Calibration and Validation of a Fast Floating Wind Turbine Model of the Deepcwind Scaled Tension-Leg Platform

To capture energy from high wind resources located offshore in deep water, wind turbines mounted on floating platforms become more economical than fixed-bottom turbines. Accurate modeling of floating wind turbines, which will see increased tower, drivetrain, and blade loading from waves and platform movement, is important for the design process, but there have been few tests conducted with which to compare simulations. With the intent of improving simulation tools, a 1/50th-scale floating wind turbine atop a tension-leg platform (TLP) was designed based on Froude scaling by the University of Maine under the DeepCwind program. This platform was extensively tested in a wave basin at the Maritime Research Institute Netherlands (MARIN) to provide data to calibrate and validate a full-scale simulation model. The data gathered include measurements from static load tests and free-decay tests, as well as a suite of tests with wind and wave forcing. The FAST simulation software developed by NREL is used, and a full-scale FAST model of the turbine-TLP system is created for comparison to the results of the tests. All comparisons are made at full scale. Analysis is conducted to validate FAST for modeling the dynamics of this floating system through comparison of FAST simulation results to wave tank measurements. First, a full-scale FAST model of the as-tested scaled configuration of the system is constructed, and this model is then calibrated through comparison to the static load, free-decay, regular wave only, and wind only tests. Part of the calibration process included modifying the airfoil properties of the wind turbine blades to more accurately characterize the aerodynamic performance achieved in the tests. The FAST model is also modified to better represent the structural response data by introducing additional platform damping and stiffness terms. Next, the calibrated FAST model is compared to the combined wind and wave tests to validate the coupled hydrodynamic and aerodynamic predictive performance. Limitations of both FAST and the data gathered from the tests are discussed.