Reliability and availability analysis of dependent–dynamic systems with DRBDs

Reliability/availability evaluation is an important, often indispensable, step in designing and analyzing (critical) systems, whose importance is constantly growing. When the complexity of a system is high, dynamic effects can arise or become significant. The system might be affected by dependent, cascade, on-demand and/or common cause failures, its units could interfere (load sharing, inter/sequence-dependency), and so on. It is also of great interest to evaluate redundancy and maintenance policies but, since dynamic behaviors usually do not satisfy the stochastic independence assumption, notations such as reliability block diagrams (RBDs), fault trees (FTs) or reliability graphs (RGs) become approximated/simplified techniques, unable to capture dynamic–dependent behaviors. To overcome such problem we developed a new formalism derived from RBDs: the dynamic RBDs (DRBDs). In this paper we explain how the DRBDs notation is able to adequately model and therefore analyze dynamic–dependent behaviors and complex systems. Particular emphasis is given to the modeling and the analysis phases, from both the theoretical and the practical point of views. Several case studies of dynamic–dependent systems, selected from literature and related to different application fields, are proposed. In this way we also compare the DRBDs approach with other methodologies, demonstrating its effectiveness.