Frequency-Domain Multi-Dynamic Analysis Using Response-Based Approach for FOWT

This paper proposes a novel frequency-domain methodology for analyzing floating offshore wind turbines (FOWTs) through stress transfer functions that consider wave and wind loads. The frequency-domain analysis model included linearizing methods of critical parameters (i.e., rotor thrusts by wind, restoring forces by the mooring system, and hydrodynamic pressures by waves). A reference wind turbine, the OC3-Hywind spar platform, was selected as the target model, and industry-standard software packages, OpenFAST and ABAQUS, were used for validation. The wave-induced motion response amplitude operators (RAOs) showed agreement with 2%, 4%, and 1% differences for the surge, heave, and pitch modes under the head–sea condition, respectively. Similarly, wind-induced motions exhibited 2% differences in the surge and pitch modes in the colinear condition. The obtained results were used to calculate the radiation pressures as an integrated form, and stress transfer functions were yielded by considering them with incident and diffraction pressures. The proposed approach showed good agreement with conventional time-domain methods in the stress spectrum, showing a 92% decrease in computational time with only a 4% difference in results. This computationally efficient methodology eliminates the need for time-domain coupled-load simulations and offers potential applications in fatigue analysis and the initial design stage of FOWTs.