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Research Papers

A Journal Bearing With Variable Geometry for the Reduction of the Maximum Amplitude During Passage Through Resonance

[+] Author and Article Information
Athanasios Chasalevris

e-mail: chasalevris@sdy.tu-darmstadt.de

Fadi Dohnal

e-mail: dohnal@sdy.tu-darmstadt.deDarmstadt University of Technology,
Strukturdynamik
Petersenstrasse 30, 64287 Darmstadt, Germany

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the Journal of Vibration and Acoustics. Manuscript received April 13, 2011; final manuscript received June 18, 2012; published online September 20, 2012. Assoc. Editor: Yukio Ishida.

J. Vib. Acoust 134(6), 061005 (Jun 20, 2012) (8 pages) doi:10.1115/1.4007242 History: Received April 13, 2011; Revised June 18, 2012

A concept for a journal bearing with variable stiffness and damping properties is developed in order to decrease the vibration amplitude of a rotor-journal bearing system during passage through resonance. The introduction of an additional fluid film thickness in the bearing is proposed in this work in order to alter the dynamic properties in the bearing. The bearing ring is divided into two parts with the upper part being fixed with the housing and the lower part being flexibly mounted by a preloaded spring in parallel with a viscous damper. This allows relative motion between the two parts of the bearing ring. The relative motion introduces an additional fluid film zone in the bearing under the passive displacement of the lower part due to increased impedance forces that are developed in the lubricant film at resonance operation. The general concept is to change the system's damping and stiffness coefficients using this extra fluid film thickness only when the system passes through its critical speed in order to quench the vibration amplitude. For rotational speeds outside of the resonant regions, the bearing is considered to be fixed in order to behave as it was designed under the nominal loading operational conditions.

Copyright © 2012 by ASME
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References

Figures

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Fig. 1

A variable geometry bearing and the definitions of the fluid film variables

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Fig. 5

Dynamic model of the rotor system in Fig. 4

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Fig. 6

Resulting force of the fluid film acting on the bearing moving part and corresponding displacement for different cases of external spring and damper properties

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Fig. 7

Vertical component of the fluid film force for a circular bearing during start up of the rotor system defined in Table 2

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Fig. 2

Journal equilibrium positions at different fixed displacements of the moving part and the corresponding radial clearance from the rotor center

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Fig. 13

Vertical response of the journal during start up at constant external stiffness and variable external damping. Top—envelope, bottom—peak-to-peak.

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Fig. 10

Horizontal dynamic response (peak-to-peak) of the rotor disk during start up at constant external damping and variable external stiffness

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Fig. 9

Vertical responses of the rotor disk during start up at constant external damping and variable external stiffness; top—envelope, bottom—peak-to-peak

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Fig. 8

Displacement of the moving part during passage through resonance at constant external damping and variable external stiffness

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Fig. 15

Ratio of the work consumed in the external damper to the work of the input force in the journal for variable external damping and stiffness values

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Fig. 4

Massless elastic shaft carrying symmetrically three masses, mounted in two journal bearings with variable geometry

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Fig. 3

Influence of the moving part displacement δc on the linear direct stiffness (top) and damping (bottom) coefficients with reference to their values for a common circular radial clearance (Kij(δc=0),Cij(δc=0)); z depicts the horizontal, y the vertical coordinate axis

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Fig. 11

Displacement of the moving part during passage through resonance at constant external stiffness and variable external damping

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Fig. 12

Top—vertical, and bottom—horizontal response (peak-to-peak) of the rotor disk during start up at constant external stiffness and variable external damping

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Fig. 14

Left: Ratio of the work consumed in the external damper to the work of the input force in the journal for variable external damping values. Right: Corresponding values for variable external stiffness value.

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