Middle plane extraction method based on normal vector

Abstract

The invention relates to the field of engineering machinery simulation, in particular to a median extraction method based on a normal vector, which comprises the following steps executed in sequence: S1, inputting a three-dimensional model, triangularizing each graph in the three-dimensional model, and obtaining all triangular patches; s2, calculating a normal vector of each triangular patch; s3, calculating a cosine value of an included angle between the normal vectors of the two adjacent triangular patches; s4, according to the cosine value obtained through calculation in the step S3, judging whether two adjacent triangular patches are in the same mid-plane area or not, performing mid-plane screening, and obtaining all mid-planes of the three-dimensional model; s5, calculating a thickness difference value of two adjacent middle surface patches; s6, according to the local thickness difference value, each middle surface of the three-dimensional model is grouped according to the thickness, and a grouping result is output; according to the mid-plane extraction method, manual intervention is not needed, the mid-plane of the three-dimensional model can be automatically identified and extracted, and the efficiency of the simulation modeling process is improved.

Description

Technical Field

[0001] The invention relates to the field of engineering machinery simulation, and in particular to a mid-surface extraction method based on normal vectors. Background Art

[0002] In the field of engineering machinery, the main load-bearing structures of machinery such as excavators, loaders, cranes, etc. usually use welded steel plates, box beams and frame structures, and their design needs to meet the requirements of high strength and high stiffness at the same time. When performing finite element simulation analysis, directly using complex three-dimensional solid models will result in excessive calculations, while simplifying them to shell elements can significantly improve calculation efficiency.

[0003] In the finite element analysis of engineering machinery, mid-surface extraction is an important step, especially in structures with large thickness variations or complex geometries. Traditional mid-surface extraction methods mostly rely on simple geometries or manual calibration, which makes it difficult to automatically process complex models. Summary of the invention

[0004] The object of the present invention is to provide a normal vector-based mid-surface extraction method capable of automatically processing complex models of engineering machinery.

[0005] In order to achieve the above object, the present invention adopts such technical solution: The mid-surface extraction method based on normal vectors includes the following steps performed in sequence: S1: input a three-dimensional model, triangulate each graphic in the three-dimensional model, and obtain all triangular facets; S2: Calculate the normal vector of each triangular face using the following formula: ; in, For triangular patches Normal vector, P1, P2, P3 are triangular patches The three vertices of S3: Calculate the cosine value of the angle between the normal vectors of two adjacent triangular facets using the following formula: : ; in, For triangular patches The normal vector of For triangular patches The normal vector of and are the modulus of the normal vector respectively; S4: Cosine value calculated according to step S3 , determining whether two adjacent triangular facets are in the same mid-surface region, performing mid-surface screening, and obtaining all mid-surfaces of the three-dimensional model; S5: Use the following formula to calculate the thickness difference between two adjacent mid-surface patches: : ; in, Mid-surface patch The normal vector of Mid-surface patch The normal vector of is the step length; S6: According to the local thickness difference, each mid-surface of the three-dimensional model is grouped by thickness, and the grouping result is output.

[0006] Preferably, in step S1, each graphic in the three-dimensional model is triangulated by constructing triangles using point cloud data.

[0007] Preferably, in step S1, each image in the three-dimensional model is triangulated by constructing triangles using an ear cutting method.

[0008] Preferably, in step S4, a threshold value of the cosine value of the normal vector angle is preset as a threshold value for determining whether the two triangular facets are in the same mid-surface region. If the cosine value calculated in step S3 is If the cosine value of the normal vector angle is within the preset threshold, then the two triangular facets are in the same mid-surface area. If the cosine value of the normal vector angle exceeds the preset threshold, the two triangular facets are not in the same mid-surface area.

[0009] Preferably, in step S6, the mid-surfaces of the three-dimensional model may be grouped according to equal frequency grouping or equal distance grouping.

[0010] A mid-surface extraction system comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, any of the above-mentioned mid-surface extraction methods is implemented.

