Development of variable-fidelity FOWT digital twins in extreme sea environments: Part I – mid-fidelity analysis

In the coming years, more Floating Offshore Wind Turbines (FOWT) are projected to be installed beyond the continental shelf in the USA and worldwide. Accurate and reliable modeling of various environmental loadings and the resulting dynamic responses are crucial for the structural design, operation, and safety of FOWTs. To develop accurate and reliable FOWT design tools, a collaborative effort between academia (Texas A & M University), industry (Technip Energies), and class society (American Bureau of Shipping), supported by the Ocean Energy Safety Institute (OESI), has been undertaken. In this project, accurate and reliable digital twin (DT) models were developed based on the high-fidelity CFD models and mid-fidelity potential-flow models. In the mid-fidelity models, the wind turbine and platform dynamically interact, exchanging loads and motions at each time step. Aerodynamic loadings on the blade elements, considering wind-inflow data, tower and blade elasticity, and blade-pitch control are included. Hydrodynamic loading is calculated using potential-flow theory with Morison' s equation, and the FEM is used to model the behavior of mooring lines. The present study is presented in two separate papers. This paper, Part I, focuses on the development and validation of two mid-fidelity DT models (OrcaFlex and MLTSIM-OpenFAST) for a 15MW semi-submersible wind turbine model. The results from the two mid-fidelity DT simulations were verified through several system identification tests and for various extreme environmental conditions. In future work, the capabilities of these models will be extended to consider the effects of submarine earthquakes and tsunami waves, expanding the design loading cases of current design guidelines.