Reliability Analysis Method Of Phased-mission Systems Based On Irrelevancy Coverage Model

Phased-mission systems(PMS)and fault-tolerant systems are widely used in key parts of military and civilian systems,and related research of reliability analysis has become an important part of reliability engineering.In a phased-mission system,even if enough redundancy exists,an uncovered component fault may directly lead to the failure of the entire mission,and the reliability can be analyzed with traditional imperfect fault coverage model(IFCM).However,the analysis method based on IFCM only considers the coverage of faulty components.Even in the initial state,relevant components will become irrelevant due to the failures of other components,and uncovered failures of irrelevant components will cause the entire PMS to fail.Scholars have proposed the irrelevancy coverage model(ICM).In this model,both faulty components and irrelevant components will be covered.Therefore,reliability analysis using the ICM will avoid the system failure caused by uncovered failure of irrelevant components,thereby improving the reliability of the system,but the ICM is limited to the reliability analysis of general single-phased mission systems(SMS).In view of the limitations of the above model,this thesis adds the consideration of the coverage of irrelevant components on the basis of the phased-mission system and imperfect fault coverage model,and proposes a phased generalized multiple-valued decision diagram(GMDD)reliability analysis method for the reliability analysis of PMS based on ICM.The details are as follows:1)In a phased-mission system,due to the possibility of irrelevant components at each phase,the uncovered failure of irrelevant components will directly cause the entire mission to fail.By covering the irrelevant components in the PMS,the reliability of the system can be improved to a certain extent.Therefore,this thesis notes that,the coverage of irrelevant components is also important for PMS.By comparing the irrelevance of components in PMS and SMS,this thesis proposes two irrelevancy coverage strategies applicable to PMS,and gives the definition and derivation method of the minimal irrelevancy trigger(MIT)of components in PMS.2)This thesis provides the construction method of phased generalized multiple-valued decision diagram(GMDD).Reliability analysis of ICM based PMS can be effectively performed by constructing phased GMDD.First of all,the Boolean logic expression that leads to the failure of the mission is derived as the algebraic basis for subsequent analysis.Then this thesis proposes a phased sorting rule.According to the Boolean logic expression that caused the mission to fail,we follow the ordering rules to construct the GMDD.3)This thesis proposes an evaluation method of phased GMDD,and starts from qualitative and quantitative aspects.In qualitative analysis,pruning and simplification of the GMDD obtained from the above structure is achieved by defining a new phase algebra,and finally traversing to obtain the sum of disjoint product(SDP)of the phase failure and mission failure;in the quantitative analysis,the unreliability of the PMS fault tree is finally obtained by summing the probabilities of all SDP.Through experiments and analysis on PMS instances,it experimentally verifies that using the method in this paper can effectively perform reliability analysis of ICM based PMS,and also verifies that the reliability analysis of ICM based PMS can get lower unreliability than that based on IFCM.Finally,the variation rule of unreliability of the instance is analyzed under different parameter settings.