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

本研究的目的是发展一种数值方法来分析船舶在大振幅波中的运动，并通过与实验数据的比较来评估该方法。获得了以下结果。（1）建立了船舶在大振幅波浪中运动的数值分析方法。四元数有3个自由度，4个变量和1个约束条件。它没有奇异性，因此适合于数值分析。在MPS（Moving Particle Semi-implicit）方法中，流体用流体粒子表示，船舶用刚体粒子表示。流体颗粒的运动是使用离散化的Navier-Stokes方程来计算的。刚体质点的计算分两步进行。（2）实验分析在国立海洋科学研究院的拖曳水池中进行了船舶运动实验，获得了船舶运动的实验数据和可视化图像。在相同的条件下，用本文的质点法进行了三维数值分析。当波长比较大时，计算的船舶运动比线性理论预测的运动小。这是因为甲板上的船舶水重量抑制了运动。最后，本文提出了一种数值方法，可以分析波浪与船舶大运动的耦合，并将计算结果与实验数据进行了比较。初步计划顺利实施。该方法也可应用于风暴中船舶操纵模拟器、海啸波来临时港口船舶运动模拟器、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.