Reliability and Availability Analysis of Dependent-Dynamic Systems with DRBD

Reliability/availability evaluation is an important, often indispensable, step in de- signing and analyzing (critical) systems, whose importance is constantly growing. When the complexity of a system is high, dynamic effects can arise or become signif- icant. The system might be affected by dependent, cascade, on-demand and/or com- mon 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 poli- cies but, since dynamic behaviors usually do not satisfy the stochastic independence assumption, notations such as reliability block diagrams (RBD), fault trees (FT) or reliability graphs (RG) become approximated/simplified techniques, unable to capture dynamic-dependent behaviors. To overcome such problem we developed a new formalism derived from RBD: the dynamic RBD (DRBD). In this paper we explain how the DRBD 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 prac- tical 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 DRBD approach with other methodologies, demonstrating its effectiveness