A method for parallel generation of hexahedral mesh of assembly in fast reactor core based on block structure method

Abstract

The application relates to the technical field of finite element mesh, and particularly discloses a hexahedral mesh parallel generation method for a fast reactor core assembly based on a block structure method, wherein Delaunay triangle partitioning is performed on the region of the same side of the wire winding, a Laplace equation is solved to generate an isopleth, and an orthogonal mesh is generated according to the isopleth to obtain a triangular surface mesh template of the same side of the wire winding; the fuel rod assembly is divided into six sections, each section is divided into a plurality of layers, the first section is taken as a base section, based on the triangular surface mesh template of the same side of the wire winding, block meshes are divided in each layer, quadrilateral surface meshes are generated in the block meshes, each layer surface mesh of other sections is obtained by rotating each layer surface mesh of the first section by a set angle, and the hexahedral mesh model is formed by connecting the layer surface meshes; the hexahedral mesh model is expanded; and the loop calling function is parallel optimized. The application solves the problems of incorrect generation of the hexahedral mesh of the fast reactor core assembly and low mesh division efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of finite element mesh, in particular to a hexahedral mesh parallel generation method for fast reactor core assembly based on block structure method. BACKGROUND

[0002] In thermal-hydraulic simulation of fast neutron reactor, the type of mesh has a significant influence on the accuracy of simulation results. Currently, the commonly used mesh types mainly include tetrahedral mesh and hexahedral mesh. Compared with tetrahedral mesh, hexahedral mesh has higher numerical precision, lower spatial complexity and higher efficiency due to its closer orthogonality, which effectively reduces the condition number of numerical calculation.

[0003] Currently, the reference "Pietroni N, Campen M, Sheffer A, et al. Hex-mesh generation and processing: a survey[J]. ACM transactions on graphics, 2022, 42(2): 1-44." Common hexahedral mesh generation algorithms include sweep method, mapping method, etc. The sweep method is a method of connecting two-dimensional quadrilateral mesh along the path to rotate, stretch and translate geometric transformation into hexahedral mesh. Among them, the initial surface is called "source", and the surface finally reached along the path is called "target". This method can easily divide the mesh by identifying the source and target. However, for more complex shapes, it may be difficult to find a suitable sweep path using the sweep method, or it may need to be divided into multiple sources or targets. The mapping method maps the complex geometry of the physical space to a regular computational space through coordinate transformation, forms a regular spatial geometry, then divides the mesh in the computational space, and finally maps back to the geometry of the physical space. However, for complex geometric shapes, the mapping method has the defects of low approximation accuracy and difficulty in automation.

[0004] The main hexahedral mesh division algorithm of mainstream commercial mesh division software mainly uses the above two methods. For example, ICEM provides three hexahedral mesh generation algorithms, including sweep method, decomposition method based on sweep and decomposition method based on hexahedral block. The method based on hexahedral block decomposition refers to first decomposing the model into a set of hexahedral blocks, and then generating hexahedral mesh for each sub-block using the mapping method. However, the hexahedral mesh generation algorithm provided by ICEM cannot generate a correct hexagonal mesh model when processing the fast reactor core assembly model, and has problems such as inconsistency between the outer boundary and the geometry, inability to match the mesh nodes of the internal flow channel, etc. (as shown in Figure 1 ) GMSH can generate hexahedral mesh through sweep method. However, due to the increased geometric complexity of the model, simple use of the sweep method cannot generate a correct mesh model.

[0005] Therefore, the technical problem to be solved by the present application is that the hexahedral mesh of the fast reactor core assembly cannot be correctly generated and the mesh partitioning efficiency is low. SUMMARY

[0006] To solve the above problems, the present application provides a hexahedral mesh parallel generation method for a fast reactor core assembly based on a block structure method, which solves the problem of incorrect generation of the hexahedral mesh of the fast reactor core assembly. Taking a 19-rod fuel assembly as a reference, the central symmetry of the hexagon is utilized to first generate a four-sided mesh with a wire pitch of one-sixth as a base segment through the block structure method, and then construct a complete assembly mesh through a 60° rotation operation, and finally extend to different rod bundle assembly models.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A hexahedral mesh parallel generation method for a fast reactor core assembly based on a block structure method, the method comprising:

