Manifold mesh generation method and system for geomechanical analysis

Abstract

The invention provides a manifold mesh generation method and system for geomechanical analysis, and belongs to the field of computational geometry, computer graphics and geomechanics, and the method comprises the steps: S1, taking a geologic body mesh C as input, selecting a background mesh BKG, and defining mathematical coverage; s2, cutting a geologic body grid C by using a background grid BKG, and cutting a geocell into a plurality of geologic body grid subcells (small cells); s3, physical coverage is constructed by analyzing the connectivity of the interior of each bkgcell and the geologic body between the bkgcells in mathematical coverage; and S4, extracting and outputting manifold element grids in physical coverage. The manifold element grid generated by the method can be used for carrying out geomechanical analysis based on a three-dimensional numerical manifold method under the condition that original volume grid information is reserved.

Description

Technical Field

[0001] The invention belongs to the fields of computational geometry, computer graphics and geomechanics, and particularly relates to a manifold element grid generation method and system for geomechanics analysis. Background Art

[0002] In the field of geomechanics, mechanical analysis of geological bodies is a very important task. By analyzing the mechanical behavior of geological bodies, we can deeply understand the distribution, structural characteristics and evolution history of strata, and predict the response of geological bodies under natural conditions (such as earthquakes, debris flows, etc.) or human activities (such as mining, tunnel excavation, etc.). In addition, mechanical analysis is also particularly important in the field of resource development, especially in the development of oil, natural gas and mineral resources. It can provide a scientific basis for the selection of drilling locations and the formulation of mining strategies, improve the efficiency of resource extraction, and enhance the safety of mining operations.

[0003] In the field of geomechanics, various problems can usually be expressed by ordinary differential equations or partial differential equations. However, due to the characteristics of geological bodies such as discontinuity, non-uniformity and unknown initial state, it is extremely difficult to solve these equations using analytical methods. Therefore, in practical applications, it is usually necessary to rely on computers for numerical simulation to obtain numerical solutions with sufficient accuracy. Effective numerical simulation often depends on accurate geological body modeling. Due to the large number of faults and strata inside the geological body, the geological body grid is often a volume grid with complex internal properties. This polyhedral grid can well describe the geometry and attribute information of the geological body and can also be used for fluid calculations. However, due to the different number of vertices on each unit and each face of this grid, it is difficult to perform mechanical analysis directly on this set of grids.

[0004] At present, the mainstream method for solving mechanical problems is the finite element method, and its basic idea is to discretize the solution domain of the problem to obtain a finite number of units. It is difficult to directly use a set of geological body meshes with complete internal geometric data and corresponding attribute data for finite element analysis. The general practice is to first use software to extract its frame surface, that is, the surface mesh, and then divide the interior into tetrahedral or hexahedral finite element meshes, and then perform finite element static analysis on this set of finite element meshes. There are two problems with this: first, it is very complicated and time-consuming to divide the internal mesh of the complex frame surface; second, the finite element mesh obtained by the internal division does not have the attributes of the geological body, and its attribute information needs to be sampled and interpolated from the original body mesh, which makes the attribute data of the original body mesh not effectively utilized.

[0005] The Numerical Manifold Method (NMM) is a discontinuous deformation analysis method, which can be regarded as an extension of the concept of the finite element method. It uses a dual covering system that combines mathematical covering and physical covering, which can uniformly handle continuous and discontinuous deformation problems. Therefore, the numerical manifold method has great prospects in the field of geology. The numerical manifold method has two sets of grids: geological body grids and manifold element grids. If the body grid is used as the material grid to construct the manifold element grid, the original body grid information can be retained on the manifold element grid and used for mechanical calculations. This method uses a dual covering system that combines mathematical covering and physical covering. It has been widely used in two dimensions, but there are relatively few studies in three dimensions, and most of them are limited to surface grids. Therefore, how to apply the numerical manifold method to three-dimensional body grids has become an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for generating a manifold element grid for geomechanical analysis, comprising the following steps:

[0007] Step S1: taking the geological body grid C as input, selecting the background grid BKG and defining a mathematical cover; wherein the geological body grid C is composed of a plurality of geological body grid units geocell, and the background grid BKG is composed of a plurality of background grid units bkgcell;

[0008] Step S2: using the background grid BKG to cut the geological body grid C, cutting the geocell into a plurality of geological body grid sub-units smallcell;

[0009] Step S3: constructing a physical cover by analyzing the connectivity of geological bodies within each bkgcell and between bkgcells in the mathematical cover;

[0010] Step S4: extracting and outputting the manifold element grid in the physical cover.

