A method and system for automatically generating non-uniform rectangular grids

Abstract

The present invention discloses a method and system for automatically generating a non-uniform rectangular grid, the method comprising: dividing an input three-dimensional geometric model to generate a surface grid; determining geometric components whose sizes are smaller than preset values ​​and / or areas reflecting flow field characteristics in the three-dimensional geometric model; determining the coordinate point information and size parameters of the geometric components through the coordinate system of the surface grid to determine the positions of the geometric components; generating a non-uniform parent grid as an initial grid based on a defined stretching ratio according to the coordinate point information; and performing non-uniform grid encryption on the initial grid based on a fork tree structure according to a preset encryption strategy to generate a non-uniform rectangular grid.

Description

Technical Field

[0001] The invention relates to the field of engineering application CAE and CFD computing technology, and in particular to a method and system for automatically generating a non-uniform rectangular grid. Background Art

[0002] Computational fluid dynamics is of great significance in aerospace and engineering applications. Non-uniform rectangular grids have the characteristics of automatic generation, grid orthogonality, storage based on fork number structure, and easy encryption. However, for small-sized geometric components, such as thin wings, gaps, local small structures, shock waves, wakes, and areas with strong viscous / inviscid interference, conventional rectangular grid generation methods use a uniform grid encryption strategy, and local encryption must be performed simultaneously in three directions. On the one hand, the uniform encryption strategy requires three directions to be performed simultaneously, resulting in a large amount of grids; on the other hand, the encryption depth of the fork number structure must be large. Most importantly, for geometric components with small gaps or small thicknesses, even with this encryption strategy, it is still difficult to successfully generate a computational grid. Summary of the invention

[0003] The purpose of the present invention is to provide a method and system for automatically generating a non-uniform rectangular grid, aiming to solve the above-mentioned problem.

[0004] The present invention provides a method for automatically generating a non-uniform rectangular grid, comprising:

[0005] S1. Divide the input three-dimensional geometric model to generate a surface mesh;

[0006] S2. Determine the geometric components in the three-dimensional geometric model whose size is smaller than a preset value and / or the area reflecting flow field characteristics;

[0007] S3. Determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface mesh to determine the position of the geometric component;

[0008] S4. Generate a non-uniform matrix grid as an initial grid based on the defined stretch ratio according to the coordinate point information;

[0009] S5. According to the pre-set encryption strategy, the initial grid is encrypted non-uniformly based on the fork tree structure to generate a non-uniform rectangular grid.

[0010] The present invention provides a non-uniform rectangular grid automatic generation system, comprising:

[0011] Surface mesh expression module: used to divide the input 3D geometric model to generate surface mesh;

[0012] Key component determination module: used to determine the geometric components whose size is smaller than a preset value and / or the areas reflecting flow field characteristics in the three-dimensional geometric model;

[0013] Position determination module: used to determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface grid, and determine the position of the geometric component;

[0014] An initial mesh generation module: used to generate a non-uniform matrix mesh as an initial mesh based on the coordinate point information and a defined stretching ratio;

[0015] Non-uniform rectangular grid generation module: used to perform non-uniform grid encryption on the initial grid based on the fork tree structure according to the set encryption strategy to generate a non-uniform rectangular grid.

[0016] By adopting the embodiment of the present invention, the mother grid of the rectangular grid can be designed in combination with the geometric characteristics and the flow field characteristics. The generated computational grid maintains the orthogonal characteristics of the rectangular grid, which can better ensure the quality of the computational grid and the success rate of grid generation.

[0017] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 is a flow chart of a method for automatically generating a non-uniform rectangular grid according to an embodiment of the present invention;

[0020] Figure 2 is a flow chart of the final non-uniform rectangular grid automatic generation method according to an embodiment of the present invention;

[0021] Figure 3 is a schematic diagram of a geometric model for generating a non-uniform rectangular grid in an embodiment of the present invention;

[0022] Figure 4 is a schematic diagram of the rectangular grid distribution and determined key points generated by an embodiment of the present invention;

[0023] Figure 5is a schematic diagram of a calculation grid and a grid near the tail wing generated by an embodiment of the present invention;

[0024] Figure 6 Schematic diagram of a non-uniform rectangular grid automatic generation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] Method Embodiment

[0029] According to an embodiment of the present invention, a method for automatically generating a non-uniform rectangular grid is provided. Figure 1 is a flow chart of a method for automatically generating a non-uniform rectangular grid according to an embodiment of the present invention. Figure 1 As shown, the method for automatically generating a non-uniform rectangular grid according to an embodiment of the present invention specifically includes:

[0030] S1. Divide the input three-dimensional geometric model to generate a surface mesh.

[0031] Use commercial meshing software to read in the 3D geometric models designed by modeling software such as Caita, AutoCAD, Pre, UG, etc. The geometric models to be processed are divided into triangular, quadrilateral or mixed type surface meshes through mesh generation software or program code, and output as *.facet format data.

[0032] S2. Determine geometric components in the three-dimensional geometric model whose sizes are smaller than preset values ​​and / or areas that reflect flow field characteristics.

