magneto-mechanical behaviour of MAEs confirms that the effect of sample shape is quite significant and cannot be neglected. On the other hand, the initial particle distribution and presumed rearrangements due to the magnetic field additionally influence the material response of MAEs. Finally, the physically motivated model of MAEs could be transformed into an invariants-based model enabling its implementation in commercial finite element software. Therefore, we have uncovered a new pathway to model MAEs based on dipole-dipole interactions, leading to a constitutive relation analogous to the macro-scale continuum approach and revealing a synergy between both modelling strategies.

This study of adaptable vibration isolating mounts sets out to capture the uniqueness of magnetorheological (MR) fluid's variable viscosity rate, and to physically alter the damping and stiffness when used inside an elastomeric mount. Apparent variable viscosity or rheology of the MR fluid has dependency on the application of a magnetic field. Therefore, this study also intends to look at the design of a compact magnetic field generator which magnetizes the MR fluid to activate different stiffness and damping levels within the isolator to create an adaptable and tunable feature. To achieve this adaptable isolator mount, a mold will be fabricated to construct the mounts. A process will then be devised to manufacture the mounts and place MR fluid inside the mount for later compatibility with the magnetic field generator. This process will then produce an MR fluid-elastic mount. Additionally for comparative purposes, passive mounts will be manufactured with a soft rubber casing and an assortment of metal and non-metal inserts. Next, the design of the magnetic field generator will be modeled using FEA magnetic software and then constructed. Stiffness or force/displacement measurements will then be analyzed from testing the isolator mount and magnetic field generator on a state-of-the-art vibration dynamometer. To vary the magnetic flux through the mount, an electro-magnet is used. To analyze the results, a frequency method of the stiffness will be used to show the isolators adaptation to various increments of magnetic flux over the sinusoidal input displacement frequencies. This frequency response of the stiffness will then be converted into a modeling technique to capture the essence of the dynamics from activating the MR fluid within the isolator mount. With this methodology for studying the adaptability of an MR fluid-elastic mount, the stiffness increases are dependent on the level of magnetic field intensity provided from the supplied electro-magnet. When the electro-magnet current supply is increased from 0.0 to 2.0 Amps, the mount stiffness magnitude increase is 78% in one of the MR fluid-elastic mounts. Through comparison, this MR fluid-elastic mount at off-state with zero magnetic field is similar to a mount made of solid rubber with a hardness of 30 Shore A. With 2 Amps of current, however, the MR fluid-elastic mount has a higher stiffness magnitude than a rubber mount and resembles a rubber casing with a steel insert. Moreover, when the current in the electro-magnet is increased from 0.0 to 2.0 Amps the equivalent damping coefficient in a MR fluid-elastic mount increases over 500% of the value at 0 Amps at low frequency. Through damping comparisons, the MR fluid-elastic mount with no current is similar to that of a mount made of solid rubber with a hardness of 30 Shore A. At full current in the electromagnet, however, the damping in the MR fluid-elastic mount is greater than any of the comparative mounts in this study. Therefore, the results show that the MR fluid-elastic mount can provide a wide range of stiffness and damping variation for real-time embedded applications. Since many aerospace and automotive applications use passive isolators as engine mounts in secondary suspensions to reduce transmitted forces at cruise speed, the MR fluid-elastic mount could be substituted to reduce transmitted forces over a wider range of speeds. Additionally, this compact MR fluid-elastic mount system could be easily adapted to many packaging constraints in those applications. / Master of Science

Since their invention in the early 1900s, Tuned Vibration Absorbers (TVAs) have shown to be effective in suppressing vibrations of machines and structures. A vibration absorber is a vibratory subsystem attached to a primary system. It normally consists of a mass, a spring, and a damper. Mounted to the primary system, a TVA counteracts the motions of the primary system, "absorbing" the primary structure's vibrations. A conventional passive TVA, however, is only effective when it is tuned properly, hence, the name "tuned" vibration absorber. In many practical applications, inevitable off-tuning (or mistuning) of a TVA occurs because of the system's operating conditions or parameter changes over time. For example, the mass in a building floor could change by moving furnishings, people gathering, etc., which can "off-tune" TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. Moreover, the off-tuned TVAs can excessively amplify the vibration levels of the primary structures; therefore, not only rendering the TVA useless but also possibly causing damage to the structures. Off-tuning is one of the major problems of conventional passive TVAs. This study proposes a novel semiactive TVA, which strives to combine the best features of passive and active TVA systems. The semiactive TVA in this study includes a Magneto-Rheological (MR) damper that is used as a controllable damping element, for providing the real-time adjustability that is needed for improving the TVA performance. This study is conducted in two phases. The first phase provides a numerical investigation on a two-degree-of-freedom (2-DOF) numerical model in which the primary structure is coupled with a TVA. The numerical investigation considers four semiactive control methods for the MR TVAs, in addition to an equivalent passive TVA. These numerical models are optimally tuned using numerical optimization techniques to compare each TVA system. These tuned systems then serve as the basis for numerical parametric studies for further evaluation of their dynamic performance. The parametric study covers the effects of damping, as well as system parameter variations (off-tuning). The results indicates that semiactive TVAs are more effective in reducing the maximum vibrations of the primary structure and are more robust when subjected to off-tuning. Additionally, the numerical study identifies the "On-off Displacement-Based Groundhook control (on-off DBG)" as the most suitable control method for the semiactive TVA among control methods considered in this study. For the second phase of this study, an experimental study is performed on a test setup, which represents a 2-DOF structure model coupled with an MR TVA. Using this setup, a series of tests are conducted in the same manner as the numerical study to evaluate the performance of the semiactive TVA. The primary purposes of the experiment are to further evaluate the most promising semiactive control methods and to serve as a "proof-of-concept" of the effectiveness of this MR TVA for floor vibration applications. The results indicate that the semiactive TVA with displacement-based groundhook control outperforms the equivalent passive TVA in reducing the maximum vibrations of the primary structure. This confirms the numerical result that identifies on-off DBG control method as the "best" control method for the MR TVA among four semiactive control schemes considered. The experimental robustness study is also conducted, focusing on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changes (mass off-tuning). The mass of the primary system varied from -23 % to +23 % of its nominal value by adding and removing external masses. The experimental results show that the semiactive TVA is more robust to changes in the primary mass than the passive TVA. These results justify the benefits of the use of semiactive MR TVAs in structures, such as building floor systems. The off-tuning analysis further suggests that, in practice, semiactive TVAs should be tuned slightly less than their optimum in order to compensate for any added masses to the structure. Additionally, the lessons learned from the experimental study have paved the way for implementing the semiactive MR TVA on a test floor, which is currently in progress under a separate study. / Ph. D.

