Nonlinear dynamic analysis of a flexible rotor supported by micropolar fluid film journal bearings

The bifurcation and chaos of dynamic response of a rotor–bearing system with nonlinear suspension are investigated on the basis of assumptions of the micropolar lubricant together with short bearing approximation. The dynamics of the rotor center and bearing center are studied. The spatial displacements in the horizontal and vertical directions are considered for various non-dimensional speed ratios. The dynamic equations are solved using the Runge–Kutta method. The analysis methods employed in this study is inclusive of the dynamic trajectories of the rotor center and bearing center, Poincaré maps and bifurcation diagrams. The maximum Lyapunov exponent analysis is also used to identify the onset of chaotic motion. The numerical results show that the stability of the system varies with the non-dimensional speed ratios. Specifically, it is found that the dynamic behaviors of the system include periodic, quasi-periodic and chaotic motions. Thus it is concluded that the bearing and rotor center trajectory had undesirable vibrations. Understanding the dynamic behaviors of these parameters provides theoretical and practical ideas for controlling rotor–bearing systems and optimizing their operation.