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Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 63-65). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 63-65). Also available on the Internet.

Energy harvesting from the surrounding environment has become a hot topic in research as an alternative powering solution. The concept deals with scavenging, as well as, harvesting energy from the surrounding energy sources. Harvesting vibrations, through Micro-Power Generators (MPGs) , has drawn a lot of attention recently due to the reduction in the power requirement of the current sensors and integrated ciruits, and the abundance of ambient vibrations in many environments. Vibration Micro-Power generators (VMPGs) use one of three transduction mechanisms: piezoelectric, electromagnetic or electrostatic. Although electrostatic MPGs are the most compatible mechanism with ICs technology, many challenges face their optimal operation including low efficiency due to power electronics switching losses, the need for pre-charge, and the inability to operate in vibration environments with low frequencies and amplitudes. The objective of this thesis is to develop novel electrostatic micro-power generators using switchless architecture to achieve low cost, small footprint, self-sustained and optimal power generation in different vibration environments including low frequencies and amplitudes. The first electrostatic MPG uses an out-of-plane capacitive transducer. The new generator is sensitive enough to extract output power at very low base excitations. It is designed to use ready-made electret as a charging source and is therefore portable and self-sustained. Moreover, the new MPG can be configured as a wideband MPG in its impact mode of operation. A bandwidth of up to 9 Hz has been realized in this mode of operation. An improved version of the MPG is also presented that produces almost 1mW output power at a base excitation amplitude and frequency of 0.08g (RMS) and 86 Hz. Two nonlinear models developed for the free-flight and impact modes of operation of the MPG are presented to allow future analysis and optimization of the system. The second electrostatic MPG uses a novel interdigitated in-plane parallel plate electrostatic transducer. The new implementation can achieve 78% more output power than the original cited implementation. The MPG is fabricated using MEMS surface micromachining. The MPG introduces a new beam suspension system in which the source voltage is unlimited by the pull-in instability and low MPG center frequency can be realized. The MPG uses charged silicon nitride as a charging source. The MPG produces 65 mV at a base acceleration amplitude and frequency of 2g and 1.1 kHz. The prototype achieves 27% less resonance frequency with only one eight the size of the previous implementation. A third electrostatic MPG architecture is introduced. The new architecture eliminates the need for restoring force elements (springs) in the MPG. The architecture can realize arbitrarily low MPG center frequency. It is suitable for both rectilinear and cylindrical structures and can be used with different vibration energy transduction methods. A prototype is fabricated and tested to demonstrate the feasibility of this architecture. The center frequency of the prototype is found to be 2 Hz demonstrating low frequency operation. The nonlinear behavior of switchless (continuous) electrostatic MPGs is further studied for optimal power operation. A consistent approximate analytical solution is developed to describe the nonlinear behavior of switchless comb-finger electrostatic MPGs. The method of multiple scales is used to develop such model. The model was found to be valid for MPGs operating under tight electromechanical coupling conditions and for moderately-large base excitations.

Energy harvesting from the surrounding environment has become a hot topic in research as an alternative powering solution. The concept deals with scavenging, as well as, harvesting energy from the surrounding energy sources. Harvesting vibrations, through Micro-Power Generators (MPGs) , has drawn a lot of attention recently due to the reduction in the power requirement of the current sensors and integrated ciruits, and the abundance of ambient vibrations in many environments. Vibration Micro-Power generators (VMPGs) use one of three transduction mechanisms: piezoelectric, electromagnetic or electrostatic. Although electrostatic MPGs are the most compatible mechanism with ICs technology, many challenges face their optimal operation including low efficiency due to power electronics switching losses, the need for pre-charge, and the inability to operate in vibration environments with low frequencies and amplitudes. The objective of this thesis is to develop novel electrostatic micro-power generators using switchless architecture to achieve low cost, small footprint, self-sustained and optimal power generation in different vibration environments including low frequencies and amplitudes. The first electrostatic MPG uses an out-of-plane capacitive transducer. The new generator is sensitive enough to extract output power at very low base excitations. It is designed to use ready-made electret as a charging source and is therefore portable and self-sustained. Moreover, the new MPG can be configured as a wideband MPG in its impact mode of operation. A bandwidth of up to 9 Hz has been realized in this mode of operation. An improved version of the MPG is also presented that produces almost 1mW output power at a base excitation amplitude and frequency of 0.08g (RMS) and 86 Hz. Two nonlinear models developed for the free-flight and impact modes of operation of the MPG are presented to allow future analysis and optimization of the system. The second electrostatic MPG uses a novel interdigitated in-plane parallel plate electrostatic transducer. The new implementation can achieve 78% more output power than the original cited implementation. The MPG is fabricated using MEMS surface micromachining. The MPG introduces a new beam suspension system in which the source voltage is unlimited by the pull-in instability and low MPG center frequency can be realized. The MPG uses charged silicon nitride as a charging source. The MPG produces 65 mV at a base acceleration amplitude and frequency of 2g and 1.1 kHz. The prototype achieves 27% less resonance frequency with only one eight the size of the previous implementation. A third electrostatic MPG architecture is introduced. The new architecture eliminates the need for restoring force elements (springs) in the MPG. The architecture can realize arbitrarily low MPG center frequency. It is suitable for both rectilinear and cylindrical structures and can be used with different vibration energy transduction methods. A prototype is fabricated and tested to demonstrate the feasibility of this architecture. The center frequency of the prototype is found to be 2 Hz demonstrating low frequency operation. The nonlinear behavior of switchless (continuous) electrostatic MPGs is further studied for optimal power operation. A consistent approximate analytical solution is developed to describe the nonlinear behavior of switchless comb-finger electrostatic MPGs. The method of multiple scales is used to develop such model. The model was found to be valid for MPGs operating under tight electromechanical coupling conditions and for moderately-large base excitations.

