Importance Measure Method for Dynamic Fault Tree Based on Isomorphic Node

In order to enhance the measure efficiency in the research field of importance measure for dynamic fault tree which contains some structural information, a new method using this information is presented. By means of creating an object for every node, identifying the isomorphic nodes and computing only once for the same kind of isomorphic nodes, this method reduces the number of states and the computation time. This method also introduces the idea of perturbation and extends the BI importance factor, then gives a concept of relative importance factor which is obtained according to the type of independent module and has no relation with the dependency within the independent module. The importance factor can be computed by the combination of the relative importance factors. Finally this method is applied on a real high reliability computer system. The analysis shows that this method can provide a credible importance measure and greatly reduce the time expense if the system structure has some replicate components or backups.