| Phased-mission systems are systems undertaking the mission which involves multiple consecutive and non-overlapped phases.This work studies the k-out-of-n phased-mission systems where both the system structures and the phase success criteria are k-out-of-n.Such k-out-of-n phased-mission systems widely exist in many key fields such as aerospace,nuclear power plants,high-performance computing systems,and wireless sensor networks.Efficient and accurate analysis of reliability is critical for determining whether the system meets reliability requirements,determining the optimal design and operating mode,and weighing system parameters such as cost and reliability.Since the k-out-of-n phased-mission systems may have different mission requirements and reliability requirements in different mission phases,the structure of the system at each phase may be different;the system operating environment may also be different,making the system component failure behavior different at different phases;besides,there are statistical dependencies between component failure states across phases.These characteristics increase the difficulty of analyzing k-out-of-n phased-mission systems.The existing analysis methods have the problems of insufficient accuracy or low analysis efficiency,and thus are not suitable for reliability analysis of large critical systems.This thesis proposes an efficient multivalued decision diagram(MDD)-based reliability analysis method for k-out-of-n phased-mission systems.Firstly,an efficient reliability analysis process is proposed,generating MDD from the root node,from top to bottom.Secondly,the rules for adding non-sink node labels are established.The label of the child node is determined by the label of its parent node and the connected edge.Thirdly,according to the parent node label,the rules for adding child nodes for each edge of the parent node are established.A complete MDD is built applying the node generation rules.In particular,starting from the root node,from top to bottom,children nodes are added until the sink nodes are achieved.Fourthly,the proposed efficient MDD reliability analysis method is applied to the reliability analysis of the example systems;Finally,the correctness and efficiency of the proposed MDD method are verified by comparing with the fault tree-based MDD method.Through the reliability analysis of the example systems,the proposed MDD method is proved to be able to analyze the system where the components failure time can follow any arbitrary distribution.Comparing with the fault tree-based MDD method,the proposed method can analyze the reliability of large-scalek-out-of-n phased-mission systems more efficiently with high accuracy. |
