Optimum support characteristics for rotor–shaft system with preloaded rolling element bearings

Preloading of rolling element bearings is often used to avoid clearance in the bearings and achieve precise dynamic requirement. Preloading gives rise to an expression of the restoring force, which is a non-linear function of the deformation of the rolling elements. In this paper, frequency-dependent optimum support characteristics have been found out by simultaneously minimizing the unbalance response (UBR) of the rotor and maximizing the stability limit speed (SLS) of a flexible horizontal rotor–shaft system comprising an unsymmetrically placed rotor disc placed on an elastic shaft mounted on preloaded rolling element bearings at the ends supported on viscoelastic polymeric supports. A sensitivity study of the UBR and SLS with respect to the support characteristics has been presented to have an idea about the permissible deviation of the support characteristics from the respective optimum, at any frequency. Thus, the sensitivity study helps the quality control man as well as the manufacturer of such supports to estimate the permissible deviation in the most sensitive frequency zones. The results presented in this work are in terms of non-dimensional parameters of the system and are, therefore, valid for any system under consideration.