Radiation transfer calculation method suitable for tetrahedral mesh

Abstract

The invention discloses a radiation transfer calculation method suitable for a tetrahedral mesh, which optimizes an original tetrahedral mesh division process into a hexahedral mesh structure which is more already solved by gradually processing tetrahedral mesh data, and effectively improves the calculation efficiency of a radiation simulation process. The tetrahedral mesh is cut into the hexahedral mesh, and the connection relation between the data is kept, so that the high efficiency and accuracy of the calculation process are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of numerical simulation solutions, and in particular relates to a radiation transmission calculation method applicable to tetrahedral grids. Background Art

[0002] Thermal radiation, one of the three basic modes of heat transfer, is a crucial heat transfer mechanism in vacuum and high-temperature environments. With the development of industry, the requirements for the accuracy and efficiency of numerical simulations of thermal radiation transfer are continuously increasing. The main computational methods for simulating radiative heat transfer processes include ray tracing and the radiative transfer equation. The ray tracing method primarily calculates surface-to-surface, surface-to-point, point-to-point, and point-to-surface radiative heat transfer. The core element of these algorithms is the calculation of the radiative transfer coefficient between geometric surfaces. In 2017, Li Fubing et al. filed patent number 201610884011.X, titled "A Method for Calculating Radiative Transfer Coefficients." This method simulates the radiative transfer coefficient of non-gray bodies and non-gray surfaces by tracing the emitted light beams generated within a spatial element. This method improves the calculation speed of the radiative transfer coefficient and, in turn, enhances the ray tracing method's ability to simulate radiative transfer processes. This method requires tracing a large number of radiative energy beams, making it difficult to solve the radiative transfer equation in multidimensional and complex structures. The mathematical method of the ray tracing method effectively avoids these issues. The core element of the latter algorithm is to solve the radiation transfer equation to calculate the radiation intensity distribution in the space. This requires discretizing the geometric space and calculating the radiation intensity at each node through mathematical methods to achieve a simulation description of the radiation physical field. The process of meshing the geometric model is very important in computational simulation. The mesh discretizes the continuous physical space into a finite number of units, allowing the solution process to be approximated by numerical methods. In numerical simulation, tetrahedral meshes and hexahedral meshes are common mesh types, corresponding to the application of unstructured meshes and structured meshes respectively. They have their own advantages and disadvantages and are suitable for different simulation scenarios.

[0003] Tetrahedral meshes, with their adaptability, excel at handling complex geometries and irregular boundaries. Due to the flexible shape of tetrahedral elements, they can easily cover any complex or curved object. This makes tetrahedral mesh generation particularly convenient when dealing with irregular geometries and complex boundaries. However, tetrahedral meshes also have some drawbacks. First, due to the irregular shape of tetrahedrons, the connection method between adjacent tetrahedrons can lead to poor convergence of the numerical solution, thus affecting the accuracy of simulation results. In 2019, Liu Peigang et al. applied for invention patent number 201910445008, entitled "A Reservoir Adaptive Tetrahedral Decomposition Method." This patent provides a reservoir-adaptive tetrahedral decomposition method that optimizes mesh quality by locally subdividing the tetrahedral mesh. Second, tetrahedral meshes are computationally less efficient than hexahedral meshes. Especially for large-scale problems, tetrahedral meshes can result in higher computational costs and longer solution times. In contrast, hexahedral meshes are generally suitable for discretizing regular geometries, offering higher computational efficiency and better numerical stability. However, hexahedral meshes have certain limitations when dealing with complex geometries. For irregular objects or models with complex boundaries, hexahedral meshes often require significant mesh adjustments and optimization to accommodate the geometry. To calculate radiation intensity for complex geometries, a numerical method that can accommodate tetrahedral meshes while also providing convenient and fast calculations is needed. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this paper provides a radiation transfer calculation method for tetrahedral meshes. By gradually processing the tetrahedral mesh data, the original tetrahedral mesh division process is optimized to a more easily solved hexahedral mesh structure, effectively improving the computational efficiency of the radiation simulation process. By dividing the tetrahedral mesh into hexahedral meshes and maintaining the connectivity between the data, the efficiency and accuracy of the calculation process are ensured.

