Modeling And Analysis Of Bending - Torsional Coupling Vibration Of Cracked Rotor

Rotating machinery is one kind of mechanical equipments most widely used in the industrial department. With the development of the society, rotating machinery is developing in the direction of high speed, overloading, automation and function diversified. As the key component of rotating machinery, the rotor system often caused many problems and than often breaks down for the complex nonlinear factors. Light affect will influence the work efficiency, and then heavy affect will cause a machine crash and immeasurable economic losses. Social harm and economic loss caused by these accidents are usually immeasurable. There fore, study of operational stability of rotating machinery is very necessary.Rotor-bearing system modeling is based on a typical Jeffcott cracked rotor, the force condition and vibration response of the rotor is studied. In this paper, coupled longitudinal-bending-torsion vibration of the rotor with transverse surface crack and slant crack are first modeled. Then, comprehensive analysis is made on crack-related stiffness variation characteristics of the cracked rotor. In the modeling of the cracked rotor, Euler and Timoshenko beam element are used. Especially, six degrees of freedom, including axial force, section shear, bending and the torque, are considered. Stiffness matrix of the cracked element is derived by the flexibility coefficients method, and these flexibility coefficients are computed using the strain energy theory. Based on stiffness computation of the cracked rotor, numerical evaluation is made on some influence factors, such as length of beam element and depth of crack, etc.The mechanisms and characteristics of the breathing crack opening/closing states are studied. In the premise of the theoretical analysis, the dynamical behaviors of the breathing crack rotor under the conditions of the bending, torsion and bending-torsion coupled vibration is analyzed by numerical analysis. Compared with the transverse crack rotor model, items of the flexibility matrix coefficients change not the same in Euler and Timoshenko beam element containing a slant crack. Stiffness matrix coefficients are not zero in Euler beam element model with slant crack, and cracked rotor in the different cracks form of different beam element model the flexibility matrix and stiffness matrix were analyzed and compared.The nonlinear dynamic behavior of a rotor-bearing system containing a transverse crack is studied experimentally. Eccentric magnitude influence on vibration response of the rotor-bearing system is qualitative studied. Research on show an unbalance response of the cracked rotor without rub and with rub is determined in the benging and torsion directions. The vibration signal obtained by fast Fourier transform, the instantaneous frequency and Hilbert Huang transform analysis. The simulation results of the preceding comparison.