Urban region gaseous radioactive pollutant diffusion simulation method based on OpenFOAM

Abstract

The invention discloses an OpenFOAM-based urban area gaseous radioactive pollutant diffusion simulation method, and relates to the technical field of computational fluid mechanics simulation, and the method comprises the steps: S1, building a three-dimensional model of an urban area based on CAD software and a user-defined script program; s2, importing a three-dimensional city model based on an OpenFOAM open source platform, and performing pretreatment on the three-dimensional city model, the pretreatment including customizing a computational domain and a boundary condition, performing grid division on the computational domain, and performing computational domain distribution; s3, the scalar transport equation is corrected, a Radioactive ScalarTransportFoam radioactivity solver is self-defined, and parallel operation is carried out on the Radioactive ScalarTransportFoam radioactivity solver; and S4, performing simulation result viewing and data collection and analysis. According to the method provided by the invention, the diffusion process of the gaseous radioactive pollutants in the city can be more flexibly, freely and accurately simulated.

Description

Technical Field

[0001] The present invention belongs to the technical field of computational fluid dynamics simulation, and in particular relates to an OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas. Background Art

[0002] Air pollutants, especially radioactive pollutants, can enter the human body through inhalation, damaging the structure and function of human cells and increasing the risk of diseases such as cancer. Furthermore, they can cause severe damage to the environment, affecting the growth and development of plants and animals and leading to a reduction in biodiversity. Furthermore, the spread of radioactive substances can contaminate soil and water sources, further affecting the balance and stability of the entire ecosystem. Therefore, it is crucial to study the diffusion mechanisms of gaseous radioactive pollutants in urban areas, optimize the spatial form of urban blocks, improve the diffusion conditions of local atmospheric pollutants, and enhance the air quality of urban areas.

[0003] In recent years, with the widespread application of computational fluid dynamics (CFD) in atmospheric science, significant progress has been made in simulating the dispersion of atmospheric pollutants in urban areas using CFD software. Meroney et al. (1999) and Yoshihide et al. (2009) used CFD to simulate the effects of buildings on the surrounding flow distribution and pollutant dispersion, comparing their results with those from wind tunnel experiments on the ground axis downwind of pollutants, achieving favorable results. In 2004, Hanna et al. used the computational fluid dynamics software FLACS CFD to simulate the two-dimensional distribution of pollutant concentrations on a plane perpendicular to the inflow direction downwind of an L-shaped building. The simulation results were in good agreement with the wind tunnel test results. In 2012, Zhao et al. used the large eddy model provided by Fluent 6.3.26 and the AERMOD model recommended by the national standard to simulate the dispersion of atmospheric pollutants under the influence of a square building. By comparing the results with the wind tunnel experiments, they evaluated the simulation capabilities of each model.

[0004] CFD is a method that studies the laws of fluid motion through numerical discretization and computational solution based on mathematical physics equations. It treats fluids as composed of a large number of discrete, tiny units and simulates their behavior by calculating the interactions between these units. It can help us accurately simulate atmospheric flow conditions, thereby better understanding the transport and diffusion of pollutants in the atmosphere and providing a scientific basis for developing effective pollution control measures. Summary of the Invention

[0005] In response to the defects in the existing technology, the purpose of the present invention is to provide an OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas. This method can more flexibly and freely simulate the process of gaseous radioactive pollutants diffusing in cities.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM includes the following steps:

[0008] S1. Build a three-dimensional model of the urban area to be simulated based on CAD software and a custom script program;

[0009] S2. Based on the OpenFOAM open source platform, the generated 3D city model is imported and pre-processed. The pre-processing includes defining a calculation domain and boundary conditions, meshing the calculation domain, and allocating the calculation domain.

[0010] S3. Modify the scalar transport equation, customize the RadioactiveScalarTransportFoam radioactive solver, and perform parallel operations;

[0011] S4. Check simulation results and collect and analyze data.

[0012] Furthermore, in the OpenFOAM-based urban area gaseous radioactive pollutant diffusion simulation method, in step S1, two-dimensional CAD data and building heights of the urban area to be simulated are obtained through field surveys or by using public data.

[0013] Furthermore, in the OpenFOAM-based urban area gaseous radioactive pollutant diffusion simulation method, the script algorithm in step S1 specifically includes:

[0014] S11. Adding a height field thickness to the two-dimensional CAD data of the urban area to form three-dimensional CAD data;

[0015] S12, looping through the 3D CAD data, and if the thickness of the height field is not zero, executing the extrude command to extrude the 2D buildings in the urban area to form a 3D CAD model; if the thickness of the height field is 0, skipping the process;

[0016] S13. Batch extrude and export the urban area building three-dimensional model in a specified format.

