Safety Analysis Of RBC Handover Based On UML And STPA

As a core part of the high-speed railway, a High-speed Railway Train Control System (HRTCS) plays a key role in ensuring the safe operation and the operation efficiency of high-speed trains. Once safety problems of the HRTCS emerge, serious accidents will be caused, such as traffic disruptions and even train collisions. Therefore, it is significant to perform scientific and effective safety analysis on the HRTCS for ensuring the safe operation of the high-speed railway. However, with the integration of computer technology, communication technology and control technology, the functions and component interactions of the HRTCS are so complex that traditional hazard analysis methods are no longer suitable. System-Theoretic Process Analysis (STPA) is a new hazard analysis method based on Systems-Theoretic Accident Model and Process (STAMP), in which dysfunctional interactions among system components are the key factors causing hazards. Therefore, the STPA method is suitable for the safety analysis of complex systems. As the most important part of the STPA method, the hierarchical control structure model is generally depicted in natural language, which could be easily affected by personal expression ability so as to be ambiguous. This will bring a challenge to the system safety analysis.For resolving the modeling problems, in this thesis, the UML (Unified Modeling Language) with extensibility is utilized to improve the existing method of building the hierarchical control structure model in STPA. The main work is summarized as following:(1) Based on the study of relevant literatures, the domestic and international researches of hazard analysis methods are reviewed. Merits and demerits of different hazard analysis methods are analyzed and compared, and the direction of research on hazard analysis method for the HRTCS is discussed.(2) The UML profile oriented to the STPA hierarchical control structure model is designed, and the class diagram and relationships in UML are extended to depict the hierarchical control structure. In other words, with the purpose of providing a possible way to describe the hierarchical control structure, a new semi-formal modeling language based on UML for the STPA method is proposed.(3) The "RBC Handover" scenario is taken as a study case, in which the static structure and the dynamic behavior of the system in this scenario are depicted by the extended modeling method to build the hierarchical control structure model. The control structure is built by the extended class diagram, the process model is built by the OCL language, and the control algorithm is built by the state diagrams.(4) Combined with the hierarchical control structure in the scenario, the hazard analysis of RBC handover is performed with the optimized STPA. As a result, the system-level safety constraint is defined, the unsafe control actions of the system are analyzed layer by layer, and finally the hazard causal scenarios are identified.