The in-plane phenomena of interaction between the tyre structural response and contact force generation are investigated in this work. The challenges of the physical tyre simulation are identified, primarily associated with the computational load imposed by the need to capture the space distributed mechanisms that prescribe the above interaction. The method of modal expansion and reduction is proposed for the moderation of this load. The theoretical framework for the transformation of a tyre modal representation into a transient contact and shear force generation model is developed. Various modelling approaches are examined with regards to their modal prediction characteristics. Linear and non linear structural features as well as the physical properties that define the broad range modal behaviour are identified. A discretised form of the ring model is derived and combined with a foundation of viscoelastic tread elements for simulating the transient contact behaviour of the tyre. The resulting pattern of the modes' excitation justifies the validity of the modal reduction method and reveals the relative importance of various mechanisms and physical properties in tyre contact behaviour. The interaction between the friction controlled shear slip of the tread, the belt compliance and the sidewall buckling is found to be reflected on the two-dimensional contact pressure distribution patterns. A method able to simulate the dynamic transient rolling and slipping operating conditions is developed, although the small displacement assumption of the modal approach is dropped. The method, which is based on the combined modal-time and space-time domain solutions, is applied on the study of the physical mechanism of the launch process. The examination of the model under steady state kinematic conditions reveals the saturation of the traction force for profound levels of slip, which highlights the contribution of the structural mechanisms on the macroscopically observed shear force performance of the tyre. The variation of the modes' level of excitation, as induced by the operating conditions, is proposed for the capture of the physical properties effect on tyre behaviour and performance.

Pulse-width modulation methods are widely used for the synthesis of ac voltages at the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth modulation (SPWM) has been used. A powerful alternative for this purpose is space-vector modulation (SVM), in which the converter is placed in a finite number of states in order to best approximate the reference voltage. This method offers better utilization of the dc bus voltage and provides several degrees of freedom for enhancement of the harmonic spectrum as well as switching losses. This thesis studies the SVM method for two- and three-level VSCs. A model for implementation of SVM in the electromagnetic transients simulation program PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear as well as overmodulation range and is used to study the performance of different SVM strategies in terms of their harmonic spectra and associated converter and harmonic losses. The model is also used to demonstrate the suitability of the method for network applications. The thesis also employs genetic algorithms to find an optimized SVM sequence for improved harmonic performance. An objective function is defined that seeks to minimize the most significant harmonic components of the generated waveform, while keeping the other harmonic components within the acceptable range outlined in the available standards. The obtained sequence shows great improvement over the conventionally-used SVM sequence. / October 2007

Pulse-width modulation methods are widely used for the synthesis of ac voltages at the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth modulation (SPWM) has been used. A powerful alternative for this purpose is space-vector modulation (SVM), in which the converter is placed in a finite number of states in order to best approximate the reference voltage. This method offers better utilization of the dc bus voltage and provides several degrees of freedom for enhancement of the harmonic spectrum as well as switching losses. This thesis studies the SVM method for two- and three-level VSCs. A model for implementation of SVM in the electromagnetic transients simulation program PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear as well as overmodulation range and is used to study the performance of different SVM strategies in terms of their harmonic spectra and associated converter and harmonic losses. The model is also used to demonstrate the suitability of the method for network applications. The thesis also employs genetic algorithms to find an optimized SVM sequence for improved harmonic performance. An objective function is defined that seeks to minimize the most significant harmonic components of the generated waveform, while keeping the other harmonic components within the acceptable range outlined in the available standards. The obtained sequence shows great improvement over the conventionally-used SVM sequence.

