The foundation represents a significant part of CAPEX for floating offshore wind. Fred. Olsen has patented the disruptive floating offshore wind (FOW) concept named “Brunel”, which is single point moored (SPM) through a turret, allowing it to self-align towards the wind direction. The concept has benefits when it comes to stability and motion control since the loads are coming from one governing direction, allowing for optimized steel design, and no need for mechanical support systems.
SPM FWTs can rotate freely due to changes in wind or current directions. Such a behaviour acts as a passive control system, which allows the turbine to face the wind despite its changes. However, yaw moments caused by aerodynamic forces and/or platform motions has an unwanted effect on SPM FWTs as it causes misalignments relative to the incoming wind. The yaw offset reduces the energy production and increases fatigue loads in the rotor, thereby reducing its useful life. In addition, wave dynamics may lead FWTs to oscillate in the yaw direction, the so-called ‘fishing tailing’ effect, which increases structural stresses and difficult the access for maintenance jobs.
Single point mooring of floating offshore structures has been in use in use in oil and gas industry for FPSOs (Floating, productions, storage, offloading). However, FPSOs have a dynamic positioning system with thrusters for aligning the vessel. The dynamic positioning system is also used to keep the vessel in correct position, meaning active compensation against the yaw motion. Hence, current state-of-the-art yaw modelling is used for FPSO and is not applicable to FOW.
In this research project Salar AS, 7Waves AS and IFE will develop a novel control system to mitigate the weathervaning of single point moored floating wind turbines (FWTs). At present, this problem lacks a proper solution in scientific literature.
Fred. Olsen has patented the disruptive floating offshore wind (FOW) concept named “Brunel”, which is single point moored through a turret, allowing it to self-align towards the wind direction.
Cost reducing benefits of single point moored FOW:
- Reduced steel weight
- Reduced need for mechanical systems
- Reduced mooring costs
FOW are naturally both larger and heavier than bottom fixed offshore wind foundations. Therefore, the foundation represents a larger part of CAPEX. The above mentioned cost reducing benefits are needed for enabling levelized cost of energy (LCOE) comparable to bottom fixed offshore wind.
SPM FWTs can rotate freely due to changes in wind or current directions. Such a behaviour acts as a passive control system, which allows the turbine to face the wind despite its changes. However, yaw moments caused by aerodynamic forces and/or platform motions has an unwanted effect on SPM FWTs as it causes misalignments relative to the incoming wind. The yaw offset reduces the energy production and increases fatigue loads in the rotor, thereby reducing its useful life. In addition, wave dynamics may lead FWTs to oscillate in the yaw direction, the so-called ‘fishing tailing’ effect, which increases structural stresses and difficult the access for maintenance jobs.
Single point mooring of floating offshore structures has been in use in use in oil and gas industry for FPSOs (Floating, productions, storage, offloading). However, FPSOs have a dynamic positioning system with thrusters for aligning the vessel. The dynamic positioning system is also used to keep the vessel in correct position, meaning active compensation against the yaw motion. Hence, current state-of-the-art yaw modelling is used for FPSO and is not applicable to FOW.
This research project tackles the development of a control system to mitigate the weathervaning of single point moored (SPM) floating wind turbines (FWTs). This problem still lacks a proper solution in scientific literature.