An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.

This dissertation deals with the instability, known as flutter, of the lifting and control surfaces of aircraft of advanced design at high altitudes and speeds. A simple model is used to represent the aerodynamics for flutter analysis of a two-degree-of-freedom airfoil system. Flutter solutions of this airfoil system are shown to be algebraically homomorphic in that solutions about different elastic axes can be found by mapping them to those about the mid-chord. Algebraic expressions for the flutter speed and frequency are thus obtained. For the prediction of flutter of a wing at transonic speeds, an accurate and efficient computer code is developed. The unique features of this code are the capability of accepting a steady mean flow regardless of its origin, a time dependent perturbation boundary condition for describing wing deformations on the mean surface, and a locally applied three-dimensional far-field boundary condition for minimizing wave reflections from numerical boundaries. Results for various test cases obtained using this code show good agreement with the experiments and other theories.

As propriedades da turbulência induzida em um fluido viscoso através da oscilação de uma grade foram investigadas experimentalmente utilizando a técnica DPIV (Digital Particle Image Velocimetry). Perfis verticais da energia cinética turbulenta, taxa de dissipação de energia, viscosidade turbulenta e escala de comprimento foram obtidos e comparados com soluções analíticas existentes. Os dados experimentais mostram uma boa concordância com as predições teóricas. Adicionalmente, foi observado que há uma variação significativa da intensidade turbulenta para distâncias próximas da grade. Com o aumento da distância, a turbulência se torna mais homogênea no plano horizontal, e estas variações tendem a desaparecer. Os resultados mostram também que o escoamento somente pode ser considerado livre de cisalhamento para grandes distâncias da grade, onde as tensões de Reynolds se aproximam de zero. Além disso, descobriu-se que são necessários no mínimo 450 campos de vetores para assegurar a precisão das medidas. Também foram realizadas medidas de turbulência em uma configuração de duas grades. Os resultados mostram que a região central entre as duas grades possui certas propriedades similares à turbulência isotrópica. Adicionalmente, foram realizadas comparações com o modelo k-&#949, mostrando que o mesmo pode ser aplicado a uma configuração de duas grades. / The properties of turbulence induced in a viscous fluid by oscillating a grid were investigated experimentally using the digital particle image velocimetry (DPIV). Vertical profiles of the turbulent energy, the dissipation rate, the eddy viscosity and a lengthscale have been obtained and compared with available analytical solutions. The experimental data agree well with the theoretical predictions. In addition, it could be observed that there are significant variations of the turbulent intensities at a small distance from the grid. With increasing distance from the grid, the turbulence becomes more homogeneous in the horizontal plane, and the variations in the turbulent intensities are reduced. The results also show that the turbulence can be considered to be shear-free only at a distance sufficiently far away from the grid, where the Reynolds shear stress aproaches zero. It became evident, furthermore, that at least 450 vector maps should be taken to ensure the accuracy of the measured velocity fluctuations. Turbulence was also measured for a two-grid configuration. It was found that the central region between the grids has certain properties similar to that of isotropic turbulence. The results show good agreement with the k-&#949 model, validating the application of the k-&#949 model to a pair of oscillating-grids.

<p>Wave power is renewable energy which is environmentally friendly. Unlike most of renewable energy resources, wave energy can produce power all the year. The wave energy is stored in the ocean worldwide and highly concentrated near the ocean surface. It can be captured by wave power devices. Wave power is considered as a competitive energy resource in future.</p><p> <strong></strong></p><p>Waves are generated by wind blows across the surface of sea. Wave energy is one kind of mechanical energy which will be used for electricity generation. Wave power can’t be used directly to generate electricity; at first the wave energy is converted into the other form of useful mechanical energy and then converted into electricity. Wave power has a high potential to be captured and used for generating electricity in future as the technology develops further.</p><p> </p><p>Wave energy has been used since 1890s. There is a lot of energy stored in waves. 94% energy of the ocean stored in the wave, and the other 6% is tidal energy.  Only small a part of the wave power is used for commercial electricity generation today.</p><p> </p><p>The China is a developing country with a very large population which annually consume about 3073TWh electricity of which 496TWh is from renewable energy.  The wave power was less than 1GWh in 2007 (reference from International Energy Agency). The World Energy Council has measured the total useful power of the ocean wave energy to be more than 2TW in the world and corresponding to 6000TWh per year. There is about 70GW useful wave power resources in China, equivalent to an annual useful wave power resource of 200TWh.</p><p> </p><p>The lowest capital cost for the wave power system is today around 0.1Euro/kWh. China will in the future focus on the development electricity generation by wave power. There will be hundreds of new wave power plant built in China during the next twenty years, and the total installed capacity will be larger than 1GW at 2030, which delivers 3TWh annually. This corresponds to less than 1 percent of the total use of electricity in China.</p><p> </p><p>This thesis focuses on the functionality, efficiency and economic pay-off of existing ocean wave power systems, as well as how easy the ocean wave power can produce electricity. Firstly it discusses the physical concepts of wave power, and then focus on the existing wave power systems around the world. It is concluded from the Chinese sea characteristics and the designed conditions of different wave power systems, that the Pelamis and Oyster wave power converters are the best suitable systems for China.</p>

