STRUCTURAL STIFFNESS AND COULOMB DAMPING IN COMPLIANT FOIL JOURNAL BEARINGS - PARAMETRIC STUDIES

This paper presents the results of the second part of the investigation on structural stiffness and Coulomb damping in compliant foil journal bearings. In the first part, a theoretical model was developed to calculate equivalent viscous damping coefficients and structural stiffness of a bump foil strip in a journal bearing or damper. A computer program was also developed to compute the eccentricity and attitude angle of the journal static equilibrium position as well as the deflections, displacements, reacting forces, and equivalent friction coefficient of each bump on the strip. This model and program enabled further parametric studies to be conducted in the second part of the investigation, the results of which are the subject of this paper. The design parameters studied were static eccentricity (bearing load), pad angle (load angle), sliding friction coefficients, and perturbation amplitude (dynamic load). In addition, more effective methods of achieving both Coulomb damping and optimum structural stiffness were examined. The results of the studies showed that stiffness and damping coefficients were highly nonlinear and anisotropic, that their values depended on the sums of the sliding friction coefficients between contact surfaces, and that they were greatly affected by the pad angle.