Bifurcation analysis of a flexible rotor supported by two fluid-film journal bearings

The effects of rotor stiffiness on the bifurcation regions of a flexible rotor supported by two identical fluid-film journal bearings are presented. It is shown that the rotor stiffness has a pronounced influence on the bifurcation characteristics at the instability threshold speed. For short bearings, two bifurcation regions exist if the dimensionless rotor stiffness (K) over bar >= 4.3. On the other hand, three bifurcation regions exist if the dimensionless rotor stiffness (K) over bar < 4.3. Information is presented that allows one to easily predict both the instability threshold speed and its bifurcation type of a rotor-bearing system with any specific set of operating parameters. The results presented have been verified by laboratory experiments as well as several published results in the open literature. Several examples are presented to illustrate the application of the. results for design purposes.