A method for selecting a heat dissipation surface

Abstract

The present invention relates to the field of hydropower engineering, and discloses a method for selecting a heat dissipation surface, comprising the following steps: first, based on the engineering structure design data, a finite element mesh model of the dam is constructed to obtain the topological relationship between the units and nodes of the model; second, by traversing the units, a list of adjacent units of each unit is determined, and the free surface of each unit is determined by comparing the centroid coordinates of each surface of the adjacent units one by one; third, an arbitrary point is marked on the heat dissipation surface to be selected, and all units are repeatedly traversed, and the mark transfer is performed within a limited coordinate range, and whether the transfer is completed is determined according to the number of marked points obtained by the two traversals; finally, the free surface with the marked point is output, which is the selected heat dissipation surface. The heat dissipation surface selection method provided by the present invention solves the problem that the surface boundary is difficult to be selected through a given coordinate range in finite element calculation, improves the pre-processing efficiency of finite element calculation, and is suitable for applying temperature boundaries to the structural analysis of water conservancy and hydropower engineering.

Description

Technical Field

[0001] The invention relates to the field of water conservancy and hydropower engineering, and in particular to a method for selecting a heat dissipation surface. Background Art

[0002] During the design phase of a concrete dam, it is necessary to analyze the stress and deformation of the dam under different working conditions, among which temperature load is a major load. During the construction period, the temperature of concrete will continue to change over time under the influence of hydration reaction, water cooling, interlayer heat dissipation, surface insulation and other effects and measures, resulting in thermal expansion and contraction. When constrained by the foundation and surrounding concrete, temperature stress will be generated, which may cause concrete cracking in severe cases. During the operation period, the hydration reaction of concrete is basically completed, and the temperature of the dam body is mainly affected by the external environment, and changes periodically with the air temperature and reservoir water temperature, thereby causing the dam to produce temperature rise and fall loads, affecting the stress and deformation state of the dam. When the dam body or section design is unreasonable, the temperature load may cause local cracking of the dam. Therefore, the correct application of temperature load is crucial for analyzing and grasping the real stress state of the dam, formulating corresponding measures, and ensuring the quality of dam construction and safe operation.

[0003] There are two main types of temperature loads, one is body load and the other is surface load. As mentioned above, body load is mainly the effect of hydration heat generated during concrete hydration and water cooling measures on concrete temperature; surface load is mainly the effect of heat exchange between concrete and air and reservoir water through the contact surface. Such surfaces for heat exchange are collectively called heat dissipation surfaces, such as the upstream and downstream surfaces of the dam, the storage surface during construction, etc. For heat dissipation surfaces in different parts, they need to be distinguished according to solar radiation and thermal insulation conditions, and then different surface temperatures and heat dissipation coefficients are given. In structural analysis, only when the heat dissipation surface selection is consistent with the actual situation can correct analysis results be obtained.

[0004] Finite element method is one of the main means of dam structure analysis. To carry out structural analysis using finite element method, it is necessary to first construct a finite element model of the dam and set boundary conditions such as temperature boundary, displacement boundary, and seepage boundary for the model. For a relatively regular dam structure, each heat dissipation surface is relatively straight. The coordinate range of the heat dissipation surface can be given, and the heat dissipation surfaces of different parts can be selected and distinguished by one or several coordinate selections. For a dam structure with curved surfaces, such as the upstream and downstream surfaces of an arch dam, the upstream is in contact with reservoir water and the downstream is in contact with air. Different temperature boundaries need to be given, but due to the overlap of coordinates, it is difficult to select the upstream or downstream surface separately when using coordinate selection. It is usually necessary to divide the curved surface into dozens or even hundreds of segments, and then select them one by one, which takes a lot of time and is prone to misoperation.

[0005] Therefore, the technical problems of the prior art are:

[0006] First, the heat dissipation surface is selected by coordinate selection, but there is a technical problem that the coordinates of the curved surface boundaries (such as the upstream and downstream surfaces of the arch dam) overlap, making the selection difficult.