[0033] Specifically, the geometric components with sizes smaller than the preset values ​​in the three-dimensional geometric model include: components with thickness smaller than the preset thickness value, components with small-scale side lengths and gaps smaller than the preset values ​​in the components with a length-to-width-to-height ratio greater than the preset ratio value. Such components can easily lead to mesh generation failure during the mesh generation process; areas that reflect flow field characteristics include areas that can generate shock waves, areas with vortex structures, or areas with severe local viscous / inviscid interference.

[0034] S3. Determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface mesh, and determine the position of the geometric component.

[0035] Specifically, the positions of the above-mentioned components or areas are mainly determined by the coordinates of the geometric components in the three-dimensional space. Therefore, it is necessary to determine the minimum coordinate positions and sizes of small-size and special area components, and to form position and size descriptions of special components, that is, to extract the coordinate point information of the starting position of the geometric components that need special encryption and the size information that needs to be encrypted according to the coordinate system of the surface mesh, and determine the positions of the components or areas.

[0036] S4. According to the coordinate point information, a non-uniform mother mesh is generated as an initial mesh based on a defined stretching ratio.

[0037] Specifically, the position and stretching ratio of mesh contraction, core encryption, and stretching are determined according to the coordinate point information, and a non-uniform parent mesh for fork tree encryption is automatically generated as an initial mesh.

[0038] The generated initial grid is different from the traditional initial grid. The traditional initial grid is an isotropic network with consistent sizes in three directions, while the non-uniform parent grid is an anisotropic grid with different sizes in three directions. The grid size has a transition form, and the grid points are distributed from sparse to dense or from dense to sparse. The grid size in important areas is small, and the grid size in external unimportant flow field areas is large. The scale ratio of adjacent grids is the stretching ratio, which needs to be defined in advance. The stretching ratio is greater than 1 or less than 1.

[0039] S5. According to the pre-set encryption strategy, the initial grid is encrypted non-uniformly based on the fork tree structure to generate a non-uniform rectangular grid.

[0040] The encryption strategy includes: fork tree encryption depth (number of fork tree layers), number of encryption layers of neighboring units and encryption criteria, etc.

[0041] Based on the above encryption strategy, the depth of the fork tree structure and the encryption strategy of the neighboring cells are determined, and the feature size and feature position determined in step S3 are encrypted based on the fork tree structure to generate a non-uniform rectangular grid of the spatial flow field.

[0042] Specifically, based on the fork tree data structure to store grid information, the grid splitting and encryption begins layer by layer (one grid is divided into two in one-dimensional case, and one grid is divided into four in two-dimensional case). Each time a layer is encrypted, the depth of the fork tree structure of the grid storage increases by 1. The grid encryption process in this embodiment is anisotropic grid encryption, and the anisotropy of the initial grid is inherited. Each time a layer is encrypted, the grid scale of the unimportant area is rapidly reduced by 2 to the power of n. Therefore, in the important component area, the grid can meet the needs of numerical calculation after a small number of encryption times.

[0043] After encryption, the generated non-uniform rectangular grid is judged by the grid generation criterion whether it meets the requirements of flow field calculation. If not, the stretching ratio and encryption criterion are adjusted, and the non-uniform rectangular grid is regenerated starting from step S3.

[0044] Figure 2 is a flowchart of the final non-uniform rectangular grid automatic generation method of the embodiment of the present invention, comprising Figure 2 It can be seen that after the non-uniform rectangular grid is generated, the boundary layer grid is generated based on the non-uniform rectangular grid by setting the stretching grid points and stretching ratio inside the boundary layer, and the spatial flow field calculation grid for numerical simulation is obtained, that is, the final non-uniform rectangular grid. After the grid is generated, a *.dat format file containing grid coordinates and unit connection information is output.

[0045] The present invention is further described in detail below in conjunction with specific embodiments:

[0046] for Figure 3 The geometric model shown in , determines that the tail rudder with small thickness is a geometric component that needs special treatment;

[0047] According to the boundary positions of the outer edge, root, and body of the tail rudder, the coordinates of the feature points are determined as follows: Figure 4 0, 1, 2, 3, 4 as shown in;

[0048] According to the grid change formula, determine the base grid size, the number of grid points on the left and right sides or the stretching ratio, and generate grid information on the left and right sides of the feature point;

[0049] Automatically generate the mother grid of non-uniform rectangular grids, design the encryption strategy such as the fork number encryption depth, the number of encryption layers of neighboring cells and the encryption criteria;

[0050] Based on the fork number structure, the mesh is encrypted. After the mesh is generated, Figure 5 shown.

[0051] By adopting the embodiments of the present invention, the mother grid of the rectangular grid can be designed in combination with the geometric characteristics and the flow field characteristics, and the grid scales in different directions can be quickly approached to the calculation requirements after encryption once. The generated calculation grid maintains the orthogonal characteristics of the rectangular grid, and at the same time has a high success rate, effectively reduces the encryption depth, and improves the effectiveness of the grid distribution. It can better guarantee the quality of the calculation grid and the success rate of the grid generation, and provide a fast and high-quality grid generation solution for CFD calculations.

