Finite element entity unit-based section internal force automatic calculation method

Abstract

The invention discloses a section internal force automatic calculation method based on a finite element entity unit, and relates to the field of finite element calculation analysis, and the method comprises the steps: carrying out the finite element calculation of a to-be-measured entity structure according to model data, determining an entity unit grid, and obtaining a finite element software calculation result; preprocessing the model data and the calculation result of the finite element software, and determining preprocessed data; carrying out block division on the entity unit grid according to the preprocessed data; determining node data on a target section in the entity unit grid according to the spatial positions of the finite element entity units and the unit nodes in each block; according to the node data, the area of the unit surface and the neutral axis of the target section are calculated, and the section internal force at the target section is calculated, entity unit grid block division and the section internal force can be automatically calculated, and an engineer can conveniently carry out engineering checking calculation based on the internal force.

Description

Technical Field

[0001] This application relates to the field of finite element calculation and analysis, and particularly to an automated calculation method for sectional internal forces based on finite element solid elements. Background Art

[0002] In the process of finite element calculation and analysis, solid elements are usually used for finite element analysis calculation and analysis evaluation, and such solid elements are finite element solid elements. However, the application of solid elements is restricted by high computational complexity, large computing power and memory consumption on the one hand. On the other hand, general finite element analysis software generally only gives stress and strain results and does not display sectional internal forces, which is not conducive to the checking and analysis work of engineering personnel. Therefore, how to obtain sectional internal force results based on the stress of solid elements is a key issue in the process of engineering application calculation and analysis. Summary of the Invention

[0003] The purpose of this application is to provide an automated calculation method for sectional internal forces based on finite element solid elements to solve the problem that sectional internal forces are not displayed in existing finite element calculation and analysis, which is not conducive to the checking and analysis work of engineering personnel.

[0004] To achieve the above purpose, this application provides the following solutions:

[0005] In the first aspect, this application provides an automated calculation method for sectional internal forces based on finite element solid elements, including:

[0006] Performing finite element calculation on the entity structure to be measured according to the model data to determine the solid element mesh and obtaining the finite element software calculation results; the model data includes analysis steps, the number of frames in the analysis step, finite element solid element types, and element node coordinates; the finite element software calculation results include the stress at each element node and the data of each component of the stress; the stress includes normal stress and shear stress;

[0007] Preprocessing the model data and the finite element software calculation results to determine the preprocessed data; the preprocessed data includes the preprocessed model data and the preprocessed finite element calculation results;

[0008] Dividing the solid element mesh into blocks according to the preprocessed data;

[0009] Determining the node data on the target section in the solid element mesh according to the spatial positions of the finite element solid elements and element nodes in each block; the node data includes node coordinates and stress data;

[0010] Calculating the area of the element surface and the neutral axis of the target section according to the node data, and calculating the sectional internal forces at the target section; the sectional internal forces include axial force, shear force, and bending moment.

[0011] According to the specific embodiments provided by the present application, the following technical effects are disclosed: Based on the calculation results of finite element software, the present application realizes the division of solid element mesh blocks and the automatic calculation of internal forces of cross-sections, significantly improving the post-processing efficiency of calculation results, facilitating engineers to perform engineering checks based on internal forces, and providing strong technical support for the stress check and analysis of structures; In addition, the present application calculates the internal force value at the target cross-section based on the stress of unit nodes, with high calculation accuracy and meeting engineering requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0013] Figure 1 It is a flowchart of an automatic calculation method for internal forces of cross-sections based on finite element solid elements provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0015] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0016] In an exemplary embodiment, as Figure 1 shown, an automatic calculation method for internal forces of cross-sections based on finite element solid elements is provided, including:

[0017] S1: Perform finite element calculation on the entity structure to be measured according to the model data, determine the solid element mesh, and obtain the calculation results of the finite element software; the model data includes the analysis step, the number of frames of the analysis step, the type of finite element solid elements, and the coordinates of unit nodes; the calculation results of the finite element software include the stress at each unit node and the data of each component of the stress in each direction; the stress includes normal stress and shear stress.

[0018] S2: Preprocess the model data and the finite element software calculation results to determine the preprocessed data; the preprocessed data includes the preprocessed model data and the preprocessed finite element calculation results.

