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Research Papers: Hydrodynamic Lubrication

Double Overhung Disk and Parameter Effect on Rotordynamic Synchronous Instability—Morton Effect—Part I: Theory and Modeling Approach

[+] Author and Article Information
Xiaomeng Tong

Mem. ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: tongxiaomeng1989@tamu.edu

Alan Palazzolo

Professor
Fellow ASME
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: a-palazzolo@tamu.edu

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 5, 2016; final manuscript received June 1, 2016; published online August 16, 2016. Assoc. Editor: Mihai Arghir.

J. Tribol 139(1), 011705 (Aug 16, 2016) (11 pages) Paper No: TRIB-16-1003; doi: 10.1115/1.4033888 History: Received January 05, 2016; Revised June 01, 2016

The Morton effect (ME) is a thermally induced instability problem that most commonly appears in rotating shafts with large overhung masses, outboard of the bearing span. The time-varying thermal bow due to the asymmetric journal temperature distribution may cause intolerable synchronous vibrations that exhibit a hysteresis behavior with respect to rotor speed. The fully nonlinear transient method designed for the ME prediction, in general, overhung rotors is proposed with the capability to perform the thermoelastohydrodynamic analysis for all the bearings and model the rotor thermal bow at both overhung ends with equivalent distributed unbalances. The more accurate nonlinear, coupled, double overhung approach is shown to provide significantly different response prediction relative to the more approximate linear method based using bearing coefficients and the single-overhung method, which assumes that the ME on both rotor ends can be decoupled. The flexibility of the bearing pad and pivot is investigated to demonstrate that the pivot flexibility can significantly affect the rotordynamics and ME, while the rigid pad model is generally a good approximation.

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References

Figures

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Fig. 1

Schematics of temperature boundary surfaces

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Fig. 2

Boundary conditions for rotor thermal deformation

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Fig. 3

Configuration for determining rotor thermal bow

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Fig. 4

Pad boundary conditions for bearing thermal deformation modeling

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Fig. 5

Depiction of synchronous force sources on a flexible rotor model

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Fig. 6

Free-body diagram of the rigid pad

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Fig. 7

Restricted DOFs of the flexible pad

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Fig. 8

Film thickness diagram

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Fig. 9

Film boundary conditions for the Reynolds equation and the energy equation

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Fig. 10

Staggered integration scheme

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Fig. 11

Rotor configuration

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Fig. 12

(a) Second bending mode shape and (b) linear unbalance response at bearings with/without coupling

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Fig. 13

ME hysteresis at the NDE bearing: (a) average temperature and PK–PK ΔT, (b) PK–PK vibration amplitude at the bearing with and without thermal bow, and (c) 1× vibration polar plot at the bearing

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Fig. 14

Steady-state ME analysis of (a) PK–PK bearing vibration amplitude and PK–PK journal ΔT, (b) resultant imbalance, and (c) minimum film thickness ratio with and without the ME

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Fig. 15

ME analysis on the NDE with various transient methods: (a) PK–PK vibration amplitude at the bearing node, (b) 1× polar plot of the bearing, and (c) PK–PK ΔT across the journal circumference

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Fig. 16

Comparison of fully nonlinear transient method and SOWM: (a) PK–PK journal ΔT on the NDE and DE, (b)1×polar plot of the DE bearing, and (c) 1× polar plot of the NDE bearing

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Fig. 17

Comparison of fully nonlinear transient method and SOWM: (a) PK–PK journal ΔT on the NDE and DE, (b)1×polar plot of the DE bearing, and (c) 1× polar plot of the NDE bearing

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