by W.G. Tuller, W.C. Galloway and F.P. Zaffarano. / "November 20, 1947." / Includes bibliographical references. / Army Signal Corps Contract No. W-36-039 sc-32037.

Wave power is renewable energy which is environmentally friendly. Unlike most of renewable energy resources, wave energy can produce power all the year. The wave energy is stored in the ocean worldwide and highly concentrated near the ocean surface. It can be captured by wave power devices. Wave power is considered as a competitive energy resource in future.   Waves are generated by wind blows across the surface of sea. Wave energy is one kind of mechanical energy which will be used for electricity generation. Wave power can’t be used directly to generate electricity; at first the wave energy is converted into the other form of useful mechanical energy and then converted into electricity. Wave power has a high potential to be captured and used for generating electricity in future as the technology develops further.   Wave energy has been used since 1890s. There is a lot of energy stored in waves. 94% energy of the ocean stored in the wave, and the other 6% is tidal energy.  Only small a part of the wave power is used for commercial electricity generation today.   The China is a developing country with a very large population which annually consume about 3073TWh electricity of which 496TWh is from renewable energy.  The wave power was less than 1GWh in 2007 (reference from International Energy Agency). The World Energy Council has measured the total useful power of the ocean wave energy to be more than 2TW in the world and corresponding to 6000TWh per year. There is about 70GW useful wave power resources in China, equivalent to an annual useful wave power resource of 200TWh.   The lowest capital cost for the wave power system is today around 0.1Euro/kWh. China will in the future focus on the development electricity generation by wave power. There will be hundreds of new wave power plant built in China during the next twenty years, and the total installed capacity will be larger than 1GW at 2030, which delivers 3TWh annually. This corresponds to less than 1 percent of the total use of electricity in China.   This thesis focuses on the functionality, efficiency and economic pay-off of existing ocean wave power systems, as well as how easy the ocean wave power can produce electricity. Firstly it discusses the physical concepts of wave power, and then focus on the existing wave power systems around the world. It is concluded from the Chinese sea characteristics and the designed conditions of different wave power systems, that the Pelamis and Oyster wave power converters are the best suitable systems for China.

Shape Memory Alloys (SMA) are a group of metallic alloys that have the ability to return to some previously defined shape or size when subjected to an appropriate thermal cycling procedure. In recent years there has been a lot of research on the development of small, light and, yet, powerful actuators for use in areas like robotics, prosthetics, biomimetics, shape control and grippers. Many of the miniaturized conventional actuators do not have sufficient power output to be useful and SMAs can be used advantageously here. The widespread use of SMAs in actuators is limited by their low bandwidth. Use of SMAs in two-way actuators requires that they undergo thermal cycling (heating and cooling). While SMAs can be heated quickly by resistive heating, conventional convection cooling mechanisms are much slower as the exothermic austenitic to martensitic phase transformation is accompanied by the release of significant amount of latent heat. While a number of cooling mechanisms have been studied in SMA actuator literature, most of the cooling mechanisms involve unidirectional forced convection. This may not be the most effective method. Oscillating flow in a channel can sometimes enhance heat transfer over a unidirectional flow. One possible explanation for this heat transfer enhancement is that the oscillatory flow creates a very thin Stokes viscous boundary-layer and hence a large time-dependent transverse temperature gradient at the heated wall. Therefore heat transfer takes place at a large temperature difference, thereby enhancing the heat transfer. In this work, the heat transfer from an SMA actuator under an oscillating channel is investigated and is compared to steady, unidirectional flow heat transfer. Oscillating flow is simulated using a finite volume based method. The resulting velocity field is made use of in solving the heat transfer problem using a finite difference scheme. A parametric study is undertaken to identify the optimal flow conditions required to produce the maximum output for a given geometry of the SMA actuator. The latent heat of transformation of the SMA is accounted for by means of a temperature dependent specific heat.

Thesis (M. Eng. Sc.)--University of Queensland, 2002. / Includes bibliographical references.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph. D.)--University of Washington, 1997. / Vita. Includes bibliographical references (leaves [99]-104).