Investigation of the effect of bending twisting coupling on the loads in wind turbines with superelement blade definition

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2014
Gözcü, Mehmet Ozan
In this thesis study, the effect of off-axis plies in the spar caps of a wind turbine blade on the damage equivalent loads in a wind turbine system is investigated. The off-axis plies in the spar caps are exploited for load alleviation in the whole turbine system since the off-axis plies induced bending-twisting coupling into blades of wind turbine. Damage equivalent load is used to assess the effect of bend twist coupled blade on the fatigue load reduction in the whole wind turbine system. NREL's 5 MW turbine is selected as reference wind turbine system. In the initial phase of the thesis, since the sectional beam properties of reference turbine blades are known, the reference blades are utilized in a 3D inverse design process, and an inverse designed reference blade is obtained such that sectional beam properties of the 3D inverse blade design approximately match the sectional beam properties of NREL's reference turbine blade. In order to appropriately account for the effect of off-axis plies on the bending-twisting coupling potential, dynamic super element of the blade is generated and imported into the multi-body dynamic model of the wind turbine system. Before using super element models of bend twist coupled blades, a comparative study is conducted by using super element blades and blades modelled as non-linear beam. Results show the appropriateness of the use of super element blades for transient aero-elastic analysis of the wind turbine system. The multi body dynamic model of the reference wind turbine system is created in Samcef Wind Turbine for transient aero-elastic analysis. The analysis of the wind turbine systems are performed for the power production case with constant wind load case and normal turbulent wind load case. Damage equivalent loads at critical monitor points are calculated by time history results of the analysis. Conclusions are inferred with regard to the effectiveness of the off-axis spar cap plies with different flapwise stiffness values of the blade structure in load alleviation and possible drawbacks of the use of off-axis plies in the spar caps. Results show that in the overall, with the use of off-axis plies in the main spar caps of the blade, damage equivalent loads associated with the critical force or moment components can be reduced in the wind turbine system.
Citation Formats
M. O. Gözcü, “Investigation of the effect of bending twisting coupling on the loads in wind turbines with superelement blade definition,” M.S. - Master of Science, Middle East Technical University, 2014.