The influence of crack-imbalance orientation and orbital evolution for an extended cracked.pdf

1 Journal home page: /science/journal The influence of crack-imbalance orientation and orbital evolution for an extended cracked Jeffcott rotor Comptes Rendus Mecanique, Volume 332, Issue 12, December 2004, Pages 955-962 J. Gómez-Mancilla, Jean-Jacques Sinou, V.R. Nosov, F. Thouverez and A. Zambrano THE INFLUENCE OF CRACK-IMBALANCE ORIENTATION AND ORBITAL EVOLUTION FOR AN EXTENDED CRACKED JEFFCOTT ROTOR J. Gómez-Mancilla 1, J-J. Sinou 2*, V.. R. Nosov 1, F. Thouverez 2, A. Zambrano R. 1 1Lab. Vibraciones Rotodinamica ESIME, Instituto Politécnico Nacional, México D.F., MEXICO. 2Laboratoire de Tribologie et Dynamique des Systèmes UMR CNRS 5513, Ecole Centrale de Lyon, 36 avenue Guy de Collongue, 69134 Ecully, France. Abstract Vibration peaks occurring at rational fractions of the fundamental rotating critical speed, here named Local Resonances, facilitate cracked shaft detection during machine shut-down. A modified Jeffcott-rotor on journal bearings accounting for gravity effects and oscillating around nontrivial equilibrium points is employed. Modal parameter selection allows this linear model to represent first mode characteristics of real machines. Orbit evolution and vibration patterns are analyzed yielding useful results. For crack detection results indicate that, instead of 1x and 2x components, analysis of the remaining local resonances should have priority, this is due to crack-residual imbalance interaction and to 2x multiple induced origins. Therefore local resonances and orbital evolution around ?, 1/3 and 1/4 of the critical speed are emphasized for various crack-imbalance orientations. Keywords: Dynamic systems, rotor dynamics, crack detection, local resonance, extended Jeffcott rotor, orbital evolution. Résumé Les pics de vibration apparaissant au passage des fractions de la vitesse de critique de rotation des systèmes tournants, appelées résonances locales, facilitent la détection de f