Dike outburst and flood routing simulation method

Abstract

The invention belongs to the technical field of hydraulic engineering, and particularly discloses an embankment burst and flood routing simulation method which comprises the following steps: step 1, subdividing a breach area of an embankment by adopting a rectangular grid, and respectively subdividing a river channel on one side of the embankment and a protection area on the other side of the embankment by adopting an unstructured grid; step 2, flood information in the unstructured grid is acquired, and the flood information is interpolated into the rectangular grid; and step 3, determining outburst information of the breach area by using the water-soil coupling kinetic model, interpolating the outburst information into the unstructured grid, and repeating the step 2 and the step 3 until a preset condition is met. According to the method, a water-soil coupling dynamic model is adopted to describe the dike burst process, parameters such as the burst rate and the final breach size of an existing model do not need to be manually given, and full-automatic simulation of the dike burst process is achieved. According to the method, the structure-non-structure double grid technology is adopted, and the precision and efficiency of the embankment outburst process and outburst flood routing calculation are both considered.

Description

Technical Field

[0001] The invention discloses a dike breach and flood evolution simulation method, belonging to the technical field of water conservancy engineering. Background Art

[0002] Levees are an important part of the flood control system, and the area protected by levees is called a protected area. For areas with long levee coastlines and complex geological conditions, insufficient flood control standards for levee construction or substandard levee quality may cause levee collapse. Once a levee collapses, it will pose a major threat to the safety of life and property of people in the protected area. Therefore, it is necessary to simulate the levee collapse and flood evolution process.

[0003] Since the boundary conditions of the evolution range of natural dam breach floods are irregular, the use of rectangular grids in the simulation process is not very adaptable to complex boundary conditions, so unstructured grids are often used to enhance adaptability to complex boundary conditions. When using unstructured grids to calculate the collapse of breach terrain, the algorithm is complicated because it involves multi-directional terrain reconstruction and gradient calculation. At the same time, in order to better simulate the breach water flow, the existing technology generally uses smaller-sized unstructured grids in the breach area and larger-sized unstructured grids in other areas. Since the calculation time step is the minimum time step of all grids, and the time step of the smallest-sized unstructured grid is often the smallest, that is, the time step in the calculation area is determined by the smallest unstructured grid size unit, which greatly limits the calculation efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a method for simulating dike breach and flood evolution to solve the technical problems of complex algorithms and low computational efficiency in the prior art of simulating dike breach and flood evolution using unstructured grids.

[0005] The present invention provides a method for simulating dike breach and flood evolution, comprising:

[0006] Step 1: using a rectangular grid to divide the breach area of ​​the levee, and using an unstructured grid to divide the river channel on one side of the levee and the protection area on the other side of the levee respectively;

[0007] Step 2: Obtain flood information in the unstructured grid, and interpolate the flood information into the rectangular grid;

[0008] Step 3: Determine the breach information of the breach area using the water-soil coupled dynamic model, and interpolate the breach information into the unstructured grid, repeat steps 2 and 3 until the preset conditions are met, and complete the levee breach and flood evolution simulation.

[0009] Preferably, the water-soil coupled dynamic model is a two-dimensional hydrodynamic model including a riverbed deformation equation; the riverbed deformation equation is determined according to the uplift flux and the sedimentation flux.

[0010] Preferably, the upward flux is determined based on the difference coefficient between the near-bottom sediment concentration and the vertical sediment concentration, the static water settling velocity of a single particle of sediment, and the saturated sediment transport rate of the local water flow bedload.

[0011] Preferably, the upward flux is determined according to the clay scouring rate and the sediment porosity.

[0012] Preferably, the sedimentation flux is determined based on the depth-averaged volumetric sediment content of the sediment, the coefficient of difference between the near-bottom sediment concentration and the vertical sediment concentration, and the static water sedimentation velocity of a single sediment particle.

[0013] Preferably, the length of the long side of the rectangular grid is shorter than the length of the shortest side of the unstructured grid.

[0014] Preferably, the unstructured grid is a triangular grid.

[0015] Preferably, the flood information includes water depth and flow velocity.

[0016] Preferably, the breach information includes water depth, flow velocity and terrain elevation.

[0017] Preferably, obtaining the flood information in the unstructured grid specifically comprises: obtaining the flood information in the unstructured grid using a two-dimensional hydrodynamic model.

