Research On System Safety Risk Analysis And Its Assessment Based On Failure

With the development of science and technology, the architecture of modern systems is more complex, the function of them is more powerful, the performance of them is higher, and at the same time, requirements for their safety is becoming more stringent. However, the existed safety risk assessment methodologies can not assess the safety risk of the system efficiently, conveniently, accurately and comprehensively. These methodologies can not guide people to identify the weak part of the system and propose the scientific control measures. The theories and methodologies of safety risk assessment need to be improved. Beginning from the factors that affect system safety risk, the thesis studied the concept and measurement method of system risk, system safety risk status assessment techniques, analysis of component failures on system safety risk, and uncertainties assessment method of safety risk. It is structured as follows:(1) The concept of system risk and its metricsStudying the concept of system risk and its metrics is the primary task of the system safety risk assessment. In this part, the thesis discussed the relationship between component failure and safety risk, the risk spread from component failure, the measurement methods of static and dynamic risk, and then, the framework and content of system risk assessment was presented based on these works.(2) The assessment methods of system safety risk statesIn this part, the system state was described firstly, and then the system states were divided into low/media/high state sets according to risk, a detailed division of the two-state system, multi-states system and process control system were discussed for the different characteristics of the system. Secondly, the calculation technique for the living risk, confidence intervals of living risk and the probability of system unacceptable risk were given. On the other hand, a model of high-risk state time of arrival from living system state was proposed. Both the time of high-risk state arriving to unacceptability and the time of arriving to high-risk state sets can be gained according to this model.(3) The analysis methods on impact of component failure on system safety riskResearch on impact of component failure on system safety risk can help us identify weak parts and control system risk, so it is an important work in safety risk assessment. This part includes risk importance analysis, identification of risk critical state and key components, diagnostic analysis. In the areas of these problems, impact of component failure in two-state system, multi-states system and process control system were discussed.(4) The assessment methods of safety risk uncertaintyTaking into account the high-safety requirements and uncertainties of system, quantitative method of uncertainty with probability was discussed. The uncertainty affecting system safety risk assessment results were divided into aleatory uncertainty and epistemic uncertainty, and safety risk margins containing uncertainty were introduced. Combining with the example of the system high-risk state probability and the system subjecting to random shocks, we obtained the uncertainty results of the system safety risk assessment with QMU method that can be used for risk decision-making.Not only more intuitive and comprehensive system risk information can be got by the system safety risk analysis and assessment techniques presented in thesis, but also the impact of component failure on the system safety can be obtained, and the uncertainty of the risk assessment results can be fully considered. All these information can be used to risk decision-making and control, and the methodologies presented have more theoretical reference value and application value.