Secondary calculation method of node stress of plate-shell frame structure based on finite element method

Abstract

The present application relates to the secondary calculation method of the node stress of the plate-shell frame structure based on the finite element method, which comprises the following steps: establishing the whole middle surface geometric model of the plate-shell frame structure according to the geometric information of the plate-shell frame structure; twice cutting the geometric model of each component between all nodes of the whole middle surface geometric model, and dividing the whole middle surface geometric model into node parts and the remaining parts; selecting the shell element type, dividing the grid of the whole middle surface geometric model, and obtaining the primary finite element grid; applying the constraints and loads of the structure on the primary finite element grid, and obtaining the stress results of the primary calculation of the structure by using the finite element method, and extracting the node part with the maximum stress; and removing the constraints and loads on the primary finite element grid, etc. The method of the present application can overcome the problems of the existing calculation method of the node stress of the plate-shell frame structure, such as complicated modeling, high calculation cost, difficulty in applying constraints and loads, and low calculation precision.

Description

Technical Field

[0001] This invention belongs to the field of simulation calculation technology in computer-aided engineering, specifically involving a secondary calculation method for nodal stress in plate and shell frame structures based on the finite element method. Background Technology

[0002] Plate and shell frame structures are widely used in engineering, such as various lifting and transportation machinery, truss steel bridges, and high towers. Because plate and shell frame structures bear various loads during operation, and their nodes have complex geometries and diverse failure modes, the rapid and accurate calculation of stress at the nodes to assess structural strength is crucial for ensuring the safety performance of engineering structures. However, due to the complexity of plate and shell frame structures and the variability of actual working conditions, theoretical analysis and experimental testing methods are insufficient to quickly and accurately obtain the stress at the nodes. Therefore, the finite element method is typically used for simulation calculations of the nodes in plate and shell frame structures.

[0003] Although obtaining the stress at nodes of plate-shell frame structures using the finite element method (FEM) is a common method in simulation computing, it is difficult to achieve a good balance between computational accuracy and cost when using FEM based on a single type of element. For example, if only shell elements are used for discretization, the details of the actual geometry of the nodes cannot be considered, resulting in low accuracy of the calculated stress. If only volume elements are used for discretization, since the plate thickness of the plate-shell frame structure is much smaller than the length of the component, the mesh size will be too large and the computational cost will increase dramatically in order to obtain a more accurate stress. Although the method of creating a hybrid body-shell mesh model by connecting volume and shell elements can reduce the mesh size, it is impossible to predict which node has the highest stress, so the entire plate-shell frame structure needs to be remodeled after the initial calculation, which makes the modeling process cumbersome, time-consuming, and costly in preprocessing. Alternatively, sub-models can be used to perform local calculations on the nodes, but the boundary conditions of the sub-models are difficult to apply accurately. Therefore, how to quickly and accurately calculate the stress at nodes of plate-shell frame structures remains a key challenge in the current strength assessment of plate-shell frame structure nodes. Summary of the Invention

[0004] The purpose of this invention is to address the difficulty in rapidly and accurately obtaining nodal stress during the strength assessment of plate and shell frame structures, by providing a secondary calculation method for nodal stress in plate and shell frame structures based on the finite element method. This method effectively overcomes the problems of low calculation accuracy or high calculation cost in existing stress calculation methods for plate and shell frame structure nodes, and can quickly provide accurate nodal stress results for the strength assessment of plate and shell frame structure nodes.

[0005] The present invention provides a secondary calculation method for nodal stress in plate and shell frame structures based on the finite element method, comprising the following steps:

[0006] (1) Based on the geometric information of the plate and shell frame structure, extract the mid-surface information of the components and establish the overall mid-surface geometric model of the plate and shell frame structure;

[0007] (2) The geometric models of each component between all nodes of the overall mid-surface geometric model are divided twice, and the shortest distance between the dividing surface of the component geometric model and the center of the adjacent structural node is taken as 1 to 3 times the maximum chord length or the maximum diagonal dimension of the corresponding component cross-section, thereby dividing the overall mid-surface geometric model into each node part Gn. i And the remaining part Gm, where i is the node number, and the overall mid-surface geometric model after the segmentation is denoted as G;

[0008] (3) Select the shell element type and apply it to each node part Gn of the global mid-surface geometric model G. i Divide the grid to obtain the part Gn of each node. i Finite element mesh Sn i The remaining part Gm of the overall mid-surface geometric model G is meshed to obtain the finite element mesh Sm and Sn of the remaining part Gm. i Together with Sm, they form the initial finite element mesh of the global mid-surface geometric model G, denoted as M1;

[0009] (4) Apply structural constraints and loads to M1, use the finite element method to solve for the initial stress results of the structure, and extract the node with the largest stress, and denot its number as k.

