Research On Nonlinear Dynamics Of Rotor-Bearing System And On-Line Elinmination Of The Oil Film Whip

The nonlinear dynamics of a rotor-bearing system is of much interest, as the rotor-bearing system with the high speed, high power and high reliability is developed. The accidents in engineering practice are more concerned to nonlinearity of the system. But most of the literature has idealized as a simple Jeffoctt rotor with the oil film journal bearings. Owing to limited in degrees of freedom of system modeling or improper bearing parameter, these analysis results are far away used in real engineering practice. In this thesis, a multi-disk rotor supported by two plain journal bearings is used for the numerical and experimental studies. The one aim is to analyze the nonlinear dynamic characteristics of the rotor system under different varying parameters; The methods of online elimination of the oil whip and subharmonic vibration are developed and studied also. Besides the expression of the nonlinear oil film force is proposed, so that the unbalance of the nonlinear rotor system may be identified online. The main work of this thesis is as follows:1. The dynamic equations of rotor-bearing system are built by combining d'Alemdert principle with Rize way. And three order polynomial is adopted as Rayleigh function, so the rotor shaft can be treated as the continue beam. The nonlinear oil film forces based on both steady and unsteady oil film model are coupled to the system with help of local function. Such system equations are local nonlinear and of high order. The equations are solved by Newmark integration method.2. The nonlinear response and the journal trajectory of the rotor-bearing system are numerically investigated. It is found that the whirling center of the journal relates not only to the rotating speed and static load but also to the vibration amplitude. Hence the nonlinear oil film force can not be well expressed by the Tarloy series. In order to make it possible that unbalance of the nonlinear rotor system may be identified online, the expression of nonlinear oil film force is improved, in which the three-order polynomial coefficients may be evaluated based on the journal orbit.3. The different forms of oil whip presented in engineering practice are verified bythe numerical examples from nonlinear theory. The influence of different mass eccentricity, rotating speed, bearing load and external damper are numerical studied also. A new phenomenon is found numerically and experimentally: even if the rotating speed of the rotor is lower, the subharmonic vibration of the rotor-bearing system may be occurred under great disturbance (unbalance). This phenomenon can't be explained by the linear theory.4. Based on the active magnetic bearing, the passive electromagnetic damper is designed, which works contactless and with DC current. The damper is mounted on the free end of the rotor. The experiments done show that the oil whip can be good damped by the passive electromagnetic damper.5. The electromagnetic actuator is developed for the same purpose. It works with DC current and has a smaller volume. The static force produced by the electromagnetic actuator can be regard as the additional bearing load. It can make the whirling center of the journal lower and enhance the stability of the system. The experiments for the online elimination of oil whip are very successful and show that the electromagnetic actuator has better effectiveness and may be used in engineering practice.