Non-linear dynamic analysis of dual flexible rotors supported by long journal bearings

Vibration characteristics of two rotors equipped with long journal bearings placed at both ends were investigated. Besides the non-linear forces of the lubricated pairs, a non-linear elastic, damped coupling was assumed between the bearings and the rotor pedestal. Rotating speed is used as the control parameter to observe various forms of periodic, quasi-periodic and chaotic vibrations. Different cross section and length of shafts, mass of bearings and even different bearing approximations are presented to analyze and discuss the difference of dynamic responses. Dynamic trajectories, Poincaré maps, bifurcation diagrams, and maximum Lyapunov exponent are used to analyze the behavior of the bearing center in the horizontal and vertical directions under different operating conditions. It is shown that the system can exhibit very rich types of periodic, quasi-periodic, and chaotic vibrations. These forms of vibrations and relevant phenomena can be effectively used to diagnose the undesired vibration in rotor–bearing systems.