Second order frequency domain analysis of moored vessels

A frequency domain analysis method for the dynamic response of a vessel moored in a random sea is presented, in which second order wave forces are included. The non-linearities occurring in the equations of motion of the vessel are accounted for by using the equivalent linearisation technique, leading to an iterative solution scheme for the mean values and covariances of the response. Application of the method to a moored drill ship indicates that the required computer time is relatively low. The method is intended for use in the preliminary stages of design where a parametric study may be required and the costs of a time domain analysis are prohibitive.