Dynamic Characteristics Analysis Of Sliding Bearing Cantilever Rotor System With Cracks

Rotor system is widely used in wind power,hydropower,petrochemical,mining and other important industries of the national economy,and it is the key equipment in the enterprise.In the process of continuous integration,automation and high-speed development of industrial production,higher requirements for efficiency and safety of the rotor system have been put forward.The failure of the rotor system will cause heavy losses to both the economy and the personnel,among which the crack is one of the most common forms of failure.Therefore,this paper studies the dynamic behavior of the rotor system with crack,can help reduce the incidence of accidents and plan out of downtime,to provide a theoretical guide for fault detection and diagnosis of rotor system.In this paper,the dynamic behavior of the sliding bearing cantilever rotor system with the characteristics of breathing crack is analyzed.Considering the effects of cracks and oil film forces,the influence of crack on the dynamic behavior of rotor system is discussed by using nonlinear theory and rotor dynamics theory.The main research work of this paper is as follows:(1)Taking the cantilever rotor system with transverse cracks on the shaft as the research object.According to the opening and closing process of the crack,the breathing function model of the crack is established.Through the cross-sectional distance method and the neutral axis theory,the function of shaft rigidity in the process of crack respiration is deduced,and the rigidity model of the rotating shaft is established.Considering single oil film support,the bearing is simplified as the journal model,and the oil film force model of bearing is deduced by Reynolds equation.Bending stiffness of the cracked shaft in a rotation cycle is decreases as the depth of the crack increases.When the crack is directly under the shaft,the shaft stiffness is the maximum.(2)Based on the model built above,the differential equations of motion of the cantilever rotor system without crack and with transverse crack are deduced.The uncracked rotor and the breathing crack rotor system at different rotational speeds are compared and analyzed by time-domain waveforms,axis trajectories,spectrograms,phase diagrams,Poincaré graphs and bifurcation diagrams.The presence of cracks will allow the rotor system to enter the chaotic state of motion earlier.(3)The influence of the parameters such as the depth of the crack,the position of the crack on the rotating shaft and the corner of the crack on the dynamic response of the cracked cantilever rotor system are studied.The influence of different crack parameters on the nonlinear vibration characteristics of cracked rotor is studied.The path of cyclic motion,quasi-periodic motion and chaotic motion of cracked cantilever rotor system under different parameters are studied.(4)The influence of eccentricity and rotational speed on the dynamic response of cracked cantilever rotor system is studied.As the eccentricity increases,the number of periodic solutions of the rotor system increases and the rotor system is out of stability.With the increase in speed,the centrifugal force gradually increased.Bearings produce high speed oil film eddy,so the rotor system is out of stability obviously.The failure characteristics of the rotor system caused by different factors are extracted,which provides the basic support for further detection and diagnosis of cantilever rotor system.