Urban Flood Simulation Method Based on Unstructured Mesh Coupled SWMM and FVCOM Models

Abstract

The application discloses a kind of urban flood simulation methods based on unstructured grid coupling SWMM and FVCOM model, adopt inspection well simplified method to characterize the exchange process of surface water flow and underground pipe network water flow, unstructured grid FVCOM is main program, SWMM is called by its subprogram.First, by using SWMM model and unstructured grid FVCOM model given basic data, the model of underground pipe network water flow and surface water flow is established respectively;Establish the topological relationship of SWMM pipe network node and FVCOM grid space;At the time step that needs to be coupled, obtain the head of pipe network water flow and surface water head of inspection well node pipe network, and calculate the exchange flow, according to the updated head and flow, simulate surface water and pipe network water flow respectively;Time progression, finally complete the whole urban flood simulation process.The application can accurately simulate the coupling effect of urban pipe network water flow and surface water flow, realize the simulation of urban flood with tortuous coastline or complex building profile.

Description

Technical Field

[0001] This invention belongs to the field of flood control technology for urban areas with complex coastlines or complex building outlines, specifically involving an urban flood simulation method that couples SWMM (Storm Water Management Model) and FVCOM (Finite Volume Coast and Ocean Model). Background Technology

[0002] To study urban flooding, several methods for simulating urban flooding have been proposed in recent years. In numerical simulations of the coupling between surface water flow and underground pipe networks during urban flooding, the use of dynamic two-way coupling models has become a trend. However, current coupling models for surface water flow and pipe network flow mostly employ structured meshes. Structured meshes cannot effectively depict the boundaries of winding coastlines or complex building outlines. For urban areas with such boundaries, unstructured meshes can better characterize them, resulting in more accurate surface water flow simulations. Summary of the Invention

[0003] In response to the aforementioned existing technologies, this invention provides an urban flood simulation method based on an unstructured mesh coupled SWMM and FVCOM model, which enables the simulation of urban flooding in areas with complex building boundaries or complex coastline boundaries. This method can provide technical support for the accurate simulation of urban flooding in cities with irregularly arranged building outlines or urban areas with complex coastline boundaries.

[0004] To address the aforementioned technical problems, this invention proposes an urban flood simulation method based on an unstructured mesh coupled with SWMM and FVCOM models. This method primarily employs a simplified manhole method to characterize the exchange process between surface water flow and underground pipe network flow. The unstructured mesh FVCOM model serves as the main program, with the SWMM model as a subroutine for the main program to call. This enables real-time dynamic bidirectional data exchange between the surface hydrodynamic model and the pipe network hydrodynamic model, simulating the coupling effect between underground pipe network flow and surface water flow. Ultimately, this achieves coupled simulation of urban flooding with tortuous coastlines or complex building outlines based on an unstructured mesh. The main process is as follows: First, using the given basic data, models of underground pipe network flow and surface water flow are established using the SWMM model and the unstructured grid FVCOM model, respectively; the spatial topological relationships between SWMM pipe network nodes and FVCOM grids are established; at the time steps requiring coupling, the pipe network water head and surface water head at the pipe network manhole nodes are obtained, the inflow or outflow at the manhole nodes in the current time step is determined, and the exchanged flow rate is calculated. The unstructured grid FVCOM model and SWMM model simulate surface water and pipe network flow respectively based on the updated water head and flow rate; the simulation progresses over time, and finally, the entire urban flood simulation process is completed. Specifically, the following steps are included:

[0005] Step 1: Obtain basic data for the study area. The basic data includes at least the distribution of drainage pipe network, ground elevation data of the study area, location of inspection wells, and outline of buildings.

[0006] Step 2: Based on the above basic data, use the SWMM model and the unstructured mesh FVCOM model to establish models of underground pipe network water flow and surface water flow respectively, so as to describe the contours of tortuous shorelines or complex buildings.

[0007] Step 3: Read the inp format file generated by the SWMM model, obtain the coordinates of the SWMM network nodes, and establish a spatial topology relationship with the FVCOM of the surface water flow.

[0008] Step 4: Based on the SWMM network node head and the FVCOM surface water head, the simplified manhole method is used to characterize the exchange process between surface water flow and underground network water flow.

[0009] Step 5: Use the unstructured mesh FVCOM model as the main program and the SWMM model as a subroutine for the main program to call;

[0010] Step 6: Start the model and begin calculations;

[0011] Step 7: At the time step where coupling is required, the two models exchange data to achieve dynamic real-time coupling, including: the SWMM model transmits the manhole node head at the current time step to the unstructured mesh FVCOM model; the FVCOM model obtains the coupling node head and network head based on the manhole node head and surface water head, calculates the exchanged flow flux, and then transmits the calculated flow to the SWMM model, thereby updating the head and flow; the FVCOM model and SWMM model simulate surface water and network water flow respectively based on the updated head and flow.

