Research On Bend-twist Coupling Model Of Large Flexible Wind Turbine Blade

In order to utilize the abundant offshore wind energy resources,long flexible composite wind turbine blades are widely used in offshore wind turbines.With the trend of large size and flexibility of wind turbine blades,the bend-twist coupling design has a broad application prospect in wind turbine blades.The composite bend-twist coupled blade can produce bending deformation and corresponding twisting deformation under the incoming wind,so as to change the blade angle of attack,improve the aerodynamic performance of wind turbine blades.In this thesis,through theoretical analysis,experimental research and numerical simulation,based on material nonlinearity,extension-shearing coupling and bend-twist coupling effects are systematically studied.The main research content of this thesis is summarized as follows:Two coupling models of unidirectional fiber composites considering material nonlinearity were established from elastoplasticity and hyperelasticity.The structure and materials of wind turbine blades were introduced from the whole blade to the local airfoils.Based on the linear elastic model of classical laminate theory commonly used in engineering,the generation mechanism of bend-twist coupling characteristics of composite blades was elaborated,and the linear relationship of extension-shearing coupling under plane stress was characterized.The general form of anisotropic hyperelastic model of composite under large deformation was introduced.On this basis,two coupling models of unidirectional fiber composite considering material nonlinearity were further derived from elastoplasticity and hyperelasticity,which provided a theoretical basis for the subsequent study of blade deformation.Based on the tensile test and DIC,the material parameters of the constitutive model were fitted,and the results of elastoplastic model and hyperelastic model were compared and analyzed.According to the international standard,the tensile specimens of composite materials and resin matrix materials were prepared.The material parameters of the constitutive equation were obtained by fitting the experimental data of uniaxial tensile composites with different fiber angles.The UANISOHYPER＿INV interface provided by ABAQUS software was used for secondary development of the intrinsic model,and the user subroutine for unidirectional fiber composites was written.The accuracy of the anisotropic hyperelastic constitutive model was verified by comparing the tensile simulation results with the experimental datas.By comparing the results of elastoplastic model and hyperelastic model,it was concluded that for the high toughness resin matrix composites,the extension-shearing coupling was mainly linear deformation in the small strain range,and the nonlinear trend appeared with the increase of deformation;the prediction results of anisotropic hyperelastic model was obviously better than those of the two-parameter associative elastoplastic model under the condition of large strain.Based on cantilever bending experiments and numerical investigation of the blade,the bend-twist coupling effects of composite laminates and wind turbine blades were studied.The experimental datas of bend-twist coupling deformation of composite laminates were obtained by the cantilever bending test.The finite element model was established based on the mechanical property parameters and the geometric dimension parameters of the laminates,and the numerical solution of the bend-twist coupling of the laminates was calculated.The experimental results were compared with the numerical solution,and the causes of the error were analyzed.Further,through numerical analysis of the finite element model of DTU 10 MW wind turbine blade,the calculation results showed the influence of material nonlinearity on the results of bendtwist coupling deformation of the blade.