A Structural Strength Analysis Method For Spar Type Floating Offshore Wind Turbine

An integrated procedure for structural strength analysis of spar typefloating offshore wind turbine （FOWT） is proposed in this paper. Althoughthere has been some investigation into structural design and analysis asoffshore floating wind turbine has proposed to become one promisingconcept for exploiting wind energy in deep coastal areas, a globalacknowledged structural strength analysis method is still lacking. Inaddition, due to the difference of multi-coupling loads suffered by FOWTsand marine structures, the global structural strength can’t be accessedeffectively by traditional offshore platform structure analysis methods.In order to develop the numerical approach needed to calculate theglobal structural strength of a floating offshore wind turbine, theNREL₅MW “Hywind” prototype is adopted here as a case study. Astochastic method is applied to calculate the global responses, and timedomain simulations are performed by an aero-hydro-servo-elasticfully-coupled tool （FAST）. The turbine is found to be susceptible toexcessive loading at extreme events, when the suggested criticalparameters reach maximal values. Selections of design load cases aredefined for further structural analysis.An in-depth study has also conducted for key technologies such asstructural modeling, load case definition and load mapping; suitablesolutions are given by using SESAM software to establish the structuralmodel and adopting the quasi-static method to apply the transient loadsonto the structural model, in which the design load parameters areidentified based on time series output. A structural design and analysis is also performed for theNREL₅MW wind turbine based on the strength analysis method proposedin this paper. The stress results and its distribution are obtained byconducting FEM analysis, thus provide basis for evaluation of globalstructure strength.In this paper, the structural design and strength analysis method for aspar type floating offshore wind turbine is verified. In addition, thismethod can be used to perform structural strength analysis for multi-typefloating offshore wind turbines. Furthermore, this research can providetechnical support for future floating wind turbine structural design andanalysis.