Performance analysis of double-bump air foil bearings

Abstract

This paper presents a theoretical model for the analysis of double-bump air foil bearings (AFBs). The stiffness and damping coefficients of the double bump vary depending on the external load and its friction coefficient. In the case of a lightly loaded condition where only the upper bump contributes to deformation, the double bump is in the single active region. In the case of a heavily loaded condition where both the upper and lower bumps contribute to deformation, the double bump is in the double active region. So the double bump can be either in the single or double active region depending on vertical deflection. The equivalent stiffness and damping coefficients of the bump system are derived from the vertical and horizontal deflection of the bump, including the friction effect. A static and dynamic performance analysis is carried out by using the finite difference method and the perturbation technique. The results of the performance analysis for a double-bump AFB are compared with those obtained for a single-bump AFB. This paper successfully proves that a double-bumped AFB has higher load capacity, stiffness, and damping than a single-bump AFB in a heavily loaded condition.