浪流激励下月池流体共振与浮体运动响应的耦合作用研究

Coupling effect between floating structure and fluid resonance in moonpool under the wave-current action is one of the hydrodynamic issues of crucial importance in the design of Floating Liquid Natural Gas (FLNG) or Floating Production Storage and Off-loading (FPSO) systems. Due to the energy dissipation and other complex phenomena in the process of fluid resonance in moonpool, the assumption of inviscid fluid and irrotational flow in the potential flow theory cannot be satisfied. Moreover, more complex coupling effect between the fluid resonance in moonpool and response of floating structure can also be aroused under the wave-current action. It is a key technical challenge on the research fields of interaction between wave-current and floating structure. In this project, the experimental and numerical methods are carried out to investigate the vortex shedding mode of the piston- and sloshing-modes of fluid resonance in moonpool, firstly. The influence of energy dissipation on the fluid resonance in moonpool is considered. And then, the effect of energy dissipation on the interaction between the large-amplitude free surface oscillation in moonpool and the wave motion outside the structure is investigated, by which an integral understanding on fluid resonance in moonpool under wave-current action can be obtained. Furthermore, the modified equation of floating structure is established for analyzing the coupling effect, where the influence of fluid resonance in moonpool with the energy dissipation discussed above can be decomposed in the form of exciting force, added mass and added damping. According to the modified motion equation, the essential mechanism behind the coupling action can be revealed. It is meaningful for the hydrodynamic design and practical operations of FLNG or FPSO.

浪流激励下月池流体共振与浮体运动响应的耦合作用是FLNG或FPSO等大型浮式结构系统水动力设计中的关键问题。月池流体共振会产生机械能耗散等复杂物理现象，突破了势流理论的适用范围，为数值模拟与理论分析均带来了挑战。本项目采用物理模型实验与CFD数值模拟方法，首先考察月池流体活塞与晃荡两种基本共振模态的涡脱落模式，分析机械能耗散对月池流体大振幅共振运动的作用机制。进一步，探索机械能耗散影响下月池流体大振幅共振运动与外场自由水面的相互作用关系，加深对浪流激励下月池流体共振现象的整体理解。在此基础上，将月池流体共振作用分解为激振力、附加质量与附加阻尼的形式，建立可考虑机械能耗散等复杂因素影响下的月池流体共振与浮体运动响应耦合作用的浮体运动方程，在把握力学本质的前提下对耦合作用机理进行深入剖析。本项目的开展可以为大型浮式结构系统的水动力设计提供理论指导与技术支持。

通过物理模型实验与计算流体力学方法，考察了月池流体活塞与晃荡两种基本共振模态的涡旋运动模式，定量分析了涡旋运动所产生能量耗散率及其对共振响应波高的影响，并考察了水流对涡脱落模式以及涡旋运动的影响；基于对涡旋运动及其产生能量耗散的影响，并结合能量方程，提出了通过修改月池底部边缘形状而提高能量耗散率，从而降低月池流体共振波高的方法。研究了波浪绕射作用下月池流体大振幅共振运动的响应特征，分析了月池流体大振幅共振运动与浮体外自由水面运动的变化规律，深入挖掘内场共振与外场流体运动的相互作用关系；进一步考察了水流存在时上述内外场流体运动的变化特征，分析了浪流激励下月池流体共振与外场自由水面运动的相互作用规律。在上述研究成果基础上，基于共振模态的研究成果，将月池流体共振对浮体的作用力分解为附加质量与附加阻尼的形式，基于绕射作用下内外场流体运动的变化特征的理解，将内场流体共振作用分解为波浪激振力的形式，从而建立可考虑机械能耗散等复杂因素影响下的月池流体共振与浮体运动响应耦合作用的浮体运动方程，从而在把握力学本质的前提下对耦合作用机理进行深入剖析。.项目执行期间，共发表项目相关文章19 篇，其中期刊论文16篇，会议论文3篇，其中SCI 索引10 篇次，EI 索引10 篇次，北大中文核心索引6 篇次；授权中国专利14 项，其中发明专利6项，实用新型专利8项，软件著作权1项。本项目共培养4名博士、13名硕士生，其中毕业硕士生8名。