CFD-based hybrid-fidelity aero-hydro-servo-elastic-mooring analysis for upscaling floating offshore wind turbines to 22 MW

Floating Offshore Wind Turbines (FOWTs) are being upscaled toward larger rated capacities to enhance offshore wind resource utilization and reduce the Levelized Cost of Energy (LCOE). However, upscaling FOWT introduces complex nonlinear coupled dynamics that are poorly captured by potential-flow approaches under extreme ocean environmental conditions. This study presents a CFD-based high-fidelity, two-way coupled simulation framework integrating OpenFAST, OpenFOAM, and MoorDyn to quantify Aero-Hydro-Servo-Elastic-Mooring (AHSEM) coupling in the upscaled VolturnUS-UMaine platform with IEA 22 MW turbine across multiple Design Load Cases (DLCs). OpenFAST resolves rotor aerodynamics, blade-tower elastic deformations, and pitch-torque servo controls, transferring tower-base loads to OpenFOAM via a Dynamic Link Library (DLL). OpenFOAM applies a RANS-based k-ω SST turbulence model to capture viscous drag, wave diffraction, and water run-up under different environmental conditions. In addition, MoorDyn is coupled with OpenFOAM via a DLL interface and computes mooring dynamics using a Lumped-Mass Model (LMM). The framework is validated against OC3, OC4, and VolturnUS-UMaine benchmarks. Parametric upscaling comparisons spanning 5 MW to 22 MW reveal that responses of upscaled FOWTs are governed by strong nonlinear hydrodynamic–mooring–rotor coupling effects, with CFD-based AHSEM responses noticeably lower than potential-flow-based AHSEM. Therefore, the CFD-based AHSEM framework, which explicitly accounts for flow separation, vortex shedding, and viscous drag, yields accurate predictions for upscaled FOWTs. This framework eliminates over-conservative structural design, reduces material usage, and effectively lowers the LCOE of large-scale FOWTs.