Low‐frequency dynamics of a floating wind turbine in wave tank–scaled experiments with SiL hybrid method

Abstract

Abstract The design of floating wind turbines needs the validation of numerical models against measurements obtained from experiments that accurately represent the system dynamics. This requires solving the conflict in the scaling of the hydrodynamic and aerodynamic forces that arises in tests with wind and waves. To sort out this conflict, we propose a hybrid testing method that uses a ducted fan to replace the rotor and introduce a force representing the aerodynamic thrust. The force is obtained from a simulation of the rotor coupled in real time with the measured platform displacements at the basin. This method is applied on a test campaign of a semisubmersible wind turbine with a scale factor of 1/45. The experimental data are compared with numerical computations using linear and non‐linear hydrodynamic models. Pitch decays in constant wind show a good agreement with computations, demonstrating that the hybrid testing method correctly introduces the aerodynamic damping. Test cases with constant wind and irregular waves show better agreement with the simulations in the power spectral density's (PSD's) low‐frequency region when non‐linear hydrodynamics are computed. In cases with turbulent wind at rated wind speed, the low‐frequency platform motions are dominated by the wind, hiding the differences from hydrodynamic non‐linearities. In these conditions, the agreement between experiments using the proposed hybrid method and computations is good in all the frequency range both for the linear and the non‐linear hydrodynamic models. Conversely, for turbulent winds producing lower rotor thrust, non‐linear hydrodynamics are relevant for the simulation of the low‐frequency system dynamics.