This paper details a methology for the active recovery of contact free levitation of a rotor from a state of persistent contact with auxiliary bearings. An analytical method to describe contact dynamics of flexible rotors is presented. It shows that synchronous unbalance forces can cause a rotor to adopt stable contact modes, which are characterized by periodic motion and a fixed contact point in a rotating frame of reference. Based on these observations, a recovery strategy is developed to return the rotor to a contact free state. Compensation forces may be applied by magnetic bearings to reduce the effective synchronous forcing which is driving the contact, so that the rotor can progress to a contact free orbit. It is shown that even in the presence of highly nonlinear contact dynamic effects, a linear finite element rotor model can be used to calculate appropriate influence coefficients. The contact recovery procedure is successfully verified by simulations and measurements on a flexible rotor test facility. Allowable bounds on the phase of the synchronous recovery forces are investigated and limitations of the method are discussed.
Synchronous Position Recovery Control for Flexible Rotors in Contact with Auxiliary Bearings
Schlotter, M., and Keogh, P. S. (February 2, 2007). "Synchronous Position Recovery Control for Flexible Rotors in Contact with Auxiliary Bearings." ASME. J. Vib. Acoust. October 2007; 129(5): 550–558. https://doi.org/10.1115/1.2731414
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