[0007] Second, when using coordinate selection (such as the upstream surface of an arch dam), the surface needs to be divided into dozens or even hundreds of segments, and the segments need to be selected one by one to avoid coordinate overlap. However, the segment-by-segment process is cumbersome and inefficient. Summary of the invention

[0008] In order to overcome the above technical problems, the purpose of the present invention is to provide a method for selecting a heat dissipation surface. On the basis of the original coordinate frame selection, a node mark transfer algorithm is added, any point on the heat dissipation surface to be selected is marked, all units are repeatedly traversed, and the mark transfer is performed within a limited coordinate range. The completion of the transfer is determined based on the number of marked points obtained from the two traversals, and the free surface with the marked points is output, which is the heat dissipation surface to be selected. The present invention solves the problem that the coordinates of the surface boundaries overlap with each other in finite element calculations and are difficult to select through a given coordinate range. The surface heat dissipation surface can be selected with only one operation.

[0009] The present invention provides the following technical solutions:

[0010] A method for selecting a heat dissipation surface, characterized in that it comprises the following steps:

[0011] S1: Based on the concrete dam engineering design data, a finite element mesh model of the dam is constructed through three-dimensional modeling, and the topological relationship between the units and nodes in the finite element mesh model is obtained, and then step S2 is entered;

[0012] S2: traverse all the units in the finite element mesh model, and for the nodes constituting the units, record the unit numbers of the units involved in the constituting units one by one, and then go to step S3;

[0013] S3: traverse all the units in the finite element mesh model again, obtain the adjacent unit information of each unit according to the unit number information of the node subordinate recorded in S2, and enter step S4;

[0014] S4: traverse all the units in the finite element mesh model, calculate the centroid coordinates of each face of each unit, and enter step S5;

[0015] S5: traverse all units in the finite element mesh model, and compare each face of each unit in the finite element mesh model with the faces of adjacent units of the unit obtained in S3 one by one according to the centroid coordinates of each face of the unit, and determine whether the face of the unit is an empty face, and enter step S6;

[0016] S6: Select any node on the heat dissipation surface to be selected, mark the node, and limit the coordinate range of the mark transmission, and then enter step S7;

[0017] S7: Traverse all units and if the following three conditions are met at the same time, mark the node:

[0018] Condition 1: There is an open surface in the unit;

[0019] Condition 2: There are marked nodes among the nodes constituting the free surface;

[0020] Condition 3: The coordinates of the nodes that constitute the free surface and have not been transferred are within the limited coordinate range;

[0021] When the above three conditions are met at the same time, the unmarked nodes belonging to the same free surface as the marked node are also marked, that is, the mark transfer is completed and the process goes to step S7-1;

[0022] S7-1: Determine whether the number of marked nodes obtained before and after the traversal has changed. If there is no change, it indicates that the mark transfer is completed and the process goes to step S8. If there is a change, the process goes to step S7.

[0023] S8: Traverse all units. If a unit has an air-facing surface and there are marking points in the nodes constituting the air-facing surface, then the air-facing surface is the heat dissipation surface to be selected.

[0024] In the above implementation, step S5 determines whether each face of each unit in the finite element mesh model is an air-facing face. The judgment method is to compare it with the faces of adjacent units one by one. If the centroid coordinates of all faces of adjacent units are different from it, then the face is judged to be an air-facing face. Steps 6 and 7 mark an arbitrary point on the heat dissipation surface to be selected, and give a mark transfer range to perform mark transfer. In this selection process, the selection of the heat dissipation surface can be completed by setting the coordinate range only once, which simplifies the selection process and improves the efficiency of finite element pre-processing.

[0025] According to some embodiments, the method for determining whether the surface of the unit is an air-facing surface in step S5 comprises the following steps:

[0026] S5-1: If the centroid coordinates of a face of an adjacent unit are the same as those of the face, the face is considered not to be an empty face;

[0027] S5-2: If the centroid coordinates of all faces of all adjacent cells are different from that of this face, then this face is considered to be an empty face.

