A calculation method for water quality risk and water supply reliability of urban water supply networks considering the negative pressure effect after earthquake

Abstract

The present invention relates to a calculation method for water quality risk and water supply reliability of urban water supply networks considering the post-earthquake negative pressure effect, belonging to the field of post-disaster water quality safety assessment of urban water supply networks. The present invention includes the steps of: calculating the leakage orifice area of pipelines under the daily operation scenario; generating earthquake damage scenarios of pipelines in the water supply network under earthquake action by Monte Carlo simulation sampling; determining the scenario of pollutant intrusion into the water supply network after the earthquake; establishing a pipeline network model for the pollutant intrusion scenario; calculating the average water quality risk of nodes; calculating the water supply reliability of the pipeline network; calculating the average value of the average water quality risk of nodes; calculating the average value of the reliability of the pipeline network. Based on the negative pressure scenario of urban water supply networks under earthquake damage, the present invention calculates the water quality risk and water supply reliability of the pipeline network through the pollution intrusion scenario, which is of great significance for guiding the post-earthquake water quality early warning and response strategies of urban water supply networks, as well as the seismic upgrade transformation and post-earthquake emergency repair measures of the pipeline network.

Description

Technical Field

[0001] The present invention relates to a method for calculating water quality risk and water supply reliability of urban water supply pipe networks considering the post-earthquake negative pressure effect, and belongs to the field of post-disaster water quality safety evaluation of urban water supply pipe networks. Background Technique

[0002] Urban water supply pipe networks are the infrastructure of lifeline system engineering and are crucial for ensuring the normal life of residents, maintaining the normal production of factories, and sustaining the normal operation of society. Historical earthquake damage records show that the occurrence of earthquake disasters not only causes physical damage to the pipelines of urban water supply pipe networks, but also causes varying degrees of pollution to the water quality of the pipe networks. Earthquakes not only damage water supply pipelines and cause a large amount of water leakage, but also damage the urban drainage system, resulting in the possibility that urban water supply pipe networks may be in a sewage environment after an earthquake. The large amount of water leakage caused by multiple pipeline damages in the pipe network will lead to continuous low pressure in local areas of the pipe network. When the internal water pressure in these areas of the pipe network is lower than the water and soil environment pressure around the pipe network or lower than the atmospheric pressure, it is called the "negative pressure" phenomenon. When negative pressure appears in the pipe network, pollutants in the surrounding environment will enter the pipe network under the action of the pressure gradient, causing water quality pollution and posing a serious threat to water supply safety. Therefore, calculating the water quality risk and water supply reliability of urban water supply pipe networks under the post-earthquake negative pressure scenario is of great significance for doing a good job in the disaster risk management of urban water supply pipe networks and guiding the post-earthquake water quality early warning and response measures of urban water supply pipe networks.

[0003] Therefore, it is necessary to establish a method for calculating the water quality risk and water supply reliability of urban water supply pipe networks considering the post-earthquake negative pressure effect to overcome the above problems. Summary of the Invention

[0004] In view of the above problems, the present invention provides a method for calculating the water quality risk and water supply reliability of urban water supply pipe networks considering the post-earthquake negative pressure effect, and the specific steps are as follows.

[0005] Step 1, determine the leakage orifice area of the pipeline under the daily operation scenario. Under the daily operation condition, a certain amount of water leakage is caused due to pipeline aging. According to the leakage water volume of the pipe network under the daily operation scenario and the principle of uniform distribution of the total leakage water volume of the pipe network along the pipe length, calculate the leakage water volume of the pipeline; in the hydraulic model of the pipe network, apply the pipeline leakage water volume to the adjacent nodes of the pipeline, and simulate the leakage water volume through the leakage orifice area of the node diffuser model. When the ratio of the total leakage water volume of the pipe network is l%, the main part of the node leakage orifice area is divided into the following two steps:

[0006] Step 1.1, determine the daily leakage water volume Q of the node L,i . According to the principle of uniform distribution of the pipe network leakage water volume along the pipe length, calculate the node leakage water volume Q of each user node under the specified pipe network leakage rate l% L,i . Its expression is:

[0007]

[0008] Where: Q L,i is the daily leakage water volume of node i; Q T is the total water supply of the pipe network; L a is the length of the upstream pipe segment a of node i; L b is the length of the downstream pipe segment b of node i; n is the total number of pipe segments in the pipe network; L j is the length of pipe j;

[0009] Step 1.2, determine the daily leakage orifice area A 0,i . Based on the orifice flow equation, according to the daily leakage water volume Q L,i of the user node, calculate the daily leakage orifice area A 0,i of the user node. The calculation formula is as follows:

[0010]

[0011] Where: A 0,i is the leakage orifice area of node i at the leakage rate of l%; μ is the orifice flow coefficient, and its value range is 0.6 - 0.9; g is the acceleration due to gravity; H i is the water head at user node i; Q L,i is the daily leakage water volume of node i.

