Numerical simulation of 6-degrees-of-freedom motions for a manoeuvring ship in regular waves

Abstract

In this study, the authors propose a numerical simulation method to estimate 6-degrees-of-freedom (DOF) motions for a manoeuvring ship in regular waves. The proposed method is classified as a unified method; that is, it directly solves a family of equations of motion for the resultant 6-DOF ship motions, without separating the motions according to frequency. The authors’ mathematical model is based on an earlier model proposed by Hamamoto and Kim (1993); however, the authors primarily improve the external wave forces and the inertial and damping components of the hydrodynamic forces induced by ship motion form those of their model, such that the authors’ model can be applied to general manoeuvres (e.g., turning) and short waves. Using the proposed method, the authors conducted numerical simulations for tanker- and container-ship models under course-keeping and turning manoeuvres in regular waves. To validate the proposed method, the authors performed a free-running model test and compared the estimations with the test results. The comparisons clarify that the proposed method can approximately estimate the manoeuvre characteristics (e.g., mean ship speed, drift angle, and check helm) under course-keeping manoeuvres and turning trajectories, as well as the 6-DOF ship motions induced by waves, although room for improvement remains. The proposed method is applicable to both blunt and slender ships.