Finite element grid construction method for free grid of regular grid foundation of arch dam in complex geology

Abstract

The invention belongs to the field of water conservancy and hydropower engineering, discloses a finite element grid construction method for free grids of a regular grid foundation of an arch dam in complex geology, and aims to realize high-precision regular grids of a dam body and flexible, diversified and quick free grids of a dam foundation so as to improve the reasonability and effectiveness of stress and overall stable calculation of the arch dam. According to the scheme, firstly, according to arch dam shape design data, a regular arch dam geometry is established; secondly, a dam foundation geometric block is built in the dam foundation near the foundation building surface, and a dam foundation foundation building surface thin layer is obtained; secondly, according to a foundation building surface, a dam foundation foundation building surface thin layer, a terrain surface, a dam foundation lithologic stratum boundary line and a fault structural surface, a geometry of the complex foundation is built; and finally, model mesh generation is carried out on the arch dam geometry, the dam foundation construction base plane thin layer and the geometry of the complex foundation in sequence, specifically, hexahedron mapping mesh generation is carried out on the arch dam geometry, then transition mesh generation from hexahedron to tetrahedron is carried out on the geometry of the dam foundation construction base plane thin layer, and model mesh generation is carried out on the geometry of the complex foundation. And finally, carrying out free mesh generation on the geometry of the complex foundation.

Description

Technical Field

[0001] The present invention belongs to the field of water conservancy and hydropower engineering, and particularly relates to a finite element mesh construction method for a free mesh of a regular mesh foundation of a complex geological arch dam. Background Art

[0002] High arch dams are mostly built in high mountain and canyon areas. Generally speaking, the geological conditions of the dam sites of high arch dams are relatively complex, and there are various foundation treatment measures. For example, in the dam site area of Jinping-I Arch Dam, the world's highest arch dam, in addition to various levels of rock masses from slightly fresh to strongly weathered, there are also a large number of fault weak structures distributed. There are f2, f5, f8, f 13 , f 14 , f 18 faults and lamprophyre veins on the left bank alone. The foundation treatment adopted a concrete cushion, consolidation grouting of the resistance body, concrete grid replacement of the f5 (f8) faults and lamprophyre veins, and force transfer tunnels, etc., which comprehensively formed the "cushion, consolidation, transfer, and plug" comprehensive reinforcement treatment plan for the left bank resistance body. A large number of plan comparisons were also carried out during the feasibility study stage, such as comparisons of different plans of concrete cushions, thrust piers, and gravity piers, comparisons of cushion forms and joint structures, comparisons of concrete replacement forms and ranges of weak rock zones, comparisons of consolidation grouting ranges, etc.

[0003] For the three-dimensional numerical analysis of the overall stability of an arch dam, the primary problem is to establish a reasonable calculation grid. On the one hand, it is required that the dam body grid is regular. The rules include several directions: ① using hexahedron grids; ② the grid is consistent with the dam segmentation, or consistent with the n-arch m-beam of the arch-beam load sharing method (generally, 3 < n ≤ 10; m = 2n - 1), which is convenient for comparative analysis and controls the grid form to avoid the phenomenon of stress concentration at the dam heel caused by too fine grids. On the other hand, there are many structural interfaces in the foundation, and the topological structure is extremely complex. Using tetrahedron free grids will save a large amount of modeling time.

[0004] However, in the current existing technology, it is very difficult to solve the problem of the connection and transition between the hexahedron regular grid of the dam body and the tetrahedron grid of the dam foundation. The main difficulty lies in that the fault occurrence exposed near the construction base surface (the interface between the dam body and the dam foundation) is random, and most of them are obliquely intersecting with the construction base surface. This makes the surface grid of the construction base surface unable to be coordinated with both the hexahedron regular grid of the dam body and the tetrahedron grid of the dam foundation controlled by faults obliquely intersecting the construction base surface at the same time. Summary of the Invention

[0005] The technical problem to be solved by the present invention is: to propose a finite element mesh construction method for a free mesh of a regular mesh foundation of a complex geological arch dam, to realize a high-precision regular grid of the dam body and a flexible, diverse, fast and free mesh of the dam foundation, and thus improve the rationality and effectiveness of the stress and overall stability calculation of the arch dam.