[0012] Step 8: Time progression. Repeat step 7 at the time steps where coupling is required, and finally realize the simulation of urban flooding with tortuous coastlines or complex building outlines.

[0013] Furthermore, in the urban flood simulation method of the present invention:

[0014] In step 4, the simplified method of manholes is used to characterize the exchange process between surface water flow and underground pipe network flow. Based on the relationship between surface water depth D1, manhole node head H2, and surface elevation Z, the interaction states of surface water flow and underground pipe network flow include the following scenarios:

[0015] (1) When D1=0, if H2≤Z, then the interaction state is that the inspection well neither flows in nor out;

[0016] (2) When D1 = 0, if H2 > Z, then the interaction state is well outflow;

[0017] (3) When D1 > 0, if H2 < Z, then the interaction state is the well inflow;

[0018] (4) When D1 > 0, if H2 = Z, then the interaction state is the well inflow;

[0019] (5) When D1 > 0, if H2 > Z and H2 < Z + D1, then the interaction state is manhole inflow;

[0020] (6) When D1 > 0, if H2 > Z and H2 = Z + D1, then the interaction state is that the inspection well neither flows in nor out;

[0021] (7) When D1 > 0, if H2 > Z + D1, then the interaction state is well outflow.

[0022] In step 5, the specific steps for using the unstructured mesh FVCOM model as the main program and the SWMM model as a subroutine for the main program to call are as follows:

[0023] Step 5-1: Compare the head at the SWMM network nodes with the head of surface water flow. Add a mass source term to the continuity equation of the FVCOM model. The continuity equation after vertical integration is as follows:

[0024]

[0025] In equation (1): ζ is the current water level of the control volume; The average flow velocity in the control volume direction; Q represents the average flow velocity in the y-direction of the control volume. sur δ represents the flow rate overflowing from the inspection well node of the underground pipeline network; D represents the water depth of the control volume; sur Let δ be the Dirichlet function, where δ is the function of the node overflow state. sur The value is 1; under the node discharge state, δ sur The value is -1; when the node neither overflows nor leaks, δ sur The value is 0;

[0026] Step 5-2, the flow conservation equations at the nodes in the SWMM model are as follows:

[0027]

[0028] In equation (2): A j η is the cross-sectional area of ​​the inspection well node; j t represents the current water level at the inspection well node; t represents time. Q represents the inflow rate of the k-th pipe connecting to this inspection well node; laterin Inbound traffic added for external custom input; Q sur The flow rate of overflow from the inspection well node of the underground pipeline network; δ sur Let δ be the Dirichlet function, where δ is the value of the function in the nodal overflow state. sur The value is 1; under the node discharge state, δ sur The value is -1; when the node neither overflows nor leaks, δ sur The value is 0.

[0029] In step 7, the FVCOM model obtains the coupled node head and network head based on the manhole node head and surface water head, and calculates the exchanged flow flux Q. exc for:

[0030]

[0031] H1 = D1 + Z (4)

[0032] H2 = D2 (5)

[0033] In equations (3) to (5): c0 is the flow coefficient, ranging from [0-1], A is the effective flow area of ​​the manhole, g represents the gravitational acceleration, H1 and H2 are the average head of the grid cell and the head of the manhole node, respectively, D1 represents the surface water depth, D2 represents the water depth inside the manhole, and Z is the surface elevation.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] This invention couples the underground pipe network flow model (SWMM) and the surface water flow model (FVCOM) using an unstructured mesh. Previous coupled models of surface water flow and underground pipe network flow often employed structured meshes. However, when urban building outlines are complex, or when there are complex coastline boundaries near the urban area, structured meshes cannot adequately characterize these complex boundaries. This invention uses an unstructured mesh for real-time dynamic coupling of SWMM and FVCOM, which can describe changes in complex boundaries. Verification with the physical model shows good agreement between calculated and experimental values, making it suitable for simulating urban flooding in areas with complex building outlines or coastline boundaries. Attached Figure Description

[0036] Figure 1 This is a flowchart of the urban flood simulation method of the present invention that couples SWMM and FVCOM models;

[0037] Figure 2 This invention describes the physical coupling process between pipe network water flow and surface water flow.

