A method for rapid design and optimization of openings on aircraft structures

Abstract

This invention belongs to the field of aircraft design and strength analysis technology, specifically relating to a rapid design and optimization method for openings in aircraft structures. The method involves: establishing a full-aircraft model for overall strength analysis; determining the location and size of the required openings on the finite element model; selecting a specific finite element region for analysis; analyzing the severe operating conditions of the finite element elements in this region; outputting the displacement and stress at the boundaries of the selected elements under severe operating conditions; importing the model and boundary conditions into software with a self-developed opening design and analysis module; performing optimized opening design and strength analysis; forming a reasonable opening reinforcement scheme; and outputting the calculation results. The method proposed in this invention can reduce weight, decrease local stress concentration, and delay or prevent the occurrence of cracks at the hole edge.

Description

Technical Field

[0001] This invention belongs to the field of aircraft design and strength analysis technology, specifically relating to a method for rapid design and optimization of openings in aircraft structures. Background Technology

[0002] Openings in flat or curved plates are very common in aircraft structures, serving various purposes: pipe through-holes for system piping; maintenance ports for easy inspection and repair; weight-reduction holes; holes necessary to meet various functional requirements; and holes for observation or personnel passage, etc. During load-bearing, cracks easily develop at the edges of these openings. Crack propagation can affect the overall load-bearing capacity of the structure. Therefore, openings are typically reinforced. For sheet metal structures, this reinforcement can involve flanging or adding reinforcing rings around the opening. For machined structures, bosses can be designed to reinforce the opening edges, thereby reducing stress levels. When reducing weight in aircraft structures or by creating openings in equipment piping, the hazards of stress concentration at the opening edges are mainly manifested in: the opening compromises structural integrity, causing load concentration in the opening area, significantly increasing stress, and thus increasing the risk of material fatigue and crack propagation. This stress concentration can lead to structural component failure, reducing the safety and reliability of the aircraft. Therefore, it is necessary to effectively prevent and mitigate the hazards of stress concentration at the hole edge through measures such as optimizing design, improving processing technology, and strengthening testing.

[0003] With the development of computational tools, simulation calculations have become more accurate and faster, allowing for increasingly detailed analysis of aircraft structures. Fatigue-critical components and structures with high local loads undergo detailed analysis to reduce local stress concentration. However, for general structures with numerous openings, the stress around the openings is multiplied by a coefficient, and small openings may be ignored. Currently, for aircraft designs with openings, such as large openings in main load-bearing structures, a full-aircraft model can be used to refine the opening area, or a sub-model can be used for calculation. Without detailed calculations for openings, directly considering coefficients and empirical reinforcement may reduce stress around the openings, but this could result in reinforced bosses with lower stress areas, increased weight, and suboptimal structural design. Furthermore, neglecting detailed calculations for openings may lead to cracks in non-fatigue-critical components. However, refining the numerous openings on an aircraft model across the entire aircraft is a significant workload. Summary of the Invention

[0004] The purpose of this invention is to propose a rapid design and optimization method for structural openings. This method allows for the design of openings on flat or curved surfaces. At locations requiring openings, the corresponding elements and high-stress calculation conditions of the full-machine finite element model are selected, outputting unit displacement / stress. While meeting the system's opening size requirements, various opening forms can be designed based on the element's stress conditions, maximizing the opening size and ensuring uniform stress distribution. Measures are taken to reduce stress at the opening edges, and the design of the edge reinforcement structure is reasonable. For example, circular holes can be reinforced with bosses. The height and width of the boss, as well as the chamfer at the bottom of the boss, need to be designed to reduce stress levels with minimal weight reduction or increase. The weight-saving approach involves designing larger openings, with the weight reduction less than the weight increase from the boss.

[0005] The technical solution of this invention: In order to achieve the above-mentioned objective, this invention provides a method for rapid design and optimization of openings in aircraft structures, comprising the following steps: Step S1: Establish a full-scale model and calculate the overall strength analysis; Step S2: Determine the location and size of the opening to be made on the finite element model; Step S3: Select a certain finite element region for analysis; Step S4: Analyze the severe working conditions of the finite element elements in this region; Step S5: Output the displacement and stress at the boundary of the selected element under severe conditions; Step S6: Import the model and boundary conditions into software with a custom-designed opening design and analysis module; Step S7: Perform optimized design and strength analysis of the opening; Step S8: Formulate a reasonable hole reinforcement scheme; Step S9: Output the calculation results.

