Study on ship's stability loss in surf-riding based on CFD
Based on Computational Fluid Dynamics, ship's righting arms of different heeling angles were calculated to study ship's stability loss in following sea. First, based on the wave-generation method of defining inlet boundary conditions, the numerical wave tank was constructed for ship's movement in surf-riding. Second, one slender ship's flow filed in calm water was numerically simulated, and the righting arms of different heeling angles were calculated. Third, the slender ship was set to navigate in surf-riding with wave crest at the midship section, and the flow field was simulated to get the righting arms of different heeling angles. The simulation results indicate that the righting arm in calm water show good agreement with experiment data; the stability loss is more serious when the wave amplitude is bigger; and ship wave's effect cannot be neglected in calculating ship's stability loss in surf-riding when ship speed is high.
Research on roll restoring variation and parametric rolling in waves
In order to study the roll restoring variation in waves and the effect of restoring variation on parametric rolling,firstly,the relative position of ship to waves is determined with heave and pitch motions obtained by a strip theory applied to an upright hull.Secondly,a general method for calculating intersections between ship and waves is presented base on transform of three coordinate systems and the instantaneous area of wet sections is calculated and then the nonlinear Froude-Krylov component of restoring variation is calculated by integrating wave pressure up to wave surface.Thirdly,radiation and diffraction components are taken into account by using radiation and diffraction force acting on a heeled hull.And then a mathematical model for parametric rolling is developed based on the calculation of restoring variation.Finally,restoring moments and parametric rolling of a container ship in regular wave are studied and roll restoring variation is an essential fact for parametric rolling prediction.
AN ANALYTICAL APPROACH TO CAPSISING OF A SHIP IN FOLLOWING SEAS
An analytical approach has been developed for the numerical simulation of ship motions leading to capsising in order to investigate the influences of the loss of transverse stability on the capsising of a ship in severe following seas. The equations of motion with respect to the horizontal body axes are presented for analysing a large amplitude motion. The results simulated by this mathematical model are compared with the results observed in experiments for the check of accuracy. Finally critical metacentric height leading to capsising is discussed for several kinds of ships.