Vibration transmission through rolling element bearings

Abstract

Current bearing models, based on either ideal boundary condition or purely translational stiffness element description, may be used to analyze the free and forced vibration of the rotor dynamic systems enclosed in a rigid casing; however, these models lack the explanation of how the vibratory motion is transmitted from the rotating shaft to the flexible or rigid casing and other connecting structures. These models can only predict in plane type of motions of the flexible casing which is actually out of plane or flexural in nature. This paradox is essentially due to the incomplete understanding of beaning as a vibratory motion transmitter in rotating mechanical equipment. In this work a mathematical model dezcribed by Lim and Singh for the precision rolling element bearings is applied to a rotor-bearing system. This model proposes a bearing stiffness matrix which demonstrates the coupling between the shaft bending motion and the motion of the casing or pedestals. Verification is made experimentally using a simple rotor-bearing system which differs from the example cases of Lim and Singh. Acceleration of the pedestals are measured and compared with the theoretical results. Theoretical force and moment transmissibilities of the bearing and mount is calculated. Making the vibration analysis in this manner alllows us to calculate the bearing moment transmissibility which can not be calculated by simple models.