베어링 간극에 따른 회전기계의 위험 회전속도 회피를 위한 주파수 분석

Abstract

This study is concerned with the abnormality monitoring of the rotor unbalance that is one of the most common causes of severe vibration of rotating machinery. This study analyze the relationship between the eccentricity and vibration characteristics for the purpose of abnormal monitoring of rotating machinery with unbalance rotor. Based on the Jeffcott rotor model, the rubbing of a rotating system composed of a rotor and a bearing was formulated to predict the displacement of the rotor in terms of the eccentricity of the rotor, the clearance between the bearing and the rotor, and the rotational speed. The coupled differential equations of Jeffcott rotor is used to analyze the nonlinear dynamic behavior of rotor caused by rub-forces between rotor and bearing. The mathematical model including the eccentricity of the rotor, the clearance between the bearing and the rotor, and the rotational speed is used to derive the motion of rotor in time domain. The motion of the rotor is analyzed both in the frequency domain and the timefrequency domain using Fast Fourier Transform and Hilbert-Huang Transform, respectively, to predict the critical speed.