畸形波与浮体相互作用研究

Freak waves are abnormal waves surprisingly appearing on the sea surface with exceptional wave height or abnormal shape and known as a maritime myth. Such a wave may cause extensive structural damages and human loss, and is of considerable concern to the stability and survivability of ships and offshore platforms. It is necessary and important for both scientists and engineers to model the extremely nonlinear wave-structure interactions and accurately estimate the forces on structures when freak waves occur.When interaction between freak waves and a floating body is dealt with, several big challenges have to be faced: distorted free surface, large-amplitude body motions and violent multiphase interactions. In this proposal, a viscous multiphase flow model is developed to study nonlinear interactions between freak waves and a floating body including wave breaking and large amplitude body motions. Main attentions are paid to violent varied free surface, large-amplitude body motions and complex multiphase flow field structure around the body under extreme conditions. The generation mechanisms of the dispersive focusing waves are presented. The influence of various parameters of freak waves on these components, the differences of behaviors the body model exhibited in different freak waves, etc are examined systematically. The computations presented in this proposal are performed by means of a CIP-based method for predicting strongly nonlinear wave-structure interactions. The method is based on the solution of the Navier-Stokes equations with the Constrained Interpolation Profile (CIP) adopted as the base numerical scheme to obtain a robust flow solver in a Cartesian grid. The numerical model considers the fluid-structure interaction as a multi-phase problem that includes water, air and solid body. A fixed Cartesian grid that covers the whole computation domain is used. The THINC/WLIC scheme (THINC: tangent of hyperbola for interface capturing; WLIC: weighed line interface calculation), is used for free surface/interface capturing. For calculation of floating body motion in the Cartesian grid, a weekly coupled procedure has been developed for this model, in which the fluid structure interaction is treated by using an immersed boundary method. For the sake of simplicity, calculations are carried out for a rigid body. This project is aimed to develop a CIP-based Cartesian grid method for quantitative prediction of strongly nonlinear freak wave-body interactions, including body motions in large-amplitude waves, resultant slamming on body's bottom and flare, the green-water impact on deck, and so on; and to reveal the mechanism of freak wave loads on a floating body, also the body response to freak waves. Some results are helpful for engineering design and disaster protection.

畸形波是目前尚未全面解释和预测的一种灾害性波浪。畸形波作用下的强非线性自由面、浮体的动力响应及复杂流场中的流固耦合问题，成为制约该问题进一步发展的主要瓶颈。本项目基于粘性流体理论，开展畸形波与浮体强非线性相互作用的研究，对畸形波作用下的波面大变形、浮体大幅值运动进行研究。具体内容包括：畸形波波浪场结构、畸形波波浪力特性、浮体运动响应、固-液-气多相流耦合流场特征。畸形波通过不同类型的色散聚焦方式得到，并开展不同影响因素的分析。模型以高阶差分法为N-S方程的基础求解器，采用多相流的方式处理畸形波-浮体-气体的耦合作用，采用高精度平衡格式的THINC方法重构自由水面，建立可处理碎波、水汽掺混等波面大变形及浮体大振幅响应多因素复杂耦合的畸形波与浮体相互作用的定量预测模型。本项目旨在阐明畸形波对浮体的作用机理、浮体对畸形波的响应机理，为开展灾害波浪的有效预防和解决工程设计问题奠定理论和技术基础。

能准确预测复杂海洋环境对海上结构响应的数值模型对港口内泊船安全和海上浮式结构正常运营有着重要的意义。本项目开展了畸形波对浮式结构作用的数值模拟研究。针对畸形波的瞬时作用过程中的强非线性界面流动和浮体的大幅值运动响应，建立了一个耦合畸形波与浮体相互作用的数学模型。项目中我们完成了可描述二维强非线性界面流动问题的数学模型开发，对畸形波与二维浮体相互作用进行了研究，并开展了模型试验研究，初步建立了极端波浪与建筑物相互作用的数值模型，计算结果表明模型可处理波浪破碎、水汽掺混和结构的动力响应等非线性问题。本课题的研究对于深入了解畸形波的内部特征、阐明畸形波对浮式结构物的作用机理具有一定的理论意义，并可对海洋运输船舶和石油钻井平台等工程结构物的设计和防护等问题的研究奠定理论和技术基础。. 发表标注本基金的资助论文33篇，其中SCI收录论文9篇，EI收录论文6篇，参加国际学术交流3人次，国内学术交流13人次，获得省部级科技奖励二等奖1项。2名硕士研究生即将在2016年3月毕业。