A nonlinear computational model, based on solving the Navier-Stokes equation, is used to study the motion of a 5 MW spar buoy floating wind turbine in moderate and extreme sea states with irregular waves. The main advantages of using the current model are that there is no limitation on the platform motion, the hydrodynamic loads do not rely on experimental data, and nonlinear hydrodynamic loads can be predicted. The current work extends a previously developed Navier-Stokes model for regular periodic waves on a tension leg platform floating wind turbine. Free decay tests are performed, and pitch, heave, and surge natural frequencies are determined. The responses of the spar buoy to operating conditions with significant wave height of 8 m and mean period of 10 s, and an extreme sea states including waves over 17 m height are studied. For the extreme sea state, a nonlinear model is required, since the platform response amplitudes are not small with respect to the spar buoy diameter. Effects not included in linear models, such as platform pitch angles higher than 10°, complete submergence of the platform tank and tether slacking are captured. Finally, a design study on spar buoy aspect ratio is performed for one sea state and it is shown that higher aspect ratio spars generally lead to lower mean pitch and surge responses as expected, but also may lead to a nonlinear trend in the standard deviations in pitch and heave, probably due to the increase in wind and wave moments on the spar.
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Research Article|
May 28 2014
Nonlinear simulation of a spar buoy floating wind turbine under extreme ocean conditions
Ali Nematbakhsh;
Ali Nematbakhsh
1Department of Mechanical Engineering,
Worcester Polytechnic Institute
, Worcester, Massachusetts 01609, USA
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David J. Olinger;
David J. Olinger
1Department of Mechanical Engineering,
Worcester Polytechnic Institute
, Worcester, Massachusetts 01609, USA
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Gretar Tryggvason
Gretar Tryggvason
2Department of Aerospace and Mechanical Engineering,
University of Notre Dame
, Notre Dame, Indiana 46556-5637, USA
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J. Renewable Sustainable Energy 6, 033121 (2014)
Article history
Received:
February 08 2014
Accepted:
May 16 2014
Citation
Ali Nematbakhsh, David J. Olinger, Gretar Tryggvason; Nonlinear simulation of a spar buoy floating wind turbine under extreme ocean conditions. J. Renewable Sustainable Energy 1 May 2014; 6 (3): 033121. https://doi.org/10.1063/1.4880217
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