Investigate On Dynamic Characteristics Of Wind Turbine Composite Blade Under Wind Resource Environment In Hexi Region

As a clean and widely distributed renewable energy,the wind power industry has become an important direction for energy development.The blade is a key component of wind turbine energy absorption.For the blade with flat,lightweight,flexible and upwind structures,the fracture failure rate is as high as 40% under random variable loads and strong gust instantaneous impact,which directly causes huge economic losses.With the increasing capacity of single wind turbine,higher requirements for static and dynamic characteristics of blade are put forward.Therefore,this research is funded by the National Natural Science Foundation of China Project "Study on Mechanism Deterioration Mechanism of Wind Turbine Blades with Variable Stiffness under Typical Wind Resource Environments in Northwest China(No.51965034)".Aiming at the load simulation calculation and static and dynamic characteristics of composite blade under specific wind conditions in Hexi Region.Taking 1.5MW horizontal axis wind turbine composite blade as the research object.By constructing the Weibull distribution model of wind speed in Hexi Region,the load distribution law of different sections of blade under regional steady-state conditions is explored.On this basis,the finite element method is used to investigate the blade finite element modeling,static analysis and dynamic characteristic analysis.This research has important reference value for regional blade structure optimization design.The main research contents and obtained research results are as follows:(1)Solve the distribution law of the load along with the flapwise,edgewise and torsion directions of the blade when the rated wind speed is 10.4m/s under steady-state conditions.Firstly,based on the characteristics of specific wind resources in Hexi Region,the probability density curve of the actual measured average wind speed in the region is plotted,and compared with the probability density curve of the average wind speed fitted by Weibull distribution.On this basis,the load types of the blade during operation are summarized,and the load distribution law of different airfoil sections of the blade under steady-state operation condition in the region is simulated.Study on the variation law of blade load along blade spanwise direction in three directions of flapwise,edgewise and torsion directions at the rated wind speed of 10.4m/s.(2)Construct the finite element model of composite blade and study on static characteristics.Firstly,according to the design principle of composite blade layer and the mechanics theory of laminated plate,the design scheme of composite blade layer is determined.Based on ACP analysis module,the finite element model of composite blade of 1.5MW horizontal axis wind turbine is constructed.Then,based on the load distribution law of different sections of the blade under the regionalized steady-state condition,combined with the finite element method,the static characteristics of the composite blade are studied to explore the stress and strain of the blade and the distribution of the load limit factor in the flapwise and edgewise directions.The results show that the load limit factors in the direction of flapwise and edgewise within 70%of the blade spanwise under steady-state condition are greater than or equal to 1.10.(3)Study on the dynamic characteristics and buckling stability of composite blade.Firstly,according to the load distribution under the steady-state condition,the modal superposition method is used for the vibration harmonic response analysis to check the frequency amplitude response of the blade,and to explore the equivalent stress distribution and deformation distribution of the blade under the natural frequency of15 Hz.The results show that when the natural frequency is 15 Hz under pressure load,the local stress distribution of the blade had mutations,and there is obvious stress concentration in the middle part of the blade.Then,by effectively introducing the differential stiffness of the blade,the first two orders nonlinear buckling eigenvalues of the blade are all greater than 1,indicating that the buckling load of the blade is greater than the actual load,that is,the overall instability of the blade will not occur when the rated wind speed is under steady-state load.(4)Calculate the fatigue life of composite blade based on the fatigue load spectrum.Firstly,the blade stability is quantitatively analyzed by modal analysis,Campbell diagram and output power curve.The results show that there is no intersection between the first four-order natural frequency of the blade and the excitation force frequency in the rated wind speed range,the blade will not resonate,and the output power meets the requirements of the previous blade stability design.Then,the linear fatigue cumulative damage rule and the glass fiber/epoxy composite SN curve are used to solve the blade fatigue load spectrum of the wind field in the Hexi Region.Finally,the fatigue cumulative damage life of the regionalized blade was further solved by introducing the load spectrum,and the result show that the blade life meets the GL design requirements for 20 years under steady-state condition.