State-of-the-art model for the LIFES50+ OO-Star Wind Floater Semi 10MW floating wind turbine

Abstract

This paper describes a state-of-the-art model of the DTU 10MW Reference Wind Turbine mounted on the LIFES50+ OO-Star Wind Floater Semi 10MW floating substructure, implemented in FAST v8.16. The purpose of this implementation is to serve as a reference for different activities carried out within the LIFES50+ project. Attention is given to the changes necessary to adapt the numerical model of the onshore DTU 10MW Reference Wind Turbine to a floating foundation. These changes entail controller, tower structural properties, floating substructure hydrodynamics and mooring system. The basic DTU Wind Energy controller was tuned in order to avoid the “negative damping” problem. The flexible tower was extended down to the still water level to capture some of the floater flexibility. The mooring lines were implemented in MoorDyn, which includes dynamic effects and allows the user to define multi-segmented mooring lines. Hydrodynamics were precomputed in the radiation-diffraction solver WAMIT, while viscous drag effects are captured by the Morison drag term. The floating substructure was defined in HydroDyn to approximate the main drag loads on the structure, keeping in mind that only circular members can be modelled. A first set of simulations for system identification purposes was carried out to assess system properties such as natural frequencies and response to regular waves. The controller was tested in a simulation with uniform wind ranging from cut-in to cut-out wind speed. A set of simulations in stochastic wind and waves was carried out to characterize the global response of the floating wind turbine. The results are presented and the main physical phenomena are discussed. The model will form the basis for further studies in the LIFES50+ project and is available for free use.