基于CFD方法的大型船舶波浪水弹性数值预报及其机理分析

The tendency of large-scale, high speed and light weight prompt researchers to give prominence to ship hydroelasticity. The accurate forecast of hydroelasticity is of significance to ship navigation’s economy and safety. The hydroelastic response is a 3-D phenomenon coupling of wave excitation, hull motion, hull deformation, which is a strong nonlinear problem. Ship hydroelasticity usually includes two forms: springing and whipping. So far, there is still no proper means to accurately predict and analyze this phenomenon. Full time domain CFD method can comprehensively consider nonlinearity caused by free surface, hull surface, speed, viscosity, vorticity, etc. It is acknowledged as a promising method for numerical prediction of hydroelastic response.However, large amount of calculation and high requirements of grid quality restrict the application of this method. This project is to consist of the following parts:.1)to couple higher order hierarchical Boussineq equation and RANS equation for the purpose of reducing the amount of computation; .2)to develop wavelet decomposition method for grid’s adaptive distribution to improve the grid quality; .3)to develop wavelet reconstruction method to solve numerical stability problems; .4)to establish time domain numerical model to predict hydroelastic response;.5)to verify the accuracy of the numerical model through physical model test;.6)to separate the springing and whipping in hydroelastic response by using wavelet time-frequency analysis method;.7)to analyze the coupling rules between the springing and whipping and respective response mechanism.

随着船舶大型化、高速化和轻量化，波浪水弹性问题日益突出，其准确预报对大型船舶航行的经济性、安全性具有重意义。船舶水弹性响应是来浪激励、船体运动、船体变形的强非线性三维流固耦合现象，往往同时包含波激振动与砰击颤振两种形式，该问题目前仍没有得到准确预报与分析。全程时域CFD方法，可一并考虑自由表面、船体表面、航速、粘性、有旋等因素带来的非线性，被认为是前景看好的水弹性响应数值预报方法。但由于其计算量大，要求计算网格质量高，制约了CFD方法的应用。本项目将基于高阶分层Boussineq方程和RANS方程的波浪耦合模型以减少计算量；发展基于小波分解方法自适应布点以提高网格质量；发展小波重构方法以解决数值稳定问题；建立时域数值模型预报水弹性响应；通过开展物理模型试验，验证数值模型精度；采用小波时频分析方法，分离水弹性响应中的波激振动和砰击颤振信号，分析两者耦合规律及响应机理。

在当前船舶大型化、高速化、轻量化的背景下，船体结构柔性特征逐渐显现，波浪水弹性问题日益突出。本项目基于CFD方法对船舶水弹性问题进行了数值分析和模型实验研究。研究内容包括：船舶水弹性波浪数值水池中涉及的两个关键问题-网格自适应和数值发散开展了研究；以KCS船型为例，基于OpenFOAM开发波浪数值水池；以二维楔形体为研究对象，研究了船体局部结构的水弹性问题；开展了船舶水弹性模型实验；畸形波危及船体结构安全，基于机器学习方法对畸形波预报开展了研究。课题研发表了10篇学术期刊论文，取得了成果如下：1）基于四叉树自适应网格的VOF方法在处理晃荡问题，通过对部分需要细化的网格加密自适应可以更加高效精确地得到相应的结果，从而有效地计算液面升高，力与力矩；2）提出双重小波滤波方法处理LDQ方法得到的包含严重数值振荡解，该方法能自适应的滤去数值振荡，得到真实的物理解；3）基于开源CFD软件OpenFOAM计算了带舵KCS船型的波浪增阻，数值计算结果与试验数据总体上吻合良好；4）基于对半解析砰击模型、弹性结构的广义力和耦合动力方程的研究，系统地建立了弹性楔形体入水冲击的流固耦合分析方法；5）基于某地形模型试验数据，发展了LSTM模型和小波神经网络对畸形波预报，具有精度高、效率快的优点。项目研究成果具有很好的科学意义和工程实际应用前景。