[0006] The technical solution adopted by the present invention to solve the above technical problems is:

[0007] The finite element mesh construction method of free mesh of regular mesh foundation of complex geological arch dam includes the following steps:

[0008] S1. Establish a regular arch dam geometry based on the arch dam shape design data;

[0009] S2. Near the foundation surface, a dam foundation geometric block is established in the dam foundation to obtain a thin layer of the dam foundation surface;

[0010] S3. Establish the geometric body of complex foundation according to the foundation surface, thin layer of dam foundation surface, terrain surface, dam foundation lithology and stratigraphic boundary and fault structure surface;

[0011] S4. Model meshing is performed on the geometry of the arch dam, the thin layer of the dam foundation surface, and the geometry of the complex foundation in turn: first, the geometry of the arch dam is meshed using hexahedron mapping, then the geometry of the thin layer of the dam foundation surface is meshed from hexahedron to tetrahedron, and finally, the geometry of the complex foundation is meshed using free meshing.

[0012] Furthermore, in step S1, the arch dam shape design data includes:

[0013] The arch-beam load sharing method is based on the arch plane shape data of typical elevations and the shape data of typical beam sections, or the arch dam joint data.

[0014] Furthermore, in step S2, the step of establishing a dam foundation geometric block in the dam foundation near the foundation surface to obtain a thin layer of the dam foundation surface includes:

[0015] By offsetting the foundation surface outward in a normal direction by several meters, a thin layer geometry of the foundation surface without fault structure is established to obtain the thin layer of the dam foundation foundation surface.

[0016] Furthermore, in step S3, the method of establishing the geometric body of the complex foundation according to the foundation surface, the thin layer of the dam foundation surface, the terrain surface, the dam foundation lithology stratum boundary and the fault structure surface includes:

[0017] According to the geometric boundary topological relationship, each block or area is enclosed to form the entire left and right banks and riverbed dam foundation model;

[0018] Alternatively, a volume is first constructed based on the outer contours of the left and right banks and the riverbed dam foundation model, and then the dam foundation geometry is cut out using the geological body boundaries and basic treatment measures using Boolean operations.

[0019] Furthermore, in step S4, the method of using hexahedral mapping meshing to divide the geometric body of the arch dam includes:

[0020] In both the transverse and vertical grids, only one grid is used for each line, and in the thickness direction, an even number of grids is used to ensure that there is a layer of grid surface at the center line of the dam body. Then, the arch dam geometry is divided into hexahedral mapping grids.

[0021] Furthermore, in step S4, the method of performing transitional meshing from hexahedron to tetrahedron on the geometric body of the thin layer of the dam foundation base surface includes:

[0022] First, the dam body side of the geometric body is divided into regular surface meshes to ensure coordination with the regular mesh of the dam body; then the dam foundation side of the geometric body is divided into free surface meshes to ensure that the mesh nodes are connected with the structural surface at the same point; finally, the geometric body is divided into free volume meshes.

[0023] Furthermore, in step S4, the method of performing free meshing on the geometric body of the complex foundation includes:

[0024] First, the faces of the complex foundation geometry are meshed from near the foundation surface to far away, and then the geometry is meshed freely in the same order.

[0025] The beneficial effects of the present invention are:

[0026] Based on the solution of the present invention, a thin layer of the dam foundation surface is constructed as a transition layer, which is coordinated with the regular grid of the dam body on one side and adapted to the connection with irregular structural surfaces such as faults on the other side, so as to realize the high-precision regular grid of the dam body and the flexible, diverse, fast and free grid of the dam foundation, thereby improving the rationality and effectiveness of the calculation of the arch dam stress and overall stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of a finite element mesh construction method of a free mesh of a regular mesh foundation of a complex geological arch dam in an embodiment;

[0028] Figure 2 is a schematic diagram of a dam body regular body grid taking an arch beam type arch dam grid as an example in the embodiment;

[0029] Figure 3 It is a schematic diagram of a regular body grid of a thin layer of a base surface on the side of a dam body in an embodiment;

