Active Detection of Small Imperfections in Structures With Cyclic Symmetry

Abstract

Structures possessing cyclic symmetry such as turbine bladed disks, ultrasonic motors, and toothed gear wheels can experience elevated vibration levels when small deviations from circumferential periodicity exist. Detection of these perturbations via classical system identification approaches is time-consuming, indirect, and exhibits low sensitivity to defects, and is affected by measurement noise. The present work utilizes low-level forces that automatically lock onto a weighted rotating projection of the system modes at resonance frequency to enhance the detectability of small structural imperfections. The spatial localization of defects is exploited to identify multiple, localized, isolated defects’ locations. The defects’ severities are estimated based on the deviation from the circular structure's analytical mode shapes. The fast and enhanced precision of defect identification is obtained by employing the modal-filtered autoresonance technique. To validate the presented method, an experimental system consisting of a ring of coupled Helmholtz acoustic resonators was developed. Experimental results show good agreement with numerical simulations, verifying the method's capabilities to identify the location and severity of multiple defects. Thus, the implementation of the suggested method provides fast and precise structural health monitoring of cyclic-symmetric systems.

Automatic traveling wave excitation of structures with imperfect cyclic symmetry

“…( 6) are no longer arbitrary, and their spatial arrangement is fixed. Furthermore, the doublet mode is split, and their respective natural frequencies are no longer identical [41], although close.…”

“…The entire experimental system is presented in Figure 12 (b). As shown in [41], considering a ring of N HRs with uniform necks and cavities, the n th equation will take the form of:…”