| The blade is the most important component of large scale direct drive wind turbine.However, its working environment is so bad that it usually works under complex random variable amplitude load.So it is prone to fatigue damage,which leads to the failure of wind wheel and even the shutdown of wind turbine.In order to improve the reliability of wind turbine, it is necessary to estimate the fatigue life of blade accurately.Before the fatigue life of the blade is analyzed,the different types of loads acting on the blade are studied in this paper. The load signal acquisition and processing system is built by using the resistance strain gauge sensor to measure the random variable amplitude load acting on the blade.At the same time, in order to obtain the original macro load data, the corresponding preprocessing operation is performed on the collected load data to filter the irrelevant signals which affect the accuracy of the signal.When analyzing and estimating fatigue life of the blade,it is necessary to analyze the strength and deformation of the blade.To solve the problem, this paper uses Profili,a airfoil design software,and Pro/E,a 3D drawing software, to construct the geometric model of wind turbine blade.Then put it into ANSYS finite element analysis software and plot numbered cell mesh for it. Next,construct a finite element model of wind turbine blade,and apply the measured macroscopic load data to the finite element model of the blade.The stress distribution and deformation of the blade were analyzed and calculated by ANSYS,and the result shows that the strength of the blade meets the design requirements.At the same time,transform the continuous load spectrum into the discrete load spectrum by calculating the equivalent amplitude of load at each level.Thus greatly reducing the workload of data processing and analysis,and all above provides effective data support for estimating fatigue life of the blade.When estimating fatigue life of the wind turbine blades,the effect of interaction between load should be taken into account,which has great influence on the accuracy in estimation of material’s fatigue life.However, the current research results in fatigue life prediction methods are difficult to account for this effect,which leads to a large error in the estimation of material’s fatigue life.In order to estimate fatigue life of the wind turbine blade more accurately,This paper provides a method which combines Poisson stochastic process theory and the coupled damage theory to analyze and estimate the fatigue life of the blade.That is using the relevant distribution functions of Poisson stochastic process of blade to illustrate the temporal distribution of random load of the wind turbine blade.At the same time,utilize the fracture mechanics theory to deeply study the mechanism of fatigue damage of materials and use the relevant distribution functions of the coupled damage theory to describe the effect of interaction between load and the influence of load order.What’s more, aftersimultaneously solving equations based on the two kinds of theory mentioned above,finally there comes to be a cumulative fatigue damage calculating method which can fully consider the effects of interaction between load.The fatigue life of 45 steel specimens under random loading condition is estimated by this method,then compare the calculated result with the experimental data,and the error of the two is only 11%,which shows that this method is more accurate compared with other fatigue life estimation method in current research.At last,the fatigue life of the wind turbine blade is estimated by this method and the result shows that using this method can meet the requirements of strength design,which provides a new way for the fatigue life analysis and reliability analysis of wind turbine blades. |
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