Experimental and numerical investigation of the slowly varying wave exciting drift forces on a restrained body in bi-chromatic waves

The paper presents an experimental and numerical investigation of the first order and slowly varying wave exciting forces on a body of simple geometry which is restrained from moving. Both monochromatic waves and three sets of bi-chromatic waves corresponding to three difference frequencies were tested. The depth effects on the second order forces are assessed by repeating the wave conditions for deep water, intermediate water depth and shallow water. The wave exciting mean drift forces and second order slowly varying forces were successfully measured and identified. However, since the magnitude of these forces is small compared to the global forces measured, there is some dispersion in the second order results.The experimental data is compared with three state of the art numerical methods which are able to compute the first and second order wave exciting forces. Two of the methods use Green's function panel methods (Wamit and HydroStar) and the third is based on an analytical solution (Diffrac-R). All methods compute the full second order solution, including the effects related to the quadratic interactions of first order quantities and to the second order diffraction potentials.