[0030] Figure 4 It is a schematic diagram of the coordination between the thin layer of the base surface and the regular grid of the dam body in the embodiment;

[0031] Figure 5 It is a schematic diagram of the free grid connection between the thin layer of the base surface and the oblique base surface fault in the embodiment;

[0032] Figure 6 Schematic diagram of the complex geological arch dam hexahedral grid and the foundation free grid in the embodiment. DETAILED DESCRIPTION

[0033] The present invention aims to provide a finite element mesh construction method for a free mesh of a regular mesh foundation of a complex geological arch dam, so as to realize a high-precision regular mesh of the dam body and a flexible, diverse and fast free mesh of the dam foundation, and improve the rationality and effectiveness of the stress and overall stability calculation of the arch dam. The core idea is: by constructing a thin layer of the dam foundation surface as a transition layer, on one side it coordinates with the regular mesh of the dam body, and on the other side it adapts to the connection of irregular structural surfaces such as faults. When the model mesh is divided, the geometric body of the arch dam is first meshed using a hexahedron mapping, and then the geometric body of the thin layer of the dam foundation surface is meshed from hexahedron to tetrahedron, and finally the geometric body of the complex foundation is meshed freely. That is, the scheme of the present invention realizes the transition from the regular mesh of the foundation surface to the free mesh of the dam foundation through the geometric body of the thin layer of the dam foundation surface, so as to better solve the connection and transition problem between the hexahedral regular mesh of the dam body and the tetrahedral mesh of the dam foundation, and finally realizes the finite element mesh construction of the hexahedral foundation tetrahedron of the complex geological arch dam, thereby improving the rationality and effectiveness of the stress and overall stability calculation of the arch dam.

[0034] The scheme of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] Example

[0036] The process of the finite element mesh construction method for the free mesh of the regular mesh foundation of the complex geological arch dam provided in this embodiment is shown in Figure 1 , which includes the following implementation steps:

[0037] S1. Establish regular arch dam geometry;

[0038] In this step, a regular arch dam geometry, such as arch-beam type, dam section type, etc., is established based on the arch dam shape design data, including the arch plane shape data of typical elevations and the shape data of typical beam sections based on the arch-beam load sharing method, or based on the arch dam joint data.

[0039] S2. Build a thin layer on the dam foundation surface;

[0040] In this step, a dam foundation geometry block is established in the dam foundation near the foundation surface. In actual operation, a simple foundation surface thin layer geometry without faults and other structural surfaces can be established by offsetting the foundation surface outward in a normal direction by several meters, generally 2 to 3 meters depending on the height of the dam body, referred to as the dam foundation foundation thin layer, as a transition layer. Through this transition layer, the dam body does not directly intersect with the fault and other structural surfaces.

[0041] S3, build complex foundation geometry;

[0042] In this step, the geometric body of the complex foundation is established according to the foundation surface, terrain surface (including natural slope and excavation slope), dam foundation rock stratigraphic boundary and fault structure surface. There are two main methods: ① Wall-building method, according to the topological relationship of geometric boundaries, each block or area is enclosed to form the entire left and right bank and riverbed dam foundation model; ② Tofu-cutting method, first construct a body according to the outer contour of the left and right bank and riverbed dam foundation model, and then use Boolean operation to cut out the dam foundation geometry using various geological body boundaries and foundation treatment measures.

[0043] S4, sequentially divide the model meshes for the geometric bodies of the arch dam, the thin layer of the dam foundation surface, and the geometric bodies of the complex foundation;

[0044] In this step, the model meshing is performed in the order of dam body, thin layer of foundation surface, and finally all dam foundations. That is, the geometry of the arch dam is first meshed with hexahedron mapping, then the geometry of the thin layer of the dam foundation surface is meshed from hexahedron to tetrahedron, and finally the geometry of the complex foundation is meshed with free meshing.

[0045] The dam body meshing method includes: for the line segments of the arch beam or dam segment block, each line is divided into only one part in the transverse and vertical directions, and divided into 4, 8, 10 and other even-numbered parts in the thickness direction to ensure that there is a layer of mesh surface on the center line of the dam body, and then the arch dam geometry is meshed using hexahedral mapping, see Figure 2 .