[0009] Performing Delaunay triangulation in the wire-wound same-side region, solving the Laplace equation to generate contour lines, and generating orthogonal meshes according to the contour lines to obtain triangular face mesh templates in the wire-wound same-side region;

[0010] Dividing the fuel rod assembly into six segments, and dividing each segment into a plurality of layers, taking the first segment as a base segment, based on the triangular face mesh templates in the wire-wound same-side region, dividing block meshes in each layer, and generating quadrilateral face meshes in the block meshes, rotating each layer face mesh by a set angle to obtain each layer face mesh of other segments, and connecting each layer face mesh to form a hexahedral mesh model;

[0011] Extending the hexahedral mesh model;

[0012] Parallel optimizing the loop call function; wherein the loop call function is used to generate quadrilateral meshes of each layer.

[0013] Further, performing Delaunay triangulation in the wire-wound same-side region, solving the Laplace equation to generate contour lines, and generating orthogonal meshes according to the contour lines to obtain triangular face mesh templates in the wire-wound same-side region, comprising:

[0014] Using Delaunay triangulation in the wire-wound same-side region according to the wire-wound information to obtain Delaunay triangular mesh points;

[0015] Solving the Laplace equation using the generated Delaunay triangular mesh points by a finite element method to obtain solutions of all mesh points;

[0016] At the boundary of the wire-wound same-side template, spline interpolation is used to make the points on the boundary uniformly angularly distributed; linear interpolation is performed between the internal grid points, the same point with the function value of the corresponding angle is found, and the same point with the function value is connected to form an isogram, the isogram is spline interpolated in the radial direction to obtain a preliminary orthogonal grid, and the corresponding grid points are obtained through spline interpolation to form the final orthogonal grid.

[0017] Further, the wire-wound information includes fuel rod center distance, fuel rod radius, wire-wound radius, wire-wound fillet radius, grid template radius, grid template center coordinates, wire-wound rotation angle, grid template half-angle angle, grid template calibration point, wire-wound cutting length, and wire-wound embedding depth.

[0018] Further, based on the wire-wound same-side triangular surface grid template, block grids are divided in each layer, and quadrilateral surface grids are generated in the block grids, including:

[0019] The center positions of the fuel rods are calculated, the center points of the fuel rods, the points on the edges, and the points on the corners are connected to form units corresponding to the fuel rods, the center points of the units are calculated, the center points of the units, the points on the fuel rod boundaries, and the points on the assembly boundaries are connected to divide block grids;

[0020] The grid points on the curved boundaries of the block network are generated based on the projection method;

[0021] The grid points on the straight boundaries of the block network are generated by using the Newton search and spline interpolation method and the projection method according to the positions of the points; the grid points on the straight boundaries of the block network include the grid points on the opposite sides of the wire winding and the grid points on the same side of the wire winding, and the grid points on the opposite sides of the wire winding are the grid points in the region with an angle greater than 90° with the wire winding direction;

[0022] The grid points in the block network near the fuel rods are generated based on the projection method;

[0023] The grid points in the block network located at the assembly boundary are generated by linear interpolation.

[0024] Further, the grid points on the curved boundaries of the block network are generated based on the projection method, including:

[0025] Points are added equidistantly along the direction of the line connecting the two endpoints of the curve, and the added points are used to find the projection points of the points with respect to the fuel rod and the wire winding in the normal direction by using the Newton method to generate the points on the curved boundaries of the block; wherein the iteration method of the Newton method is as follows:

[0026]

[0027] Wherein, x0 is the point of the last iteration, x1 is the point of the current iteration, dx is the distance between the points of the last two iterations, z1 is the shortest distance between the fuel rod and the wire in the last iteration, and dz is the difference between the shortest distances of the last two iterations.

