SPECTRAL ANALYSIS OF GAS BEARING SYSTEMS FOR STABILITY STUDIES

Abstract : Stability map for a gas-bearing supported rotor can be constructed from the periodic dynamic perturbation solution of the gas bearing equation about the equilibrium condition. A complete frequency range of the perturbation solution is required. Effective system stiffness and damping can be defined in terms of the perturbation solution of the gas bearing. The condition of neutral stability corresponds to the vanishing of the effective damping, yielding the characteristic frequency, and resonance at the characteristic frequency with the equivalent stiffness, yielding the critical mass. An excess of rotor mass causes instability if the effective damping increases with frequency, at the characteristic frequency, and conversely. For unloaded, journal bearings possessing rotational symmetry, the stability map can be constructed from their steady-whirl solutions. An example illustrating the latter case is given in terms of a herringbone-grooved journal bearing. This method of stability analysis is applicable to both thrust and journal bearings for both whirl and pneumatic-hammer instabilities.