Interaction of Solitary Waves with a Submerged Breakwater and Experimental Visualizations of Induced Vortex Characteristics

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A combined analytical and experimental investigation of solitary waves interacting with a submerged impermeable breakwater is presented in this study to examine the fluid flow aspects of the wave overtopping phenomena. To the leading order of approximation, the integral forms of the analytical solutions of reflected and transmitted velocity potentials and wave elevations are derived according to the Fourier integral approach proposed by Isaacson (1983). The unknown coefficients are determined from the mixed breakwater boundary conditions using the method of least squares. Laboratory experiments were conducted to get the data in terms of wave elevations in the reflected and transmitted regions under various wave and breakwater conditions in a wave tank for validating the analytical solutions. This data was obtained using resistance- type wave gauges that were connected to the data accusation system. Generally, the analytically predicted incident and transmitted wave profiles are found to agree reasonably well with the experimental measurements while the analytical model in the cases with greater breakwater height overestimates the peak of the reflected waves. The variations of wave transmission and reflection related solution coefficients versus the breakwater height are analyzed. The effect of breakwater height on the peak of reflected and transmitted waves is also examined. It is found that with an increase of the breakwater height the transmission coefficient decreases. Also, more wave energy is transmitted through the breakwater than is contributed to the reflected waves even under the cases with high ratio of breakwater height to the water depth. The other contribution in this study emphasized the vortices visualization and tracing the flow patterns induced during solitary wave encountering with submerged oblique breakwaters using planar laser-induced fluorescence (PLIF) technique. Again, resistance-type wave gauges were utilized to measure the water surface elevation. The effects of water depth to breakwater height, water wave amplitude, and angles of breakwater inclination were examined experimentally. In addition, images of the flow field and vortices near the breakwater at particular instant of times were extracted after recording the whole experiment by video camera and then processing for comparison with a numerical model of Chang et al. (2011). The reflection and transmission of the incoming wave after encountering with the submerged breakwater are another topics to be studied. In general, both results from the experiments and the numerical model seemed to to agree reasonably well with each other and the phases of the wave profiles match fairly well. To the best of the author’s knowledge, the experiments have extensively demonstrated the usefulness of the PLIF technique for wave-breakwater interaction problems and proven to be very reliable to illustrate and reveal detailed features of vortices evolution processes.

Solitary Waves, Submerged Breakwater, Laboratory Experiments, Vortices Visualization, Planar Laser-Induced Fluorescence Technique