• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 403
  • 126
  • 74
  • 53
  • 12
  • 9
  • 5
  • 4
  • 4
  • 3
  • 1
  • 1
  • 1
  • 1
  • 1
  • Tagged with
  • 858
  • 858
  • 161
  • 145
  • 144
  • 136
  • 107
  • 106
  • 101
  • 100
  • 92
  • 91
  • 70
  • 65
  • 65
  • 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.
51

Design and Implementation of Control Techniques for Differential Drive Mobile Robots: An RFID Approach

Miah, Suruz 27 September 2012 (has links)
Localization and motion control (navigation) are two major tasks for a successful mobile robot navigation. The motion controller determines the appropriate action for the robot’s actuator based on its current state in an operating environment. A robot recognizes its environment through some sensors and executes physical actions through actuation mechanisms. However, sensory information is noisy and hence actions generated based on this information may be non-deterministic. Therefore, a mobile robot provides actions to its actuators with a certain degree of uncertainty. Moreover, when no prior knowledge of the environment is available, the problem becomes even more difficult, as the robot has to build a map of its surroundings as it moves to determine the position. Skilled navigation of a differential drive mobile robot (DDMR) requires solving these tasks in conjunction, since they are inter-dependent. Having resolved these tasks, mobile robots can be employed in many contexts in indoor and outdoor environments such as delivering payloads in a dynamic environment, building safety, security, building measurement, research, and driving on highways. This dissertation exploits the use of the emerging Radio Frequency IDentification (RFID) technology for the design and implementation of cost-effective and modular control techniques for navigating a mobile robot in an indoor environment. A successful realization of this process has been addressed with three separate navigation modules. The first module is devoted to the development of an indoor navigation system with a customized RFID reader. This navigation system is mainly pioneered by mounting a multiple antenna RFID reader on the robot and placing the RFID tags in three dimensional workspace, where the tags’ orthogonal position on the ground define the desired positions that the robot is supposed to reach. The robot generates control actions based on the information provided by the RFID reader for it to navigate those pre-defined points. On the contrary, the second and third navigation modules employ custom-made RFID tags (instead of the RFID reader) which are attached at different locations in the navigation environment (on the ceiling of an indoor office, or on posts, for instance). The robot’s controller generates appropriate control actions for it’s actuators based on the information provided by the RFID tags in order to reach target positions or to track pre-defined trajectory in the environment. All three navigation modules were shown to have the ability to guide a mobile robot in a highly reverberant environment with variant degrees of accuracy.
52

A Genetic Programming Approach to Solving Optimization Problems on Agent-Based Models

Garuccio, Anthony 17 May 2016 (has links)
In this thesis, we present a novel approach to solving optimization problems that are defined on agent-based models (ABM). The approach utilizes concepts in genetic programming (GP) and is demonstrated here using an optimization problem on the Sugarscape ABM, a prototype ABM that includes spatial heterogeneity, accumulation of agent resources, and agents with different attributes. The optimization problem seeks a strategy for taxation of agent resources which maximizes total taxes collected while minimizing impact on the agents over a finite time. We demonstrate how our GP approach yields better taxation policies when compared to simple flat taxes and provide reasons why GP-generated taxes perform well. We also look at ways to improve the performance of the GP optimization method. / McAnulty College and Graduate School of Liberal Arts; / Computational Mathematics / MS; / Thesis;
53

