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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Development and Applications of Finite Elements in Time Domain

Park, Sungho 04 December 1996 (has links)
A bilinear formulation is used for developing the time finite element method (TFM) to obtain transient responses of both linear, nonlinear, damped and undamped systems. Also the formulation, used in the h-, p- and hp-versions, is extended and found to be readily amenable to multi-degree-of-freedom systems. The resulting linear and nonlinear algebraic equations for the transient response are differentiated to obtain the sensitivity of the response with respect to various design parameters. The present developments were tested on a series of linear and nonlinear examples and were found to yield, when compared with other methods, excellent results for both the transient response and its sensitivity to system parameters. Mostly, the results were obtained using the Legendre polynomials as basis functions, though, in some cases other orthogonal polynomials namely, Hermite, Chebyshev, and integrated Legendre polynomials were also employed (but to no great advantage). A key advantage of TFM, and the one often overlooked in its past applications, is the ease in which the sensitivity of the transient response with respect to various design parameters can be obtained. Since a considerable effort is spent in determining the sensitivity of the response with respect to system parameters in many algorithms for parametric identification, an identification procedure based on the TFM is developed and tested for a number of nonlinear single-and two-degree-of-freedom system problems. An advantage of the TFM is the easy calculation of the sensitivity of the transient response with respect to various design parameters, a key requirement for gradient-based parameter identification schemes. The method is simple, since one obtains the sensitivity of the response to system parameters by differentiating the algebraic equations, not original differential equations. These sensitivities are used in Levenberg-Marquardt iterative direct method to identify parameters for nonlinear single- and two-degree-of-freedom systems. The measured response was simulated by integrating the example nonlinear systems using the given values of the system parameters. To study the influence of the measurement noise on parameter identification, random noise is added to the simulated response. The accuracy and the efficiency of the present method is compared to a previously available approach that employs a multistep method to integrate nonlinear differential equations. It is seen, for the same accuracy, the present approach requires fewer data points. Finally, the TFM for optimal control problems based on Hamiltonian weak formulation is proposed by adopting the p- and hp-versions as a finite element discretization process. The p-version can be used to improve the accuracy of the solution by adding more unknowns to each element without refining the mesh. The usage of hierarchical type of shape functions can lead to a significant saving in computational effort for a given accuracy. A set of Legendre polynomials are chosen as higher order shape functions and applied to two simple minimization problems for optimal control. The proposed formulation provides very accurate results for these problems. / Ph. D.
2

Déploiement adaptatif d’un réseau de capteurs mobiles pour le suivi d’un phénomène évolutif décrit par des équations aux dérivées partielles. / Adaptive deployment of a mobile sensors network to optimize the monitoring of an evolutionary phenomenon described by partial differential equations.

Vergnaud, Alban 04 December 2015 (has links)
De nos jours la protection de l’environnement et des personnes nécessite le recours à des capteurs permettant de suivre le déplacement de phénomènes mobiles pour prédire et agir sur leur évolution (ex : nuages polluants, incendies,nappe d’hydrocarbures). Ces phénomènes physiques sont souvent modélisables par des équations aux dérivées partielles (EDP) éventuellement non linéaires. La mise au point d'un outil prédictif pour l'aide à la décision nécessite l'évaluation de certains paramètres d'entrée. Dans ces domaines, les capteurs sont en général coûteux et en nombre limité. Toutefois, avec les récentes avancées technologiques il devient envisageable de concevoir des systèmes mobiles peu coûteux et de déployer un groupe de véhicules en réseau dans un certain nombre d'environnements à risque.Le sujet de recherche étudié et présenté dans ce rapport concerne le développement et la validation de stratégies optimales de déplacement d'un ensemble de capteurs pour l'identification paramétrique en ligne des systèmes d' EDP caractérisés par une ou plusieurs sources mobiles. Le travail présenté est destiné à développer une méthodologie complète(théorie, méthodes numériques, plate-forme expérimentale)en vue de réaliser une conception optimale d'expériences dans le cadre de problèmes mal posés non-linéaires associés à l'évaluation de paramètres dans des systèmes décrits par des EDP en génie thermique. / Nowadays the environment and people protection requires the use of sensors in order to monitor the movement of mobile phenomena and to predict and act on their evolution (ex: polluting cloud, fires, oil spill). These physical phenomena are often modelled by nonlinear partial differential equations (PDE). Development of a predictive tool for the decision support requires the assessment of some input parameters. In such a context, sensors were generally expensive. However, recent technological advances have reduced manufacturing costs and it becomes possible to develop low-cost mobile systems and to deploy a group of networked vehicles in potentially risky environments.Research topic studied and presented in this thesis concerns the development and validation of optimal strategies for moving a set of sensors for the parametric identification of PDE systems characterized by one or more mobile heating sources. This work is intended to develop a comprehensive methodology (theory, numerical methods, and experimentation) in order to achieve an optimal design of experiments in the context of nonlinear ill-posed problems related to the evaluation of parameters in systems described by PDE in thermal engineering.
3

