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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Luneno, J.-C., Aidanpää, J.-O., and Gustavsson, R., 2011, “Model Based Analysis of Coupled Vibrations Due to the Combi-Bearing in Vertical Hydroturbogenerator Rotors,” ASME J. Vibr. Acoust., 133, pp. 061012. [CrossRef]
Luneno, J.-C., Aidanpää, J.-O., and Gustavsson, R., 2011, “Experimental Verification of a Combi-Bearing Model for Vertical Rotating Systems,” ASME J. Vibr. Acoust. (in press). [CrossRef]
Ecker, H. and Pumhössel, T., 2011, “Parametric Excitation of a Rotor System Due to a Periodic Axial Force,” ENOC, Rome, Italy, July 24–29.
Friswell, M. I., Penny, J. E. T., Garvey, S. D., and Lees, A. W., 2010, Dynamics of Rotating Machines, Chap. 7, Cambridge University Press, New York, Chap. 7.
Cartmell, M., 1990, Introduction to Linear, Parametric and Nonlinear Vibrations, T. J. Press, Ltd, Padstow, Cornwall, UK, Chap. 2.
Childs, D., 1993, Turbomachinery Rotordynamics: Phenomena, Modeling, and Analysis, Wiley-Interscience, New York, Chap. 1.
Giancarlo, G., 1999, Vibration of Structures and Machines, Springer-Verlag, New York, Chap. 3.


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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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