LAUSR

Purpose The purpose of this paper is to investigate dynamic characteristics of opposed-conical gas-dynamic bearings considering five degree-of-freedom motion, including translation and tilt. Design/methodology/approach The steady-state Reynolds equation and perturbed Reynolds equations are solved on the surface of conical bearings, and both stiffness and damping coefficients are calculated. A formula for quickly calculating critical mass is deduced to discriminate the stability of the rotor considering the five degree-of-freedom motion. Findings Results show that the stability of the rotor is mainly determined by translation rather than tilt. The formula of critical mass is validated by comparing the results with traditional Routh–Hurwitz criterion. Originality/value The formula proposed in this paper greatly simplifies the solution of critical mass, which facilitates the rotor stability design. It is applicable for opposed-conical bearings, opposed-hemispherical bearings and spherical bearings. The results provide theoretical guidance for the design of gas-dynamic bearings.