A rainwater pipe network design calculation method based on motion wave simulation

Abstract

A rainwater pipe network design calculation method based on motion wave simulation belongs to the technical cross field of urban rainwater pipe network and hydraulic model. The method adopts the way of runoff coefficient and phi index method to simulate the surface runoff process, is coupled with the equal flow time line method, and completes the calculation of the inflow process line of the rainwater inlet. Based on the secondary development of SWMM, the motion wave module of SWMM is called to simulate the pipe section confluence process, and the simulation results are read. With the flow process line calculation as the core, from the upstream pipe section, the rainwater inlet inflow process line of the design pipe section and the flow process line of the upstream pipe section connected with the design pipe section are superposed, and the peak value is taken as the design flow of the pipe section. Based on the GDAL development technology, the traditional hydraulic design method is adopted to realize the step-by-step design of the pipe network from top to bottom. The motion wave is used to calculate the pipe section confluence, the whole flow process is considered, the actual flow state of the rainwater pipe network is closer, and the design precision of the rainwater pipe network is improved.

Description

TECHNICAL FIELD

[0001] The application relates to a rainwater pipe network design calculation method based on motion wave simulation, and belongs to the technical cross field of urban rainwater pipe network and hydraulic model. BACKGROUND

[0002] In China, the reasoning formula method combined with the constant uniform flow theory has been used for a long time to calculate the design flow of rainwater pipe network. With the increase of the design scale of the pipe network, the calculation error is seriously accumulated, and when applied to a large catchment area, the calculation precision is low. Therefore, the “Outdoor Drainage Design Standard” (GB 50014-2021) proposes that when the catchment area is greater than 2km 2 , the mathematical model method is used to determine the rainwater design flow.

[0003] At present, there are mainly two types of model technology applied in the design of rainwater pipe network: one type is to apply the model technology to the checking of the design scheme, that is, to simulate the design scheme by the reasoning formula method, to take the node overflow or pipe segment overload as the checking index, and to complete the adjustment of the design scheme; the other type is to combine the model technology with the pipe diameter and slope optimization, to use the optimization algorithm, to comprehensively consider the economic performance and hydraulic performance of the pipe network, and to realize more accurate design. The model technology is applied to the optimization of the hydraulic performance of the rainwater pipe network or the checking of the design scheme, and the design of the checked or optimized pipe network is still determined by the reasoning formula method, and the model cannot be directly applied to the calculation of the design flow of the rainwater pipe network.

[0004] The rainwater pipe network model is composed of a surface runoff model, a surface concentration model and a pipe network concentration model, and the model calculation involves a large number of parameters and only provides a reasonable value range. The design parameters of the rainwater pipe network in China are few, and there is no measured data at the design stage of the pipe network, which is difficult to be scientifically quantified and cannot be checked, and blind application may cause large design deviation. Therefore, in order to ensure the reliability of the mathematical model method in the design application, the key lies in that the model parameters are set to be consistent with or equivalent to the design parameters of the rainwater pipe network.

[0005] The SWMM model is a stormwater runoff model developed by the U.S. Environmental Protection Agency, which can completely simulate the urban rainfall runoff process and the pollutant transfer process, and is currently widely used in stormwater runoff simulation and urban drainage system management. The SWMM model provides a motion wave simulation method for the water dynamic module of the pipe network. When the motion wave simulation is applied, the pipe channel water surface slope is equal to the pipe channel bottom slope, and the maximum flow capacity of the pipe segment is equal to the normal full pipe design flow of the pipe. It can simulate the space-time variation process of water flow in the pipe channel, which is more consistent with the actual flow state of the rainwater pipe channel. The application of the motion wave simulation method to calculate the pipe segment concentration process has higher precision compared with the reasoning formula method. SUMMARY

[0006] In view of the above problems, this paper proposes a design calculation method for rainwater pipe networks based on motion wave simulation by setting equivalent model parameters and pipe network design parameters.

[0007] The technical solution of this method is as follows:

[0008] A method for designing and calculating stormwater pipe networks based on motion wave simulation includes the following steps:

[0009] Step 1, Stormwater Pipeline Delineation: Based on the topography and street distribution within the design area, pipeline alignment and sub-catchment division are carried out; then, based on the land parcel data of the design area, the storm intensity formula and design storm return period are selected according to the "Outdoor Drainage Design Standard" (GB 50014-2021), and the surface water collection time, flow runoff coefficient, and rainfall runoff coefficient of each sub-catchment are determined;

[0010] Step 2: Select the design rainfall process line, and calculate the inflow process line of each sub-catchment area through surface runoff and surface runoff simulation;

[0011] Step 3: Couple the surface runoff generation model, surface runoff confluence model, and SWMM kinematic wave module obtained in Step 2;

[0012] Step 4: Perform GIS processing on the designed pipe section, complete the creation of the inp file, calculate the design flow rate of the rainwater pipe section, and complete the hydraulic calculation of the pipe section accordingly to determine the cross-sectional dimensions and laying slope, thus completing the design of the pipe section.

