To utilize floating structure under heavy environmental condition in sea safely, motions of the floating structure and the mooring forces have to be reduced. To decrease these motions and mooring forces, fins attached structure has been proposed. In this paper, as a first step of the study, two vortex methods, the Random-Walk method and the Core-Spreading method, are applied to vertical oscillating plate under free surface. Hydrodynamic forces on the plate are calculated and compared with experimental results.


It has been required that the ocean space is effectively used in Japan surrounded by the sea and various floating structures for development of ocean resources or oceanographic survey, etc. have been proposed. In recent years, the floating structures for utilizing ocean energy such as offshore wind farms or ocean thermal energy conversions are required because of depletion of fossil fuels, global warming and the accident in the nuclear power plant by the eastern Japan earthquake. Moreover, the floating structure seems to be useful as disaster prevention bases or shelters, because the damage of the floating structures in the tsunamis caused by the eastern Japan earthquake were relatively small. Therefore, various types of floating structure will be required in future. To utilize floating structure in safely economically under severe wind and wave conditions around our country, motions of the floating body and mooring forces acting on the body have to be reduced. To decrease these motions and mooring forces, fins attached structure has been proposed (Fig. 1). The attached fin seems to dissipate the energy of the motion as viscous damping and reduce the mooring forces due to so-called "wave devouring propulsion" effect. To put this method to practical use, the calculation method to design optimum shape and arrangement of the fin has to be developed.

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