[0006] Furthermore, in step S1, conventional full-machine finite element modeling is performed, and full-machine load conditions are applied and overall strength analysis of the entire machine is conducted.

[0007] Furthermore, in step S2, the coordinates of the opening and the structure that needs to be opened are determined, the corresponding structure is found on the finite element model, the unit position that coincides with the hole on the structure is found according to the coordinates, and then the unit position of the opening is determined according to the size of the hole.

[0008] Furthermore, in step S3, the selected finite element unit region is a plate element centered on the hole, and the surrounding elements are analyzed together. The selected region should have a hole edge reinforcement zone design range and the calculation constraint position should be a certain distance from the reinforcement zone.

[0009] Furthermore, in step S3, the selected finite element region should be as relatively regular in shape as possible, such as a quadrilateral region.

[0010] Furthermore, in step S4, the selected finite element unit region is analyzed for severe working conditions, and one or more working conditions with higher stress are selected.

[0011] Furthermore, in step S5, the selected finite element unit region, such as the four sides of a quadrilateral, is output, along with the displacement and stress of the nodes on the sides under severe conditions.

[0012] Furthermore, in step S6, the self-designed hole design and analysis module includes multiple boss reinforcement schemes. Different hole types (such as round holes, trapezoidal holes, elliptical holes, chamfered triangular holes, chamfered rectangular holes, and custom holes) and boss types (symmetric on both sides, asymmetrical on both sides, equal thickness on one side, unequal thickness on one side, and custom) can be selected, and the geometric feature parameters of the boss can be modified. The selected hole type can be designed, the hole edge can be chamfered, and the parameters of the hole and the chamfer can be modified.

[0013] Furthermore, in step S6, the self-compiled opening design and analysis module can use the selected finite element unit as the design area. After selecting the opening type, the design area designs the size of the opening. For areas that need reinforcement, the size of the boss and chamfer need to be designed. The designed model is converted into a three-dimensional structure. Mesh generation is selected, and the mesh will be automatically generated. Material properties are selected, and linear interpolation is used according to the displacement / force boundary conditions to constrain the nodes on the boundary of the three-dimensional solid element. The working condition can be selected to perform calculations.

[0014] Furthermore, in step S7, the design dimensions can be quickly adjusted, the adjusted model can be re-meshed, and the selected working conditions can be rapidly calculated and iterated.

[0015] Furthermore, in step S8, various types of bosses are used for design and analysis to find a solution with lower stress and lighter weight after hole reinforcement.

[0016] Furthermore, in step S9, this method can automatically generate a calculation report, which can be used as a design scheme report or a strength verification report. Advantages or positive effects compared to existing technologies: Unlike conventional methods, previous boss reinforcement schemes generally involved adding [a specific type of boss]. The main advantages are as follows: 1) Multiple opening types and boss types can be selected for design based on the opening requirements and stress distribution in the opening area. The parameters can be adjusted and the results can be calculated quickly.

[0017] 2) The shape and parameters of the boss can be adjusted and optimized to reduce stress concentration in the opening area and minimize weight.

[0018] 3) It can realize detailed design of openings in non-fatigue critical areas. Previously, the height and width of the boss and the chamfer were set according to the size of the hole based on experience. This method can realize the fine design of the boss and avoid stress concentration at the chamfer and the edge of the opening. Attached Figure Description

