Ship propulsion system health monitoring based on safety control functions

The ship propulsion system safety is not only a function of many environmental and operation factors, but also it is dynamic and complex. There are strong dependency relationships between the safety factors. The paper proposed a new approach that is applied to the evaluation of a safety function, a risk function and other safety characteristics of ship propulsion composed of a number of subsystems having an essential influence on the ship safety. First of all a basic safety structure of a multi-state system of the electric propulsion components with degrading safety states was defined. Further, a fuzzy analytical network process (FANP) for the considered system operation modeling was applied. This approach allows decision makers to evaluate risk factors using linguistic terms such as certain, very high, high, slightly high, medium, slightly low, low, very low or none rather than precise numerical values, allows them to express their opinions independently, and also provides algorithms to aggregate the assessments of multiple ship propulsion risk factors. A case study is investigated using the fuzzy logic package for Mathematica to illustrate its applications in risk assessment. It is shown that the fuzzy logic approach offers a flexible, practical and effective way of modeling risks assessment.