Implementation of wave basin spring-rope mooring system for floating offshore wind turbines

Abstract Scaled hydrodynamic testing in wave basins is an important tool for developing designs for floating offshore wind turbine platforms. When designing such scale tests, accurate representation of the mooring system behaviour is crucial. However , designers must overcome challenges including: the availability of materials that replicate mooring static and dynamic stiffness and truncation of the mooring footprint to match the wave basin’s dimensions and its scaled depth. This study proposes a method to represent a scaled catenary mooring using a tensioned spring-rope configuration in a wave basin. This mooring system is designed by analytically calculating the mooring line elasticity acquired from the linear mooring stiffness matrix. This catenary-equivalent mooring system is then experimentally tested in the wave basin at the FloWave Ocean Energy Research Facility using a 1:50 scale VolturnUS-S semi-submersible platform fitted with the 15 MW IEA reference wind turbine. This method shows that the mooring system captures surge variability and pitch dynamics well, with pitch errors under regular waves ranging from 0.14% to 14.69%. However, mooring tensions exhibited large deviations in mean values, despite standard deviation ratios generally remaining close to 1. These results underscore the limitations of spring-rope systems in replicating catenary restoring forces and highlight the importance of accurately modelling mooring properties when simulating semi-taut configurations.