Modeling and control of The DC-DC Buck-Boost converter using parametric identification techniques / Modelagem e controle do conversor CC-CC Buck-Boost usando tÃcnicas paramÃtricas de identificaÃÃo

Gabriel Ribeiro Bezerra 16 April 2015 (has links)
CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / This work presents procedures for modeling a Buck-Boost converter based on offline parametric identification techniques, with employment of black box and gray box models. For the identification of the control-to-output-voltage transfer function, the nonlinear Hammerstein model is employed, a particularly interesting structure to identify DC-DC converters for its ability to incorporate nonlinear static characteristic aside from the dynamic behavior of the plant. The identification of the mentioned transfer function is achieved from input and output data, obtained in simulations. In order to identify transfer function parameters, a restricted least squares algorithm is used. As for the identification of the control-to-inductor-current transfer function, a linear black box first order model is considered, with its parameters being determined from systemâs frequency response. In order to show the modelâs utility, a control system is designed based on the identified expressions. The control system employed is the digital version of type 3 compensator for the voltage loop and type 2 compensator for the current loop, both operating under or logics. The identification results of the system presented excellent agreement between the obtained parametric models and the converterâs behavior, showing the reliability of the identification techniques employed in this work. Furthermore, the control system designed from the identified transfer functions presented good performance, providing stability and quick disturbance rejection, bolstering the validity of parametric identification methods applied to the Buck-Boost converter. / Este trabalho apresenta procedimentos para a modelagem de um conversor Buck-Boost com base em tÃcnicas de identificaÃÃo paramÃtricas offline com emprego de modelos matemÃticos tipo caixa preta e caixa cinza. Para a identificaÃÃo da funÃÃo de transferÃncia que relaciona a tensÃo de saÃda e a razÃo cÃclica, à empregado o modelo nÃo linear de Hammerstein, estrutura particularmente interessante para aplicaÃÃo em identificaÃÃo de conversores CC-CC por incorporar a caracterÃstica estÃtica nÃo linear da planta de forma dissociada ao seu comportamento dinÃmico. A identificaÃÃo da funÃÃo de transferÃncia citada à feita a partir de dados de entrada e saÃda do sistema, medidos em simulaÃÃo. Para determinaÃÃo dos parÃmetros da funÃÃo de transferÃncia que relaciona a tensÃo de saÃda e a razÃo cÃclica, à utilizado um algoritmo de mÃnimos quadrados nÃo recursivo com restriÃÃes. Quanto à identificaÃÃo da funÃÃo de transferÃncia que relaciona a corrente no indutor e a razÃo cÃclica, à empregado um modelo caixa preta linear de primeira ordem, sendo os parÃmetros de tal modelo determinados a partir da resposta em frequÃncia do sistema. Visando mostrar a utilidade dos modelos paramÃtricos, à realizado um projeto de controle com base nas expressÃes identificadas. O sistema de controle adotado à a versÃo digital de um compensador tipo 3 para a malha de tensÃo e de um compensador tipo 2 para a malha de corrente, que operam de forma alternada segundo a lÃgica ou. Os resultados de identificaÃÃo do sistema apresentam uma excelente concordÃncia entre os modelos paramÃtricos obtidos e o comportamento do conversor, mostrando a confiabilidade das tÃcnicas de identificaÃÃo empregadas nesse trabalho. Adicionalmente, o sistema de controle projetado a partir das funÃÃes de transferÃncia estimadas apresentou bom desempenho, garantindo estabilidade e rÃpida rejeiÃÃo a distÃrbios, reforÃando a validade dos mÃtodos de identificaÃÃo paramÃtrica aplicados ao conversor Buck-Boost.
4

