Wind Turbine Blade Damage Calculation Method Based On Biaxial Fatigue Test Data

Blade is an important component of wind turbines.In order to guarantee a service life of 20 years,it is necessary to verify the reliability of the blade to determine whether it meets the requirements of use.Full-scale structural fatigue testing is currently the most accurate method of modeling the evolution of blade damage.With the continuous development of wind turbine technology and increasing size of the blades,single-axis fatigue test technology has been unable to meet the requirements of blade quality and reliability testing,while biaxial fatigue test to ensure the accuracy and improve the efficiency of testing,has gradually replaced the single-axis test as the main research direction in the industry.Therefore,this thesis is set in the context of biaxial fatigue testing of wind turbine blades,to investigate the difficulties in processing data and the inability to calculate damage during testing.The main contents are as follows:(1)A morphological filtering-based strain data processing method for wind turbine blades is proposed.Firstly,a morphological filter with different structural elements and a three-point smoothing algorithm are established to filter and smooth the original signal.Based on this,a peak detection algorithm is designed to detect peaks and valleys of the signal to complete the data processing.Finally,experiments using a biaxial resonant full-scale structural fatigue test principle prototype,the result show that the method can accurately output the peak and trough values of the signal while guaranteeing the original signal characteristic values,which effectively completes the data processing.(2)A method for repairing abnormal strain data from wind turbine blade fatigue tests.The abnormal strain data generated during the biaxial fatigue test were extracted to obtain the three main types of abnormalities: baseline drift signal,zeropoint drift signal and missing signal.The abnormalities were repaired by fitting trend terms,sliding average and mean interpolation,respectively.The results show that the patched data can reflect the loading process and can be used to deal with the abnormal strain data that occurs during biaxial testing.(3)A damage calculation method for biaxial fatigue testing of wind turbine blade is proposed.According to the wind turbine blade fatigue damage mechanism,considering the random superposition effect of structural stress under biaxial loading,the S-N curve and CLD model of the blade are established based on the real-time strain data,and the linear Miner cumulative damage theory is used to calculate the cumulative damage of the blade under test.Fatigue tests on a 52.5m blade were carried out on a wind turbine blade fatigue test rig and damage calculations showed that the method is effective in calculating the damage to the blade under stress superposition.It is also found that the load in the flap-wise direction under biaxial loading has a greater effect on the strain response at the leading and trailing edges of the blade,causing the strain response to decrease relative to uniaxial loading,and the load in the edgewise direction has a smaller effect on the strain response in the main beam direction,causing the strain response on the main beam to increase relative to uniaxial loading,resulting in different damage patterns of the blade under uniaxial and biaxial loading.(4)Design of an online real-time assessment system for wind turbine blade fatigue damage.Combining the strain data processing method and the biaxial loading damage calculation method proposed in this thesis,an online real-time assessment system for wind turbine blade damage was designed.Using 52.5m blade biaxial fatigue test data for offline and online damage calculations respectively,the results show that real-time online damage calculations are faster and more accurate,which is more conducive to control the test process.