Intermittent behaviour of a cracked rotor in the resonance region

Vibrations of the Jeffcott rotor are modelled by a three degree of freedom system including coupling between lateral and torsional modes. The crack in a rotating shaft of the rotor is introduced via time dependent stiffness with off-diagonal couplings. Applying the external torque to the system allows to observe the effect of crack ‘‘breathing” and gain insight into the system. It is manifested in the complex dynamic behaviour of the rotor in the region of internal resonance, showing a quasi-periodic motion or even non-periodic behaviour. In the present paper report, we show the system response to the external torque excitation using nonlinear analysis tools such as bifurcation diagram, phase portraits, Poincaré maps and wavelet power spectrum. In the region of resonance, we study intermittent motions based on laminar phases interrupted by a series nonlinear beats.