Abstract :
This work reports on a numerical investigation on the bifurcations of a flexible rotor
response in active magnetic bearings taking into account the nonlinearity due to the geometric
coupling of the magnetic actuators as well as that arising from the actuator forces
that are nonlinear function of the coil current and the air gap. For the values of design and
operating parameters of the rotor-bearing system investigated in this work, numerical
results showed that the response of the rotor was always synchronous when the values
of the geometric coupling parameter a were small. For relatively larger values of a, however,
the response of the rotor displayed a rich variety of nonlinear dynamical phenomena
including sub-synchronous vibrations of periods-2, -3, -6, -9, and -17, quasi-periodicity and
chaos. Numerical results further revealed the co-existence of multiple attractors within
certain ranges of the speed parameter X. In practical rotating machinery supported by
active magnetic bearings, the possibility of synchronous rotor response to become nonsynchronous
or even chaotic cannot be ignored as preloads, fluid forces or other external
excitation forces may cause the rotor’s initial conditions to move from one basin of attraction
to another. Non-synchronous and chaotic vibrations should be avoided as they induce
fluctuating stresses that may lead to premature failure of the machinery’s main
components.