[0018] Compared with the prior art, the levee breach and flood evolution simulation method of the present invention has the following beneficial effects:

[0019] The present invention adopts a water-soil coupling dynamic model to describe the levee breach process, and does not require artificially given parameters such as the breach rate and final breach size of the existing model, thus achieving a fully automatic simulation of the levee breach process. The present invention adopts a structured-unstructured dual grid technology, taking into account the accuracy and efficiency of the levee breach process and the breach flood evolution calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figure is a flow chart of a method for simulating dike breach and flood evolution according to an embodiment of the present invention.

[0021] Figure 2 It is a schematic diagram of constructing a levee breach model based on a double grid according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0023] The embodiment of the present invention provides a method for simulating dike breach and flood evolution, such as Figure 1 and Figure 2 As shown, including:

[0024] Step 1: Use rectangular grids to divide the breach area of ​​the levee, and use unstructured grids to divide the river channel on one side of the levee and the protection area on the other side of the levee, such as Figure 2 shown.

[0025] After segmentation, the embodiment of the present invention interpolates the corresponding terrain onto rectangular grid nodes and unstructured grid nodes respectively.

[0026] Step 2: Obtain flood information in the unstructured grid and interpolate the flood information into the rectangular grid.

[0027] For example, given the initial conditions, boundary conditions, roughness and other parameter values ​​of the unstructured grid, the calculation is started using the existing two-dimensional hydrodynamic model, and the calculation starts at time t = 0. The above initial conditions include the initial water depth and flow velocity.

[0028] In the embodiment of the present invention, it is first necessary to determine whether the time t is less than the preset maximum time t max , that is, t<t max , if so, after calculating a time step ΔT, the water depth and flow velocity of each node in the unstructured grid at time t are obtained as flood information.

[0029] After obtaining the flood information, the present invention interpolates the flood information into a rectangular grid, specifically: interpolating the water depth and flow velocity of each node in the unstructured grid into the rectangular grid of the dike breach area. The specific interpolation method can adopt linear interpolation or natural neighbor interpolation.

[0030] Step 3: Use the water-soil coupled dynamic model to determine the breach information of the breach area, and interpolate the breach information into the unstructured grid. Repeat steps 2 and 3 until the preset conditions are met to complete the levee breach and flood evolution simulation.

[0031] After the interpolation in step 2 is completed, the embodiment of the present invention runs the water-soil coupling dynamic model and obtains the breach information of the breach area at time t+ΔT. The breach information of the breach area that can be obtained includes parameters such as breach topography, breach flow process, breach flow velocity, water depth, water level, breach topography elevation, etc.

[0032] Exemplarily, the present invention back-interpolates the water depth, flow velocity and terrain elevation on the rectangular grid nodes of the breach area into the unstructured grid, and then repeats steps 2 and 3 until t≥t max The interpolation here preferably adopts the inverse distance weighted method.

[0033] The model used in the prior art to determine the breach information of the breach area is a two-dimensional shallow water dynamic control equation, which assumes that the development process of the levee breach is considered uniformly, and does not take into account the physical mechanism, resulting in inaccurate breach information. To solve the above problem, the embodiment of the present invention uses a water-soil coupling dynamic model in the breach area. The water-soil coupling dynamic model takes into account the movement of the water-sand mixture, making the resulting breach information more accurate. The water-soil coupling dynamic model of the present invention is as follows:

[0034] The two-dimensional shallow water dynamics control equations based on the basic conservation laws of fluid mechanics include the mass conservation equation and the momentum conservation equation. In order to adapt to the complex water flow state and irregular terrain existing in natural rivers, the present invention organizes the basic control equations into a harmonious conservation form:

[0035]

[0036] Where U is the conserved variable, F and G are flux variables, and S is the source term vector.

[0037]

[0038] Where U is the conserved quantity vector; h is the water depth; u and v are the water flow velocities in the x and y directions respectively; x and y are the spatial coordinates; and c is the depth-averaged volumetric sediment content of the sediment.

[0039]

[0040] Where F is the convective flux vector in the x direction; h is the water depth; u and v are the water flow velocities in the x and y directions respectively; x and y are spatial coordinates; c is the depth-averaged volumetric sediment content of the sediment; g is the gravitational acceleration, which is 9.8 m / s 2 .

[0041]

[0042] Where G is the convective flux vector in the y direction; h is the water depth; u and v are the water flow velocities in the x and y directions respectively; x and y are spatial coordinates; c is the depth-averaged volumetric sediment content of the sediment; g is the gravitational acceleration, which is taken as 9.8 m / s 2 .

