A brief overview is given of researches on the prediction methods of hydrodynamic force on a body moving in waves and having a steady -advance speed. Then two methods developed by the present author for computing hydrodynamic forces are presented and their results are discussed. These two methods are based on different assumptions of the steady flow field around the body.
Prediction of hydrodynamic forces on off-shore structures in current as well as in waves or towed in waves must be based on the correct understanding of current-wave interaction effect. There are other less obvious contexts in which this effect must be considered. Slow drift oscillation in waves is of so large amplitude and long period compared with wave motions that it may be considered as a quasi-steady movement. Damping of the motion may be predicted as a steady force when assuming they move at a steady speed in waves backward or forward. Tilt moment on the structures in waves is caused by vertical steady force. This will be affected when they make slow drift oscillations. That means the tilt moment is also to be predicted taking into consideration that the structures are moving in waves at steady speed. In this chapter I give a brief, I never intend it complete, review of recent researches on prediction of hydrodynamic forces on bodies moving at constant speed in waves. Description is restricted to the potential theories. Correct prediction of hydrodynamic forces on a floating body moving at steady velocity in waves has been mainly a concern of ship hydrodynamics. In the contexts-of seakeeping of ship, however, ship" s geometrical form is often assumed very slender. Prediction of those forces on bluff bodies such as off-shore structures is quite a different problem.