Advanced rotor-bearing design requires increasingly nonlinear analysis to give a comprehensive view of the effects caused by journal bearings. Journal bearings introduce into the system a nonlinear asymmetry and strong damping. Unstable region predict from linear analysts of the bearing (i.e. using stiffness and damping matrices) are understood as region in which amplitude of vibrations increases with time. The non linear mechanism limits the amplitudes of vibration of unstable rotor bearing systems and forms limit cycles
