Study On Breathing Mechanism And Vibration Behavior Of A Transverse-cracked Rotor System

Crack is one of the most common faults in the rotor shaft.When the rotor is in the running process,if the crack cannot be detected early,it will not only affect the normal operation of the machine,but also cause extremely serious damage to the economy and personal safety once the rotor shaft is broken due to the crack.Therefore,it is necessary to study the breathing mechanism and vibration behavior of the crack,so we can obtain the method of rotor crack diagnosis and identification,realize the real time monitoring of rotor system,prevent the crack initiation and propagation of the shaft and take effective protective measures to ensure the safe and stable operation of the rotor system.In this paper,the finite element method is used to study the breathing mechanism and vibration behavior of a transverse-cracked rotor system.Firstly,in order to identify the equivalent stiffness of rotor bearing joint accurately,the method of combining finite element parametric model,modal test result and BP neural network is adopted.The results show that this method is effective in identifying the equivalent stiffness of the rotor bearing joint,and the radial equivalent stiffness of the rotor bearing joint is 4.48 × 10~5N/m,and the axial equivalent stiffness of the rotor bearing joint is 5.05 × 10~5N/m.The results provide accurate stiffness parameters for the finite element model of a transverse-cracked rotor system.Based on the equivalent stiffness of the identified rotor bearing joint,the finite element model of a transverse-cracked rotor system is established by ABAQUS,the breathing mechanism of transverse crack is simulated when the gravity dominates;The results of transverse crack breathing behavior determined by the neutral axis method,the stress intensity factor method and the finite element method,are compared,the correctness of the finite element model of a transverse-cracked rotor system is verified,the breathing mechanism of transverse cracks in rotor operation are summarized.The results show that when the rotor is in the running process,the transverse crack is more inclined to open and the crack closure line is approximately arc.The crack breathing effect which is determined by the finite element model is more reasonable,and more in line with the true crack opening and closing conditions.By adjusting the rotating speed of the shaft,changing the position of the crack,increasing the relative depth of the crack,and applying torsional excitation,the influence of the above parameters on the vibration characteristics of a transverse-cracked rotor system is studied by simulation.The existence of the transverse crack does change the vibration response of the rotor.In the two horizontal directions,the amplitude of frequency doubling which appears in the spectrum contains 1X,2X and 3X obviously,and other high frequency component amplitude is smaller.When the rotor frequency is less than the first order natural frequency,the amplitude of 2X in the transverse vibration response spectrum is more obvious.Therefore,the rotor system can be based on the spectrum of 2X and other obvious frequency components to diagnose whether there is a transverse crack or not.Compared with the change of the position of the transverse crack on the shaft,the change of the relative depth of the crack is more likely to cause the change of the amplitude of the transverse vibration frequency.The phenomenon of flexural torsional coupling vibration is not obvious,so the method to identify the transverse crack on rotor system by coupled bending torsional vibration is not desirable.The research work will not only provide an effective method for parameter identification of mechanical structure joint,but also provide a reference for finite element model of a transverse-cracked rotor system,at the same time it will provide reliable theoretical basis for on-line inspection of a transverse-cracked rotor system.