Variable-size reinforced structure design method based on stress traces

Abstract

The invention relates to the technical field of computer graphic processing and computational mechanics, in particular to a variable-size reinforced structure design method based on a stress trace, which comprises the following steps of: inputting a node number, a boundary condition and a load working condition of a two-dimensional plane graph, and generating the stress trace by calculating a stress tensor; converting the stress trace graph into a voxel unit model, endowing each voxel unit with a volume attribute, obtaining the voxel units with the volume being 1, and obtaining the voxel units on the stress trace track; building variable height and variable thickness units based on the voxel unit model; the initial height and the initial thickness of the reinforcing ribs are designed according to the average stress of the stress traces; variable-height and variable-thickness rib size design is carried out through a BESO topological optimization method, and a variable-size reinforced structure is obtained. According to the method, variable-size ribs with different heights and thicknesses can be designed for a thin-wall structure according to different stress distribution conditions, and the thin-wall reinforced structure with high specific stiffness is obtained.

Description

Technical Field

[0001] The present invention relates to the technical fields of computer graphics processing and computational mechanics, and particularly relates to a variable-size stiffened structure design method based on stress trajectories. Background Art

[0002] The optimal design of thin-walled structures is an important direction in current computational mechanics research. Among them, stiffened structures are an important means to improve the load-bearing capacity of thin-walled structures. They can not only greatly improve the comprehensive performance of thin-walled structures but also ensure the overall performance of the structure, and have important application value in the structural design of high-end equipment such as aerospace. The development of additive manufacturing technology provides a larger design space for the design of ribs. The variable-size stiffened structure design gives full play to the functional advantages of thin-walled structures and is conducive to realizing the automatic variable-size stiffening design of thin-walled structures under service conditions.

[0003] However, there are the following defects in the current optimal design of thin-walled stiffening: First, traditional rib structures represented by "grid-shaped" and "cross-shaped" are relatively regular in shape, have a single construction mode, and it is difficult to accurately balance the structural stress distribution, and the performance improvement of thin-walled shell structures has reached its limit; second, there is a lack of a general and efficient design method for stiffeners of thin-walled structures, it is difficult to achieve the coordinated optimization of the height and thickness of ribs, and the performance advantages of thin-walled structures cannot be fully utilized, which limits the in-depth application of thin-walled structures in major projects. Therefore, the present invention proposes a variable-size stiffening optimization scheme based on stress trajectories to achieve the optimization goal of designing variable-size stiffeners according to the stress distribution on thin-walled structures and obtain a thin-walled stiffened structure with high specific stiffness performance. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a variable-size stiffened structure design method based on stress trajectories, which solves the problems that traditional rib structures are relatively regular in shape, have a single construction mode, it is difficult to accurately balance the structural stress distribution, and it is difficult to achieve the coordinated optimization of the height and thickness of ribs. The present invention can achieve the optimization goal of designing variable-size stiffeners according to the stress distribution on thin-walled structures and obtain a thin-walled stiffened structure with high specific stiffness performance, thereby better solving the above problems existing in the prior art.

[0005] To solve the above technical problems, the present invention provides the following technical solutions: A variable-size stiffened structure design method based on stress trajectories, comprising the following steps:

[0006] S1. Input the node numbers, boundary conditions, and load conditions of a two-dimensional planar graph, and generate stress trajectories by calculating the stress tensor;

[0007] S2. Convert the stress trace line graph into a voxel unit model, assign the vary attribute to each voxel unit, obtain the voxel units with vary equal to 1, and get the voxel units on the stress trace line trajectory;

[0008] S3. Construct a variable height and variable thickness unit voxel model based on the voxel unit model;

[0009] S4. Design the initial height and initial thickness of the rib according to the average stress magnitude of the stress trace line, so that the size of the rib matches the stress distribution of the structure;

[0010] S5. Design the size of the variable height and variable thickness rib by the BESO topology optimization method to obtain a variable size stiffened structure.