[0011] Beneficial effects:

[0012] 1. The prior art usually requires preprocessing of the geological body mesh, such as re-dividing the internal mesh after extracting the frame surface. The process is cumbersome and the attribute information inside the original mesh is easily lost. However, the present invention directly uses the original body mesh of the geological body as input, and completely retains these attribute information in the process of constructing the manifold element mesh. Moreover, since the manifold element mesh and the geological body mesh have an explicit mapping relationship, it is convenient to map the attributes, so that the subsequent mechanical analysis can make full use of the original characteristics of the geological body and improve the accuracy and reliability of the analysis results.

[0013] 2. Although the numerical manifold method has been widely used in two dimensions, there are relatively few studies on it in three dimensions and it is mostly limited to surface grids. Most implementations use the surface grid of the geological body as input. The present invention uses the three-dimensional body grid as input and directly constructs the manifold element grid on the three-dimensional body grid, so that the numerical manifold method can be applied in three-dimensional geomechanical analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of a flow chart of a method for generating a manifold element grid for geomechanical analysis according to the present invention;

[0015] Figure 2 It is a schematic diagram of the geological body grid;

[0016] Figure 3 is a schematic diagram of a virtual grid unit;

[0017] Figure 4 It is a schematic diagram of physical coverage;

[0018] Figure 5A The original geological body grid diagram in Example 1 is shown below;

[0019] Figure 5B This is a schematic diagram of the fault plane extracted from the manifold element grid in Example 1;

[0020] Figure 5C This is a schematic diagram of the artificial interface extracted from the manifold element grid in Example 1;

[0021] Figure 5D This is a schematic diagram of the ground plane extracted from the manifold element grid in Example 1;

[0022] Fig. 6A This is the schematic diagram of the original geological body grid in Example 2;

[0023] Figure 6B The following is a schematic diagram of the deformation of the geological body under the background grid with a step length of 50 meters in Example 2;

[0024] Figure 6C The following is a schematic diagram of the deformation of the geological body under the background grid with a step length of 100 meters in Example 2;

[0025] Fig.6D The following is a schematic diagram of the deformation of the geological body under the background grid with a step length of 200 meters in Example 2;

[0026] Figure 7 The present invention is a structural block diagram of a manifold element grid generation system for geomechanical analysis. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Embodiment 1

[0029] like Figure 1 As shown, a method for generating a manifold element grid for geomechanical analysis provided by an embodiment of the present invention includes the following steps:

[0030] Step S1: taking the geological body grid C as input, selecting the background grid BKG and defining the mathematical coverage; wherein the geological body grid C is composed of a plurality of geological body grid units geocell, and the background grid BKG is composed of a plurality of background grid units bkgcell;

[0031] Step S2: Use the background grid BKG to cut the geological body grid C, and cut the geocell into multiple geological body grid sub-units smallcell;

[0032] Step S3: constructing the physical coverage by analyzing the connectivity of the geological bodies within each bkgcell and between bkgcells in the mathematical coverage;

[0033] Step S4: Extract and output the manifold element mesh in the physical cover.

[0034] In one embodiment, the above step S1: taking the geological body grid C as input, selecting the background grid BKG and defining the mathematical coverage; wherein the geological body grid C is composed of a plurality of geological body grid units geocell, and the background grid BKG is composed of a plurality of background grid units bkgcell; specifically includes:

[0035] A three-dimensional regular hexahedral grid that completely covers the geological body grid C is selected as the background grid BKG, where the rotation direction of BKG is arbitrary; the space occupied by 8 bkgcells with common vertices in BKG is selected as the mathematical cover.

[0036] The physical grid of the model is used to describe the boundaries, internal sections, details and properties of the object. In the present invention, the physical grid of the model is defined as the geological body grid. The geological body grid is a mathematical model that discretizes the geological body in three-dimensional space. It divides the geological body into multiple layered units (such as hexahedrons, etc.), each unit contains specific geological properties, thereby realizing the digital description of the geological structure. In the present invention, the input geological body grid is as follows Figure 2As shown in the figure, the attribute information it contains includes the type type representing the surface and the identifier id of the surface. These two values ​​combined together provide a unique identifier for the surface attribute information. Each geological body grid cell has a series of attributes, which can be represented as a series of attribute arrays.

[0037] In one embodiment, the above step S2: using the background grid BKG to cut the geological body grid C, cutting the geocell into a plurality of geological body grid sub-units smallcell; specifically includes:

[0038] Traverse all geocells of the geological body grid C, cut the geocells with BKG, and obtain the geological body inside each bkgcell.