[0012] Step 2, use Monte Carlo simulation sampling to generate the seismic damage scenarios of pipelines in the pipe network under earthquake action. According to the seismic failure probability of pipelines, use the Monte Carlo simulation method to randomly sample and generate the post-earthquake states of pipelines {intact / leaking / disconnected}, and calculate the leakage orifice areas A L,i of the disconnection points and leakage points generated by the seismic damage of pipelines;

[0013] Step 3, conduct hydraulic simulation of the pipe network under the post-earthquake damage scenario. According to the scenario of multiple pipeline damage points generated under earthquake action, add the leakage water volume models of disconnection points and leakage points to the original pipe network model to establish a post-earthquake hydraulic model, and simulate the post-earthquake node water supply and pressure states of the pipe network under the scenario of a large amount of water leakage from multiple pipelines in the pipe network at the same time. Post-earthquake low-pressure or negative-pressure nodes generally appear in areas with relatively large elevation or areas with serious water leakage.

[0014] Step 4, determine the scenario of post-earthquake pollutant intrusion into the pipe network. Based on the low pressure or negative pressure of nodes in the pipe network and the sewage water head and concentration of the soil and water environment where the pipelines are located, determine the location, pollutant intrusion volume, and pollutant concentration of pollutant intrusion into the pipe network. There are mainly the following 4 steps:

[0015] Step 4.1, Set the sewage head and concentration around the nodes of the pipe network model. Considering the deterministic scenario or the uncertainty scenario, select one of the following methods to set the groundwater head and sewage concentration at each node. The nodes include user nodes, disconnection points and leakage points caused by earthquake damage:

[0016] ① The groundwater head and sewage concentration in the environment at the nodes of the pipe network model adopt a unified fixed value, that is, the groundwater heads at different nodes relative to the elevation h of the nodes of the pipe network model i,0 are all set to the same value, and the groundwater sewage concentrations c at different nodes i,0 are all set to the same value;

[0017] ② The groundwater head in the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater heads at different nodes relative to the elevation h of the nodes of the pipe network model i,0 are all set to the same value, and the groundwater sewage concentration is a random value. Set the groundwater concentration range as c1~c2, and obtain values within the range through the Monte Carlo simulation method to randomly determine the sewage concentration c of each node of the pipe network model i,0 ;

[0018] ③ The groundwater sewage concentration in the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater sewage concentrations c at different nodes i,0 are all set to the same value, and the groundwater head is a random value. Set the groundwater head relative to the elevation h of the nodes of the pipe network model as h1~h2, and obtain values within the range through the Monte Carlo simulation method to randomly determine the relative groundwater head h of the environment of each node of the pipe network model i,0 ;

[0019] ④ The groundwater head and sewage concentration in the environment at the nodes of the pipe network model are both random values. Set the groundwater head relative to the elevation h of the nodes of the pipe network model as h1~h2, set the groundwater concentration range as c1~c2, and obtain values within the range through the Monte Carlo simulation method to randomly determine the relative groundwater head h of the environment of each node of the pipe network model i,0 and the sewage concentration c of the node i,0 .

[0020] Step 4.2, Determine the pollutant intrusion location. According to the groundwater head h0 of the nodes of the pipe network model in Step 4.1 and the pipe network hydraulic simulation results under the post-earthquake damage scenario in Step 3, identify the nodes (which may exist in the user nodes of the pipe network model and the disconnection and leakage nodes caused by earthquake damage) where the node pressure in the simulation results at different post-earthquake times is lower than the groundwater head h0 in the environment. These nodes are the pollutant intrusion nodes.

[0021] Step 4.3, Calculate the pollutant intrusion amount. At each moment, the amount of sewage entering the pipe network from the intrusion nodes, according to the daily leakage area A of the pollutant intrusion nodes0,i Calculate, or calculate according to the leakage area A of the disconnected and leaking nodes caused by the earthquake L,i The calculation is carried out as follows:

[0022]

[0023] In the formula: V i,t is the sewage volume entering the node i of the pipe network model at time t; μ is the orifice flow coefficient, and the value range is 0.6 to 0.9; A i is the leakage area of node i. For the daily leakage A i = A 0,i , which is determined by step 1. For the disconnected and leaking nodes caused by earthquake damage, A i = A L,i , which is determined by step 2; g is the acceleration of gravity; h i,0 is the relative groundwater head at user node i, which is determined by step 4.1; h i,t is the node pressure of user node i at time t, which is obtained from step 3; T is the time step of the pipe network model simulation, which is the simulation time step in the model of step 3;

[0024] Step 4.4, calculate the concentration of pollutants after entering the node. The specific calculation expression is as follows:

[0025]

[0026] In the formula: c i,t is the pollutant concentration of node i of the pipe network model at time t, c i,0 is the sewage concentration of the groundwater in the environment at node i, which is determined by step 4.1, V i,t is the sewage volume entering node i at time t, which is determined by step 4.3, q i,t is the pipe network water volume passing through node i in the pipe network at time t, which is calculated by the model of step 3;