[0011] Furthermore, in step S1, input the node numbers, boundary conditions, and load conditions of the two-dimensional planar graph, and generate stress trace lines by calculating the stress tensor. The specific process includes the following steps:

[0012] S11. Input the node numbers, boundary conditions, and load conditions of the two-dimensional planar graph;

[0013] S12. Adopt a seed point layout method of uniform sampling, change the size of the mesh resolution control parameter Density to determine the distribution density of the seed points, and control the sparsity of the stress trace lines by defining the seed point density. The Density parameter defines the minimum distance ΔX between the seed points, that is, controls the density size of the seed points. The minimum distance between the seed points can be described by the following formula:

[0014]

[0015] where, ΔX is the minimum distance between the seed points; D is the size of the design domain for drawing the stress trace line; Density is the mesh resolution control parameter;

[0016] S13. Starting from the given initial seed points, calculate the stress magnitude and direction at this point according to the following formula:

[0017]

[0018] σ p 3 -I 1 σ p 2 +I 2 σ p -I 3 =0

[0019] In the formula, σ x 、σ y 、σ z 、σx σ y 、σ y σ z 、σ z σ x are the stress tensors; τ xy 、τ yz 、τ zx are the shear stresses; I 1 、I 2 、I 3 are the stress invariants; σ p are the principal stresses;

[0020] S14. Substitute the invariants I 1 、I 2 、I 3 to obtain the solutions σ p1 、σ p2 、σ p3 of the three stresses and the corresponding stress directions:

[0021]

[0022] where l 1 、l 2 、l 3 are the function values of the directions corresponding to the principal stresses;

[0023] S15. Based on the Runge - Kutta numerical integration method, simulate the tracking of the stress trajectories according to the calculated stresses and the corresponding stress directions, and gradually update the positions of the stress trajectories to calculate the paths of the stress trajectories.

[0024] Furthermore, in step S14, in order to improve the accuracy of numerical integration when generating stress trajectories, k 2 is introduced as an intermediate prediction point for the second - order Runge - Kutta method, and the tracking steps of the stress trajectories are:

[0025]

[0026] where h is the iteration step size, y n is the stress state of the current seed point, y n+1 is the state of the next tracking point, k 1 is used to represent various information for calculating the prediction point, and k 2 is the information for calculating the intermediate point.

[0027] Furthermore, for step S15, it also includes displaying the primary and secondary stress trajectories of the structure through visualization technology, and filtering out the shorter stress lines because they cannot fully express the main force - transmission paths inside the material.

[0028] Further, in step S2, the stress trace graph is converted into a voxel unit model, the vary attribute is assigned to each voxel unit, and the voxel units with vary equal to 1 are obtained to get the voxel units on the stress trace trajectory. The specific process includes the following steps:

[0029] S21. Convert the stress trace graph into a voxel unit model through the STL model, and discretize the STL model into a hexahedron voxel unit model, with each unit having a unique unit number;

[0030] S22. Extract the unit numbers of the units passing through each stress trace on the two-dimensional planar graph, and identify the intersection units of the stress trace and the voxel unit;

[0031] S23. Assign the vary attribute to each voxel unit. The vary attribute of the unit belonging to the stress line is recorded as 1, indicating that the unit is part of the stress line trajectory; on the contrary, for the unit not belonging to the stress line, the vary attribute is recorded as 0, indicating that the unit is not on the stress line trajectory, so as to obtain the voxel units with the vary attribute of 1 and get the voxel units on the stress trace.

[0032] Further, in step S3, a variable-height and variable-thickness unit voxel model is constructed based on the voxel unit model. The specific process includes the following steps:

[0033] S31. Construct variable-height units based on the voxel model, and assign height attribute values to all units in the voxelized model: the bottommost unit of the model is assigned the attribute 0, the smallest-height unit that forms a rib together with the bottommost unit is assigned the attribute 1, and the units that can be freely added or deleted are assigned the attribute 2;

[0034] S32. Construct variable-thickness units based on the voxel model, and assign thickness attribute values to all units in the voxelized model: the units with non-deletable thickness are assigned the attribute 3, and the thickness units that can be freely added or deleted are assigned the attribute 4;

[0035] S33. In the process of optimizing the height and thickness of the rib, determine whether a unit can be added or deleted through the outer surface unit attributes of the variable-height and variable-thickness units.

