1.1 Introduction Condition Monitoring is a technique of monitoring the operating characteristics of plants, equipment or systems in such a way that changes in the monitored characteristics can be used to predict the need for maintenance before a serious deterioration or breakdown occurs. It aims at detecting condition leading to catastrophic breakdown and loss of service, reducing maintenance overhauls, fine tuning of operating equipment, increasing production and operating efficiency, minimizing replacement parts, inventory. Condition Monitoring is very much essential for floating vessels like dredgers, where machinery like propulsion drive, dredge pump drive, jet pump drive etc. are subjected to high vibration levels during the process of dredging. The effective performance and the operational efficiency of a dredger depend upon the periodical maintenance of the dredging equipment and other components functioning in underwater and also the overboard fittings. The maintenance of a dredger and its dredging equipment is highly expensive. By deferring or neglecting the maintenance function, the dredging operations may lead to be ineffective and the breakdown costs become uncontrollable. In the present work, Condition Monitoring using vibration analysis has been taken up on two trailing suction hopper dredgers. These two dredgers differ in the power drive units for propulsion and dredging machinery. By implementing vibration monitoring to various key points of both the port and starboard sides on various systems like propeller shaft, propulsion gear box , engine shaft, shaft generator on propulsion drive; dredge pump shaft, dredge pump gear box, dredge pump motor shaft on dredge pump drive; jet pump shaft and jet pump motor shaft on jet pump drive; vibration parameters i.e. Root Mean Square (RMS) velocity and vibration echo levels are measured and probable faults are detected and suggestions to rectify the defects are made to improve the performance of the dredgers. In the present work, the theoretical investigation has been carried out to monitor the vibration condition of propeller, dredge pump and jet pump shafts. The natural frequencies for the first five modes of these shafts are computed by Finite Element Analysis using Inverse Iteration Technique and Jacobi's method. The frequencies are also verified using classical Rayleigh - Ritz method. For 1
an optimum rotational speed, the displacement and acceleration are calculated for each natural frequency. A comparison has been made between theoretical and measured values. Frequency spectra for propeller shaft, dredge pump shaft and Jet pump shafts have been obtained using data collector. The vibration parameters have been measured by conducting experimental investigation onboard the dredgers using sophisticated instruments i.e. Data Collector, Integrating Vibration Meter and Bearing Echo Meter. The data has been obtained in the four quarters, each of duration three months in a year. Based on vibration parameters, various plots like overall trend plots for each point, average trend plots, exception ratio plots for each system and the whole drive have been obtained using a software, developed in C ++
language. From these plots, diagnostic analysis has
been performed for suggesting probable causes of failure of each machine in each quarter and remedial measures have been suggested in the succeeding quarters of the year for improving the performance of dredgers. Finally, a computer system has been suggested for on line monitoring of the systems onboard the dredgers to increase the efficiency of the dredgers.
1.2.1. Introduction to Condition Monitoring Condition Monitoring has only recently come to the forefront of Maintenance Engineering as a further tool in the ongoing effort to maintain high levels of plant availability. Condition Monitoring, in the opinion of Mcmahon, is the technique of monitoring the operating characteristics of...