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.

References

References
1.
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. 061012.10.1115/1.4005002
2.
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).10.1115/1.4023052
3.
Ecker
,
H.
and
Pumhössel
,
T.
,
2011
, “
Parametric Excitation of a Rotor System Due to a Periodic Axial Force
,” ENOC, Rome, Italy, July 24–29.
4.
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.
5.
Cartmell
,
M.
,
1990
,
Introduction to Linear, Parametric and Nonlinear Vibrations
,
T. J. Press, Ltd
,
Padstow, Cornwall
, UK, Chap. 2.
6.
Childs
,
D.
,
1993
,
Turbomachinery Rotordynamics: Phenomena, Modeling, and Analysis
,
Wiley-Interscience
,
New York
, Chap. 1.
7.
Giancarlo
,
G.
,
1999
,
Vibration of Structures and Machines
,
Springer-Verlag
,
New York
, Chap. 3.
You do not currently have access to this content.