Optimization of a floating offshore wind turbine platform and mooring lines according to an innovative wind farm wake control technique

The floating offshore wind resource has a very large expected impact on the overall energy production scenario. Regardless, the exploitation of such valuable resource remains a technological challenge due to the harsh environment in which they operate and higher costs of installation and maintenance. A crucial component of a floating offshore wind turbine is represented by the floating platform, which provides the hydrostatic stability and absorbs the loads coming from both sea-waves and by wind acting on the turbine. While often seen as a disadvantage of the floating offshore wind turbines, the possibility of enhancing the floater motion can be exploited to control the evolution of the wake structure behind the wind turbine rotors, re-energizing the flow in the wake and increasing in this way the power production of rotors set behind the upstream turbine. Designing the floater and mooring lines configuration to enhance yaw oscillations at a certain frequency is expected to increase this behaviour. In this work we apply a simulation-based approach with the aim of designing a floating platform and mooring lines configuration optimized for their integration within this new control strategy based on wake-mixing in wind farms. The optimization process is applied to the DTU 10MW reference wind turbine supported by a semi-submersible floater composed of three spars ("Triple Spar" concept). The modification of the floating platform spar arrangement and mooring lines properties allowed to tune the yaw natural frequency of the system in accordance with the excitation frequency of the wake control technique, while controlling the deviation of operational constraints and costs from baseline configuration.