强非线性内孤立波与背景剪切流的耦合作用机理研究

The large amplitude internal solitary waves, pose a serious threat for the underwater moving body. There are not only large amplitude internal waves but also shear currents in the South China Sea. Now only some research on the effect of a linear background shear current on large amplitude internal solitary wave for two-layer fluid system have been done. In South China Sea, the profiles of background shear currents are irregular, the water is continuously stratified, density changes continuously along the water depth, and the seabed is uneven. This project studies the wave-current interaction in two different fluids: two-layer fluids with two different constant densities, a continuously stratified fluid with continuous change on density. The effect of background linear shear currents, nonlinear shear currents and arbitrary shear currents on large amplitude internal solitary waves are studied. The effect of bottom topography is also considered. The strongly nonlinear directed fluid sheet GN wave model is used for the numerical analysis. No small parameters nor irrotational assumption are introduced in the GN wave model. The GN wave model is suit for the analysis of the effect of various background shear currents on large amplitude internal solitary waves. Physical experiments are also conducted to validate the numerical results of the GN wave model. The purpose of this program is to help us to have a well understanding of the interaction among large amplitude internal solitary waves, various background shear currents, seabed topography. This program provides a scientific environment description for the interaction between the underwater moving body and the large amplitude solitary waves in the South China Sea.

大幅内孤立波，对于水下航行体的安全构成严重的威胁。在我国南海，不仅大幅内波频发，而且存在海流的影响。目前国际上仅开展了线性背景剪切流对两层流体间内孤立波影响的研究。实际海洋中的剪切流剖面并不是如此规则的，而且海水是连续分层的，密度沿水深方向连续变化，海底也是起伏不平的。本项目关于波流场的研究分为具有两种不同密度的两层流体、密度连续变化的连续分层流体两种情况，研究线性背景剪切流、二次非线性背景剪切流和任意形式背景剪切流对大幅内孤立波的影响，同时考虑海底地形的影响。数值计算主要采用强非线性的层析GN波浪模型。层析GN波浪模型没有引入任何小参数，没有引入无旋假定，适合分析各种形式背景剪切流对大幅内孤立波的影响。同时开展物理实验，对数值分析结果进行验证。通过研究，深刻认识大幅内孤立波、各种形式背景剪切流、海底地形间的相互作用，为南海水下航行体与大幅内孤立波的相互作用提供科学的环境描述。

大幅内孤立波，对于水下航行体的安全构成严重的威胁。在我国南海，不仅大幅内波频发，而且存在海流的影响。目前国际上仅开展了线性背景剪切流对两层流体间内孤立波影响的研究。实际海洋中的剪切流剖面并不是如此规则的，而且海水是连续分层的，密度沿水深方向连续变化，海底也是起伏不平的。本项目关于波流场的研究分为具有两种不同密度的两层流体、密度连续变化的连续分层流体两种情况，研究线性背景剪切流、二次非线性背景剪切流和任意形式背景剪切流对大幅内孤立波的影响，同时考虑海底地形的影响。数值计算主要采用强非线性的层析GN波浪模型。研究结果表明，对于两层流体间的内孤立波，与内孤立波传播方向相同的背景剪切流会使内波的波形变宽，波速减小。而与内孤立波传播方向相反的背景剪切流会使内波的波形变窄，波速增大。而对于连续分层流体间的内孤立波，背景剪切流不仅会影响给定某一层波幅的内孤立波波形及波速，还会影响其它层内孤立波的波幅。另外，结果表明背景剪切流与海底地形相互作用会产生内波界面处产生明显的下凹区，该区域流速较大。内波通过该区域时波幅及波速也会显著地变化。通过研究，深刻认识大幅内孤立波、各种形式背景剪切流、海底地形间的相互作用，为南海水下航行体与大幅内孤立波的相互作用提供科学的环境描述。