[0036] Further, in step S4, the initial height and initial thickness of the stiffener are designed according to the average stress magnitude of the stress trace, so that the size of the rib matches the stress distribution of the structure. The specific process includes the following steps:

[0037] S41. Number all the stress lines in the two-dimensional graph, and calculate the average stress magnitude of each stress trace. The calculation formula is:

[0038]

[0039] In the formula, i represents the number of stress trace lines; represents the average stress magnitude of the i-th stress trace line; n i represents the total number of elements passing through the i-th stress line;

[0040] S42. According to the calculated stress magnitude σ mean Define the stress threshold threshold. According to the threshold, the model is divided into several optimization regions with variable height and variable thickness. If there are A optimization regions, then A - 1 stress thresholds threshold need to be defined. The stress threshold threshold is calculated by the following formula:

[0041]

[0042] S43. According to the average stress magnitude Sort the stress trace lines. According to the average stress sorting result, design the initial height and initial thickness of the optimization region. Determine the initial height and initial thickness of different optimization regions by comparing the average stress value of each stress line with the threshold. If there are three optimization regions, it is specifically shown by the following formula:

[0043]

[0044] In the formula, x is the minimum size of the thin-walled structure, x 1 , x 2 , x 3 are custom initial size parameters.

[0045] Furthermore, step S5 specifically includes: performing variable height and variable thickness rib size design through the BESO topology optimization method to obtain a variable size stiffened structure, specifically including: constructing a variable height and variable thickness element voxel model, given boundary conditions, load conditions, and the optimized volume fraction, and performing variable height and variable thickness rib size design through the BESO topology optimization method to obtain a variable size stiffened structure. The expression of the optimization problem is as follows:

[0046] Find: x = {x 1 , x 2 , … x n T}

[0047] Min: C = F T U

[0048]

[0049] In the formula, x is the element density matrix, x nis the design variable of the nth element, where a design variable of 0.001 means that the element needs to be deleted, i.e., it is an empty element, and a value of 1 means that the element is a solid element; K is the overall stiffness matrix of the structure; U is the displacement matrix; F is the overall force matrix of the structure; C represents the flexibility of the structure; V 0 is the volume before structural optimization; v f is the optimized volume fraction; v i is the volume of the ith element.

[0050] With the above technical solutions, the present invention provides a variable-size stiffened structure design method based on stress trajectories, which has at least the following beneficial effects:

[0051] The variable-size structure design method based on stress trajectories proposed by the present invention has a certain universality in the optimal design of thin-walled structures; the stress line visualization algorithm of the stress field lays a solid theoretical foundation for the initial layout design of the variable-size rib structure; it realizes setting the initial height and initial thickness of the ribs according to the average stress magnitude and distribution of the stress lines, so that the size of the ribs matches the stress distribution of the structure; through the topology optimization method, the self-increase and deletion of the rib height and thickness are realized, and the optimization goal of designing variable-size stiffeners according to the stress distribution on the thin-walled structure is achieved, realizing the design of variable-size ribs with different heights and thicknesses on the thin-walled structure according to different stress distribution situations, and obtaining a thin-walled stiffened structure with high specific stiffness performance; it solves the problems that the traditional rib structure has a relatively regular shape, a relatively single construction mode, it is difficult to accurately balance the structural stress distribution, and it is difficult to realize the coordinated optimization of the rib height and thickness. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0053] Figure 1 is the overall flow schematic diagram of the variable-size structure design method based on stress trajectories of the present invention;

[0054] Figure 2 is the stress line visualization schematic diagram of the cantilever beam structure and the three-point bending structure at different densities;

[0055] Figure 3 is the schematic diagram of the construction process of the height unit and the thickness unit;

[0056] Figure 4 is the schematic diagram of the variable-size stiffened design results of the cantilever beam structure and the three-point bending structure at different densities;

[0057] Figure 5 is the schematic diagram of the comparison of the finite element simulation results and performance parameters before and after rib optimization. Detailed implementation manners

[0058] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners. Thereby, a full understanding of how the present application uses technical means to solve technical problems and achieve the realization process of technical effects can be obtained and implemented accordingly.

[0059] Those of ordinary skill in the art can understand that all or part of the steps in the methods of the above embodiments can be completed by instructing relevant hardware through a program. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program codes.

[0060] Please refer to Figures 1-5 , which shows a specific implementation manner of this embodiment. In this embodiment, the initial height and initial thickness of the rib are set according to the average stress magnitude and distribution of the stress line, so that the size of the rib matches the stress distribution of the structure; the self-increasing and deleting of the rib height and thickness are realized through the topology optimization method, and the optimization goal of variable-size stiffeners is designed on the thin-walled structure according to the stress distribution, so as to realize the variable-size ribs with different heights and thicknesses designed on the thin-walled structure according to different stress distribution situations, and obtain a thin-walled stiffened structure with high specific stiffness performance.

