(Dr. Itzhak Green, advisor)

"Crack Detection in a Rotor Dynamic System"

Abstract

This thesis presents a research project in which the feasibility of utilizing an existing monitoring system to detect an additional type of system fault is explored. The existing monitoring system has the ability to detect seal face contact in a flexibly mounted rotor (FMR) mechanical face seal, by directly monitoring the dynamic response of the rotor, and eliminate or reduce the severity of the contact with real-time active control. The primary objective of this research is to explore the feasibility of utilizing the exiting mechanical face seal monitoring system to detect a transverse crack in the shaft of the test rig.

Two theoretical analyses, global and local asymmetry crack models, have been utilized to identify characteristics of the system response that may be directly attributed to the presence of a transverse crack in the shaft of the test rig system.  A 2X harmonic component of the system response was shown to be the primary response characteristic resulting from the introduction of a crack. Once the unique characteristics of the system response were identified, these predicted indicators then served as target observations for the monitoring system.  The monitoring system, which was developed for seal face contact detection, provides signals from which useful information for crack diagnostics can be obtained.

Experiments were performed utilizing a modified test rig and a manufactured crack to verify the predicted behavior of the 2X harmonic component of the system response.  The theoretical analyses have been shown to provide accurate prediction of the qualitative behavior of the 2X harmonic component of the response of the cracked system.