Estimation of Rotating Unbalance in Rotor Bearing System using Operating Deflection Shape

Abstract

Rotating unbalance is one of the main sources of vibration in a rotor system. Vibration due to unbalance may cause noise, decreased life of bearings, unsafe work conditions, and reduced machine life. Different methods have been studied on the identification of unbalance in the rotor system. This study aims to estimate the unbalance using frequency response function of the rotor system and operating deflection shape, i.e., vibration responses under the unbalance. Frequency response function is obtained by conducting eigen-analysis in MATLAB using equations of motion obtained by Jeffcott rotor model. The commercial finite element package, COMSOL Multiphysics software is used to model the rotor system with rotating unbalance and computes the forced vibration response. Frequency response function and frequency domain response are used to inverse estimate the rotating unbalance. The estimation error between estimated unbalances and corresponding prescribed values is lower than 0.1%. This study also shows the use of COMSOL Multibody Dynamics module to simulate the vibration due to the rotating unbalance.