[0019] Figure 1 is a flowchart illustrating the specific implementation of a method for rapid design and optimization of structural openings. Figure 2 A schematic diagram of conventional aperture refinement analysis for a rapid design and optimization method of structural apertures; Figure 3 A schematic diagram showing the selection of the opening area and the output of calculation results under severe working conditions for a rapid design and optimization method for structural openings; Figure 4 A schematic diagram of a boss with unequal thickness on one side of a circular hole, which is a method for rapid design and optimization of structural openings. Figure 5 A schematic diagram of the three-dimensional solid and mesh generation and boundary conditions for a rapid design and optimization method for structural openings; Figure 6 A schematic diagram of stress distribution and safety margin for a rapid design and optimization method for structural openings; Figure 7 A schematic diagram comparing the results of a rapid design and optimization method for structural openings with no reinforcement and different reinforcement methods; Figure 8 This is a schematic diagram of the analysis report after the reinforcement of a structural opening, which is a rapid design and optimization method for structural openings. Detailed Implementation The technical solution of the present invention will be clearly and completely described in conjunction with the accompanying drawings and embodiments, and the process is as follows: Figure 1 As shown in the figure. The following is a detailed explanation of the method for rapid design and optimization of structural openings in this embodiment, using a flat plate with a round hole and a reinforcing boss design.

[0020] The detailed model for hole reinforcement can be implemented in two ways on the full-machine finite element model: one is to use plate elements to refine the hole area; the other is to use solid elements for refinement. Specific methods are as follows: Figure 2As shown. Refining the opening area using plate elements and creating bosses allows for relatively easy calculation by changing the circle size and boss thickness, but it cannot reflect the boss chamfer information. Using solid elements (tetrahedral elements) can display detailed structural information, but after changing parameters, it requires re-importing the geometry, meshing, and connecting the mesh to surrounding nodes; adjusting parameters is time-consuming and laborious. Unless it's a critical structure with large openings, these two methods are not suitable for detailed verification. For aircraft with numerous openings, large-scale calculations are difficult, and refined design and optimization are impossible. This method is aimed at... Figure 2 The design process for one hole is described in detail.

[0021] Step 1: Establish a full-scale model and calculate the overall strength analysis.

[0022] Following the conventional finite element modeling and calculation method for the entire aircraft, a finite element model of the entire aircraft is established, and loads under the entire aircraft load conditions are applied. Then, the overall strength analysis of each structural component of the entire aircraft is performed, such as displacement and stress / strain analysis.

[0023] Step 2: Determine the location and size of the opening on the finite element model.

[0024] Determine the coordinates of the opening and the structure to be opened. Locate the corresponding structure on the finite element model. Based on the coordinates, find the element position on the structure that coincides with the opening. Then, based on the size of the opening, determine which element positions the opening belongs to. Step 3: Select a certain finite element region for analysis.

[0025] The selected finite element region is a plate element centered on the opening, with surrounding elements analyzed together. The selected region should include the design range of the reinforcement zone around the opening, and the calculation constraint positions should be at a certain distance from the reinforcement zone. When using displacement / force boundary conditions, according to Saint-Venant's principle, the opening area should be at a certain distance from the boundary. The selected finite element region should ideally be a relatively regular shape. For example, in a stiffened panel, the opening will not be located at the location of the stiffeners; a quadrilateral region with the stiffeners as the boundary can be selected.

[0026] Step 4: Analyze the severe working conditions of the finite element elements in this region.

[0027] The maximum uniaxial stress and maximum von Mises stress of the plate element requiring perforation are determined by cloud maps and other methods. The calculation results for the corresponding working conditions are output by selecting elements that are at least 1.5 times the maximum size of the perforated plate grid.

[0028] Step 5: Output the displacement and stress of the selected element boundary under severe conditions.

[0029] Output the selected finite element region, such as the four sides of a quadrilateral, and output the displacement and stress at the nodes on the sides under severe conditions, such as... Figure 3 As shown. Figure 3 The four points in the diagram are control points for the opening area. The central quadrilateral opening represents approximately 1.5 times the area, and the four edges are the output force / displacement boundary conditions used as boundary constraints for detailed calculations. This step subdivides the relatively coarse mesh in the full-machine finite element model. The more nodes calculated on the boundaries, the more accurate the detailed analysis. Typically, in a full-machine finite element model, this mesh has only one cell, and only two corner points can be output per edge. After subdivision, five nodes are formed on each edge.

[0030] Step 6: Import the model and boundary conditions into the self-programmed opening design and analysis module. The analysis module can perform parametric design.