[0017] Furthermore, in the OpenFOAM-based urban area gaseous radioactive pollutant diffusion simulation method described above, in step S2, the BlockMesh and SnappyHexMesh commands are used to mesh the computational domain, creating a three-dimensional spatial grid that meets the requirements, thereby discretizing the continuous three-dimensional urban space into discontinuous spatial points.

[0018] Furthermore, in the OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas, the DecomposePar command is used in step S2 to distribute the computational domain to a multi-core solver for parallel computing.

[0019] Furthermore, in the above-mentioned OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas, step S3 is specifically as follows:

[0020] The SIMPLE algorithm is used to deal with steady-state incompressible pressure-velocity coupling. For each different radioactive pollutant, its half-life is used to correct the source term of the scalar transport equation, and the corresponding scalar transport equation is solved to simulate the migration, diffusion and decay of radioactive pollutants in the computational domain.

[0021] Furthermore, in the OpenFOAM-based urban area gaseous radioactive pollutant diffusion simulation method, the specific calculation formula of the scalar transport equation in step S3 is:

[0022]

[0023] In formula (1), is the pollutant scalar to be determined, Γ is the diffusion coefficient, S is the source term, U j is the speed, t is the time;

[0024] The continuity equation, momentum equation, and component transport equation are discretely solved by the finite volume method. Based on the pressure and velocity coupling, the SIMPLE algorithm and the first-order upwind scheme are used to solve them.

[0025] According to the initial concentration of each radioactive substance and decay period T, calculate the pollutant scalar to be determined

[0026]

[0027] Based on formulas (1) and (2), the steady-state results are obtained by parallel computation iteration.

[0028] Compared with the existing technology, the OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas provided by the present invention has the following beneficial effects:

[0029] The method provided by the present invention does not need to rely on dedicated commercial software and has higher flexibility and freedom to simulate the process of gaseous radioactive pollutants spreading in the city. When pollution diffusion occurs, the urban pollution status can be immediately judged through simulation, and the treatment plan can be further determined. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of a method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM, provided in an embodiment of the present invention;

[0031] Figure 2 for Figure 1 Another flow chart of the method;

[0032] Figure 3 This is a 3D model of the urban area in the embodiment;

[0033] Figure 4 This is the simulation result of the diffusion of gaseous radioactive pollutants in the urban area of ​​the embodiment. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementations.

[0035] Figure 1 and Figure 2 A flow chart of a method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM provided in an embodiment of the present invention is shown. The method includes the following steps:

[0036] S1. Based on CAD software and custom script program, a three-dimensional model of the urban area to be simulated is established.

[0037] 3D modeling of urban areas is the first step in numerical simulation. For urban areas, 2D CAD data and building heights can be obtained through field surveys or by using publicly available data. Once this data is obtained, 3D modeling is performed using CAD software and custom scripts to create a 3D city model. The specific script algorithm is as follows:

[0038] S11. Adding a height field thickness to the two-dimensional CAD data of the urban area to form three-dimensional CAD data;

[0039] S12, looping through the 3D CAD data, and if the thickness of the height field is not zero, executing the extrude command to extrude the 2D buildings in the urban area to form a 3D CAD model; if the thickness of the height field is 0, skipping the process;

[0040] S13. Batch extrude and export the urban area building three-dimensional model in a specified format.

[0041] S2. Based on the OpenFOAM open source platform, the generated 3D city model is imported and pre-processed on the 3D city model. The pre-processing includes customizing the computational domain and boundary conditions, meshing the computational domain, and allocating the computational domain.

[0042] OpenFOAM is an open source computational fluid dynamics software toolkit that provides a series of functions and modules for simulating fluid flow and related phenomena. It can be used to study various fluid-related problems, including the diffusion of atmospheric pollutants.

[0043] Create a new case on the OpenFOAM platform and import the 3D city model generated in step S1. Before performing CFD numerical simulation, necessary preprocessing is required, including customizing the computational domain, boundary conditions, meshing, and computational domain allocation. Specifically, meshing can be performed using the BlockMesh and SnappyHexMesh commands to create a 3D spatial mesh that meets the requirements, thereby discretizing the continuous 3D city space into discrete spatial points. Finally, use the DecomposePar command to allocate the computational domain to a multi-core solver for parallel computing.

[0044] S3. Modify the scalar transport equation, customize the RadioactiveScalarTransportFoam radioactive solver, and perform parallel calculations.

[0045] Conventional solvers are unable to simulate the diffusion of radioactive materials. This paper uses the SIMPLE algorithm to handle steady-state incompressible pressure-velocity coupling. For each different radioactive contaminant, the half-life is used to modify the source term of the scalar transport equation, solving the corresponding scalar transport equation to simulate the migration, diffusion, and decay of radioactive contaminants within the computational domain. The specific calculation formula for the scalar transport equation is as follows:

[0046]

[0047] In formula (1), is the pollutant scalar to be determined, Γ is the diffusion coefficient, S is the source term, U j is velocity, and t is time. The continuity equation, momentum equation, and component transport equation are discretized and solved using the finite volume method. Based on the pressure-velocity coupling, the SIMPLE algorithm and the first-order upwind scheme are used to solve them.

