基于多域耦合模型的高海况下航行船舶非线性运动和载荷响应高阶混合预报方法研究

高海况下航行船舶易产生非线性大幅运动和载荷响应。传统单一格林函数法在有航速水动力分析中存在计算复杂不稳定或离散量大、辐射条件难满足等不足，阻碍了其在非线性响应研究中的发展。项目拟引入虚构控制面将船外流场分为内外两部分，考虑内域非线性，依据流动连续性，结合频域势流理论，建立波浪中航行船舶的非线性多域耦合水动力模型；分别利用Rankine源能处理各种边界条件、移动脉动源满足辐射条件的优势在内外域构建积分方程，建立混合格林函数法。数值实现时，根据遭遇频率和船姿态变化，实时更新计算域、船体几何并用高阶面元离散边界，以计及非线性、兼顾精度和效率；推导与移动脉动源相关影响系数的解析公式，解决匹配的稳定、准确性和效率问题。基于此，结合频谱理论开发高海况下船舶非线性响应计算程序，开展运动和载荷预报研究，揭示船-波非线性作用机理。本项研究对完善非线性水动力模型，提高船舶耐波性和安全性具有重要理论和应用价值。

When ships sailing in rough sea, nonlinear large amplitude motions and loads will be induced by waves. Over the past few decades, Green’s function methods based on potential flow theory have been the most popular methods to predict wave-structure interactions. But when it comes to hydrodynamic problems with forward speed, these traditional methods are either complex and unstable or time-consuming and hard to satisfy the radiation condition, which hinders their development in the research of nonlinear wave-ship interaction. In this project, an artificial control surface is introduced to decompose the fluid domain into an inner and an outer domains. By considering the influence of nonlinearity in the inner domain and the continuity between two subdomains, a nonlinear multi-domain coupled hydrodynamic model is established based on frequency-domain potential theory. Then a hybrid Green’s function method, which adopts Rankine source and translating-pulsating source to construct boundary integral equations in inner and outer domains respectively, is developed to take advantage of the superiorities and overcome the defects of the two traditional methods. In this method, the size of the computational domain, the geometry of the ship hull and the higher-order curved elements will be altered and updated automatically according to the encounter frequency and ship motion attitude, while an analytical expression will be derived to evaluate the influence coefficients related to the translating-pulsating source in the outer boundary integral equation. So an efficient numerical algorithm with high accuracy, which considers the nonlinear effects, can be established. Based on this algorithm and wave spectrum theory, a reliable and effective program for the calculation of nonlinear responses of ships advancing in rough sea is developed. By utilizing this program, the wave-induced motion responses and loads on ships are predicted, and the mechanism of the nonlinear wave-ship interaction is studied systematically. The present work has important theoretical and practical values for enriching the theoretical framework of nonlinear ship hydrodynamics and improving the seakeeping performance and safety of ships sailing in the sea.