Dynamic characteristics and stability analysis of rotor mounted on fluid film bearings

Abstract

Stability analysis of high speed machinery based on rigid rotor model mounted on rigid supports was found to be inadequate for stability predictions. Critical speeds of a rotor are frequently computed assuming the bearing to act as rigid supports whereas in actual practice bearings have some flexibility resulting lower critical speeds. Fluid film bearings commonly used in heavy rotating machines play a significant role in the dynamic behavior of rotors as the stiffness and the damping properties of the oil film significantly alter the critical speeds of a rotor. Dynamic coefficients of fluid film bearing are speed dependent and these coefficients also change with the geometry of the bearing and other operating conditions. Hydrodynamic bearings are regarded as the best source of dumping. Generally plain circular bearings do not suit the stability requirements of high-speed machines and precision machine tools and new bearing designs are sought to meet the new requirements. These bearings are usually characterized by their non-circular cross sections which will enhance shaft stability and also reduce power losses and increase oil flow thus reducing temperatures under proper conditions.