| The wind turbine blade is a crucial component for wind energy capture.Its working load is complex and variable,while the structural design theory is not yet perfect,so that there is often a significant deviation between the actual and design life.Therefore,it is necessary to test structure design rationale and manufacturing process specification through full-scale structural fatigue testing.Ensure that the blade performance of the subsequent batch operation is consistent with the design index.However,the widely used uniaxial resonance full-scale structural fatigue testing technology can no longer meet the needs of blade quality inspection.In order to improve test accuracy and efficiency,biaxial resonance full-scale structural fatigue test technology has become a natural choice for the industry.With this as a background,several theoretical aspects of biaxial resonance full-scale structural fatigue testing technology are investigated.The mai n research contents and contributions are as follows:(1)A modeling method of P-S-N curve for wind turbine blade composites under small-sample fatigue test data is proposed.The equivalent transformation model of fatigue life is established using the consistency principle of fatigue life probability quantile,and the sample data under different stress levels are equivalently expanded.Based on this,a particle swarm optimization algorithm based on backward statistical inference is constructed to estimate the parameters of the P-S-N curve.This method is applied to model the P-S-N curve of fatigue test data of carbon fiber/epoxy resin composites with different sample numbers.The prediction results me et the requirements of accuracy and stability,which verified the effectiveness of the method.(2)A P-CLD modeling method for wind turbine blade composites based on spatial mapping relationship is proposed.The spatial mapping relationship between P-S-N curves and P-CLD models is first constructed.Based on this,P-CLD models are established on two assumptions that P-CLD models follow a linear equation,and the equal probability quantiles of static strength distribution and fatigue life distribution are on the same straight line.The P-CLD model of glass fiber/polyester resin composites is established by this method.The prediction results tend to be conservative compared with the P-S-N curve,which verified the effectiveness of this method.(3)A method for calculating the target load of full-scale structural fatigue testing of wind turbine blades is proposed based o n cross-sectional load spectrum.The bending moment-life(M-N)curve is first defined from the relationship between blade section stress,strain,and bending moment.The CLD model associat ed with the M-N curve is established using the mapping relationship between the S-N curve and the CLD model to realize the rapid calculation of cumulative damage for fatigue load spectrum and target load.This method is used to calculate the target load of the Ned Wind 25 blade section in the National Renewable Energy Laboratory of the United States.The error between the computed results and the given results meet the accuracy requirements,which verified the reasonableness and validity of the M-N curve and its CLD model.(4)A load distribution optimization method is proposed for biaxial resonance full-scale structural fatigue testing of wind turbine blades.The dynamic analysis model of the multi-degree freedom system of the finite beam element of the tested blade is first established to calculate the test load amplitude.The dynamic analysis model and the target load calculation method are integrated into the particle swarm optimization algorithm to optimize the fatigue test load distribution of biaxial resonance full-scale structural fatigue testing.The proposed method is applied to design a biaxial resonance full-scale structural fatigue testing loading scheme with a 2.5mw-52.5m wind turbine blade.The results show that this method can quickly and accurately adjust the optimization parameters on the premise that the cumulative fatigue damage caused by the test load is not less than the cumulative damage of the target load.(5)A strain response decoupling method for fatigue test of biaxial resonance full-scale structural fatigue testing of wind turbine blades is proposed.Based on the theoretical analysis of the strain response under uniaxial and biaxial resonant loading conditions,a method of decoupling the strain response using correction coefficients is proposed.The effectiveness of this method is verified by experiments on the principle prototype of biaxial resonance full-scale structural fatigue testing.The results show that the modified strain response is higher than the original strain response,and the modified strain response is composed of the strain response caused by the equivalent test load of the blade section and its small quantity.This method can provide a reference for controlling the loading system of the biaxial resonance full-scale structure fatigue testing. |
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