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

Floating Offshore Wind Turbines (FOWTs) 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 environmental conditions they are exposed to, there remain 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 hydrodynamic study of a 15 MW semi-submersible FOWT under a range of environmental conditions, informing the design criteria for the damper system. The study presents both findings in the time- and frequency- domain. In the first instance the time-domain was used to determine the dominant motion characteristics. The initial study identified that the pitch motion is of main concern. As a consequence, in the frequency-domain study the focus is given to the pitch motion. Excitation modes were observed at both, eigenfrequency and excitation frequency, dependent on wave conditions. Within the discussion a dual damper system is suggested to increase stability of the platform.