[0011] By adopting the aforementioned design scheme, the beneficial effects of the present invention are as follows: the present application triangulates each graphic in the three-dimensional model, and then calculates the normal vector of each triangular face, determines whether two adjacent triangular facets are the same mid-surface by the angle between the normal vectors, and then calculates the thickness difference between the two adjacent mid-surfaces for thickness grouping, which can accurately extract the mid-surface area in the complex model and avoid misjudgment; and the mid-surface extraction method of the present application does not require manual intervention, and can realize automatic identification and extraction of the mid-surface of the three-dimensional model, which significantly improves the efficiency of the simulation modeling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a structural schematic diagram of the three-dimensional model of the forklift; Figure 2 This is a schematic diagram of the thin-walled structure of a forklift. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only partial embodiments of the present invention, rather than all 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.

[0014] The terms "first", "second", "third", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices.

[0015] The mid-surface extraction method based on normal vectors includes the following steps performed in sequence: S1: Input a 3D model, triangulate each graphic in the 3D model, and obtain all triangular facets; In this embodiment, in step S1, triangles can be constructed using point cloud data to triangulate each graphic in the three-dimensional model, or triangles can be constructed using the ear cutting method to triangulate each image in the three-dimensional model; other conventional methods can also be used to triangulate each image in the three-dimensional model.

[0016] S2: Calculate the normal vector of each triangle patch using the following formula: ; in, For triangular patches Normal vector, P1, P2, P3 are triangular patches The three vertices of S3: Use the following formula to calculate the cosine of the angle between the normal vectors of two adjacent triangle patches: : ; in, For triangular patches The normal vector of For triangular patches The normal vector of and are the modulus of the normal vector respectively; S4: Cosine value calculated according to step S3 , determine whether two adjacent triangular facets are in the same mid-surface area, perform mid-surface screening, and obtain all mid-surfaces of the three-dimensional model; In this embodiment, in step S4, a threshold of the cosine value of the normal vector angle is preset as a threshold value for determining whether two triangular facets are in the same mid-surface region. If the cosine value calculated in step S3 is If the cosine value of the normal vector angle is within the preset threshold, then the two triangular facets are in the same mid-surface area. If the cosine value of the normal vector angle exceeds the preset threshold, the two triangle facets are not in the same mid-surface area. ,The preset normal vector angle cosine value threshold can be dynamically adjusted according to the geometric features and ,precision requirements of the model.

[0017] S5: Use the following formula to calculate the thickness difference between two adjacent mid-surface patches: : ; in, Mid-surface patch The normal vector of Mid-surface patch The normal vector of is the step size, which indicates the scale of thickness change. Ability to precisely control the calculation of local thickness; In this embodiment, the step length is used Perform size transformation and convert the deviation of the normal vector into thickness change. ≈ When , it means that the local geometry changes are small and the thickness difference Also relatively small; when and Thickness difference when the direction is different (such as sharp corners) It becomes larger, indicating that the thickness changes dramatically.

[0018] Adjust step size To control the calculation accuracy, the larger Suitable for global thickness variation analysis and preliminary detection of local inhomogeneities; small Suitable for detail analysis and for capturing small local thickness variations.

[0019] In general, λ can be set according to the average value of the material thickness, for example:

[0020] in, , Represent the maximum thickness and minimum thickness respectively, N is the number of divided layers.

[0021] S6: According to the local thickness difference, each mid-surface of the three-dimensional model is grouped by thickness, and the grouping result is output.

[0022] In this embodiment, in step S6, the mid-surfaces of the three-dimensional model can be grouped according to equal-frequency grouping or equal-distance grouping, wherein equal-frequency grouping means that each group contains the same amount of thickness data, that is, the number of mid-surface patches in each group is the same; equal-distance grouping means dividing the area into several intervals according to the thickness range.

[0023] This embodiment further explains the above mid-surface extraction method by taking a forklift as an example.

[0024] Figure 1 For the 3D model of the forklift, automatically obtain Figure 2 The thin-walled structure of the forklift shown above uses the above-mentioned mid-surface extraction method to automatically extract the mid-surface: S1: triangulate each figure in the forklift thin-walled structure to obtain all triangular facets; S2: Calculate the normal vector of each triangle patch: ; S3: Calculate the cosine of the angle between the normal vectors of two adjacent triangle patches : ; S4: Cosine value calculated according to step S3 , determine whether two adjacent triangular facets are in the same mid-surface area, perform mid-surface screening, and obtain all mid-surfaces of the three-dimensional model. In this embodiment, the number of mid-surfaces smaller than It is the preset normal vector angle cosine value threshold; S5: Calculate the thickness difference between two adjacent mid-surface patches : ; S6: According to the local thickness difference, each mid-surface of the three-dimensional model is grouped by thickness, and the grouping result is output.

