Structural modeling for flexible floating offshore wind turbine: Flexible model vs rigid model

For modeling floating offshore wind turbine (FOWT) structure, it is questionable whether to consider the flexibility of the main floater while it is almost common to account for the flexibility of the tower and blades. Most of the numerical simulation tools developed consider the floater to be a rigid body and flexibility of floating structure is not considered. The present authors have developed a coupled simulation tool which combines hydrodynamic analysis and aerodynamic analysis codes. With the present simulation code, flexibility of floating structure is incorporated into the analysis of FOWT systems. The present research is thus targeted to overcome the limitation of the floating structure as a rigid body. Effects of modeling level, i.e. the difference between flexible foundation vs rigid foundation is clarified. Transient response of SPAR type floating foundation for 5MW wind turbine under the increased thrust load due to malfunction of the pitch control system is considered.