A fully nonlinear numerical wave tank (NWT) is applied to estimation of the wave drift force acting on two-dimensional fixed and floating bodies. This is a time domain simulation program which solves simultaneous equations of ideal fluid motion and floating body motion. Using this NWT, the diffraction problem and the radiation-diffraction problem of a two-dimensional Lewis form body in regular waves are simulated and the wave drift force is calculated both from transmitted wave and from direct pressure integral on the wetted body surface. To examine the accuracy of NWT, the first harmonic components of simulated hydrodynamic forces, body motions, wave reflection and transmission coefficients and wave drift force are compared with linear theory and experimental data of Nojiri (1975). The first harmonic components of the nonlinear simulation are confirmed to be in good agreement with linear theory.
Recently, forecasting of the course and speed of drifting wrecked ship is one of the urgent topics. When a ship is in distress in rough seas, the coastal guard has to keep tracking of the ship and send rescue boats in minimum delay. If the location of the ship is lost, accurate forecasting systems are indispensable for rescue team to save the human lives and properties. In particular, in the case of wrecked oil carrier, it will be disaster unless rescued swiftly. As a part of development of the forecasting system, the authors study the wave drift force acting on floating body with arbitrary shape in large amplitude waves. Evaluation of the wave drift force is important also for the power evaluation of towing boats. For this purpose, we should consider the effect of forward velocity on the drift force. If the towed ship is in shallow area, the shape of sea bottom may also affect the drift force.