[0025] The thickness distribution of the thin-walled structure of the forklift is uneven, and it is necessary to use equal frequency grouping or equal distance grouping method for optimization: Equal frequency grouping (applicable to local stress analysis): Applicable to structures with large thickness variations, such as reinforced areas and connection parts on booms. By counting global thickness data, it is ensured that each group contains the same number of thickness data points, making the meshing more reasonable.

[0026] Equidistant grouping (suitable for overall stiffness analysis): suitable for structures with relatively uniform thickness, such as frames and support beams; using fixed thickness intervals (such as 5mm, 10mm, 15mm) to ensure clear levels of the simulation model.

[0027] This embodiment also provides a system for implementing the above method.

[0028] A mid-surface extraction system comprises a memory and a processor. A computer program is stored in the memory. When the computer program is executed by the processor, any of the mid-surface extraction methods described above is implemented.

[0029] To summarize, the present application triangulates each graphic in the three-dimensional model, calculates the normal vector of each triangular face, determines whether two adjacent triangular facets are the same mid-face through the angle between the normal vectors, and then calculates the thickness difference between the two adjacent mid-faces for thickness grouping, which can accurately extract the mid-face area in the complex model and avoid misjudgment; and the mid-face extraction method of the present application does not require manual intervention, and can realize automatic identification and extraction of the mid-face of the three-dimensional model, which significantly improves the efficiency of the simulation modeling process; the mid-face extraction method can adapt to geometric models of different complexities, automatically adjust relevant parameters, and process models of different scales and precision requirements; by dynamically adjusting parameters and optimizing algorithms, large-scale complex models can be quickly processed while ensuring accuracy, thereby improving the efficiency of simulation analysis.

[0030] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mid-surface extraction method based on normal vectors, characterized in that: The process includes the following steps: S1: input a three-dimensional model, triangulate each graphic in the three-dimensional model, and obtain all triangular facets; S2: Calculate the normal vector of each triangular face using the following formula: ； in, For triangular patches Normal vector, P1, P2, P3 are triangular patches The three vertices of S3: Calculate the cosine value of the angle between the normal vectors of two adjacent triangular facets using the following formula: ： ； in, For triangular patches The normal vector of For triangular patches The normal vector of and are the modulus of the normal vector respectively; S4: Cosine value calculated according to step S3 , determining whether two adjacent triangular facets are in the same mid-surface region, performing mid-surface screening, and obtaining all mid-surfaces of the three-dimensional model; S5: Use the following formula to calculate the thickness difference between two adjacent mid-surface patches: : ； in, Mid-surface patch The normal vector of Mid-surface patch The normal vector of is the step length; S6: According to the local thickness difference, each mid-surface of the three-dimensional model is grouped by thickness, and the grouping result is output.

2. The mid-surface extraction method based on normal vectors according to claim 1, characterized in that: In step S1, each figure in the three-dimensional model is triangulated by constructing triangles through point cloud data.

3. The mid-surface extraction method based on normal vectors according to claim 1, characterized in that: In step S1, each image in the three-dimensional model is triangulated by constructing triangles using the ear cutting method.

4. The mid-surface extraction method based on normal vectors according to claim 1, characterized in that: In step S4, a threshold of the cosine value of the normal vector angle is preset as a threshold value for determining whether the two triangular facets are in the same mid-surface region. If the cosine value calculated in step S3 is If the cosine value of the normal vector angle is within the preset threshold, then the two triangular facets are in the same mid-surface area. If the cosine value of the normal vector angle exceeds the preset threshold, the two triangular facets are not in the same mid-surface area.

5. The mid-surface extraction method based on normal vectors according to claim 1, characterized in that: In step S6, the mid-surfaces of the three-dimensional model may be grouped according to equal frequency grouping or equal distance grouping.

6. A mid-surface extraction system, comprising a memory and a processor, wherein a computer program is stored in the memory, characterized in that: When the computer program is executed by a processor, the mid-surface extraction method described in any one of claims 1 to 5 is implemented.

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