[0010] (5) Remove constraints and loads on M1;

[0011] (6) Mesh Sn of the node with the highest stress k Replace the mesh Vn with a solid element type to obtain a secondary finite element mesh for the plate and shell frame structure, denoted as M2;

[0012] (7) Apply structural constraints and loads to M2, and use the finite element method again to obtain the stress result of the second calculation of the node with the largest stress, and use it as the final stress result of the node with the largest stress.

[0013] Specifically, step (6) includes the following steps:

[0014] (a) Remove the mesh Sn at the node with the highest stress. k ;

[0015] (b) Delete the mid-surface geometry model Gn of the node with the highest stress. kAnd establish a corresponding three-dimensional solid geometric model;

[0016] (c) Select the three-dimensional solid element type, mesh the three-dimensional solid geometric model, and obtain the mesh Vn of the solid element type of the three-dimensional solid geometric model;

[0017] (d) Use the multi-point constraint method to connect the solid element type mesh Vn and the shell element type mesh that is in contact with Vn.

[0018] The present invention provides a secondary calculation method for the stress of nodal nodes in plate and shell frame structures based on the finite element method. This method not only effectively overcomes the problems of low calculation accuracy or high calculation cost in existing stress calculation methods for plate and shell frame structure nodes, but also avoids repeatedly building models of plate and shell frame structures and avoiding the application of boundary conditions on local models. Thus, it provides a fast and accurate calculation method for obtaining the stress of nodal nodes in plate and shell frame structures for strength assessment. At the same time, the method of the present invention is simple and easy for designers to master. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the geometric model of the plate-shell frame structure in the method of the present invention.

[0020] Figure 2 This is a schematic diagram of the overall mid-surface geometric model of the plate-shell frame structure in the method of the present invention.

[0021] Figure 3 This is a cloud map showing the distribution of stress results from the initial calculation of the plate-shell frame structure.

[0022] Figure 4 This is a three-dimensional solid geometric model of the nodal section where the stress is greatest in a plate-shell frame structure.

[0023] Figure 5 This is a schematic diagram of a two-dimensional finite element mesh for a plate-shell frame structure at the node with the highest stress.

[0024] Figure 6 This is a cloud map showing the distribution of stress results from secondary calculations at the nodes where the stress is greatest in a plate-shell frame structure. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0026] The specific implementation steps of the secondary calculation method for nodal stress in plate and shell frame structures based on the finite element method of the present invention are as follows:

[0027] (1) Based on the geometric information of the plate and shell frame structure, extract the mid-surface information of the components and establish the overall mid-surface geometric model of the plate and shell frame structure;

[0028] (2) The geometric models of each component between all nodes of the overall mid-surface geometric model are divided twice, and the shortest distance between the dividing surface of the component geometric model and the center of the adjacent structural node is taken as 1 to 3 times the maximum chord length or the maximum diagonal dimension of the corresponding component cross-section, thereby dividing the overall mid-surface geometric model into each node part Gn. i And the remaining part Gm, where i is the node number, and the overall mid-surface geometric model after the segmentation is denoted as G;

[0029] (3) Select the shell element type and apply it to each node part Gn of the global mid-surface geometric model G. i Divide the grid to obtain the part Gn of each node. i Finite element mesh Sn i The remaining part Gm of the overall mid-surface geometric model G is meshed to obtain the finite element mesh Sm and Sn of the remaining part Gm. i Together with Sm, they form the initial finite element mesh of the global mid-surface geometric model G, denoted as M1;

[0030] (4) Apply structural constraints and loads to M1, use the finite element method to solve for the initial stress results of the structure, and extract the node with the largest stress, and denot its number as k.

[0031] (5) Remove constraints and loads on M1;

[0032] (6) Mesh Sn of the node with the highest stress k Replace the mesh Vn with a solid element type to obtain a secondary finite element mesh for the plate and shell frame structure, denoted as M2. The specific steps are as follows:

[0033] (a) Remove the mesh Sn at the node with the highest stress. k ;

[0034] (b) Delete the mid-surface geometry model Gn of the node with the highest stress. k And establish a corresponding three-dimensional solid geometric model;

[0035] (c) Select the three-dimensional solid element type, mesh the three-dimensional solid geometric model, and obtain the mesh Vn of the solid element type of the three-dimensional solid geometric model;

[0036] (d) Use the multi-point constraint method to connect the solid element type mesh Vn and the shell element type mesh that is in contact with Vn.

[0037] (7) Apply structural constraints and loads to M2, and use the finite element method again to obtain the stress result of the second calculation of the node with the largest stress, and use it as the final stress result of the node with the largest stress.

[0038] The following is an application of the method of the present invention to a specific embodiment to test the performance of the method of the present invention.

