High- and mid-fidelity digital twins and numerical simulations for dynamic responses of a moored 15 MW FOWT under tsunami wave conditions

This study examines the dynamic interactions among a 15 MW floating offshore wind turbine (FOWT), its mooring system, and tsunami wave using both high-fidelity computational fluid dynamics (CFD) model and a mid-fidelity body-nonlinear approach. The adjusted-Tohoku tsunami was represented by a superposition of three sech 2 (*)-profile waves. A novel Euler-overlay method (EOM) is developed and coupled with a commercial CFD solver to efficiently simulate the interactions between the tsunami and moored-floater. The body-nonlinear approach incorporates the instantaneous wetted surface of the structure and the corresponding updated panel discretization to compute the nonlinear Froude-Krylov (FK), hydrostatic (HS), and Morison drag forces at each time step. The accuracy of the mid-fidelity approach was validated against the high-fidelity CFD results in terms of platform motions and mooring tensions. Following validation, the model was employed to evaluate the global performance of the FOWT under a range of tsunami conditions. For the present FOWT subjected to tsunami loading, viscous drag forces were found to dominate the surge and pitch responses, whereas FK and HS forces primarily governed the heave motion. The load distribution among mooring lines was observed to vary significantly with tsunami height and incident angle. Furthermore, the use of a shorter mooring system substantially reduces heave motion; however, this reduction is accompanied by a marked increase in buoyancy forces and mooring tensions.