Analysis On Instabilitation Induced By Oil Film Whirling In Sliding Bearing-Rotor Systems

Large-scale rotary machinery is one of the most important equipments in the modern industrialized society, in the plenty of nonlinear stimulations that effect stability of rotor system, nonlinear oil film force is the key factor of rotor machine's instability. In fact, most of the vital accidents in rotary machinery take place arising from the instability growth of low-frequency vibration. So it is necessary to study the low-frequency instability mechanism of rotor system excited by nonlinear oil film force, which is one of the most important problems in the nonlinear rotor dynamics.In the practical engineering, multi-span flexible rotor system composing large-scale rotary machinery. So just study the single-span rotor system can not reveal all the unique nonlinear phenomenon of the rotary machinery. Now, the study of rotor system stability is main focus on single-span Jeffcott rotor, the research on high-dimensional nonlinear rotor dynamic system are less to report. Use the basic theory and method of nonlinear dynamics to study the stability problem of single-span rigid Jeffcott rotor and 2-span 3-support rotor system in the paper, several parts included in the thesis are as follow:1. The study on the nonlinear dynamics of rotor at broad and domestic are summarized;2. A rigid Jeffcott rotor dynamical model is established,obtain the bifurcation equation of autonomous and Non-autonomous system by generalized averaging method, drawing the Hopf bifurcation diagrams of system;3. Compute the Jeffcott model by numerical method, study the oil whirl and low-frequency vibrate situation of system, the time histories, the phase portraits, Poincare maps and frequency spectrums of the system in different parameter regions are acquired. The results show that, dimensionless eccentricity can effect the move characteristic of system in a certain extent,in the same time, two outburst instability phenomenon of rigid rotor are found;4. 6DOF flexible rotor model is established, discuss the dynamic characteristic of rotor system, compared conclusion with Jeffcott rotor;5. 2-span 3-support flexible rotor dynamical model is established, study the instability rotating speed change under the dimensionless eccentricity, the lubricating oil dynamic viscosity coefficient, the bearing slenderness ratio, and the location of disc on the shaft in different regions, take out one span of 2-span 3-support rotor system to research the influence of location of disc on the shaft to move characteristic and instability rotating speed of the single-span flexible rotor system.In the paper, further and detailed investigations are given from three sides of single-span rigid rotor,flexible rotor and 2-span flexible rotor system, reveal some rules of nonlinear rotor dynamics, the study can provide basis to diagnose and control the instability of the rotor.