Aerodynamic Damping on a Semisubmersible Floating Foundation for Wind Turbines

The objective of this work is to study the effect of the rotor thrust on the motions of a semisubmersible floating foundation for Horizontal Axis Wind Turbines (HAWT). The main targets are the drift motions and the additional damping caused by the operating rotor, so-called aerodynamic damping. The semisubmersible used in the Offshore Code Comparison Collaboration Continuation (OC4) project, which operated under International Energy Agency (IEA) Wind Task 30, is chosen for this study. Two numerical models are built in aNyPHATAS, a coupled hydrodynamic and aerodynamic tool for simulations of floating wind turbines. The numerical model of the original design of the semisubmersible (OC4), and a numerical model calibrated against model tests (OC5) are compared with measurements. For practical reasons, the physical model at the scale of the basin needs to be adjusted. One key modification is done on the rotor of the wind turbine so that its performance remains equivalent while Froude scaling is applied. This comparison is done for two load cases: operational waves only, operational waves and steady wind simultaneously with a turbine operating at fixed rotation speed (without control). It serves to check the extent to which a design concept and a physical model built at small scale match.