A linear and a fully nonlinear numerical wave tanks (NWTs) were applied to study wave drift force acts on a two-dimensional Lewis form body in finite depth wave flume. These NWTs are based on potential theory and the fluid and floating body motions are directly simulated in time domain. Boundary value problems both on the velocity potential ф and its time derivative ∂ ф/∂t are solved at each time step. The coupling condition between fluid and floating body is imposed as the implicit boundary condition of Oф/Ot on wetted body surface. The radiation condition at both tank ends are satisfied by artificial damping technique. Using these NWTs, effects of the floor step of the flume on wave drift force were studied. Measurement of wave drift force was also conducted in our two dimensional wave flume. In this second report, the resuits of simulations and measurements are presented and the effect of the floor step on wave drift force is discussed.
A joint research project named "On the drifting prevention of disabled ships in rough waves" is conducted by Ship Research Institute, Maritime Safety Agency, Osaka University, Kyushu University, rope manufactures and a salvage company. In this project, a prototype onboard towing support system for rescue ships is expected to be developed as a final output. As a part of this project, the authors are studying wave drift force and drift motion of a freely floating body under various conditions. Shape of the sea floor is one of the important condition. When a disabled ship is drifting to coast and be in danger of running aground, accurate estimation of required power for rescue ships as well as estimation of drifting speed and course is very important to avoid disaster.