[0013] Step 5: Design each pipe segment sequentially from upstream to downstream until the entire pipeline network design is completed.

[0014] Furthermore, the specific steps in step 2 are as follows:

[0015] 1) Based on the rainstorm intensity formula and design return period selected in step 1, determine the same frequency distribution rain pattern with a rainfall duration of 180 min and a time step of 1 min.

[0016] 2) Adopt The index method uses Horton infiltration to calculate infiltration intensity, aims at the equivalence of flow runoff coefficient and rainfall runoff coefficient, determines the parameters of Horton infiltration equation through trial calculation, completes surface runoff simulation, and obtains net rainfall process line, that is, net rainfall at different times.

[0017] f i =f c +(f0-f c )e -ki (1)

[0018]

[0019]

[0020]

[0021] Where: i represents the rainfall period (min); j represents the partial rainfall period; f0 represents the initial infiltration rate (mm / min); f c The stable infiltration rate (mm / min); k is the attenuation coefficient; f i R is the infiltration intensity (mm) at minute i; i P represents the net rainfall (mm) in the i-th minute. i Let C be the rainfall in the i-th minute (mm); C is the rainfall-runoff coefficient; C max This represents the flow-runoff coefficient.

[0022] ① Flow-runoff coefficient equivalence criterion: The average runoff coefficient of the net rainfall process line over a maximum of 15 minutes (all using j+14) is equal to the flow-runoff coefficient of the sub-catchment area;

[0023] ② Rainfall-runoff coefficient equivalence criterion: The ratio of total runoff to total rainfall is equal to the rainfall-runoff coefficient.

[0024] 3) Using the surface water catchment time and net rainfall process line as input, the surface runoff process is calculated by applying the isochronous method with the linear runoff curve type, and the inflow process line of each sub-catchment area is calculated.

[0025]

[0026] In the formula: i and j are the rainfall times, as in formulas (1)-(4); t k Q represents the surface water catchment time (min) of the sub-catchment area; i R represents the flow rate at time i (L / s); i-j R represents the net rainfall intensity (mm) during the time period ij. When ij ≤ 0, R i-j Set to 0; F is the catchment area of ​​the region (m²) 2 ); α is the unit conversion factor.

[0027] Furthermore, the specific steps in step 3 are as follows:

[0028] 1) Apply step 2 to simulate surface runoff generation and runoff in all sub-catchments, and calculate the stormwater inflow process line of each sub-catchment according to formulas (1)-(5);

[0029] 2) When SWMM's motion wave module is called for simulation, the inflow process line of the rainwater inlet of each sub-catchment area is input into the corresponding inspection well of each sub-catchment area in the form of node inflow, so as to realize the coupling of surface runoff generation and pipeline runoff;

[0030] Furthermore, the specific steps for determining the design flow rate of the rainwater pipe section in step 4 are as follows:

[0031] 1) When the design pipe section is the starting pipe section, the calculation method of its design flow rate is as follows: the peak flow rate of the inflow process line of the rainwater inlet of the sub-catchment corresponding to the upstream inspection well of the pipe section is taken as the design flow rate;

[0032] 2) When the design pipe segment is not the starting pipe segment, the calculation method of its design flow rate is as follows: ① Call the function interface in the SWMM dynamic link library to complete the simulation of the inp file, and read the flow simulation results of all upstream pipe segments connected to the design pipe segment; ② Superimpose the inflow process line of the rainwater inlet of this design pipe segment and the flow process lines of all upstream pipe segments connected to this design pipe segment, and use the peak flow rate as the design flow rate of this design pipe segment.

[0033] Further, the creation of the .inp file is performed as follows:

[0034] 1) Based on the GDAL development technology, the vectorized topology of the pipeline network is constructed according to the coordinate information of the pipeline network. The design results (number, pipe diameter, slope and elevation, etc.) are synchronously written into the attribute table. The inspection well, water outlet and pipe section are output as .shp format files respectively, and named inspection well.shp, water outlet.shp and pipe section.shp respectively.

[0035] 2) Write information such as pipe section.shp, inspection well.shp, outlet.shp, and rainwater inlet flow process line into the inp file for use in SWMM dynamic link library call simulation.

[0036] The beneficial effects of this invention are mainly reflected in:

[0037] 1. By comparing the runoff coefficient with The combination of the index method and the isochron method for calculating surface runoff processes can effectively achieve equivalence of design conditions and ensure the reliability of model application.

