| Urban water distribution system faces many kinds of water pollution risks.Once the water contamination was detected qualitatively,in order to provide warning information about the degree of pollution and the emergency solution,the quantitative evaluation of contaminant concentration is particularly important.It is of great significance to implement pollution tracing and source tracking,improve rapid response ability and ensure the safety of water distribution system.The online monitoring indicator of water distribution system is difficult to increase infinitely and the abundant information contained in the online monitoring data is not yet fully excavated.Aiming to these,online quantitative analysis methods of accidental contaminant in urban water distribution system are studied.In this paper,a technical scheme for the analysis of contaminant concentration by the fusion of multi water quality online monitoring parameters is proposed.The correlative response relationship between online monitoring indicators of water quality and different contaminants and data fusion method of multi water quality indicators are discussed,which provides new technical support for emergency monitoring and emergency disposal of sudden pollution incident in water distribution system.The main contents and innovative points are summarized as follows:(1)By studying relative sensor response to contaminant with different contaminant concentration and sensor array,the phenomenon that different contaminations may cause different correlative responses of sensors and the degree of responses is related to the concentration of contamination injected is discussed.The concept of relative responding value was introduced in order to calculate the differences between water quality parameters and their baselines.This type of phenomenon can be used for online quantitative analysis for a known contamination in water distribution system.Before that,the feasibility analysis of the proposed method is conducted by using off-line experimental data.(2)Information contained in a single water quality indicator is limited,and information contained in multi water quality indicators should not be simply added.Therefore,the data fusion method of multi water quality indicators to deduce contaminant concentration is studied.In this paper,the online quantitative evaluation method of contaminant concentration based on D-S evidence fusion has been proposed to deal with the malposition and angulation in online monitoring data of water quality parameters.According to the characteristics of online water quality data,the basic probability assignment function of D-S evidence theory has been designed,and the similarity coefficient between water quality parameters are utilized as basis of evidence conflict management.Take the online experimental data of potassium ferricyanide as an example,this method can combine multi-dimensional water quality parameters and effectively analyze the concentration of potassium ferricyanide not less than 2.5mg/L.(3)Considering that contaminant samples with lower concentrations leads that the relative response of some water quality parameters is not obvious and the amount of training samples may not increase too many in emergency monitoring,the online quantitative evaluation method of contaminant concentration based on least square support vector machine(LS-SVM)regression model has been presented.Parameter optimization has been carried out by four different optimization methods in the process of modeling.The results imply that the regression model based on LS-SVM has better generalization ability and make up for the lack in the quantitative analysis of lower contaminant concentration.Meanwhile,the results show the validity of the proposed approach in concentration evaluation for potassium ferricyanid more than 0.5mg/L in water distribution system.(4)The robustness of two algorithms of quantitative evaluation has been analyzed with small disturbance and disturbance causing the conflict of evidence respectively.Combining with experiment and simulation,the method based on D-S evidence theory shows better robustness when disturbance cause the conflict of evidence.In the condition of small disturbance,the stability of the two algorithms depends on the type of the water quality parameter.In addition,the boundary problem in quantitative evaluation algorithm of contamination concentration has been analyzed.Two feasible methods have been put forward to solve the boundary problem.The online quantitative evaluation method of contamination concentration proposed in this paper provides a technical scheme without secondary pollution and implements data fusion between multi water quality parameters.It can be applied to water quality early warning system and emergency monitoring system,and has potential application value to ensure the safety of urban water distribution system. |
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