[0038] Figure 3 This is a schematic diagram of the interaction between surface water flow and underground pipe flow according to the present invention;

[0039] Figure 4 This is a schematic diagram of the physical model experimental setup for verifying this invention;

[0040] Figure 5-1 and Figure 5-2 This is a comparison chart of the errors between experimental and simulated values ​​in the physical model experiment used to verify this invention. Figure 5-1 This is a comparison chart of the error between experimental and simulated values ​​of interactive traffic. Figure 5-2 This is a comparison chart of the error between the experimental and simulated values ​​of the water depth at the measuring point. Detailed Implementation

[0041] The design concept of the urban flood simulation method proposed in this invention is as follows: Previous coupled models of surface water flow and underground pipe network flow often used structured meshes. However, when the outlines of urban buildings are complex, or when there are complex coastline boundaries near the urban area, structured meshes cannot adequately characterize these complex boundaries. This invention uses an unstructured mesh to dynamically couple the underground pipe network flow model (SWM) and the surface water flow model (FVCOM) in real time. This can describe the changes in complex boundaries. Verification with the physical model shows good agreement between the calculated and experimental values. It can be used to simulate urban flooding in areas with complex building outlines or coastline boundaries, providing technical support for accurate simulation of urban flooding in cities with irregularly arranged building outlines or complex coastline boundaries. The method mainly includes: using a simplified manhole method to characterize the exchange process between surface water flow and underground pipe network flow; using the rewritten unstructured mesh FVCOM model as the main program; and using SWMM as a subroutine for calling. First, using given basic data, models of underground pipe network flow and surface water flow are established using SWMM and FVCOM respectively. At the time steps requiring coupling, the water head of the pipe network and the surface water head at the manhole nodes are obtained, and the exchanged flow rates are calculated. With time progression, the entire urban flood simulation process is completed. This invention enables real-time dynamic data exchange between the two models, accurately simulating the coupling effect of urban pipe network flow and surface water flow, and realizing the simulation of urban flooding with tortuous coastlines or complex building contours based on an unstructured mesh coupling model.

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0043] like Figure 1 As shown, the present invention proposes an urban flood simulation method based on an unstructured mesh coupled SWMM and FVCOM model, which is implemented according to the following steps:

[0044] Step 1: Obtain basic data for the study area. The basic data includes at least the distribution of drainage pipe network, ground elevation data of the study area, location of inspection wells, and outline of buildings.

[0045] Step 2: Based on the basic data, use the SWMM and the unstructured mesh FVCOM model to describe the contours of the meandering shoreline or complex buildings using the unstructured mesh of FVCOM.

[0046] Step 3: Read the .inp format file generated by SWMM, obtain the coordinates of the SWMM network nodes, and establish a spatial topology relationship with the surface water flow model FVCOM. The physical coupling process is as follows: Figure 2 As shown, within the framework of FVCOM as the main program, real-time dynamic bidirectional coupling between FVCOM and SWMM is achieved by calling SWMM subroutines.

[0047] Step 4, based on the SWMM network node head and surface water flow head, such as Figure 3 The simplified method of inspection wells is used to characterize the exchange process between surface water flow and underground pipe network. Based on the different states of surface water flow and pipe network flow, the interaction states of surface water flow and pipe network flow are divided into seven types.

[0048] Step 5: Use the unstructured mesh FVCOM model as the main program and the SWMM model as a subroutine for the main program to call;

[0049] Step 6: Start the model and begin calculations.

[0050] Step 7: At the time steps where coupling is required, the two models exchange data to achieve dynamic real-time coupling. SWMM transmits the manhole node head at the current time step to the unstructured mesh FVCOM model. FVCOM calculates the flow flux exchanged between the two models based on the manhole node head and the surface water head, and then transmits the calculated flow flux back to SWMM.

[0051] Step 8: FVCOM and SWMM simulate surface water and pipe network water flow respectively based on the updated head and flow rate. Step 7 is repeated at time steps where coupling is required, and finally the simulation of urban flooding with tortuous coastlines or complex building outlines is realized.

[0052] A further feature of this invention is that step 4, based on the different states of surface water flow and pipe water flow, such as... Figure 3 The interaction between surface water flow and pipe water flow is divided into seven types as shown below:

[0053] ((1) When D1=0, if H2≤Z, then the interaction state is that the inspection well neither flows in nor out;

[0054] (2) When D1 = 0, if H2 > Z, then the interaction state is well outflow;

[0055] (3) When D1 > 0, if H2 < Z, then the interaction state is the well inflow;

[0056] (4) When D1 > 0, if H2 = Z, then the interaction state is the well inflow;

[0057] (5) When D1 > 0, if H2 > Z and H2 < Z + D1, then the interaction state is manhole inflow;

[0058] (6) When D1 > 0, if H2 > Z and H2 = Z + D1, then the interaction state is that the inspection well neither flows in nor out;

[0059] (7) When D1 > 0, if H2 > Z + D1, then the interaction state is well outflow.

