Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America RESEARCH ARTICLE Advanced Science Letters Vol. 4, 2782–2789, 2011 Analysis of Dynamic Characteristics for a Dual-Disk Rotor System with Single Rub-Impact Hui Ma ∗ , Xingyu Tai, Jian Sun, and Bangchun Wen School of Mechanical Engineering and Automation, Northeastern University, Shenyang 110819, China This paper presents a finite element (FE) model of a dual-disk rotor system with single rub-impact fault and ana- lyzes the effects of different rotating speeds on its dynamic characteristics. The numerical simulations based on the FE model are conducted to study the rotor transverse vibrations of the rotor system. The results are further compared to experimentally measured vibrations. The simulation results show that the motion of the rotor varies from period-one through period-two to period-three with the increasing of the rotating speed; the corresponding frequency components are from multiple frequency components through 1/2 fractional harmonic components to 1/3 fractional harmonic components; and rotor trajectory mainly shows inner concave phenomenon, two nested ellipses and three nested ellipses along rub-impact direction, respectively. In corresponding experimental mea- surements, combination frequency components including the first natural frequency can be observed besides these features obtained by simulation. These results will provide theory bases for single rub-impact monitoring and diagnosis. Keywords: FE Model, Dual-Disk Rotor System, Dynamic Characteristic, Single Rub-Impact. 1. INTRODUCTION Due to the increasing demand for high speed and high effi- ciency, the clearance between rotors and stators in modern rotat- ing machinery is becoming smaller and smaller. As a result, the rub-impact, which refers to the contact between the rotating and non-rotating structures in a machine, has become one of the most common damaging malfunctions of rotating machinery. 1 Further investigation on mechanism of the rub-impact phenomenon and its dynamic characteristics is indispensable to the improvement of the current fault diagnosis of rotor systems. Muszynska dis- cussed chaotic response of unbalance rotor-bearing-stator sys- tems with rubbing. 2 The results showed that at low rotational speeds, the rotor’s response exhibits 1X vibration as the low- est frequency component. At a speed roughly equal to twice the rotor’s first lateral natural frequency, a 1X/2 sub-synchronous vibration component appears, and continuous until the rotational speed reaches 3 times the rotor’s first natural frequency. Then, the 1X/2 is replaced by 1X/3 vibration as the lowest frequency component. Muszynska also pointed out that there was evidence of rotor chaotic responses at some speeds. Zhang presented a rub-impact micro-rotor model with scaling nonlinear rub-impact force and the nonlinear dynamic characteristics of micro-electro- mechanical system (MEMS) were investigated when the rota- tional speed, imbalance, damping coefficient, scale length, and ∗ Author to whom correspondence should be addressed. fractal dimension were regarded as the control parameters. 3 Ehrich observed the higher order subharmonic vibrations as well as chaotic vibration in a high speed turbomachine. 4 Chu dis- cussed some typical periodic, quasi-periodic and chaotic motions by using the chaos-bifurcation theory for a Jeffcott rotor system with rub-impact. 5 Recently, many researchers studied rotor fault by using finite element method which may take into account many factors, such as mass, moment inertia, internal damping, bending and torsion vibration coupling effects. Jing studied the nonlinear dynamic behavior of a rotor-bearing system based on a continuum model using the finite element method in his analysis. 6 By establishing a FE model, Han investigated the periodic motions of a rotor sys- tem with two disks where rub-impacts occur at fixed limiter for a test rig with dual disks. 7 The simulations demonstrate differ- ent rotor motions including periodic, quasi-periodic or complex characteristics, which coincide with experimental measurements. In another paper by Han, the stability of periodic motions of a dual-disk rotor system, in which rub-impacts occur between a disk and a fixed limiter, was investigated. 8 Nelson introduced the rotor dynamical analysis with FE method firstly. 9 In the book of LaLanne, the rotor dynamics were fully discussed with FE models. 10 In a book, nonlinear modeling and responses were explained in detail based on FE method for rotor-bearing-support systems of turbine generator units. 11 2782 Adv. Sci. Lett. Vol. 4, No. 8/9/10, 2011 1936-6612/2011/4/2782/008 doi:10.1166/asl.2011.1446