The Nonlinear Dynamic Characteristics Of Rigid Rotor System Under The Oil-Film Force And Steam Exciting-Force

Large-scale rotary machinery is one of the important equipments in the modern industrialized society, and the nonlinear stimulations are the key factors in the large-scale rotary machines. In fact, most of the vital accidents in rotary machinery take place arising from the instability growth of subharmonic (or low-frequency) vibrations. So it is necessary to study the instability mechanism of subharmonic vibration of the rotor excited by various types of nonlinear stimulations, which is one of the important problems in the nonlinear rotor dynamics.The steam-excited vibration of rotors is the main problem of the stability of the turbine rotor, especially for the supercritical and ultra supercritical steam turbines. Now, there are more studies on the model of airflow exciting-vibration force (Alford force) than on the mechanism of the steam-excited vibration, and the problem of instability as a result of the effect of both Alford force and nonlinear oil-film force have not been studied up to now. The stability of a rigid unbalanced Jeffcott rotor supported by two short journal bearings was discussed in the paper, in order to analyse the nonlinear aspects of the rotor under the nonlinear oil-film force and Alford force. Several parts included in the thesis are as follow:1 The study on the nonlinear dynamics of rotor at broad and homes is summarized, especially on the effect of nonlinear oil-film force and Alford force;2 The nondimensional motion differential equation of the rigid Jeffcott (with mass unbalance) system is set up;3 We use the method of multiple scales to get the average equation of the system, and then the bifurcation characteristics of the unbalanced rigid Jeffcott rotor in the neighborhood of the threshold for 1/2 subharmonic resonance are studied. The study shows that the critical instability speed is brought forward when the relative velocity of the airflow (V) increasing; The amplitude of subharmonic vibration is enhanced and the critical instability speed is ahead when the system parameter (μ1) of the nondimensional mass is increasing;4 The bifurcation diagrams of the system in different parameter regions, the phase portraits, Poincare maps, the time histories, axis orbit plots and frequency spectrums of the system at some parameter points are acquired with numerical method.The results of calculations show that, for the case both under only the oil-film force and under the two kinds of forces, the responses of the system are all very complex,...