A NUMERICAL INVESTIGATION OF THE WATER-LINE INTEGRAL EFFECT ON WAVE DIFFRACTION BY TRANSLATING BODIES

This paper compares three water line (WL) numerical models for the analysis of wave diffraction by a 3-D body having forward speed. A boundary element method with constant distributed source panels, based on a convolution equation involving a timedependent Green function, is employed to investigate the effect of the water line. Numerical results for linear exciting forces, mean drift forces, and wave elevations are presented for the case of a truncated surface-piercing cylinder and a hemisphere. The WL integral has little effect on the linear exciting forces, for which it could be neglected in practice. The 2nd-order drift forces are strongly affected by the water line and should be treated carefully. It is suggested that the field point position, where the wave run-up along the WL is calculated (which is used to evaluate the drift forces), should be at a distance of about the draft/1000 below the free surface while the position of the WL source in the integral equation is at z = 0. Under such conditions the effect of the WL in the integral equation can be modelled satisfactorily for calculating the drift forces on the cylinder and the hemisphere.