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With the widespread use of the Internet, the popularity of web applications has significantly increased. Such applications are subject to unpredictable workload conditions that vary from time to time. For example, an e-commerce website may face higher workloads than normal during festivals or promotional schemes. Such applications are critical and performance related issues, or service disruption can result in financial losses. Cloud computing with its attractive feature of dynamic resource provisioning (elasticity) is a perfect match to host such applications. The rapid growth in the usage of cloud computing model, as well as the rise in complexity of the web applications poses new challenges regarding the effective monitoring and management of the underlying cloud computational resources. This thesis investigates the state-of-the-art elastic methods including the models and techniques for the dynamic management and provisioning of cloud resources from a service provider perspective. An elastic controller is responsible to determine the optimal number of cloud resources, required at a particular time to achieve the desired performance demands. Researchers and practitioners have proposed many elastic controllers using versatile techniques ranging from simple if-then-else based rules to sophisticated optimisation, control theory and machine learning based methods. However, despite an extensive range of existing elasticity research, the aim of implementing an efficient scaling technique that satisfies the actual demands is still a challenge to achieve. There exist many issues that have not received much attention from a holistic point of view. Some of these issues include: 1) the lack of adaptability and static scaling behaviour whilst considering completely fixed approaches; 2) the burden of additional computational overhead, the inability to cope with the sudden changes in the workload behaviour and the preference of adaptability over reliability at runtime whilst considering the fully dynamic approaches; and 3) the lack of considering uncertainty aspects while designing auto-scaling solutions. This thesis seeks solutions to address these issues altogether using an integrated approach. Moreover, this thesis aims at the provision of qualitative elasticity rules. This thesis proposes a novel biologically-inspired switched feedback control methodology to address the horizontal elasticity problem. The switched methodology utilises multiple controllers simultaneously, whereas the selection of a suitable controller is realised using an intelligent switching mechanism. Each controller itself depicts a different elasticity policy that can be designed using the principles of fixed gain feedback controller approach. The switching mechanism is implemented using a fuzzy system that determines a suitable controller/- policy at runtime based on the current behaviour of the system. Furthermore, to improve the possibility of bumpless transitions and to avoid the oscillatory behaviour, which is a problem commonly associated with switching based control methodologies, this thesis proposes an alternative soft switching approach. This soft switching approach incorporates a biologically-inspired Basal Ganglia based computational model of action selection. In addition, this thesis formulates the problem of designing the membership functions of the switching mechanism as a multi-objective optimisation problem. The key purpose behind this formulation is to obtain the near optimal (or to fine tune) parameter settings for the membership functions of the fuzzy control system in the absence of domain experts’ knowledge. This problem is addressed by using two different techniques including the commonly used Genetic Algorithm and an alternative less known economic approach called the Taguchi method. Lastly, we identify seven different kinds of real workload patterns, each of which reflects a different set of applications. Six real and one synthetic HTTP traces, one for each pattern, are further identified and utilised to evaluate the performance of the proposed methods against the state-of-the-art approaches.

The thesis describes theoretical and experimental studies on the chaotic behaviour of a peak current-mode controlled boost converter, a parallel two-module peak current-mode controlled DC-DC boost converter, and a peak current-mode controlled power factor correction (PFC) boost converter. The research concentrates on converters which do not have voltage control loops, since the main interest is in the intrinsic mechanism of chaotic behaviour. These converters produce sub-harmonics of the clock frequency at certain values of the reference current I[ref] and input voltage V[in], and may behave in a chaotic manner, whereby the frequency spectrum of the inductor becomes continuous. Non-linear maps for each of the converters are derived using discrete time modelling and numerical iteration of the maps produce bifurcation diagrams which indicate the presence of subharmonics and chaotic operation. In order to check the validity of the analysis, MATLAB/SIMULINK models for the converters are developed. A comparison is made between waveforms obtained from experimental converters, with those produced by the MATLAB/SIMULINK models of the converters. The experimental and theoretical results are also compared with the bifurcation points predicted by the bifurcation diagrams. The simulated waveforms show excellent agreement, with both the experimental waveforms and the transitions predicted by the bifurcation diagrams. The thesis presents the first application of a delayed feedback control scheme for eliminating chaotic behaviour in both the DC-DC boost converter and the PFC boost converter. Experimental results and FORTRAN simulations show the effectiveness and robustness of the scheme. FORTRAN simulations are found to be in close agreement with experimental results and the bifurcation diagrams. A theoretical comparison is made between the above converters controlled using delayed feedback control and the popular slope compensation method. It is shown that delayed feedback control is a simpler scheme and has a better performance than that for slope compensation.