[0038] 2. The motion wave method is used to simulate the flow process of pipe sections, which is more consistent with the actual flow pattern of rainwater pipes and canals, and helps to improve the design accuracy of rainwater pipe networks;

[0039] 3. Based on SWMM and GDAL development technologies, an automatic calculation framework for stormwater pipe section design flow is proposed. It can realize the stormwater pipe network design process of motion wave simulation, which is simple to operate, avoids the complexity of manual calculation, and improves work efficiency. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the process of the present invention, "A method for calculating the design flow of rainwater pipe network based on model calculation";

[0041] Figure 2 Mapping the stormwater drainage network;

[0042] Figure 3 This is a schematic diagram illustrating the calculation principle of the surface runoff model.

[0043] Figure 4 This is a schematic diagram illustrating the calculation principle of the surface runoff model.

[0044] Figure 5 A spatial distribution diagram of the selected comparison pipe sections;

[0045] Figure 6 Design a flow rate comparison chart for the inference formula method and the motion wave method. Detailed Implementation

[0046] To better understand and implement this invention, a detailed explanation is provided below using a Beijing example. The specific steps are as follows:

[0047] Taking the stormwater drainage network in a certain area of ​​Beijing as an example, the total catchment area is 4.506 km². 2 Based on the topography and street distribution within the design area, the pipeline network was routed and the catchment area was divided. The routed pipeline network has 62 nodes, with a total pipeline length of 12.403 km. Figure 2 As shown; then, according to the "Standard for Calculation of Rainstorm Runoff in Urban Rainwater System Planning and Design" (DB11 / T 969-2016), the rainstorm intensity formula for District II of Beijing is selected, as shown in formula (6). The design return period is 3 years, the runoff coefficient of the catchment area is 0.65, and the corresponding rainfall runoff coefficient is 0.53.

[0048]

[0049] The designed rainstorm pattern was derived by the Beijing Hydrological Station based on the rainstorm intensity formula for Zone II, using the same-frequency amplification method. The rainfall duration was 180 minutes, with a time step of 1 minute. The index method utilizes Horton infiltration to calculate infiltration intensity. It aims to achieve equivalence between the runoff coefficient and rainfall equivalence coefficient within the catchment area. The parameters of the Horton infiltration equation are determined through trial and error, and the net rainfall hydrograph is calculated. The results are as follows: Figure 3 As shown.

[0050] Using surface water catchment time as input, and employing a linear runoff curve type, the isochronous method is used to calculate the inflow process lines of stormwater inlets in each sub-catchment area, with a catchment area of ​​3.5 hm². 2 Taking a catchment area with a surface water collection time of 7 minutes as an example, the calculation results are as follows: Figure 4 As shown.

[0051] The design flow rate of the stormwater pipe network was calculated sequentially using both the inference formula method and the kinematic method. The pipe diameter and slope of the stormwater pipe sections were then designed based on full-pipe no-pressure flow. A consistent principle was maintained throughout the selection of design parameters, and stormwater pipe network design schemes for both methods were determined sequentially. Taking the longest catchment section P0–P18 in the case study as an example, the spatial distribution of the selected pipe sections is as follows: Figure 5 As shown in Table 1, the calculation results of the statistical inference formula method and the motion wave method are presented, and a comparison of the design flow rates of the two methods is also shown. Figure 6 As shown.

[0052] The design flow rates of the pipeline network calculated using the kinematic wave method are all greater than those calculated using the inference formula method. As the catchment area of ​​the designed pipe section increases and the catchment time lengthens, the difference in design flow rates tends to widen gradually, reaching its maximum at the terminal pipe section P18, where the design flow rate difference is 10.44 m. 3 / s. my country's outdoor drainage design standards stipulate that drainage lines exceeding 2km... 2 The design of stormwater drainage systems should employ a model-based approach to calculate design flow. For the example in this study, when the design catchment area reaches 2 km²... 2 At that time, the flow rate difference reached 7.50m. 3 / s, the flow rate calculated by the motion wave method is about 31.58% higher than that calculated by the inference formula method. It can be seen that for the design of large-scale projects, the use of the inference formula method does indeed pose a significant design risk.

