Abstract: For flexible rod-fastening rotor bearing system (FRRBS), a dynamic model of tie rods distributed along the circumference is built by using Hamilton principle, and the general expressions of the additional stiffness matrix and additional generalized moment caused by n rods are obtained. The result shows that if the number of rods is greater than or equal to 3 and they are distributed uniformly along the circumference, the additional stiffness matrix caused by n rods keeps isotropy; and the unbalanced pre- tightening force of n rods leads to a constant generalized added-moment rotating at working speed. At the same time, the shaft is considered as an integral structure and is modeled by using Timoshenko beam-shaft element which can take the effects of axial load into consideration, so the whole dynamic model of FRRBS is obtained. Then the model is reduced by a component mode synthesis method, which can conveniently account for nonlinear oil film forces of the bearing. Afterward, the periodic motions and their stability margin are obtained by using shooting method and path-following technique, and the local stability and bifurcation behaviors of periodic motions are obtained by Floquet theory. The results indicate that mass eccentricity and unbalanced pre-tightening forces of tie rods have great influence on nonlinear stability and bifurcation of the T periodic motion of system, cause the spillover of system nonlinear dynamics and degradation of stability and bifurcation of T periodic motion.

Key words: Bearing-rotor system, Bifurcation, Nonlinear, Rod, Stability