Analysis of the lateral vibrations of an unbalanced Jeffcott rotor

Abstract

This paper examines experimentally and analytically the lateral vibrations of a Jeffcott rotor running at various unbalance states. Using a Bently Nevada RK-4 rotor kit, three states of eccentric mass unbalance were assumed in this study: 0.4g, 0.8g and 1.2g. Measurements of the startup data and the steady state data at rigid and flexible rotor condition were collected using a setup that mimics the vibration monitoring industrial practices. Lagrange method was assumed to construct a linear mathematical model of the investigated rotor, based on rigid rotor assumptions, that can predict analytically the lateral vibrations. The dynamic characteristics of the system, including the linearized bearing induced stiffness, were solely extracted from startup data. It was concluded that the developed twodegrees- of-freedom model was able to predict the lateral vibration at the rigid condition with an error around 5%. Whereas it failed to predict the response at flexible condition with matching accuracy. Unlike the majority of the work done in this field where complex, nonlinear mathematical model were used to model real systems, this work validates the applicability of using simple mathematical models in predicting the response of a real rotorsystem with an acceptable accuracy.