Stability and Transient Motion of a Plain Journal Mounted in Flexible Damped Supports

This paper treats the effect of support damping and flexibility on the response characteristics of a symmetric rotor mounted in journal bearings. The successful operation of turbomachinery utilizing fluid-film bearings is shown to be very dependent upon the bearing support structure for high-speed applications. A stability analysis is discussed based upon the application of both the Routh criteria and the calculation of damped eigenvalues. Results are plotted for typical rotor support properties. The analysis also discusses the influence of rotor imbalance on the stability of rotor systems, and time transient orbits of shaft and support motions clearly indicate their dynamic behavior for both the stable and unstable operating speeds. Simplified design criteria are given for the selection of the support stiffness and damping based upon rotor weight and journal clearance to promote optimum stability. The stability analysis shows that the stability threshold with a damper support may increase the stability level over four times the value of a journal bearing on a rigid support. A nonlinear transient analysis is presented to show the size the journal limit cycles and forces transmitted with and without a damper support.