Aero-hydrodynamic studies of a 15 MW semi-submersible FOWT to assess the suitability of the inclusion of a damper system

Abstract

Floating offshore wind turbines can exploit the high energy density experienced in offshore environments, with turbines now reaching up to 15 MW in size. However, given the larger size of these turbines and the severe offshore environment, there remains significant challenges in motion stabilization. To overcome these challenges, the inclusion of a damper system could be considered to reduce motions. This paper conducts a numerical dynamic analysis of a 15 MW semi-submersible floating offshore wind turbine under a range of environmental conditions, informing the design criteria for such a damper system. The study presents the findings under different environmental loading conditions. In the first instance, the time domain results of hydrodynamic study were used to determine the dominant characteristics. The initial study identified the pitch motion of main concern. The simulations were carried out under wave-only and wind-wave loading. In the wave-only conditions study, excitation modes were observed at both the eigenfrequency and excitation frequency, dependent on wave conditions. When the wind loads were introduced, a large mean pitch offset and amplitude relative to the mean offset were observed. Within the discussion, a dual damper system is suggested to increase the stability of the platform.