[0053] Table 1 Comparison of Design Flow Rates Using the Reasoning Formula Method and the Kinematic Wave Method

[0054]

Claims

1. A method for designing and calculating rainwater pipe networks based on motion wave simulation, characterized in that, Includes the following steps: Step 1, Stormwater Pipeline Delineation: Based on the topography and street distribution within the design area, pipeline alignment and sub-catchment division are carried out; then, based on the land parcel data of the design area, the storm intensity formula and design storm return period are selected according to the "Outdoor Drainage Design Standard" (GB 50014-2021), and the surface water collection time, flow runoff coefficient, and rainfall runoff coefficient of each sub-catchment are determined; Step 2: Select the design rainfall process line, and calculate the inflow process line of each sub-catchment area through surface runoff and surface runoff simulation; Step 3: Couple the surface runoff generation model, surface runoff confluence model, and SWMM kinematic wave module obtained in Step 2; Step 4: Perform GIS processing on the designed pipe section, complete the creation of the inp file, calculate the design flow rate of the rainwater pipe section, and complete the hydraulic calculation of the pipe section accordingly to determine the cross-sectional dimensions and laying slope, thus completing the design of the pipe section. Step 5: Design each pipe segment sequentially from upstream to downstream until the entire pipeline network design is completed; The specific steps for step 2 are as follows: 1) Based on the rainstorm intensity formula and design return period selected in step 1, determine the same frequency distribution rain pattern with a rainfall duration of 180 min and a time step of 1 min. 2) Using the φ-index method, the infiltration intensity is calculated using the Horton infiltration method. With the equivalence of flow runoff coefficient and rainfall runoff coefficient as the objective, the parameters of the Horton infiltration equation are determined by trial calculation to complete the surface runoff simulation and obtain the net rainfall process line, i.e., the net rainfall at different times. (1) (2) (3) (4) Where: i represents the rainfall period (min); j represents the partial rainfall period; f0 represents the initial infiltration rate (mm / min); f c The stable infiltration rate (mm / min); k is the attenuation coefficient; f i R is the infiltration intensity (mm) at minute i; i P represents the net rainfall (mm) in the i-th minute. i Let C be the rainfall in the i-th minute (mm); C is the rainfall-runoff coefficient; C max This refers to the flow-runoff coefficient. ① Flow-runoff coefficient equivalence criterion: The average runoff coefficient of the net rainfall hydrograph over a maximum of 15 minutes is equal to the flow-runoff coefficient of the sub-catchment area; ② Rainfall-runoff coefficient equivalence criterion: The ratio of total runoff volume to total rainfall volume is equal to the rainfall-runoff coefficient; 3) Using the surface water catchment time and net rainfall process line as input, the surface runoff process is calculated by applying the isochronous method with the linear runoff curve type, and the inflow process line of each sub-catchment area is calculated. (5) In the formula: i and j are the rainfall times, as in formulas (1)-(4); t k Q represents the surface water catchment time (min) in the sub-catchment area. i R is the flow rate at time i (L / s); i-j R represents the net rainfall intensity (mm) during the time period ij. When ij ≤ 0, R i-j Set to 0; F is the catchment area of ​​the region (m²) 2 ); α is the unit conversion factor; The specific steps for step 3 are as follows: 1) Apply step 2 to simulate surface runoff generation and runoff in all sub-catchments, and calculate the stormwater inflow process line of each sub-catchment according to formulas (1)-(5); 2) When SWMM's motion wave module is called for simulation, the inflow process line of the rainwater inlet of each sub-catchment area is input into the corresponding inspection well of each sub-catchment area in the form of node inflow, so as to realize the coupling of surface runoff and pipeline runoff.

2. The method according to claim 1, characterized in that, The specific steps for determining the design flow rate of the rainwater pipe section in step 4 are as follows: 1) When the design pipe section is the starting pipe section, the calculation method of its design flow rate is as follows: the peak flow rate of the inflow process line of the rainwater inlet of the sub-catchment corresponding to the upstream inspection well of the pipe section is taken as the design flow rate; 2) When the design pipe segment is not the starting pipe segment, the calculation method of its design flow rate is as follows: ① Call the function interface in the SWMM dynamic link library to complete the simulation of the inp file, and read the flow simulation results of all upstream pipe segments connected to the design pipe segment; ② Superimpose the inflow process line of the rainwater inlet of this design pipe segment and the flow process lines of all upstream pipe segments connected to this design pipe segment, and use the peak flow rate as the design flow rate of this design pipe segment; The specific steps for creating an .inp file are as follows: 1) Based on GDAL development technology, a vectorized topology structure of the pipeline network is constructed according to the coordinate information of the pipeline network. The design results are synchronously written into the attribute table. The manholes, outlets and pipe segments are output as .shp files respectively, and named manhole.shp, outlet.shp and pipe segment.shp respectively. The design results include number, pipe diameter, slope and elevation. 2) Write the flow process information of pipe section.shp, inspection well.shp, outlet.shp and rainwater inlet into the inp file for use in the SWMM dynamic link library for simulation.

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