Numerical Analysis of Ship Motion in Large Amplitude Waves Using a Particle Method

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The purposes of the present study are to develop a numerical method for the analysis of ship motion in large amplitude waves and to evaluate the method in comparison with experimental data. The following results are obtained.(1)Development of a numerical method to analyze ship motion in large amplitude wavesQuaternion is employed to represent the rotation angles for large motion of a ship. Quaternion has 3 degrees of freedom with 4 variables and 1 constraint condition. It has no singularity, so that it is fitted to numerical analysis. In MPS (Moving Particle Semi-implicit) method, the fluid is represented by fluid particles and the ship is represented by rigid-body particles. Motion of the fluid particles is calculated using discretized formulation of Navier-Stokes equations. The rigid-body particles are calculated by two steps.(2)Experiment analysisExperimental data of ship motion and visualized images have been obtained in a towing tank of National Maritime Research Institute. A three-dimensional numerical analysis using the present particle method is carried out with the same condition. The calculated ship motion is smaller than that predicted by the linear theory when the ratio of the wave length to the ship length is large. This is because the shipping water weight on the deck suppresses the motion. This tendency was also observed in the experiment.In conclusion, a numerical method which ca analyze the coupling between waves and large motion of a ship, and then the calculation result is compared with experimental data. The initial plan is successfully performed. The present method can also be applied to ship handling simulator in storm, ship motion in a harbor when a tsunami wave comes, ship capsizing etc.