Structural Stiffness and Coulomb Damping in Compliant Foil Journal Bearings: Theoretical Considerations

Ku, C.-P.R. and Heshmat, H. “Structural Stiffness and Coulomb Damping in Compliant Foil Journal Bearings:  Theoretical Considerations,” STLE Annual Meeting, Calgary, Canada, May 17-20, 1993, (1994) STLE Tribology Transactions, Volume 37 (3), pp. 525-533.

Compliant foil bearings operate on either gas or liquid, which makes them very attractive for use in extreme environments such as in high-temperature aircraft turbine engines and cryogenic turbopumps. However, a lack of analytical models to predict the dynamic characteristics of foil bearings forces the bearing designer to rely on prototype testing, which is time-consuming and expensive. In this paper, the authors present a theoretical model to predict the structural stiffness and damping coefficients of the bump foil strip in a journal bearing or damper. Stiffness is calculated based on the perturbation of the journal center with respect to its static equilibrium position. The equivalent viscous damping coefficients are determined based on the area of a closed hysteresis loop of the journal center motion. The authors found, theoretically, that the energy dissipated from this loop was mostly contributed by the frictional motion between contact surfaces. In addition, the source and mechanism of the nonlinear behavior of the bump foil strips were examined. With the introduction of this enhanced model, the analytical tools are now available for the design of compliant foil bearings.

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