Nonlinear Dynamics Of Complex Rotor-bearing System Subject To A Holonomic Constraint Of Rotor Misalignment

Traditionally, the motion constrains and coupling relationships between two rotors wereneglected in the analysis of rotor-bearing system with a misaligned fault. However, they playa significant role in dynamic characteristics of rotor system in some cases. Accordingly, thestudy on nonlinear dynamics of the complex rotor-bearing coupling system subject to amisalignment constraint is of great significance for the dynamic design and fault diagnosis ofcomplex rotor-bearing system.Based on rotordynamics, nonlinear dynamics, and hydrodynamic lubrication and so on, thedynamic model of the multi-rotor coupling system subject to a holonomic constraint isestablished, which describes the relationship of the generalized displacements between twomisaligned rotors. Nonlinear dynamic behaviours of rotor-bearing system under the action ofnon-linear oil film forces were mainly investigated by using both the numerical approach andexperiment method, respectively, in which the scleronomous or rhenomous holonomicconstraints for misalignment faults were embedded. The vibration mechanisms andcharacteristics of rotor system with parallel and angular misalignments were paid moreattention in this thesis. The main contents and contributions are summarized as follows:The mechanical model of rotor-bearing system was developed after considering the effectsof the unsymmetrical and flexible shafts with the faults of the parallel misalignment and massunbalance for a practical generator set. In order to study the dynamic behaviors of the system,a numerical method was introduced and the parametric effects on dynamic characteristicswere also discussed. The results indicate that the steady-state responses in lateral direction aresynchronous with rotating speed for the case of tiny misalignment at low speed. As increasingthe speed, some harmonic components occurs and the vibration amplitudes increase.Furthermore, some parameters such as the parallel misalignment, asymmetry of rotor stiffnessand mass unbalance exert a significant influence on dynamics of rotor system, which cancause a series of complex nonlinear characteristics, for example, bifurcation, jump phenomenon and chaotic motion.The nonlinear dynamic behaviours of rotor-bearing system with angular misalignmentwere investigated, in which the rhenomous holonomic constraint characterized by the motionrelation between two rotors was embedded. Then, the nonlinear vibration characteristics ofthe system were discussed and parameter study on dynamic behaviours was carried out. Thenumerical results show that the angular misalignment has little influence on dynamicresponses of rotor-bearing system at low speed. As increasing rotational speed, however,rotor orbits present obviously an8shape curve with doubling frequency component inspectrum diagram. At high speed, some nonlinear phenomena such as doubling-periodbifurcation and chaotic oscillation occur. Additionally, the angular misalignment, shaftstiffness and mass unbalance play an important role in the vibration of rotor-bearing system.In order to study the dynamic characteristics of the misaligned rotor system, a test rig ofthe system supported on four oil film bearings was established. The displacement responsesunder the conditions of misalignment faults, such as the rotor orbit and frequency spectra,were measured. The experimental results show that the steady-state responses of misalignedrotor system is mainly composed of the components of the synchronous and its integermultiple frequencies, in which the ones of1X and2X are dominant. Meanwhile, there alsoexist some components of non-synchronous frequencies as well as their combinations. All ofthese vibration characteristics prove that the proposed dynamic models in the thesis areavailable.