[0039] Since the geological unit may be a polyhedron in space, this form of polyhedron is not convenient for direct cutting. Since the three points must be on the same plane, it is necessary to triangulate the surface to make it a plane sheet. The specific steps are as follows:

[0040] First, the surface of the geocell is triangulated and converted into a surface triangulated mesh. During the triangulation process, the starting triangle in the polygon is selected strictly according to fixed rules for recursive triangulation. At the same time, the topological consistency check algorithm is used to ensure the topological consistency of the common surfaces of adjacent geocells.

[0041] Then, the mesh is cut in depth first, the size of the bounding box of the mesh is calculated, and all the interference surfaces in the x direction are calculated and stored in an array. For each interference surface in the x direction in the array, the Boolean operation of CGAL (Computational Geometry Algorithms Library) is used to make intersection and difference between the interference surface and the mesh. The part of the mesh inside the interference surface in the x direction is the intersection, and the part outside is the difference between the space represented by the cut unit and the cutting plane. The difference is left in the loop for further cutting, and the intersection is cut in the y direction in the same way as above, and then the intersection is cut out in the y direction for cutting in the z direction, and the difference is left in the loop for further cutting. Finally, the intersection obtained after cutting by the interference surface in the z direction is the so-called smallcell of the geological body grid subunit obtained after cutting, which must belong to a certain background grid unit completely. The set of smallcells belonging to the same background grid unit is the geological body inside the background grid unit bkgcell.

[0042] In one embodiment, the above step S3: constructing a physical cover by analyzing the connectivity of geological bodies within each bkgcell and between bkgcells in the mathematical cover; specifically includes:

[0043] Traverse the bkgcell and obtain the set of smallcells in the current bkgcell. According to the connectivity between each smallcell, obtain all connected domains inside the bkgcell. Each connected domain adds a corresponding physical coverage to the mathematical coverage at the 8 vertices of the bkgcell where it is located. Construct a virtual grid cell VC to record the tuple relationship between the connected domain, the bkgcell where it is located, and the 8 introduced physical coverages. According to the connectivity between the virtual grid cells VC, merge the physical coverages to obtain the final physical coverage PC.

[0044] Physical coverage is obtained by dividing mathematical coverage by geological bodies. Disconnected geological bodies in a mathematical coverage belong to different physical coverages. In the present invention, constructing a physical coverage PC requires traversing the background grid units, first finding the connected domain inside each background grid unit, and then finding the connected domain between adjacent background grid units. First, one physical coverage is added to the mathematical coverage at the eight vertices of the background grid unit where the current connected domain is located, and a total of eight physical coverages are added. In order to more conveniently record these eight physical coverages and the geological bodies in each connected domain, the present invention proposes a new data structure-virtual grid unit. For each background grid unit, a new virtual grid unit is created each time a connected domain appears, and the geological bodies in the connected domain, that is, the set of smallcells, are recorded in this virtual grid unit. At the same time, the eight newly added physical coverages are recorded at the eight vertices recorded in the virtual grid unit, which is equivalent to adding one physical coverage PC to the mathematical coverage represented by these eight vertices. Each virtual grid unit records the number of the smallcell contained therein, as well as the physical coverage number on the eight vertices. Figure 3 As shown in the figure, the left side is a background grid cell whose interior is completely occupied by geological bodies, but there is a geological interface that makes two connected domains exist. For this purpose, two virtual grid cells are constructed as shown on the right. The disconnected geological bodies inside the background grid cell bkgcell are not necessarily disconnected in the mathematical coverage. After the initial physical coverage is completed, the physical coverages between virtual grid cells are independent of each other. The connected geological bodies that originally belonged to the same mathematical coverage will also be divided into different physical coverages. Therefore, it is necessary to group and merge the physical coverages. The physical coverage PCs that need to be merged on adjacent virtual grids are as follows: Figure 4 shown.

[0045] The specific steps to build a physical overlay are as follows:

[0046] First, traverse all background grid cells bkgcell, obtain the set of smallcells from the current background grid cell bkgcell, determine the connectivity between each smallcell, and create a new virtual grid cell for each connected domain. Create 8 new physical coverages for it, where the physical coverage number and the smallcell number in the current connected domain are stored in the member variables of the virtual grid cell.

[0047] Then, the virtual grid cell set of each background grid cell is traversed to determine whether the virtual grid cell set is connected to the virtual grid cell set of the background grid cells adjacent to it in the x, y, and z directions. If connected, the four groups of physical coverage on the common surface are merged two by two, and the physical coverage is renumbered. This step obtains the virtual grid cells on all background grid cells, each of which contains an internally connected small cell set and 8 final physical coverage numbers.

