Abstract
A new method to predict hydrodynamic forces acting on semi-submersible drilling units is proposed. A simplified Green's function is used to solve the boundary value problems where the wave lengths of incident waves are assumed to be significantly larger than the cross-sections of the structual elements. It is found that this method is more useful than both the strip method and the three-dimensional source distribution method which have been used to predict hydrodynamic forces acting on semi-submersible drilling units so far. Because the present method takes the hydrodynamic interaction effects into account together with the other structual elements, it improves the accuracy much more than that of the strip method. On the other hand it decreases the computing time much less than that of the three-dimensional source distribution method. In order to confirm its validity for radiation forces and wave exciting forces, the results obtained by the present method are compared with those obtained by the three-dimensional source distribution method and the experimental ones. It has been made clear that the present results are in good agreements with the theoretical ones and the experimental ones.