[0005] The technical solutions adopted by the present invention to solve the technical problems are as follows:

[0006] Step 1: First, define the spatial domain, angular domain, and refractive index parameters for the radiative transfer calculation. Then, obtain the tetrahedral mesh to be calculated and parse the mesh information line by line to identify the structural data of the tetrahedral mesh and extract the boundary conditions and other key information.

[0007] Step 2: Extract the geometric information of the tetrahedral elements one by one in the tetrahedral mesh, including the information of the nodes, faces, and elements of the tetrahedral mesh, and calculate the coordinates of the midpoint of each edge, the center of each face, and the center of gravity of each tetrahedral element; cut each tetrahedral element into four hexahedral elements, and maintain the connection relationship of the tetrahedral mesh during the cutting process;

[0008] Step 3: After the hexahedral elements are cut, the nodes of the generated hexahedral elements are arranged one by one, including detailed information about the nodes, faces, and elements. The vertex coordinates of the hexahedral elements are calculated based on the point coordinates of the tetrahedral elements. The node coordinates on the edges of the hexahedral elements are then calculated based on the vertex coordinates. The nodes on the faces are then generated based on the node coordinates of each edge. Finally, the node coordinates within the hexahedral elements are mapped based on the nodes on the corresponding faces.

[0009] Step 4: Based on the discrete angles determined in the angle domain, the discrete angles and the normal directions of the tetrahedral element faces are judged to determine the calculation order within the tetrahedral element. Then, in the hexahedral elements divided by a tetrahedral element, the calculation order of the hexahedral elements is also sorted based on the discrete angle directions and the distribution of the centroid positions of the hexahedral elements.

[0010] Step 5: Extract discrete angles and calculate the radiation intensity within each unit in the order of the spatial domain units. After extracting the tetrahedral unit, calculate the angular radiation intensity distribution of each hexahedral unit within the tetrahedral unit in turn according to the unit's boundary conditions and the medium's radiation source terms. After the current calculation is completed, the calculation result of this hexahedral unit is used as the boundary condition of the next hexahedral calculation unit to perform the calculation of the next hexahedral unit.

[0011] Step 6: After all hexahedral elements within the tetrahedral element are calculated, the next tetrahedral element is extracted from the tetrahedral mesh according to the calculation direction, and the radiation intensity is calculated repeatedly until the angular radiation intensity is calculated.

[0012] Step 7: After calculating the radiation intensity in all directions, calculate the input radiation in the spatial domain and compare the relative error between the input radiation in the current calculation step and the input radiation in the previous calculation step. If the convergence condition is not met, return to step 5, determine the calculation angle, and calculate the radiation intensity on the node element by element according to the element calculation order until the convergence condition is met. Then output the radiation intensity in the spatial domain at each angle to realize the radiation transfer simulation of the tetrahedral mesh.

[0013] Furthermore, the radiation intensity is described as a function of angle and space, specifically expressed as:

[0014]

[0015] Where r is the spatial coordinate of the radiation intensity; Ω is the angular coordinate of the radiation intensity; Represents the partial derivative of radiation intensity with respect to spatial coordinates, θ represents the value of the zenith angle, ξ represents the projection of the unit vector of the angular coordinate on the z-axis, μ represents the projection of the unit vector of the angular coordinate on the x-axis, η represents the projection of the unit vector of the angular coordinate on the y-axis, I(r,Ω) represents the radiation intensity value, represents the value of the circular angle, κa represents the absorption coefficient, κ s represents the scattering coefficient, I b (r) represents the blackbody radiation intensity value on the spatial coordinate, Ω′ represents the angular coordinate on other incident spatial coordinates; the derivatives α, β and γ of the refractive index n with respect to space are:

[0016]

[0017] Furthermore, the radiation source term is:

[0018]

[0019] Furthermore, the step 3 is specifically as follows:

[0020] First, the vertices of the hexahedral unit obtained by splitting are extracted from the nodes of the original tetrahedral unit. Then, according to the expected number of nodes set in the hexahedral unit, they are evenly divided on each edge to obtain the nodes on each edge of the hexahedral unit; after that, the nodes on each edge are connected in sequence to form the intersection points on the surface. Finally, based on the surface composed of the center of gravity of the original tetrahedron and its opposite surface, the points between the two surfaces are connected and evenly divided according to the expected number of nodes set in the hexahedral unit to obtain the nodes inside the hexahedron.

