A Coupled Aero-Hydro-Elastic-Mooring Simulation Framework for Floating Offshore Multi-Rotor Wind Turbines

This paper presents WSMAQ (WEC-Sim-MoorDyn-AeroelasticQ), a coupled aero-hydro-elastic-mooring simulation framework for floating offshore multi-rotor wind turbines. The framework integrates WEC-Sim for platform hydrodynamics; MoorDyn-C for mooring-line dynamics; and in-house aeroelastic code, AeroelasticQ, for rotor-level aerodynamic and blade structural calculations. These modules are coupled within MATLAB/Simulink/Simscape 2023a. The novelty of WSMAQ lies in three coupling-oriented methodological extensions. First, for deep-draft spar platforms, the WEC-Sim body is configured using the physical mass and inertia at the true center of gravity, the full unadjusted added-mass matrix is retained in the radiation-load calculation, and a three-block integrator filter is used to break the added-mass–acceleration algebraic loop. Second, the WEC-Sim mooring class is extended to pass the non-zero initial platform orientation to MoorDyn-C. Third, AeroelasticQ is integrated with the multibody wind turbine model through a rotor-count-parameterized Level-2 C++ MEX S-function. The framework was benchmarked against OpenFAST through aeroelastic, platform-mooring, and full-wind-turbine tests on the OC3 spar with the 5 MW reference turbine developed by the National Renewable Energy Laboratory. Across the primary response channels, the mean relative error remained below 2% in most cases. Multi-rotor capacity was demonstrated using three NREL WindPACT 1.5 MW turbines mounted on the OC3 spar. In this case study, an asymmetric rotor-parked condition generated a mean yaw offset of approximately 4°, which did not appear in the symmetric-load cases.