A geometric multigrid aggregation method based on front advancing

Abstract

A geometric multi-grid aggregation method based on array advancement belongs to the technical field of numerical calculation of aerodynamics. In order to establish an efficient and fast geometric multi-grid aggregation method, the present invention includes establishing a fine grid control body based on a generated grid suitable for numerical solution of flow field for hierarchical marking; selecting seed units to be aggregated; constructing an advancement array with unaggregated surrounding adjacent units for the obtained seed units to be aggregated, and establishing a list of units to be aggregated; optimizing the units to be aggregated in the list of units to be aggregated, obtaining the optimal units to be aggregated and adding them to the coarse grid control body; calculating the aggregation rate of the coarse grid control body, judging whether the aggregation is completed according to the obtained aggregation rate of the coarse grid control body, and if it is completed, performing the next coarse grid aggregation; if it is not completed, continuing the aggregation; detecting whether all seed units in the fine grid control body have completed the aggregation, judging if it is not, continuing the aggregation, judging if it is, removing the isolated units, and ending the aggregation.

Description

Technical Field

[0001] The invention belongs to the technical field of aerodynamic numerical calculation, and in particular relates to a geometric multi-grid aggregation method based on array advancement. Background Art

[0002] Modern computational fluid dynamics (CFD) software mainly uses iterative methods to solve and converge the flow field. The iterative method requires a long number of calculation steps and time, so multi-grid technology is often used to speed up the convergence of the flow field. Multi-grid technology aims at different coarse and fine grid sequences, and accelerates convergence by eliminating high-frequency residuals on fine grids and low-frequency residuals on coarse grids. The geometric multi-grid method requires the construction of a series of grid sequences of different levels, and the number of grids is usually achieved by decreasing the multiple.

[0003] Geometric multigrid usually adopts the form of grid aggregation. The grid given by the user is used as the finest grid level. A grid sequence can be established by aggregating multiple grids to form a coarser grid. The number and form of grid aggregation will have a great impact on multigrid technology. Grids with poor aggregation quality will cause the accuracy of the calculation results and even cause the flow field to not converge stably. Therefore, it is crucial to establish a high-quality and highly robust grid aggregation method for industrial CFD software design. Summary of the invention

[0004] The problem to be solved by the present invention is to establish an efficient and fast geometric multi-grid aggregation method, and propose a geometric multi-grid aggregation method based on array advancement.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A geometric multigrid aggregation method based on front advancement includes the following steps:

[0007] S1. Generate a grid suitable for numerical solution of flow field based on CFD pre-processing software, and establish a fine grid control volume based on the generated grid suitable for numerical solution of flow field, including volume, outer envelope area, and adjacency relationship;

[0008] S2. Hierarchical labeling of the fine grid control volume obtained in step S1;

[0009] S3. Based on the hierarchical labeling of step S2, selecting the seed unit to be aggregated;

[0010] S4. For the seed unit to be aggregated obtained in step S3, construct a propulsion front with the surrounding adjacent units that are not aggregated, and establish a list of units to be aggregated;

[0011] S5. Optimize the units to be polymerized in the list of units to be polymerized obtained in step S4 to obtain the optimal unit to be polymerized;

[0012] S6. Adding the optimal unit to be aggregated obtained in step S5 to the coarse grid control volume;

[0013] S7. Calculate the polymerization rate of the coarse grid control body obtained in step S6, and determine whether the polymerization is completed according to the polymerization rate of the coarse grid control body. If completed, return to step S3 for the next coarse grid polymerization; if not completed, return to step S4 to continue polymerization;

[0014] S8. Check whether all seed units of the fine grid control body have completed aggregation. If it is not, return to step S3 to continue aggregation. If it is, remove the isolated units and end the aggregation.

[0015] Furthermore, the specific implementation method of step S1 includes the following steps:

[0016] S1.1. Establish a fine mesh control volume based on the generated mesh suitable for numerical solution of the flow field;

[0017] S1.2. Traverse the mesh boundary and extract the mesh boundary of the fine mesh control volume;

[0018] S1.3. Traverse the mesh surface and count the outer envelope area of ​​the fine mesh control volume;

[0019] S1.4. Count the adjacency relationships of each fine grid control volume.