[0043]

[0044] Where S is the source vector; h is the water depth; u and v are the water flow velocities in the x and y directions respectively; x and y are spatial coordinates; c is the depth-averaged volumetric sediment content of the sediment; g is the gravitational acceleration, which is 9.8 m / s 2 ; E is the upward flux; D is the total sedimentation flux; p0 is the sediment porosity; S bx and S by are the riverbed slopes in the x and y directions respectively; S fx =-τ bx / ρ and S fy =-τ by / ρ are the resistance in the x and y directions respectively; ρ w and ρ s are the densities of clean water and sediment, respectively, taking 1.0×10 3 kg / m 3 and 2.65×10 3 kg / m 3 ; ρ = ρ w (1-c)+ρ s c is the density of water-sand mixture; ρ0=ρ w p0+ρ s (1-p0) is the saturated wet density of bed sand.

[0045] The riverbed deformation equation in the embodiment of the present invention is as shown in formula (6):

[0046]

[0047] Where t is time; z is riverbed elevation; E is upwelling flux; D is total sedimentation flux; p0 is sediment porosity.

[0048] Some unknown quantities in the above control equations cannot be directly obtained by solving the equations, and additional relationships are required to determine them. The Manning roughness formula is used to calculate the bed resistance:

[0049]

[0050] In the formula, τ bx is the bed resistance in the x direction; τ by is the bed resistance in the y direction; ρ is the density of the water-sand mixture; g is the acceleration due to gravity, which is 9.8 m / s 2; h is the water depth; n is the Manning roughness coefficient; q x is the flow rate in the x direction; q y is the flow rate in the y direction.

[0051] The sediment exchange between the water flow near the riverbed and the riverbed includes two different mechanisms, namely, sediment uplift caused by turbulence and sediment settling caused by gravity. The difference between the uplift flux and the settling flux reflects the non-equilibrium characteristics of water flow and sediment transport. The settling flux calculation expression is:

[0052] D=αwc (9)

[0053] Where α is the difference coefficient between the near-bottom sediment concentration and the vertical sediment concentration; w is the static water settling velocity of a single particle of sediment, calculated using Zhang Ruijin's formula; and c is the depth-averaged volumetric sediment content of the sediment.

[0054] For the levee breach process with sandy materials as the main material, since it is mainly non-cohesive sand, the sediment initiation and transport are simulated by the basic formula of bedload sediment in river dynamics. Since the Mayer Peter-Muller formula (1948) is derived with a wide range of data and has strong adaptability, the present invention uses it to calculate the bedload saturated sediment transport rate. The upward flux calculation formula is:

[0055] E=αwc e (10)

[0056] Where α is the difference coefficient between the sediment concentration near the bottom and the sediment concentration in the vertical line; w is the static water settling velocity of a single particle of sediment; c e is the saturated sediment transport rate of local water bed load, specifically the saturated sediment transport rate of water bed load near the bed surface, which is determined according to formula (11):

[0057]

[0058] In the formula, q b is the saturated bed load transport rate; h is the water depth; u, v are the water flow velocities in the x and y directions respectively; x, y are the spatial coordinates.

[0059] The above q b Determine according to formula (12):

[0060]

[0061] Where θ is the Shields parameter, also known as relative drag force, τ b is τ bx and τ by The resultant force of water and sand; ρ is the density of the water-sand mixture; ρ s is the density of sediment, take 2.65×10 3kg / m 3 ; d is the particle diameter; s is the relative density.

[0062] For embankment materials mainly composed of clay, viscosity plays an important role in its destruction process. Therefore, it is more appropriate to use the soil erosion destruction formula to simulate the breach process. The present invention uses the scour rate formula to calculate the scour rate, and then obtains the uplift flux calculation expression.

[0063] E=ε(1-p0) (13)

[0064] Where ε is the soil scouring rate; p0 is the sediment porosity; ε is determined according to formula (14):

[0065] ε=k d (τ b -τ c ) (14)

[0066] In the formula, k d is the soil scouring rate coefficient; τ b is τ bx and τ by The resultant force; τ c Critical starting shear stress of soil.

[0067] The present invention achieves consistency between the equation and numerical algorithm for embankment breach simulation by adopting different upwelling flux calculation methods for different embankment materials. At the same time, the traditional scour rate formula can only calculate the scour process during the breach process, but cannot calculate the sedimentation process downstream of the breach during the breach formation stage. However, when DE>0, the model of the present invention can calculate the sedimentation process downstream of the breach during the breach formation stage. It can be seen that the flux method used in the present invention can overcome the above problems existing in the traditional scour rate formula.

