STRUCTURAL RELIABILITY OF A MARINE DIESEL ENGINE PROPULSION SHAFTING SYSTEM (PROBABILISTIC, ANALYSIS)

A method for estimating the reliability of the propulsion shafting system of a diesel ship is presented, involving: (a) probabilistic modeling of the diesel engine and the propeller torsional excitations; (b) determination of the statistical properties of the torsional vibratory stress amplitude at any point on the shaft; (c) analysis of first excursion and fatigue failure modes; and (d) estimation of each shafting segment failure probability. Examples using an existing propulsion shafting system are presented. It is shown that the requirement of a high value for the traditional safety factor does not always ensure that the system is safe. Significant criticals that cannot be identified by the traditional deterministic analysis are revealed when the probabilistic method is applied. Furthermore, the shafting segments most likely to fail are different from the segments with the higher mean stress as determined by the traditional deterministic analysis. The reliability based analysis is more realistic and provides a better measure of structural safety to the designer than the traditional deterministic analysis.