Investigation on the stability and bifurcation of a rod-fastening rotor bearing system

The stability and bifurcation of a flexible rod-fastening rotor bearing system (RBS) is investigated in this paper. The rod-fastening rotor has two kinds of special structural features - rods and interfaces. The circumferentially distributed rods are modeled as a constant stiffness matrix and an add-on moment vector, which is caused by the unbalanced pre-tightening forces. The stiffness matrix of interface is composed of normal and tangential contact stiffness, which are determined by the pre-tightening forces. After the shaft is discretized by Timoshenko elements, the system is reduced by a component mode synthesis. Periodic motions and stability margins are obtained by using the shooting method and path-following technique, and the local stability of system is obtained by using the Floquet theory. Comparisons indicate that the rod-fastening and complete RBS have a general resemblance in the bifurcation characteristics when mass eccentricity and rotating speed are changed. The unbalanced over-tightening of rods brings initial bending to the rotor, which leads to obvious influence on the nonlinear responses of the system. Moreover, the pre-tightening forces should be sufficiently applied because the small pre-tightening forces make the system more flexible and unstable through the effect of contact interfaces. Generally, this paper presents a method for analyzing the stability and bifurcation of the rod-fastening RBS.