An Efficient Time Domain Structural Assessment of a Floating Wind Turbine Structure

Abstract Unlike conventional offshore production platform, a substructure supporting floating offshore wind turbine has unique structural characteristics due to higher frequency aeroelastic loading from wind turbine in addition to wave loading. Due to periodic rotation of turbine, a floating offshore turbine substructure experiences higher fatigue load than conventional offshore platform. A reliable fatigue assessment is required to achieve the structural safety and integrity of the floating wind turbine platform. Accordingly, class societies recommend fully coupled time domain analysis because of nonlinear transient aeroelastic turbine behavior coupled with platform response in irregular waves. However, conventional coupled time domain structural analyses take huge computational resources and time, which is impractical to be applied in a floating wind turbine structural design. Present paper introduces an efficient method for time domain structural assessment. An efficient pseudo-spectral stress synthesizer is introduced to accelerate time domain structural analysis, to enable response-based determination of the extreme structural responses. Through synthesizing the pseudo-spectral stress components with the time series of external and inertial loadings from global hull motion analysis, a time series of structural response is obtained efficiently in terms of stress components at any finite element of structural model. As an application, hot spot fatigue assessments of a floating offshore wind turbine platform designed for Korean offshore wind farm projects are performed.