A Single–Degree–of–Freedom Solution Procedure to Determine Dynamic Characteristics of Air–Bearing

DYNAMIC CHARACTERISTICS OF AIR–BEARING

Abstract

An externally–pressurized journal air–bearing for a heavy, rigid, and balanced rotor is analyzed. The dynamic characteristics of air–bearing are determined during the investigation, at various angular velocities of the journal and angular frequencies of journal vibration. The dynamic characteristics of the air–bearing are found by a numerical simulation procedure. The journal air–bearing system is modeled to have a single–degree–of–freedom. The journal follows a predefined harmonic motion during the simulation. This motion is caused by self–exciting forces resulting from flow dynamics within a real air–bearing. Pressure distribution in the air–bearing is computed by solving the two–dimensional Reynolds equation. Alternating–direction finite–difference method is implemented using MATLAB to find the numerical solutions for pressure. The dynamic load–carrying capacity is calculated via the numerical integration of pressure distribution. The dynamic characteristics of air–bearing are calculated using the time series of displacements, velocities of the geometric center of the journal, and air–bearing forces. The stiffness coefficients and damping coefficients of air–bearing, as well as the eccentricity ratio and attitude angle of the journal, are compared with the findings in the literature. The average percentage differences in the results are attributed to the minor differences in the mathematical models of air–bearing used in this research and the literature. The dynamic stability of the rotor air–bearing system against self–excited vibration can be examined using the dynamic characteristics of the air–bearing.