Nonlinear Vibration And Bifurcation Analysis For Rotor-Bearing-Seal Systems

Rotary machines have been higher-speed, stronger in load-capacity, lighter in weight andmore automated along with the recent development of engineering and technology. Thesemachines are playing important roles in various engineering fields and are drawing attentionof people to their failures in operations. It has been gradually realized that there exists greatinfluence of nonlinear excitations occurring in clearances on the global dynamic performanceof the rotor systems. Therefore, investigations of nonlinear dynamics on large-scaled rotarymachines are urgently needed to understand the mechanism of the failures and to control oreven eliminate the possibility of them. There are many contributions of excitations, e.g.oil-fihn force in journal bearings, fluid excitation in labyrinth seals, impact and dry frictions,to the dynamic properties of rotor systems. Nonlinear science is in great demand since mostproblems of the rotor dynamics are nonlinear.In this dissertation, nonlinear vibration problems resulted from seal force, oil-film forceand magnetic force that act in clearance field of the rotor are investigated, respectively, basedon previous researches. They are summarized as follows:(1) Nonlinear response of a Jeffcott rotor excited by seal forces. It is pointed out that theamplitude varies with the rotor speed. Time histories, orbits of the rotor center and Poincaremaps are adopted to show the dynamic characteristics.(2) The influences of varying pressures and seal length on the system response.(3) The responses of the system that are solved under the seal aerodynamic force coupledwith oil-film excitation of bearings. The discussion shows that the amplitude varies with therotor speed. Time histories, orbits of the rotor center and Poincare maps are used todemonstrate the dynamic features.(4) The influences of varying pressures and seal length on the system response for theabovementioned coupled motion.(5) The nonlinear vibration and stability of a Jeffcott rotor under the unbalancedmagnetic excitation in clearance.This dissertation is funded by the Natural Science Foundation of China under Contracts10472021 and 10421202 and bythe SRF for ROCS and the Program for Changjiang Scholarsand Innovative Research Team in University of China (PCSIRT).