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UBC Theses and Dissertations

Non-linear wave forces on floating breakwaters Niwinski, Chris T.


A non-linear numerical method of calculating wave forces on floating bodies is investigated. A computer program has been developed that will time step a given wave past a fixed two-dimensional rectangular breakwater. The effect of various input parameters on the accuracy of results is investigated, and optimal values of the parameters are determined. The required initial condition for the time stepping procedure has a specified incident wave attenuated to zero flow in the vicinity of the body. Incident waves predicted by both linear wave theory and Stokes' fifth order wave theory are tested. The decay length and group velocity of the incident wave train are varied. It is found that a decay length of approximately one wavelength is optimal, and that the group velocity of the developed flow is relatively independent of the initially specified group velocity. Different time step sizes, segment lengths, and time stepping equations are investigated. The tests conducted indicate that twenty-five time steps and ten segments per wave period are sufficient for accurate results. The Adams-Bashforth three step method is found to be the preferred time stepping technique. Forces on the fixed body and transmitted wave heights are obtained from the program. The results compare well with previously published results and clearly demonstrate the non-linearity of the method, with different force curves resulting from varying wave heights.

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