Stability and power performance of a floating wind-current energy system under tidal turbine operating mode variations

Hybrid energy systems have recently attracted widespread attention due to their significant advantages and immense potential in advancing renewable energy. In this study, an integrated floating energy system (IFES) comprising a NREL 5 MW wind turbine and two tidal turbines jointly supported by the OC4 semi-submersible platform, is proposed and investigated. The two tidal turbines are positioned at platform bottom, and their operating modes are shown to strongly influence the dynamic responses of the whole system. To address this, a fully coupled numerical framework MultiF2A is developed to capture the aero-hydro-servo-elastic interactions of wind-current IFES. Dynamic responses are evaluated under three representative operating conditions, including cases where the two tidal turbines operate inconsistently due to controller faults. The results reveal that inconsistencies in operating modes have only insignificant effects on surge and pitch motions. In contrast, both the average and maximum values of platform yaw increase significantly relative to the consistently normal operation, posing potential threat to platform stability. Specifically, the maximum value of platform yaw increases by up to 163.16 % under the rated-below condition. Variations in fairlead tension of the mooring lines remain small, indicating no significant risk to platform safety. However, overall generator power decreases when controller fault occurs in one of the tidal turbines, indicating the negative impact of mismatch operating modes on power performance. These findings emphasize the importance of avoiding unfavorable dynamic interactions between tidal turbines in the IFES. Careful consideration of tidal turbines’ operating modes is essential to maintain platform stability and optimize performance under complex offshore environmental conditions.