Development and Verification of Analysis Code "UTWind" for Rotor-Floater-Mooring Coupled Response of a Floating Offshore Wind Turbine

Rotor-floater-mooring coupled response analysis is essentially important for design of Rotor Nacelle Assembly (RNA) and floating support structure of Floating Offshore Wind Turbine (FOWT). The authors have developed an analysis code UTWind for the analysis of the coupled response. Blades and floater are modeled as frame structure with beam elements. Lumped mass model is use for mooring. Aerodynamic load on blade is calculated by Blade Element Momentum Theory (BEM), and hydrodynamic load is calculated by Hooft's method, and Morison equation was modified to be applicable to cylindrical element with cross section with two axes of line symmetry. The equations of motion of rotor, floater and mooring are solved in time domain by weak coupling algorithm.The numerical results by the code were compared with experimental results in wave and wind-wave coexisting condition with/without blade pitch control and showed good agreement. Response by negative damping was reproduced by the code and showed good agreement with experiments.