The paper develops an integral equation for the calculation of the second order steady potential. Some mathematical transformations are used to get rid of the second derivatives of velocity potentials from the intergral equation. Distribution of the second order steady potential is given for a uniform cylinder and a truncated cylinder. Numerical examinations are made on the contribution of the second order steady potential on the second order drift force on bodies moving with forward speeds. The convergence testing is made on the radii of meshes on the free surface, and comparison with experimental results is made on an array of four cylinders. It was found that the convergence of drift force with the radii of the meshes on the free surface is fast and good agreements exist between the present calculation and experimental results.
Tension leg platforms (TLPs) are semi-submersible structures moored to seabed with a number of pre-tensioned vertical cables (tethers). The response motion of upper structure with wave exciting induces tethers vibrating continuously, which will break when their fatigue life has been reached. Damping can decrease amplitude of response of structures. Thus, accurately predicting damping is important for the prediction of fatigue life of tethers. Usually damping of a floating structure can be divided into the viscous damping, the radiation damping and the "wave drift damping". The wave drift damping, defined by Wiches and Sluijs (1979), is due to the increase of drift force with forward moving speed of a floating body. Its calculation needs the nonlinear knowledge on wave diffraction and radiation in a steady flow. In this respect, significant progress has been made recently. Matsui, Lee and Sano (1991) and Emmerhoffand Sclavounos (1992) have derived analytic solutions for uniform cylinders in finite and infinite water depth.