Self-excited reverse precessional full annular rub, known as "dry whip", is a secondary phenomenon resulting from a primary cause and may lead to a machine catastrophic failure; i.e., "coexistence of oil and dry whips" which occurs repeatedly with constant frequency and amplitude in small clearance cases. This paper presents a technique using an electromagnetic actuator, which can raise the threshold of instability of fluid-film bearings and then eliminate both oil and dry whips in the normal, operational range. The study constructs a set of experimental setup, sets up a general model of a rotor-bearing-seal system with an electromagnetic actuator to derive the corresponding governing motion equations, evaluates the supplemental stiffness supplied by the electromagnetic actuator, judges instabilities by root locus plots, and finally establishes a set of criterion for eliminating coexistence of oil and dry whips. Experimental results demonstrate that the coexistence of the oil and dry whips of the rotating machine can be removed effectively. The proposed technique can be used to diagnose rub and fluid-induced instability in this kind of rotating machine. (C) 2010 Elsevier Ltd. All rights reserved.
