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

TL;DR

This paper investigates how crack orientation and orbital evolution influence local resonances in a modified Jeffcott rotor, enhancing crack detection methods by analyzing specific fractional speed resonances.

Contribution

It introduces a linear model of a cracked Jeffcott rotor that accounts for gravity and equilibrium points, emphasizing the importance of local resonances at fractional speeds for crack detection.

Findings

Local resonances at fractional speeds are more indicative of cracks than 1x and 2x components.

Crack-residual imbalance interaction affects vibration patterns and detection.

Orbital evolution around 1/2, 1/3, and 1/4 of critical speed is crucial for crack diagnosis.

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. 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 1/2, 1/3 and 1/4 of the critical speed are emphasized for various crack-imbalance orientations.