[0027] Step 5, establish a pipe network hydraulic and water quality analysis model for the pollutant intrusion scenario. Adopt the post-earthquake pipe network hydraulic model established in step 3, write the pollutant intrusion information calculated in steps 4.3 and 4.4 into the model to establish a post-earthquake pipe network hydraulic and water quality model, and through hydraulic and water quality simulation, simulate the attenuation and diffusion of pollutants in the pipe network, and calculate and obtain the hydraulic and water quality results of each node;

[0028] Step 6, calculation of the water quality risk index R i of the pipe network model node. Based on the water quality threshold index (minimum limit of residual chlorine concentration) and pollutant limit index, according to the model analysis results of step 5, calculate the water quality risk index R i,t of each user node at time t, and calculate the water quality risk index R of the node during the entire evaluation periodi :

[0029]

[0030]

[0031] Where: R i is the water quality risk index of user node i in the pipe network during the entire evaluation period; t0 and t E are the start time of the earthquake event and the end time of the water quality assessment respectively, determined by the post-earthquake pipe network hydraulic model in step 3; R i,t is the water quality risk index of user node i in the pipe network at time t; q i (t) is the water quality of node i at time t, calculated in step 5, q b is the water quality threshold; c i,t is the pollutant concentration of node i at time t, calculated in step 5, c b is the pollutant limit;

[0032] Step 7, calculation of the water supply reliability of the pipe network. A large amount of water leakage caused by earthquake damage will lead to a decrease in the water supply capacity of the pipe network and the invasion of pollutants, reducing the reliability of node water supply. Taking the flow rate and water quality of user nodes as indicators, calculate the overall water supply reliability of user nodes and the pipe network. Specifically, there are the following two steps:

[0033] Step 7.1, calculation of the post-earthquake water supply reliability of nodes. According to the hydraulic and water quality results of each node calculated in step 5, use the ratio of the water supply volume to the water demand volume of nodes under the earthquake scenario, combined with the node water quality risk index R i,t calculated at different times in step 6, calculate the post-earthquake water supply reliability SI i, of the nodes, which is represented by the minimum value of the water supply reliability of the nodes at different times. The specific calculation formula is as follows:

[0034]

[0035]

[0036] Where: SI i is the water supply reliability of user node i in the pipe network; SI i,t represents the water supply reliability of node i at time t; t0 and t E are the start time of the earthquake event and the end time of the water quality assessment respectively; represents the minimum value of the water supply reliability of node i at different times between time t0 and t E ; R i,t is the water quality risk index of user node i in the pipe network at time t, calculated by formula (6) in step 6; Qi (t) is the actual water supply of node i at time t, which is calculated by step 5; Q 0,i (t) is the water demand of node i at time t;

[0037] Step 7.2, calculation of the overall reliability of the water supply in the pipe network after the earthquake. The overall reliability SI of the water supply in the pipe network after the earthquake is calculated by calculating the mean value of the water supply reliability of all nodes after the earthquake. The calculation formula is:

[0038]

[0039] In the formula: SI is the overall reliability of the water supply in the pipe network after the earthquake; SI i is the water supply reliability of user node i in the pipe network; m is the total number of user nodes;

[0040] Step 8, repeat steps 2 to 7 until the specified number of simulations N is reached; where N is the number of samples of the seismic damage of the pipe network generated by the Monte Carlo simulation;

[0041] Step 9, calculation of the mean value of the node water quality risk index For the water quality risk index R of each user node in the pipe network obtained in step 6 in each simulation i Calculate the mean value of N Monte Carlo simulations

[0042] Step 10, calculation of the mean value of the pipe network reliability. For the water supply reliability SI of the nodes after the earthquake obtained in step 7 in each simulation i, and the overall reliability SI of the water supply in the pipe network after the earthquake, calculate the mean value of N Monte Carlo simulations and The beneficial effects of the present invention are:

[0043] ① The present invention first proposes a calculation method for water quality risk and water supply reliability of urban water supply pipe networks considering the negative pressure effect after the earthquake, and evaluates the water quality safety of the water supply in urban water supply pipe networks after the earthquake;

[0044] ② The present invention simulates the post-earthquake pressure state of the pipe network under the scenario of a large amount of water leakage at multiple pipes in the pipe network based on the post-earthquake damage scenario of the pipe network hydraulic model, identifies the low-pressure or negative-pressure nodes after the earthquake, and determines the pipe network pollution scenario according to the groundwater head and sewage concentration of the environment where the nodes in the pipe network model are located;

[0045] ③ The present invention calculates the water quality risk of nodes through the water quality of nodes and pollutant concentration. Considering the uncertainty of earthquake damage, by calculating the mean value of multiple Monte Carlo simulations, it reflects the water quality risk situation of nodes after the earthquake, which is of great significance for evaluating the water supply safety of nodes after the earthquake and guiding the post-earthquake water quality early warning and response measures of urban water supply pipe networks;

