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Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 345-354).

Shelf tidal streams are accelerated by coastal features, such as headlands and islands. In the search for sustainable forms of electricity generation, such locations may become attractive for tidal stream power. For many prospective sites, however, little is known about the intricacies of the local tidal dynamics: knowledge which is crucial to understanding the resource and the potential environmental consequences of its extraction. This thesis explores tidal stream energy in the Pentland Firth (Scotland, UK). This channel contains some of the most promising tidal stream energy sites in the world and is set to become host to the first large-scale arrays of tidal stream turbines, but its detailed characteristics were previously unknown. A hydrodynamic model was used to investigate the complex tidal dynamics of the Pentland Firth. This demonstrated, for the first time, the hydrodynamic mechanisms driving the exceptionally fast tidal currents through this channel. The model was then refined at a key site within the Pentland Firth, the Inner Sound. The results provided insight into complex flow characteristics, such as displacement and misalignment of peak flood and ebb tides, which must be considered when contemplating the exploitation of this energy resource. Tidal stream turbines were simulated in the hydrodynamic model. Artificial energy extraction was parameterised at the sub-grid-scale via added seabed drag. Turbine drag of varying magnitude was represented by a novel analytical model based on published characteristics of horizontal axis turbines. This new formulation reflects the non-linear dynamics of tidal turbine operation. Using the new turbine model, arrays of turbines were simulated within the Inner Sound. Complex interactions between the dynamics of energy extraction and flow required individual turbines to be parameterised in-concert with all other turbines in the array. This required extra effort, but offered enhanced insight into the behaviour of turbine arrays. Accounting for nonlinear turbine dynamics at high current speeds limited the magnitude of peak energy dissipation. Tidal stream velocities decreased both upstream and downstream of the extraction zone and were accelerated around it. At peak energy extraction, changes in tidal velocity were detectable several kilometres from the array, but were confined to the shallow waters of the Inner Sound and its environs. Implications for array modelling are discussed in the context of environmental impact assessments.

Thesis (MScEng)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

 As fossil energy is depleting and global warming effect is worsening rapidly, developing renewable energies becomes the top priority in most countries. In recent years, wave energy has attracted more and more attention due to its high energy density and enormous global capacity. The goal of this study is to carry out a numerical study of the hydrodynamic performance of a point-absorbing wave energy converter. In this study, an accurate and efficient numerical wave fume was established first. Commercial software code FLUENT?, which is a state-of-the-art computer program package for modeling fluid flow and heat transfer, was used for the numerical simulation. Based on the Navier-Stokes equations for viscous, incompressible fluid and Volume of fluid (VOF) method, a numerical wave tank was developed. Dynamic meshing method was used to simulate the wavemaker, and Geo-Reconstruct scheme was used to capture and reconstruct the free surface. A wave-absorbing method employing porous medium model was proposed to act as the wave absorbing beach, which can absorb the wave energy efficiently. A series of regular waves were simulated using the proposed numerical method. Validation has been made by physical experiments. After developing the wave flume model, a cylinder, which represents the point-absorbing wave energy converter (WEC), was added into the wave flume. The hydrodynamic behavior of the WEC was studied. The numerical results were also compared with physical experiments. Based on the numerical simulation results, suggestions on optimizing the point-absorber are provided. In this study, eight wave cases, with different wave period and wave length were simulated. The results show that the numerical simulation can match well with the physical wave tank result. Both the wave height and wave period in different cases can match well between the numerical simulation and physical wave tank results. In the wave-cylinder simulation, the results also show a good match in the numerical study and physical study. This numerical model is very significant in ocean structure design. The cylinder tested in this study can be easily changed to a ship or an offshore-platform. Compared with the physical experiment, numerical simulation is more flexible. The simulation can be carried on a large time span and spatial scale. The geometry can be changed easily. Also the cost of numerical simulation is relatively cheap compared with the physical experiment. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

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Graduation date: 1997