Physical Vulnerability Evaluation And Control Of Urban Metro Network System

As an important part of the urban public transport, urban metro network system is a complex public transportation system. Once operational accident occurs, it will cause operation delay or outage, stranded passengers can not be evacuated as soon as possible or even result in paralysis of the whole metro network, major equipment destruction, casualties and heavy economic losses. With more and more metro lines being put into operation, safety issues under conditions of network operation have aroused widespread attention of many researchers and practitioners. Metro accident statistics analysis shows that:due to equipment and facilities susceptible to interference, the degradation, failure and their propagation are the main causes of operational accident. Therefore, the study of urban metro network system physical vulnerability has great theoretical significance and application value to improve the metro safety. From the perspective of vulnerability research, the researcher first analyzes the formation mechanism of the metro physical vulnerability. Then, a scientific and rational method is used to identify, evaluate physical vulnerability. In the end, the researcher proposes targeted control methods and measures of metro physical vulnerability.(1) The researcher combs through many of the existing research literature, sums up the theories and methods of safety, risk and vulnerability studies, describes the vulnerability of the research direction and research status, points out the lack of vulnerability research on urban metro network system. On this basis, the researcher introduces the concept, physical configuration and operational characteristics of the urban metro network system, analyzes the urban metro network physical vulnerability connotation, characteristics and formation mechanism. Furthermore, the researcher sets up the physical vulnerability research levels, including network topology level, equipment and facilities level, and failure mode level, the failure mode is the visual consequences of excited physical vulnerability.(2) Based on the principle of complex network theory, network vulnerability measurement method and network model construction method are proposed, and signal system is employed as an example of empirical analysis. Then, the urban metro network system is divided into 31 functional modules, and the relationships with each other are identified. Pajek software is employed to build a physical network model. Based on the analysis of the basic topological characteristics, simulation strategy is proposed, the network vulnerability measurement method is used to study the physical vulnerability of urban metro network system and the key vulnerable regions are identified. The results show that:using complex network to research urban metro network system physical vulnerability is feasible; the two highest vulnerable subsystems are automatic train supervision system and vehicle system. In terms of the failure sequence, vulnerability descending order is degree sequence, betweenness sequence, and random sequence. The failure scale of vulnerability is in accordance with Pareto Law,20% of the important node failure will cause the loss of 80% of system functionality.(3) Different subsystems contain different equipment and facilities, some equipment and facilities are susceptible to interference, which make huge threat to metro safety. Therefore, it is necessary to identify and control these critical vulnerabilities. Based on the analysis of the operational characteristics of metro system, index system is established, including one thousand kilometers failure rate, ability to resist interference, functional importance, operational impact, safety hazard degree, and difficulty of failure detection. The vulnerable point evaluation model of urban metro network system is established based on grey correlation analysis and technique for order preference by similarity to ideal solution (TOPSIS). In this study, vehicle system is employed as an example to do empirical analysis. The research data are acquired through field research and expert questionnaire, and the fuzzy set theory is used to quantize these data, which provides a strong support to study the vehicle system. The results show that:grey correlation analysis and TOPSIS method is feasible. In vehicle system, the most vulnerable point is door system, following by train control and management system.(4) Based on the complex network of immune theory and principle of entropy, combining physical vulnerability hierarchical feature, an effective strategy of physical vulnerability control is proposed, which is controlling the running status of key equipment and facilities. Based on this control strategy, the researcher analyzes the evolution of running status of equipment and facilities, describes the analytical method of deterioration degree, builds a status evaluation model, and employs wheel set as an example for empirical analysis. Equipment and facilities status evaluation can provide important reference for setting the device status warning threshold to improve equipment maintenance effect, which has great theoretical significance and application value. On the basis of the summary the development process of maintenance mode, the researcher proposes a logical decision graph for the control of physical vulnerability in equipment and facilities maintenance. The results show that:the proposed control strategy in this study is scientific and reasonable, on the conditions of technically feasible and economically viable, preventive maintenance can greatly reduce the excitation probability of physical vulnerability.(5) A direct consequence of the physical vulnerability excitation is a wide variety of failure modes and their propagation, resulting in disabler within uncertainty range of equipment and facilities, therefore, from the perspective of fault pre-control to study physical vulnerability control is necessary. The research data are obtained by field research and expert questionnaire, and the fuzzy set theory is used to quantize these data. Failure mode, effects and criticality analysis (FMECA) method is employed to analysis failure modes of equipment and facilities, and the t influence diagram theory is employed to identify the key factors of failure modes, which provides a strong support for proposing the feasible and effective control measures. The results show that:bogie system failure mode is the most harmful damage to the wheel set, following by the shock absorber oil spill. The key factors of wheel set damage are imperfect maintenance schedule, lack of maintenance skill, lack of driving skill, temperature changes and harsh weather. In practice, by improving the maintenance schedule, personnel skills, and other measures to reduce the failure frequency can effectively reduce the physical vulnerability, which is in accordance with the actual situation of metro operation.