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.

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