Multi-Rotor-Based Real-Time Hybrid Model Testing and Coupled Dynamic Response Analysis of a 17 MW Semi-Submersible Floating Offshore Wind Turbine

This paper addresses the fundamental bottleneck of traditional floating offshore wind turbine (FOWT) basin testing—namely, the inability to reproduce full-scale turbulent wind fields and aerodynamic loads because of the irreconcilable Froude–Reynolds scaling conflict. A real-time hybrid model (RTHM) framework tailored to a 17 MW semi-submersible FOWT is therefore proposed and implemented. By integrating high-fidelity numerical simulation with physical-model testing, the framework enables real-time data exchange and closed-loop control between numerical and physical substructures through a UDP/IP protocol. First, the AeroDyn aerodynamic module of OpenFAST was recompiled to support UDP/IP communication, so that hub-motion feedback can be accepted on-the-fly and aerodynamic loads can be computed online with a blade-element-momentum (BEM) solver. Second, a bespoke multi-rotor loader—six independently controlled propellers—was developed to replicate full-scale thrust and moments on a 1:65 Froude-scaled model. Systematic wave-basin campaigns were then conducted under pure-wind and combined wind–wave conditions. The results show that the mean errors of thrust and torque remain below 5 % in pure wind and that amplitude and phase are faithfully preserved under combined wind–wave excitation, validating the ability of the RTHM framework to reproduce complex aero-hydro coupling. The close agreement with fully coupled numerical predictions further demonstrates the reliability and accuracy of the hybrid strategy for predicting the dynamic response of next-generation ultra-large FOWTs.