Prediction of Dynamic Characteristics of a Bump-Type Foil Bearing Structure with Consideration of Dynamic Friction

Friction forces within the foil structure, which provide most of the damping characteristics of gas foil bearings (GFBs), depend not only on surface topology and normal force but also on foil materials, displacement, and relative velocity of contact surfaces; therefore, describing the dynamic behavior of GFBs through Coulomb friction yields insufficient results. This article presents a numerical model of a bump-type foil bearing structure, for which the dynamic friction forces within the foil structure are considered. Each bump is simulated as a horizontally spaced spring and two rigid links. The contact surfaces between the bump strip and the top foil, as well as those between the bumps and the housing, are considered interfaces through elastic bristles. A dynamic friction model, the LuGre model (C. Canudas de Wit, etal., 1995, IEEE Transactions on Automatic Control, Vol. 40), is used to calculate the variations in friction forces from the deformation of the foil structure. An important feature of the proposed model is that it can simulate the effect of excitation frequency on dynamic friction force. The predictions of a six-bump strip show that both dynamic friction force and energy dissipation vary with excitation frequency. The calculated hysteresis loop shows good agreement with published experimental data. Results of a full GFB structure show that the dynamic characteristics are largely affected by excitation amplitude and frequency, friction coefficient, and bearing assembly preload. To a certain extent, the calculation results match well with published test data, which shows that the proposed model is reasonable for predicting the dynamic characteristics of foil structures.