Este trabalho contempla o projeto de um manipulador robótico cilindro atuado por motores de passo com cinco juntas de atuação. As etapas do projeto do robô, que tratam este estudo, foram divididas em: projeto mecânico; modelagem matemática; projeto do controlador; e simulações. O projeto mecânico apresenta uma proposta de configuração e dimensionamento mecânicos que supre a demanda exigida para a operação analisada. O modelo matemático apresenta as características elétricas e mecânicas do atuador e as características mecânicas do robô. O projeto de um controlador linear é realizado por meio da alocação dos polos do sistema em malha fechada através da realimentação dos estados de posição e de velocidade angulares do rotor unidos a um integrador do erro de posição angular. Para o primeiro grau de liberdade, por conta da variação do momento de inércia de massa associado a essa junta, um controlador com ganhos parametrizados foi projetado, no qual os ganhos são calculados baseado no modelo matemático relativo ao momento de inércia de massa associado a essa junta. Por meio de simulações computacionais, avaliou-se o projeto dos controladores no movimento ponto a ponto dos cinco eixos de atuação e a variação do momento de inércia de massa sobre a primeira junta. Os resultados dessas simulações mostraram que os controladores propostos cumprem com a dinâmica desejada nos cinco graus de liberdade do robô. / This work contemplates the design of a robotic manipulator, which is operated by a stepper motor with five actuation joints. The robot design steps were divided into: mechanical design; mathematical modeling; controller design; and simulations. The mechanical design presents a proposal of mechanical configuration and sizing that supplies the required demand for the analyzed operation. The mathematical model presents the electrical and mechanical characteristics of the actuator and the mechanical characteristics of the robot. The design of a linear controller is accomplished by allocating the poles of the closed loop system by states feedback of the position and angular speed of the rotor attached to an angular position error integrator. For the first degree of freedom, due to the variation of mass moment of inertia associated with this joint, a controller with parameterized gains was projected, in which the gains are calculated based on the mathematical model related to the mass moment of inertia associated to this joint. By means of computational simulations, we evaluated the design of the controllers in the point-to-point movement of the five actuation joints and the variation of the mass moment of inertia on the first joint. The results of these simulations showed that the proposed controllers comply with the desired dynamics in the robot’s five degrees of freedom.

Este trabalho contempla o projeto de um manipulador robótico cilindro atuado por motores de passo com cinco juntas de atuação. As etapas do projeto do robô, que tratam este estudo, foram divididas em: projeto mecânico; modelagem matemática; projeto do controlador; e simulações. O projeto mecânico apresenta uma proposta de configuração e dimensionamento mecânicos que supre a demanda exigida para a operação analisada. O modelo matemático apresenta as características elétricas e mecânicas do atuador e as características mecânicas do robô. O projeto de um controlador linear é realizado por meio da alocação dos polos do sistema em malha fechada através da realimentação dos estados de posição e de velocidade angulares do rotor unidos a um integrador do erro de posição angular. Para o primeiro grau de liberdade, por conta da variação do momento de inércia de massa associado a essa junta, um controlador com ganhos parametrizados foi projetado, no qual os ganhos são calculados baseado no modelo matemático relativo ao momento de inércia de massa associado a essa junta. Por meio de simulações computacionais, avaliou-se o projeto dos controladores no movimento ponto a ponto dos cinco eixos de atuação e a variação do momento de inércia de massa sobre a primeira junta. Os resultados dessas simulações mostraram que os controladores propostos cumprem com a dinâmica desejada nos cinco graus de liberdade do robô. / This work contemplates the design of a robotic manipulator, which is operated by a stepper motor with five actuation joints. The robot design steps were divided into: mechanical design; mathematical modeling; controller design; and simulations. The mechanical design presents a proposal of mechanical configuration and sizing that supplies the required demand for the analyzed operation. The mathematical model presents the electrical and mechanical characteristics of the actuator and the mechanical characteristics of the robot. The design of a linear controller is accomplished by allocating the poles of the closed loop system by states feedback of the position and angular speed of the rotor attached to an angular position error integrator. For the first degree of freedom, due to the variation of mass moment of inertia associated with this joint, a controller with parameterized gains was projected, in which the gains are calculated based on the mathematical model related to the mass moment of inertia associated to this joint. By means of computational simulations, we evaluated the design of the controllers in the point-to-point movement of the five actuation joints and the variation of the mass moment of inertia on the first joint. The results of these simulations showed that the proposed controllers comply with the desired dynamics in the robot’s five degrees of freedom.

