Substructure optimization for a semi-submersible floating wind turbine

The design driving loading and dynamics of a floating offshore wind turbine (FOWT) substructure generally result from the extreme environmental load cases. Using these conditions, the substructure and foundation of a 10-MW FOWT were optimized using an equivalent mass approach for cut-out extreme wind and wave conditions. Equivalent mass is a cost metric that relates the substructure components' mass to the component material, manufacturing, and installation cost contributions. An optimization scheme of the individual substructure components was used to both size the components and understand their influence on the dynamic behaviour of the system. The components investigated include the mooring lines and anchors, legs, stem, and buoyancy cans. Each component was optimized to reduce substructure equivalent mass while meeting determined system constraints. The results indicated significant reductions in substructure equivalent mass and tower-base, leg, and stemleg connection cable loading. The range of components' influence on key system responses was determined. This is the first comprehensive study to use the substructure equivalent mass with a set of system constraints for optimizing FOWT substructure design for parked conditions. However, further work is needed to consider operational conditions and component loading.