WAVE-FORCES ON A LARGE, HORIZONTAL SUBMERGED CYLINDER

A numerical boundary integral equation method combined with a non-line ar time stepping procedure is used for the calculation of wave forces on a large, submerged, horizontal circular cylinder. As the method is based on potential theory, all computations are performed in the inert ia dominated domain, that is, for small Keulegan-Carpenter numbers. Co mputations are carried out for the Eulerian mean current under wave tr ough level equal to zero. When the cylinder is moved towards the sea b ed the computations show that the inertia coefficients increase signif icantly, which is associated with a blockage effect. Furthermore, the effect of the wave steepness is reduced when the submergence of the cy linder is increased. In the vicinity of the free water surface the ver tical inertia coefficient is highly dependent upon the wave steepness, which tends to reduce it, whereas the horizontal inertia coefficient is only slightly dependent on the wave steepness. Computations are als o carried out for cylinder diameters comparable with the wave length. Finally, inertia coefficients computed by the present method are compa red with some analytical results by Ogilvie [(1963), First and second order forces on a cylinder submerged under a free surface. J. Fluid Me ch. 16, 451-472]. As long as the assumptions leading to Ogilvie's theo ry are fulfilled (cylinder radius small compared to the wave length), the results are quite similar.