内波诱导的柔性构件流向大位移运动规律研究

Long flexible marine structures, such as mooring lines, risers, etc, are essential members of deep water floating platforms. Their hydrodynamic response to internal waves have drawn more and more attention due to the fact that they frequently induce mooring line or riser failures, which are deemed as the major cause of deep water platform accidents. Previous investigations on hydrodynamic response of long structures have been done for years, but mainly focused on vortex induced vibrations of vertical cylinders of low flexibility in uniform or linear shear flows. However, internal wave induced flow is much more complex in that its velocity of the upper water layer is opposite to that of the lower water layer with strong shear at the pycnocline. Theories and models obtained can hardly be applied to the highly nonlinear large displacement in-line motion of ultra-flexible long structures in the complex flows of internal solitary waves. This project aims to manifest the sophisticated flow structure of internal solitary waves and successive solitons, explore hydrodynamic force of long flexible structures exerted by internal solitary waves, build up dynamic modeling theory, and derive new knowledge of the nonlinear interaction between the sophisticated flow and the long flexible vertical cylinders and catenary mooring lines. The proposed research will certainly promote the theories and methodologies of fluid structure interactions, and will serve to supply scientific basis for the ongoing deep-water platform construction, which is therefore of scientific and practical significance.

立管、锚链等大长径比柔性管缆是深海浮式装备的必备构件，复杂水动力条件导致的水下管缆破坏是深海浮式装备发生重大事故的主要原因，内波作用下的水动力响应是其中的关键科学问题之一。然而，以往相关研究主要针对直立刚性或低柔性圆柱体等简单细长结构，所涉及的水动力条件也是相对简单的流场，且主要研究涡脱落导致的涡激振动，因而很难精确反映柔性管缆在内孤立波导致的上下层反向强剪切流中的水动力响应机制，特别是流体拖曳力导致的流向大位移运动，因而难以用于工程设计。鉴于此，本项目将深入研究内孤立波及其分裂孤立子串诱导的流场特征，探索内孤立波特殊流场中大长径比超柔性管缆的水动力载荷特征与描述方法，建立流向大位移、强非线性水动力响应的力学模型，研究大长径比直立和悬链线管缆对内孤立波的响应规律。本项目的研究将发展流固耦合力学的理论、模型和方法，并为深水工程设计提供科学依据，具有重要的科学意义和工程应用前景。

立管、锚链等大长径比柔性管缆是深海浮式装备的必备构件，复杂水动力条件导致的水下管缆破坏是深海浮式装备发生重大事故的主要原因，内波作用下的水动力响应是其中的关键科学问题之一。然而，以往相关研究主要针对直立刚性或低柔性圆柱体等简单细长结构，所涉及的水动力条件也是相对简单的流场，且主要研究涡脱落导致的涡激振动，因而很难精确反映柔性管缆在内孤立波导致的上下层反向强剪切流中的水动力响应机制，特别是流体拖曳力导致的流向大位移运动，因而难以用于工程设计。本项目针对这一问题开展了深入细致的研究，获得了预期的研究成果。.本项目建立了适用于真是海洋环境条件的内孤立波演化模型，深入研究了内孤立波经突变地形的分裂规律，提出了由两个先锋孤立子波幅预测所有分裂孤立子数目和波幅的简便方法；提出了适用性更广泛的海洋密度剖面的修正模型；获得了内孤立波流场中直立立管水动力响应的理论解，可有效描述立管响应的主要特征；建立了内孤立波特殊流场中大长径比超柔性结构流向大位移响应的三维力学模型，阐明了顶张力立管位移、力矩、应力与内孤立波波幅的关系，阐明了悬链线立管位移、应力与水深、内孤立波波幅和传播方向的关系。.本项目研究所取得的研究成果发展了流固耦合力学的理论、模型和方法，为深水工程建设提供了科学的论证途径和设计工具。