Ship and Offshore Floating Platform Motions in Extreme Seas

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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.