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Determination of the bending twisting coupling potential of composite materials via digital image correlation and its implementation in wind turbine blades

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2017
Şener, Özgün
In this thesis study, the main objective is to investigate the effect of bending-twisting coupling in composite wind turbine blades on the load alleviation, power generation and structural performance of the wind turbine system. For this purpose, experimental and numerical study is initially conducted to determine the bend-twist coupling potentials of composite materials. Bending-twisting behavior of composite materials are determined through a comparative study via the Digital Image Correlation (DIC) system and the finite element analysis, and the outcome of the numerical and experimental study is utilized to form a basis on the selection of material and fiber angle configuration for wind turbine blade designs with the purpose of load alleviation in the whole wind turbine system. Experimental and numerical study of the bending twisting coupling behavior of composite materials is performed on composite plates and box beams which simulate the flange region in wind turbine blades in much smaller scale. In order to validate the results of the finite element analyses, orthotropic properties of E-Glass and Carbon materials are determined through following several international tensile test procedures via DIC system and strain gage application. Bend-twist coupling potentials determined by the DIC system and the finite element analyses are compared, and a reliable database for the effect of bend-twist coupling due to different materials and different fiber angle orientations is generated. Based on this study, material selection and off-axis fiber angle range to be utilized in the bend-twist coupled turbine blade designs are determined. Wind turbine models with designed bend-twist coupled blades are set up in a multi-body dynamic code with the aim of investigating and comparing the effect of bend-twist coupling on the load reduction in subcomponents of turbine system and on the power generation and structural performance of the wind turbine system. The effect of bend-twist coupling due to different composite materials and fiber angle orientations in turbine blades is examined under realistic working scenarios with six different turbulent wind profiles. In overall, results show that the bending twisting coupling effect in the wind turbine blades contribute to the reduction in loads at the critical points in the whole turbine system without significant disadvantages.