Coupled aero-hydro-servo-elastic methods for floating wind turbines

To meet the demand of the development of floating wind turbines, coupled aero-hydro-servo-elastic methods were developed and then were programmed as an integrated code DARwind (short for Dynamic Analysis for Response of Wind Turbines) for simulating floating wind turbines. This paper first presents the theoretical background, including Kane's dynamical equations in combination with the Cardan angles method, the hybrid coordinate dynamic analysis method, and the adjacent array approach for kinematics and kinetics. The blade element/momentum method with aerodynamic corrections was used for aerodynamic simulation. Potential-flow theory, the second-order wave forces and the Morison formula with the strip theory were used for hydrodynamics, and a quasi-static mooring modelling approach was developed for the catenary mooring system. A generator-torque controller and a full-span rotor-collective blade-pitch controller were adopted for control strategies. The code was then verified by a series of code-to-experiment comparisons, including the mooring system, the structural elasticity, the aerodynamic performance, the hydrodynamic performance and the control strategy. The comparisons demonstrated that the coupled aero-hydro-servo-elastic methods have a satisfactory ability to perform fully coupled simulations for floating wind turbines.