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http://dx.doi.org/10.12989/ose.2015.5.3.139

Global performances of a semi-submersible 5MW wind-turbine including second-order wave-diffraction effects  

Kim, H.C. (Texas A&M University, College Station)
Kim, M.H. (Civil Engineering, Texas A&M University, College Station)
Publication Information
Ocean Systems Engineering / v.5, no.3, 2015 , pp. 139-160 More about this Journal
Abstract
The global performance of the 5MW OC4 semisubmersible floating wind turbine in random waves was numerically simulated by using the turbine-floater-mooring fully coupled and time-domain dynamic analysis program FAST-CHARM3D. There have been many papers regarding floating offshore wind turbines but the effects of second-order wave-body interactions on their global performance have rarely been studied. The second-order wave forces are actually small compared to the first-order wave forces, but its effect cannot be ignored when the natural frequencies of a floating system are outside the wave-frequency range. In the case of semi-submersible platform, second-order difference-frequency wave-diffraction forces and moments become important since surge/sway and pitch/roll natural frequencies are lower than those of typical incident waves. The computational effort related to the full second-order diffraction calculation is typically very heavy, so in many cases, the simplified approach called Newman's approximation or first-order-wave-force-only are used. However, it needs to be justified against more complete solutions with full QTF (quadratic transfer function), which is a main subject of the present study. The numerically simulated results for the 5MW OC4 semisubmersible floating wind turbine by FAST-CHARM3D are also extensively compared with the DeepCWind model test results by Technip/NREL/UMaine. The predicted motions and mooring tensions for two white-noise input-wave spectra agree well against the measure values. In this paper, the numerical static-offset and free-decay tests are also conducted to verify the system stiffness, damping, and natural frequencies against the experimental results. They also agree well to verify that the dynamic system modeling is correct to the details. The performance of the simplified approaches instead of using the full QTF are also tested.
Keywords
wind energy; FOWT (Floating Offshore Wind Turbine); OC4 semi-submersible; dynamic coupling; mooring tension; second order wave diffraction effect; QTF; FAST-CHARM3D; 5MW wind-turbine; viscous drag;
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Times Cited By KSCI : 2  (Citation Analysis)
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