[0028] According to some implementations, in step S4, the calculation formula of the centroid coordinates is as follows:

[0029]

[0030] In the above formula, i represents the global number of the unit; j represents the surface number of the unit, (x ij 0 ,y ij 0 ,z ij 0 ) represents the centroid coordinates of the jth face of the i-th element, n represents the number of nodes constituting the jth face, (x k ,y k ,z k ) represents the coordinate value of the kth node constituting the jth face.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention provides a method for selecting a heat dissipation surface in finite element calculation. On the basis of the original coordinate frame selection, a node mark transfer method is added. For special-shaped structures containing curved surfaces, the heat dissipation surface selection is completed through one operation, that is, one frame selection and coordinate transfer, which simplifies the selection process and improves the efficiency of finite element pre-processing. The present invention solves the technical problem that the heat dissipation surface is selected by coordinate frame selection in the prior art, and the coordinates overlap at the curved surface boundary (such as the upstream and downstream surfaces of the arch dam), and the curved surface needs to be divided into dozens or even hundreds of segments when using coordinate frame selection (upstream surface of the arch dam), and the frame selection is performed segment by segment to avoid the technical problem of coordinate overlap. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flow chart of the heat dissipation surface selection method provided according to the present invention.

[0034] Figure 2 This is a three-dimensional finite element model of an arch dam with a foundation according to the first embodiment of the present invention.

[0035] Figure 3 It is a three-dimensional finite element model of the arch dam body according to the first embodiment of the present invention.

[0036] Figure 4 This is the unit topological relationship of the finite element model according to the first embodiment of the present invention.

[0037] Figure 5 It is a schematic diagram of the free surface of the arch dam body according to the first embodiment of the present invention.

[0038] Figure 6 Schematic diagram of the upstream heat dissipation surface of the arch dam according to the first embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention is described in detail below in conjunction with the embodiments and drawings, but it should be understood that the embodiments and drawings are only used to exemplify the present invention and do not constitute any limitation on the protection scope of the present invention. All reasonable changes and combinations within the scope of the inventive concept of the present invention fall within the protection scope of the present invention.

[0040] like Figure 1 , which is a flow chart of a method for selecting a heat dissipation surface provided by the present invention. The heat dissipation surface selection can be completed by only performing a frame selection and coordinate transfer, which simplifies the selection process and improves the efficiency of finite element pre-processing.

[0041] The present invention will be further described below in conjunction with the accompanying drawings.

[0042] Embodiment 1

[0043] Taking a concrete arch dam as an example, using its public engineering data, this embodiment is described, and the heat dissipation surface of the concrete arch dam is selected. In this embodiment, the heat dissipation surface selection includes the following steps:

[0044] Step 1: Based on the concrete arch dam engineering design data, the 3D modeling technology is used to construct a 3D finite element mesh model of a concrete arch dam. Figure 2 , Figure 3 As shown in the figure, the topological structure of the units and nodes of the finite element model is as follows Figure 4 As shown, Figure 4 J1~J8 are the eight nodes that make up the square unit, and M1~M6 are the six faces that belong to the square unit.

[0045] In step 1, the three-dimensional finite element modeling of the concrete dam and the topological structure of the units and nodes in the finite element model are basic methods in this field and will not be described in detail here.

[0046] Step 2: traverse all units, and for each node that constitutes a unit, record the unit numbers of the units that it participates in constituting, as shown in Table 1.

[0047] Table 1 Unit information of each node involved in the construction

[0048]

[0049]

[0050] In step 2, traversing the cells means looping through all the cells. First, cell 1 is the first. The nodes that make up cell 1 are 1, 2, 3, 4, 5, 6, 7, and 8. Each of these 8 nodes is assigned a piece of information, indicating that the node participates in the formation of cell 1. Then, the traversal continues. When traversing to cell 2, it is found that node 2 also participates in the formation of cell 2. This is also recorded, and the traversal continues. When traversing to cell 8, it is found that node 5 also participates in the formation of cell 8. This is recorded again. And so on, finally Table 1 is obtained.

[0051] Step 3: traverse all units. According to the information recorded in step 2, if two units share a node, the two units are determined to be adjacent units. Based on this, the adjacent unit information of each unit can be obtained, as shown in Table 2.