[0028] Further, the grid points on the straight boundary of the block network are generated by using the Newton search and the spline interpolation method and the projection method according to the positions of the points, and the method comprises the following steps:

[0029] The grid points on the opposite side of the wire find the projection point of the starting point on the fuel rod by the gradient descent method, and after obtaining the projection point, the grid points on the opposite side of the wire are generated along the projection point direction; wherein the iteration formula of the gradient descent is:

[0030]

[0031] Wherein, x0 is the point of the last iteration, x1 is the point of the current iteration, h is the step size, grd is the gradient of the current point relative to the fuel rod, that is, the direction of the shortest path from the current point to the fuel rod, and norm(grd) is the norm of the gradient vector.

[0032] For the grid points on the same side of the wire, the position of the starting point in the triangular face grid template is determined by the Newton search; in the process of finding the position of the grid point, the process of the Newton search is regarded as finding the solution of the function (x, y) = f(s, t) at x = x0, y = y0; wherein x0, y0 are the coordinates of the starting point, s is the radial distribution position of the grid template, and t is the angle of the grid point in the template; after obtaining the radial distribution position and the angle of the starting point, the distribution position s' of the point on the row of the starting point is calculated according to the radial distribution position of the starting point, and then the grid points on the same side of the wire are obtained by interpolation according to the distribution position s' and the angle t.

[0033] Further, the layer face grid of each segment is obtained by rotating the layer face grid once by a set angle, and the hexahedral grid model is formed by connecting the layer face grids, and the method comprises the following steps:

[0034] The layer face grid of a wire length component is obtained by rotating the base segment five times by 60 degrees each time. The layer face grids are connected, and then the grid around the central fuel rod is translated to the block which has not been divided into grids to obtain the hexahedral grid model.

[0035] Further, the hexahedral grid model is the hexahedral grid model of a 19pin component, and the hexahedral grid model of a 7pin component is obtained by extending the hexahedral grid model through the following steps:

[0036] The fuel rods and the blocks of the 19pin component are numbered according to the positions and types;

[0037] According to the position of the fuel rod and the block, the number on the 19pin assembly is corresponded to the 7pin assembly;

[0038] According to the position of the block in the 19pin assembly and the 7pin assembly, the distance to be translated of the fuel rod is calculated, and based on the distance to be translated of the fuel rod, the block of the 19pin assembly is translated to the corresponding position of the 7pin assembly.

[0039] Further, the loop calling function is parallel optimized, including:

[0040] The loop calling function is parallel processed by using the parfor tool provided by Matlab.

[0041] The present application has at least the following beneficial effects:

[0042] (1) The problem of difficulty in generating hexahedral mesh of fast reactor core assembly is solved. The hexahedral mesh generated by the present application can well conform to the geometry and can meet the calculation requirement of thermal fluid simulation program;

[0043] (2) The problem of low efficiency in generating hexahedral mesh is solved. The program is parallel optimized by using the parfor tool, and the efficiency of the program is significantly improved. In the case of four-core parallel, the speedup ratio of the parallel program can reach 3.51, close to linear speedup ratio. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 A single-channel hexahedral mesh model generated according to the CEM of the prior art is shown, and the outer boundary thereof does not conform to the geometry.

[0045] Figure 2 A flowchart of a hexahedral mesh parallel generation method of a fast reactor core assembly based on a block structure method according to an embodiment of the present application is shown.

[0046] Figure 3 A block mesh component part schematic diagram according to an embodiment of the present application is shown, wherein (a) shows the components of the block around the wire, and (b) shows the block component part of the assembly boundary.

[0047] Figure 4 A block mesh grid template part parameter schematic diagram according to an embodiment of the present application is shown,

[0048] Figure 5 A 19pin assembly unit and block schematic diagram according to an embodiment of the present application is shown, wherein (a) shows the unit divided on the 19pin assembly, and (b) shows the block divided on the 19pin assembly.

[0049] Figure 6Figure 1 shows a schematic diagram of a 19-pin assembly fuel rod and type number according to an embodiment of the present application; wherein (a) shows the numbering of the 19-pin assembly fuel rod, from bottom to top, from left to right, the serial number increases, (b) shows the type number of the 19-pin assembly fuel rod, classified according to the location of the fuel.

