Development of CIP/Cartesian Grid Method for Strongly Nonlinear Interaction between Free Surface and Floating Body

本项目旨在开发一种基于约束内插剖面的笛卡尔网格方法，用于定量预报强非线性耐波性问题，如船舶在大振幅波浪中的运动、船底撞击和耀斑的合成以及绿水对甲板的冲击等。在两年的时间里，取得了以下成果：(1)为了提高自由面计算的效率，改进了一种新的交错捕捉格式--THINC格式，并将其应用到CIP/笛卡尔网格程序中。用改进后的程序对一个修正的Wigley模型在大头规则波中的运动进行了数值模拟，与原基于CIP的界面捕捉格式的计算结果进行了比较，结果表明，采用THINC格式可以显著提高甲板上的波浪冲击压力和船舶运动的预报精度。(2)提出了一种计算实际船舶的CIP/笛卡尔网格程序的新方法。该方法通过在物体表面分布虚拟粒子来逼近物体。设计了一种算法，用于从具有上层建筑的实际船舶的CAD数据中生成此类粒子。通过对S-175型集装箱船模型的数值模拟，验证了该方法的有效性。(3)从实际应用的角度出发，研究了基于PC集群的并行计算技术。CIP/笛卡尔网格程序的压力解部分已并行化。此外，还开发了POV-Ray可视化技术来演示计算结果。

This project was aimed at developing a OP (Constrained Interpolation Profile) based Cartesian grid method for quantitative prediction of strongly nonlinear seakeeping problems, such as ship motions in large-amplitude waves, resultant slamming on ship's bottom and flare, the green-water impact on deck, and so on. Dur ing the two years' project term, the following results have been obtained.(1) To improve the efficiency of the free surface calculation, a new interlace-capturing scheme, THINC (Tangent of Hyperbola for Interface Capturing) scheme, has been improved and implemented into the CIP/Cartesian grid code. Numerical simulation by the improved code on a modified Wigley model moving in large regular head waves has been carried out By comparing to the computed results obtained by using former CIP based interface-capturing scheme, the use of THINC scheme can siginificantly improve the prediction accuracy about the wave impact pressures on the deck and the ship motions.(2) A new method has been developed for the CIP/Cartesian grid code for computing actual ships. By this method, the body is approximated by distributing virtual particles on the surface. An algorithm has been designed to generate such particles from CAD date of a real ship with super structures. The efficiency of the method has been confirmed by numerical simulation of a container ship model (S-175).(3) For practical application purpose, a study on parallel computation technique using a PC cluster has been made. The pressure solution part of the CIP/Cartesian grid code has been parallelized. Further, visualization technique by POV-RAY has been developed for demonstrating the computed results.