[0019] S3: Divide the solid element mesh into blocks according to the preprocessed data.

[0020] S4: Determine the node data on the target cross-section in the solid element mesh according to the spatial positions of the finite element solid elements and element nodes in each block; the node data includes node coordinates and stress data.

[0021] S5: Calculate the area of the element face and the neutral axis of the target cross-section according to the node data, and calculate the internal forces of the cross-section at the target cross-section; the internal forces of the cross-section include axial force, shear force, and bending moment.

[0022] In an exemplary embodiment, S1 can be replaced by the following steps. For the sake of convenience of description, in this application, the finite element solid element is abbreviated as element, and the solid element network is a model formed by using finite element software to process the entity structure to be measured.

[0023] Taking the Abaqus finite element calculation software as an example, briefly describe the process of obtaining the model data and the finite element software calculation results. The operation methods of other general finite element software can refer to relevant materials.

[0024] Based on the secondary development function of the software, users can develop custom modules or plugins according to their own needs to expand and enhance the software functions. In this application, information such as the session module, odb data, analysis step (step), and part instance (instance) of the model is obtained through the application programming interface of Abaqus.

[0025] Based on the model analysis step, all its frame information, field output (fieldOutput) data, and the output values (such as stress) of all element types and element nodes therein can be obtained; among them, the element types include 8-node hexahedron elements.

[0026] Based on the part instance, the element node coordinate values can be obtained.

[0027] In an exemplary embodiment, S2 can be replaced by the following steps.

[0028] S21: Determine the output positions of the calculation results according to the calculation results of the model components in the solid element mesh at each analysis step; the output positions include integration point positions, node positions, etc.

[0029] S22: Based on the output position, discard the finite element software calculation results that do not meet the calculation requirements, and determine the screened data; the screened data is the preprocessed finite element calculation results.

[0030] S23: According to the model type and geometric features of the solid element mesh, perform coordinate transformation on the unit node coordinates to determine the transformed data; the transformed data is the preprocessed model data.

[0031] S24: Determine the preprocessed data by using the screened data and the transformed data, and store the preprocessed data in the order of serial numbers.

[0032] Furthermore, S2 is to obtain or create regularized data that can be used for subsequent internal force calculations, mainly including the following: According to the calculation results of the model components at each analysis step, check the output positions of the calculation results (such as integration points, nodes, etc.), and discard the stress output results that do not meet the calculation requirements; According to the model type and geometric features, judge whether it is necessary to perform coordinate transformation on the obtained node coordinates to facilitate subsequent unit mesh block division; Store the screened and transformed data in the order of serial numbers for the calculation and analysis work of the next step.

[0033] Among them, judging whether coordinate transformation is required according to the model type and geometric features includes the following steps:

[0034] Judge whether the model has cylindrical or spherical features. If the structural model is a cylinder (such as the concrete structure of a nuclear power plant containment), then convert the node coordinates (x, y, z) in the Cartesian coordinate system to the cylindrical coordinate system, and the node coordinates in the cylindrical coordinate system are (r, θ, z); If the structural model is a spherical shell, then convert the node coordinates (x, y, z) in the Cartesian coordinate system to the spherical coordinate system, and the node coordinates in the spherical coordinate system are (r, φ, θ).

[0035] Furthermore, preprocessing the model data and finite element software calculation results includes data judgment and screening, coordinate transformation, data storage, etc.

[0036] The main process is as follows: First, judge whether the element type and result output position meet the requirements based on the obtained data. For example, if only C3D8R can be used and the result output position is at the node, the data that does not meet the requirements cannot be used for internal force calculation.

[0037] According to the geometric features of the engineering model, judge whether it is necessary to perform coordinate transformation on the unit node coordinates.

[0038] For example, for the concrete structure of a nuclear power plant containment, its middle part is usually a cylindrical structure and the top part is a hemispherical shell or semi-elliptical shell structure. In this case, a local coordinate system should be created based on the structural geometric characteristics.

[0039] For the cylindrical structure, a cylindrical coordinate system should be adopted, and the node coordinates in the Cartesian coordinate system should be converted to this cylindrical coordinate system.

