Nonlinear analysis is increasingly applied in the dynamics analysis of rotor bearing systems. The use of tilting-pad bearings is now a standard feature of many types of rotor systems. The concern for oil film excitation of the rotor lowest natural frequency is eliminated by the use of the tilting pad journal bearings. For new higher speed or larger low speed applications, the possibility of the pad flutter instability still remains and most commonly used design tools do not consider the pad inertia as a standard feature. In this paper, taking the Jeffcott rotor supported by two 4 pad bearings as an example, the influence of pad inertia and journal diameter were studied. The influence of shaft diameter and pad inertia was determined by the transient response of a simple rotor-bearing system operating over a wide design speed range. The tilting pad journal bearing oil-film force was calculated by a database method. The resulting nonlinear transient vibration is discussed using bifurcation diagrams, orbits, frequency spectrum plots, phase trajectories, and Poincare maps. The results directly show that journal diameter and pad inertia greatly influence the nonlinear vibrations of the journal and rotor center.

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