Study On6-DOF Numerical Model Of Ship Maeuvering Motions In Waves

Ship maneuverability is one of the most important ship navigatingperformance. When study ship maneuvering motion in waves,sea-keeping motions cannot be ignored. This paper carries out studies onfree running model tests and6-DOF (6degrees of freedom) numericalsimulation based on this engineering background.In the experiment part, a new free running model tests system has beenused to study maneuvering motions of a S175model. The tests concludesea-keeping tests, turning circle tests and zigzag tests in different waveconditions&rudder conditions. And tests results have been analyzed inchapter2.In the simulation part, this paper presents a mathematical model whichcombines traditional3-DOF MMG model with sea-keeping motions ofroll, pitch and heave to simulate the ship maneuvring motions couplingwith sea-keeping motions in waves. Hydrodynamic derivatives, propellerand rudder forces are estimated by empirical formulas using basic shipparameters. As for wave forces, the first order ones are evaluated intime-domain by using Cummins impulse response function; the second order ones are solely taking its mean average part into account.Further more, the6-DOF model is employed to simulate maneuvring andsea-keeping motions of a container ship S175simultaneously. A code ofthis model is developed. And it is verified by the measured data obtainedfrom sea-keeping experiments and free running model tests. Themodelling method is given in chapter3.This paper also proposes a method in studying the coupling effectsbetween maneuvring motions and sea-keeping motions.3-DOF and6-DOF models have been used to study the effects of sea-keepingmotions on maneuvring motions. And the drift-with and drift-out modelshave been used to study the effects of maneuvring motions onsea-keeping motions. The results show that turning motions are moresensitive than zigzag motions to the coupling effects.In the end, this paper studies the effects on turning trajectories and rollresponses under various wave conditions and for other different factorsand gives out suggestions for ship steering program. A curve of limit waveparameters bounded by critical capsizing angle is also given out.