Simulation approach for modeling of dynamic reliability using time dependent acyclic graph (original) (raw)
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Dependability evaluation is an important, often indispensable, step in design and analyze (critical) systems, acquiring importance with the systems complexity growth. When the complexity of a system is high and/or increases, for example automizing or expanding some parts, dynamic effects, not present or manifested before, could arise or become significant in terms of reliability/availability. The system could be affected by common cause failures, the system components could interfere each other or could become inter/sequencedependent, effects due to load sharing arise and therefore should be considered, and so on. Moreover could be interesting to evaluate redundancy and maintenance policies. In those cases it is not possible to recur to notations as reliability block diagrams (RBD), fault trees (FT) or reliability graphs (RG) to represent the system, since the statistical independence assumption is not satisfied. Also more enhanced formalisms as dynamic FT (DFT) could not result adequate to the objective. To overcome those problems we developed a new formalism derived from RBD: the dynamic RBD (DRBD). In this paper we explain how to use the DRBD notation in system modeling and analysis, coming inside a methodology that, starting from the system structure, drives to the overall system availability evaluation following modeling and analysis phases. To do this we use an example drawn from literature, consisting of a multiprocessor distributed computing system. By this we also compare our approach with the DFT one.