Nonlinear characterization of the rotor-bearing system with the oil-film and unbalance forces considering the effect of the oil-film temperature

Abstract

The nonlinear phenomena of the rotor-bearing systems, i.e., the oil whirl, oil whip, quenching and pulling out, due to the oil-film temperature are not yet clear. To characterize these phenomena, a mathematical model of the rotor-bearing system is proposed to consider the effect of the oil-film temperature using the revised Walther empirical equation. Bifurcation diagram, cascade spectrum, time history, phase portrait, power spectrum and Poincare section are employed to investigate the impacts of the rotational speed, oil-film temperature and rotor eccentricity on the stability of the rotor-bearing system. As the rotational speed increases, the system becomes unstable due to the oil whirl/whip. The oil whirl appears at the medium rotational speeds. In the middle of such speed range, it is suppressed by the synchronous vibration. Quenching and pulling out occur at the thresholds and end of the suppression, respectively. The oil-whirl range of the rotational speed increases with the oil-film temperature. Due to the existence of the oil whirl, the system undergoes period-2, period-3, period-4, period-5, period-6, period-8, quasi-periodic and chaotic motions. At the high rotational speeds, the oil whirl is replaced by the oil whip. The synchronous vibration of the bearing is suppressed as long as the oil whip appears. The oil whip dominates the system and leads to the severe vibrations. The oil whip range of the oil-film temperature increases with the rotational speed. The rotor eccentricity is prone to increase the stability of the system due to the fact that increasing synchronous vibration suppresses the oil whirl/whip.