Study On Vibrations And Crack Propagation Control Of Asymmetrical Cracked Rotor Based On Three-Dimensional Finite Element Model

In recent years,rotating machinery is developing towards high-speed,high-automatic integration and social production needs to adapt to complex environment.People put forward higher requirements for its safety.The rotor is prone to a crack initiation under the action of high temperature,high pressure and alternating load.If it is not found and controlled in time,it will further expand and cause catastrophic damage.The crack is a hidden danger to the rotor fault,and the deep and detailed study can improve the stability and safety of the operation of the rotor system,so as to avoid the occurrence of unnecessary safety problems.In this paper,a three-dimensional finite element model of asymmetrical cracked rotor is established by using nonlinear contact element method to solve the vibration problem of asymmetrical cracked rotor.The free interface modal synthesis method is used to reduce the order of the model to shorten the calculation time.The effects of crack position angle,crack position and asymmetrical rotor flatness on the main resonance instability region and vibration characteristics are analyzed by simulation.At the same time,the disturbance observer is used to control the electromagnetic actuator(EMA)to realize the active control of the rotor system vibration.Secondly,based on the rotor dynamics theory and the crack opening and closing mapping method proposed in this paper,the effects of the rotation speed,unbalance mass and the flatness of the asymmetric rotor on the crack opening and closing characteristics of the rotor are studied.An effective method for delaying crack growth is proposed.At the same time,based on the stress intensity factor method of crack,the influence of the position and size of the unbalance mass on the respiration state of the crack is analyzed.The effectiveness of the control method is verified by experiments.The results show that:(1)The variation of crack position angle has an effect on the main resonance and super harmonic resonance positions of the asymmetrical rotor,and the unstable region near the main resonance region will become narrower.The location of cracks in the asymmetrical rotor affects the amplitude of vibration,the resonance frequency and the range of the unstable region.(2)When the mass,speed and flatness of the asymmetrical rotor are changed,the degree of opening and closing and the opening and closing period of respiratory cracks are affected to a certain extent.Especially,the degree of crack opening and closing can be reduced when the flatness decreases,and the closing time is prolonged.In addition,the unbalance mass reduction of the asymmetric rotor system can effectively attenuate the respiration effect of the crack.(3)The amplitude of the vibration of the cracked asymmetric rotor in the main resonance and super harmonic resonance can be effectively reduced by the electromagnetic actuator.The unstable region of the rotor disappears.The rotor can keep a relatively stable rotation during operation,and the breathing crack is in a closed state for a long time,and the crack propagation is delayed.The experiments show that EMA can restrain the vibration of cracked rotor and the effect of crack respiration,and the effectiveness of the control method is verified.