EVENT-TREE ANALYSIS BY FUZZY PROBABILITY

A method is explained for dealing with event-tree analysis under uncertainty. In conventional event-tree analysis, probabilities and consequences are treated as exact values. In many engineering applications, however, it is difficult to evaluate the probabilities and consequences from past experience, because of dynamic environments of systems, and especially because there are situations where past experience does not exist. Fuzzy-set logic is used to account for imprecision and uncertainty in data while employing event-tree analysis. The fuzzy event-tree logic allows the use of verbal statements for the probabilities and consequences; such as very high, moderate, and low probability. The technique enables us to analyze the qualitative evaluation of event tree to gain the quantitative results. The application of fuzzy event-trees is further demonstrated by using a set of event-trees for an electric power protection system to assess the viability of the method in complex situations. Such analysis can not be made by hand calculations due to complexity of the trees. Hence a computer algorithm has to be developed.