[0048] In one embodiment, the above step S4: extracting and outputting the manifold element grid in the physical coverage specifically includes:

[0049] According to the definition of manifold element, that is, manifold element is the intersection of physical cover PC, the geological body inside the virtual grid cell VC and the 8 physical covers covering the geological body are extracted as the manifold element grid, and BKG, VC, PC and smallcell are output in the form of files for subsequent calculation and analysis.

[0050] For the background grid BKG, due to the regularity of the grid, only the step size and minimum coordinates of the background grid in three directions, as well as the number of bkgcells in three directions can fully describe this background grid, so its attribute information is stored separately in a fixed order in a file; for the serial numbers of all manifold elements in each background grid cell, that is, the serial numbers of the virtual grid cells corresponding to the background grid cell, since the number of virtual grid cells derived from a background grid cell is inconsistent, they are stored in two array files. The first array stores the serial numbers of all manifold elements in each background grid cell in sequence, and the second array is used to identify the start and end indexes of the manifold element index of each background grid cell in the first array; for the physical coverage information of the manifold elements and the background grid cell number information The information is also stored in two arrays; for smallcells, each smallcell is serialized and output in order. First, the number of triangular facets and the stratum number of the small cell surface are output, and then the three vertex coordinates on each face are output in turn and stored in an array file. Another array file is used to record the attribute type and id values ​​of each face on each smallcell, as well as the face normal vector information; for the output of smallcells in manifold elements, since the number of smallcells in each manifold element is different, its information is stored in two array files, one array file is used to describe the number of smallcells in each manifold element, and the other is used to describe the start and end indexes of the smallcells in the first array.

[0051] The following example verifies that the manifold element grid generated by the method of the present invention contains information of the original geological body grid and is suitable for geomechanical analysis:

[0052] Example 1: Verify that the manifold element grid generated by the method of the present invention contains the information of the original geological body grid:

[0053] The input original geological body grid is as follows Figure 5A As shown, Figure 5B , 5C , 5D are respectively the fault plane, artificial interface and stratigraphic surface extracted from the manifold element grid after the manifold element grid is constructed for the geological body. It can be seen that the information of these interfaces is complete and correct, which indicates that the manifold element grid constructed by the method of the present invention inherits the geometry and attribute information of the original geological body well.

[0054] Example 2: Verify that the manifold element grid generated by the method of the present invention can be used for geomechanical analysis:

[0055] The input original geological body grid is as follows Fig. 6A The material geometric properties and mechanical properties of the geological body are shown in Table 1.

[0056] Table 1 Geometric and mechanical properties of geological materials

[0057] When constructing the manifold element grid, experiments were conducted using background grids with step sizes of 50 meters, 100 meters, and 200 meters in the x, y, and z directions. The sides of the model on both sides of the x direction were fixed to observe how it naturally fell under gravity. By default, there is a fixed contact relationship on both sides of the interface during static analysis.

[0058] The deformation diagrams of the geological body under the background grid with a step length of 50 meters, 100 meters, and 200 meters are shown below: Figure 6B , Figure 6C and Fig.6D As shown. From the above figure, it can be seen that under different background grid step sizes, the static analysis of the same complete geological body under the same mechanical scenario shows that the overall displacement drops downward and the displacement shape is roughly the same. It is observed that there is no intrusion or fracture of the material body around the interface of the geological body. This phenomenon is in line with the law of mechanics. Furthermore, the specific experimental data of the three experiments under different step sizes are shown in Table 2. As the step size is halved each time, the displacement range between different step sizes gradually decreases, which shows that the displacement results are indeed converging as the step size becomes smaller and smaller. And because the working area of ​​the model itself is 4000 meters 2800m 1240.4 m, so the difference between the displacements at different step lengths in Table 2 is acceptable, which shows that the manifold element grid generated by the method of the present invention is applicable to the real geological body.

[0059] Table 2 Experimental data at different step lengths

[0060] Embodiment 2

[0061] like Figure 7 As shown, an embodiment of the present invention provides a manifold element grid generation system for geomechanical analysis, comprising the following modules:

[0062] Constructing a background grid and mathematical overlay module 51, for defining the background grid specification, position, and rotation direction;

[0063] The geological body grid cutting module 52 is used to cut the geological body grid C using the background grid BKG, cut the geocell of the geological body grid C into a plurality of geological body grid sub-units smallcell, and classify them into the corresponding background grid unit bkgcell;

[0064] A physical coverage building module 53 is used to analyze the connectivity of geological bodies within each bkgcell and between bkgcells in the mathematical coverage to build the physical coverage;

[0065] The manifold element grid acquisition module 54 is used to extract and output the manifold element grid from the physical cover.

