Reliability and Dependability Modeling and Analysis of Dynamic Aspects in Complex Systems

Today's reliability methodologies and tools need to assess increasingly large, complex systems. Moreover, in order to adequately evaluate the system dependability it is necessary to take into the right consideration the system dynamics, which depends on the components' dynamics, on the inter-dependencies arising among such components (load-sharing, standby redundancy, interferences, etc) and on their reliability relationships, that can also be variable (phased-mission systems). Combinatorial techniques can be adopted in case the system's units are two-state (Boolean) and stochastically independent. Otherwise, it is requested to recur to lower level techniques and formalisms, such as: state space methods, or simulation. This paper analyzes the dependability of large, complex systems affected by dependent/dynamic behaviors. Starting from dynamic reliability block diagrams, a notation we developed by extending the reliability block diagrams, we detail how this modeling approach captures dynamic reliability behaviors. In order to demonstrate the effectiveness of such technique, we investigate some common/specific dynamic reliability/availability behaviors, providing the guidelines for their representation and evaluation.