[0061] Please refer to Figure 1 , this embodiment proposes a method for designing a variable-size stiffened structure based on stress trajectories, and the method includes the following steps:

[0062] S1. Input the node numbers, boundary conditions, and load conditions of the two-dimensional planar graph, and generate stress trajectories by calculating the stress tensor;

[0063] As a preferred implementation manner of step S1, in step S1, input the node numbers, boundary conditions, and load conditions of the two-dimensional planar graph, and generate stress trajectories by calculating the stress tensor. The specific process includes the following steps:

[0064] S11. Input the node numbers, boundary conditions, and load conditions of the two-dimensional planar graph;

[0065] S12. Adopt a seed point layout method of uniform sampling, change the size of the grid resolution control parameter Density to determine the distribution density of the seed points, and control the sparsity of the stress trajectories by defining the seed point density, such as Figure 2As shown, the Density parameter defines the minimum distance ΔX between seed points, that is, it controls the density of seed points. The minimum distance between seed points can be described by the following formula:

[0066]

[0067] where ΔX is the minimum distance between seed points; D is the size of the design domain for drawing stress traces; Density is the grid resolution control parameter;

[0068] S13. Starting from the given initial seed point, calculate the stress magnitude and direction at this point according to the following formula:

[0069]

[0070] σ p 3 -I 1 σ p 2 +I 2 σ p -I 3 =0

[0071] In the formula, σ x 、σ y 、σ z 、σ x σ y 、σ y σ z 、σ z σ x are stress tensors; τ xy 、τ yz 、τ zx are shear stresses; I 1 、I 2 、I 3 are stress invariants; σ p is the principal stress;

[0072] S14. Substitute the invariants I 1 、I 2 、I 3 to obtain the solutions of the three stresses σ p1 、σ p2 、σ p3 and the corresponding stress directions:

[0073]

[0074] where l 1 、l 2 、l 3 are the function values of the directions corresponding to the principal stresses;

[0075] More specifically, to improve the accuracy of numerical integration when generating stress traces, k is introduced. 2 As an intermediate prediction point for the second-order Runge-Kutta method, the tracking steps of the stress trace are as follows:

[0076]

[0077] In the formula, h is the iteration step size, y n is the stress state of the current seed point, y n+1 is the state of the next tracking point, k 1 is used to represent various information for calculating the prediction point, and k 2 is the various information for calculating the intermediate point;

[0078] S15. Based on the Runge-Kutta numerical integration method, simulate the tracking of the stress trace according to the calculated stress and the corresponding stress direction, and gradually update the position of the stress trace, thereby calculating the path of the stress trace;

[0079] More specifically, the primary and secondary stress traces of the structure are displayed through visualization technology. The shorter stress lines are filtered out because they cannot fully express the main force transmission path inside the material. The primary stress lines are drawn in orange, and the secondary stress lines are represented by green lines, as Figure 2 shown.

[0080] S2. Convert the stress trace graph into a voxel unit model, assign the vary attribute to each voxel unit, and obtain the voxel units with vary equal to 1 to get the voxel units on the stress trace trajectory;

[0081] As a preferred implementation of step S2, convert the stress trace graph into a voxel unit model, assign the vary attribute to each voxel unit, and obtain the voxel units with vary equal to 1 to get the voxel units on the stress trace trajectory. The specific process includes the following steps:

[0082] S21. Convert the stress trace graph into a voxel unit model through the STL model, discretize the STL model into a hexahedron voxel unit model, and each unit has a unique unit number;

[0083] S22. Extract the unit numbers passing through each stress trace on the two-dimensional plane graph and identify the intersection units of the stress trace and the voxel unit;

[0084] S23. Assign the vary attribute to each voxel unit. The vary attribute of the unit belonging to the stress line is recorded as 1, indicating that the unit is part of the stress line trajectory; on the contrary, for the unit not belonging to the stress line, the vary attribute is recorded as 0, indicating that the unit is not on the stress line trajectory, so as to obtain the voxel units with the vary attribute of 1 and get the voxel units on the stress trace line.

