Abstract: Based on a multi-degree-of-freedom nonlinear dynamic model of a geared rotor bearing system with time-varying stiffness and backlash, the mass unbalance response of the system is investigated by applying the numerical simulation over a range of speeds. When the speed increases near to the second critical speed, the motion of the system changes from periodic, quasiperiodic to chaotic state after a series of bifurcation. Under chaotic state, the amplitude of response and average deformation of the system are much larger than others. The system should not operate in resonant region in order to avoid chaotic motion. When the speed exceeds some value, the chaotic motion suddenly changes into periodic motion. Except for chaotic state, the linear model can be substituted for the nonlinear model in engineering.

Key words: Bifurcation, Chaos, Gear, Response, Rotor