Nowadays, the fully nonlinear conditions can be treated by using CFD programs, but it is beyond our present study. It should be mentioned that the dynamic conditions include the time-difference terms of the basis flow. When the body speed is a function of time, these terms should be considered. Furthermore, even for the case which the body speed is steady, the basis flow in the weak-scatterer formulation is not steady since the body surface is varying depending on the exact wetted surface. This will be mentioned later.