Jinfu Yang

Research on Nonlinear Fluid-Solid Interaction Dynamic Lubrication in Floating Ring Bearings

An experiment of floating ring bearings and flexible rotor in a micro turbo-engine is carried out. Nonlinear behavior of fluid-solid interaction in floating bearings is studied. And frequency characteristics And frequency characteristics of five typical vibrations regions in floating ring bearings test are presented. Furthermore, the difference and correlation between synchronous frequency characteristic in critical speed and subsynchronous whirl frequency harmonic response characteristic are illustrated._Based on the analytical expressions of load capacity and whirl frequency in single oil film lubrication bearings, the stability of inner and outer film in floating ring bearings is analyzed. It is shown that when half-speed oil whirl occurs in outer and inner oil film, the journal whirl ratios approach 0.5 and 0.3 respectively, which fairly corresponds with theoretical analysis. The paper can be a experimental and theoretical support for future performance evaluation and design of floating ring bearings.Copyright

An Analytic Model of Oil-Film Force on Hydrodynamic Journal Bearing of Finite Length

In order to more clearly express the interrelation between the oil-film force on hydrodynamic journal bearing of finite length and the wedging, whiling, and squeezing motions of journals, an analytic model with well-defined physical meaning is proposed in this paper by introducing the non-slip boundary condition for the oil-film velocity gradient without modifying the basic assumption for Reynolds equation to formulate the expression of oil-film pressure distribution, obtaining the analytic solution of oil-film force through integration of circumferential pressure, and defining the effect coefficients for wedging, whirling and squeezing motions, which are related to the clearance ratio and eccentricity ratio of bearings. The proposed model is compared with an existing model to show off its advantage. The proposed model was also applied to a 200MW steam turbine low-pressure rotor-bearing system to simulate the dynamic response of the rotor during the speed-up process. The analytic results of this application proved the validity of the proposed model.Copyright

Experimental Study on Nonlinear Dynamics Characteristics of High-Speed Rotor-Gas Lubrication Bearing System

An experimental study was done with the nonlinear dynamics characteristics of high-speed rotor-gas lubrication bearing system analyzed using the orbits of shaft center, 3D frequency coupling diagram, frequency spectrum and bifurcation diagram. Experimental results indicate that gas whirl is the main cause for the nonlinear instability of the high-speed rotor-gas lubrication bearing system, and the double periodic bifurcation resulting from gas whirl leads to the chaos vibration of the rotor-bearing system. It is therefore concluded that it is a new way to improve the nonlinear stability of a rotor-bearing system to keep the instability rotation speed far away from the design rotation speed by modulating the coupling between the natural frequency of the system and the gas whirl frequency, and to use the boundary nature of chaos verified through experiments to control the amplitude of vibration.© 2008 ASME

Research on Circumferential Fluid Pressure Distribution and Whirl Stability of Rotor-Bearing System

This paper presents a theoretical analysis of the mechanism of oil whirl, oil whip, and hysteresis in oil whip. A qualitative analysis of the interrelation between whirl frequency, natural frequency, and eccentricity ratio versus speed was conducted using the rotor-bearing load balance equation. By analyzing the interrelation among whirl speed, eccentricity ratio versus speed, rotating speed, oil supply pressure and bearing load, and observing the oil-film load circumferential fluid pressure distribution in the three phases of oil-film load attenuation, instability transition, and oil-film load instability, it was found that in the whirl instability transition phase, the amplitude of rotor whirl speed exceeds half the value of rotor rotation speed, which causes the pressure change in the oil convergent wedge to change from positive to negative, and the pressure change in the divergent wedge to change from negative to positive, and the change in oil-film pressure distribution causes the instability of oil whirl; These changes in oil film pressure distribution are the indicator of oil whirl instability. An experimental study on the whirl instability in a pump supported on fluid film bearings is also presented in this paper to validate the theoretical approach.Copyright