数值模拟在事故动态风险评估中的应用

Application of numerical simulation in dynamic risk assessment of accidents

突发水污染事故的动态风险评估对水质安全和社会稳定具有重要影响。而数值模拟可以显示突发事故后污染物的扩散和衰减过程,为可能发生且无基础样本数据的环境突发事故的动态风险评估提供因子量化赋值。建立了突发水污染事故的动态风险评估模型,以数值方法计算事故后污染物在水体中的运移特征,基于实时水文条件下事故后污染区域的演化规律和应急措施后的消减趋势等的数值模拟结果对风险因子进行量化赋值,结合层次分析法的风险度计算结果,运用模糊判定理论计算和评估风险类别。进一步以长江上游在急流条件下的医院细菌污水事故排放为应用对象,实例计算其风险值和风险级别,并讨论和分析了应急措施对降低事故后果的动态风险补偿幅度。模型计算结果符合实际。

This paper is aimed at introducing our research results on how to apply the numerical simulation method to the dynamic risk assessment of the accidents by taking risk assessments of an E. coli pollution accident with the flood in Yangtze River as a case study sample. As is known, it is of great significance to do the effective dynamic risk assessment of water pollution accidents in China for the purpose to keep the water environment safety and efficient water-pollution emergency control. But the reliable predictive assessment experience has to rely to a considerable extent on the information and data gained from the numerical simulation, for they can help to achieve a better quantification, especially when the investigation data and simi- larity experiments are not enough available due to the limited labora- tory conditions or computational technology inefficiency. It is for the above said reasons that in this paper we would like to develop a dy- namic risk assessment method for water pollution accidents based on the real time numerical simulation results. The proposed evaluation method can be applied together with the master logic diagram to identify the contributing events, the analytic hierarchy process for weight calculation and fuzzy clustering for risk grading. Besides, the flow model can be coupled with the topography generated based on the measured boundary and bathymetry data to study the dynamic characteristics of the fluid substance by the simulated flow velocity in comparison with the measured data to be found in the chosen areas. What is more, we have also compared the numerical simulation results of the migration of the pollutants and toxic chemicals in the accident spill scenarios with the emergency situations that are likely to take place in the reservoir. In addition, we have also simulated and illustrated the toxic chemicals under accidental spill scenarios specifically by coupling a water quality model with the hydrodynamic module based on the investigated hazards on the said river banks. And, finally, we have simulated and analyzed the decay process and recovery mechanism of the polluted water by adding artificial emergency accidents to the pollution area in hoping to pursue the pollution evolvement regularity in the reservoir so as to make what we have found for the analysis of the risk compensation probabilities. Thus, the results of our simulated method show that numerical simulation should be used as a kind of efficient methods for the dynamic risk assessment and the emergency control and management.