CHAOTIC RESPONSES OF UNBALANCED ROTOR-BEARING STATOR SYSTEMS WITH LOOSENESS OR RUBS

The first part of this paper presents results of numerical simulation of the dynamic behavior of a one-lateral-mode unbalanced and radially side-loaded rotor with either a loose pedestal (looseness in a stationary joint), or with occasional rotor-to-stator rubbing. The nonlinearities of these systems (variable stiffness, impacting, and friction) are associated with the rotor intermittent contacts with the stationary element. The results, based on a newly developed local impact model [P. Goldman and A. Muszynska, Analytical and experimental simulation of loose pedestal dynamic effects on a rotating machine vibrational response, Rotating Machinery Dynamics, DE-Vol. 35, ASME, Miami, Florida, pp. 11-17 (1991); P. Goldman and A. Muszynska, Analytical model of the impact between rotating and nonrotating elements and its application in rotor-to-stator rubbing, BRDRC Report 1, (1992); P. Goldman and A. Muszynska, Chaotic behavior of rotor-to-stator systems with rubs, ASME Turbo EXPO Conference, 93-GT-34, Cincinnati, Ohio, Transactions of the ASME (to appear); P. Goldman and A. Muszynska, Dynamic effects in mechanical structures with gap and impacting: Order and chaos, Trans. of ASME, J. Vibration and Acoustics (1994)] exhibit regular periodic vibrations of synchronous (1x) and subsynchronous (1/2x, 1/3x, ...) orders, as well as chaotic vibration patterns of the rotor, all accompanied by higher harmonics. The second part of the paper presents experimental vibration characteristics of rotors with looseness or rubs, Obtained from rotor rigs. The results display similar patterns as those obtained analytically.