Dynamic Characteristics And Fault Diagnosis Of Cracked Rotor-Rolling Bearing System

During aerospace engine operation,the nonlinear opening and closing behavior of the crack,the transient collision friction between the moving and moving parts,and the misalignment of the coupling,will arouse the nonlinear vibration of the rotor.And different fault excitation sources interact,resulting in complex fault coupling modes,causing crack damage to the unit,posing a huge threat to the safe operation of the rotor system.Therefore,studying the failure mechanism of the shaft crack under coupled fault conditions has certain theoretical guiding significance for ensuring the safe operation of the aero engine.The research outline of this paper is:The vibration characteristics of the rotor system model with two types of double faults are studied separately: 1.crack-impact rotor system;2.crack-misaligned rotor system.Based on the rotor vibration theory of the local influence of transverse fatigue crack on rotor flexibility,the analytical law of crack opening and closing characteristics,the evolution of rubbing between rotating parts,the phase difference generated by the parallel and off-angle directions of the coupling,and the rigid power of Rolling bearing under the unbalanced force,the Lagrange equation is used to establish the dynamic model of a two-span rotor system with a transverse crack under the support of rolling bearings.According to the strong nonlinear characteristics of the system,the 4/5-order Runge-Kutta algorithm,the ode45 solver in MATLAB,is used to compare the numerical simulation of the system crack,rubbing,misalignment and its coupled fault response.Through the time displacement diagram,the axial trajectory diagram,the Poincaré section diagram,the amplitude spectrum diagram,etc,the motion state of the system in some specific parameter domains can be visually seen.According to the characteristic behaviors of system motion reflected on the bifurcation map and the waterfall graph,the unique response generated by the system under external excitation speed,crack depth and angular position,rolling bearing clearance,misalignment and other parameters are analyzed,and the simulation diagnosis is made.The simulated signal obtained in the crack-bump and crack-disconnection coupling rotor system model studied above is taken as the original signal,and the empirical modal decomposition method(EMD)is used to decompose the fluctuation components of different specific gravity and different frequencies hidden in the fault signal step by step.This series of time series components with different fault feature scales is called the Intrinsic mode function(IMF).Then,The Hilbert transform is performed on each IMF component in order to obtain a marginal spectrum for easy observation of the instantaneous physical state of the faulty system.The characteristic fault signal is distinguished by comparing the multiplication relationship shown in the marginal spectrum of the single fault and the coupled fault,and the feasibility and effectiveness of the simulation diagnosis are verified.