[0040] For the hemispherical shell structure, the node coordinates should be converted to the spherical coordinate system.

[0041] If it is a semi-elliptical shell structure, more complex coordinate transformation should be carried out.

[0042] After all data processing is completed, the data should be stored in a data structure that is convenient for users to obtain and index. For example, stress data can be stored in a dictionary according to different analysis steps, frames, and numbers.

[0043] In an exemplary embodiment, S3 can be replaced by the following steps.

[0044] S31: Calculate the centroid coordinates of the element according to the unit node coordinates in the preprocessed model data.

[0045] S32: Based on the centroid coordinates of the element, divide the solid element mesh according to the element block position and element block size; wherein, the element block size is determined according to the actual engineering requirements.

[0046] Furthermore, S3 first determines the shape and size of the element block according to the model geometric characteristics. For the cylinder of the concrete structure of a nuclear power plant containment, the geometric shape of the element block is a sector block, and its thickness direction (radial direction) should be included in one block. The number of elements in the circumferential and vertical directions can usually be determined according to the meaning and accuracy of the internal forces on the target section during the actual checking calculation process.

[0047] If the number of model elements and nodes is huge and the calculation consumption is large, then only a certain area can be calculated. For example, for the concrete structure of a nuclear power plant containment, usually only the internal force values at several key elevations of the cylinder, near the gate, and at the target section of the dome area need to be obtained, and the rest can be excluded from the calculation scope.

[0048] In an exemplary embodiment, S32 can be replaced by the following steps.

[0049] S321: If in the Cartesian coordinate system, divide the solid element mesh according to the three-axis components of the centroid coordinates of the element; wherein, the shape of the divided block is a rectangular block.

[0050] S322: If in the cylindrical coordinate system, based on the centroid coordinates of the element, the entity element mesh is divided into blocks according to the radial position, circumferential angle, and vertical elevation of the finite element solid element; wherein, the shape of the divided block is a sector block.

[0051] S323: If in the spherical coordinate system, based on the centroid coordinates of the element, the entity element mesh is divided into blocks according to the radial position, circumferential angle, and vertical angle of the finite element solid element; wherein, the shape of the block is a flat shell.

[0052] Furthermore, the size of the element block can be determined according to the actual engineering requirements. For example, for a cylindrical structure model, the elements in its thickness direction (radial direction) should usually be all included in the same block, and the circumferential size and vertical size are determined according to the internal force position and calculation accuracy.

[0053] In addition, the range of the element mesh block division can be determined according to the actual needs and calculation efficiency. If the engineer only focuses on the internal force calculation results of a certain part of the model, or the number of elements and nodes in the model is huge and the calculation time is long, the block division range can be limited to a part of the area.

[0054] In an exemplary embodiment, S4 can be replaced by the following steps.

[0055] S41: For each block, obtain the finite element solid elements at the target cross-section position, and perform normalization processing on the element node coordinates of all finite element solid elements.

[0056] S42: Based on the component data of the normalized node coordinates in different coordinate axes, judge the spatial position of the element nodes in the finite element solid element, and number all the element nodes.

[0057] S43: According to the spatial position and number of the element nodes, determine the node data on the target cross-section in the entity element mesh.

[0058] Furthermore, in S4, for each block, obtain the elements at the target cross-section position, calculate the node positions and numbers at the cross-section according to the node coordinates of the elements, and then obtain the stress values of the cross-section nodes.

[0059] Among them, in the process of obtaining the element nodes at the cross-section above, sorting of the nodes is involved. The spatial coordinates of the element nodes can be normalized, and the spatial position of the nodes in the element can be judged based on the components of the normalized coordinates in different coordinate axes, and the nodes are numbered.

[0060] Furthermore, since the target cross-section only passes through some layers of elements and nodes in the block, it is necessary to screen out these elements and nodes for subsequent internal force calculation.

[0061] In the process of screening the elements at the target cross-section, the target elements can be obtained according to the spatial positions of the elements and the tolerance value set by the user. This tolerance value should be less than the size of the element in the corresponding direction, and its purpose is to obtain the nodes that are not in the same plane among the elements in the layer where the target cross-section is located.