Mean Field Games for Jump Non-Linear Markov Process

Basna, Rani January 2016 (has links)
The mean-field game theory is the study of strategic decision making in very large populations of weakly interacting individuals. Mean-field games have been an active area of research in the last decade due to its increased significance in many scientific fields. The foundations of mean-field theory go back to the theory of statistical and quantum physics. One may describe mean-field games as a type of stochastic differential game for which the interaction between the players is of mean-field type, i.e the players are coupled via their empirical measure. It was proposed by Larsy and Lions and independently by Huang, Malhame, and Caines. Since then, the mean-field games have become a rapidly growing area of research and has been studied by many researchers. However, most of these studies were dedicated to diffusion-type games. The main purpose of this thesis is to extend the theory of mean-field games to jump case in both discrete and continuous state space. Jump processes are a very important tool in many areas of applications. Specifically, when modeling abrupt events appearing in real life. For instance, financial modeling (option pricing and risk management), networks (electricity and Banks) and statistics (for modeling and analyzing spatial data). The thesis consists of two papers and one technical report which will be submitted soon: In the first publication, we study the mean-field game in a finite state space where the dynamics of the indistinguishable agents is governed by a controlled continuous time Markov chain. We have studied the control problem for a representative agent in the linear quadratic setting. A dynamic programming approach has been used to drive the Hamilton Jacobi Bellman equation, consequently, the optimal strategy has been achieved. The main result is to show that the individual optimal strategies for the mean-field game system represent 1/N-Nash equilibrium for the approximating system of N agents. As a second article, we generalize the previous results to agents driven by a non-linear pure jump Markov processes in Euclidean space. Mathematically, this means working with linear operators in Banach spaces adapted to the integro-differential operators of jump type and with non-linear partial differential equations instead of working with linear transformations in Euclidean spaces as in the first work. As a by-product, a generalization for the Koopman operator has been presented. In this setting, we studied the control problem in a more general sense, i.e. the cost function is not necessarily of linear quadratic form. We showed that the resulting unique optimal control is of Lipschitz type. Furthermore, a fixed point argument is presented in order to construct the approximate Nash Equilibrium. In addition, we show that the rate of convergence will be of special order as a result of utilizing a non-linear pure jump Markov process. In a third paper, we develop our approach to treat a more realistic case from a modelling perspective. In this step, we assume that all players are subject to an additional common noise of Brownian type. We especially study the well-posedness and the regularity for a jump version of the stochastic kinetic equation. Finally, we show that the solution of the master equation, which is a type of second order partial differential equation in the space of probability measures, provides an approximate Nash Equilibrium. This paper, unfortunately, has not been completely finished and it is still in preprint form. Hence, we have decided not to enclose it in the thesis. However, an outlook about the paper will be included.
54

Spontaneous changes of human behaviors and intervention strategies: human and animal diseases

Zhao, Songnian January 1900 (has links)
Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Chih-Hang Wu / The topic of infectious disease epidemics has recently attracted substantial attentions in research communities and it has been shown that the changes of human behaviors have significant impacts on the dynamics of disease transmission. However, the study and understanding of human reactions into spread of infectious disease are still in the very beginning phase and how human behaviors change during the spread of infectious disease has not been systematically investigated. Moreover, the study of human behaviors includes not only various enforced measures by public authorities such as school closure, quarantine, vaccination, etc, but also the spontaneous self-protective actions which are triggered by risk perception and fear of diseases. Hence, the goal of this research is to study the impacts of human behaviors to the epidemic from these two perspectives: spontaneous behavioral changes and public intervention strategies. For the sake of studying spontaneous changes of human behaviors, this research first time applied evolutionary spatial game into the study of human reactions to the spread of infectious disease. This method integrated contact structures and epidemics information into the individuals’ decision processes, by adding two different types of information into the payoff functions: the local information and global information. The new method would not only advance the field of game theory, but also the field of epidemiology. In addition, this method was also applied to a classic compartmental dynamic system which is a widely used model for studying the disease transmission. With extensive numerical studies, the results first proved the consistency of two models for the sake of validating the effectiveness of the spatial evolutionary game. Then the impacts of changes of human behaviors to the dynamics of disease transmission and how information impacts human behaviors were discussed temporally and spatially. In addition to the spontaneous behavioral changes, the corresponding intervention strategies by policy-makers played the key role in process of mitigating the spread of infectious disease. For the purpose of minimizing the total lost, including the social costs and number of infected individuals, the intervention strategies should be optimized. Sensitivity analysis, stability analysis, bifurcation analysis, and optimal control methods are possible tools to understand the effects of different combination of intervention strategies or even find an appropriate policy to mitigate the disease transmission. One zoonotic disease, named Zoonotic Visceral Leishmaniasis (ZVL), was studied by adopting different methods and assumptions. Particularly, a special case, backward bifurcation, was discussed for the transmission of ZVL. Last but not least, the methodology and modeling framework used in this dissertation can be expanded to other disease situations and intervention applications, and have a broad impact to the research area related to mathematical modeling, epidemiology, decision-making processes, and industrial engineering. The further studies can combine the changes of human behaviors and intervention strategies by policy-makers so as to seek an optimal information dissemination to minimize the social costs and the number of infected individuals. If successful, this research should aid policy-makers by improving communication between them and the public, by directing educational efforts, and by predicting public response to infectious diseases and new risk management strategies (regulations, vaccination, quarantine, etc.).
55