[0050] Figure 7 Figure 2 shows a schematic diagram of a different Pennisetum 7-pin assembly fuel rod and type number according to an embodiment of the present application; (a) shows the numbering of the 7-pin assembly fuel rod, from bottom to top, from left to right, the serial number increases, (b) shows the type number of the 7-pin assembly fuel rod, classified according to the location of the fuel. DETAILED DESCRIPTION

[0051] The embodiments of the present application will be described in detail with specific reference felt to drawings. The advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the present specification. The present application can also be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0052] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings and examples.

[0053] The embodiment of the present application provides a hexahedral mesh parallel generation method for a fast reactor core assembly based on a block structure method. The present application is further described by taking a 7-pin assembly hexahedral mesh model with a wire winding pitch of 100 mm (i.e. one wire winding pitch) as an example. In this model, every sixth pitch is divided into 48 layers, and each layer is divided into 3 rows and 50 columns. The program is optimized in parallel using 4 cores on an Intel i-9300HF processor.

[0054] Referring to Figure 2 , a flowchart of the hexahedral mesh parallel generation method for a fast reactor core assembly based on a block structure method is shown. As Figure 2 shown, the method comprises the following steps:

[0055] Step S1, generate a triangular surface mesh template on the same side of the wire winding: perform Delaunay triangulation in the region on the same side of the wire winding, solve the Laplace equation to generate contour lines, and generate orthogonal mesh according to the contour lines.

[0056] Because of the complex geometry of the wire-wrapped side (i.e. the region where the grid point and the wire-wrapped direction have an angle less than 90°), it is difficult to directly divide the quadrilateral grid in the block. Therefore, it is necessary to generate the orthogonal grid template of the wire-wrapped side before dividing the quadrilateral grid to assist the subsequent generation of the quadrilateral grid.

[0057] In some embodiments, the specific steps of the triangular surface grid template generation are as follows:

[0058] Step S11, according to the basic information of the wire-wrapped, the Delaunay triangle is used in the wire-wrapped side region, wherein the wire-wrapped information includes the fuel rod center distance, the fuel rod radius, the wire-wrapped radius, the wire-wrapped fillet radius, the radius of the grid template, the center coordinates of the grid template, the rotation angle of the wire-wrapped, the half-angle angle of the grid template, the calibration point of the grid template, the truncated length of the wire-wrapped, and the embedding depth of the wire-wrapped (such as Figure 4 ). The obtained Delaunay triangle grid points are used for subsequent finite element method calculation.

[0059] Step S12, the generated Delaunay triangle grid points are used to solve the Laplace equation by the finite element method to obtain the solution of all grid points. Because the solution of the Laplace equation has good orthogonality, the contour lines can be generated by using these solutions to assist the generation of the orthogonal grid.

[0060] Step S13, at the boundary of the wire-wrapped side template, the points on the boundary are distributed at a more uniform angle by using spline interpolation. Linear interpolation is performed between the internal grid points to find points with the same function value as the corresponding angle. These points with the same function value are connected to form contour lines. According to the contour lines, spline interpolation is performed in the radial direction to obtain the preliminary orthogonal grid.

[0061] Step S14, in order to improve the grid quality, the distribution of the grid points on the boundary is adjusted again so that the points near the wire-wrapped fillet are more concentrated, and the corresponding grid points are obtained by spline interpolation to form the final orthogonal grid.

[0062] Step S2, hexahedral grid division based on block structure: the 19-pin fuel rod assembly is divided into six segments, and each segment is further divided into several layers. The first segment is taken as the base segment, and the block grid is divided in each layer, and then the quadrilateral surface grid is generated in the block grid (such as Figure 3 ). The surface grid of each layer is rotated by 60° to obtain the surface grid of each layer of other segments. Finally, the surface grids of each layer are connected to form the hexahedral grid.