[0020] Furthermore, the specific implementation method of step S2 includes the following steps:

[0021] S2.1. Select the boundary of the fine mesh control volume obtained in step S1. If there is a surface boundary, select the surface boundary; if there is no surface boundary, select an arbitrary boundary;

[0022] S2.2. Traverse the selected boundary, mark the fine mesh control bodies adjacent to it as the first layer, and put the marked fine mesh control bodies into the advancing front list;

[0023] S2.3. Traverse the advancement front list, mark the unmarked adjacent fine grid control volumes as the second layer, and form a new advancement front list, repeating steps S2.1 to S2.3 until all fine grid control volumes are marked.

[0024] Furthermore, the specific implementation method of step S3 includes, based on the hierarchical marking of step S2, if there is an object surface boundary, preferentially selecting any fine mesh control volume located at the object surface as the seed unit to be aggregated; if there is no object surface boundary, selecting a fine mesh control volume at any other boundary as the seed unit.

[0025] Furthermore, the specific implementation method of step S4 includes the following steps:

[0026] S4.1. Construct a list of units to be aggregated for the seed units to be aggregated obtained in step S3, confirm whether the adjacent units are not aggregated, extract the unaggregated units, and construct the advancing front of the unaggregated surrounding units;

[0027] S4.2. For the unaggregated unit obtained in step S4.1, determine whether it is in the list of units to be aggregated; if it is in the list of units to be aggregated, count the repeated area information; if it is not in the list of units to be aggregated, put it in the list of units to be aggregated and record the outer envelope area of ​​the unaggregated unit.

[0028] Furthermore, the specific implementation method of step S5 includes the following steps:

[0029] S5.1. Calculate the aggregation rate of the units to be aggregated in the list of units to be aggregated;

[0030] S5.2. Based on the fine grid obtained in step S1, determine whether the unit to be aggregated is located in the object surface boundary layer. If the unit to be aggregated is not in the object surface boundary layer, directly proceed to step S5.3. If the aggregated unit is in the object surface boundary layer, perform optimization as follows:

[0031] S5.2.1. If the polymerization rate of the unit to be polymerized is less than the tangential polymerization rate, tangential polymerization is performed;

[0032] S5.2.2. If the polymerization rate of the unit to be polymerized is less than the tangential polymerization rate, normal polymerization is performed, and the number of layers of the unit to be polymerized is equal to the number of layers of the last unit that has been polymerized plus 1;

[0033] S5.2.3. Sort and remove the units to be aggregated to form a new list of units to be aggregated;

[0034] S5.3. Perform a second optimization for the new list of units to be aggregated;

[0035] S5.3.1. Calculate the mass f of the grid cell and the outer envelope area of ​​the coarse grid cell after adding the unit to be aggregated and total volume , calculate the quality criterion , where C is the coefficient, C=1 / 2 for a two-dimensional grid and C=2 / 3 for a three-dimensional grid;

[0036] S5.3.2. If the aggregation unit is not located at the boundary, the unit with the smallest f value is selected as the optimal unit to be aggregated;

[0037] S5.3.3. If the aggregation unit is located at the boundary, calculate whether the number of boundaries adjacent to the coarse grid changes after the unit to be aggregated is added. If the number of boundaries increases, it is not the optimal unit; if the number of boundaries remains unchanged, select the unit with the smallest f value as the optimal unit to be aggregated.

[0038] Furthermore, the specific implementation method of step S6 includes the following steps:

[0039] S6.1. For the optimal unit to be aggregated, merge the units of the coarse grid to form a list;

[0040] S6.2. For the optimal unit to be aggregated, merge the boundary information;

[0041] S6.3. For the optimal unit to be aggregated, remove the adjacent surfaces and merge them to establish a new outer envelope surface;

[0042] S6.4. For the optimal unit to be aggregated, merge the volume information of the coarse grid to obtain the coarse grid control volume.

[0043] Furthermore, the specific implementation method of step S7 includes the following steps:

[0044] S7.1. Calculate the aggregation rate of the coarse grid control volume;

[0045] S7.2. If the current aggregation rate is equal to the required aggregation rate, update the advancement front and return to step S3 for the next coarse grid aggregation. If the current aggregation rate is less than the required aggregation rate, return to step S4 to continue aggregation.

[0046] Beneficial effects of the present invention:

[0047] The geometric multi-grid aggregation method based on array advancement described in the present invention performs hierarchical marking on the grid starting from the object surface, which can effectively improve the aggregation efficiency and aggregation quality.

[0048] The geometric multi-grid aggregation method based on array advancement described in the present invention adopts an array advancement strategy to start aggregation from the object surface, which can effectively improve the aggregation quality of the grid in the boundary layer, ensure robustness for viscous flow calculation in the boundary layer, and facilitate flow field convergence.

