Modeling the coupled aero-hydro-servo-dynamic response of 15 MW floating wind turbines with wind tunnel hardware in the loop

Accurate modeling and design tools are required to lower the cost of floating wind and enable the rapid growth that is expected in the next years. This paper presents a hardware-in-the-loop (HIL) wind tunnel experiment, showing it is a valuable tool to investigate the coupled response of two 15 MW floating wind turbines. In the HIL experiment, the wind turbine is emulated with a physical scale model, that is a 1:100 version of the IEA 15 MW, with reference closed-loop control functionalities. Rotor aerodynamic loads are continuously measured and fed back to a numerical simulation of the floater response. The output of the simulation are platform motions that are recreated in the wind tunnel with a robot. The two floating wind turbines are tested with various wind, waves, and turbine control conditions. It is shown the turbine scaled model matches with good accuracy the response of the IEA 15 MW, thanks to the aerodynamic re-design of blades and the adopted closed-loop control strategy. The HIL control system reproduces the coupling between turbine and platform with very small errors. In operational conditions, aerodynamic damping of platform motion is sensitive to wind speed when the turbine is controlled in closed loop, and it is shown that this is due to the coupling between platform pitch and rotor. The amount of aerodynamic damping just below the rated wind speed is found to be more uncertain than in other wind conditions.