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.
Misalignment in Combi-Bearing: A Cause of Parametric Instability in Vertical Rotor Systems
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.
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Luneno, J., Aidanpää, J., and Gustavsson, R. (February 21, 2013). "Misalignment in Combi-Bearing: A Cause of Parametric Instability in Vertical Rotor Systems." ASME. J. Eng. Gas Turbines Power. March 2013; 135(3): 032501. https://doi.org/10.1115/1.4007882
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