[0046] The meshing method of the thin layer of the dam foundation surface geometry includes: firstly, the dam body side of the geometry is meshed regularly, see Figure 3 , to ensure coordination with the regular grid of the dam body, see Figure 4 ; Then, the free surface meshing is performed on the side of the dam foundation of the geometric body to ensure that the mesh nodes are connected with the structural surface at the same point, see Figure 5 ; Finally, the geometry is free-volume meshed.

[0047] The meshing method of the geometric body of the complex foundation includes: first, the surface meshing of each surface of the dam foundation geometric body is carried out from the near foundation surface to the farthest distance; then, the volume meshing is carried out in the same order. The meshing accuracy can be controlled by setting the seed point according to the calculation accuracy requirements, and the focus is on controlling the meshing accuracy of the weak structure and treatment measures, see Figure 6 .

[0048] Finally, it should be noted that the above embodiments are only preferred implementations and are not intended to limit the present invention. It should be pointed out that for those skilled in the art, several modifications, equivalent replacements, improvements, etc. can be made without departing from the scope of the present invention and the scope of protection of the claims, and all of these should be included in the protection scope of the present invention.

Claims

1. A finite element mesh construction method for free mesh of regular mesh foundation of complex geological arch dam, characterized by: The following steps are involved: S1. Establish a regular arch dam geometry based on the arch dam shape design data; S2. Near the foundation surface, a dam foundation geometric block is established in the dam foundation to obtain a thin layer of the dam foundation surface; S3. Establish the geometric body of complex foundation according to the foundation surface, thin layer of dam foundation surface, terrain surface, dam foundation lithology and stratigraphic boundary and fault structure surface; S4. Model meshing is performed on the geometry of the arch dam, the thin layer of the dam foundation surface, and the geometry of the complex foundation in turn: first, the geometry of the arch dam is meshed using hexahedron mapping, then the geometry of the thin layer of the dam foundation surface is meshed from hexahedron to tetrahedron, and finally, the geometry of the complex foundation is meshed using free meshing.

2. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S1, the arch dam shape design data includes: The arch-beam load sharing method is based on the arch plane shape data of typical elevations and the shape data of typical beam sections, or the arch dam joint data.

3. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S2, the step of establishing a dam foundation geometric block in the dam foundation near the foundation surface to obtain a thin layer of the dam foundation surface includes: By offsetting the foundation surface outward in a normal direction by several meters, a thin layer geometry of the foundation surface without fault structure is established to obtain the thin layer of the dam foundation foundation surface.

4. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S3, the method of establishing the geometric body of the complex foundation according to the foundation surface, the thin layer of the dam foundation foundation surface, the terrain surface, the dam foundation lithology stratum boundary and the fault structure surface includes: According to the geometric boundary topological relationship, each block or area is enclosed to form the entire left and right banks and riverbed dam foundation model; Alternatively, a volume is first constructed based on the outer contours of the left and right banks and the riverbed dam foundation model, and then the dam foundation geometry is cut out using the geological body boundaries and basic treatment measures using Boolean operations.

5. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S4, the method of using hexahedral mapping meshing to divide the arch dam geometry includes: In both the transverse and vertical grids, only one grid is used for each line, and in the thickness direction, an even number of grids is used to ensure that there is a layer of grid surface at the center line of the dam body. Then, the arch dam geometry is divided into hexahedral mapping grids.

6. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S4, the method of performing transitional meshing from hexahedron to tetrahedron on the geometric body of the thin layer of the dam foundation base surface comprises: First, the dam body side of the geometric body is divided into regular surface meshes to ensure coordination with the regular mesh of the dam body; then the dam foundation side of the geometric body is divided into free surface meshes to ensure that the mesh nodes are connected with the structural surface at the same point; finally, the geometric body is divided into free volume meshes.

7. The finite element grid construction method of free grid of regular grid foundation of complex geological arch dam as claimed in claim 1, characterized in that: In step S4, the method of performing free meshing on the geometric body of the complex foundation includes: First, the faces of the complex foundation geometry are meshed from near the foundation surface to far away, and then the geometry is meshed freely in the same order.

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