[0052] Table 2 Adjacent units of each unit

[0053]

[0054]

[0055] In step three, traverse the cells, that is, loop over all cells, starting with cell 1. The nodes that make up the cell are 1, 2, 3, 4, 5, 6, 7, and 8, a total of 8 nodes. According to Table 1, node 1 only participates in the formation of cell 1, and node 2 participates in the formation of cells 1 and 2, so cell 2 is the adjacent cell of cell 1. Then, node 3 participates in the formation of cells 1, 2, and 3, so cell 3 is also the adjacent cell of cell 1, and so on. Finally, all the cells adjacent to cell 1 are: cells 2, 3, 4, 5, 6, 7, and 8.

[0056] Below is unit 2. The nodes that make up unit 2 are “…”. By analogy with the above method, we can obtain all the adjacent units of unit 2, and finally form Table 2.

[0057] Step 4: traverse all units and calculate the centroid coordinates of each face of each unit, as shown in Formula 1.

[0058]

[0059] In formula 1, i represents the global number of the unit; j represents the surface number of the unit, (x ij 0 ,y ij 0 ,z ij 0 ) represents the centroid coordinates of the jth face of the i-th element, n represents the number of nodes constituting the jth face, (x k ,y k ,z k) represents the coordinate value of the kth node constituting the jth face.

[0060] In step 4, from Figure 4 It can be seen that the square unit has a total of 6 faces, each of which is composed of 4 nodes. According to the coordinates of these 4 nodes, the centroid coordinates of the face can be calculated.

[0061] Step 5: traverse all cells, and for each face j of cell i, compare it with the faces of the adjacent cells of cell i one by one:

[0062] 1) If the centroid coordinates of a face of an adjacent unit are the same as those of face j, then face j of unit i is considered not to be an empty face.

[0063] 2) If the centroid coordinates of all faces of all adjacent units are different from the centroid coordinates of face j, then face j of unit i is considered to be an empty face.

[0064] The free surface of the arch dam obtained in step 5 is as follows Figure 5 shown. Figure 5 The upstream face, downstream face and dam top face can be seen in the figure.

[0065] In step five, the purpose of judging whether a unit is an air-facing surface is that only the air-facing surface of the dam will come into contact with the air and reservoir water and become a heat dissipation surface, and the non-air-facing surface cannot become a heat dissipation surface.

[0066] Step six, select any node on the upstream surface to be selected, mark the node, and use the dam top elevation of 750m as the upper limit Zmax of the coordinate range transmitted by the node mark.

[0067] In step six, for example, a node is randomly selected on the upstream surface of the finite element model, the node number is 137766, and the node is marked to indicate that the node is the point on the upstream surface to be selected. For example, a specific implementation method is used in this method to construct a one-dimensional array. The values ​​in the array correspond to the nodes of the finite element in turn, which are used to store the label of each node. The array value corresponding to the unmarked node is 0, and the corresponding array value of the marked node is 1.

[0068] Step 7: traverse all units, and if the following three conditions are met at the same time, mark the node:

[0069] 1) There is an empty surface j′ in unit i;

[0070] 2) There are marked points among the nodes constituting the free surface j′;

[0071] 3) The z coordinate of the node k′ that constitutes the free surface j′ and has not yet been transferred is less than the set coordinate upper limit Zmax.

[0072] At this time, the node k′ is marked and transferred.

[0073] In step seven, the traversal is to loop through all units. When looping to unit i, determine whether there is any free surface among the 6 surfaces of subordinate unit i (this determination was made in step five. This is the significance of first determining the free surface. Only the free surface can become a heat dissipation surface). If the j′th surface of unit i is a free surface, further determine whether there are any marked points on the j′ surface (the corresponding array value is 1). If there are marked points, check whether there are any unmarked points on the j′ surface. If there are, further determine whether the ordinate of this unmarked point is less than 750. If so, mark and transfer this point (the corresponding array value is changed from 0 to 1).