[0063] In this embodiment, step S2 takes the assembly of 19 fuel rods as the reference, and the assembly base section of the six-pitch is subdivided into several layers. In each layer, the large block grid is divided first, and then the quadrilateral grid is divided in the block grid. The base section is rotated to obtain the layer grid of one pitch. Finally, the layer grids are connected to form the hexahedral grid model. When generating the quadrilateral grid, only the grid points of the boundary block, the block around the outermost fuel rod, and the block around the central fuel rod are generated. The grid of other blocks can be obtained by translating the grid of the block around the central fuel rod. The specific implementation is as follows:

[0064] Step S21, the center positions of each fuel rod are calculated, the center points of the fuel rods, the points on the edges, and the points on the corners are connected to form large units (such as Figure 5 ), and the center points of each unit are calculated. The center points of the units, the points on the boundaries of the fuel rods, and the points on the boundaries of the assembly are connected to divide the block grid. Each block will be subsequently divided into a specified number of quadrilateral grids.

[0065] Step S22, the grid points on the curved boundaries of the blocks are obtained by the projection method. First, points are added equidistantly along the direction of the line connecting the two end points of the curve, and then the points are used to find the projection points of the fuel rod and the wire by the Newton method in the normal direction, thereby generating the points on the curved boundaries of the blocks. The iteration method of the Newton method is as follows:

[0066]

[0067] where x0 is the point of the last iteration, x1 is the point of the current iteration, h is the step size, grd is the gradient of the current point relative to the fuel rod, that is, the direction of the shortest path from the current point to the fuel rod, and norm(grd) is the norm of the gradient vector.

[0068] Step S23, the grid points on the straight boundaries of the blocks are generated by the Newton search and spline interpolation method and the projection method according to the positions of the points.

[0069] The grid points located on the opposite side of the wire (that is, the region where the grid points have an angle greater than 90° with the wire direction) are generated by the projection method. The projection point of the starting point (the vertex of the block or the point on the boundary of the block) on the fuel rod is found by the gradient descent method. The iteration formula is as follows:

[0070]

[0071] where h is the step size, grd is the gradient of the current point relative to the fuel rod, that is, the direction of the shortest path from the current point to the fuel rod, and norm(grd) is the norm of the gradient vector. After obtaining the projection point, the points are generated uniformly along the direction of the projection point to form the quadrilateral grid in the block.

[0072] Because of the complex geometry of the wire-wrapped side, the grid template of the wire-wrapped side is needed to assist the generation of the grid points. In the process of generating the grid points, the position of the starting point in the grid template needs to be found. This process is realized by Newton search. In the process of finding the position of the grid point, the process of Newton search is regarded as finding the solution of the function (x, y) = f(s, t) at x = x0, y = y0. Where x0, y0 is the coordinate of the starting point, s is the radial distribution position of the grid template, and t is the angle of the grid point in the template. After obtaining the radial distribution position and angle of the starting point, the distribution position s' of the point in the row is calculated according to the radial distribution position of the point, and then the grid point is obtained by interpolation according to the distribution position s' and the angle t.

[0073] Step S24, the generation mode of the grid points in the block near the fuel rod is similar to that of the grid points on the curved boundary of the block. According to the position of the point, the method of Newton search and spline interpolation and the method of projection are used to generate.

[0074] Step S25, the block grid points located at the boundary of the assembly are directly generated by linear interpolation.

[0075] Step S26, the basic section is rotated 5 times, each time by 60°, to obtain a layer grid of a wire-wrapped length assembly. The layer grids are connected, and then the grid around the central fuel rod is translated into the block which has not been divided into grids, to complete the hexahedral grid division of the 19pin assembly.

[0076] Step S3, grid model extension: extending the hexahedral grid model of the 19pin assembly to the assembly model of other rod bundles.

[0077] In some embodiments, the hexahedral grid model of the 19pin assembly can be extended to the assembly model of other rod bundles by grid model extension. The following takes the 7pin assembly as an example to illustrate the specific steps as follows:

[0078] Step S31, the fuel rods and blocks of the 19pin assembly are numbered according to the position and type (such as the attached Figure 6 ).

[0079] Step S32, the numbers on the 19pin are corresponded to the 7pin according to the position of the fuel rods and blocks (such as the attached Figure 7 ).

[0080] Step S33, according to the position of the block in the 19pin assembly and the 7pin assembly, the distance that the fuel rod needs to be translated is calculated. Then, the block of the 19pin is translated to the corresponding position of the 7pin.