Fenômenos aeroelásticos podem levar à drástica redução na vida útil de uma aeronave ou ainda resultam em danos severos à estrutura. Para manter as respostas dinâmicas em níveis aceitáveis técnicas como as estruturas adaptativas têm sido aplicadas. Este conceito explora a integração entre os elementos ativos (atuadores e sensores) e o controlador à estrutura. Dentre os materiais próprios para uso em estruturas adaptativas estão os fluidos eletro-reológicos e magneto-reológicos que tem se mostrado como um dos mais promissores materiais ativos. Estes materiais apresentam rápidas mudanças nas suas propriedades reológicas devido à ação de um campo elétrico ou magnético. Para sua incorporação em uma estrutura é utilizada uma viga sanduíche que tem seu comportamento dinâmico modelado através do método GHM para incorporar a dependência da freqüência dos fluidos ER/MR em um modelo estrutural no domínio do tempo. Através do acoplamento deste modelo com o método da malha de vórtices, é possível estudar a resposta aeroelástica temporal. Também é analisada a eficiência dos fluidos ER/MR no atraso da ocorrência de flutter. Isto é feito com o auxílio do método PK que determina a velocidade crítica de flutter. / Aeroelastic phenomena can lead to a drastic reduction in the fatigue life of aircraft or result in severe structural damage. To keep the dynamical responses at acceptable levels techniques such as the so-called adaptive structures have been adopted. This approach integrates active elements and controllers (actuators and sensors) to the structure. Among the materials suitable for adaptive structures are the electro-rheological (ER) and magneto-rheological fluids which are some of the most promising active materials. This kind of materials presents change in their rheological properties due to action of an external field, such as electrical or magnetic. In order to integrate these kind of fluids in the structure a sandwich beam with ER/MR fluids core is studied. The dynamical behaviour is modelled through a GHM method to incorporate the frequency dependence of the ER/MR fluids in a structural time domain model. By coupling this model to a vortex lattice model, it is possible to study the aeroelastic response in time domain. The ER/MR fluids efficiency to delay the flutter occurrence is also studied by using a PK-method that determines a critical velocity of flutter.

Fenômenos aeroelásticos podem levar à drástica redução na vida útil de uma aeronave ou ainda resultam em danos severos à estrutura. Para manter as respostas dinâmicas em níveis aceitáveis técnicas como as estruturas adaptativas têm sido aplicadas. Este conceito explora a integração entre os elementos ativos (atuadores e sensores) e o controlador à estrutura. Dentre os materiais próprios para uso em estruturas adaptativas estão os fluidos eletro-reológicos e magneto-reológicos que tem se mostrado como um dos mais promissores materiais ativos. Estes materiais apresentam rápidas mudanças nas suas propriedades reológicas devido à ação de um campo elétrico ou magnético. Para sua incorporação em uma estrutura é utilizada uma viga sanduíche que tem seu comportamento dinâmico modelado através do método GHM para incorporar a dependência da freqüência dos fluidos ER/MR em um modelo estrutural no domínio do tempo. Através do acoplamento deste modelo com o método da malha de vórtices, é possível estudar a resposta aeroelástica temporal. Também é analisada a eficiência dos fluidos ER/MR no atraso da ocorrência de flutter. Isto é feito com o auxílio do método PK que determina a velocidade crítica de flutter. / Aeroelastic phenomena can lead to a drastic reduction in the fatigue life of aircraft or result in severe structural damage. To keep the dynamical responses at acceptable levels techniques such as the so-called adaptive structures have been adopted. This approach integrates active elements and controllers (actuators and sensors) to the structure. Among the materials suitable for adaptive structures are the electro-rheological (ER) and magneto-rheological fluids which are some of the most promising active materials. This kind of materials presents change in their rheological properties due to action of an external field, such as electrical or magnetic. In order to integrate these kind of fluids in the structure a sandwich beam with ER/MR fluids core is studied. The dynamical behaviour is modelled through a GHM method to incorporate the frequency dependence of the ER/MR fluids in a structural time domain model. By coupling this model to a vortex lattice model, it is possible to study the aeroelastic response in time domain. The ER/MR fluids efficiency to delay the flutter occurrence is also studied by using a PK-method that determines a critical velocity of flutter.