[0049] The present invention discloses a geometric multi-grid aggregation method based on array advancement. In grid aggregation, the tangential and normal directions can be controlled separately, thereby improving the regularity of the coarse grid after boundary layer grid aggregation and effectively improving the grid quality. At the same time, the aggregation rate in the boundary layer can be increased through combined control in two directions, which is convenient for load balancing of partitioned parallel computing.

[0050] The present invention describes a geometric multi-grid aggregation method based on array advancement, which establishes a grid optimization strategy during the aggregation process. It greatly improves the aggregation quality of the grid by taking measures such as prioritizing tangential aggregation, measuring the change in the grid surface normal vector angle, introducing grid quality criteria, not increasing the number of boundaries after merging, and eliminating isolated units.

[0051] The geometric multi-grid aggregation method based on front advancement described in the present invention does not introduce new boundaries during the aggregation process, ensures that the number of boundaries adjacent to coarse grid units does not increase, maintains the physical properties of the units, and can effectively improve the stability of the convergence process.

[0052] The geometric multigrid aggregation method based on array advancement described in the present invention is applied in the numerical solution of software flow field, aiming to accelerate the convergence speed of flow field, improve the accuracy of calculation results, and reduce the flow field oscillation caused by low-quality aggregated grids. This method is based on the array advancement method of the object surface. After the grid units are layered and marked, the tangential and normal directions are aggregated separately to achieve different aggregation processing methods for the inner and outer grids of the boundary layer. It has good aggregation quality and can greatly improve the robustness of the geometric multigrid technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of a geometric multi-grid aggregation method based on front advancement according to the present invention;

[0054] Figure 2 It is a schematic diagram of grid layered marking of the present invention;

[0055] Figure 3 is a schematic diagram of tangential polymerization of the present invention;

[0056] Figure 4 It is a schematic diagram of normal polymerization of the present invention;

[0057] Figure 5 is a schematic diagram of an isolated unit of the present invention;

[0058] Figure 2 Among them, 1 is the first layer of grid, 2 is the second layer of grid, and 3 is the third layer of grid. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the specific embodiments described are only part of the embodiments of the present invention, rather than all of the specific embodiments. The components of the specific embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations, and the present invention can also have other embodiments.

[0060] Therefore, the following detailed description of the specific embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected specific embodiments of the present invention. Based on the specific embodiments of the present invention, all other specific embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0061] In order to further understand the content, features and effects of the present invention, the following specific implementation methods are given as examples, and the attached Figure 1 -Attached Figure 5 The detailed instructions are as follows:

[0062] Embodiment 1:

[0063] A geometric multigrid aggregation method based on front advancement includes the following steps:

[0064] S1. Generate a grid suitable for numerical solution of flow field based on CFD pre-processing software, and establish a fine grid control volume based on the generated grid suitable for numerical solution of flow field, including volume, outer envelope area, and adjacency relationship;

[0065] Furthermore, the specific implementation method of step S1 includes the following steps:

[0066] S1.1. Establish a fine mesh control volume based on the generated mesh suitable for numerical solution of the flow field;

[0067] S1.2. Traverse the mesh boundary and extract the mesh boundary of the fine mesh control volume;

[0068] S1.3. Traverse the mesh surface and count the outer envelope area of ​​the fine mesh control volume;

[0069] S1.4. Count the adjacency relationships of each fine grid control volume.

[0070] S2. Perform hierarchical labeling on the fine grid control volume obtained in step S1, such as Figure 2 As shown;

[0071] Furthermore, the specific implementation method of step S2 includes the following steps:

[0072] S2.1. Select the boundary of the fine mesh control volume obtained in step S1. If there is a surface boundary, select the surface boundary; if there is no surface boundary, select an arbitrary boundary;

[0073] S2.2. Traverse the selected boundary, mark the fine mesh control bodies adjacent to it as the first layer, and put the marked fine mesh control bodies into the advancing front list;

[0074] S2.3. Traverse the advancement front list, mark the unmarked adjacent fine grid control volumes as the second layer, and form a new advancement front list, repeating steps S2.1 to S2.3 until all fine grid control volumes are marked.