[0031] The self-developed hole design and analysis module allows you to use the selected finite element units as the design area. After selecting the hole type, the module designs the hole size within the design area. It also designs the size and chamfer of the boss at the location where hole reinforcement is needed. The designed model is converted into a 3D structure. You can then select mesh generation, which will automatically generate the mesh. After selecting material properties, linear interpolation is used based on displacement / force boundary conditions to constrain the nodes on the boundary of the 3D solid element. By selecting the working condition, you can calculate the stress at the hole edge.

[0032] First, you can select different hole types (round hole, trapezoidal hole, elliptical hole, chamfered triangular hole, chamfered rectangular hole, custom hole) and boss types (symmetrical on both sides, asymmetrical on both sides, equal thickness on one side, unequal thickness on one side, custom). This example uses a round hole with a boss of unequal thickness on one side for design. Figure 4 As shown. You need to input the left side of the center of the opening and the radius of the circle. For bosses with unequal thickness on one side, this refers to cases where the thickness of the boss and the thickness of the plate are not equal. Set the height, width, and bottom chamfer parameters of the boss. After designing the parameters, the 3D structure of the boss can be formed. Select the mesh size and the material of the structure, select the appropriate working conditions, and perform interpolation calculations on the boundary surfaces of the detailed model to obtain the safety margin of the opening area, such as... Figure 5 and Figure 6 As shown. By Figure 5 It can be seen that the displacement of the node on one side of the derived quadrilateral is applied to the structural boundary divided by the hexahedron after interpolation calculation.

[0033] As shown in this example, the plate thickness is 4mm, the radius of the opening is 20mm, the width of the boss is 15mm, the height is 10mm, and the chamfer is 3mm. After inputting the parameters, meshing is performed, aluminum alloy is selected as the material, and the boundary conditions for severe working conditions are imported for calculation.

[0034] Step 7: Perform optimized design and strength analysis of the opening.

[0035] Stress levels around holes can be controlled through stress control or safety margin control, based on the importance of the structure. If the safety margin is too large for all operating conditions, the boss parameters in step 6 can be modified to increase the radius of the circular hole. If the result from the contour plot shows lower stress on the outer side of the boss in the width direction, the width and height of the boss can be reduced. This can be done by directly modifying the parameters in the sketch and performing calculations. When the calculated safety margin reaches the desired value, the reinforcement scheme is considered the optimized and reasonable solution.

[0036] When the safety margin is large under all operating conditions, the parameters in step 6 can be adjusted: increase the radius of the opening circle or decrease the height / width of the boss. After the parameters are modified, the safety margin can be quickly calculated using the above method.

[0037] If the stress on the boss is found to be low during inspection, the height of the boss can be reduced to 8mm. After recalculation, the safety margin is reduced to about 0.2 compared with the previous results, which is considered to meet the strength design requirements.

[0038] Step 8: Develop a reasonable hole reinforcement plan.

[0039] The latest boss design features a 20mm radius opening, a 15mm width, a 10mm height, and a 3mm chamfer.

[0040] For general boss reinforcement designs, if the calculated safety margin is too large, the radius of the circular hole can be increased. If, due to area limitations, one side of the enlarged hole approaches the rib, other boss types should be used for design and analysis to find a solution with lower stress and lighter weight after reinforcement. For example, with a circular hole, the stress on both sides is lower, so an elliptical hole with a boss can be used. Alternatively, based on the stress distribution, the opening in the low-stress area can be enlarged using a custom method, followed by peripheral reinforcement. The optimal solution is one that achieves a reasonable stress distribution and the lowest weight.

[0041] In the specific implementation of this invention, the optimization process proposed above can reduce weight, reduce local stress concentration, delay the appearance of hole edge cracks, or prevent cracks from appearing.

[0042] The setup is achieved by using the same diameter for the round hole boss and different chamfer thicknesses and thickness directions. Figure 7 As shown in Table 1, the maximum stress occurs at the edge of the hole. Three points were selected from this location for comparison, and the reduction rate of the maximum stress was compared with that of the unreinforced case.

[0043] Table 1 Comparison of maximum stress values ​​for different models

[0044] The analysis uses symmetrical loads. A circular boss can be selected. With a fixed boss diameter and bottom chamfer, the thickness and whether the boss is reinforced on one or both sides can be changed directly to quickly calculate and compare results. For an elliptical boss, the major and minor axis parameters need to be set; other parameters remain the same.

