Experimental and Numerical Investigation of a Novel Constant Tension Mooring System for a Semi-submersible Floating Wind Turbine

• A novel constant tension mooring design is applied on a 16MW semi-submersible floating wind turbine. • A fully coupled aero-hydro-servo-elastic-mooring framework has been developed for the constant tension mooring floating wind turbine. • The overall performance of the constant tension mooring design is validated through experimental and numerical investigations. • The unique mooring characteristics of the constant tension mooring are analyzed. The deployment of semi-submersible floating wind turbines in medium depth and shallow waters is significantly constrained by mooring system challenges. Catenary mooring designs require excessively long and heavy mooring lines to achieve sufficient restoring stiffness, while taut and semi-taut mooring designs struggle with peak load and fatigue damage. Constant tension mooring systems represent an innovative alternative that significantly reduces peak mooring line loads while decreasing footprint requirements. In this paper, a novel constant tension mooring system for a 16MW semi-submersible floating wind turbine is proposed and verified through experimental and numerical analyses. The restoring stiffness is derived to determine key design parameters. Wave basin model tests are conducted under rated, cutout, and extreme sea states respectively, with the excitation from different combinations of wind, wave and current loads. A fully coupled aero-hydro-servo-elastic-mooring framework has been developed for the constant tension mooring floating wind turbine. To accurately capture the dynamic response, a contact analysis model based on Coulomb friction is incorporated to characterize the intrinsic damping and friction within the constant tension mechanism. The results indicate that the proposed constant tension design provides satisfactory positioning performance and excellent survivability in extreme sea states while effectively controlling peak mooring loads, with a safety factor of 1.98 for the mooring load.