Este trabalho contempla o projeto de um manipulador robótico cilindro atuado por motores de passo com cinco juntas de atuação. As etapas do projeto do robô, que tratam este estudo, foram divididas em: projeto mecânico; modelagem matemática; projeto do controlador; e simulações. O projeto mecânico apresenta uma proposta de configuração e dimensionamento mecânicos que supre a demanda exigida para a operação analisada. O modelo matemático apresenta as características elétricas e mecânicas do atuador e as características mecânicas do robô. O projeto de um controlador linear é realizado por meio da alocação dos polos do sistema em malha fechada através da realimentação dos estados de posição e de velocidade angulares do rotor unidos a um integrador do erro de posição angular. Para o primeiro grau de liberdade, por conta da variação do momento de inércia de massa associado a essa junta, um controlador com ganhos parametrizados foi projetado, no qual os ganhos são calculados baseado no modelo matemático relativo ao momento de inércia de massa associado a essa junta. Por meio de simulações computacionais, avaliou-se o projeto dos controladores no movimento ponto a ponto dos cinco eixos de atuação e a variação do momento de inércia de massa sobre a primeira junta. Os resultados dessas simulações mostraram que os controladores propostos cumprem com a dinâmica desejada nos cinco graus de liberdade do robô. / This work contemplates the design of a robotic manipulator, which is operated by a stepper motor with five actuation joints. The robot design steps were divided into: mechanical design; mathematical modeling; controller design; and simulations. The mechanical design presents a proposal of mechanical configuration and sizing that supplies the required demand for the analyzed operation. The mathematical model presents the electrical and mechanical characteristics of the actuator and the mechanical characteristics of the robot. The design of a linear controller is accomplished by allocating the poles of the closed loop system by states feedback of the position and angular speed of the rotor attached to an angular position error integrator. For the first degree of freedom, due to the variation of mass moment of inertia associated with this joint, a controller with parameterized gains was projected, in which the gains are calculated based on the mathematical model related to the mass moment of inertia associated to this joint. By means of computational simulations, we evaluated the design of the controllers in the point-to-point movement of the five actuation joints and the variation of the mass moment of inertia on the first joint. The results of these simulations showed that the proposed controllers comply with the desired dynamics in the robot’s five degrees of freedom.

A Left Ventricular Assist Device (LVAD) is a mechanical pump that helps patients with heart failure conditions. This rotary pump works in parallel to the ailing heart and provides an alternative path for blood flow from the weak left ventricle to the aorta. The LVAD is controlled by the power supplied to the pump motor. An increase in the pump motor power increases the pump speed and the pump flow. The LVAD is typically controlled at a fixed setting of pump power. This basically means that the controller does not react to any change in the activity level of the patient. An important engineering challenge is to develop an LVAD feedback controller that can automatically adjusts its pump motor power so that the resulting pump flow matches the physiological demand of the patient. To this end, the development of a mathematical model that can be used to accurately simulate the interaction between the cardiovascular system of the patient and the LVAD is essential for the controller design. The use of such a dynamic model helps engineers and physicians in testing their theories, assessing the effectiveness of prescribed treatments, and understanding in depth the characteristics of this coupled bio-mechanical system. The first contribution of this dissertation is the development of a pump power-based model for the cardiovascular-LVAD system. Previously, the mathematical models in the literature assume availability of the pump speed as an independent control variable. In reality, however, the device is controlled by pump motor power which, in turn, produces the rotational pump speed. The nonlinear relationship between the supplied power and the speed is derived, and interesting observations about the pump speed signal are documented. The second contribution is the development of a feedback controller for patients using an LVAD as either a destination therapy or a bridge to transplant device. The main objective of designing this controller is to provide a physiological demand of the patient equivalent of that of a healthy individual. Since the device is implanted for a long period of time, this objective is chosen to allow the patient to live a life as close to normal as possible. The third contribution is an analysis of the aortic valve dynamics under the support of an LVAD. The aortic valve may experiences a permanent closure when the LVAD pump power is increased too much. The permanent closure of the aortic valve can be very harmful to the patients using the device as a bridge to recovery treatments. The analysis illustrates the various changes in the hemodynamic variables of the patient as a result of aortic valve closing. The results establish the relationship between the activity level and the heart failure severity with respect to the duration of the aortic valve opening.

