Research On The Coupled Bending And Torsional Vibrations Characteristics Of Rotor Systems

During the running of rotating machinery, the rotor shows a complicated non-linear dynamic characteristic caused by the interaction of bending and torsional vibrations of rotor, especially under the effects of liquid seal. The rotor showed more complicated dynamic characteristics, whereas that is much closer with the condition of real vibrations of rotor.In this paper, the rotor model with multi-disc was established according to the real rotor. Considering the gravity and damping, the coupled bending and torsional vibrations dynamic differential equations of imbalance rotor was concluded. Through the numerical simulation, the coupled bending and torsional vibrations characteristic diagram of rotor under running rotating speed was obtained and analyzed. Furthermore, under different eccentricities, with the rotating speed as the bifurcation characteristic parameter, the bifurcation characteristics of rotor were studied.In order to investigate the dynamic characteristics of rotor under real running conditions, the coupled bending and torsional vibrations rotor model with multi-disc under the effects of liquid seal was established. Through the numerical simulation, several diagrams of rotor under the running condition were obtained, such as spectrum graph, Poincare graph and so on. From the analysis of those graphs, the results as follow were obtained: the effect of coupled bending and torsional vibrations became more obvious and showed more complicated non-linear dynamic characteristics; the coupled bending and torsional vibrations of rotor under running rotating speed was quasi-periodic motion, so there was latent instability in the system. From this study, eccentricity was found to play an important role in the coupled bending and torsional vibrations of rotor.In the last part, the real running condition of rotor was changed, and enhance the speed of the rotor exceed the running rotating speed as possible, we did some research of the dynamic characteristic from trial of the rotor in this paper. After made some analysis of the results from the trial we can know that there were low frequencies in the vibration of the rotor; there was no obvious vibration before the rotating speed of 19 krpm, i. e. the speed is still lower than the first critical speed and the system has not turn into the first critical area, which indicated that the first critical speed should be higher than 20 krpm and this exactly acted in accord with the numerical simulation result. The small peak vibration before the highest rotating speed is caused by the effects of liquid seal.