Real-Time Hybrid Model Tests of a Braceless Semi-Submersible Wind Turbine: Part III — Calibration of a Numerical Model

In this paper, a numerical model of a braceless semi-submersible floating wind turbine (FWT) is calibrated against model test data. Experimental data from a 1:30 scaled model tested at MARINTEK’s Ocean Basin in 2015 using real-time hybrid model testing (ReaTHM) is used for the calibration of the time-domain simulation model. In these tests, aerodynamic loads were simulated in real-time and applied to the physical model. The simulation model is based on the as-built model at full scale. The hull and turbine are considered as rigid, while bar elements are used to model the mooring system in a coupled finite element approach. Frequency-dependent added mass, radiation damping, and excitation forces/moments are evaluated using a panel method based on potential theory. Distributed viscous forces on the hull and mooring lines are added to the numerical model applying Morison’s equation. The viscous drag coefficients in Morison’s equation are calibrated against selected test data, including decay tests in calm water and test with irregular waves. Simulations show that the drag coefficients change when waves are present. Aerodynamic loads are included as time varying loads applied directly at the hub based on the actual physical loads from the experiment. This way, uncertainties related to the aerodynamic loads in the calibrations are removed. The calibrated numerical model shows good agreement with experimental data.