This work examines the dynamic response of a single semi-submersible wind turbine (SSWT) based on different hydrodynamic theories. Comparisons of platform motions and structural responses in the wind turbine are shown for simulations for a model with linear potential flow solution and quadratic drag and simulations with only Morison-type forces. The SSWT modelled in this study is based on WindFloat and carries the NREL 5MW wind turbine and should be considered a large volume structure. This implies that diffraction effects should be considered by using potential flow theory and viscous effects by Morison's equation. A new coupled simulation code was developed by linking the SIMO and RIFLEX hydrodynamic, structural, and control system computational tools, from MARINTEK, with the aerodynamic forces and wind field generation capabilities of AeroDyn and TurbSim, from NREL. In contrast to other available simulation codes, this combination enabled the implementation of these two different hydrodynamic theories and offered the possibility of finite element mooring line models. Wave-only simulations were considered first, in order to tune and compare potential theory versus the inertia term in Morison's equation. Some limited coupled wave-wind simulations give an indication of the extent to which hydrodynamic modelling affects the global response. The SSWT case study showed that the Morison model with forces integrated up to wave elevation gave a good representation of the motions compared to the potential flow model with quadratic drag forces. It also showed that motions are sensitive to choice of added mass coefficients, stretching and dynamic pressure under the columns. Combined wind and wave simulations, using a non-optimized control approach, showed that pitch motions influence the power production and blade bending moments. (C) 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of SINTEF Energi AS. Open access under CC BY-NC-ND license.
