This paper discusses the numerical characteristics of time-domain dynamic analysis of floating structures considering instantaneous phase difference between the floating body and waves. It was confirmed analytically that the nonlinearity induced by considering the instantaneous position of the floating structure causes a slowly-varying drift motion similar to wave drift force even when the analysis considers only first-order diffraction forces. However, its frequency characteristics would seem to be essentially different from that of the wave drift force obtained by potential theory. Subsequently, this paper investigates the numerical model that removes the low frequency motion caused from the nonlinearity of the instantaneous position of the floating structure by using a low pass filter. This model would be effective for time-domain analysis of wave frequency and low frequency motions simultaneously. Finally, these models are compared with the commercial code OrcaFlex, and it is confirmed that the numerical results obtained by the presented method and the numerical results by OrcaFlex are equivalent.
Doi et al. (Wed,) studied this question.