The Dynamic Coupling Effects of a MUFOWT (Multiple Unit Floating Offshore Wind Turbine) with Partially Broken Blade

In this study, an advanced numerical simulation tool has been developed for the rotor-floater-mooring coupled dynamic analysis of a Multiple Unit Floating Offshore Wind Turbine (MUFOWT) in the time domain including aero-blade-multiple tower dynamics and control, mooring dynamics, and platform motion. In particular, the developed numerical tool is extended from the single turbine analysis tool FAST, which has been developed by the National Renewable Energy Laboratory (NREL) for years. For the linear and nonlinear hydrodynamics of a floating platform and the generalized coordinate-based Finite Element Method (FEM) mooring line dynamics, CHARM3D is used. Therefore, the entire dynamics of a floating offshore wind turbine were obtained by coupling FAST-CHARM3D in the time domain, which has been further extended to include additional coupled dynamics among multiple turbines. The global coefficient matrix, including one floating platform and a number of turbines, is built at each time step of the simulation and is solved simultaneously to obtain the responses of the entire degrees of freedom (DOFs) of the MUFOWT system. To investigate the dynamic coupling effects between the platform and turbines, a five-turbine semisubmersible is modeled and simulated. Then 1P excitation from one turbine is intentionally generated by the partial breaking of a blade, and the loads transferred to the platform and other turbines are investigated. The analysis shows that the dynamic load imbalance of one turbine in the MUFOWT may induce appreciable changes in the performance of the other turbines or the floating platform.