Ship and Offshore Floating Platform Motions in Extreme Seas

提出的研究目标是发展数值方法来计算极端海洋中船舶和海上平台的运动。随着深水油气的开发，用于勘探、生产和钻井的浮式系统变得越来越重要。虽然海上浮式结构为海底碳氢化合物的定位和开采提供了唯一安全和经济有效的手段，但它们可能会遇到在其位置发生的所有极端条件。船只在航行途中也经常遇到巨浪。极端海环境下船舶和海上浮式结构的响应预测对其安全高效运行至关重要。在极端的海洋环境中，船舶和海上结构可能会经历高度非线性的现象，如绿水、撞击和波浪起伏，这些现象涉及自由水面破碎和多相流。相关荷载可引起局部和整体结构损伤。尽管基于势流的方法在求解非线性船舶运动问题方面取得了很大进展，但在处理高度扭曲或断裂的自由表面方面存在很大困难。随着高性能计算机的发展，基于求解Navier-Stokes方程的计算流体动力学（CFD）方法可以克服这些困难。拟议的研究将侧重于开发一种CFD方法，用于预测极端海洋中船舶和海上平台的运动。研究结果如下：(1)将进一步发展基于约束插值剖面（CIP）的有限差分方法，以计算考虑多相流和自由面破裂的船舶和平台近场流动和运动；(2)由于CFD方法对远场波的模拟能力一般有限，因此将基于势流的Rankine方法与CIP方法相结合，考虑远场波效应；(3)将对各种船舶和平台进行验证研究。此外，还将对极端波浪下的船舶模型进行模型试验。实验结果和其他已发表的数据将用于验证数值工具。通过本研究，将培养具有较强计算能力的海洋流体力学领域的高素质人才。所提出的研究将对国内外船舶和近海水动力学领域，特别是对极端海域和破溃自由面大振幅船舶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.