[0075] S3. Based on the hierarchical labeling of step S2, selecting the seed unit to be aggregated;

[0076] Further, the specific implementation method of step S3 includes, based on the hierarchical marking of step S2, if there is an object surface boundary, preferentially selecting any fine mesh control volume located at the object surface as the seed unit to be aggregated; if there is no object surface boundary, selecting a fine mesh control volume at any other boundary as the seed unit;

[0077] S4. For the seed unit to be aggregated obtained in step S3, construct a propulsion front with the surrounding adjacent units that are not aggregated, and establish a list of units to be aggregated;

[0078] Furthermore, the specific implementation method of step S4 includes the following steps:

[0079] S4.1. Construct a list of units to be aggregated for the seed units to be aggregated obtained in step S3, traverse all faces of the seed units to be aggregated, confirm whether the adjacent units are not aggregated, extract the unaggregated units, and construct the advancing front of the unaggregated surrounding units;

[0080] S4.2. For the unpolymerized unit obtained in step S4.1, determine whether it is in the list of units to be polymerized; if it is in the list of units to be polymerized, count the repeated area information; if it is not in the list of units to be polymerized, put it in the list of units to be polymerized and record the outer envelope area of ​​the unpolymerized unit;

[0081] S5. Optimize the units to be polymerized in the list of units to be polymerized obtained in step S4 to obtain the optimal unit to be polymerized;

[0082] Furthermore, the specific implementation method of step S5 includes the following steps:

[0083] S5.1. Calculate the aggregation rate of the units to be aggregated in the list of units to be aggregated;

[0084] S5.2. Based on the fine grid obtained in step S1, determine whether the unit to be aggregated is located in the object surface boundary layer. If the unit to be aggregated is not in the object surface boundary layer, directly proceed to step S5.3. If the aggregated unit is in the object surface boundary layer, perform optimization as follows:

[0085] S5.2.1. If the polymerization rate of the unit to be polymerized is less than the tangential polymerization rate, tangential polymerization is performed;

[0086] Furthermore, the specific determination method of tangential aggregation is as follows: if the unit to be aggregated and the aggregated unit are in the same layer, it is considered as tangential aggregation and meets the quality requirements. If no unit with the same quality requirements is found in the same layer, the same layer will no longer be aggregated, and the current aggregation rate will replace the required tangential aggregation rate, and the total aggregation rate will be modified to the product of the tangential aggregation rate and the normal aggregation rate.

[0087] Furthermore, the quality requirement is that the change in the deflection angle of the normal vector of the mesh surface is less than 45 degrees, which is considered to meet the normal change requirement;

[0088] S5.2.2. If the polymerization rate of the unit to be polymerized is less than the tangential polymerization rate, normal polymerization is performed, and the number of layers of the unit to be polymerized is equal to the number of layers of the last unit that has been polymerized plus 1;

[0089] S5.2.3. Sort and remove the units to be aggregated to form a new list of units to be aggregated;

[0090] S5.3. Perform a second optimization for the new list of units to be aggregated;

[0091] S5.3.1. Calculate the mass f of the grid cell and the outer envelope area of ​​the coarse grid cell after adding the unit to be aggregated and total volume , calculate the quality criterion , where C is the coefficient, C=1 / 2 for a two-dimensional grid and C=2 / 3 for a three-dimensional grid;

[0092] S5.3.2. If the aggregation unit is not located at the boundary, the unit with the smallest f value is selected as the optimal unit to be aggregated;

[0093] S5.3.3. If the aggregation unit is located at the boundary, calculate whether the number of boundaries adjacent to the coarse grid changes after the unit to be aggregated is added. If the number of boundaries increases, it is not the optimal unit; if the number of boundaries remains unchanged, select the unit with the smallest f value as the optimal unit to be aggregated;

[0094] S6. Adding the optimal unit to be aggregated obtained in step S5 to the coarse grid control volume;

[0095] Furthermore, the specific implementation method of step S6 includes the following steps:

[0096] S6.1. For the optimal unit to be aggregated, merge the units of the coarse grid to form a list;

[0097] S6.2. For the optimal unit to be aggregated, merge the boundary information;

[0098] S6.3. For the optimal unit to be aggregated, remove the adjacent surfaces and merge them to establish a new outer envelope surface;

[0099] S6.4. For the optimal unit to be aggregated, the volume information of the coarse grid is merged to obtain the coarse grid control volume;

[0100] S7. Calculate the polymerization rate of the coarse grid control body obtained in step S6, and determine whether the polymerization is completed according to the polymerization rate of the coarse grid control body. If completed, return to step S3 for the next coarse grid polymerization; if not completed, return to step S4 to continue polymerization;

[0101] Furthermore, the specific implementation method of step S7 includes the following steps:

[0102] S7.1. Calculate the aggregation rate of the coarse grid control volume;

[0103] S7.2. If the current aggregation rate is equal to the required aggregation rate, update the advancement front and return to step S3 for the next coarse grid aggregation. If the current aggregation rate is less than the required aggregation rate, return to step S4 to continue aggregation;

[0104] S8. Check whether all seed units of the fine grid control body have completed aggregation. If it is not, return to step S3 to continue aggregation. If it is, remove the isolated units and end the aggregation.

