Thesis (M.A.)--University of Hong Kong, 2001. / Includes bibliographical references. Also available in print.

L’étude des silicates fondus présente un intérêt dans divers domaines de recherche comme la géologie ou la fabrication des verres avec des applications technologiques importantes telles que par exemple, le confinement des déchets nucléaires. Ces recherches demandent des informations fondamentales sur la structure et la dynamique de ces liquides au niveau microscopique mais l’acquisition des données est très souvent limitée par les températures de fusion élevées des composés étudiés. Notre travail s’est donc basé sur l’utilisation de techniques sans contact afin de s’affranchir de cette difficulté. Dans le cadre de cette thèse, nous nous sommes intéressés à l’étude des propriétés structurales et dynamiques de divers aluminosilicates de calcium (CAS) fondus. Pour cela, nous avons développé un dispositif utilisant la lévitation aérodynamique afin d’effectuer des expériences de diffusion quasi-élastique des neutrons. En combinant ces mesures avec la diffusion inélastique des rayons X, nous avons pu obtenir des résultats sur la dynamique microscopique des CAS à l’état liquide ainsi que dans le régime de surfusion. En particulier, nous avons pu déterminer l’évolution de la viscosité avec la température et les coefficients de diffusion cohérents. Nous avons pu aussi étudier l’évolution de la dynamique de ces verres en fonction de l’augmentation de la quantité de silice dans la composition. En parallèle de nos travaux sur la dynamique, nous avons aussi réalisé des expériences de diffraction de neutrons et de rayons X sur les mêmes compositions et températures afin d’examiner l’ordre atomique local et essayer de le corréler aux propriétés dynamiques observées. / Because of their interesting properties as glass-forming systems, molten silicates play an important role in the geology of the Earth’s crust and mantle and are also of industrial interest for nuclear waste treatment. Research in these areas requires fundamental information on the microscopic structure and dynamics of silicate melts, but such measurements are hampered by the very high melting points of these systems. By extending the technique of aerodynamic levitation to inelastic neutron scattering, and also making use of inelastic synchrotron x-ray scattering, we have obtained results on the microscopic dynamics of silicates both above the melting point and in the supercooled regime. In particular, we have determined the temperature evolution of the viscosity and diffusion coefficient of calcium aluminosilicates, and thereby quantified the decrease in fragility of this glass-forming system as a function of increasing silica content. In parallel with our dynamical studies, we have performed x-ray and neutron diffraction experiments on the same compositions and temperatures in order to examine the local chemical order pertinent to the observed dynamical properties.

Acoustic levitation is a method which uses sound radiation to suspend matter in a medium. The main use of this phenomenon is for the contactless processing of matter, allowing to manipulate small objects without any solid contact. Contactless processing of matter presents many advantages in, for example, the fabrication of MEMS (microelectromechanical systems) where handling the components is challenging because of their fragile and surface-sensitive characteristics or in the chemical/biological industry when handling high-purity or hazardous materials. Thus, a new device for noncontact linear transportation of small solid objects is presented here. In this device, ultrasonic flexural vibrations are generated along the ring shaped vibrator using two Langevin transducers and by using a reflector parallel to the vibrator, small particles are trapped at the nodal points of the resulting acoustic standing wave. The particles are then moved by generating a traveling wave along the vibrator, which can be done by modulating the vibration amplitude of the transducers. The working principle of the traveling wave along the vibrator has been modeled by the superposition of two orthogonal standing waves, and the position of the particles can be predicted by using finite element analysis of the vibrator and the resulting acoustic field. A prototype consisting of a 3 mm thick, 220 mm long, 50 mm wide and 52 mm radius aluminum ring-type vibrator and a reflector of the same length and width was built and small polystyrene spheres have been successfully transported along the straight parts of the vibrator. / Levitação acústica é um método para suspender matéria em um meio através de pressão de radiação acústica gerada por intensas ondas de som. O principal uso desse fenômeno é na manipulação de partículas sem contato solido. Esse fenômeno tem várias aplicações para pesquisas onde deve ser evitado todo o contato como, por exemplo, na área de biologia, química, e na fabricação de MEMS. Assim, um novo sistema de transporte linear de partículas por levitação acústica está apresentado aqui. Nesse sistema, vibrações flexurais estão geradas em uma placa tipo anel com dois transdutores tipo Langevin, e colocando um refletor paralelo ao oscilador, partículas estão presas no pontos nodais da onda acústica gerada. As partículas estão deslocadas modulando a amplitude dos transdutores. Assim, este trabalho tem como objetivos a modelagem do fenômeno de levitação acústica, o dimensionamento de um protótipo de sistema de transporte linear de partículas por levitação acústica, bem como a fabricação e o controle desse protótipo. Um protótipo consistindo de uma estrutura tipo anel de alumínio de 3 mm de espessura, 220 mm de comprimento e um raio de 52 mm foi fabricado e o transporte de pequenas esferas de isopor foi realizado com êxito nas parte retas do vibrador.