Power management of hybrid military vehicles using optimal control

Lu, Boran January 1900 (has links)
Master of Science / Department of Electrical and Computer Engineering / Balasubramaniam Natarajan / Noel Schulz / With increasing costs for fuel there is a growing interest in improving fuel efficiency and performance of military vehicles by employing (1) hybrid drive train architecture; (2) reliable vehicle power system structure, and (3) effective power management strategies of multiple power sources (engine, battery and ultracapacitor) and vehicle electrical loads. However, current ruled-based power management strategies that focus primarily on traction fail to meet the rapidly increasing requirements of military vehicles, including: (1) better fuel economy; (2) the ability to support pulsed power weapon loads; (3) maintaining battery SOC for power offloading applications, and (4) the ability to perform load scheduling of vehicle non-traction electrical loads to save energy. In this thesis, we propose an optimal control based algorithm in conjunction with a rule-based control strategy to optimally manage three power sources (engine, battery and pulsed power supply module) and an effective power management solution for vehicle non-traction electrical loads such that: (1) all traction, non-traction and pulsed power needs are met; (2) power drawn from the engine for specific mission is minimized; (3) a certain desired battery SOC is guaranteed for offloading power, and (4) the ability to perform load scheduling based on different mission requirements. The proposed approach is validated using simulation of a mission specific profile and is compared with two other popular control strategies. The improvements in power efficiency, desired SOC level and ability to perform optimal load scheduling are demonstrated.
56

Quasiminimality and coercivity in the calculus of variations

Chen, Chuei Yee January 2013 (has links)
No description available.
57

Sistema de controle ótimo para veículo submersível semi-autônomo. / Optimal control system for a semi-autonomous underwater vehicle.

Fernandes, Daniel de Almeida 27 June 2008 (has links)
Este trabalho apresenta aspectos teóricos e práticos relevantes do desenvolvimento do Sistema de Navegação e Controle (SNC) a ser implementado em um Veículo Submarino Semi-Autônomo (VSSA), tipo não carenado e auto propelido, que está em desenvolvimento e construção na Escola Politécnica da USP, para a Petrobrás. Os três graus de liberdade horizontais são controlados para seguirem trajetórias pré-definidas, enviadas como sinais de referência para navegação por uma estação de apoio localizada na superfície, responsável pela guiagem do veículo. Os sinais de referência enviados são acústicos propagados pela água. A implementação física do SNC e o controle dos três graus de liberdade verticais não fazem parte do escopo deste trabalho. O SNC consiste em um controlador determinístico, um seguidor de trajetórias linear quadrático alimentado por um vetor de estados estimado assintoticamente. Por segurança, em caso de falha de algum sensor, e para filtrar ruídos nos sinais medidos, um estimador de estados de ordem plena é utilizado conjuntamente. Pela simplicidade de síntese e implementação, esta arquitetura de controle é considerada a melhor alternativa para capacitar o VSSA a executar os movimentos semi-autônomos desejados. As técnicas de controle utilizadas requerem a linearização do modelo matemático não-linear que descreve o comportamento dinâmico do veículo. O modelo é obtido de maneira simplificada. Os resultados são gerados por simulações com o modelo não-linear. / This work presents theoretical and practical aspects of the development of the Navigation and Control System (NCS) to be implemented into a Petrobras\' Semi-Autonomous Underwater Vehicle (SAUV), an open-frame and self-propelled type, which is being developed and built at Escola Politécnica of the University of São Paulo (EPUSP). The three horizontal Degrees-of-Freedom (DoF) are controlled so that they can follow a pre-defined trajectory sent as navigation reference signals to the NCS by a support ship, responsible for the guidance of the vehicle and placed on the ocean surface. Reference signals are sent as acoustic signals through the ocean water. The implementation and the control of the three vertical DoF are not in the scope of the present work. The NCS is based upon a deterministic controller, a Linear Quadratic (LQ) trajectory follower fed by an asymptotically estimated state vector, even though all the state variables are available by direct measurents. For safety, if some sensor fails, and for filtering noise on measured signals, a full-order state estimator is also designed. Since the LQ controller architecture is rather simple to design and implement, it was elected to control the SAUV manoeuvers. The control techniques require a linear model of the dynamics of the vehicle. Hence, a linearization procedure is applied to the system of nonlinear differential equations that describe the dynamic behavior of the SAUV. The results presented are provided by computer-aided simulations with the nonlinear model of the plant.
58