[0074] Step 8, repeat step 7. If the number of marked nodes before and after the traversal does not change, it means that the transfer is completed and go to step 8. Otherwise, continue to step 7.

[0075] In step eight, all cells are iterated through a loop until all eligible nodes are marked as passed.

[0076] Step 9: traverse all units. If there is an empty surface in the unit and there is a marked point in the node constituting the empty surface, then the empty surface is the upstream surface to be selected, such as Figure 6 shown.

[0077] In step nine, the upstream surface to be selected is output to achieve the purpose of the present invention. A coordinate range is given and a mark is transferred, and the upstream surface is selected at one time, which is a curved surface.

[0078] Concrete dam finite element modeling usually uses commercial software such as ANSYS, ABQUS, and HyperMesh. In these software, corresponding algorithms can be selected to easily select the free surface or upstream and downstream surfaces. However, it is difficult to further distinguish the upstream and downstream surfaces because the coordinates of the upstream and downstream surfaces overlap. Figure 5 As shown, even if the existing selection method is used, the surface is divided into several segments and selected segment by segment to avoid the problem of overlapping upstream and downstream coordinates. The present invention proposes a selection method based on marker transfer, which can greatly reduce the workload of heat dissipation surface selection and is suitable for applying temperature boundaries in water conservancy and hydropower engineering structure analysis.

[0079] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for selecting a heat dissipation surface, characterized in that: The following steps are involved: S1: Based on the concrete dam engineering design data, a finite element mesh model of the dam is constructed through three-dimensional modeling, and the topological relationship between the units and nodes in the finite element mesh model is obtained, and then step S2 is entered; S2: traverse all the units in the finite element mesh model, and for the nodes constituting the units, record the unit numbers of the units involved in the constituting units one by one, and then go to step S3; S3: traverse all the units in the finite element mesh model again, obtain the adjacent unit information of each unit according to the unit number information of the node subordinate recorded in S2, and enter step S4; S4: traverse all the units in the finite element mesh model, calculate the centroid coordinates of each face of each unit, and enter step S5; S5: traverse all units in the finite element mesh model, and compare each face of each unit in the finite element mesh model with the faces of adjacent units of the unit obtained in S3 one by one according to the centroid coordinates of each face of the unit, and determine whether the face of the unit is an empty face, and enter step S6; S6: Select any node on the heat dissipation surface to be selected, mark the node, use the dam top elevation as the upper limit of the coordinate range transmitted by the node mark, and enter step S7; S7: Traverse all units and if the following three conditions are met at the same time, mark the node: Condition 1: There is an open surface in the unit; Condition 2: There are marked nodes among the nodes constituting the free surface; Condition 3: The z coordinate of the node that constitutes the free surface and has not been transferred is less than the dam crest elevation; When the above three conditions are met at the same time, the unmarked nodes belonging to the same free surface as the marked node are also marked, that is, the mark transfer is completed and the process goes to step S7-1; S7-1: Determine whether the number of marked nodes obtained before and after the traversal has changed. If there is no change, it indicates that the mark transfer is completed and the process goes to step S8. If there is a change, the process goes to step S7. S8: Traverse all units. If a unit has an air-facing surface and there are marking points in the nodes constituting the air-facing surface, then the air-facing surface is the heat dissipation surface to be selected.

2. The method for selecting a heat dissipation surface according to claim 1, characterized in that: The method for determining whether the surface of the unit is an empty surface in step S5 comprises the following steps: S5-1: If the centroid coordinates of a face of an adjacent unit are the same as those of the face, the face is considered not to be an empty face; S5-2: If the centroid coordinates of all faces of all adjacent cells are different from that of this face, then this face is considered to be an empty face.

3. The method for selecting a heat dissipation surface according to claim 1, characterized in that: In step S4, the calculation formula of the centroid coordinates is as follows: In the above formula, i represents the global number of the unit; j represents the surface number of the unit, represents the centroid coordinates of the jth surface of the i-th unit, n represents the number of nodes constituting the jth surface, (x k ,y k ,z k ) represents the coordinate value of the kth node constituting the jth face.

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