Many electrically propelled, and magnetically levitated and guided actuation systems (maglev) use either linear induction or synchronous machine topologies. From the cost, reliability, fault tolerance, and phase independence points of view, linear switched reluctance topologies are attractive for transportation application. This thesis investigates a novel topology in which a linear switched reluctance machine (LSRM) propulsion drive is incorporated in the magnetically levitated and guided vehicle. Designs of the LSRM and dc electromagnet, analytical aspects of modeling and dynamics of the vehicle, and closed loop control of propulsion, levitation, and guidance systems are discussed with comprehensive simulations and experimental results. Due to the lack of standard design procedure for LSRM, a novel design procedure is proposed using the current knowledge and design procedure of rotating switched reluctance machines. Analysis procedures for the phase winding inductance, propulsion and normal forces with translator position are developed with a lumped-parameter magnetic circuit model and the results from it are verified with two-dimensional finite element analysis. Extensive experimental correlation of inductance, propulsion and normal forces to validate the analysis and design procedure is presented. For the stable operation of the electromagnetic levitation and guidance systems, which have inherent unstable characteristics, the air gap position and force/current control loops are designed using PID (or PD) and PI controllers, respectively, and implemented and tested. The step-by-step design procedures for each controller are systematically derived. A feedforward compensation strategy for the levitation air gap control is proposed to reject the external force disturbance mainly caused by the normal force component generated in the LSRM propulsion drive system. The reduction of mechanical vibration and hence the enhancement of ride quality is achieved. Extensive dynamic simulations and experimental results for the integrated maglev system are presented with a 6 m long prototype system. Experimental correlation proves the validity of the controller design procedure based on the single-input and single-output model, and shows the feasibility of the LSRM-propelled electromagnetic levitation and guidance systems. A novel maglev topology in which only two sets of LSRMs are utilized to control individually propulsion, levitation, and guidance forces is proposed. One set of the linear switched reluctance actuator produces the levitation and propulsion forces and the other set generates the propulsion and guidance forces. The proposed architecture, thereby, obviates the need for design, development, and implementation of separate actuation systems for individual control of propulsion, levitation, and guidance forces and in contrast to most of the present practice. Further, the proposed system utilizes each of the linear switched reluctance actuation system for producing the propulsion force, thereby giving an overall high force density package for the entire system. The feasibility of the proposed system by finite element analysis is demonstrated. / Ph. D.

No description available.

Electromagnetic levitation has been commonly researched for the use in ground transit systems. It is ideal for high-speed applications that require low friction. The principle is simple, use electromagnetic force to balance the force imposed by gravity. However, for attractive levitation the system is unstable and nonlinear. Two dominant approaches to this problem have been to use a state feedback control system or a simple linear PID compensated control architecture. State feedback is a well-known control technique, but is complicated to implement and can rely on linearization of the system dynamics. The simple PID control structure is very easy to implement, but can have severe performance degradation in the presence of noise. This system can usually be identified by its large acoustic noise. This is primarily due to the differential term in the controller. This thesis proposes a solution that uses two concepts: Current Command Generation (CCG) and a closed velocity loop. CCG linearizes the control structure by utilizing the known magnetic properties of the system to convert a desired force to a current for any given air gap. This removes squared command terms from the control structure. This allows for a reliable and predictable implementation of linear feedback control systems. The PID implementation of an attractive levitation system uses two control loops. The inner loop is a current controller, which receives current commands from the outer position loop. The proposed control architecture uses three loops. The innermost loop is the current controller, which receives current commands for the CCG. The middle loop is a velocity controller, which receives commands from the position (outer most) loop and produces force command output used as inputs to the CCG. The three loops consist of two Proportional Integral (PI) controllers for the current and velocity controllers and a Proportional (P) controller. There is no derivative term, making the proposed solution's performance far less dependent on noise. This architecture removes the necessity of nonlinear elements in the control architectures and improves noise rejection through the use of the velocity loop. The acoustic noise performance of this system is enhanced by both of these methodologies and is shown in the experimental setup. / Master of Science

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 268-278). Also available via the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

