For more economic power generation, the blade size of offshore floating wind turbine becomes bigger than floating substructure. Consequently, structural load from wind turbine to floating substructure under unsteady turbulent wind condition becomes more important for structural strength assessment. In conventional load-based structural strength assessment, the coupling effect between hull motion and turbine loading is ignored so that the strength assessment based on the conventional methods has high uncertainties. Therefore, class societies recommend fully coupled time-domain analysis of the floating offshore wind turbine and subsequent response-based structural analysis to assess the structural strength.
Present paper introduces an efficient time-domain structural analysis for buckling and ultimate strength assessment. For various design load cases, full-blown time-domain structural analyses are performed by mapping the aero-elastic, hydrodynamic, hydrostatic, inertial and mooring loadings to finite-element structural model. An efficient pseudo-spectral stress synthesizer based on ‘lodal’ response analysis is introduced to enhance the computational efficiency of time-domain structural analysis.
As an application, a floating offshore wind turbine platform designed for Korean offshore wind farm projects is used. Based on full-blown time domain structural analysis, buckling and ultimate strength assessments are performed following the Class Rule provided by Korean Register.