[0066] A manifold element grid generation device for geomechanical analysis includes one or more electronic devices, wherein the one or more electronic devices are used to implement a manifold element grid generation method, system and device for geomechanical analysis.

[0067] An electronic device comprises: one or more processors; a memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement a method, system and device for generating a manifold element grid for geomechanical analysis.

[0068] A computer-readable storage medium stores executable instructions, which, when executed by a processor, enable the processor to implement a method, system and device for generating a manifold element grid for geomechanical analysis.

[0069] A non-transitory computer-readable storage medium stores a computer program, which, when executed by a processor, implements a method, system and device for generating a manifold element grid for geomechanical analysis.

[0070] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A method for generating manifold element grids for geomechanical analysis, characterized in that: include: Step S1: taking the geological body grid C as input, selecting the background grid BKG and defining a mathematical cover; wherein the geological body grid C is composed of a plurality of geological body grid units geocell, and the background grid BKG is composed of a plurality of background grid units bkgcell; Step S2: using the background grid BKG to cut the geological body grid C, cutting the geocell into a plurality of geological body grid sub-units smallcell; Step S3: constructing a physical cover by analyzing the connectivity of geological bodies within each bkgcell and between bkgcells in the mathematical cover; Step S4: extracting and outputting the manifold element grid in the physical cover.

2. The method for generating a manifold element grid for geomechanical analysis according to claim 1, characterized in that: The step S1: taking the geological body grid C as input, selecting the background grid BKG and defining the mathematical coverage; wherein the geological body grid C is composed of a plurality of geological body grid units geocell, and the background grid BKG is composed of a plurality of background grid units bkgcell; specifically includes: A three-dimensional regular hexahedral grid that completely covers the geological body grid C is selected as the background grid BKG, wherein the rotation direction of BKG is arbitrary; and the space occupied by 8 bkgcells with common vertices in BKG is selected as the mathematical cover.

3. The method for generating a manifold element grid for geomechanical analysis according to claim 2, characterized in that: The step S2: using the background grid BKG to cut the geological body grid C, cutting the geocell into a plurality of geological body grid sub-units smallcell; Specifically include: Traverse all geocells of the geological body grid C, cut the geocells with BKG, and obtain the geological body inside each bkgcell.

4. The method for generating a manifold element grid for geomechanical analysis according to claim 3, characterized in that: The step S3: constructing a physical cover by analyzing the connectivity of the geological bodies within each bkgcell and between bkgcells in the mathematical cover; specifically includes: Traverse the bkgcell to obtain the set of smallcells in the current bkgcell, and according to the connectivity between each smallcell, obtain all connected domains inside the bkgcell, wherein each connected domain adds a corresponding physical coverage to the mathematical coverage at the 8 vertices of the bkgcell where it is located; construct a virtual grid unit VC to record the tuple relationship between the connected domain, the bkgcell where it is located, and the introduced 8 physical coverages; according to the connectivity between the virtual grid units VC, merge the physical coverages to obtain the final physical coverage PC.

5. The method for generating a manifold element grid for geomechanical analysis according to claim 4, characterized in that: The step S4: extracting and outputting the manifold element grid in the physical overlay specifically comprises: According to the definition of manifold element, that is, manifold element is the intersection of physical cover PC, the geological body inside VC and the 8 physical covers covering the geological body are extracted as the manifold element grid, and BKG, VC, PC and smallcell are output in the form of files for subsequent calculation and analysis.

6. A manifold element grid generation system for geomechanical analysis, characterized in that: Includes the following modules: Construct background grid and mathematical overlay modules to define background grid specifications, positions, and rotation directions; The cutting geological body grid module is used to cut the geological body grid C using the background grid BKG, cut the geocell of the geological body grid C into multiple geological body grid sub-units smallcell, and classify them into the corresponding background grid unit bkgcell; Construct physical coverage module, which is used to analyze the connectivity of geological bodies within each bkgcell and between bkgcells in mathematical coverage, and construct physical coverage; Get Manifold Metagrid module, which extracts and outputs a manifold metagrid from a physical cover.

7. A manifold element grid generation device for geomechanical analysis, characterized in that: The method comprises one or more electronic devices, wherein the one or more electronic devices are used to implement the method according to any one of claims 1 to 5.

8. An electronic device, characterized in that: include: one or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1 to 5.

9. A computer-readable storage medium, characterized in that: Executable instructions are stored thereon, and when the instructions are executed by a processor, the processor implements the method according to any one of claims 1 to 5.

10. A non-transitory computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 5 are implemented.

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