The thesis introduces an approach for obtaining higher level decision support information using electromagnetic transient (EMT) simulation programs. In this approach, a suite of higher level driver programs (decision support tools) control the simulator to gain important information about the system being simulated. These tools conduct a sequence of simulation runs, in each of which the study parameters are carefully selected based on the observations of the earlier runs in the sequence. In this research two such tools have been developed in conjunction with the PSCAD/EMTDC electromagnetic transient simulation program. The first tool is an improved optimization algorithm, which is used for automatic optimization of the system parameters to achieve a desired performance. This algorithm improves the capabilities of the previously reported method of optimization-enabled electromagnetic transient simulation by using an enhanced gradient-based optimization algorithm with constraint handling techniques. In addition to allow handling of design problems with more than one objective the thesis proposes to augment the optimization tool with the technique of Pareto optimality. A sequence of optimization runs are conducted to obtain the Pareto frontier, which quantifies the tradeoffs between the design objectives. The frontier can be used by the designer for decision making process. The second tool developed in this research helps the designer to study the effects of uncertainties in a design. By using a similar multiple-run approach this sensitivity analysis tool provides surrogate models of the system, which are simple mathematical functions that represent different aspects of the system performance. These models allow the designer to analyze the effects of uncertainties on system performance without having to conduct any further time-consuming EMT simulations. In this research it has been also proposed to add probabilistic analysis capabilities to the developed sensitivity analysis tool. Since probabilistic analysis of a system using conventional techniques (e.g. Monte-Carlo simulations) normally requires a large number of EMT simulation runs, using surrogate models instead of the actual simulation runs yields significant savings in terms of shortened simulation time. A number of examples have been used throughout the thesis to demonstrate the application and usefulness of the proposed tools.

Natural lightning strikes induce impulsive overvoltages on transmission lines and its terminal equipment. These overvoltages may cause failures in insulation mechanisms of electrical devices in the power system. It is important to test the insulation strength of a device against these impulsive overvoltages. Usually, Marx generators are used to generate impulse waveforms for testing purposes. A novel approach is proposed to obtain resistor settings of a Marx generator for impulse testing of power transformers. This approach enables us to overcome most of the major challenges in the commonly used trial-and-error method, including excessive time consumption and potential damage to the transformer. The proposed approach uses the frequency response of the transformer to synthesize a circuit model. Then, a genetic algorithm based optimization-enabled electromagnetic transient simulation approach is used to obtain the resistor settings. The proposed approach is validated by a real impulse test conducted on a three phase power transformer.

Pulse-width modulation methods are widely used for the synthesis of ac voltages at the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth modulation (SPWM) has been used. A powerful alternative for this purpose is space-vector modulation (SVM), in which the converter is placed in a finite number of states in order to best approximate the reference voltage. This method offers better utilization of the dc bus voltage and provides several degrees of freedom for enhancement of the harmonic spectrum as well as switching losses. This thesis studies the SVM method for two- and three-level VSCs. A model for implementation of SVM in the electromagnetic transients simulation program PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear as well as overmodulation range and is used to study the performance of different SVM strategies in terms of their harmonic spectra and associated converter and harmonic losses. The model is also used to demonstrate the suitability of the method for network applications. The thesis also employs genetic algorithms to find an optimized SVM sequence for improved harmonic performance. An objective function is defined that seeks to minimize the most significant harmonic components of the generated waveform, while keeping the other harmonic components within the acceptable range outlined in the available standards. The obtained sequence shows great improvement over the conventionally-used SVM sequence.

The thesis introduces an approach for obtaining higher level decision support information using electromagnetic transient (EMT) simulation programs. In this approach, a suite of higher level driver programs (decision support tools) control the simulator to gain important information about the system being simulated. These tools conduct a sequence of simulation runs, in each of which the study parameters are carefully selected based on the observations of the earlier runs in the sequence. In this research two such tools have been developed in conjunction with the PSCAD/EMTDC electromagnetic transient simulation program. The first tool is an improved optimization algorithm, which is used for automatic optimization of the system parameters to achieve a desired performance. This algorithm improves the capabilities of the previously reported method of optimization-enabled electromagnetic transient simulation by using an enhanced gradient-based optimization algorithm with constraint handling techniques. In addition to allow handling of design problems with more than one objective the thesis proposes to augment the optimization tool with the technique of Pareto optimality. A sequence of optimization runs are conducted to obtain the Pareto frontier, which quantifies the tradeoffs between the design objectives. The frontier can be used by the designer for decision making process. The second tool developed in this research helps the designer to study the effects of uncertainties in a design. By using a similar multiple-run approach this sensitivity analysis tool provides surrogate models of the system, which are simple mathematical functions that represent different aspects of the system performance. These models allow the designer to analyze the effects of uncertainties on system performance without having to conduct any further time-consuming EMT simulations. In this research it has been also proposed to add probabilistic analysis capabilities to the developed sensitivity analysis tool. Since probabilistic analysis of a system using conventional techniques (e.g. Monte-Carlo simulations) normally requires a large number of EMT simulation runs, using surrogate models instead of the actual simulation runs yields significant savings in terms of shortened simulation time. A number of examples have been used throughout the thesis to demonstrate the application and usefulness of the proposed tools.