[0021] Furthermore, the mesh nodes are distributed in the hexahedral unit and can be calculated using a three-dimensional shape function. The shape function in the hexahedral unit is expressed as the product of the shape functions in three dimensions:

[0022]

[0023] Where, Represents the Lagrange interpolation basis functions on the x, y, and z axes respectively; K v Represents the shape function after orthogonal multiplication of the basis functions on the three coordinate axes;

[0024] The physical quantities within the hexahedral unit are expressed by shape functions. For the spatial coordinate x, the radiation intensity I is expressed as:

[0025]

[0026] Where, Respectively represents the number of nodes on the x, y, and z axes in each unit, x v Indicates the x-coordinate value of each node in the element, I v Indicates the radiation intensity value at each node in the element;

[0027] The partial derivative of the radiation intensity with respect to the spatial coordinate is expressed by the shape function, and the radiation transfer equation is expressed by discrete nodes in the spatial domain. The coefficient matrix A of the radiation transfer equation is calculated, and the radiation intensity matrix B is calculated according to the source term and boundary conditions of the radiation transfer equation. The calculation matrix AI=B is constructed to obtain the radiation intensity value on the hexahedral unit node currently being calculated.

[0028] Furthermore, in step 5, after the radiation intensity is calculated in the hexahedral unit, the radiation intensity is assigned to the next hexahedral unit through the adjacent faces between the nodes according to the propagation direction of the angle. When the next hexahedral unit is calculated, this part of the radiation intensity is used as the boundary condition, and together with the radiation source items of other nodes, the calculation matrix AI=B is constructed to complete the cyclic calculation of each unit.

[0029] Furthermore, in step 7, the input radiation is the integral of the radiation intensity in all directions in the spatial domain, which is expressed as:

[0030] G(r)=∫ 4π I(r,Ω)dΩ

[0031] By calculating the input radiation error of the two iterative processes, it is determined whether the current calculation has reached the radiation balance state. When the error reaches the convergence condition, it is determined that the calculation has reached the radiation balance. At this time, the radiation intensity of each spatial node at each angle can describe the process of radiation transmission.

[0032] The beneficial effects of the present invention are as follows:

[0033] The beneficial effect of the present invention is that it provides a radiation transfer calculation method suitable for tetrahedral meshes, which realizes the fine simulation of the radiation transfer process in complex structures. This method optimizes the original tetrahedral mesh division process into a hexahedral mesh structure that is easier to solve by gradually processing the tetrahedral mesh data, effectively improving the calculation efficiency of the radiation simulation process. By cutting the tetrahedral mesh into hexahedral meshes and maintaining the connection relationship between the data, the efficiency and accuracy of the calculation process are ensured. Furthermore, the tetrahedral units and hexahedral units are calculated and sorted respectively according to the directional characteristics of the radiation transfer, which conforms to the physical process of radiation transmission, and expands the simulation calculation of radiation transmission to more complex geometric structures, providing technical support for industrial radiation analysis and radiation measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the method of the present invention;

[0035] Figure 2 Schematic diagram of the process of discretizing a tetrahedral mesh into a hexahedral mesh according to the present invention;

[0036] Figure 3It is a partitioning diagram after the tetrahedral units are extracted by the partitioning method of the present invention;

[0037] Figure 4 It is a schematic diagram of the radiation transfer within the hexahedral unit of the calculation method of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and examples.

[0039] The present invention provides a radiation transfer calculation method applicable to tetrahedral meshes. Specifically, the tetrahedral mesh is converted into a hexahedral mesh while keeping the mesh adapted to the original geometric structure, and the radiation transfer calculation information is transmitted through the hexahedral mesh. The calculation process is as follows: Figure 1 The present invention provides the following technical solution, which specifically includes the following steps:

[0040] Step 1: First, define the spatial domain, angular domain, and refractive index parameters for the radiation transfer calculation. Then, obtain the tetrahedral mesh model to be calculated, parse the mesh information line by line, identify the structural data of the tetrahedral mesh, and extract the boundary conditions and other key information.

[0041] Step 2: Extract the geometric information of each tetrahedral mesh element in the spatial domain, including the node, face, and cell information of the original tetrahedral mesh element. Calculate the coordinates of the midpoint of each edge, the center of each face, and the centroid of each tetrahedral element. Cut each tetrahedral element into four hexahedral elements, maintaining the connectivity of the tetrahedral mesh during the cutting process.

