Vibration Analysis of Rotating Shaft System Taking into Account the Dynamic Stiffness of Bearing Foundation

The vibration characteristics of rotating shaft system should be computed considering the dynamic stiffness of bearing foundation, especially if this stiffness is rather low. But the accurate characteristics of such a system has not been computed, as far as known, so that the dynamic stiffness of the bearing foundation can have hardly been obtained.In this paper, a method to estimate the dynamic stiffness of bearing foundations by measuring their compliances dynamically is presented. On the other hand, the critical speeds and damping ratios of a model shafting system, consists of shaft, bearings and their foundations, was measured on the testing rig, and was compared to the estimated ones by using the dynamic stiffness obtained by the above mentioned method.There is good agreement between the measured and estimated ones, though the stiffness of bearing foundations of the testing rig is relatively low compared with actual machinaries. It is expected that the method described in this paper is useful to predict the vibration characteristics of rotating shaft system of actual machineries.