On the Behavior of Gas-Lubricated Journal Bearings Subjected to Sinusoidally Time-Varying Loads

Abstract

Linearized steady-state time-dependent solutions to the equations of journal motion are obtained for sinusoidally time-varying radial loads by utilizing the “linearized ph” technique to approximate lubricant pressure forces. An exemplary check for vibration at half-rotor frequency shows that the nonlinear terms can be neglected provided the total eccentricity ratio (static plus dynamic) remains less than one half. A typical journal-bearing frequency response exhibits two distinct types of resonances: One at half-rotor frequency and another at a frequency given by K/M, where K is the effective spring constant due to the bulk modulus of the gas lubricant and M is the mass of the supported rotor. As the static eccentricity ratio ∊0 increases, the amplitude of the half-rotor frequency resonance decreases drastically, but the amplitude of the K/M resonance increases slightly. Rotating load response can be synthesized by superimposing the responses to two 90 deg out-of-phase radial loads acting along perpendicular axes. The resulting response is a nearly circular ellipse centered about the static equilibrium position.