[0042] Step 3: After the hexahedral mesh is cut, the nodes of the generated hexahedral elements are arranged one by one, including detailed information on nodes, faces, and elements. The vertex coordinates of the hexahedral elements are calculated based on the point coordinates of the original tetrahedral elements. Then, the node coordinates on the edges of the hexahedral elements are calculated based on the vertex coordinates. Then, the nodes on the faces are generated according to the node coordinates of each edge. Finally, the node coordinates within the hexahedral element are mapped according to the nodes on the corresponding faces.

[0043] Step 4: Based on the discrete angle determined by the angle domain, determine the discrete angle and the normal direction of the tetrahedral element face to determine the calculation order within the tetrahedral element. Then, in the hexahedral element divided by a tetrahedral element, sort the calculation order of the hexahedral elements based on the discrete angle direction and the distribution of the center of gravity of the hexahedral elements.

[0044] Step 5: Extract discrete angles and calculate the radiation intensity within the unit one by one according to the calculation order of the spatial domain unit. After extracting the tetrahedral unit, calculate the angular radiation intensity distribution of each hexahedral unit within this tetrahedral unit according to the boundary conditions of the unit and the radiation source term of the medium. After the current calculation is completed, the calculation result of this hexahedral unit is used as the boundary condition of the next hexahedral calculation unit to perform the calculation of the next hexahedral unit.

[0045] Step 6: After all the hexahedral elements within the tetrahedral element are calculated, the next tetrahedral element is extracted according to the calculation direction, and the radiation intensity is calculated repeatedly until the angular radiation intensity is calculated.

[0046] Step 7: After calculating the radiation intensity in all directions, calculate the input radiation in the spatial domain and compare the relative error between the input radiation in the current calculation step and the input radiation in the previous calculation step. If the convergence condition is not met, return to step 5, determine the calculation angle, and calculate the radiation intensity on the node element by element according to the element calculation order until the convergence condition is met. After that, the radiation intensity in the spatial domain at each angle can be output to realize the radiation transfer simulation of the tetrahedral mesh structure.

[0047] The emission, absorption, and scattering processes of radiation transmission can be expressed by equations, and the radiation intensity can be described as a function of angle and space, specifically as follows:

[0048]

[0049] In the above formula, r is the spatial coordinate of the radiation intensity; Ω is the angular coordinate of the radiation intensity; the radiation simulation method described in the above steps first discretizes the angle and then discretizes the spatial domain.

[0050] The spatial derivatives α, β and γ of the refractive index n are:

[0051]

[0052] The radiation source term described in the above steps is the right side of the equation:

[0053]

[0054] The expression of radiative transfer and the spatial discretization process described in steps 2 and 3 are as follows: Figure 2 As shown in the figure, after the calculation angle is determined, the transmission order of the tetrahedral elements is first determined according to the direction, and then the tetrahedral elements are extracted one by one and decomposed into hexahedral elements for solution.

[0055] The tetrahedral units extracted in step 2 are as follows Figure 3 As shown, the original tetrahedron element nodes described in the subsequent steps are replaced by Figure 3Nodes 1 to 15 of the tetrahedron are described, including the vertices of the tetrahedron: node 1, node 2, node 3, node 4, the center of the tetrahedron: node 5, the centers of the tetrahedron faces: node 6, node 7, node 8, node 9, and the midpoints of the tetrahedron edges: node 10, node 11, node 12, node 13, node 14, node 15. The specific partitioning method is to partition along the center of the tetrahedron, the center of the face, and the midpoint of the edge, that is, along Figure 3 The surface composed of the following nodes is divided: the surface composed of nodes 5, 6, 10, and 7; the surface composed of nodes 5, 7, 11, and 8; the surface composed of nodes 5, 8, 12, and 6; the surface composed of nodes 5, 6, 14, and 9; the surface composed of nodes 5, 7, 13, and 9; and the surface composed of nodes 5, 8, 15, and 9.

[0056] The example of hexahedral element node reconstruction described in step 3 is as follows Figure 4 As shown, according to the expected number of nodes to be set in the hexahedron, nodes are constructed from points to edges, from edges to faces, and from faces to bodies. Specifically, the vertices of the hexahedron units obtained by splitting are first extracted from the nodes of the original tetrahedron unit, and then, according to the expected number of nodes to be set in the hexahedron unit, the nodes on each edge of the hexahedron unit are evenly divided at equal intervals. After that, the nodes on each edge are connected in sequence to form the intersection points on the surface. Finally, based on the surface composed of the center of gravity of the original tetrahedron and its opposite surface, the points between the two surfaces are connected, and the nodes in the hexahedron body are evenly divided according to the expected number of nodes to be set in the hexahedron unit.

