Research On Key Technologies Of Reliability Analysis Of Dynamic Systems

With the development of science and technology, especially computer technology, various control and fault tolerate techniques are widely applied, and the structure is becoming more and more complex for many systems. Since the components among system are interrelated and interactional, the reliability behaves some characteristics, such as completely, sequence, interdependence, nonmonotonicity, multi-state, etc, which make reliability analysis face the challenge. Three typical characteristics of dynamic system are complexity, sequence and interdependence. This thesis will consider these three characteristics and research the reliability analysis models of dynamic system from four aspects, i.e. modular analysis, failure mode of dynamic system, imperfect coverage model, and reliability simulation.The main contents and conclusions of the thesis are outlined as follows:1. Research on the technology of reliability analysis based on modularizationAn identification method of independent module based on kinship dependency relation is proposed. This method converts DFT to dependent tree, which only contains the dependency relations among the events, and removes the logic meaning of each logic gate. Through the amelioration of depth-first search algorithm, this method can be applied to DFT with repeated events. Through attaching ancestor property and dependency property for each node, this method is appropriate to deal with the interdependent relation among the events. This method identifies independent modules through the ancestor property and dependency property, and has no relation with the dependent basic events, repeated events or dynamic logic gates, so that it can be applied to dynamic fault tree with dependent basic events and repeated events. Both the practical case and simulation indicate that this method can be applied to DFT with dependent basic events and repeated events.An analysis method of fault tree is proposed based on isomorphic object. Through identifying the isomorphic object, decomposes the fault tree into various groups of independent modules. Since each group of independent module is only computed once, this method can greatly reduce the computing cost and improve the analysis efficiency for those systems with structural characteristics.This research makes existing modular analysis methods to be more easily applied to dynamic system.2. Research on system failure mode based on extended cut sequenceAn extended cut sequence (ECS) model to analyze the failure behaviors of dynamic system qualitatively and quantitatively is proposed. The concept of ECS is firstly proposed, which is the set of basic events under some temporal constraints. ECS enlarges the extension and the expressive capabilities, and does not require the basic events in a particular order, not even temporal constraints. Generative algorithm and disjoint algorithm of minimal ECS set are given, and then standard ECS set is transformed from disjoint ECS. Then, the test of conflict, the refinement of temporal restriction set and the topology sort of basic event set are carried out to quantitatively analyze each standard ECS. Finally the system reliability parameters are settled through synthetic solving. The experiment on OBC system shows that this method can decrease the time cost from 14.42s to 5.82s compared to aother recent model.The reliability analysis model based on ECS can locate the failure modes of dynamic system and solve the problem how to compute the unreliability of dynamic systems using these failure modes.3. Research on the reliability analysis based on imperfect coverage modelA modular solving method for imperfect coverage model (IPCM) is proposed. This method expands the table-based algorithm. Based on ELC (Elementary Level Coverage) model and FLC (Fault Level Coverage) model, each logic gate is analyzed, and the algorithm and formula is given. This method discards the recursive call in the original algorithm, and uses the recursive function which is supported in almost all the modern programming techniques.A solving method based on ECS for IPCM is proposed. This method expands SEA (Simple & Efficient Algorithm) algorithm. Based on the conception of disjoint ECS set, the IPCM failures is separated into two terms to compute the system reliability. This method can use the model of ECS to compute the second term, by slightly alter the reliability parameters of each component.This research solves the problem of IPCM reliability analysis for dynamic system to a certain degree.4. Research on the reliability simulation model of repairable system under generalized renewal processIn order to accurately acquire the sampling time of residual life, an auto adjust approximate sampling (AAAS) method is proposed for general distribution. Based on the feature of the distribution function, AAAS can automatically adjust the fitting parameter to quickly and accurately sample the simulation time. The experiment indicates that this method has higher accuracy than another recent method under the same number of time segments.With respect to the reliability analysis of repairable system, a reliability simulation model under generalized renewal process is proposed. This model samples the next simulation time by the method of AAAS, and uses the repair effective parameter to represent the state after repair. Then ECS theory is used to give the repair strategy. Finally based on the above considerations, from the aspect of successful accomplishing the task, the logic relationships are acquired by means of event lists. According to the identification of system state, the result of simulation provides the entire history of the mission and statistics of reliability parameters.This research make the simulation reflect the truer picture of the run process of the system.In a conclusion, this thesis carries out the research on the technology of reliability analysis with respect to the characteristics of dynamic system, such as complexity, sequence, interdependency, etc. Some researchs solve the unsolved problem. Some researches expand the fundamental theory based on the immature method, and improve the expression capabilities and solving efficiency. Some researches improve the existing technologies and enlarge the applicability. Some researches are carried out from the aspect which received less attention.