[0081] Step S4, parallel optimization: using the parfor tool provided by Matlab, the functions for dividing the quadrilateral grids of each layer are processed in parallel.

[0082] In this embodiment, as shown in Table 1, the program is optimized in parallel using the parfor tool provided by Matlab. When using the parfor loop to execute parallel tasks, MATLAB will automatically distribute independent loop iterations to multiple Matlab workers in the parallel pool. Each worker is assigned to a task and executes the code in the loop body exclusively in a process.

[0083] Table 1 Parallel optimization process

[0084]

[0085] In the process of serially executing the hexahedral mesh generation program, since the quadrilateral mesh needs to be divided hierarchically, the program needs to call the function gen_ess_blocks_L to generate the quadrilateral mesh of each layer, and the data volume of the function gen_ess_blocks_L is large. This results in a large proportion of the time required to execute this loop body in the total program running time. Taking a model of 7 fuel rod assemblies with a length of 100 mm (1 wire wrap pitch) as an example, on a Windows 11 operating system with 16.0 GB of memory, using an Intel i-9300HF processor to serially generate about 1 million hexahedral meshes takes about 2915 seconds, and the execution time of the function gen_ess_blocks_L is about 2746 seconds, accounting for 94.2% of the total program execution time.

[0086] Therefore, the present application uses parfor to execute this function in parallel according to Table 1. In the case of 4 threads executing in parallel, it takes about 831 seconds to generate the same hexahedral mesh, with a speedup ratio of about 3.51, which is basically close to the linear speedup ratio, significantly improving the efficiency of mesh generation.

[0087] The above embodiments are only used to illustrate the present application, and are not intended to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, therefore all equivalent technical solutions also belong to the scope of the present application, the patent protection scope of the present application should be defined by the claims.

Claims

1. A method for parallel generation of hexahedral mesh of a block structure method based fast reactor core assembly, characterized in that, The method includes; Delaunay triangulation is performed on the region on the same side of the wire, the Laplace equation is solved to generate contour lines, and an orthogonal mesh is generated based on the contour lines to obtain the triangular mesh template on the same side of the wire. The fuel rod assembly is divided into six segments, each segment is further divided into several layers. The first segment is used as the base segment. Based on the triangular mesh template on the same side of the winding wire, block meshes are divided in each layer, and quadrilateral meshes are generated in the block meshes. The meshes of each layer are rotated by a set angle to obtain the meshes of other segments. The meshes of each layer are connected to form a hexahedral mesh model. The hexahedral mesh model is extended; Parallel optimization is performed on the loop call function; wherein, the loop call function is used to generate the quadrilateral mesh of each layer; Delaunay triangulation is performed on the region on the same side as the wire, the Laplace equation is solved to generate contour lines, and an orthogonal mesh is generated based on the contour lines to obtain the triangular mesh template on the same side as the wire, including: Based on the wire winding information, Delaunay triangulation is used in the same side region of the wire winding to obtain Delaunay triangulation points. Using the generated Delaunay triangle mesh points, the Laplace equation is solved using the finite element method to obtain the solution for all mesh points; At the boundary of the template on the same side as the wire winding, spline interpolation is used to make the points on the boundary distributed at a uniform angle; linear interpolation is performed between the internal grid points to find the points with the same function value as the corresponding angle, and the points with the same function value are connected to form contour lines. Based on the radial spline interpolation of the contour lines, a preliminary orthogonal grid is obtained, and then the corresponding grid points are obtained through spline interpolation to form the final orthogonal grid. Based on the triangular mesh template on the same side of the winding wire, each layer is divided into block meshes, and quadrilateral meshes are generated within the block meshes, including: Calculate the center position of each fuel rod, connect the center point, edge points and corner points of the fuel rod to form the element corresponding to the fuel rod, calculate the center point of each element, connect the center point of each element, the point on the boundary of the fuel rod and the point on the boundary of the assembly, and divide the block mesh; Grid points on the curved boundary of the block network are generated based on the projection method; Based on the location of the points, the grid points on the straight boundary of the block network are generated using Newton's search and spline interpolation methods and projection methods respectively; the grid points on the straight boundary of the block network include grid points on the opposite side of the winding wire and grid points on the same side of the winding wire, and the grid points on the opposite side of the winding wire are grid points in the region where the angle with the winding wire direction is greater than 90°. Generating grid points within the block network near the fuel rods using a projection method; Generate grid points within the block network located at component boundaries using linear interpolation; Rotate each layer of mesh by a set angle to obtain the meshes of other segments. Connect the meshes of each layer to form a hexahedral mesh model, including: Rotate the base segment 5 times, 60° each time, to obtain a layered mesh of a wire length component. Connect the layered meshes and then translate the mesh around the central fuel rod into the block that has not yet been meshed to obtain a hexahedral mesh model. The hexahedral mesh model is a hexahedral mesh model of the 19-pin assembly, and the hexahedral mesh model is extended to obtain a hexahedral mesh model of a 7-pin assembly through the following steps: The fuel rods and blocks of the 19-pin assembly are numbered according to positions and types; The numbers on the 19-pin assembly are corresponded to the 7-pin assembly according to the positions of the fuel rods and blocks; According to the positions of the blocks in the 19-pin assembly and the 7-pin assembly, the distance to be translated of the fuel rods is calculated, and the blocks of the 19-pin assembly are translated to the corresponding positions of the 7-pin assembly based on the distance to be translated of the fuel rods.

