Abstract
It is important to estimate slowly varying drift forces on very large floating structures (VLFS), since it may be happen that slowly varying drift forces would have frequencies close to eigen frequencies of VLFS-mooring systems. Considering with real seas, we should estimate slowly varying drift forces in multidirectional seas and, to carry out such estimations numerically, we may need large effort because of hydroelastic behaviors of VLFS. This is our first report to propose a method to evaluate slowly varying drift forces rather easily even in multidirectional seas. We showed that it is possible to neglect contributions from bottom slopes of VLFS to slowly varying drift forces when deflections of VLFS are small comparing with wave amplitudes. We validated the present method with model tests in long crested irregular waves.