[0046] ④The present invention calculates the node water supply reliability and the overall reliability of the pipe network through the node water supply volume and node water quality, and reflects the comprehensive performance of the post-earthquake pipe network water supply by calculating the mean value of multiple Monte Carlo simulations, which is of great significance for guiding the seismic upgrade transformation of the pipe network and post-earthquake emergency repair measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flowchart of the method proposed by the present invention;

[0048] Figure 2 is a plan layout diagram of the water supply pipe network of the embodiment;

[0049] Figure 3 is a distribution diagram of the mean value of the average water quality risk of the node after the earthquake;

[0050] Figure 4 is a distribution diagram of the mean value of the water supply reliability of the node after the earthquake. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] The following further describes in detail the embodiments of the present invention with reference to the drawings and embodiments. The following embodiments are used to illustrate the present invention, but cannot be used to limit the scope of the present invention.

[0052] See Figure 1 , a method for calculating the water quality risk and water supply reliability of an urban water supply pipe network considering the post-earthquake negative pressure effect provided in this embodiment includes the following steps:

[0053] Step 1, determine the leakage area of the pipeline under the daily operation scenario. Under the daily operation condition, due to pipeline aging, a certain amount of water leakage occurs. According to the leakage water volume in the daily operation scenario of the pipe network, calculate the leakage water volume of the pipeline according to the principle of uniform distribution of the total leakage water volume of the pipe network along the pipe length; in the pipe network hydraulic model, apply the pipeline leakage water volume to the adjacent nodes of the pipeline, and simulate the leakage water volume through the leakage area of the node diffuser model. When the ratio of the total leakage water volume of the pipe network is l%, the main part of the node leakage area is divided into the following two steps:

[0054] Step 1.1, determine the daily leakage water volume Q L,i of the node. According to the principle of uniform distribution of the pipe network leakage water volume along the pipe length, calculate the node leakage water volume Q L,i of each user node under the specified pipe network leakage rate l%. Its expression is:

[0055]

[0056] In the formula: Q L,i is the daily leakage water volume of node i; Q T is the total water supply of the pipe network; L a is the length of the upstream pipe section a of node i; L bis the length of the downstream pipe segment b of node i; n is the total number of pipe segments in the pipe network; L j is the length of pipeline j;

[0057] Step 1.2, determine the daily leakage orifice area A 0,i . Based on the orifice flow equation, according to the daily leakage water volume Q L,i of the user node, calculate the daily leakage orifice area A 0,i of the user node. The calculation formula is as follows:

[0058]

[0059] In the formula: A 0,i is the orifice area of node i at the leakage rate of l%; μ is the orifice flow coefficient, and its value range is 0.6 - 0.9; g is the acceleration due to gravity; H i is the water head at the user node i; Q L,i is the daily leakage water volume of node i.

[0060] Step 2, use Monte Carlo simulation sampling to generate the seismic damage scenarios of pipelines in the pipe network under earthquake action. According to the seismic failure probability of pipelines, use the Monte Carlo simulation method to randomly sample and generate the post - earthquake states of pipelines {intact\leaking\broken}, and calculate the orifice areas A L,i of the break points and leakage points generated by the seismic damage of pipelines;

[0061] Step 3, conduct hydraulic simulation of the pipe network under the post - earthquake damage scenario. According to the scenario of multiple pipeline damage points generated under earthquake action, add the leakage water volume models of break points and leakage points to the original pipe network model, establish a post - earthquake hydraulic model, and simulate the water supply volume and pressure states of nodes in the pipe network under the scenario of simultaneous large - scale water leakage from multiple pipelines in the pipe network. Post - earthquake low - pressure or negative - pressure nodes generally appear in areas with relatively large elevation or areas with serious water leakage.

[0062] Step 4, determine the scenario of pollutant intrusion into the pipe network after the earthquake. Based on the low - pressure or negative - pressure of nodes in the pipe network and the sewage water head and concentration of the soil and water environment where the pipelines are located, determine the location, pollutant intrusion volume, and pollutant concentration of pollutant intrusion into the pipe network. There are mainly the following 4 steps:

[0063] Step 4.1, set the sewage water head and concentration around the nodes of the pipe network model. Considering the deterministic scenario or the uncertain scenario, select one of the following methods to set the groundwater water head and sewage concentration at each node. The nodes mentioned include user nodes and break points and leakage points generated by seismic damage:

[0064] ⑤ The groundwater water head and sewage concentration of the environment at the nodes of the pipe network model adopt a unified fixed value, that is, the groundwater water heads of different nodes are relative to the elevation h i,0are all set to the same value, and the groundwater sewage concentration c of different nodes i,0 are all set to the same value;

[0065] ⑥ The groundwater head of the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater heads of different nodes relative to the elevation h of the pipe network model nodes i,0 are all set to the same value, the groundwater sewage concentration is a random value, the groundwater concentration range is set as c1~c2, and values are taken within the range through the Monte Carlo simulation method to randomly determine the sewage concentration c of each node of the pipe network model i,0 ;

[0066] ⑦ The groundwater sewage concentration of the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater sewage concentration c of different nodes i,0 are all set to the same value, the groundwater head is a random value, the relative groundwater head of the groundwater relative to the elevation h of the pipe network model nodes is set as h1~h2, and values are taken within the range through the Monte Carlo simulation method to randomly determine the relative groundwater head h of the environment of each node of the pipe network model i,0 ;

[0067] ⑧ The groundwater head and sewage concentration of the environment at the nodes of the pipe network model are both random values. The relative groundwater head of the groundwater relative to the elevation h of the pipe network model nodes is set as h1~h2, the groundwater concentration range is set as c1~c2, and values are taken within the range through the Monte Carlo simulation method to randomly determine the relative groundwater head h of the environment of each node of the pipe network model i,0 and the sewage concentration c of the node i,0 .

