Crack Detection of Propeller Shaft on board Marine Ship using Microphone Array

Vibration due to rotation of a shaft of a ship propeller may cause crack due to lack of proper maintenance. It is considered to be hazardous area to conduct a direct measurement on rotating shaft using accelerometer. In this paper, acoustic emission using linear microphone array is proposed to collect acoustical data emitted from the rotation of the shaft. In a semi-anechoic chamber, the proposed technique using single microphone may have detected a crack in propeller shaft by observing the peak of the main spectrum. In engine room on a ship with highly noisy background, we propose microphone co-linear array to increase microphone sensitivity. First, the normal shaft sound was recorded using single sensor, thereafter used as baseline. The cracks were intentionally introduced to the shaft with depth 0.25, 0.5, and 0.75 diameter of the shaft respectively. The sound mixture was separated using frequency domain independent component analysis (TFICA) and then, compared to the accelerometer. The results showed that the measurement accuracy was increased from one sensor to the array and comparable to the direct measurement. These results suggest that the proposed technique may be used as an easy-to-deploy vibration monitoring in a noisy and hazardous engine room.