Performance evaluation of a 15 MW semi-submersible floating offshore wind turbine with a synthetic fiber mooring system

The present study investigates the influence of permanent elongation and dynamic stiffness variation in polyester ropes on the dynamic and structural behaviors of 15-MW taut-moored semi-submersible floating offshore wind turbine (FOWT) platforms. Numerical models of FOWTs were developed, incorporating the permanent elongation and dynamic stiffness variations of polyester ropes under various environmental conditions using the Syrope methodology. Three mooring configurations were analyzed: chain-only and chain–polyester–chain systems, with and without updates for permanent elongation and dynamic stiffness. Results were assessed through statistical parameters and time histories of platform motions and hub accelerations as dynamic responses and mooring tensions and tower-base moments as structural responses. The findings reveal that accounting for permanent elongation and stiffness variation amplifies global motions and structural responses compared to cases neglecting these effects. In taut-mooring configurations, the observed behavioral changes are associated with slack-taut transitions and snap loading phenomena, markedly intensified when considering elongation and dynamic stiffness.