Describing-function analysis of slow-drift oscillations of vessels moored in random-sea conditions

Abstract

Slow-drift oscillations of moored vessels in the open sea have become a topic of some importance in recent years. In this study we make use of the describing-function technique, which has been well-developed and much used in the analysis of nonlinear control systems, to deal with the dynamical equations representing probabilistic surge motion of vessels moored in random-sea conditions. Before the illustrations of this method of solution we outline the elegant mathematical approach to this problem by Roberts [1], some of whose results concerning the treatment of wave-forces we incorporate in the describing-function approach.