Damping ratio and natural frequency bifurcations in rotating systems

Campbell diagrams are very common in the analysis of rotating machines. They show the variation of natural frequencies as a function of rotational speed. Typically the natural frequencies change with speed because of gyroscopic effects and bearing characteristics. Usually the topology of the Campbell diagram is very simple, particularly if the supports are isotropic and the rotor symmetric. The main purpose of this paper is show that viscous damping in the bearings can produce bifurcations in both the Campbell diagram and the plot of damping ratio against shaft speed.