Abstract: In view of the currently low utilization rate of renewable energy and to effectively use deep-sea wind energy, we probed into the stability of the foundation part of the designed OC3-Hywind 5MW Spar floating platform under wind, wave, and current loads. By simulating the coupled motion response of the structure in the frequency domain and time domain respectively using hydrodynamic module AQWA in ANSYS, we compared and analyzed the motion response extreme values of the floating foundation under various degrees of freedom in different working conditions, as well as the influence of counterweights at different positions of the mooring on the response value of structure motion and mooring tension. Results revealed that the extreme value of the motion response of the floating foundation platform in the direction of the pitch degree of freedom in different cases was mainly affected by wind load; as wind speed increased, the extreme value of the response also increased. The extreme value of response in other degrees of freedom was less affected by wind and wave loads. Changing the position of counterweights on the mooring line had a significant impact on the movement of the floating foundation platform in the pitch and yaw degrees of freedom; the closer the counterweight was to the anchoring point, the greater the response value was, which is not conducive to the stability of the foundation platform. The tension of the mooring system in the absence of counterweight was higher than that in the presence of counterweight; as the counterweight was farther from the anchoring point, the mooring force reduced, which ensured the survivability of the floating foundation platform under severe sea conditions.

Key words: floating foundation platform, stability analysis, wind wave current load, AQWA, motion response, mooring force