[0085] S3. Build a variable-height and variable-thickness unit voxel model based on the voxel unit model;

[0086] As a preferred implementation manner of step S3, build a variable-height and variable-thickness unit voxel model based on the voxel unit model. The specific process includes the following steps:

[0087] S31. Build variable-height units based on the voxel model, and assign height attribute values to all units in the voxelized model: the bottommost unit of the model is assigned the attribute 0, the smallest-height unit that forms the rib together with the bottommost unit is assigned the attribute 1, and the units that can be freely added or deleted are assigned the attribute 2;

[0088] S32. Build variable-thickness units based on the voxel model, and assign thickness attribute values to all units in the voxelized model: the units with non-deletable thickness are assigned the attribute 3, and the thickness units that can be freely added or deleted are assigned the attribute 4;

[0089] S33. During the height and thickness optimization process of the rib, judge whether the unit can be added or deleted through the outer surface unit attributes of the variable-height and variable-thickness units.

[0090] S4. Design the initial height and initial thickness of the stiffener according to the average stress magnitude of the stress trace line, so that the size of the rib matches the stress distribution of the structure;

[0091] As a preferred implementation manner of step S4, design the initial height and initial thickness of the stiffener according to the average stress magnitude of the stress trace line, so that the size of the rib matches the stress distribution of the structure. The specific process includes the following steps:

[0092] S41. Number all stress lines in the two-dimensional graph, and calculate the average stress magnitude of each stress trace line. The calculation formula is:

[0093]

[0094] In the formula, i represents the number of stress trace lines; represents the average stress magnitude of the i-th stress trace line; n i represents the total number of units passing through the i-th stress line;

[0095] S42. According to the calculated stress magnitude σ meanDefine the stress threshold threshold. According to the threshold, the model is divided into several optimization regions with variable heights and variable thicknesses. If there are A optimization regions, then A - 1 stress thresholds threshold need to be defined. The stress threshold threshold is calculated by the following formula:

[0096]

[0097] S43. According to the magnitude of the average stress Sort the stress trajectories. According to the sorting result of the average stress, design the initial height and initial thickness of the optimization regions, as Figure 3 shown; Determine the initial height and initial thickness of different optimization regions by comparing the average stress value of each stress line with the threshold. If there are three optimization regions, it is specifically shown by the following formula:

[0098]

[0099] In the formula, x is the minimum size of the thin-walled structure, x 1 , x 2 , x 3 are custom initial size parameters.

[0100] S5. Perform the variable-height and variable-thickness rib size design through the BESO topology optimization method to obtain a variable-size stiffened structure.

[0101] As a preferred implementation manner of step S5, step S5 specifically includes: Perform the variable-height and variable-thickness rib size design through the BESO topology optimization method to obtain a variable-size stiffened structure, specifically including: Based on the construction of a variable-height and variable-thickness unit voxel model, given boundary conditions, load conditions, and the optimization volume fraction, perform the variable-height and variable-thickness rib size design through the BESO topology optimization method to obtain a variable-size stiffened structure. The expression of the optimization problem is as follows:

[0102] Find: x = {x 1 , x 2 , … x n T}

[0103] Min: C = F T U

[0104]

[0105] In the formula, x is the element density matrix, x n is the design variable of the nth element, where the design variable of 0.001 means that the element needs to be deleted, i.e., an empty element, and 1 means that the element is a solid element; K is the overall stiffness matrix of the structure; U is the displacement matrix; F is the overall force matrix of the structure; C represents the compliance of the structure; V0 is the volume before structural optimization; v f is the optimized volume fraction; v i is the volume of the i-th unit.

[0106] After completing the variable-size stiffener design based on stress trajectories, the obtained variable-size structure is compared with the traditional grid structure through finite element simulation. Variable-size stiffener designs for the cantilever beam structure, grid stiffener design for the cantilever beam, variable-size stiffener design for the three-point bending structure, and grid stiffener design for the three-point bending structure are carried out respectively, as Figure 4 shown in the schematic diagram of the variable-size stiffener design results of the cantilever beam structure and the three-point bending structure at different densities; four different optimized structures are compared, as Figure 5 shown, Figure 5 The finite element simulation results of four groups of structures are presented. It can be seen from the figure that the obtained variable-size stiffened structure after optimization has higher specific stiffness performance. Compared with the grid stiffener design for the cantilever beam, the specific stiffness of the variable-size stiffener design for the cantilever beam structure is increased by 28%; compared with the grid stiffener design for the three-point bending, the specific stiffness of the variable-size stiffener design for the three-point bending structure is increased by 118%. The effectiveness and necessity of the proposed stiffener design method are verified.

