Ship and Offshore Floating Platform Motions in Extreme Seas

拟议研究的目标是发展数值方法来计算船舶和近海平台在极端海面上的运动。 随着深水石油和天然气的开发，浮式系统在勘探、生产和钻井中的作用日益重要。虽然近海浮式结构物是定位和从海底提取碳氢化合物的唯一安全和具有成本效益的手段，但它们很可能会遇到其所在位置发生的所有极端条件。船只在航线上也经常遇到极端的海浪。船舶和海洋浮式结构物在极端海况下的响应预报对其安全高效运行具有重要意义。 在极端海洋中，船舶和近海结构物可能会经历高度非线性的现象，如绿水、砰击和波浪抬高，其中涉及自由表面破裂和多相流。相关载荷可能会导致局部和全局结构破坏。尽管基于势流的方法在解决非线性船舶运动问题方面取得了很大的进展，但在处理高度扭曲或破裂的自由面方面仍然存在很大的困难。随着高性能计算机的发展，基于求解Navier-Stokes方程的计算流体力学(CFD)方法可以克服这些困难。拟议的研究将集中于开发一种CFD方法，用于预测船舶和近海平台在极端海面上的运动。主要研究内容如下：(1)将进一步发展基于约束内插剖面(CIP)的有限差分方法来计算考虑多相流和破碎自由面的船舶和平台的近场流动和运动；(2)由于CFD方法对远场波浪的模拟能力有限，将基于势流的Rankine方法与CIP方法相结合，以考虑远场波浪的影响；(3)将针对不同的船舶和平台开展验证研究。还将对极端海浪中的船模进行模型试验。实验结果和其他已发表的数据将被用来验证数值工具。 通过拟议的研究，将培训具有很强计算能力的海洋流体力学领域的高素质人员。这项拟议的研究将对国内外船舶和近海水动力学领域，特别是对极端海面和自由破碎面中船舶大幅运动的数值研究作出贡献。

The objective of the proposed research is to develop numerical methods to compute motions of ships and offshore platforms in extreme seas. With the oil and gas development in deepwater, floating systems for exploration, production and drilling are becoming increasingly important. While the offshore floating structures provide the only safe and cost effective means for the location and extraction of hydrocarbons from the sea bottom, they are likely to encounter all the extreme conditions that occur at their locations. Ships also often encounter extreme waves in their routes. The prediction of responses of ships and offshore floating structures in extreme seas is of vital importance to their safe and efficient operations. In extreme seas, ships and offshore structures can experience highly nonlinear phenomena such as green water, slamming and wave run-ups, which involve free-surface breaking and multi-phase flows. The associated loads can cause local and global structural damages. Although great progress has been made in solving the nonlinear ship motion problems with potential-flow based methods, there are great difficulties in treating highly distorted or breaking free surfaces. With the advance of high performance computers, these difficulties can be overcome by the computational fluid dynamics (CFD) methods based on solving the Navier-Stokes equations. The proposed research will focus on the development of a CFD method for predicting ship and offshore platform motions in extreme seas. The research is summarized as follows: (1) A constrained interpolation profile (CIP)-based finite difference method will be further developed to compute the near-field flows and motions of ships and platforms considering multi-phase flow and breaking free surfaces; (2) Since CFD methods generally have limited capability for simulating the waves in the far field, a potential-flow based Rankine method will be coupled with the CIP method to take the far-field wave effect into account; (3) Validation studies will be carried out for various ships and platforms. Model tests will also be conducted for a ship model in extreme waves. The experimental results and other published data will be used to validate the numerical tool. Through the proposed research, highly qualified personnel in the area of marine hydrodynamics with strong computational skills will be trained. The proposed research will contribute nationally and internationally to the field of ship and offshore hydrodynamics, especially the numerical studies of large-amplitude ship motions in extreme seas and breaking free surfaces.