[0052] System Example

[0053] According to an embodiment of the present invention, a non-uniform rectangular grid automatic generation system is provided. Figure 6 is a schematic diagram of a non-uniform rectangular grid automatic generation system according to an embodiment of the present invention. Figure 6 As shown, the non-uniform rectangular grid automatic generation system according to an embodiment of the present invention specifically includes:

[0054] Surface mesh expression module 60: used to divide the input three-dimensional geometric model to generate surface mesh;

[0055] Key component determination module 62: used to determine geometric components whose sizes are smaller than preset values ​​and / or areas reflecting flow field characteristics in the three-dimensional geometric model;

[0056] Position determination module 64: used to determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface grid, and determine the position of the geometric component;

[0057] Initial grid generation module 66: used to generate a non-uniform matrix grid as an initial grid based on the coordinate point information and a defined stretching ratio;

[0058] The non-uniform rectangular grid generation module 68 is used to perform non-uniform grid encryption on the initial grid based on the fork tree structure according to the set encryption strategy to generate a non-uniform rectangular grid.

[0059] The system also includes a spatial flow field calculation grid generation module: used to generate a boundary layer grid based on the non-uniform rectangular grid by setting the stretching grid points and stretching ratio inside the boundary layer, and finally obtain a spatial flow field calculation grid for numerical simulation.

[0060] The embodiment of the present invention is a system embodiment corresponding to the above-mentioned method embodiment. The specific operations of each module can be understood by referring to the description of the method embodiment, which will not be repeated here.

[0061] Obviously, those skilled in the art should understand that the above modules or steps of the present invention can be implemented by a general computing device, they can be concentrated on a single computing device, or distributed on a network composed of multiple computing devices, and optionally, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be executed in a different order than here, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. Thus, the present invention is not limited to any specific combination of hardware and software.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for automatically generating a non-uniform rectangular grid, characterized in that: include: S1. Divide the input three-dimensional geometric model to generate a surface mesh; S2. Determine the geometric components in the three-dimensional geometric model whose size is smaller than a preset value and / or the area reflecting flow field characteristics; S3. Determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface mesh to determine the position of the geometric component; S4. Generate a non-uniform matrix grid as an initial grid based on the defined stretch ratio according to the coordinate point information; S5. According to a preset encryption strategy, the initial grid is encrypted non-uniformly based on a fork tree structure to generate a non-uniform rectangular grid; By setting the stretching grid points and stretching ratio inside the boundary layer, a boundary layer grid is generated based on the non-uniform rectangular grid, and finally a spatial flow field calculation grid for numerical simulation is obtained.

2. The method according to claim 1, characterized in that The method for selecting small-sized geometric components is: determined based on the geometric scale of the components, including: the small-scale side length of components whose thickness is less than a preset thickness value or the length, width and height ratio of components is greater than a preset ratio value; the areas that reflect the characteristics of the flow field include areas that can generate shock waves, areas where vortex structures exist, or areas where local viscous / inviscid interference is severe.

3. The method according to claim 1, characterized in that: The method described in S3 specifically includes: extracting coordinate point information of key points of geometric components that need special encryption and size information that needs to be encrypted based on the surface mesh, and determining the position of the component or area.

4. The method according to claim 1, characterized in that The method described in S4 is specifically: determining the position and stretching ratio of mesh contraction, core encryption, and stretching according to the coordinate point information, and generating a mother mesh for starting non-uniform rectangular mesh encryption as an initial mesh.

5. The method according to claim 4, characterized in that The initial grid is an anisotropic grid with different sizes in three directions, and the stretching ratio is greater than 1 or less than 1.

6. The method according to claim 1, characterized in that The encryption strategy includes: fork tree encryption depth, number of encryption layers of neighbor units and encryption criteria.

7. The method according to claim 1, characterized in that The method further includes: judging whether the non-uniform rectangular grid generated in step S5 meets the requirements of flow field calculation through a grid generation criterion; if not, adjusting the stretching ratio and encryption criterion, and re-executing the non-uniform rectangular grid generation step starting from step S3.

8. A non-uniform rectangular grid automatic generation system, characterized in that: include: Surface mesh expression module: used to divide the input 3D geometric model to generate surface mesh; Key component determination module: used to determine the geometric components whose size is smaller than a preset value and / or the areas reflecting flow field characteristics in the three-dimensional geometric model; Position determination module: used to determine the coordinate point information and size parameters of the geometric component through the coordinate system of the surface grid, and determine the position of the geometric component; An initial mesh generation module: used to generate a non-uniform matrix mesh as an initial mesh based on the coordinate point information and a defined stretching ratio; Non-uniform rectangular grid generation module: used to perform non-uniform grid encryption on the initial grid based on the fork tree structure according to the set encryption strategy to generate a non-uniform rectangular grid.

9. The system according to claim 8, characterized in that The system also includes a spatial flow field calculation grid generation module: used to generate a boundary layer grid based on the non-uniform rectangular grid by setting the stretching grid points and stretching ratio inside the boundary layer, and finally obtain a spatial flow field calculation grid for numerical simulation.

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