[0107] Specifically, the present application also provides an electronic device, including: a memory and a processor. The memory is used to store a computer program, and the processor runs the computer program to enable the electronic device to execute the above-mentioned method for designing a variable-size stiffened structure based on stress trajectories.

[0108] Specifically, the present application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the above-mentioned method for designing a variable-size stiffened structure based on stress trajectories.

[0109] In summary, the present invention has certain universality in the optimal design of thin-walled structures; the stress line visualization algorithm of the stress field lays a solid theoretical foundation for the initial layout design of the variable-size stiffener structure; it is realized to set the initial height and initial thickness of the stiffener according to the average stress magnitude and distribution of the stress lines, so that the size of the stiffener matches the stress distribution of the structure; the self-adding and deleting of the height and thickness of the stiffener are realized through the topology optimization method, and the optimization goal of designing variable-size stiffeners according to the stress distribution on the thin-walled structure is achieved, and variable-size stiffeners with different heights and thicknesses are designed on the thin-walled structure according to different stress distribution situations, obtaining a thin-walled stiffened structure with high specific stiffness performance.

[0110] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. Moreover, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0111] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a definite sequence list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by an instruction execution system, apparatus, or device (such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device), or used in combination with these instruction execution systems, apparatus, or devices.

[0112] The above embodiments have introduced the present invention in detail. Specific examples are used herein to elaborate on the principles and embodiments of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, 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 invention.

Claims

1. A design method for variable-size reinforced structures based on stress traces, characterized in that: The following steps are involved: S1. Input the node number, boundary conditions and load conditions of the two-dimensional plane figure, and generate stress traces by calculating the stress tensor; S2, converting the stress trace graph into a voxel unit model, assigning a vary attribute to each voxel unit, obtaining the voxel unit with a vary value of 1, and obtaining the voxel unit on the stress trace track; S3, constructing a variable height and variable thickness unit voxel model based on the voxel unit model; S4. Design the initial height and initial thickness of the reinforcement ribs according to the average stress of the stress trace, so that the size of the ribs matches the stress distribution of the structure; S5. The variable height and variable thickness ribs are designed by BESO topology optimization method to obtain a variable size reinforced structure.

2. The method for designing a variable-size reinforced structure based on stress trace according to claim 1, characterized in that: In step S1, the node number, boundary conditions and load conditions of the two-dimensional plane figure are input, and the stress trace is generated by calculating the stress tensor. The specific process includes the following steps: S11. Input the node number, boundary conditions and load conditions of the two-dimensional plane figure; S12, adopt the seed point arrangement method of uniform point selection, change the size of the grid resolution control parameter Density to determine the distribution density of the seed points, and control the sparsity of the stress traces by defining the seed point density. The Density parameter defines the minimum distance ΔX between the seed points, that is, controls the density of the seed points. The minimum distance between the seed points can be described by the following formula: Where ΔX is the minimum distance between seed points; D is the size of the design domain for drawing stress traces; Density is the grid resolution control parameter; S13. Starting from a given initial seed point, the stress magnitude and direction at the point are calculated, and the formula is as follows: s p 3 -I1σ p 2 +I2σ p -I3=0 In the formula, σ x , σ y , σ z , σ x σ y , σ y σ z , σ z σ x is the stress tensor; τ xy , τ yz , τ zx is the shear stress; I1, I2, I3 are stress invariants; σ p is the principal stress; S14. Substitute the invariants I1, I2, and I3 to obtain the solutions σ for the three stresses. p1 , σ p2 , σ p3 And the corresponding stress direction: Where l1, l2, and l3 are the function values ​​of the directions corresponding to the principal stresses; S15. Based on the Runge-Kutta numerical integration method, the tracking of the stress trace is simulated according to the calculated stress and the corresponding stress direction, and the position of the stress trace is gradually updated to calculate the path of the stress trace.

3. The method for designing a variable-size reinforced structure based on stress traces according to claim 2, characterized in that: In step S14, in order to improve the accuracy of numerical integration when generating stress traces, k2 is introduced as an intermediate prediction point for the second-order Runge-Kutta method. The tracing steps of the stress traces are: In the formula, h is the iteration step length, y n is the stress state of the current seed point, y n+1 is the state of the next tracking point, k1 is used to represent various information of the calculated prediction point, and k2 is used to represent various information of the calculated intermediate point.