[0105] Furthermore, the specific implementation method of step S8 is:

[0106] S8.1. Traverse all fine grid cells and check whether they have all been aggregated;

[0107] S8.2. If there is a coarse grid cell that consists of only one fine grid cell, it is considered an isolated cell, such as Figure 5 As shown, C1 represents the number of the coarse grid after four fine grids are aggregated, C2 represents the number of the coarse grid after three fine grids are aggregated, C3 represents the number of the coarse grid after three fine grids are aggregated, C4 represents the number of the coarse grid after six fine grids are aggregated, C5 represents the number of the coarse grid after three fine grids are aggregated, C6 represents the number of the coarse grid after three fine grids are aggregated, and C7 represents the number of the coarse grid after two fine grids are aggregated; C8 represents the number of the coarse grid composed of one fine grid unit, then C8 is regarded as an isolated unit, and the C8 fine grid unit is merged into other coarse grid units by the following method;

[0108] S8.2.1. When there is only one adjacent coarse grid cell, only this coarse cell can be selected;

[0109] S8.2.2. Secondly, it is preferred to select adjacent coarse grid cells that do not increase the number of original coarse grid boundaries;

[0110] S8.2.3. Again, the adjacent coarse grid cells with the smallest aggregation rate are preferentially selected;

[0111] S8.2.4. Finally, if the convergence rates are the same, find the adjacent coarse grid with the smallest volume.

[0112] This implementation method is aimed at the grid sequence construction form of geometric multi-grid technology, and invents a method based on grid layer identification and array advancement. This method can achieve the establishment of a coarse grid by aggregating fine grid units based on the finest grid level and aggregation parameters given by the user, and adopts different aggregation strategies for the inside and outside of the boundary layer respectively, and fully considers the two directions of tangential and normal aggregation along the object surface, so as to obtain a high-quality coarse grid, improve the quality and robustness of aggregation, and lay a good foundation for accelerating the convergence of the flow field with multi-grid technology.

[0113] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0114] Although the present application has been described above with reference to specific embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, as long as there is no structural conflict, the various features in the specific embodiments disclosed in the present application may be used in combination with each other in any manner, and the fact that these combinations are not exhaustively described in this specification is only for the sake of omitting space and saving resources. Therefore, the present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A geometric multigrid aggregation method based on front advancement, characterized in that: The steps include: S1. Generate a grid suitable for numerical solution of flow field based on CFD pre-processing software, and establish a fine grid control volume based on the generated grid suitable for numerical solution of flow field, including volume, outer envelope area, and adjacency relationship; S2. hierarchically mark the fine grid control volume obtained in step S1; S3. Based on the hierarchical marking of step S2, selecting the seed unit to be aggregated; S4. For the seed unit to be aggregated obtained in step S3, construct a propulsion front with the surrounding adjacent units that have not been aggregated, and establish a list of units to be aggregated; S5. Optimizing the units to be aggregated in the list of units to be aggregated obtained in step S4 to obtain the optimal unit to be aggregated; The specific implementation method of step S5 includes the following steps: S5.

1. Calculate the polymerization rate of the units to be aggregated in the list of units to be aggregated; S5.

2. Based on the fine grid obtained in step S1, determine whether the unit to be aggregated is located in the object surface boundary layer. If the unit to be aggregated is not in the object surface boundary layer, directly proceed to step S5.

3. If the aggregated unit is in the object surface boundary layer, perform optimization as follows: S5.2.

1. If the polymerization rate of the unit to be polymerized is less than the tangential polymerization rate, tangential polymerization is performed; S5.2.

2. If the polymerization rate of the unit to be polymerized is greater than or equal to the tangential polymerization rate, normal polymerization is performed, and the number of layers of the unit to be polymerized is equal to the number of layers of the last unit that has been polymerized plus 1; S5.2.