Controle ótimo estocástico a tempo discreto e espaço de estado contínuo aplicado a derivativos. / Discrete-time, continuous state-space ctochastic optimal control applied to derivatives.

Maiali, André Cury 23 June 2006 (has links)
Nesta tese abordamos o problema do hedging de mínima variância de derivativos em mercados incompletos usando a teoria de controle ótimo estocástico com critério quadrático de otimização. Desenvolvemos um modelo geral de apreçamento e hedging de derivativos em mercados incompletos, a tempo discreto, que é capaz de acomodar qualquer tipo de payoff com característica européia que dependa de n ativos de risco. Nesse modelo, o mercado pode apresentar diferentes modos de operação, o que foi formalizado matematicamente por meio de uma cadeia de Markov. Também desenvolvemos um modelo geral de apreçamento e hedging de derivativos em mercados incompletos, a tempo discreto e espaço de estados contínuo, que é capaz de acomodar qualquer tipo de payoff com característica européia que dependa de um ativo de risco cujos retornos sejam representados por um processo de difusão com saltos. Desenvolvemos, ainda, expressões analíticas fechadas para o apreçamento e hedging de uma opção de compra européia vanilla em duas situações: (1) quando os retornos do ativo de risco são representados por um processo de difusão com saltos, e (2) quando os retornos do ativo de risco são representados por um processo de Wiener. Por fim, realizamos simulações numéricas para o controle (hedging) de uma opção de compra européia vanilla quando os retornos do ativo de risco são representados por um processo de Wiener, e comparamos os resultados obtidos com a estratégia de controle derivada do modelo de Black & Scholes. / In this thesis we approach the mean-variance hedging problem of derivatives in incomplete markets employing the theory of stochastic optimal control with quadratic optimization criteria. We developed a general derivatives pricing and hedging model in incomplete markets, in discrete time, capable of accommodating any type of European payoff contingent on n risky assets. In this model, the market may exhibit different operating modes, which were mathematically formalized by means of a Markov chain. We also developed a general derivatives pricing and hedging model in incomplete markets, in discrete time and continuous state space, capable of accommodating any type of European payoff contingent on one risky asset whose returns are described by a jump diffusion process. Even further, we developed closed-form analytical expressions for the pricing and hedging of a European vanilla call option in two situations: (1) when the risky asset returns are described by a jump diffusion process, and (2) when the risky asset returns are described by a Wiener process. Finally, we simulated the control (hedging) of a European vanilla call option when the risky asset returns are described by a Wiener process, and compared the results to those obtained with the control strategy derived from the Black & Scholes model.
59

Controlador de trajetória para o robô móvel Ariel: solução de controle ótimo. / Trajectory controller for the Ariel mobile robot: optimal control solution.

