Reliability Analysis Of Dependable Real-Time Multiple-Phase Systems

A DEpendable Real-time Multiple-phased system (DERMS) is defined as a system, which is subject to multiple, consecutive, non-overlapping phases of operation. During each phase it has to accomplish a specified task. Thus, the system configuration, failure criteria, and failure behavior can change from phase to phase. Many DERMS instances are deployed in various critical applications. Because of their deployment in critical applications, the reliability analysis of DERMS is an issue of primary relevance that has been widely investigated. Much work has been proposed either based on combinatorial models or on state space oriented models. Our research shows that two main problems can be found in the analysis methods proposed in the literature:1) For the BDD-based fault tree analysis of static DERMS, how to generate the system BDD efficiently is the most important thing. Our research work shows that the existing methods in the literature are too inefficient to be used for industrial DERMS instances, and 2) For the sake of a cost effective analytical solution, state space oriented methods necessarily need to introduce many simplifying modeling and analytical assumptions, which make them become inapplicable to real dynamic DERMS instances. This paper focuses on these two problems and produces some beautiful results.Variable ordering for static DERMS fault tree is critical to the BDD method. Several ordering schemes proposed in the literature have various deficiencies in applicability and performance. To attack the weak points of the state-of-the-art, this paper builds an ordering heuristic library based on a heuristic classification. It includes PDO ordering heuristic, combining ordering heuristic, simple ordering heuristic and revised simple ordering heuristic. A heuristic selection method based on branch-and-bound technique is also presented to avoid the intensive computation of some extremely bad ordering heuristics. The set of possible selection choices are 10 alternative heuristics, and the widely used ordering heuristic backward PDO has a 7/16 chance to become the best ordering heuristic from the set of 10 for the test set of 16 given DERMS and there is such an ordering heuristic backward PDO has more than 5/8 chance to become the best ordering heuristic from the set of 10, so the presented heuristic selection method is a very practical method. For the problem of system BDD generation of static DERMS fault tree, this paper starts from the PDO operation and PDO algorithm presented by Zhang, and improves the original algorithm to obtain a better algorithm, which can be applicable to much more DERMS instances and has better performance. The test data show that for a slightly complex static DERMS with a final system BDD with 155 nodes, the existed algorithm needs 2 minutes computation time and 358,575 nodes storage space, but our algorithm only needs 1.2 seconds computation time and 155 nodes storage space.For the problem of reliability analysis of single phase, this paper starts from the classic structure characteristics of dynamic DERMS and presents a two-phase analysis methodology, which firstly analyzes independent component quorums and then produces phase reliability from the quorum reliability results. All component quorums can be divided into three groups: share-repair quorums, self-repair quorums and no-repair quorums. Based on the MRGP-based analysis method for share-repair quorums proposed by the related work, this paper makes some improvements on the derivation and computation for the kernel matrices. The existed analysis methods for self-repair quorums proposed by the related work are based on Markov process, but this paper considers generally distributed repair activities and derives an efficient combinatorial formulation for their reliability analysis.For the problem of reliability analysis of system mission, this paper starts from branching matrix, which is used to bind all single phase results, and the assumption that memory is losable at phase boundaries, and then presents a general analysis formulation, and proposes two special solutions: analytical solution and numerical solution, according to different types of phase duration and intraphase stochastic processes. Equipped with our dynamic DERMS reliability analysis methods, the design scheme for a custom-tailor system can be verified quickly and the application scenario selection can be achieved for general purpose systems.With the help of the algorithms and analysis solutions presented by this paper, the reliability of many large-scale industrial DERMS can be efficiently analyzed.