[0045] Step 9: Output the calculation results.

[0046] This method can automatically generate calculation reports, which can be used as design schemes to guide the design of opening reinforcement, or as strength verification reports to conduct detailed analysis of opening reinforcement. The resulting calculation result analysis report is as follows: Figure 8 As shown.

[0047] Advantages or positive effects of this invention compared to existing technologies Compared to existing technologies, it has two advantages: I. Optimized Design. For openings of the same size, different boss designs are needed under varying stress conditions. Conventional methods rely on empirical design, primarily based on the opening size, the ratio of boss thickness to plate thickness, and the ratio of width to hole diameter. Sometimes, increasing the volume of the boss can fill the hole's volume, achieving the same strength as the original un-opened plate. However, this approach can sometimes result in overly thick and wide bosses, increasing weight, or unsuitable parameters, such as a small bottom chamfer leading to high stress. This crude design approach is unsuitable for aircraft reliability and long service life requirements. Therefore, a more refined design is needed to reduce localized stress, delay crack initiation, or prevent cracking altogether.

[0048] Second, the analysis is more accurate or faster. There are two common methods for calculating bosses in the full machine model. One is to use plate elements, which is more accurate than plate element calculation. The other is to use solid elements, which requires calculation in the full machine model or importing the boundary conditions into other software for hole calculation. The calculation speed of the latter is much slower than this method.

[0049] The above description is merely a specific embodiment of the present invention, providing a detailed description of the invention. Parts not covered herein are conventional techniques. However, the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for rapid design and optimization of openings in aircraft structures, characterized in that, Includes the following steps: Step S1: Establish a full-scale model and calculate the overall strength analysis; Step S2: Determine the location and size of the opening to be made on the finite element model; Step S3: Select a certain finite element region for analysis; Step S4: Analyze the severe working conditions of the finite element elements in this region; Step S5: Output the displacement and stress at the boundary of the selected element under severe conditions; Step S6: Import the model and boundary conditions into software with a custom-designed opening design and analysis module; Step S7: Perform optimized design and strength analysis of the opening; Step S8: Formulate a reasonable hole reinforcement scheme; Step S9: Output the calculation results.

2. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S1, conventional full-aircraft finite element modeling is performed, and full-aircraft load conditions are applied, followed by overall strength analysis of the entire aircraft.

3. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S2, the coordinates of the opening and the structure that needs to be opened are determined. The corresponding structure is found on the finite element model. The unit position that coincides with the hole on the structure is found according to the coordinates. Then, according to the size of the hole, it is determined which units the opening position belongs to.

4. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S3, the selected finite element unit region is the plate element centered on the hole, and the surrounding elements are analyzed together. The selected region should have the design range of the hole edge reinforcement area and the calculation constraint position should be at a certain distance from the reinforcement area.

5. The method for rapid design and optimization of openings in aircraft structures as described in claim 4, characterized in that, In step S3, the selected finite element region should be as relatively regular in shape as possible.

6. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S4, the selected finite element unit region is analyzed for severe working conditions, and one or more working conditions with high stress are selected.

7. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S5, the selected finite element unit region, such as the four sides of a quadrilateral, is output, along with the displacement and stress of the nodes on the sides under severe conditions.

8. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S6, the self-compiled hole design and analysis module includes multiple boss reinforcement schemes. Different hole types and boss types can be selected, and the geometric feature parameters of the boss can be modified. The selected hole type is designed, the hole edge is chamfered, and the parameters of the hole and the chamfer are modified.

9. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S6, the self-compiled hole design and analysis module takes the selected finite element unit as the design area, selects the hole type, designs the hole size in the design area, and designs the size and chamfer of the boss for areas that need reinforcement. The designed model is converted into a three-dimensional structure, the mesh is automatically generated, the material properties are selected, and linear interpolation is used according to the displacement and force boundary conditions to constrain the nodes on the boundary of the three-dimensional solid element. The working condition can be selected to perform the calculation.

10. The method for rapid design and optimization of openings in aircraft structures as described in claim 1, characterized in that, In step S7, the design dimensions can be quickly adjusted, the adjusted model can be re-meshed, and the selected working conditions can be quickly calculated and iterated.

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