Unavailability Analysis of Dynamic Systems of which the Configuration Changes with Time

A dynamic system has a state at any given time which can be represented by a point in an appropriate state space and it is much more difficult to estimate the reliability or availability than a static system. As the classic fault tree cannot be used to model the time requirements, dynamic fault tree methods have been developed for the analysis of dynamic systems. They are time-dependent fault trees, so they can capture the dynamic behaviors of the system failure mechanisms. There exist two types of dynamic fault trees to analyze various dynamic properties of the system failure mechanisms. One dynamic fault tree handles failure mechanisms composed of sequence-dependent events using dynamic gates and the other one handles failure mechanisms of which the system configuration changes with time using house event matrix. In this paper, the second dynamic failure mechanism is assessed using a reliability graph with general gates (RGGG) which is an extended reliability graph model and allows more intuitive modeling of target systems compared to the fault tree. In order for the RGGG method to analyze such dynamic failure mechanism, a novel concept of reliability matrix for the RGGG is introduced and Bayesian Networks are used to quantify the modeled RGGG. The proposed method provides much easier way to model dynamic systems and understand the actual structure of the system compared to the dynamic fault tree with house events