[0057] In the hexahedral grid, grid nodes are distributed, which can be calculated using three-dimensional shape functions. The shape function within the unit can be expressed as the product of the shape functions in three dimensions:

[0058]

[0059] The physical quantities within the hexahedral unit can be expressed by shape functions. For example, the spatial coordinate x, the radiation intensity I can be expressed as:

[0060]

[0061] By expressing the partial derivative of radiation intensity with respect to spatial coordinates through shape functions, the radiation transfer equation can be expressed in discrete nodes in the spatial domain. The coefficient matrix A of the radiation transfer equation can be calculated based on this, and the radiation intensity matrix B can be calculated based on the source terms and boundary conditions of the radiation transfer equation. By constructing the calculation matrix AI=B, the radiation intensity value at the hexahedral unit node currently being calculated can be obtained.

[0062] In the calculation unit information transmission described in step 5, after the radiation intensity is calculated in the hexahedral unit, the radiation intensity is assigned to the next hexahedral unit through the adjacent faces between nodes according to the propagation direction of the angle. When the next hexahedral unit is calculated, this part of the radiation intensity is used as the boundary condition, and together with the radiation source items of other nodes, the calculation matrix AI = B is constructed to complete the cyclic calculation of each unit.

[0063] The input radiation described in step 6 is the integral of the radiation intensity in all directions in the spatial domain, which is expressed as:

[0064] G(r)=∫ 4π I(r,Ω)dΩ

[0065] By calculating the input radiation error of the two iterative processes, it can be determined whether the current calculation has reached the radiation equilibrium state. When the error reaches the convergence needle, as described in step 7, the calculation is considered to have reached radiation equilibrium. At this time, the radiation intensity of each spatial node at each angle can describe the radiation transmission process.

Claims

1. A radiation transfer calculation method suitable for tetrahedral grids, characterized in that: The steps include: Step 1: First, define the spatial domain, angular domain, and refractive index parameters for the radiative transfer calculation. Then, obtain the tetrahedral mesh to be calculated and parse the mesh information line by line to identify the structural data of the tetrahedral mesh and extract the boundary conditions and other key information. Step 2: Extract the geometric information of the tetrahedral elements one by one in the tetrahedral mesh, including the information of the nodes, faces, and elements of the tetrahedral mesh, and calculate the coordinates of the midpoint of each edge, the center of each face, and the center of gravity of each tetrahedral element; cut each tetrahedral element into four hexahedral elements, and maintain the connection relationship of the tetrahedral mesh during the cutting process; Step 3: After the hexahedral elements are cut, the nodes of the generated hexahedral elements are arranged one by one, including detailed information about the nodes, faces, and elements. The vertex coordinates of the hexahedral elements are calculated based on the point coordinates of the tetrahedral elements. The node coordinates on the edges of the hexahedral elements are then calculated based on the vertex coordinates. The nodes on the faces are then generated based on the node coordinates of each edge. Finally, the node coordinates within the hexahedral elements are mapped based on the nodes on the corresponding faces. Step 4: Based on the discrete angles determined in the angle domain, the discrete angles and the normal directions of the tetrahedral element faces are judged to determine the calculation order within the tetrahedral element. Then, in the hexahedral elements divided by a tetrahedral element, the calculation order of the hexahedral elements is also sorted based on the discrete angle directions and the distribution of the centroid positions of the hexahedral elements. Step 5: Extract discrete angles and calculate the radiation intensity within each unit in the order of the spatial domain units. After extracting the tetrahedral unit, calculate the angular radiation intensity distribution of each hexahedral unit within the tetrahedral unit in turn according to the unit's boundary conditions and the medium's radiation source terms. After the current calculation is completed, the calculation result of this hexahedral unit is used as the boundary condition of the next hexahedral calculation unit to perform the calculation of the next hexahedral unit. Step 6: After all hexahedral elements within the tetrahedral element are calculated, the next tetrahedral element is extracted from the tetrahedral mesh according to the calculation direction, and the radiation intensity is calculated repeatedly until the angular radiation intensity is calculated. Step 7: After calculating the radiation intensity in all directions, calculate the input radiation in the spatial domain and compare the relative error between the input radiation in the current calculation step and the input radiation in the previous calculation step. If the convergence condition is not met, return to step 5, determine the calculation angle, and calculate the radiation intensity on the node element by element according to the element calculation order until the convergence condition is met. Then output the radiation intensity in the spatial domain at each angle to realize the radiation transfer simulation of the tetrahedral mesh.

