Forensic Investigation on the Propulsion Train System for Vibration Induced Phenomenon Onboard a Naval Vessel Using Fast Fourier Transform

Abstract

Vibration is a phenomenon that produces sound waves. For a naval vessel reducing the acoustic signature was vital in order for her to fulfill her role as an effective weapon platform because sound waves can reveal the vessel’s position to enemy warship especially submarines which in turn will deploy acoustic seeking torpedoes to destroy the vessel. The research was to investigate the source of excessive vibration onboard a naval vessel. This abnormally was probably caused by the major repair on the vessel during the scheduled maintenance. Data were taken at various locations in the machinery room among them were at the propeller shaft, main bearing, gear box, plummer block, main engine and auxiliary engines using an accelerometer and SKF MICROLOG analyzer. All together thirty-eight points were taken. The arrival of advanced signal processing tools such as MATLAB greatly change the sphere of development of vibration study. The spectral analysis, time synchronous signal averaging, high frequency envelop analysis and time-frequency analysis can be analyzed by using MATLAB software. The time domain data were converted to frequency domain using Fast Fourier Transform (FFT). The frequency data was analyzed for each item of the propulsion train system and compared against the Vibration Criteria Chart from classification society. It was found that the propeller and propeller shaft were having excessive reading beyond the allowable limits. It was recommended that the propeller be balanced accordingly and the propeller shaft to be straightened and realigned.