A new digital twin model of floating offshore wind turbine for cost-effective structural health monitoring

Floating Offshore Wind Turbine (FOWT) technology is a promising energy solution that contributes to global Net Zero Target. Current industry is facing huge obstacles in expanding the development due to extremely high cost. The Operational and Maintenance Expenses (OPEX) occupy 36.6% of total lifetime cost for FOWT farm (BVG Associates, 2023). Especially maintaining the structural integrity of seakeeping mooring system is critical under severe wind and wave conditions in open sea. Historically in Oil and Gas, failure of mooring led to total loss in capital and fatal accidents. Structural Health Monitoring (SHM) system is usually adopted. Common SHM practices with human diver inspections and remote robot vehicles are expensive with daily cost 30,000 EUR (EU MooringSense project 2020) and risky under harsh sea environment. Hence, building the Digital Twin (DT) for FOWT, for real time monitoring and decision control, is essential. Sensor technology can assist SHM in real-time. Yet, the fragility, poor accuracy and repairment of pricey underwater sensors are frequent problems in practice. In this presentation, the limitations of existing DT in academia and industry were reviewed and followed by presenting the new structural FOWT DT for indirect virtual sensing of underwater unmeasurable states, wave forces and mooring force, based on easily achievable floating platform and nacelle motion measurements with GPS and Motion Reference Unit. The DT was further enhanced with the integration of Machine Learning for internal forces and fatigue prediction. A preliminary study of realistic irregular wave sea state with aerodynamic coupling on FOWT was also revealed. Without relying on frequent repairment of underwater inspection equipment, adoption of this DT will reduce the OPEX substantially and safeguard structural integrity.