[0068] Step 4.2, determine the pollutant intrusion location. According to the groundwater head h0 of the nodes of the pipe network model in Step 4.1, and according to the pipe network hydraulic simulation results under the post-earthquake damage scenario in Step 3, identify the nodes in the simulation results at different post-earthquake times where the node pressure is lower than the groundwater head h0 in the environment (which may exist in the user nodes of the pipe network model and the disconnected and leaking nodes caused by earthquake damage). These nodes are the pollutant intrusion nodes

[0069] Step 4.3, calculate the pollutant intrusion amount. At each moment, the amount of sewage entering the pipe network from the intrusion nodes is calculated according to the daily leakage area A of the pollutant intrusion nodes 0,i or calculated according to the leakage area A of the disconnected and leaking nodes caused by the earthquake L,i for calculation, and the calculation method is as follows:

[0070]

[0071] In the formula: V i,t is the amount of sewage entering node i of the pipe network model at time t; μ is the orifice flow coefficient, and the value range is 0.6~0.9; A iis the leakage area of node i. For the daily leakage port A i = A 0,i , determined by step 1. For the disconnected and leaking node A caused by earthquake damage i = A L,i , determined by step 2; g is the acceleration due to gravity; h i,0 is the relative groundwater head at user node i, determined by step 4.1; h i,t is the node pressure of user node i at time t, obtained from step 3; T is the time step simulated by the pipe network model, which is the simulated time step in the model of step 3;

[0072] Step 4.4, calculate the concentration of pollutants after entering the node. The specific calculation expression is as follows:

[0073]

[0074] In the formula: c i,t is the pollutant concentration of node i in the pipe network model at time t, c i,0 is the sewage concentration of the groundwater in the environment at node i, determined by step 4.1, V i,t is the amount of sewage entering node i at time t, determined by step 4.3, q i,t is the amount of water in the pipe network passing through node i at time t, calculated from the model of step 3;

[0075] Step 5, establish a pipe network hydraulic and water quality analysis model for the pollutant invasion scenario. Using the post-earthquake pipe network hydraulic model established in step 3, write the pollutant invasion information calculated in step 4.3 and step 4.4 into the model to establish a post-earthquake pipe network hydraulic and water quality model. Through hydraulic and water quality simulation, simulate the attenuation and diffusion of pollutants in the pipe network, and calculate and obtain the hydraulic and water quality results of each node;

[0076] Step 6, calculation of the water quality risk index R i of the pipe network model nodes. Based on the water quality threshold index (minimum limit of residual chlorine concentration) and pollutant limit index, according to the model analysis results of step 5, calculate the water quality risk index R i,t of each user node at time t, and calculate the water quality risk index R i of the node during the entire evaluation period:

[0077]

[0078]

[0079] In the formula: R i is the water quality risk index of user node i in the pipe network during the entire evaluation period; t0 and t EThey are the start time of the earthquake event and the end time of the water quality assessment respectively, which are determined by the post-earthquake pipe network hydraulic model in Step 3; R i,t is the water quality risk index of user node i in the pipe network at time t; q i (t) is the water quality of node i at time t, which is calculated in Step 5, q b is the water quality threshold; c i,t is the pollutant concentration of node i at time t, which is calculated in Step 5, c b is the pollutant limit;

[0080] Step 7, calculation of the water supply reliability of the pipe network. A large amount of water leakage caused by earthquake damage will lead to a decrease in the water supply capacity of the pipe network and the invasion of pollutants, reducing the reliability of node water supply. Taking the flow rate and water quality of user nodes as indicators, calculate the overall water supply reliability of user nodes and the pipe network. There are specifically the following two steps:

[0081] Step 7.1, calculation of the post-earthquake water supply reliability of nodes. According to the hydraulic and water quality results of each node calculated in Step 5, adopt the ratio of the water supply volume to the water demand volume of nodes under the earthquake scenario, and combine the node water quality risk index R i,t calculated in Step 6 at different times, calculate the post-earthquake water supply reliability SI i, of the node, which is represented by the minimum value of the node water supply reliability at different times. The specific calculation formula is as follows:

[0082]

[0083]