[pt] Este trabalho apresenta o estudo do escoamento transiente em difusores radiais com fronteira móvel alimentados axialmente. O problema é resolvido acoplando-se a modelagem do fluido à dinâmica do movimento da palheta. Admite-se o comportamento Newtoniano para o fluido de trabalho (ar). O escoamento é considerado incompressível, laminar e isotérmico numa geometria axisimétrica. As equações de conservação são resolvidas pelo método dos volumes-finitos utilizando-se um código numérico comercial, o FLUENT, adaptado de modo a permitir que o posicionamento da fronteira móvel faça parte da solução do problema. Analise-se os casos de movimentação súbita imposta à palheta e de fluxo mássico de alimentação periódica. Resultados do comportamento temporal da força axial do fluido sobre a palheta são apresentados. Determina-se também o campo de geração de entropia para o escoamento bem como sua variação para diversos instantes de tempo. / [en] This work presents the study of unsteady flow in a axially fed radial flow between parallel disks on a situation in which the frontal disk can move. The problem is solved coupling the fluid flow modeling and the valve dynamics movement. The fluid (air) is assumed to have a Newtonian behavior. The flow is incompressible, laminar and isothermal in an axisymmetric geometry. The governing equations are solved by finite volume methodology using a commercial software, FLUENT, which have been modified to admit boundary movement as part of the solution. The flow characteristics presented herein relate to situations where: I. the frontal disk is suddenly moved to a new location and ii. prescribed mass flux at the inlet orifice. Results for the behavior of the axial force in the frontal disk can be seen. Another important parameter analyzed is the entropy generation and its time variation.

No description available.

Combined Cooling, Heating, and Power (CHP) systems have been widely recognized as a key alternative for electric and thermal energy generation because of their outstanding energy efficiency, reduced environmental emissions, and relative independence from centralized power grids. The systems provide simultaneous onsite or near-site electric and thermal energy generation in a single, integrated package. As CHP becomes increasingly popular worldwide and its total capacity increases rapidly, the research on the topics of CHP performance assessment, design, and operational strategy become increasingly important. Following this trend of research activities to improve energy efficiency, environmental emissions, and operational cost, this dissertation focuses on the following aspects: (a) performance evaluation of a CHP system using a transient simulation model; (b) development of a dynamic simulation model of a power generation unit that can be effectively used in transient simulations of CHP systems; (c) investigation of real-time operation of CHP systems based on optimization with respect to operational cost, primary energy consumption, and carbon dioxide emissions; and (d) development of optimal supervisory feedorward control that can provide realistic real-time operation of CHP systems with electric and thermal energy storages using short-term weather forecasting. The results from a transient simulation of a CHP system show that technical and economical performance can be readily evaluated using the transient model and that the design, component selection, and control of a CHP system can be improved using this model. The results from the case studies using optimal real-time operation strategies demonstrate that CHP systems with an energy dispatch algorithm have the potential to yield savings in operational cost, primary energy consumption, and carbon dioxide emissions with respect to a conventional HVAC system. Finally, the results from the case study using a supervisory feedorward control system illustrate that optimal realistic real-time operation of CHP systems with electric and thermal energy storages can be managed by this optimal control using weather forecasting information.