Study On Dynamic Characteristics Of The Rotor-rubber Bearing System With Rub-impact

Rotating machinery is widely used in many industrial sectors, such as marine shafting, deep-well pump shafting, aero-engine, and various electromotors, etc. Any abnormal vibration of the rotating machinery may seriously threaten the steady operation of machines and can even lead to disastrous consequences of the machines. Along with the constant progress and development of the technology, the machine facilities with higher performance are of great need, some malfunctions that cause by the nonlinear characteristic and rub-impact etc. gradually get people’s concern.So far the abnormal vibration and noise of the rotor-rubber bearing system that may cause the hull structural vibration and radiates noise usually happen during the operation process, which not only affect the stability of the applications but also seriously degrade the security, elusive and viability of the underwater vehicles. Therefore, it is important to study the complex nonlinear dynamical characteristics of rub-impact between the rotor and rubber bearing in order to offer wonderful insights into the relationship between the dynamical behaviours and the system parameters and find out the causes of the rich responses of the system. This investigation has important science and application values to improve the work efficiency, stability and reliability of the rotor-rubber bearing system. The main works are given in detail as follows:(1) From the viewpoint of theoretical analysis and engineering application, the background and significance of the selected topic are discussed. The development situation, advances and trends of the application situation of the rubber bearing, dynamics of the rotor system, the coupling bending and torsional vibration characteristics of the rotor system and so on are analyzed in detail. The specific research points are decided, and the research contents of this paper are introduced.(2) The rotor system supported by the rubber bearing that is simplified into a nonlinear elastic spring is presented. The rotor rubbing system is analyzed and investigated by the modern nonlinear dynamics and bifurcation theories. The boundaries for the existence of the no-rub responses are determined analytically, and the synchronous full annular rub solution are derived and the stability is analyzed to determine the region of the synchronous full annular rub response. A systematic study on the influence of the system parameters such as friction coefficient, damping ratio, nonlinearity stiffness coefficient, stiffness coefficient and imbalance coefficient on the dynamics characteristics is carried out. An picture of the response characteristics of this model is then obtained by drawing the existence boundaries in the parameter space. Moreover, the jumping phenomenon may occur when the rotor system parameters appear in a certain range.(3) A mathematical model is established for the investigation of the dynamic characteristics of rotor system. The advantage of this model is found in the nonlinear stiffness of the rubber bearing and the Stribeck friction model which cause the friction force depending the relative velocity. Through numerical calculation, the influences of rotational speed, decaying factor, stiffness coefficient, nonlinearity stiffness coefficient and imbalance coefficient on nonlinear dynamic characteristics of the rotor system are investigated in detail. It is found that rich dynamic phenomena, such as the periodic no-rub motion, the periodic annular rub motion, the period-multiplying motions, the quasi-periodic motions as well as the jumping phenomena. When the rotational speed is very low or very high, the response of the rotor system is the period no-rub motion. With the increase/decrease of the rotational speed, the rub motion will occur and the vibration will be more serious. Under certain system parametric ranges, the Hoph bifurcation may occur and the response of the system becomes very complicated. With the rotational speed changes, the different system parameters lead to the response of the rotor system have different evolution process. Moreover, the jump phenomena that the sudden change of vibration amplitude can occur. When the rub motion occurs, with the changes of the rotational speed, decaying factor, stiffness coefficient, nonlinearity stiffness coefficient and imbalance coefficient, the response of the rotor system undergoes changes between the period motion, the period-multiplying motions and the quasi-periodic motions.(4) The coupled bending and torsion motion equation of unbalance rotor is established by the Lagrange approach and the coupled vibration characteristics of the rotor system with rub-impact is analyzed through numerical calculation. It is take into accounts that the unbalance, the friction force depending the relative velocity and the nonlinear stiffness of the rubber bearing. The bifurcation diagrams, waterfall plots, times-history, phase phone portraits and Poincare maps were obtained to analyze dynamic characteristics of the system and the results reveal multiform complex nonlinear dynamic behavior of the rotor-bearing system with rub-impact. Moreover, the influences of the system parameters on the vibrations of the rotor system are analyzed.(5) A coupled bending and torsion nonlinear dynamics model of the rotor-rubber bearing system is presented. The coupled bending and torsion motion equation of the rotor-rubber bearing system is established by the Lagrange approach and the coupled vibration characteristics of the rotor-rubber bearing system with rub-impact is analyzed through numerical calculation. The waterfall plots, times-history, spectrum plots, axes contrails and phase phane portraits are obtained to analyze dynamic characteristics of the system and the results reveal multiform complex nonlinear dynamic behavior of the rotor-bearing system with rub-impact. Moreover, the influences of the system parameters on the vibrations of the rotor-rubber bearing system are analyzed.(6) The experimental study on the coupled bending and torsion nonlinear vibration of the rotor-rubber bearing system with rubbing is carried out. The self-excited vibration of the rotor-rubber bearing system that is caused by the friction force depending the relative velocity, and the main frequency ingredient of the torsional vibration response is the natural frequency of rubber bearing tensional vibration. Because of the lateral and torsional coupling effect, the corresponding frequency component exists in the bending vibration response. The experiment research reveal the abnormal self-excited vibration and the influences of radial loads on the abnormal self-excited vibration, which verified the result of the theoretical analysis.