[0039] See Figure 1 The embodiment is a plate-shell frame structure.

[0040] according to Figure 1 The geometric information of the plate-shell frame structure is used to extract the mid-surface information of the components, establish an overall mid-surface geometric model of the plate-shell frame structure, and then perform two subdivisions on the geometric models of each component between all nodes of the overall mid-surface geometric model to obtain the subdivided overall mid-surface geometric model G, as shown below. Figure 2 As shown, the node portion of G is as follows: Figure 2 Gn i As shown, the rest of G is as follows Figure 2 As shown in Gm.

[0041] Figure 3 This is a distribution cloud map of the initial stress results for a plate-shell frame structure. Figure 3 It can be seen that the node part Gn is located in the middle of the right side of the plate and shell frame structure. k The stress is the highest, with a maximum value of 438e9 Pa. However, since the overall mid-surface geometry model ignores the geometric details of the nodes, this maximum stress value is not the actual nodal stress and contains a large error, leading to distorted calculation results.

[0042] Gn k Grid Sn k Clear and delete Gn k Then establish with Gn k The corresponding three-dimensional solid geometric model, such as Figure 4 As shown. Select the 3D solid element type, and then... Figure 4 The three-dimensional solid geometric model shown is meshed to obtain a solid element type mesh Vn. A multi-point constraint method is then used to connect the solid element type mesh Vn with the shell element type mesh in contact with Vn, resulting in a secondary finite element mesh M2 for the plate-shell frame structure. A schematic diagram of M2 at the node with the highest stress is shown below. Figure 5 As shown in the figure. Constraints and loads are applied to the structure on M2, and the secondary calculated stress results for the nodal portion with the highest stress are obtained again using the finite element method. The distribution contour plot is shown in the figure. Figure 6 As shown. By Figure 6 It can be seen that Gn k The maximum stress value is 192e9 Pa. Clearly, due to the consideration of the actual geometry of the nodes, Gn kThe secondary calculation result of the maximum stress value is much lower than that of the initial calculation result and is more accurate. At the same time, when performing the secondary calculation, only the node part with the maximum stress needs to be remodeled, which greatly simplifies the modeling process, shortens the modeling time, and reduces the calculation cost.

[0043] Although the present invention has been described with reference to preferred embodiments, the above description does not limit the scope of protection of the present invention. All technical solutions that fall within the scope of the present invention are within the scope of protection of the present invention. Any modifications or improvements within the spirit and principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A secondary calculation method for nodal stress in plate and shell frame structures based on the finite element method, characterized in that... The steps include the following: (1) Based on the geometric information of the plate and shell frame structure, extract the mid-surface information of the components and establish the overall mid-surface geometric model of the plate and shell frame structure; (2) The geometric models of each component between all nodes of the overall mid-surface geometric model are divided twice, and the shortest distance between the dividing surface of the component geometric model and the center of the adjacent structural node is taken as 1 to 3 times the maximum chord length or the maximum diagonal dimension of the corresponding component cross-section, thereby dividing the overall mid-surface geometric model into each node part Gn. i And the remaining part Gm, where i is the node number, and the overall mid-surface geometric model after the segmentation is denoted as G; (3) Select the shell element type and apply it to each node part Gn of the global mid-surface geometric model G. i Divide the grid to obtain the part Gn of each node. i Finite element mesh Sn i The remaining part Gm of the overall mid-surface geometric model G is meshed to obtain the finite element mesh Sm and Sn of the remaining part Gm. i Together with Sm, they form the initial finite element mesh of the global mid-surface geometric model G, denoted as M1; (4) Apply structural constraints and loads to M1, use the finite element method to solve for the initial stress results of the structure, and extract the node with the largest stress, and denot its number as k. (5) Remove constraints and loads on M1; (6) Mesh Sn of the node with the highest stress k Replace the mesh Vn with a solid element type to obtain a secondary finite element mesh for the plate and shell frame structure, denoted as M2; (7) Apply structural constraints and loads to M2, and use the finite element method again to obtain the stress result of the second calculation of the node with the largest stress, and use it as the final stress result of the node with the largest stress.

2. The secondary calculation method for nodal stress in a plate-shell frame structure based on the finite element method according to claim 1, characterized in that: Step (6) includes the following steps: (a) Remove the mesh Sn at the node with the highest stress. k ; (b) Delete the mid-surface geometry model Gn of the node with the highest stress. k And establish a corresponding three-dimensional solid geometric model; (c) Select the three-dimensional solid element type, mesh the three-dimensional solid geometric model, and obtain the mesh Vn of the solid element type of the three-dimensional solid geometric model; (d) Use the multi-point constraint method to connect the solid element type mesh Vn and the shell element type mesh that is in contact with Vn.

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