Parametric studies on static performance and nonlinear stability of bump-type foil bearings

A theoretical analysis is presented to investigate the nonlinear dynamic behavior, i.e., the stability and unbalance response of bump-type foil bearings. The link-spring model, presented and validated in a previous study, is used to describe the foil structure of bump-type foil bearings in this research. The orbit of the shaft is simulated from the iteration calculation of the motion equation at each time step, which is coupled to the Reynolds' equation and the foil structure model. Parametric studies on the mumber of bumps, the size of bumps, the thickness of the foils and the material of the foils are presented using the bearing load prediction and the nonlinear orbit simulations. The static loads of the foil bearing with various parameters are predicted to find out some guidelines for the design of foil bearings. The critical speeds of the rotor with a certain bearing load are also calculated. The analysis on unbalance response is presented by depicting journal trajectories as a function of mass unbalance. And the FFT analysis of the computed results is performed to show the variation of amplitudes in frequency domain.