Arquitetura aberta para controle de robôs manipuladores

Santini, Diego Caberlon January 2009 (has links)
Este documento trata da especificação de uma arquitetura aberta para controle de robôs manipuladores. A arquitetura é implementada utilizando o framework do projeto OROCOS, ambiente que já foi utilizado com sucesso em alguns sistemas de controle de robôs. Esta arquitetura é especificada para um robô manipulador genérico de N juntas, definindo componentes que abstraem o hardware dos robôs. A arquitetura é implementada com três tipos de controladores diferentes: PID independente por junta, controlador de torque calculado e controlador com feedforward. A sua validação é feita através da sua implementação em um robô real. Para isso é utilizada uma placa de acionamento, utilizando o barramento CAN devido ao seu determinismo e a sua taxa de comunicação. Também é necessário a utilização do modelo dinâmico do robô para as estratégias de controle de torque calculado e com feedforward. A obtenção de tal modelo é feita neste trabalho de forma analítica, e a seguir os parâmetros são identificados usando o sistema proposto. / This work deals with the specification of an open architecture for control of manipulator robots. The architecture is implemented by using the OROCOS framework. The architecture is specified for a generic manipulator robot with N joints, through definition of components which abstract the hardware of the robot. Three different controllers are implemented: an independent PID for each joint, a computed torque controller and a controller with feedforward. The validation is made through the implementation on the Janus robot. For this purpose, an actuator card is defined. This card uses the CAN bus due its determinism and bus rate. The dynamic model of Janus, used in computed torque and feedforward controllers, is obtained in an analytical way. After that, the parameters of this model are identified using the least squares method.
5

Arquitetura aberta para controle de robôs manipuladores

Santini, Diego Caberlon January 2009 (has links)
Este documento trata da especificação de uma arquitetura aberta para controle de robôs manipuladores. A arquitetura é implementada utilizando o framework do projeto OROCOS, ambiente que já foi utilizado com sucesso em alguns sistemas de controle de robôs. Esta arquitetura é especificada para um robô manipulador genérico de N juntas, definindo componentes que abstraem o hardware dos robôs. A arquitetura é implementada com três tipos de controladores diferentes: PID independente por junta, controlador de torque calculado e controlador com feedforward. A sua validação é feita através da sua implementação em um robô real. Para isso é utilizada uma placa de acionamento, utilizando o barramento CAN devido ao seu determinismo e a sua taxa de comunicação. Também é necessário a utilização do modelo dinâmico do robô para as estratégias de controle de torque calculado e com feedforward. A obtenção de tal modelo é feita neste trabalho de forma analítica, e a seguir os parâmetros são identificados usando o sistema proposto. / This work deals with the specification of an open architecture for control of manipulator robots. The architecture is implemented by using the OROCOS framework. The architecture is specified for a generic manipulator robot with N joints, through definition of components which abstract the hardware of the robot. Three different controllers are implemented: an independent PID for each joint, a computed torque controller and a controller with feedforward. The validation is made through the implementation on the Janus robot. For this purpose, an actuator card is defined. This card uses the CAN bus due its determinism and bus rate. The dynamic model of Janus, used in computed torque and feedforward controllers, is obtained in an analytical way. After that, the parameters of this model are identified using the least squares method.
6

Arquitetura aberta para controle de robôs manipuladores

Santini, Diego Caberlon January 2009 (has links)
Este documento trata da especificação de uma arquitetura aberta para controle de robôs manipuladores. A arquitetura é implementada utilizando o framework do projeto OROCOS, ambiente que já foi utilizado com sucesso em alguns sistemas de controle de robôs. Esta arquitetura é especificada para um robô manipulador genérico de N juntas, definindo componentes que abstraem o hardware dos robôs. A arquitetura é implementada com três tipos de controladores diferentes: PID independente por junta, controlador de torque calculado e controlador com feedforward. A sua validação é feita através da sua implementação em um robô real. Para isso é utilizada uma placa de acionamento, utilizando o barramento CAN devido ao seu determinismo e a sua taxa de comunicação. Também é necessário a utilização do modelo dinâmico do robô para as estratégias de controle de torque calculado e com feedforward. A obtenção de tal modelo é feita neste trabalho de forma analítica, e a seguir os parâmetros são identificados usando o sistema proposto. / This work deals with the specification of an open architecture for control of manipulator robots. The architecture is implemented by using the OROCOS framework. The architecture is specified for a generic manipulator robot with N joints, through definition of components which abstract the hardware of the robot. Three different controllers are implemented: an independent PID for each joint, a computed torque controller and a controller with feedforward. The validation is made through the implementation on the Janus robot. For this purpose, an actuator card is defined. This card uses the CAN bus due its determinism and bus rate. The dynamic model of Janus, used in computed torque and feedforward controllers, is obtained in an analytical way. After that, the parameters of this model are identified using the least squares method.
7

Identificação de parametros de mancal através de analise de correlações / Bearing parameters identification through correlation analysis

