On the simultaneous forward and backward whirling in flexible rotors: numerical analysis and experimental verification

Abstract

This paper discusses the existence of the mixed operational modes in flexible rotors. In this condition, some stations of the rotating machine describe their precessional movement in the forward direction while others move in the backward direction. A complex coordinate based finite element model is used to compute the steady state complex response of the system when it is subjected to multiple unbalance forces applied on some station of the rotor. The Shape and Directivity Index Plot is used to identify the rotational speed range where the phenomenon occurs. The influence of the spatial distribution of the unbalance forces as well as the effect of the bearing stiffness is analyzed numerically. Experimental results are presented to corroborate the numerical study and to prove the existence of the simultaneous forward and backward whirling on flexible rotors.

Keywords:

• flexible rotor
• forward whirling
• backward whirling

Additional information

Notes on contributors

M Dias

Milton Dias received the BS, MS and PhD degrees in mechanical engineering from the Faculty of Mechanical Engineering of the State University of Campinas, Campinas, Brazil in 1984, 1987 and 1994, respectively. From 1999 to 2000, he was a visiting research assistant at the Structural Dynamics Research Laboratory of the University of Cincinnati, Cincinnati, USA. His research and teaching interests include dynamics and control of mechanical systems, modal analysis of structures, mechanical vibrations and signal processing. He is currently an associated professor at the Faculty of Mechanical Engineering of the State University of Campinas, Campinas, Brazil, where he is the coordinator of the course of Automation and Control Engineering.

S J Idehara

Sérgio Idehara received the graduate and MS degrees in mechanical engineering from the University of Campinas in 2001 and 2003, respectively. He is currently studying at the same university for the PhD degree. His research interests include signal processing, parameter identification of rotative systems under non-stationary condition and modal analysis.

A L A Mesquita

Ubatan Miranda recieved the BS degree in mechanical engineering in 1999 from the Federal University of Bahia, Salvador, Brazil, and the MS degree in solid mechanics from the State University of Campinas, Campinas, Brazil, in 2002. He is currently a PhD student in solid mechanics at the Department of Mechanical Design of the Faculty of Mechanical Engineering, State University of Campinas, Campinas, Brazil. His research interests include the dynamic behavior of mechanical systems, in particular rotating systems, using signal processing and time-frquency analysis techniques. His current activity is focused on the time-frequency vibrational features of cracked rotors.

U A Miranda

Alexandre Mesquita recieved the BS degree in mechanical engineering in 1992 from the Federal University of Pará, Belém, Brazil; the MS degree in solid mechanics in 1996 from the University of Brasília (UnB), Brasília, Brazil, and the PhD degree in mechanical engineering from the State University of Campinas, Campinas, Brazil, in 2004. He is currently a professor at the Department of Mechanical Engineering of the Federal University of Pará. His research interests include vibration, modal anaysis, and dynamic of rotating systems.