Optimization of a Flexible Rotor-Sliding Bearing System With a Squeeze Film Damper

A dynamic model of a flexible rotor-sliding bearing system ( FRSBS ) with asqueeze film damper ( SFD) is established. Considered in the model are oil film inertia force,damping farce, clearance excitation force, interference force of different frequencies and staticload, as opposed to previous research. On the basis of this model, the optimal design of the systemis deeply studied. Simulation shows that the system optimization design can effectively improve thesystem stability.

Optimization Method of Bearing Support Positions in a High-Speed Flexible Rotor System

Bearing support position is one of main factors affecting vibration characteristics of rotor systems. To optimize the bearing support positions in a high-speed flexible rotor system (HSFRS) based on the vibration characteristics, an optimization method of bearing support positions in the HSFRS is proposed. In this method, a finite element (FE) model of a high-speed flexible rotor (HSFR) was established. The natural frequencies and mode shapes of the HSFRS were used to obtain the initial design scheme of the bearing support positions. A frequency characteristic equation of the HSFRS was established to obtain the critical speeds of the HSFRS. And a dynamic model of the HSFRS was established to analyze the vibration characteristics for different bearing support position cases. The problem of optimizing bearing support positions in the HSFRS was solved by the developed method. The results showed that vibration amplitudes of the HSFRS were more stable when the bearing support positions were optimized. This study can provide a new method for optimizing bearing support positions of rotor systems.

Theoretical and experimental study on the self-excited vibration of a flexible rotor system with floating spline

The internal friction of floating spline can cause self-excited vibration of a supercritical flexible rotor system.To address this issue,a high-efficiency dynamic modeling method is proposed to investigate the self-excited vibration behavior and instability evolution of the rotor.Experiments are conducted to validate the theoretical results.The coupled dynamic equations for the rotor system connected with the floating spline are derived through the combination of finite element method and lumped parameter model.A hybrid numerical approach of precise integration and Runge-Kutta method is adopted to examine the effects of the friction coefficient of spline’s tooth surface,torque,and eccentricity on the self-excited vibration of the rotor system.The results show that the spline friction leads to negative damping and inputs energy into the rotor system under supercritical conditions,triggering self-excited vibration when the input energy exceeds a specific level.With the same parameters,the experimentally obtained axial trajectory and primary frequency components are consistent with the theoretical results,verifying the accuracy of the proposed theoretical model.This study can serve as a useful theoretical guide for the dynamic stability design of flexible rotor systems with the floating spline.

Modal characteristics analysis for a flexible rotor with non-smooth constraint due to intermittent rub-impact

Intermittent rub-impact, during which the contact between rotor and stator is characterized by a ‘‘bouncing＂ or intermittent type of behavior, is one of the most common rubbing forms in rotating machinery. When the intermittent rub-impact occurs, the non-smooth constraint, which is the phenomenon that the system stiffness changes with respect to the state of contact and noncontact, will appear. The paper aims at discovering the possible effects of the non-smooth constraint on the flexible rotor＇s modal characteristics by theoretical and experimental methods. The qualitative description for non-smooth constraint is given for the intermittent rub-impact process, and the dynamic modeling for a rotor system with non-smooth constraint is carried out. Meanwhile, the analysis method is developed by Floquet theory and Hill＇s method to obtain the rotor＇s modal characteristics. The results reveal that the non-smooth constraint produced by the intermittent rubimpact will increase the modal frequencies and critical speeds of the rotor system significantly.Due to the time-varying features of the constraint stiffness, the modal frequencies for the intermittent rub-impact rotor present fluctuant changes with the increase of rotation speed, which is different from the general linear rotor system. The non-smooth constraint is possible to lead the rotor＇s instability, and the rotor＇s instable regions can be expanded significantly for the increase of average constraint stiffness, constraint amplitude and contact time ratio. Non-smooth constraint could also expand the resonance speed and resonance sideband of the rotor system, which sometimes results in amplitude jump phenomenon.

Control of a flexible rotor active magnetic bearing test rig: a characteristic model based all-coefficient adaptive control approach

Active magnetic bearings （AMBs） have found a wide range of applications in high-speed rotating machinery industry. The instability and nonlinearity of AMBs make controller designs difficult, and when AMBs are coupled with a flexible rotor, the resulting complex dynamics make the problems of stabilization and disturbance rejection, which are critical for a stable and smooth operation of the rotor AMB system, even more difficult. Proportional-integral-derivative （PID） control dominates the current AMB applications in the field. Even though PID controllers are easy to implement, there are critical performance limitations associated with them that prevent the more advanced applications of AMBs, which usually require stronger robustness and performance offered by modern control methods such as H-infinity control and if-synthesis. However, these advanced control designs rely heavily on the relatively accurate plant models and uncertainty characterizations, which are sometimes difficult to obtain. In this paper, we explore and report on the use of the characteristic model based all-coefficient adaptive control method to stabilize a flexible rotor AMB test rig. In spite of the simple structure of such a characteristic model based all-coefficient adaptive controller, both simulation and experimental results show its strong performance.