Sanches, Fabio Dalmazzo, 1975- 12 August 2018 (has links)
Orientador: Robson Pederiva / Dissertação (mestrado) -Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-12T18:23:14Z (GMT). No. of bitstreams: 1 Sanches_FabioDalmazzo_M.pdf: 633170 bytes, checksum: a1620e7b33649f4441407be8d0f78500 (MD5) Previous issue date: 2008 / Resumo: Este trabalho apresenta uma metodologia de identificação dos parâmetros de rigidez e amortecimento dos mancais de rolamento de um sistema mecânico rotativo. O método proposto é baseado na equação matricial de Ljapunov e na representação do sistema na forma de espaço de estados. Através da definição de correlações, inserida na equação matricial, monta-se um estimador que relaciona os parâmetros físicos do sistema com as matrizes de correlações das variáveis medidas no domínio do tempo, não sendo necessário o conhecimento da excitação. O objetivo do trabalho é fazer um estudo teórico da aplicação dessa metodologia de identificação em sistemas reais. São feitas simulações considerando-se um sistema rotativo de vinte graus de liberdade excitado aleatoriamente, caso estático, e por desbalanceamento em diversas freqüências de rotação e de características de mancal. Os resultados numéricos demonstram que o método proposto é robusto e viável, podendo ser aplicado na identificação de uma máquina real / Abstract: This work presents an identification methodology of stiffness and damping parameters of rolling bearings in a rotor-bearing system. The proposed method is based on Ljapunov matrix equation and state space representation. Through the definition of correlations used in matrix equation, it is possible to generate an algorithm that relates system physical parameters to the correlation matrixes of the measured variables in time domain without the knowledge of the external input forces. The purpose of this work is to make a theoretical study of the viability of this methodology used in real systems. Simulations were performed considering a rotating system with twenty degrees of freedom excited by random forces, system at rest, and by unbalance forces considering several rotation frequencies and bearing characteristics. The numerical results show the proposed method is feasible and it can be used to identify real machines / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica
8

Exploitation des mesures électriques en vue de la surveillance et du diagnostic en temps réel des piles à combustible pour application transport automobile / Monitoring and real-time diagnosis of fuel cells using electrical measurements for automotive Application

Taleb, Miassa 30 November 2015 (has links)
Dans le contexte énergétique mondial actuel, les piles à combustible à membrane échangeuse de protons constituent une solution prometteuse au futur développement d'une nouvelle génération de véhicules électrifiés, permettant une autonomie plus importante que celle des véhicules électrifiés à batteries. Néanmoins, le développement à grand échelle des piles à combustible reste à ce jour limité en raison de certains verrous technologiques, tel que la gestion de l'eau. Afin de permettre une production de masse des piles à combustible, de tels problèmes doivent être résolus. Plusieurs axes de travail peuvent être envisagés, tant sur les aspects matériels sur la structure de la pile, que du point de vue de la commande en développant des outils algorithmiques permettant le suivi de l'état de fonctionnement du système en vue de détecter les défaillances éventuelles, ou la dégradation des conditions de fonctionnement, et permettre ainsi d'y apporter une solution au moyen du système de commande ou de supervision.Les travaux de cette thèse s'inscrivent dans cette seconde approche et portent plus particulièrement sur la mise en évidence des phénomènes d'engorgement ou d'asséchement du cœur de pile afin de diagnostiquer les éventuels problèmes d'hydratation conduisant à la réduction du rendement, à la diminution des performances ou encore à un vieillissement prématuré.Les méthodes développées au cours de ces travaux se fondent sur des stratégies de suivi de paramètres significatifs d'un modèle de pile dont les évolutions, comparativement à des valeurs de référence, sont caractéristiques de l'état hydratation du cœur de pile. Le suivi en temps réel de ces paramètres permet ainsi de mettre en évidence les phénomènes d'engorgement ou d'asséchement du cœur de pile.Les modèles adoptés pour ces travaux font appel à une représentation de l'impédance électrique de la pile.Ainsi, en suivant cette approche, la stratégie adoptée se fonde alors sur le développement de deux modèles de type circuit électrique : un modèle d'ordre entier puis un modèle d'ordre fractionnaire. Cette deuxième formulation des modèles, plus proche de la réalité physique des phénomènes de transports se produisant au cœur de pile, permet une meilleure représentation de la pile tant du point de vue temporel que fréquentiel. En effet, les analyses effectuées en utilisant des résultats expérimentaux obtenus au moyen d'une cellule de pile (surface active de 100 cm2 conçue par la société UBzM) ont permis de valider que le modèle d'ordre fractionnaire, en contrepartie d'une augmentation de la complexité, permet de mieux reproduire d'une part les résultats temporels de la pile (suivi de tension pour un profil de courant donnée), d'autre part une meilleure approximation de l'impédance mesurée.Des méthodes d'identification paramétrique, conventionnelles et adaptées aux systèmes d'ordre fractionnaire, sont ensuite utilisées afin d’extraire les paramètres des modèles développés à partir de données expérimentales temporelles (tension/courant de la pile), ou fréquentielles (spectroscopie d'impédance). Une étude de sensibilité permet alors de définir les paramètres les plus indicatifs des phénomènes d'engorgement et d'assèchement. L'évolution de ces paramètres, associés à la tension et le spectre d'impédance de la pile, sont alors combinés afin de construire une stratégie de diagnostic de l’engorgement et de l’asséchement du cœur de pile. / In the current global energy context, proton exchange membrane fuel cells represent a promising solution to the future development of a new generation of electrified vehicles, allowing greater autonomy than electrified vehicles using batteries.Nevertheless, the large-scale development of fuel cells remains limited due to some technological locks, such as water management. To enable mass production of fuel cells, such problems must be solved. Several working axes may be envisaged both on the hardware aspects of the fuel cell structure, and from the point of view of control, by developing algorithmic tools for monitoring the operating state of the system to detect any failures, or degradations that may occur.The work of this thesis falls within this second approach and focuses specifically on the identification of drying and drowning phenomena which can appear in a fuel cell, to diagnose any moisture problems leading to yield reduction.The methods developed in this work are based on the monitoring of relevant parameters of the fuel cell model which changes, compared to reference values, are characteristic of the state of the fuel cell hydration.The real-time monitoring of these parameters can highlight the drying and drowning phenomena.Adopted models for this work are based on a representation of the electrical impedance of the fuel cell.Thus, following this approach, the adopted strategy is then based on the development of two electrical models: an integer order model and a fractional order model. It appears that the second model formulation is closer to the physical reality of transport phenomena occurring in the fuel cell. It allows a better representation of the fuel cell behavior in time and frequency domain. Indeed, the analyzes based on experimental results performed using a single fuel cell (100 cm2 active area designed by UBzM company) have validated that the fractional order model, in return for an increase of complexity, allows better reproduce, in the one hand of the fuel cell time-series voltage response (voltage monitoring for a given current profile), on the other hand a better approximation of the measured impedance. Conventional and of fractional order parametric identification methods are then used to extract the model’s parameters from time-series experimental data (voltage / current from the battery) or frequency data (impedance spectroscopy).A sensitivity analysis allows then the defining of the most indicative parameters of the drowning and drying phenomena. The evolution of these parameters associated with the voltage and impedance spectrum of the fuel cell are then combined to build a diagnosis strategy of the fuel cell water management.
9