4. The method for designing a variable-size reinforced structure based on stress traces according to claim 3, characterized in that: Step S15 also includes displaying the primary and secondary stress traces of the structure through visualization technology, and shorter stress lines are filtered because they cannot fully express the main force transmission paths inside the material.

5. The method for designing a variable-size reinforced structure based on stress traces according to claim 1, characterized in that: In step S2, the stress trace graph is converted into a voxel unit model, each voxel unit is given a vary attribute, and the voxel unit with vary being 1 is obtained to obtain the voxel unit on the stress trace trajectory. The specific process includes the following steps: S21, converting the stress trace graph into a voxel unit model through the STL model, discretizing the STL model into a hexahedral voxel unit model, each unit having a unique unit number; S22, extracting the unit number passing through each stress trace on the two-dimensional plane figure, and identifying the intersection unit of the stress trace and the voxel unit; S23. Assign a vary attribute to each voxel unit. The vary attribute of the unit on the stress line is recorded as 1, indicating that the unit is part of the stress line trajectory. On the contrary, for the unit not on the stress line, the vary attribute is recorded as 0, indicating that the unit is not on the stress line trajectory, thereby obtaining a voxel unit with a vary attribute of 1, and obtaining a voxel unit on the stress trace.

6. The method for designing a variable-size reinforced structure based on stress traces according to claim 1, characterized in that: In step S3, a variable height and variable thickness unit voxel model is constructed based on the voxel unit model. The specific process includes the following steps: S31, constructing variable height units based on the voxel model, assigning height attribute values ​​to all units in the voxelized model: the bottom unit of the model is assigned attribute 0, the minimum height unit that forms a rib together with the bottom unit is assigned attribute 1, and the unit that can be freely added or deleted is assigned attribute 2; S32, constructing variable thickness units based on the voxel model, and assigning thickness attribute values ​​to all units in the voxelized model: assigning attribute 3 to non-deletable thickness units, and assigning attribute 4 to freely added or deleted thickness units; S33. During the optimization of the rib height and thickness, the outer surface unit properties of the variable height and variable thickness units are used to determine whether the units can be added or deleted.

7. The method for designing a variable-size reinforced structure based on stress traces according to claim 1, characterized in that: In step S4, the initial height and initial thickness of the reinforcing ribs are designed according to the average stress magnitude of the stress trace, so that the size of the ribs matches the stress distribution of the structure. The specific process includes the following steps: S41. Number all stress lines in the two-dimensional graph and calculate the average stress magnitude of each stress trace. The calculation formula is: In the formula, i represents the number of stress traces; represents the average stress magnitude of the i-th stress trace; n i Represents the total number of elements passing through the i-th stress line; S42, according to the calculated stress magnitude σ mean Define the stress threshold threshold, and divide the model into several variable height and variable thickness optimization areas according to the threshold. If there are A optimization areas, then A-1 stress threshold thresholds need to be defined. The stress threshold threshold is calculated by the following formula: S43, according to the average stress The stress traces are sorted, and the initial height and initial thickness of the optimization area are designed according to the average stress sorting results. The initial height and initial thickness of different optimization areas are determined by comparing the average stress value of each stress line with the threshold. If there are three optimization areas, the specific formula is as follows: Where x is the minimum size of the thin-walled structure, and x1, x2, and x3 are custom initial size parameters.

8. The method for designing a variable-size reinforced structure based on stress traces according to claim 1, characterized in that: Step S5 specifically includes: designing the size of variable height and variable thickness ribs by using the BESO topology optimization method to obtain a variable size reinforced structure, specifically including: based on the construction of a variable height and variable thickness unit voxel model, given boundary conditions, load conditions and optimized volume fractions, designing the size of variable height and variable thickness ribs by using the BESO topology optimization method to obtain a variable size reinforced structure, and the expression of the optimization problem is as follows: Find:x={x1,x2,…x n T } Min:C=F T U Where x is the cell density matrix, x n is the design variable of the nth unit, where a design variable of 0.001 means that the unit needs to be deleted, i.e., it is an empty unit, and a design variable of 1 means that the unit is a solid unit; K is the overall stiffness matrix of the structure; U is the displacement matrix; F is the overall force matrix of the structure; C represents the flexibility of the structure; V0 is the volume before structural optimization; v f To optimize the volume fraction; v i is the volume of the ith unit.

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