A Journal Bearing with Variable Geometry for Reduction of Rotor Resonance Vibration

摘要

An idea for a journal bearing with variable stiffness and damping properties is developed in order to decrease the vibration amplitude of a rotor-journal bearing system during passage through resonance. The introduction of an additional fluid film thickness in the bearing is proposed in this work in order to alter the dynamic properties in the bearing. The bearing ring is divided into two parts with the upper part being fixed with the housing and the lower part being flexibly mounted by a preloaded spring in parallel with a viscous damper. This allows relative motion between the two parts of the bearing ring. The relative motion introduces an additional fluid film zone in the bearing under the passive displacement of the lower part due to the higher impedance forces that are developed in the lubricant film close to resonance. The general concept is to change the system's damping and stiffness coefficients using this extra fluid film thickness only when the system passes through its critical speed in order to quench the vibration amplitude. In the rest rotational speeds the bearing is considered to be fixed in order to behave as it was designed under the normal loading operational conditions. A numerical simulation of a simple elastic shaft model supported by two journal bearings with variable geometry verifies that the vibration amplitude in the rotor's mid-span is reduced by up to 70% compared to conventional journal bearing, while the vibration amplitude of the journal whirling inside each bearing do not show sensible difference.