Parameter Identification of Nonlinear Systems Using Perturbation Methods and Higher-Order Statistics

Fung, Jimmy Jr. 21 August 1998 (has links)
A parametric identification procedure is proposed that combines the method of multiple scales and higher-order statistics to efficiently and accurately model nonlinear systems. A theoretical background for the method of multiple scales and higher-order statistics is given. Validation of the procedure is performed through applying it to numerical simulations of two nonlinear systems. The results show how the procedure can successfully characterize the system damping and nonlinearities and determine the corresponding parameters. The procedure is then applied to experimental measurements from two structural systems, a cantilevered beam and a three-beam frame. The results show that quadratic damping should be accounted for in both systems. Moreover, for the three-beam frame, the parametric excitation is much more important than the direct excitation. To show the flexibility of the procedure, numerical simulations of ship motion under parametric excitation are used to determine nonlinear parameters govening the relation between pitch, heave, and roll motions. The results show a high level of agreement between the numerical simulation and the mathematical model with the identified parameters. / Master of Science
10

Maximum Likelihood Estimation of Hammerstein Models / Maximum Likelihood-metoden för identifierig av Hammersteinmodeller

Sabbagh, Yvonne January 2003 (has links)
<p>In this Master's thesis, Maximum Likelihood-based parametric identification methods for discrete-time SISO Hammerstein models from perturbed observations on both input and output, are investigated. </p><p>Hammerstein models, consisting of a static nonlinear block followed by a dynamic linear one, are widely applied to modeling nonlinear dynamic systems, i.e., dynamic systems having nonlinearity at its input. </p><p>Two identification methods are proposed. The first one assumes a Hammerstein model where the input signal is noise-free and the output signal is perturbed with colored noise. The second assumes, however, white noises added to the input and output of the nonlinearity and to the output of the whole considered Hammerstein model. Both methods operate directly in the time domain and their properties are illustrated by a number of simulated examples. It should be observed that attention is focused on derivation, numerical calculation, and simulation corresponding to the first identification method mentioned above.</p>

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