Research On Nonlinear Dynamical Charateristics Of A Bearing-Cracked Rotor-Box System

In this thesis, a mass of research has been done on the nonlinear dynamic character of cracked rotor system of scale large rotating machinery, in which most systemic theory research and numerical emulation has been done mainly in the influence of the nonlinear dynamic character of cracked rotor system caused by nonlinear stiffness ,unsteady oil-film force and rub-impact between cracked rotor and box. The results provide a reference basis for the safe operation and the fault diagnosis of a rotor system.1. The paper summarizes engineering background, significance of the cracked rotor study and study actuality, and introduces the phylogeny of nonlinear dynamic and chaos.2. Three kind of cracked rotor mathematical models: linear period time-dependent system model, nonlinear whirling motion mode, the nonlinear whirling with rotor disc inclination angle model were derived.3. Considering the nonlinear stiffness, the crack mode and dynamic model of cracked rotor system is established, and the dimensionless processing is made on dynamic model. The nonlinear dynamic behaviors in running are investigated widely on the rotor system, the influence of the rotate speed rate and imbalance on bifurcation and chaos of the rotor system is analyzed, and nonlinear chaos behaviors of the system are discovered. The effect of parameters such as, time history curve, phase plane portrait, axes track, Poincare map, amplitude spectra etc, on the nonlinear dynamic properties was discussed, the bifurcation behaviors and chaos motion of the system were analyzed in detail.4. Unsteady oil-film force is one of the most important causes to the stability of cracked rotor system. The dynamic model of bearing-rotor system is established on the basis of short bearing unsteady oil-film force coupled with nonlinear stiffness of the cracked rotor, and the dimensionless processing is made. The numerical simulation on nonlinear dynamic behaviors of bearing-rotor system caused by unsteady oil-film force coupled with nonlinear stiffness is carried out. The characteristic of bifurcation and chaos caused by the rotate speed and imbalance parameter, and abundant nonlinear phenomena such as periodic motion, quasi-periodic motion and chaos are found out.5. As the interval between cracked rotor and rotor-box is smaller and smaller, the possible of rub-impact between rotor and rotor-box is increasing. Considering the coupling of nonlinear rub-impact force, oil-film force and nonlinear stiffness of cracked rotor the dynamic model of bear-cracked rotor-rotor box is established, and the dimensionless processing is made. Analyze the nonlinear dynamic properties of this system.