Research On Modal Sensitivity And Robust Optimization Of Composite Blades For Wind Turbines

Wind energy,as a rich and clean renewable energy source,has developed rapidly in recent years.The blade is a key component of the energy absorption of wind turbines.The blade has a flat,lightweight,and flexible upwind structure that works under the effects of random wind loads and the instantaneous impact of strong gusts.The blade failure rate is as high as 40%,which directly causes a huge economy loss.This study is based on the National Natural Science Foundation of China: Study on the Rigid-Flexible Coupling Vibration Mechanics of Wind Turbine Blades under Wind Conditions in Hexi Region(No.51565028)and Study on Mechanism Deterioration Mechanism of Wind Turbine Blades with Variable Stiffness under Typical Wind Resource Environments in Northwest China(No.51965034),with 1.5MW composite blades as the research object,the composite blade structure optimization research is carried out to address the problem of blades with insufficient strength and fracture failure under the action of complex alternating loads.Specific research methods and conclusion as follows:(1)Aiming at the problem of the local buckling failure of the wind turbine blade trailing edge under the static strength load,an adaptive single-objective optimization algorithm was adopted to couple the aerodynamic center of the blade with the airfoil curve,and the blade tip deflection was selected as the optimization target to optimize the blade trailing edge structure.The trailing edge buckling deformation is analyzed and compared with the blade static strength test data provided by an enterprise.The results show that the optimized blade model has lower errors in yield strength,tip deflection and strain than the traditional shell model 18%,15.7% and 10.6%,the results of the study provided a finite element model for the optimization of blade structure accuracy.(2)Aiming at the influence of the thickness of the blade root,the spar flange and the leading and trailing edges of the blade on the its flap-wise and edge-wise stiffness,taking into account the complex layer structure in different regions of the blade,the layer thickness in each region is reasonably selected as a design variable based on the modal sensitivity.Taking the blade weight as the constraint condition,the blade first-order flap-wise and edge-wise modal frequencies as its structural optimization target,a mathematical model of blade structure optimization was constructed,and then the quantitative relationship between the thickness of the layer at different parts of the blade and the natural frequency of the blade was explored to reveal the change law of the dynamic performance of the blade structure.The results show that the proposed blade modal sensitivity and structural optimization design method have improved the first-order flap-wise and edge-wise modal frequencies of the blade by 12% and 10.4%,respectively.(3)Based on the kriging model,a robust optimization method is proposed.This method has the advantage of improving the dynamic performance of the blade while improving the robustness of the dynamic performance of the blade.Two optimization examples are proposed and implemented using the blade as the research object.Example 1 employs the conventional optimization method without considering the fluctuation of the blade layer parameters.The results show that the conventional optimization method increases the first-order natural frequency of the blade by 19%,and the 6σ robustness analysis reveals that the 6σ level of the conventional optimized blade is lower 61% than the initial blade.It can be seen that although the conventional optimization method can significantly improve the inherent dynamic performance of the blade,it is hard to improve the robustness of the blade inherent dynamic performance simultaneously.The robust optimization method utilized in Example 2 takes the mean and variance of the frequency response as optimization targets.The results show that the robust optimization method increases the first-order natural frequency of the blade by 15.4%,and increases the 6σ robustness level of the blade’s inherent dynamic performance by 90% compared to the initial blade.In short,in terms of the improvement of the natural frequency of the blade,although the robust optimization method is slightly inferior to the conventional optimization method,the robust optimization method can significantly improve the robustness of the inherent dynamic performance of the blade.Therefore,the proposed robust optimization method of blade structure has better optimization effect than the traditional structural optimization methods.