Fundamental study on damping characteristics of externally pressurized porous gas bearing (Analysis of annular thrust bearing with orifice and capillary models)

An externally pressurized porous gas bearing is known to provide high stiffness. Although damping is also important to realize a high-dynamic-stiffness bearing, few studies have been done on the damping characteristics and their relationships to the stiffness and static characteristics of a porous bearing. This paper reports on the analytical investigation of an externally pressurized porous annular thrust gas bearing using the orifice and capillary models from the aspect of improving its damping characteristics. It is found that stiffness and damping are determined only by the static stiffness, the reaction force of gas film and the ratio of squeeze number to the squeeze number at which damping takes an extreme value. It is also found that the damping ratio ζ is determined only by the ratio of squeeze numbers and the ratio of the static stiffness to the reaction force of gas film. Approximated simple formulas representing the relationship between dynamic quantities and static quantities are presented. The validity of the simple formulas is confirmed in a practical range of design parameters by comparison with the results of numerical calculation.