A Case Study of Abnormal Noise and Ultra-High Frequency Vibration Characteristics in the Propulsion Shaft Bearing of the Naval Vessel

In this paper, abnormal noise and vibration occurring in the propulsion shaft system of a naval ship were measured, and the methods and procedures for the cause analysis based on the results were discussed. To investigate the cause, in this study, accelerometers were attached to the bearings supporting the shaft to measure the vibrations. The analysis revealed that the abnormal vibration on the port side was most strongly identified at the stern tube bearing, and it was confirmed that these vibrations exhibited ultra-high frequency(20,000 Hz ~) characteristics. Additionally, through DEMON analysis, it was confirmed that this characteristic appeared in synchronization with rotation of the shaft. In this paper, it is assumed that the cause of theses ultra-high frequency vibration has been generated by stress waves resulting from processes such as grinding, scratching and impact. Furthermore, directions for inspection of the stern tube bearing are proposed.