[0068] In order to better simulate the breach flow, the prior art generally uses a smaller size unstructured grid in the breach area and a larger size unstructured grid in other areas. Since the calculation time step is the minimum time step of all grids, and the time step of the smallest size unstructured grid is often the smallest, that is, the time step in the calculation area is determined by the smallest unstructured grid size unit, which greatly limits the calculation efficiency. The present invention adopts the structure-unstructured dual grid technology, and limits the length of the long side of the rectangular grid to be less than the length of the shortest side of the unstructured grid, so as to realize the use of small-size rectangular grids to calculate the breach development process and water flow process, and use large-size unstructured grids to calculate the flood evolution process in other areas. When calculating the collapse of the rectangular grid, only two directions need to be considered, the calculation steps are simple, and the use of small-size grids can accurately simulate the breach process and water flow field. The use of large-size unstructured grids in the entire calculation area can increase the time step and reduce the number of calculation steps. For example, when calculating the flood storage area, the above-mentioned small-size rectangular grid is meter-level and the large-size unstructured grid is about 100m; for indoor experiments, the small size is centimeter-level and the large size does not exceed 0.5m. Furthermore, the present invention uses an interpolation method to transfer water depth, flow velocity and terrain information between the rectangular grid and the unstructured grid. This method takes into account both calculation accuracy and efficiency.

[0069] The unstructured mesh in the embodiment of the present invention may be a polygonal mesh, preferably a triangular mesh.

[0070] The present invention adopts a water-soil coupling dynamic model to describe the levee breach process, and does not require artificially given parameters such as the breach rate and final breach size of the existing model, thus achieving a fully automatic simulation of the levee breach process. The present invention adopts a structured-unstructured dual grid technology, taking into account the accuracy and efficiency of the levee breach process and the breach flood evolution calculation.

[0071] The above are only several embodiments of the present invention and are not intended to limit the present invention in any form. Although the present invention is disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the above disclosed technical content to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for simulating dike breach and flood evolution, characterized in that: include: Step 1: using a rectangular grid to divide the breach area of ​​the levee, and using an unstructured grid to divide the river channel on one side of the levee and the protection area on the other side of the levee respectively; Step 2: Obtain flood information in the unstructured grid, and interpolate the flood information into the rectangular grid; Step 3: Determine the breach information of the breach area using the water-soil coupled dynamic model, and interpolate the breach information into the unstructured grid, repeat steps 2 and 3 until the preset conditions are met, and complete the levee breach and flood evolution simulation.

2. The method for simulating dike breach and flood evolution according to claim 1, characterized in that: The water-soil coupled dynamic model is a two-dimensional hydrodynamic model including a riverbed deformation equation; The riverbed deformation equation is determined based on the uplift flux and the settling flux.

3. The method for simulating dike breach and flood evolution according to claim 2, characterized in that: The upward flux is determined based on the difference coefficient between the near-bottom sediment concentration and the vertical sediment concentration, the static water settling velocity of a single particle of sediment, and the saturated sediment transport rate of the local water flow bedload.

4. The method for simulating dike breach and flood evolution according to claim 2, characterized in that: The upward flux is determined based on the clay scouring rate and the sediment porosity.

5. The method for simulating dike breach and flood evolution according to claim 2, characterized in that: The sedimentation flux is determined based on the depth-average volumetric sediment content of the sediment, the coefficient of difference between the near-bottom sediment concentration and the vertical sediment concentration, and the static water sedimentation velocity of a single sediment particle.

6. The method for simulating dike breach and flood evolution according to claim 1, characterized in that: The length of the long side of the rectangular grid is shorter than the length of the shortest side of the unstructured grid.

7. The method for simulating dike breach and flood evolution according to claim 6, characterized in that: The unstructured grid is a triangular grid.

8. The method for simulating dike breach and flood evolution according to claim 1, characterized in that: The flood information includes water depth and flow velocity.

9. The method for simulating dike breach and flood evolution according to claim 1, characterized in that: The breach information includes water depth, flow velocity and terrain elevation.

10. The method for simulating dike breach and flood evolution according to claim 1, characterized in that: Obtain flood information in the unstructured grid, specifically: A two-dimensional hydrodynamic model is used to obtain flood information within the unstructured grid.

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