[0084] In the formula: SI i is the water supply reliability of user node i in the pipe network; SI i,t represents the water supply reliability of node i at time t; t0 and t E are the start time of the earthquake event and the end time of the water quality assessment respectively; represents the minimum value of the water supply reliability of node i at different times between time t0 and t E ; R i,t is the water quality risk index of user node i in the pipe network at time t, which is calculated by formula (6) in Step 6; Q i (t) is the actual water supply volume of node i at time t, which is calculated in Step 5; Q 0,i (t) is the water demand volume of node i at time t;

[0085] Step 7.2, calculation of the overall post-earthquake water supply reliability of the pipe network. Calculate the overall post-earthquake water supply reliability SI of the pipe network by calculating the mean value of the post-earthquake water supply reliability of all nodes. The calculation formula is:

[0086]

[0087] In the formula: SI is the overall post-earthquake water supply reliability of the pipe network; SI i is the water supply reliability of user node i in the pipe network; m is the total number of user nodes;

[0088] Step 8, repeat Steps 2 to 7 until the specified number of simulations N is reached; where N is the number of pipe network earthquake damage samples generated by Monte Carlo simulation;

[0089] Step 9, calculation of the mean value of the node water quality risk index For the water quality risk index R of each user node in the pipe network obtained in Step 6 of each simulation i Calculate the mean value of N Monte Carlo simulations

[0090] Step 10, calculation of the mean value of the pipe network reliability. For the post-earthquake water supply reliability SI of the node obtained in Step 7 of each simulation i, and the overall post-earthquake water supply reliability SI of the pipe network, calculate the mean value of N Monte Carlo simulations and

[0091] Application example:

[0092] I. Pipe network information

[0093] Taking a benchmark water supply pipe network (Modena pipe network) as an example, illustrate the usage and effect of the above method. The Modena pipe network consists of 268 user nodes and 317 pipeline segments. The schematic diagram of the pipe network is as Figure 2 shown.

[0094] II. Parameter settings

[0095] (1) Earthquake parameter settings. In Step 2, referring to the China Earthquake Intensity Scale (2020), the earthquake intensity is degree X, and the earthquake damage scenarios of the pipelines are generated;

[0096] (2) Pipe network leakage rate settings. The leakage rate is set to 15%, that is, l = 15;

[0097] (3) Settings of the sewage head and concentration around the nodes of the pipe network model. Adopt Method ① in Step 4.1, the groundwater head is 0 m relative to the node elevation, and the groundwater sewage (Escherichia coli) concentration is 40000 CFU / L;

[0098] (4) Water quality index settings. The residual chlorine threshold (q b ) is set to 0.2 mg / L, and the concentration limit (c b ) of the pollutant (Escherichia coli) is set to 1

[0099] CFU / 100mL;

[0100] (5) Calculation times setting, the calculation times N is set to 1000 times;

[0101] III. Result analysis

[0102] Water quality risk index R of each user node in the pipe network i Calculate the mean value of 1000 Monte Carlo simulations As Figure 3 shown, the post-earthquake water supply reliability SI of the node i, Calculate the mean value of 1000 Monte Carlo simulations As Figure 4 shown, the mean value of the overall post-earthquake water supply reliability of the pipe network is 0.39.