2. The hexahedral mesh parallel generation method for a block-structured method-based fast reactor core assembly according to claim 1, wherein, The wire winding information includes a fuel rod center distance, a fuel rod radius, a wire winding radius, a wire winding fillet radius, a radius of a mesh template, a center coordinate of the mesh template, a rotation angle of the wire winding, a half-angle angle of the mesh template, a calibration point of the mesh template, a cutting length of the wire winding and an embedding depth of the wire winding.

3. The hexahedral mesh parallel generation method for a block-structured method-based fast reactor core assembly according to claim 1, wherein, The grid points on the curved boundary of the block network are generated based on a projection method, including: Points are added equidistantly along the direction of the line connecting the two endpoints of the curve, and the added points are used to find the projection points of the points on the fuel rod and the wire winding in the normal direction by using Newton method, to generate the points on the curved boundary of the block; wherein the iterative method of Newton method is as follows: ， wherein, x 0 is the point of the last iteration, x 1 is the point of the current iteration, dx is the distance between the points of the last two iterations, z 1 is the shortest distance to the fuel rod and wire in the last iteration, dz is the difference of the shortest distances of the last two iterations.

4. The hexahedral mesh parallel generation method for a block-structured method-based fast reactor core assembly according to Claim 1, wherein, The grid points on the straight boundary of the block network are generated according to the positions of the points by using Newton search and spline interpolation method and projection method, including: The grid points on the opposite side of the wire winding are found by using gradient descent method to find the projection point of the starting point on the fuel rod, and after the projection point is obtained, the grid points on the opposite side of the wire winding are generated by generating points uniformly distributed along the direction of the projection point; wherein the iterative formula of gradient descent is as follows: ， in, x 0 is the point from the previous iteration. x 1 is the point of the current iteration. h Step size, grd It is the gradient of the current point relative to the fuel rod, that is, the direction of the shortest path from the current point to the fuel rod. norm ( grd ) is the norm of the gradient vector; For the grid point on the same side of the wire, the position of the starting point in the triangular face grid template is determined by Newton search; the process of Newton search in the process of finding the position of the grid point is regarded as finding the function At the solution of ; wherein is the coordinate of the starting point, s is the radial distribution position of the grid template, t is the angle of the grid point in the template, after obtaining the radial distribution position and the angle of the starting point, the distribution position s' of the point on the row where the starting point is located is calculated according to the radial distribution position of the starting point, and then the grid point on the same side of the wire is obtained by interpolation according to the distribution position s' and the angle t.

5. The hexahedral mesh parallel generation method for a block-structured method-based fast reactor core assembly according to Claim 1, wherein, The loop calling function is parallel optimized, including: The loop calling function is parallel processed by using the parfor tool provided by Matlab.

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