[0060] Where D1 represents the surface water depth, H2 represents the water head at the inspection well node, and Z represents the surface elevation.

[0061] Step 5 is as follows:

[0062] Step 5-1: Compare the head at the SWMM network nodes with the head of surface water flow. To account for the impact of underground networks on surface water flow, a mass source term needs to be added to the FVCOM continuity equation. The improved continuity equation after vertical integration is as follows:

[0063]

[0064] In the formula: ζ is the current water level of the control volume; The average flow velocity in the control volume direction; Q represents the average flow velocity in the y-direction of the control volume. sur δ represents the flow rate overflowing from the inspection well node of the underground pipeline network; D represents the water depth of the control volume; sur The value is 1 for overflow state, -1 for venting state, and 0 for neither overflowing nor venting state.

[0065] Step 5-2, to reflect the flow exchange between the pipe network and surface water, the flow conservation equation at the nodes in the SWMM is rewritten as follows:

[0066]

[0067] In the formula: A j η is the cross-sectional area of ​​the inspection well node; j t represents the current water level at the inspection well node; t represents time. Q represents the inflow rate of the k-th pipe connecting to this inspection well node; laterin Inbound traffic added for external custom input; Q sur The flow rate of overflow from the inspection well node of the underground pipeline network; δ sur The value is 1 for overflow state, -1 for venting state, and 0 for neither overflowing nor venting state.

[0068] In step 6, the coupled node head and network head are obtained, and the exchanged flow flux is calculated as follows:

[0069]

[0070] H1 = D1 + Z (4)

[0071] H2 = D2 (5)

[0072] In the formula: c0 is the flow coefficient, ranging from [0-1], A is the effective flow area of ​​the manhole, g represents the gravitational acceleration, H1 and H2 are the average head of the grid cell and the head of the manhole node, respectively, D1 represents the surface water depth, D2 represents the water depth inside the manhole, and Z is the surface elevation.

[0073] Verification experiments of the method described in this invention:

[0074] The FVCOM-SWMM coupling method was validated using physical experimental data on the interaction between surface water flow and underground pipe network flow from publicly published literature (Rubinato, et al. Experimental calibration and validation of sewer / surface flow exchange equations in steady and unsteady flow conditions. Journal of Hydrology, 2017, 552:421-432.). A schematic diagram of the model layout is shown below. Figure 4 The test flume was 8m long and 4m wide, with a slope of 1:1000. An open manhole, circular in shape with an inner diameter of 240mm, was located 2.5m from the midpoint of the upstream boundary. A circular pipe with an inner diameter of 75mm connected to the manhole. A pressure gauge was placed 0.478m from the bottom of the flume to the bottom of the pipe, and 480mm upstream from the center of the manhole. The roughness of the flume was set to 0.02, and the roughness of the pipe was 0.009. The initial water depth in both the flume and the pipe was zero. The numerical model was consistent with the experimental model. In the model simulation, the downstream boundary of the surface water flow and the downstream outlet boundary of the drainage system were free outflow open boundaries, while the upstream boundary was a constant inflow boundary.

[0075] Simulated values ​​of water depth and interactive flow rate at the measuring point can be obtained through calculation, and these can be compared with experimental values ​​in the literature, such as... Figure 5-1 and Figure 5-2 As shown, the simulated values ​​agree well with the experimental values, verifying the accuracy of the coupling method.

[0076] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many improvements and changes under the guidance of the present invention without departing from the spirit of the present invention, and these improvements and changes are all within the protection scope of the present invention.