[0103] The results of the embodiments show that a calculation method for water quality risk and water supply reliability of urban water supply pipe networks considering the post-earthquake negative pressure effect proposed by the present invention can comprehensively evaluate the post-earthquake node water quality risk and the water supply reliability of the pipe network, and is of great significance for guiding the post-earthquake water quality early warning and response strategies of urban water supply pipe networks, as well as the seismic upgrade transformation and post-earthquake emergency repair measures of the pipe network.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calculation method for water quality risk and water supply reliability of urban water supply networks considering the negative pressure effect after an earthquake, characterized in that, It includes the following steps: Step 1: Determine the leak area of the pipeline under the daily operation scenario; under the daily operation condition, a certain amount of water leakage is caused by pipeline aging; according to the leakage water volume in the daily operation scenario of the pipe network, and based on the principle of uniform distribution of the overall leakage water volume of the pipe network along the pipe length, calculate the leakage water volume of the pipeline; in the pipe network hydraulic model, apply the pipeline leakage water volume to the adjacent nodes of the pipeline, and simulate the leakage water volume through the leak area of the node diffuser model; when the overall leakage water volume ratio of the pipe network is l%, the calculation of the node leak area is divided into the following two steps: Step 1.1, determine the daily leakage water volume Q of the node L,i ; According to the principle that the leakage water volume of the pipe network is evenly distributed according to the pipe length, calculate the node leakage water volume Q of each user node under the specified pipe network leakage rate of l%. L,i , and its expression is: Where: Q L,i is the daily leakage water volume of node i; Q T is the total water supply of the pipe network; L a is the length of the upstream pipe segment a of node i; L b is the length of the downstream pipe segment b of node i; n is the total number of pipe segments in the pipe network; L j is the length of pipe j; Step 1.2, determine the daily leakage orifice area A 0,i ; Based on the orifice outflow equation, according to the daily leakage water volume Q L,i of the user node, calculate the daily leakage orifice area A 0,i of the user node. The calculation formula is as follows: Where: A 0,i is the leakage orifice area of node i at the leakage rate of l%; μ is the orifice discharge coefficient, with a value range of 0.6 to 0.9; g is the acceleration due to gravity; H i is the water head at the user node i; Q L,i is the daily leakage water volume of node i; Step 2: Monte Carlo simulation sampling to generate the seismic damage scenarios of the pipelines in the pipe network under earthquake action; According to the seismic failure probability of pipelines, the Monte Carlo simulation method is used to randomly sample and generate the post-earthquake states of pipelines {intact\leaking\broken}, and calculate the leakage areas A of the break points and leakage points generated by the seismic damage of pipelines L,i ; Step 3: Conduct the hydraulic simulation of the pipe network under the post-earthquake damage scenario; according to the scenario of multiple pipeline damage points generated under earthquake action, add the leakage water volume models of disconnection points and leakage points to the original pipe network model to establish a post-earthquake hydraulic model, and simulate the water supply volume and pressure status of the post-earthquake nodes in the pipe network under the scenario of a large amount of water leakage from multiple pipelines in the pipe network at the same time; post-earthquake low-pressure or negative-pressure nodes generally appear in areas with a relatively large elevation or areas with serious water leakage; Step 4: Determine the scenario of pollutant intrusion into the pipe network after the earthquake; based on the low pressure or negative pressure of the nodes in the pipe network and the sewage head and concentration of the soil and water environment where the pipelines are located, determine the location, pollutant intrusion volume, and pollutant concentration of pollutant intrusion into the pipe network, which mainly includes the following 4 steps: Step 4.1: Set the sewage head and concentration around the nodes of the pipe network model; considering the deterministic scenario or the uncertain scenario, select one of the following methods to set the groundwater head and sewage concentration at each node. The nodes mentioned include user nodes and disconnection points and leakage points generated by earthquake damage: ① The groundwater head and sewage concentration at the nodes of the pipe network model adopt unified fixed values, that is, the groundwater heads at different nodes are set to the same value relative to the elevation h of the nodes of the pipe network model i,0 and the groundwater sewage concentrations c at different nodes i,0 are all set to the same value; ② The groundwater head of the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater heads of different nodes are set to the same value relative to the elevation h of the nodes of the pipe network model i,0 The groundwater sewage concentration is a random value. The groundwater concentration range is set as c1 to c2, and values are taken within this range through the Monte Carlo simulation method to randomly determine the sewage concentration c of each node of the pipe network model i,0 ; ③ The groundwater sewage concentration in the environment at the nodes of the pipe network model adopts a unified fixed value, that is, the groundwater sewage concentration c at different nodes i,0 are all set to the same value, the groundwater head is a random value, and the groundwater head relative to the elevation h1~h2 of the nodes of the pipe network model is set. Values are taken within the range through the Monte Carlo simulation method, and the relative groundwater head h of the environment at each node of the pipe network model is randomly determined i,0 ; ④ The groundwater head and sewage concentration at the nodes of the pipe network model are both random values. Set the groundwater head relative to the elevation of the nodes of the pipe network model as h1~h2, and set the range of groundwater concentration as c1~c2. Values are taken within the range by the Monte Carlo simulation method, and the relative groundwater head h of the environment at each node of the pipe network model is randomly determined i,0 and the sewage concentration c of the node i,0 ; Step 4.2: Determine the pollutant intrusion location; according to the groundwater head h0 of the nodes of the pipe network model in Step 4.1, and based on the hydraulic simulation results of the pipe network under the post-earthquake damage scenario in Step 3, identify the nodes whose node pressures are lower than the groundwater head h0 in the environment in the simulation results at different post-earthquake times. These nodes are the pollutant intrusion nodes; Step 4.3, calculate the pollutant intrusion volume; at each moment, the sewage volume entering the pipe network from the intrusion node is calculated according to the daily leakage area A of the pollutant intrusion node 0,i or calculated according to the leakage area A of the disconnected