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International Journal of Rotating Machinery
Volume 2010 (2010), Article ID 540101, 5 pages
Research Article

Approximated Stiffness Coefficients in Rotor Systems Supported by Bearings with Clearance

Division of Computer Aided Design, Department of Applied Physics and Mechanical Engineering, LuleƄ University of Technology, 971 87 LuleƄ, Sweden

Received 29 June 2009; Accepted 9 January 2010

Academic Editor: Kazuhiko Kawaike

Copyright © 2010 Magnus Karlberg. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Many kinds of rotating machinery are supported by bearings with clearance, which are further clamped in a supporting structure. When designing such machinery it is important to be able to predict dynamics and hence valid models are needed. Due to gravity, the shaft often vibrates close to a static equilibrium position leading to a possibility to linearise the equation of motion. Although several studies on bearings with clearance exist, there are still no reports on how such clearances affects the stiffness coefficients close to a static equilibrium position. Therefore, analytical expressions for such approximated pedestal stiffness coefficients have been derived in this paper. By using such approximated pedestals in simple rotordynamical models, it was found that the eigenfrequencies decrease significantly with clearance. It is further shown that the approximated pedestal stiffness coefficients only will be valid for vibrations close to the static equilibrium position.