Frictional effects on the nonlinear dynamics of an overhung rotor

•It is shown for the first time that in the presence of friction there are two fundamentally different forms of asynchronous bouncing motion that can coexist in the same system.•It was observed that the synchronisation condition holds in the presence of friction as seen by the presence of the SBW, FW and Ω^ frequency components in bouncing type solutions.•High amplitude responses were observed for moderate to hard forcing, these turned out to be SBW solutions.•The spectral intensity plots also showed that the SBW solutions which are full annular in nature have their frequency content migrating towards higher frequency values because of a larger stiffening effect as compared to bouncing type solutions. An overhung rotor model is explored to determine the effect of friction during contact between the rotor and stator. The model has two degrees of freedom with rotor stator contact and the equations of motion are non-dimensionalised. A parametric study of the friction coefficient and eccentricity is conducted and the results displayed on three dimensional bifurcation plots, orbit plots, Poincaré maps and spectral intensity plots to classify the solutions. It is shown for the first time that in the presence of friction there are two fundamentally different forms of asynchronous bouncing motion, that can coexist in the same system. Furthermore, the analysis shows that the synchronisation of rotor spin speed, backward whirl (BW) and forward whirl (FW) persists in presence of friction. Also, additionally it was observed from the bifurcation diagram that besides the primary resonance there is a region with high radial displacement; the dominant frequency component was the backward whirling frequency of the stiffened system in this region. The region with backward whirling solutions is seen to expand as the friction coefficient is increased.