O controle e otimização da operação da suspensão eletromagnética de um protótipo de veículo MAGLEV são apresentados neste trabalho. Este tipo de sistema é inerentemente instável e altamente não linear, sendo um excelente exemplo para o estudo e comparação de diferentes metodologias de controle. Nos últimos anos, experiências significativas com veículos levitados têm ganhado força. A arquitetura do veículo consiste de quatro atuadores eletromagnéticos, quatro sensores de entreferros e quatro acelerômetros, todos instalados nos cantos do veículo. A dinâmica do sistema é descrita através de três modelos matemáticos diferentes: modelo de corpo rígido com três graus de liberdade (movimentos vertical, de rolagem e de arfagem), modelo de corpo não rígido, onde está presente mais um grau de liberdade (movimento de torção), e modelo SISO com quatro movimentos verticais independentes. Blocos de compatibilização de variáveis são utilizados devido à diferença no número de variáveis do modelo matemático com o número de variáveis medidas e de atuação disponíveis no veículo. Os acelerômetros, usados para estimar as velocidades do veículo, foram instalados com o objetivo de estudar-se o controle ótimo da suspensão por realimentação de estados com o emprego da técnica do Regulador Linear Quadrático (RLQ) e utilização do método do lugar das raízes para definição dos pólos de malha fechada. Para efeito de comparação foi implementado um controle H'IND.2'/H'INFINITO' por realimentação da saída. Controladores independentes para cada grau de liberdade foram simulados no software MATLAB e depois implementados e testados no veículo utilizando uma placa de aquisição de dados instalada no microcomputador. A preocupação principal do projeto dos controladores foi a estabilidade do sistema na ocorrência de perturbações que desviem o entreferro de seu valor nominal.Exceto para o sistema com controle RLQ e modelo de corpo rígido, os resultados experimentais obtidos com o protótipo mostram que o sistema em malha fechada é estável e apresenta uma resposta transiente satisfatória. O sistema com controle RLQ e modelo de corpo não rígido apresentou a melhor performance entre todas as alternativas testadas. / The control and optimization of the electromagnetic suspension operation of a MAGLEV vehicle prototype are presented in this work. This kind of system is inherently unstable and highly nonlinear, being an excellent example for the study and comparison of different control methodologies. In the last years significant experience has been gained with levitated vehicles. The vehicle architecture consists of four electromagnetic actuators, four air gap sensors and four accelerometers, all located at the corners of the vehicle. The vehicle dynamics is described through three different mathematical models: rigid body model, with three degrees of freedom (heave, roll and pitch motions), not-rigid body model, with an additional degree of freedom (torsion motion) and SISO model, with four independent heave motions. Blocks to make variables compatible are used in based on the difference between the number of variables of the mathematical model and the number of measured and actuation variables available in the vehicle. The accelerometers, used to estimate the speeds of the vehicle, were installed in order to study the optimal control of the suspension for states feedback. The Linear Quadratic Regulator (LQR) technique combined with the root locus method for definition of the closed-loop poles were used. The H'IND.2'/H'INFINITE' controller with output feedback was implemented for sake of comparison. Independent controllers for each degree of freedom were simulated with MATLAB then implemented and tested in the vehicle using AD/DA converter installed in the microcomputer. The first goal of the controllers' design was the system stability when subject to disturbances that drive the air away from its nominal value. Except for the system with RLQ controller and rigid body model, the experimental results obtained with the prototype show that the closed-loop system is stable and exhibits a satisfactory transient response.The system with the RLQ controller and not-rigid body model exhibits the best performance among all the alternatives tested.

<p>The aim of this work has been to develop new knowledge about macromodelling of microsystems. Doing that, we have followed two different approaches for generating macromodels, namely model order reduction and lumped modelling. The latter is a rather mature method that has been widely recognized and used for a relatively long period of time. Model order reduction, on the other hand, is a relatively new area still in rapid development. Due to this, the parts considering reduced order modelling is strongly biased towards methodology and concepts, whereas parts on lumped modelling are biased towards systems and devices.</p><p>In the first part of this thesis, we focus on model order reduction. We introduce some approaches for reducing model order for linear systems, and we give an example related to squeeze-film damping. We then move on to investigate model order reduction of nonlinear systems, where we present and use the concept of invariant manifolds. While the concept of invariant manifolds is general, we utilize it for reducing models. An obvious advantage of using invariant manifold theory is that it offers a conceptually clear understanding of effects and behaviour of nonlinear system.</p><p>We exemplify and investigate the accuracy of one method for identifying invariant manifolds. The example is based on an industrialized dual-axis accelerometer.</p><p>A new geometrical interpretation of external forcing, relating to invariant manifolds, is presented. We show how this can be utilized to deal with external forcing in a manner consistent with the invariance property of the manifold. The interpretation also aids in reducing errors for reduce models.</p><p>We extend the asymptotic approach in a manner that makes it possible to create design-parameter sensitive models. We investigate an industrialized dual-axis accelerometer by means of the method and demonstrate capabilities of the method. We also discuss how manifolds for nonlinear dissipative systems can be found.</p><p>Focusing on lumped modelling, we analyse a microresonator. We also discuss the two analogies that can be used to build electrical equivalents of mechanical systems. It is shown how the f → V analogy, linking velocity to voltage, is the natural choice. General properties of lumped modelling are investigated using models with varying degrees of freedom.</p><p>Finally, we analyse an electromagnetic system, intended for levitating objects, and we demonstrate the scaling effects of the system. Furthermore, we prove the intrinsic stability of the system, although the floating disc will be slightly tilted. This is the first analysis done assessing the stability criterions of such a systems. The knowledge arising from the analysis gives strong indications on how such a system can be utilized, designed, and improved.</p>