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TECHNICAL PAPERS

Synchronous Position Recovery Control for Flexible Rotors in Contact with Auxiliary Bearings

[+] Author and Article Information
Michael Schlotter, Patrick S. Keogh

Department of Mechanical Engineering, University of Bath, BA2 7AY, UK

J. Vib. Acoust 129(5), 550-558 (Feb 02, 2007) (9 pages) doi:10.1115/1.2731414 History: Received July 25, 2006; Revised February 02, 2007

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.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Flexible rotor/magnetic bearing system. Sensor planes indicated by S1,…,S4; auxiliary bearings by B1,…,B6; and magnetic bearings by MB1, MB2

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Figure 13

Measured rotor motion at selected times in the rotating and stationary frames during the mass loss experiment showing successful recovery. The rotational speed was Ω=151rad∕s.

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Figure 14

The contact recovery fails and the contact location in the rotating frame changes if ϵ∠Fr is too large

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Figure 10

(a) Threshold and quadrants to ascertain the nature of the contact mode. (b) Diagram to determine allowable bounds on ∠Fr to enable successful contact recovery.

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Figure 11

Allowable bounds for the estimate of −ψ+π at Ω=151rad∕s as a function of the disturbance force amplitude and the contact mode period ratio. The solid line in (b) shows the optimal estimate −ψe+π for successful recovery.

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Figure 12

Measured rotor response and applied contact recovery force after mass loss of 520gcm at t=1s. The rotational speed was Ω=151rad∕s.

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Figure 2

Plots of Π(ωc) whose roots determine possible contact frequencies

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Figure 3

Plots of Eq. 20 at (a)Ω=151rad∕s and (b)Ω=226rad∕s for two different contact frequencies ωc

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Figure 4

Slope κ and minimum required synchronous disturbance force Fdmin for all possible supersynchronous periodic contact mode frequencies

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Figure 5

Contact response at Ω=151rad∕s of a rotor subject to linear variation of synchronous force at the nondriven end with ∣Fd(t=1s)∣=0N, ∣Fd(t=9s)∣=200N, and ∣Fd(t=17s)∣=0N

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Figure 6

Contact modes in rotating reference frame with small (a) and large (b) bounce amplitude at Ω=151rad∕s due to an unbalance of 520gcm at the nondriven end

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Figure 7

Measured rotor response in rotating reference frame after mass loss (a) which increases the unbalance from 200gcm to 520gcm. The established contact mode of (b) follows. The rotational speed is Ω=151rad∕s.

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Figure 8

Recovery results at Ω=151rad∕s with Fr applied at the nondriven end contact plane (AJ) and the nondriven end magnetic bearing (MB). Each point represents one simulation: ∙=contact condition has not changed; •=recovery succeeded; ×=additional contact at other auxiliary bearings.

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Figure 9

Recovery results at Ω=226rad∕s with Fr applied at the nondriven end contact plane (AJ) and the nondriven end magnetic bearing (MB). Each point represents one simulation: ∙=contact condition has not changed; •=recovery succeeded; ∘=contact recovered at original location but new contact at other nodes; ×=additional contact at other auxiliary bearings.

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