The influence of crack-imbalance orientation and orbital evolution for an extended cracked Jeffcott rotor

摘要

Vibration peaks occurring at rational fractions of the fundamental rotatingcritical speed, here named Local Resonances, facilitate cracked shaft detectionduring machine shut-down. A modified Jeffcott-rotor on journal bearingsaccounting for gravity effects and oscillating around nontrivial equilibriumpoints is employed. Modal parameter selection allows this linear model torepresent first mode characteristics of real machines. Orbit evolution andvibration patterns are analyzed, yielding useful results. Crack detectionresults indicate that, instead of 1x and 2x components, analysis of theremaining local resonances should have priority; this is due to crack-residualimbalance interaction and to 2x multiple induced origins. Therefore, localresonances and orbital evolution around 1/2, 1/3 and 1/4 of the critical speedare emphasized for various crack-imbalance orientations.