The purpose of this study is to predict and to understand the hydrodynamic forces and their nonlinear behaviors of fluid motion around the submerged plate oscillating near a free surface. To achieve this objective, we have developed a composite grid method for the solution of the radiation problem. We divide the domain into two different grids; one is a moving grid system and the other is a fixed grid system. The moving grid is employed the body fitted coordinate system and moves with the body. This numerical method is applied to calculation of the radiation forces generated by the submerged plate oscillating near a free surface. In order to investigate the characteristics of the radiation forces, we have performed the forced heaving tests with several amplitudes and different submergences near a free surface. These experimental results are compared with the numerical ones obtained by the present method and a linear potential theory. Finally, we have evaluated the effect of nonlinear and viscous damping on the hydrodynamic forces acting on the submerged plate.
There are many studies about the hydroelastic response of a Very Large Floating Structure, and some of them have proposed the breakwater to reduce the hydroelastic deformation. Takaki et al.(2001) proposed the new-type floating breakwater system which could increase the merits of VLFS. The system consists of Floating Breakwater using Submerged Plate(FBSP) and VLFS with attached submerged plate. The submerged plate built into VLFS is called as ‘the third submerged plate’. Fujikubo et al.(2002) and Takaki et al.(2002) carried out the studies of the effect of the third submerged plate to reduce the hydroelastic response of VLFS. In particular, it has made clear that the third submerged plate can reduce the wave exciting force in short waves (Takaki et al., 2002).