Rotating machinery supported by the journal bearing may be subject to instability. This instability is classified as the Hopf bifurcation. Either a sub-critical bifurcation or super-critical bifurcation appears depending on the parameters of rotor systems. Conventionally, an infinitely short journal bearing model was used for the investigation of this bifurcation. In this paper, the force transmitted by the oil film of the journal bearing is represented by the finite length model. Nonlinear numerical simulation is performed at around instability point of the flexible rotor supported by the journal bearing. The bifurcation characteristic and the change of bifurcation type are investigated when the ratio L/D , which is the ratio of bearing length L to the bearing diameter D, increases.
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