[0062] For the obtained layer of elements, the nodes are sorted according to their spatial coordinates. For example, for the elements in the cylindrical coordinate system, the element node coordinates can be normalized; for the vertical direction, the nodes with the normalized z coordinate less than 0.5 can be considered to be located at the bottom, and the nodes with the normalized z coordinate greater than or equal to 0.5 can be considered to be located at the top. The node sorting process in other directions is the same.

[0063] Based on the sorted element nodes, the element faces in different directions can be obtained, and then the node coordinates and stress data at the target cross-section can be obtained.

[0064] In an exemplary embodiment, in S5, according to the node coordinates on the target cross-section, the area of the element face is obtained by the method of vector cross product.

[0065] For the block shapes of different structural models and the geometric characteristics of the elements within the blocks, the corresponding neutral axis positions within the target cross-section are calculated. For example, for the block with a fan-shaped shape, if the element face is rectangular, it can be simply considered that the neutral axes in different directions are located at the centroids of the element faces in those directions.

[0066] For each element node, the distance between it and the neutral axis can be calculated.

[0067] Based on the above information and the element node stress data on the target cross-section, the internal forces of the cross-section can be calculated according to the following formula.

[0068] S5 can be replaced by the following steps.

[0069] S51: Use to calculate the axial force at the target cross-section within the block; where N is the axial force at the target cross-section within the block; σ Gni is the normal stress at the centroid of the i-th element face; A i is the area of the i-th element face; n is the number of elements at the target cross-section within the block; i is the serial number of the finite element solid element at the target cross-section within the block.

[0070] S52: Use to calculate the shear force at the target cross-section within the block; where Q is the shear force at the target cross-section within the block; τ Gni is the shear stress at the centroid of the i-th element face.

[0071] S53: Use Calculate the bending moment at the target cross-section within the calculation block; where M is the bending moment at the target cross-section within the block; d i is the distance between the centroid of the i-th unit surface and the neutral axis.

[0072] In an exemplary embodiment, after S5, S6 is further included: Create a new frame according to the calculated cross-section internal force results for each analysis step, and assign the cross-section internal force data for later contour plot display. That is, create a new frame at the end of the frame for each analysis step, which is specifically used to display the internal force calculation results.

[0073] Furthermore, assign the internal force values calculated on the target cross-section within the block to all the elements within the block, that is, the internal force values displayed by the elements within the same block in the contour plot are the same. If necessary, output information such as the internal force values at the control cross-section to an external file for easy viewing and comparison by engineers.

[0074] The main process of S6 is as follows:

[0075] Since usually the calculation results output to an external table are not intuitive enough and are not conducive to engineers comparing and checking the results, the cross-section internal force calculation results can be output to a contour plot for display.

[0076] Based on the internal force calculation results on the target cross-section in all element blocks, add a new frame after a certain frame in each analysis step, which is specifically used to store the internal force calculation values.

[0077] For the Abaqus software, the addData method can be used to assign the calculation results to the field output variables of the newly created frame. Although not all elements and nodes within the block are used for internal force calculation, in this step, all elements within the same block are assigned the same internal force calculation values for easy contour plot display. At the same time, output the cross-section internal force calculation data to an external file, which can be combined with the contour plot for later checking and analysis.

[0078] This application realizes the division of solid element mesh blocks and the automatic calculation of cross-section internal forces based on the calculation results of general finite element software, significantly improving the post-processing efficiency of the calculation results and facilitating engineers to perform engineering checks based on internal forces.

[0079] This application calculates the internal force values at the target cross-section of the model based on the element node stresses, with high calculation accuracy and meeting the engineering requirements.

[0080] This application is feasible and accurate, and has strong analysis performance, and can provide strong technical support for the checking and analysis work in actual engineering.

