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

本研究的目的是发展一种分析船舶在大振幅波浪中运动的数值方法，并与实验数据相比较来评价该方法。发展了一种分析船舶在大浪中运动的数值方法。用四元数来表示船舶大范围运动的转角。四元数具有3个自由度、4个变量和1个约束条件。它没有奇异性，适合于数值分析。在MPS(运动粒子半隐式)方法中，流体用流体粒子表示，船用刚体粒子表示。流体颗粒的运动采用离散形式的Navier-Stokes方程。用两步法计算刚体质点。(2)实验分析在国家海事研究所拖曳水池中获得了船舶运动的实验数据和可视化图像。在相同条件下，用本质点方法进行了三维数值分析。当波长与船长之比较大时，计算的船体运动小于线性理论所预测的运动。这是因为甲板上的装运水重量抑制了运动。在实验中也观察到了这种趋势。最后，提出了一种分析波浪与船舶大运动耦合的数值方法，并将计算结果与实验数据进行了比较。初步计划已成功执行。该方法也适用于风浪船舶操纵模拟器、海啸波来港船舶运动模拟器、船舶倾覆模拟器等。

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.