Research Papers: Nuclear Power

Misalignment in Combi-Bearing: A Cause of Parametric Instability in Vertical Rotor Systems

[+] Author and Article Information
Jean-Claude Luneno

e-mail: jean-claude.luneno@ltu.se

Jan-Olov Aidanpää

e-mail: jan-olov.aidanpaa@ltu.se
Division of Mechanics of Solid Materials,
Luleå University of Technology,
SE 971 87 Luleå, Sweden

Rolf Gustavsson

Vattenfall Research and Development AB,
814 26 Älvkarleby, Sweden
e-mail: rolf.gustavsson@vattenfall.com

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received April 27, 2012; final manuscript received October 19, 2012; published online February 21, 2013. Assoc. Editor: Patrick S. Keogh.

J. Eng. Gas Turbines Power 135(3), 032501 (Feb 21, 2013) (8 pages) Paper No: GTP-12-1107; doi: 10.1115/1.4007882 History: Received April 27, 2012; Revised October 19, 2012

The dynamic characteristics of the combi-bearing (combined thrust-journal bearing) in vertical rotor systems were analytically modeled and experimentally verified in the authors’ previous publications. An angular misalignment, which may be caused by a possible manufacturing or assembling error, is introduced in the combi-bearing’s rotating collar. A new model of the defective combi-bearing has been derived. The derived model shows that the angular misalignment in the combi-bearing’s rotating collar generates an asymmetry in the rotor system at the combi-bearing’s location. The rotor system’s stiffness in its two translational X and Y directions differ at the combi-bearing’s location. Constant parameters and/or coefficients in rotating asymmetric structures appear to change with time when observed in the stationary frame. These time dependent parameters (coefficients) are the source of the so-called parametric instability in rotating systems. If the collar angular misalignment is located in the X-Z plane all rotor motions in this plane at the contact point between the combi-bearing and the rotor will be coupled. A parametric instability is observed within certain ranges of the rotor speed, depending on the magnitude of the angular misalignment.

Copyright © 2013 by ASME
Topics: Bearings , Rotors
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Fig. 1

(a) Schematic view (right) of a vertical hydropower unit together with a discretized rotor (left), and (b) the symmetry plane of a vertical rotor model with a misaligned collar

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Fig. 2

(a) The X-Z symmetry plane of the combi-bearing, and (b) an upper view of the thrust bearing without misalignment

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Fig. 3

(a) Translation in the X, Z directions and rotation about the Y-axis, (b) insertion of angular misalignments α and β in the X-Z plane, and (c) free body diagram

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Fig. 4

Real part of the rotor system’s eigenvalues in the rotating frame. The blue color is for α=β=1 deg and the red color is for α=β=5 deg. (b), (c) The magnifications of the regions of interest in (a).

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Fig. 5

Real part of the rotor system’s eigenvalues in the rotating frame. The blue color represents β=1 deg, α=-1 deg, and the red color represents β=5 deg, α=-5 deg. (b), (c) The magnifications of the regions of interest in (a).

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Fig. 6

Imaginary part of the eigenvalues in the rotating frame

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Fig. 7

Rotor time-response in the vertical Z direction at node 2: (a) α=β and N = 1355 rpm, (b) α=-β and N = 2600 rpm

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Fig. 8

Rotor steady-state response at node 2: (a) α=β, and (b) (α=-β)




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