[0081] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0082] Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A method for automatic calculation of cross-sectional internal forces based on finite element solid units, characterized in that: The automatic calculation method of cross-sectional internal force based on finite element solid units includes: Perform finite element calculation on the solid structure to be measured according to the model data, determine the solid unit mesh, and obtain the calculation results of the finite element software; the model data includes the analysis step, the frame number of the analysis step, the finite element solid unit type and the unit node coordinates; the calculation results of the finite element software include the stress at each unit node and the data of the various components of the stress; the stress includes normal stress and shear stress; Preprocessing the model data and the finite element software calculation results to determine preprocessed data; the preprocessed data includes the preprocessed model data and the preprocessed finite element calculation results; Dividing the entity unit grid into blocks according to the preprocessed data; Determine the node data on the target section in the solid unit grid according to the spatial positions of the finite element solid units and unit nodes in each block; the node data includes node coordinates and stress data; The area of ​​the unit surface and the neutral axis of the target section are calculated according to the node data, and the section internal force at the target section is calculated; the section internal force includes axial force, shear force and bending moment.

2. The automatic calculation method of cross-sectional internal forces based on finite element entity units according to claim 1 is characterized in that: Preprocessing the model data and the calculation results of the finite element software to determine the preprocessed data specifically includes: Determining the output position of the calculation result according to the calculation result of the model component in the solid unit grid at each analysis step; the output position includes the integration point position and the node position; Based on the output position, the finite element software calculation results that do not meet the calculation requirements are discarded to determine the filtered data; the filtered data is the pre-processed finite element calculation results; According to the model type and geometric features of the entity unit grid, coordinate transformation is performed on the unit node coordinates to determine transformed data; the transformed data is preprocessed model data; The filtered data and the converted data are determined as preprocessed data, and the preprocessed data are stored in sequence.

3. The automatic calculation method of cross-sectional internal forces based on finite element entity units according to claim 1 is characterized in that: The block division of the entity unit grid according to the preprocessed data specifically includes: Calculating the coordinates of the unit center of gravity according to the unit node coordinates in the preprocessed model data; Based on the unit centroid coordinates, the entity unit grid is divided into blocks according to the unit block position and the unit block size; wherein the unit block size is determined according to actual engineering requirements.

4. The automatic calculation method of cross-sectional internal forces based on finite element entity units according to claim 3 is characterized in that: Based on the unit centroid coordinates, the entity unit grid is divided into blocks according to the unit block position and unit block size, specifically including: If in a Cartesian coordinate system, the entity unit grid is divided into blocks according to the three-axis components of the unit centroid coordinates; wherein the divided blocks are rectangular blocks; If in a cylindrical coordinate system, based on the coordinates of the unit centroid, the entity unit grid is divided into blocks according to the radial position, annular angle and vertical elevation of the finite element entity unit; wherein the divided blocks are in the shape of fan-shaped blocks; In a spherical coordinate system, based on the coordinates of the unit centroid, the entity unit grid is divided into blocks according to the radial position, annular angle and vertical angle of the finite element entity unit; wherein the block shape is a flat shell.

5. The automatic calculation method of cross-sectional internal force based on finite element entity unit according to claim 1 is characterized in that: According to the spatial positions of the finite element entity units and unit nodes in each block, the node data on the target section in the entity unit grid is determined, specifically including: For each block, the finite element solid unit at the target section position is obtained, and the unit node coordinates of all finite element solid units are normalized; Based on the component data of the normalized node coordinates under different coordinate axes, the spatial position of the unit node in the finite element entity unit is determined, and all the unit nodes are numbered; According to the spatial position and number of the unit node, the node data on the target cross section in the solid unit grid is determined.

6. The method for automatic calculation of cross-sectional internal forces based on finite element entity units according to claim 1, characterized in that: Calculating the area of ​​the unit surface and the neutral axis of the target cross section according to the node data, and calculating the cross-sectional internal force at the target cross section, specifically includes: use Calculate the axial force at the target section in the block; where N is the axial force at the target section in the block; σ Gni is the normal stress at the center of gravity on the i-th unit surface; A i is the area of ​​the i-th unit surface; n is the number of units at the target section in the block; i is the finite element entity unit number at the target section in the block; use Calculate the shear force at the target section in the block; where Q is the shear force at the target section in the block; τ Gni is the shear stress at the center of gravity on the i-th unit surface; use Calculate the bending moment at the target section in the block; where M is the bending moment at the target section in the block; d i is the distance between the centroid and the neutral axis on the i-th unit surface.

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