M.S. - Ocean and Resources Engineering
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ItemBottom-Discontinuous Riemann Solver for Modeling of Wave Overtopping([Honolulu] : [University of Hawaii at Manoa], [August 2015], 2015-08)Depth-integrated numerical models represent an adequate and efficient method to describe near-shore processes including wave breaking. A limitation to these models is encountered as a wave overtops a vertical breakwater. The vertical flow structure cannot be recreated, leading to inaccurate results or numerical instabilities. The Riemann solver containing a bottom discontinuity presented by Murillo and Garcia-Navarro (2010; 2012, Journal of Computational Physics) may alleviate this limitation. In this study, a review of the Riemann solver and its incorporation into a one-dimensional second-order MUSCL-Hancock scheme are presented. The first series of validation tests mimics the Riemann problem with an emphasis on overtopping over a bottom discontinuity. The model results give good overall agreement to those from OpenFOAM (an open-source computational fluid dynamics code), but show underestimation of the downstream propagation speed when free fall of water is involved. A laboratory experiment was conducted in a 9.14 m long flume to provide validation data for solitary wave overtopping of a vertical breakwater. The numerical model shows slightly more reflection from the breakwater and underestimates the overtopping volume. Despite the discrepancies, the bottom-discontinuous Riemann solver performs reasonably well in approximating the overall processes given the simplicity of its formulation.
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ItemIn-ocean experiments of a wave energy conversion device with a drogue and wave power calculations([Honolulu] : [University of Hawaii at Manoa], [August 2013], 2013-08)This research describes the experimental and numerical modeling of a heaving point source wave energy conversion (WEC) device developed by Trex Enterprises of Maui and tested by the University of Hawaii at Manoa. The principle of operation of the WEC device is to convert the vertical heave displacement into a rotational action, which generates electrical power. The heave displacement is created by the WEC system riding incoming waves relative to an anchoring system. Two deployment cases of the single WEC device were ocean tested with the goal of collecting power data based on the type of the anchoring method. The anchoring methods are referred to as the single-body case (moored system) and double-body case (drogue anchored system). The experiments were carried out on the South shore of Oahu during the summer of 2012. The WEC system was equipped with sensors to measure and record the heave displacements of the WEC system, the generated power output, and the surface elevation. The real time experimental data were collected and analyzed to determine the power generation profile, the WEC system's heave displacements, surface elevation, and heave response amplitude operator (RAO) for both cases. A numerical modeling program was built to perform hydrodynamic analysis in the time domain in irregular seas for the single-body or double-body case. The program solves for the individual body motion. It is used to predict the WEC device's power production over the time series.