Fault Diagnosis Method Of Fan Blade With Crack Based On Wavelet Analysis

Ventilators are widely used in factories,mines and buildings,which rely on input mechanical energy to increase gas pressure and send gas.The ventilator can not only regulate the air volume,humidity and temperature in the environment,but also dilute and eliminate toxic and harmful gases,so as to ensure the safety of the staff and the smooth operation of the production.As the most important parts of the ventilator,the blade can easily produce cracks due to the stress concentration,fatigue and so on.This will bring serious threat to the safe operation of the whole unit,and even lead to the occurrence of major accidents.Therefore,it is very important and valuable to realize the diagnosis and recognition of blade crack failure,whether in economy or safety.In order to diagnose the blade crack accurately,the theoretical analysis is carried out in this paper.The mathematical relationship between the modal shape of the blade and the crack position and depth is deduced.A simple and effective method for identifying the blade cracks based on the modal shape data and the wavelet analysis is proposed,and the feasibility of the proposed method is verified by the modal test.The main contents of the work are as follows:(1)The mathematical model of the twisted blade with crack is established,the expression of blade kinetic energy,strain energy and crack release energy are obtained on the premise of blade twist angle,and the kinematics equation of blade is derived according to Rayleigh Ritz method and Hamilton principle.Theoretical analysis shows that there is a mathematical relationship between modal shape and crack location and depth.(2)The three-dimensional modeling software SolidWorks is used to establish the model of twisted blade with crack.The model was set up in two groups,with five groups in each group.In the first group,the crack depth is the same and the location is different.The crack location of the second groups is the same,and the depth is different.The two groups of models are imported into ANSYS Workbench for modal analysis,and the first six modal shapes of the structure are obtained through modal analysis.(3)The modal shape data of the first group is exported.MATLAB is used to carry out two-dimensional wavelet transform of the modal shape data,and the diagram of the wavelet coefficient is obtained,and the maximum value of the wavelet coefficient is the position of the blade crack.The method is used to identify the crack location of the first set of models.(4)The vibration data of the second group is exported.MATLAB is used to carry out one dimension multi-scale continuous wavelet transform of the modal shape data and the maximum value of the wavelet coefficients at various scales is obtained.The logarithm of the maximum value of the wavelet coefficients and the logarithm of the scales are taken respectively,and the relation curve of them is drawn,then the value of concentration factor obtained.Finally,the crack depth identification of the second sets of models is realized through functional relation between concentration factor and crack depth.(5)The modal test platform of cracked blade is built,and the result of simulation is verified by experiment.The hammering method is used to stimulate the cracked blade.The natural frequency and modal shape of the blade are obtained by the software DASP.According to the above method,the modal shape data is transformed by wavelet transform to identify the position and depth of the crack.The experimental results verified the validity and feasibility of the identification method of crack location and depth.