3. Sort and remove the units to be aggregated to form a new list of units to be aggregated; S5.

3. Perform a second optimization for the new list of units to be aggregated; S5.3.

1. Calculate the mass f of the grid unit and the outer envelope area S of the coarse grid unit after adding the unit to be aggregated. out and the total volume V sum , calculate the quality criterion Where C is the coefficient, C = 1 / 2 for a two-dimensional grid, and C = 2 / 3 for a three-dimensional grid; S5.3.

2. If the aggregation unit is not located at the boundary, the unit with the smallest f value is selected as the optimal unit to be aggregated; S5.3.

3. If the aggregation unit is located at the boundary, calculate whether the number of boundaries adjacent to the coarse grid changes after the unit to be aggregated is added. If the number of boundaries increases, it is not the optimal unit; if the number of boundaries remains unchanged, select the unit with the smallest f value as the optimal unit to be aggregated; S6. adding the optimal unit to be aggregated obtained in step S5 to the coarse grid control volume; S7. Calculate the polymerization rate of the coarse grid control body obtained in step S6, and determine whether the polymerization is completed according to the obtained polymerization rate of the coarse grid control body. If completed, return to step S3 to perform the next coarse grid polymerization; if not completed, return to step S4 to continue polymerization; S8. Check whether all seed units of the fine grid control body have completed aggregation. If it is not, return to step S3 to continue aggregation. If it is, remove the isolated units and end the aggregation.

2. The geometric multigrid aggregation method based on front advancement according to claim 1, characterized in that: The specific implementation method of step S1 includes the following steps: S1.

1. Establish a fine grid control volume based on the generated grid suitable for numerical solution of the flow field; S1.

2. Traverse the grid boundary and extract the grid boundary of the fine grid control volume; S1.

3. Traverse the mesh surface and count the outer envelope area of ​​the fine mesh control volume; S1.

4. Count the adjacency relationships of each fine grid control volume.

3. The geometric multigrid aggregation method based on front advancement according to claim 2, characterized in that: The specific implementation method of step S2 includes the following steps: S2.

1. Select the boundary of the fine mesh control volume obtained in step S1. If there is a surface boundary, select the surface boundary; if there is no surface boundary, select an arbitrary boundary; S2.

2. Traverse the selected boundary, mark the fine mesh control bodies adjacent to it as the first layer, and put the marked fine mesh control bodies into the advancing front list; S2.

3. Traverse the propulsion front list, mark the unmarked adjacent fine grid control bodies as the second layer, and form a new propulsion front list, repeating steps S2.1 to S2.3 until all fine grid control bodies are marked.

4. The geometric multigrid aggregation method based on front advancement according to claim 3, characterized in that: The specific implementation method of step S3 includes, based on the hierarchical marking of step S2, if there is an object surface boundary, preferentially selecting any fine mesh control volume located at the object surface as the seed unit to be aggregated; if there is no object surface boundary, selecting a fine mesh control volume at any other boundary as the seed unit.

5. The geometric multigrid aggregation method based on front advancement according to claim 4, characterized in that: The specific implementation method of step S4 includes the following steps: S4.

1. Construct a list of units to be aggregated for the seed units to be aggregated obtained in step S3, traverse all faces of the seed units to be aggregated, confirm whether the adjacent units are not aggregated, extract the unaggregated units, and construct a propulsion front for the unaggregated surrounding units; S4.

2. For the unpolymerized unit obtained in step S4.1, determine whether it is in the list of units to be polymerized; If it is in the list of units to be aggregated, the repeated area information is counted; if it is not in the list of units to be aggregated, it is put into the list of units to be aggregated and the outer envelope area of ​​the unaggregated units is recorded.

6. The geometric multigrid aggregation method based on front advancement according to claim 5, characterized in that: The specific implementation method of step S6 includes the following steps: S6.

1. For the optimal unit to be aggregated, merge the units of the coarse grid to form a list; S6.

2. For the optimal unit to be aggregated, merge the boundary information; S6.

3. For the optimal unit to be aggregated, remove the adjacent surfaces and merge them to establish a new outer envelope surface; S6.

4. For the optimal unit to be aggregated, merge the volume information of the coarse grid to obtain the coarse grid control volume.

7. The geometric multigrid aggregation method based on front advancement according to claim 6, characterized in that: The specific implementation method of step S7 includes the following steps: S7.

1. Calculate the aggregation rate of the coarse grid control volume; S7.

2. If the current aggregation rate is equal to the required aggregation rate, update the advancement front and return to step S3 for the next coarse grid aggregation. If the current aggregation rate is less than the required aggregation rate, return to step S4 to continue aggregation.

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