Research On Fault Diagnosis Of Cracked Rotor System

Rotors are the the most important part of rotating machinery,and the crack is one of the most common faults in the rotating shaft.If the crack in the rotating shaft cannot be detected in time,the crack propagation may cause shafting fracture and lead to catastrophic accidents,which poses a major threat to economic property and personal safety.Therefore,the dynamic characteristics of cracked rotor are studied,and the state of the rotor is monitored on-line to identify the crack parameter of the rotating machinery,which is of enormous significance for ensuring the safety of the rotating machinery and avoiding the occurrence of major accidents.A finite element model of a cracked rotor system with a breathing crack is established.The typical dynamic characteristics of the cracked rotor system at subcritical speed are analyzed.A crack detection method for the rotor system is proposed without disturbance from a medium fault,and four states of the rotor system are classified and verified by experiments.Finally,the quantitative identification of the crack parameters for operating rotors is realized.Based on the fracture mechanics theory,the stress intensity factor at the crack tip of the rotor is calculated,and the stiffness of the crack element is calculated according to the strain energy release theory.The opening and closing state of the breathing crack is determined by the zero stress intensity factor method.The stiffness matrix of the straight crack and the slant crack is derived,and the finite element model of the rotor system with cracks is established.Finally,the modal experiment shows that the finite element model of the rotor system is corrected.By calculating the stiffness of crack element,it is found that the increase of crack depth will reduce the stiffness of crack element.The main stiffness and coupling stiffness of straight and oblique cracks have strong non-linear characteristics,and show a certain periodicity and symmetry.Slant cracks have obvious coupling phenomena in all directions,while the bending-torsion coupling of straight cracks is not obvious.By analyzing the dynamic characteristics of the rotor system,it is found that the 2X superharmonic component of the rotor shaft near 1/2 critical speed and the 3X superharmonic component near 1/3 critical speed are the important characteristics of cracks in the rotor.The dynamic model of rotor system with misalignment fault of coupling is established.The dynamic characteristics of rotor system with crack fault,misalignment fault and misalignment-crack coupling fault are compared with that of healthy rotor.In order to eliminate the interference of misalignment fault on rotor crack detection,the convolution neural network is used to classify the four states of the system,and the experimental results are given.The effectiveness of the proposed method is demonstrated.Aiming at the problem of on-line quantitative identification of crack parameters,the problem of quantitative identification of crack parameters is transformed into a multi-objective optimization problem.Based on Kriging surrogate model,the relationship between crack parameters and the corresponding superharmonic component amplitude is established,and the prediction of the superharmonic component amplitude of the rotor is realized instead of the finite element calculation process that obtains the dynamic response of the cracked rotor.The improvement of nsga-iii algorithm accelerates the convergence speed of the objective function in the optimization process and improves the accuracy and efficiency of crack parameter identification.Finally,based on the improved nsga-iii and Kriging surrogate models,the location,depth and type of the cracks can be identified in the running state of the rotor.In this paper,a reliable crack detection method,locating method and quantitative identification method for rotors are proposed under the condition of rotor operating,and cutting-edge theories such as deep learning,Kriging surrogate model and nsga-iii algorithm are applied to the crack detection problem of traditional rotor system,which has certain practical value.