The subject of this study is the verification and the validation of existing numerical codes for floating offshore wind turbine structures using wave tank model tests as part of the INNWIND.EU project. A model of the OC4-DeepCwind semisubmersible platform, together with a Froude scaled rotor model with low-Reynolds airfoils is tested in a combined wind-and-wave basin. The simulation environment comprises the multibody software SIMPACK with the HydroDyn module for the hydrodynamic loads, MAP++ for the mooring line forces and AeroDyn for the aerodynamic loads. The focus of this paper is the validation of the hydrodynamics of a modified model hull shape, which compensates for the excess mass of the nacelle. Furthermore also first steady wind simulations without wave excitation have been carried out. The results show that the model is validated and gives the basis for further research based on the conducted experiments.
The theoretical potential of offshore wind energy can be estimated to 192,800 TWh where more than 52 % of the energy potential is located in areas with water depths from 50 to 200 m (Arent et al., 2012). To be able to use this potential with respect to financial and commercial aspects new foundation systems for the wind turbines have to be applied. With higher water depths the use of floating structures is more reasonable than fixed bottom structures such as monopiles, tripods and jackets (Musial et al., 2006).
A floating wind turbine experiences many different loading conditions. Besides the aerodynamic loads, hydrodynamic loads the six DOFs floater motion has to be considered. A floating wind turbine is therefore a very complex system. Until now not many floating offshore wind turbine prototypes have been built. For example the Fukushima Forward-Project which started 2013 (Fukushima Offshore Wind Consortium, 2016) and the Hywind Scotland Pilot Park project (Statoil ASA, 2014) can be listed as current floating turbine prototypes.
In order to design wind turbines with high reliabilities for floating offshore turbines there is the need for validated simulation codes to predict the forces on the system structure and their dynamic responses for combined stochastic wave and wind loadings (Musial et al., 2006). Even though several verification test for the simulation tools have been done e.g. Robertson et al. (2013), Huijs et al. (2014), the simulation of the coupled floating wind turbine is still a part of current research projects. The research which is reported in Deliverable D4.2.4 of the INNWIND.EU project (Lemmer et al., 2014) focuses on the verification and validation of design methods for floating structures.