2. The radiation transfer calculation method applicable to tetrahedral grids according to claim 1, characterized in that: The radiation intensity is described as a function of angle and space, specifically expressed as: Where r is the spatial coordinate of the radiation intensity; Ω is the angular coordinate of the radiation intensity; Represents the partial derivative of radiation intensity with respect to spatial coordinates, θ represents the value of the zenith angle, ξ represents the projection of the unit vector of the angular coordinate on the z-axis, μ represents the projection of the unit vector of the angular coordinate on the x-axis, η represents the projection of the unit vector of the angular coordinate on the y-axis, I(r,Ω) represents the radiation intensity value, represents the value of the circular angle, κ a represents the absorption coefficient, κ s represents the scattering coefficient, I b (r) represents the blackbody radiation intensity value on the spatial coordinate, Ω′ represents the angular coordinate on other incident spatial coordinates; the derivatives α, β and γ of the refractive index n with respect to space are:

3. The radiation transfer calculation method applicable to tetrahedral grids according to claim 2, characterized in that: The radiation source term is:

4. The radiation transfer calculation method applicable to tetrahedral grids according to claim 3, characterized in that: The step 3 is specifically as follows: First, the vertices of the hexahedral unit obtained by splitting are extracted from the nodes of the original tetrahedral unit. Then, according to the expected number of nodes set in the hexahedral unit, they are evenly divided on each edge to obtain the nodes on each edge of the hexahedral unit; after that, the nodes on each edge are connected in sequence to form the intersection points on the surface. Finally, based on the surface composed of the center of gravity of the original tetrahedron and its opposite surface, the points between the two surfaces are connected and evenly divided according to the expected number of nodes set in the hexahedral unit to obtain the nodes inside the hexahedron.

5. The radiation transfer calculation method applicable to tetrahedral grids according to claim 4, characterized in that: The hexahedral unit is distributed with mesh nodes, which can be calculated using three-dimensional shape functions. The shape function in the hexahedral unit is expressed as the product of the shape functions in three dimensions: Where, Represents the Lagrange interpolation basis functions on the x, y, and z axes respectively; K v Represents the shape function after orthogonal multiplication of the basis functions on the three coordinate axes; The physical quantities within the hexahedral unit are expressed by shape functions. For the spatial coordinate x, the radiation intensity I is expressed as: Where, Respectively represents the number of nodes on the x, y, and z axes in each unit, x v Indicates the x-coordinate value of each node in the element, I v Indicates the radiation intensity value at each node in the element; The partial derivative of the radiation intensity with respect to the spatial coordinate is expressed by the shape function, and the radiation transfer equation is expressed by discrete nodes in the spatial domain. The coefficient matrix A of the radiation transfer equation is calculated, and the radiation intensity matrix B is calculated according to the source term and boundary conditions of the radiation transfer equation. The calculation matrix AI=B is constructed to obtain the radiation intensity value on the hexahedral unit node currently being calculated.

6. The radiation transfer calculation method applicable to tetrahedral grids according to claim 5, characterized in that: In step 5, after the radiation intensity is calculated in the hexahedral unit, the radiation intensity is assigned to the next hexahedral unit through the adjacent surfaces between the nodes according to the propagation direction of the angle. When the next hexahedral unit is calculated, this part of the radiation intensity is used as the boundary condition, and together with the radiation source items of other nodes, a calculation matrix of AI=B is constructed to complete the cyclic calculation of each unit.

7. The radiation transfer calculation method applicable to tetrahedral grids according to claim 6, characterized in that: In step 7, the input radiation is the integral of the radiation intensity in all directions in the spatial domain, which is expressed as: G(r)=∫ 4π I(r,Ω)dΩ By calculating the input radiation error of the two iterative processes, it is determined whether the current calculation has reached the radiation balance state. When the error reaches the convergence condition, it is determined that the calculation has reached the radiation balance. At this time, the radiation intensity of each spatial node at each angle can describe the process of radiation transmission.

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