[0048] According to the initial concentration of each radioactive substance and decay period T, calculate the pollutant scalar to be determined

[0049]

[0050] Based on formulas (1) and (2), the steady-state results can be obtained by parallel computing iteration.

[0051] S4. Check simulation results and collect and analyze data.

[0052] After obtaining the calculation results, you can use post-processing software to view the image, or you can directly extract data from the results for analysis.

[0053] Example

[0054] The above method is used to simulate the diffusion of gaseous radioactive pollutants in a certain urban area. The specific steps are as follows:

[0055] Step 1: Use CAD modeling to build a 3D model of the city based on the 2D data of the city. Figure 3 shown.

[0056] Step 2. Create a new Openfoam example, place the 3D model in the constant / geometry folder of the openfoam example, configure the decomposeParDict file, use the decomposePar command to divide the computational domain, configure the blockMeshDict file, use the blockMesh command to perform preliminary mesh division, then configure the snappyHexMeshDict file in the system folder and execute the snappyHexMesh command to complete the final mesh division.

[0057] Step 3: Set the boundary conditions, set it to steady-state calculation, iterate 1000 steps, set the boundary conditions such as inlet wind and temperature profile; configure the scalar transport equation and perform parallel operation. The scalar transport equation is:

[0058]

[0059] Since the concentration of the pollutant Phi changes over time and decays continuously, Equation (2) must be introduced to solve the transport of radioactive substances. The solver after introducing Equation (2) is the custom RadioactiveScalarTransportFoam radioactivity solver.

[0060] Step 4: Get the simulation results and analyze the results. Figure 4 shown.

[0061] The OpenFOAM-based method for simulating the diffusion of gaseous radioactive pollutants in urban areas, provided by this paper, can accurately simulate the diffusion of radioactive pollutants in urban areas. This method is not limited to specialized commercial copyrighted software and allows for highly flexible customization. Simulations can assess urban pollution levels and provide data support for further development of remediation plans.

[0062] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM, comprising the following steps: S1. Building a three-dimensional model of the urban area to be simulated based on CAD software and a custom script program; S2. Based on the OpenFOAM open source platform, the generated three-dimensional city model is imported and pre-processed on the three-dimensional city model, wherein the pre-processing includes customizing the calculation domain and boundary conditions, meshing the calculation domain, and allocating the calculation domain; S3, modify the scalar transport equation, customize the RadioactiveScalarTransportFoam radioactive solver, and perform parallel operations; S4. Check simulation results and collect and analyze data.

2. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to claim 1, characterized in that: In step S1, two-dimensional CAD data and building heights of the urban area to be simulated are obtained through field surveys or by using public data.

3. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to claim 2 is characterized in that: The script algorithm in step S1 specifically includes: S11, adding a height field thickness to the two-dimensional CAD data of the urban area to form three-dimensional CAD data; S12, looping through the 3D CAD data, if the height field thickness is not zero, executing the extrude command to extrude the 2D buildings in the urban area to form a 3D CAD model, if the height field thickness is 0, skipping; S13. Batch extrude and export the three-dimensional building models of urban areas in a specified format.

4. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to any one of claims 1 to 3, characterized in that: In step S2, the BlockMesh and SnappyHexMesh commands are used to mesh the computational domain and create a three-dimensional spatial grid that meets the requirements, thereby discretizing the continuous three-dimensional urban space into discontinuous spatial points.

5. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to claim 4, characterized in that: In step S2, the DecomposePar command is used to distribute the computational domain to the multi-core solver to prepare for parallel computing.

6. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to claim 5, characterized in that: Step S3 is specifically as follows: The SIMPLE algorithm is used to deal with steady-state incompressible pressure-velocity coupling. For each different radioactive pollutant, the half-life is used to correct the source term of the scalar transport equation, and the corresponding scalar transport equation is solved to simulate the migration, diffusion and decay of radioactive pollutants in the computational domain.

7. The method for simulating the diffusion of gaseous radioactive pollutants in urban areas based on OpenFOAM according to claim 6, characterized in that: The specific calculation formula of the scalar transport equation in step S3 is: In formula (1), is the pollutant scalar to be determined, Γ is the diffusion coefficient, S is the source term, U j is the speed, t is the time; The continuity equation, momentum equation, and component transport equation are discretely solved by the finite volume method, and the SIMPLE algorithm and the first-order upwind scheme are used to solve them according to the coupling of pressure and velocity; According to the initial concentration of each radioactive substance and decay period T, the desired pollutant scalar is calculated Based on formulas (1) and (2), the steady-state results are obtained by parallel calculation iteration.

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