A novel integrated approach to efficiently model viscous effects on wave-structure interaction in extreme sea

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Many offshore structures for exploiting oil/gas in ocean and for harnessing marine renewable wave energy, tidal current energy and offshore wind energy have been and will be designed and operated. During the design of these structures, it is essential to consider their responses in the worst situation possibly met(extreme sea). In such situation, the breaking wave impact and the viscous effects are widely recognized to be important. These factors disqualified the well-established linear or second-order wave diffraction analysis based in the frequency domain which has been usually used during the design. However, the Computational Fluid Dynamics (CFD) tools with ability to model the wave impact and viscously may take several days or weeks to produce reliable results for the response of structures in a required large sea area with dimensions at the level of tens or hundreds of wavelengths in 3-D and for many wave periods. Alternative tools based on the fully nonlinear potential theory (FNPT) have relatively higher computational efficiency, e.g. the Quasi Arbitrary Lagrangian Eulerian Finite Element method (QALE-FEM) may complete the simulation within an overnight. However, they cannot deal with the breaking wave impact and take the viscous/ effects into account. Therefore, how to efficiently model viscosity/turbulence and the breaking wave impact associated with wave-structure interaction remains to be a key challenge in offshore and marine engineering. This project will carry out the research to tackle the challenge by developing a novel approach to efficiently model the interaction between large-domain 3D extreme waves and the offshore structures with consideration of viscous/turbulent effects and breaking wave impact. The new method takes the advantage of the CFD tools and the FNPT based methods by integrating them in a single approach. It is expected to have the computational efficiency at a similar level to the FNPT based QALE-FEM , i.e. simulating wave-structure interaction with viscosity and wave breaking in a required large 3D sea area on modern PCs within an overnight. The new development may make it possible to simulate large floating structures subjected to extreme waves in time domain and so give more realistic results.A preliminary test has been carried out. The results demonstrate the feasibility and the promising features of the proposed approach.