Effects of bearing and shaft asymmetries on the instability of rotors operating at near-critical speeds

Information about the stability of vibratory motions becomes essential for ensuring safer designs of rotor-bearing systems and the operational safety. In particular, the influences of shaft and bearing parameters on the stability characteristics have to be quantified for design and diagnostic purposes. Such an analytical investigation is the objective of the present paper. Expressions for amplitude and phase modulation functions that quantify the effects of slowly varying the rotational speed on the motion characteristics are derived. Based on the modulation functions, stability regions in the parameter space are determined. The effects of bearing and shaft asymmetries on the stability of the rotor are illustrated.