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The increasing demand for offshore wind energy is leading the industry to look for expansions into deep oceans. This development has compelled the industry to venture in to floating offshore installations for wind turbines. The floating installations lead to complex rotor motions in 6 degrees of freedom. The current work focusses on various aerodynamic effects on the turbine rotor due to coupled wind and wave forces. In this research work, the dynamic effects of the platform pitching motion on the rotor for OC3 phase IV case 5.1 are studied with rigid body assumption using high fidelity CFD (Computational Fluid Dynamics) commercial tool and semi empirical tool called FAST which is developed by NREL, USA. The hydrodynamic effects leading to the pitching motion of the turbine platform are extracted from the NREL FAST software. These pitching motions are coupled with the rotating blades to study transient flow behaviors using CFD tools. The results are compared with the standard BEM based methods to identify the discrepancies if any. Moreover, fine variation of rotor power/load due to dynamic pitching of the floating platform is also compared. The induction factors are extracted from the CFD results for every time step and are compared with those obtained with BEM based methods. Moreover, the application of CFD induction factor methods are introduced for cyclic load variations due to the rotor plane motions to check the validity of the BEM for FOWT application.

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In this study, advanced numerical CFD tools based on OpenFOAM are developed to generate extreme waves for the investigation of wave-in-deck loads on fixed offshore structures. The numerical method employs a Navier-Stokes solver with the free-surface captured by the volume of fluid (VOF) approach. The advantages of numerical simulation through CFD are: 1) full scale simulation of nonlinear phenomena; 2) potentially more accurate prediction as viscous and inertia forces are included whereas a model test based on Froude scaling can only scale the inertia forces; and 3) detailed insight into the flow and resulting loads. The numerical simulations for long-crested extreme waves capture the evolution of impact loads and free surface during the interaction with the platform deck. CFD provides more accurate results than analytical tools and the flow physics can be studied in detail, providing further insight that can lead to improvements in the analytical tools. This study also provides a benchmark set of problems for wave loading on platform decks.