On the Use of Rotor-Bearing Instability Thresholds to Accurately Measure Bearing Rotordynamic Properties

Abstract

A re-examination of rotor-bearing instability has led to a fresh approach that can potentially improve measurement accuracy of journal bearing rotordynamic coefficients. The approach uses a two-degree-of-freedom system and has three major parts. First, bearing stiffness coefficients are measured using static loading. Second, measured orbital motion at an adjustable threshold speed is used to extract the bearing damping coefficients by inverting the associated Eigen problem. Third, multiple displacement-measurement coordinate systems are used to allow an averaging approach which uses to advantage the tensor transformation property of bearing rotordynamic coefficients. The fundamental advantages of the overall approach stem from the physical requirement for an exact internal energy balance between positive and negative damping influences at an instability threshold, and that it does not require the measurement of dynamic forces.