Time-Domain Response-Based Structural Analysis on a Floating Offshore Wind Turbine

As the turbine blade size becomes larger for economic power production, the coupling effect between wind turbine and floating substructure becomes important in structural assessment. Due to unsteady turbulent wind environment and corresponding coupled substructure response, time-domain analysis is required by international electrotechnical commission and class societies. Even though there are a few numerical tools available for the time domain structural analysis based on conventional coupled motion analysis with wind turbine, the application of conventional time domain analysis is impractical and inefficient for structural engineers and hull designers to perform structural strength and fatigue assessment for the required large number of design load cases since it takes huge simulation time and computational resources. Present paper introduces an efficient time-domain structural analysis practically applicable to buckling and ultimate strength assessment. Present method is based on 'lodal' response analysis and pseudo-spectral stress synthesizing technique, which makes timedomain structural analysis efficient and practical enough to be performed even in personal computing system. Practical buckling assessment methodology is also introduced applicable to the time-domain structural analyses. For application of present method, a 15-MW floating offshore wind turbine platform designed for Korean offshore wind farm projects is applied. Based on full-blown time domain structural analysis for governing design load cases, buckling and ultimate strength assessments are performed for the extreme design environments, and the class rule provided by Korean Register is checked.