Water Wave Absorber by Making Use of Oscillating Hydrofoil

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Relating to the ocean space utilization, marine culture, marine leisure and so on, the needs of a good wave absorber in deep water have increased recent years. One main problem of such a wave absorber, however, is the mooring systems in deep water, because the wave absorber can not escape from the action of the wave drifting force even if it can absorb the incident waves completely. To overcome the wave drifting force on a wave absorber, we studied about the feasibility of the hydrofoil to the wave absorber. It is well-known as experimental facts that the oscillating hydrofoil generates the thrust, but the exact treatment is difficult because the nonlinear effects become severe in the actual situations. Hydrodynamic characteristics of thrust generated by a hydrofoil among waves are obtained by the linear potential theory in two- and three-dimensional problems. Model experiments for some thick wings were carried out in the diffraction and radiation problems to check the validity of the numerical calculations. The thrust generated by the hydrofoil among waves was studied as a function of the submergence of the wing, the angle of attack, the frequency of the incident waves and it was confirmed both in theory and experiments. To realize the mooring system of the wave absorber in deep water, a positioning system of the small power to compensate the errors in the cancellation of the drifting force should be developed in the next stage.