Claims

1. A method for urban flood simulation based on coupling SWMM and FVCOM models based on unstructured grids, characterized in that, The exchange process of surface water flow and underground pipe network water flow is characterized by using the inspection well simplified method, and a non-structured grid FVCOM model is taken as a main program, and a SWMM model is taken as a subprogram for calling by the main program, so that the real-time dynamic two-way data exchange of the surface water dynamic model and the pipe network water dynamic model is performed, the coupling effect of the underground pipe network water flow and the surface water flow is simulated, and finally the coupling simulation of urban waterlogging with a tortuous coastline or a complex building contour based on the non-structured grid is realized, and the process is as follows: Firstly, the models of the underground pipe network water flow and the surface water flow are respectively established by using the SWMM model and the non-structured grid FVCOM model according to given basic data; the spatial topological relationship between the SWMM pipe network nodes and the FVCOM grid space is established; at a time step needing coupling, the pipe network inspection well node water head and the surface water head are obtained, the current time step inspection well node inflow or outflow is judged, the exchanged flow is calculated, and the non-structured grid FVCOM model and the SWMM model respectively perform the simulation of the surface water and the pipe network water flow according to the updated water head and flow; time is advanced, and finally the whole urban waterlogging simulation process is completed; Specifically, the following steps are included: Step 1, basic data of a research region are obtained, and the basic data at least include drainage pipe network distribution, ground elevation data of the research region, positions of inspection wells and building contours; Step 2, the models of the underground pipe network water flow and the surface water flow are respectively established by using the SWMM model and the non-structured grid FVCOM model according to the basic data, and the description of the tortuous coastline or the complex building contour is realized; Step 3, an inp format file generated by the SWMM model is read, the SWMM pipe network node position coordinates are obtained, and the spatial topological relationship with the FVCOM of the surface water flow is established; Step 4, the exchange process of the surface water flow and the underground pipe network water flow is characterized by using the inspection well simplified method according to the SWMM pipe network inspection well node water head and the FVCOM surface water head; Step 5, the non-structured grid FVCOM model is taken as a main program, and the SWMM model is taken as a subprogram for calling by the main program; the specific content is as follows: Step 5-1, the SWMM pipe network inspection well node water head is compared with the FVCOM surface water head, a mass source term is added in a continuity equation of the FVCOM model, and the continuity equation after vertical integration is as follows: （1）； In formula (1): is the current water level of the control volume, is time; is is the control volume directional average flow rate; is is the control volume directional average flow rate; is the flow rate of the overflow from the underground pipe network inspection well node; D is the water depth of the control volume; is the Dirac function, where, is equal to 1; the node is in overflow state, is equal to -1; the node is in underflow state, is equal to 0; the node is in neither overflow nor underflow state, Step 5-2, the flow conservation equation of the node in the SWMM model is as follows: （2）； In formula (2): is the cross-sectional area of the inspection node; is the current water level of the inspection node; is the time; is the flow rate of the first pipe inflow connected to the inspection node; is the externally defined added inflow; is the outflow rate of the inspection node of the underground pipe network; is the Dirac function, where, is 1 in the node overflow state; is -1 in the node outflow state; is 0 in the node neither overflow nor outflow state; Step 6, the model is started to begin calculation; Step 7, at a time step needing coupling, the two models exchange data to realize dynamic real-time coupling, including that the SWMM model transmits the inspection well node water head of the current time step to the non-structured grid FVCOM model, the FVCOM model obtains the coupling node water head and the network water head according to the inspection well node water head and the surface water head, calculates the exchanged flow flux, and then transmits the calculated flow to the SWMM model, so that the water head and the flow are updated; the FVCOM model and the SWMM model respectively perform the simulation of the surface water and the pipe network water flow according to the updated water head and flow; Step 8, time progression, repeat step 7 at the time step when coupling is needed, finally achieve the simulation of urban flood with tortuous coastline or complex building profile.

2. The urban flood simulation method of claim 1, wherein, In step 4, in the exchange process between surface water flow and underground pipe network flow, according to the relationship among surface water depth D1, inspection well node water head H2 and surface elevation Z, the interaction state of surface water flow and underground pipe network flow includes the following situations: (1) When D1=0, if H2≤Z, the interaction state is that the inspection well neither inflows nor outflows; (2) When D1=0, if H2>Z, the interaction state is that the inspection well outflows; (3) When D1>0, if H2Z+D1, the interaction state is that the inspection well inflows; (4) When D1>0, if H2=Z, the interaction state is that the inspection well inflows; (5) When D1>0, if H2>Z and H2Z+D1, the interaction state is that the inspection well inflows; (6) When D1>0, if H2>Z and H2=Z+D1, the interaction state is that the inspection well neither inflows nor outflows; (7) When D1>0, if H2>Z+D1, the interaction state is that the inspection well outflows.

3. The urban flood simulation method of claim 1, wherein, In Step 7, the FVCOM model obtains the coupled node water head and the network water head from the inspection well node water head and the surface water head, and calculates the exchanged flux flux is: （3）； （4）； （5）； in formula (3) to formula (5): is the flow coefficient, ranging [0-1], is the effective flow area of the inspection well, represents the acceleration of gravity, and are the average water head of the grid unit and the inspection well node head, respectively, represents the surface water depth, is the water depth in the inspection well, is the surface elevation.

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