and leaking nodes caused by the earthquake L,i The calculation method is as follows: Where: V i,t is the sewage volume entering the node i of the pipe network model at time t; μ is the orifice flow coefficient, and the value range is 0.6 to 0.9; A i is the leakage area of node i. For daily leakage, A i = A 0,i , which is determined by step 1. For the disconnected and leaking nodes caused by earthquake damage, A i = A L,i , which is determined by step 2; g is the acceleration due to gravity; h i,0 is the relative groundwater head at user node i, which is determined by step 4.1; h i,t is the node pressure of user node i at time t, which is obtained by step 3; T is the time step of the pipe network model simulation, which is the simulation time step in the model of step 3; Step 4.4: Calculate the concentration of pollutants after entering the nodes; the specific calculation formula is as follows: Where: c i,t is the pollutant concentration of the node i in the pipe network model at time t, c i,0 is the sewage concentration of the groundwater in the environment at node i, determined by step 4.1, V i,t is the sewage volume entering node i at time t, determined by step 4.3, q i,t is the pipe network water volume passing through node i in the pipe network at time t, calculated by the model in step 3; Step 5: Establish a hydraulic and water quality analysis model of the pipe network for the pollutant intrusion scenario; adopt the post-earthquake pipe network hydraulic model established in Step 3, write the pollutant intrusion information calculated in Step 4.3 and Step 4.4 into the model to establish a post-earthquake hydraulic and water quality model of the pipe network, and through hydraulic and water quality simulation, simulate the attenuation and diffusion of pollutants in the pipe network, and calculate and obtain the hydraulic and water quality results of each node; Step 6, calculation of the water quality risk index R of the pipe network model nodes i Based on the water quality threshold index and the pollutant limit index, calculate the water quality risk index R of each user node at time t according to the model analysis results in Step 5 i,t and calculate the water quality risk index R of the node during the entire evaluation period i : Where: R i is the water quality risk index of user node i in the pipe network during the entire evaluation period; t0 and t E are respectively the start time of the earthquake event and the end time of the water quality assessment, determined by the post-earthquake pipe network hydraulic model in Step 3; R i,t is the water quality risk index of user node i in the pipe network at time t; q i (t) is the water quality of node i at time t, calculated in Step 5, q b is the water quality threshold; c i,t is the pollutant concentration of node i at time t, calculated in Step 5, c b is the pollutant limit; Step 7: Calculate the water supply reliability of the pipe network. The large amount of water leakage caused by earthquake damage will cause a decline in the water supply capacity of the pipe network and the intrusion of pollutants, reducing the reliability of node water supply. Taking the flow rate and water quality of user nodes as indicators, calculate the water supply reliability of user nodes and the overall pipe network, which specifically includes the following two steps: Step 7.1, Calculation of the post-earthquake water supply reliability of nodes. According to the hydraulic and water quality results of each node calculated in Step 5, using the ratio of the water supply volume to the water demand volume of the nodes under the earthquake scenario, combined with the node water quality risk index R at different times calculated in Step 6 i,t , calculate the post-earthquake water supply reliability SI of the nodes i, , which is represented by the minimum value of the node water supply reliability at different times. The specific calculation formula is as follows: Where: SI i is the water supply reliability of user node i in the pipe network; SI i,t represents the water supply reliability of node i at time t; t0 and t E are respectively the start time of the earthquake event and the end time of the water quality assessment; represents the minimum value of the water supply reliability at different times of node i between time t0 and t E ; R i,t is the water quality risk index of user node i in the pipe network at time t, calculated by formula (6) in step 6; Q i (t) is the actual water supply of node i at time t, obtained by calculation in step 5; Q 0,i (t) is the water demand of node i at time t; Step 7.2: Calculate the overall water supply reliability of the pipe network after the earthquake. Calculate the overall water supply reliability SI of the pipe network after the earthquake by calculating the mean value of the water supply reliability of all nodes after the earthquake. The calculation formula is: Where: SI is the overall reliability of the water supply in the pipe network after the earthquake; SI i is the water supply reliability of user node i in the pipe network; m is the total number of user nodes; Step 8, repeat Step 2 to Step 7 until the specified number of simulation times N is reached; where N is the number of samples of seismic damage to the pipe network generated by Monte Carlo simulation. Step 9, calculation of the average water quality risk index of nodes ; For the water quality risk index R of each user node in the pipe network obtained in Step 6 in each simulation i calculate the average value of N Monte Carlo simulations Step 10, calculation of the mean value of the pipe network reliability. Calculate the post-earthquake water supply reliability SI of the nodes obtained in Step 7 for each simulation i, and the mean value of N Monte Carlo simulations of the overall post-earthquake water supply reliability SI of the pipe network and 2. The calculation method for water quality risk and water supply reliability of urban water supply networks considering the post-earthquake negative pressure effect according to claim 1, characterized in that, Based on the pipe network hydraulic model under the post-earthquake damage scenario, simulate the post-earthquake pressure state of the pipe network when a large number of pipes leak simultaneously at multiple locations in the pipe network, identify the low-pressure or negative-pressure nodes after the earthquake, and determine the pipe network pollution scenario according to the groundwater head and sewage concentration of the environment where the nodes of the pipe network model are located; calculate the water quality risk of the nodes through the water quality and pollutant concentration of the nodes. Considering the uncertainty of earthquake damage, the mean value of multiple Monte Carlo simulations is calculated to reflect the water quality risk of the nodes after the earthquake, which is of great significance for evaluating the water supply safety of the nodes after the earthquake and guiding the post-earthquake water quality early warning and response measures of urban water supply pipe networks; calculate the water supply reliability of the nodes and the overall reliability of the pipe network through the water supply volume and water quality of the nodes. By calculating the mean value of multiple Monte Carlo simulations, the comprehensive performance of the post-earthquake water supply of the pipe network is reflected, which is of great significance for guiding the seismic upgrade and transformation of the pipe network and the post-earthquake emergency repair measures.

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