Advanced Structures & Composites Center

Published: 2012

Publication Name: Proceedings of the ISOPE 2012, The 22nd International Ocean and Polar Engineering Conference, Rhodes, Greece, June 17-22, 2012

Publication URL: https://www.nrel.gov/docs/fy12osti/54822.pdf

Abstract:

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 Consortium. 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 the
National Renewable Energy Laboratory (NREL) was used, and a fullscale FAST model of the turbine-TLP system was created for
comparison to the results of the tests. All comparisons were made at
full scale.
Analysis was 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 astested scaled configuration of the system was constructed, and this
model was then calibrated through comparison to the static load, freedecay, 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 was also modified to better
represent the structural response data by introducing additional
platform damping and stiffness terms. Next, the calibrated FAST model
was 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 in this paper.