New Artificial Intelligence (AI) approaches such as simulated annealing, genetic algorithms, simulated evolution, neural networks, tabu search, fuzzy logic and their hybrid techniques have been applied in recent years to solving Generator Maintenance Scheduling (GMS) problems. This paper presents a review of these AI approaches for the GMS problem. The formulation of problems and the methodologies of solution are discussed and analysed. A case study is also included which presents the application of a genetic algorithm to a test system based on a practical power system scenario.

The aim of generator maintenance scheduling (GMS) in an electric power system is to allocate a proper maintenance timetable for generators while maintaining a high system reliability, reducing total production cost, extending generator life time etc. In order to solve this complex problem a genetic algorithm technique is proposed here. The paper discusses the implementation of GAs to GMS problems with two approaches: generational and steady state. The results of applying these GAs to a test GMS problem based on a practical power system scenario are presented and analysed. The effect of different GA parameters is also studied

Esse trabalho propõe a investigação da geometria dos contornos internos de eixos vazados para aerogeradores quando aplicados mandris com diferentes diâmetros ao longo de seu comprimento no forjamento incremental em matriz aberta. Tem-se por finalidade a fabricação de um mandril que proporcione à peça forjada formato mais perto do formato final proposto. Foram estudados através do uso de simulações numéricas computacionais com o software Simufact.forming 12 e ensaios com o material modelo plasticina possíveis geometrias de mandris, variando a angulação na região de troca de diâmetros ao longo do comprimento entre 0˚, 30˚ e 60˚, e analisados o comportamento do escoamento do material na região. Com o processo simulatório concluído, foi produzido o mandril que apresentou melhor desempenho e foram realizados testes práticos. No total, duas peças foram forjadas e analisados seus resultados. A geometria proposta da peça foi alcançada, confirmando a escolha da cinemática do processo. A temperatura do mandril foi aferida e comparada com a temperatura durante a simulação, onde no último passe, a medida foi 720°C e a simulada em torno de 620°C. As forças de forjamento apresentaram diferença entre a simulação e forjado na média de 7,6%. / This work proposes the investigation of the internal contour of hollow shafts for wind turbines when applied mandrels with different diameters along its length in incremental open-die forging. It is intended to manufacture a mandrel to provide a forged part closer to the final proposed geometry. Studies were conducted using the numerical computer simulations software Simufact.forming 12 and models of plasticine aiming possible mandrel geometries, varying the angle of the different-diameters region along the length between 0˚, 30˚ and 60˚ and analyzed the behavior of the material flow in the region. As the simulation process was concluded, the mandrel with the best performance was produced and practical tests were performed. In total, two workpieces were forged and analyzed its results. The proposed geometry was achieved, confirming the choice of process kinematics. The temperature of the mandrel was measured and compared with the temperature during the simulation at the last pass, the measurement resulted in 720°C and the simulated around 620°C. The forging forces showed differences between simulation and forging of an average of 7.6%.

Thesis (M. Eng.)--Memorial University of Newfoundland, 1998. / Restricted until June 1999. Bibliography: leaves 95-98.

Esse trabalho propõe a investigação da geometria dos contornos internos de eixos vazados para aerogeradores quando aplicados mandris com diferentes diâmetros ao longo de seu comprimento no forjamento incremental em matriz aberta. Tem-se por finalidade a fabricação de um mandril que proporcione à peça forjada formato mais perto do formato final proposto. Foram estudados através do uso de simulações numéricas computacionais com o software Simufact.forming 12 e ensaios com o material modelo plasticina possíveis geometrias de mandris, variando a angulação na região de troca de diâmetros ao longo do comprimento entre 0˚, 30˚ e 60˚, e analisados o comportamento do escoamento do material na região. Com o processo simulatório concluído, foi produzido o mandril que apresentou melhor desempenho e foram realizados testes práticos. No total, duas peças foram forjadas e analisados seus resultados. A geometria proposta da peça foi alcançada, confirmando a escolha da cinemática do processo. A temperatura do mandril foi aferida e comparada com a temperatura durante a simulação, onde no último passe, a medida foi 720°C e a simulada em torno de 620°C. As forças de forjamento apresentaram diferença entre a simulação e forjado na média de 7,6%. / This work proposes the investigation of the internal contour of hollow shafts for wind turbines when applied mandrels with different diameters along its length in incremental open-die forging. It is intended to manufacture a mandrel to provide a forged part closer to the final proposed geometry. Studies were conducted using the numerical computer simulations software Simufact.forming 12 and models of plasticine aiming possible mandrel geometries, varying the angle of the different-diameters region along the length between 0˚, 30˚ and 60˚ and analyzed the behavior of the material flow in the region. As the simulation process was concluded, the mandrel with the best performance was produced and practical tests were performed. In total, two workpieces were forged and analyzed its results. The proposed geometry was achieved, confirming the choice of process kinematics. The temperature of the mandrel was measured and compared with the temperature during the simulation at the last pass, the measurement resulted in 720°C and the simulated around 620°C. The forging forces showed differences between simulation and forging of an average of 7.6%.