Orientador: Edvaldo Assunção / Resumo: Neste trabalho são propostos resultados para a estabilidade de sistemas lineares sujeitos a parâmetros variantes no tempo (do inglês, Linear Parameter Varying - LPV) e incertezas paramétricas. De início, apresenta-se um método para o projeto de um controlador robusto e gain scheduled via desigualdades matriciais lineares (do inglês, Linear Matrix Inequalitities - LMIs), com base na teoria de estabilidade segundo Lyapunov, com parâmetro variante no tempo e empregando a realimentação derivativa. Propõe-se um método para projetar o controlador gain scheduled usando realimentação derivativa, considerando também incertezas paramétricas. Esta nova formulação foi obtida utilizando o Lema de Finsler, o que permitiu determinar o ganho do controlador sem a necessidade de inverter uma matriz literal. Condições menos conservadoras foram projetadas para um controlador gain scheduled considerando a realimentação dos estados do sistemas. Simulações computacionais com exemplos numéricos mostram que os teoremas propostos neste trabalho são menos conservadores do que os existentes na literatura. A metodologia apresentada foi implementada no sistema de suspensão ativa. / Abstract: In this work, results for the stability of linear parameter-varying (LPV) systems and parametric uncertainties are poposed. At first, a method for desining a gain scheduled and robust controller is described via linear matrix inequalities (Linear Matrix Inequalitities - LMIs), based on the stability theory of Lyapunov, with time-variant parameters and using state derivative feedback. A method to design a gain scheduling controller using state derivative feedback and also considering parametric uncertains is proposed. This new formulation was manipulated using the Finsler’s Lemma, and allowed to determine the control law without having to invert a symbolic matrix. Less conservative conditions were designed for a gain scheduled controller considering system state feedback. Computational simulations with numerical examples show that the theorems proposed in this work are less conservative than those in the literature. The presented methodology was implemented in the active suspension system. / Doutor

<p>The aim of this thesis is to investigate how the absolute accuracy of an industrial robot can be increased by monitoring the position of the robot. The motive is to automate high precision, low volume production such as aircraft industry. A laser tracker that can measure both position and orientation with very high accuracy isused to monitor the robot tool position. The robot and laser tracker are integrated via a standard computer. </p><p>The abilities and performance of the robot, with and without feedback from the laser tracker, are investigated. Robotic drilling is performed with supervision and control from the laser tracker. </p><p>The system is implemented and tested on parts of a demonstrator for new aircraft assembly techniques. The ability to position components with internal friction to (+/-)0.05 mm absolute accuracy is shown.</p>

The aim of this thesis is to investigate how the absolute accuracy of an industrial robot can be increased by monitoring the position of the robot. The motive is to automate high precision, low volume production such as aircraft industry. A laser tracker that can measure both position and orientation with very high accuracy isused to monitor the robot tool position. The robot and laser tracker are integrated via a standard computer. The abilities and performance of the robot, with and without feedback from the laser tracker, are investigated. Robotic drilling is performed with supervision and control from the laser tracker. The system is implemented and tested on parts of a demonstrator for new aircraft assembly techniques. The ability to position components with internal friction to (+/-)0.05 mm absolute accuracy is shown.