Research On Blade Damage Identification Of Active Wind Turbine Based On Modal Parameters

The fan blades in the running state are damaged due to the complicated working environment and the vibration and deformation generated during operation,which affects the smooth operation of the fan.In this paper,based on the damage identification principle of blade modal parameter changes before and after damage,damage experiments and finite element simulations of blades before and after damage in static and rotating states are carried out.Then,based on the weighted flexibility curvature damage index,the damage position is located and the damage degree is quantitatively judged,so as to achieve online blade monitoring and detection.The main conclusions are as follows:1.Through the damage test research on the blades in the stall and running state,the results show that the damage will reduce the natural frequency value of the blade,and as the damage area increases,the frequency decreases more.At the same time,when the blade is under certain damage,the closer to the blade root,the more the frequency drops.In the running state,due to the stiffening effect of the rotation,the natural frequency value of the blade increases regardless of whether the blade is damaged or not.However,within a certain speed range,the damaged blade frequency value is lower than the complete blade frequency value.The above research shows that we can judge whether the blade is damaged by the change of the frequency value,but we cannot determine the location of the damage.2.Establish a finite element model by measuring the size of the blade used in the test.First,perform a modal analysis of the same damage type and damage area as the test blade,and compare it with the test.The results show that the conclusions are consistent and mutually confirm.Secondly,by reducing the modulus of elasticity,the modal analysis of multiple damage degrees and multiple damage conditions under stall and running conditions is carried out to obtain the frequency change law and the influence on the vibration mode.It is also concluded that the damage will reduce the natural frequency of the blade,and at a certain degree of damage,the single damage will drop more than the two.When the blade rotates around the hub,through the relationship between the first ten orders of natural frequency and speed,it can be seen that the frequency increases with the increase of the speed.It shows that the frequency change rate is less sensitive to damage identification.When the speed increases from 0 rad/s to 15 rad/s,the natural frequency of the blade is still less than the natural frequency of the blade.At this time,the natural frequency can be used to determine whether damage has occurred.3.At the single-damage and multi-damage nodes,the weighted flexibility curvature value is much larger than that at other non-destructive locations,which is manifested as a peak bulge at the location of the damage,and decreases at the nearby nodes.Regardless of the degree of damage,the overall trend is basically the same,indicating that the weighted flexibility curvature value has a significant effect on identifying the damage location.As the degree of damage increases,the value of the weighted flexibility curvature at the damage location increases,showing that the peak protrusion is more obvious.The fitting function of the weighted flexibility curvature value and the stiffness damage value is verified,and the difference is 1.46%,indicating that the effect is obvious,indicating that the damage value of the damage stiffness can be predicted by measuring its modal frequency and mode value.By verifying the correlation coefficient R~2,the results show that the fitting curve has the highest reliability.