DESIGN OF EXTERNALLY PRESSURIZED GAS BEARINGS FOR DYNAMIC APPLICATIONS (SQUEEZE FILMS, STIFFNESS, EXPERIMENTS)

This work accurately predicts the dynamic stiffness of gas bearings over a broad frequency range and shows that externally pressurized gas bearings can exhibit significant damping when properly designed.;The dynamic stiffness of the bearing is sensitive to only five of the ten dimensionless parameters selected for the model. Because of additional independent parameters in the hybrid model, tuning of bearing stiffness and damping is simplified relative to the lumped parameter model. A systematic design procedure is developed using the five significant bearing parameters to satisfy design constraints and optimize bearing stiffness. In addition, a design procedure is developed for a double restrictor bearing. In these bearings the stiffness at low frequency can be significantly increased while the damping at high frequency is maintained.;The experimental results support the validity of the hybrid model. In particular, the high-frequency stiffnesses and poles determined from experiments were predicted by the theory within 15%. The static measurements of flowrate, load, supply pressure, and gap thickness are also compared to theoretical predictions to illustrate the sensitivity of the dynamic stiffness to these bearing parameters. The experiments demonstrate that a well damped bearing of large stiffness is practical to design, build, and operate. The experimental test cases further show that errors in the magnitude and frequency of the band of significant damping can exceed 1000% if they are predicted by a lumped parameter model. (Abstract shortened with permission of author.).;A new hybrid model of the dynamic stiffness of externally pressurized gas bearings is developed that incorporates the dominant distributed parameter characteristics of the bearing. This is accomplished by extending the analysis of squeeze films to include time-dependent-pressure boundary conditions and by linearly approximating the nonlinear frequency dependence of the flowrate and load solutions, including the geometry of the film. A dimensionless formulation of the model isolates the dominant bearing parameters to the extent possible and facilitates the dynamic analysis of thrust bearings with a large interior region. The new model is validated by numerical analyses and by experiments. The hybrid model of dynamic stiffness is more accurate than a lumped parameter model over a wide frequency range, and it maintains a linear frequency dependence, which eases bearing design.