Cozman, Fabio Gagliardi 02 December 1991 (has links)
Este trabalho estuda o sistema de controle de um robô móvel, termo que designa veículos sem motorista humano e com capacidade de trafegar por rotas livremente escolhidas. As arquiteturas de controle utilizadas em robôs móveis são analisadas. A arquitetura adotada neste trabalho, de caráter funcional,é apresentada e discutida. O trabalho se concentra nos níveis mais simples de controle, relacionados ao controle de trajetória, cujo objetivo é garantir que o robô móvel percorra uma rota pré-definida. Um controlador de trajetória é proposto e projetado. O controlador resulta da aplicação da teoria de controle ótimo a um modelo de robô móvel em referencial fixo. Uma técnica recente de controle de robôs (técnica de atgs) é empregada para melhorar a robustez do controlador. O desempenho do controlador obtido com uso de atgs é comparado com o desempenho do controlador obtido inicialmente. Com o objetivo de validar esta proposta de controlador de trajetória, resultados fornecidos por simulações são discutidos. A análise do controlador foi respaldada com dados experimentais obtidos junto a um robô móvel, denominado Ariel, desenvolvido no laboratório de automação e sistemas (mecatrônica) da Escola Politécnica da Universidade de São Paulo. / This work studies the Control System of a Mobile Robot, term which refers to vehicles without human driver and with ability to follow arbitrary routes. This work analyses the Control Architectures frequently employed in Mobile Robots. The Architecture here adopted is a functional one, which is presented and described. This work focuses on the simplest levels of Control, those which are mainly related to the Trajectory Control, and whose objective is to guarantee that the Mobile Robot follows a specified route. A Trajectory Controller is proposed and designed. The Controller is based on Optimal Control Theory. A recently developed technique for robot control (called ATGS techinique) is used in order to improve the Controller robustness. Simulation results are discussed in order to validate the proposed Controller. The Controller analysis is tested in a real Mobile Robot (named Ariel) currently developed at Laboratório de Automação e Sistemas (Mecatrônica) , at Escola Politécnica of Universidade de São Paulo.
60

Mathematical modelling and optimisation of Venturi-enhanced hydropower

Benham, Graham P. January 2018 (has links)
In this thesis we study a novel type of hydropower generation which uses a Venturi contraction to amplify the pressure drop across a turbine, allow- ing for cost-effective hydropower generation in situations where the head drop is small, such as in rivers and weirs. The efficiency is sensitive to how the secondary flow, which passes through the turbine, mixes with the accelerated primary flow, which is diverted around the turbine, within the confines of a closed geometry. In particular, it is important to understand the behaviour of the turbulent shear layers between the primary and sec- ondary flows, which grow downstream, mixing the flows together. The behaviour of the shear layers in the expanding part of the Venturi con- traction is strongly dependent on the shape of the channel. An important consequence of the channel shape, and hence the flow behaviour, is the degree of pressure amplification across the turbine, which determines the amount of generated power. We focus on mathematically modelling the mixing of the flows in turbu- lent shear layers, and we investigate two different ways to increase pres- sure amplification: optimising the shape of the channel, and using swirl to enhance mixing. The channel shape optimisation reveals an interest- ing balance between the effects of mixing and wall drag. Wide channel expansion tends to accentuate non-uniform flow, causing poor pressure amplification, whilst shallow expansion creates enhanced wall drag, which is also detrimental to pressure amplification. We show how the maximum power is generated with a channel shape that strikes a balance between these two effects. We find that swirl enhances mixing by increasing shear layer growth rates, but it produces large pressure losses in doing so, and for large amounts of swirl a slowly recirculating region can form along the channel centreline. Whilst swirl does not improve efficiency, there may be some inevitable swirl present in the flow, and we show how this affects the optimum channel shape. We also establish the criteria for the existence of such a recirculation region so that it may be avoided.

Page generated in 0.0922 seconds