High-quality computer simulations are required when designing floating wind turbines because of the complex dynamic responses that are inherent with a high number of degrees of freedom and variable metocean conditions. In 2007, the FAST wind turbine simulation tool, developed and maintained by the U.S. Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL), was expanded to include capabilities that are suitable for modeling floating offshore wind turbines. In an effort to

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... idate FAST and other offshore wind energy modeling tools, DOE funded the DeepCwind project that tested three prototype floating wind turbines at 1/50 th scale in a wave basin, including a semisubmersible, a tension-leg platform, and a spar buoy. This paper describes the use of the results of the spar wave basin tests to calibrate and validate the FAST offshore floating simulation tool, and presents some initial results of simulated dynamic responses of the spar to several combinations of wind and sea states. Wave basin tests with the spar attached to a scale model of the NREL 5-megawatt reference wind turbine were performed at the Maritime Research Institute Netherlands under the DeepCwind project. This project included free-decay tests, tests with steady or turbulent wind and still water (both periodic and irregular waves with no wind), and combined wind/wave tests. The resulting data from the 1/50 th model was scaled to full size and used to calibrate and validate a full-size simulated model in FAST. Results of the model calibration and validation include successes, subtleties, and limitations of both wave basin testing and FAST modeling capabilities. MARIN wave tank testing (1/50 th scale) Tests were carried out in MARIN's wind/wave basin on a 1/50 th Froude-scaled model of the spar system built by UMaine and MARIN [7] . Researchers conducted static offset tests, six DOF decay tests, periodic wave tests with and without wind, and combinations of stochastic wind and wave conditions. In addition, hammer tests were performed on the system to obtain fundamental modal responses. Data recorded during the tests included six platform DOF positions and accelerations; rotor torque and position; accelerations at three locations spanning the tower, forces, and moments at the tower base and tower top; and mooring line tensions. The sampling frequency was 100 hertz (Hz), corresponding to a Froude-scaled sampling frequency at full scale of roughly 14 Hz. All data from the MARIN tests were converted to full scale using Froude scaling prior to analysis [8] . All test data provided in this paper were presented at full scale, unless otherwise noted.