Design method for aircraft parts and manufacturing method for aircraft parts
The FEM-based method with 3D convex hull analysis simplifies and enhances the strength calculation of aircraft components, particularly for FRP materials, by identifying critical load cases efficiently, ensuring robustness and safety.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SUBARU CORP
- Filing Date
- 2022-09-28
- Publication Date
- 2026-06-02
AI Technical Summary
Existing methods for calculating the strength of aircraft components are complex and inefficient, particularly when dealing with numerous load cases, especially for components made of FRP materials with anisotropic properties.
A method using finite element analysis (FEM) to simulate aircraft components, representing loads as three-component forces, and employing 3D convex hull calculations to identify critical load cases, thereby simplifying the strength calculation process.
This approach allows for rapid identification of critical load cases, reducing unnecessary calculations and ensuring aircraft component strength, thus enhancing safety and efficiency in aircraft design and manufacturing.
Smart Images
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Abstract
Description
Technical Field
[0001] Embodiments of the present invention relate to a method for designing an aircraft component and a method for manufacturing an aircraft component.
Background Art
[0002] When the design of an aircraft component is completed, a check is made to determine whether the strength of the designed aircraft component is sufficient by calculating the strength of the aircraft component. In the strength calculation of an aircraft component, the strength is evaluated under various conditions that may occur, such as when the aircraft is flying under various flight conditions such as altitude, speed, and acceleration of the aircraft, or when the aircraft is receiving a load on the ground.
[0003] The maximum load that is expected to be applied to an aircraft component during the operation of the aircraft is called the limit load, and the load obtained by multiplying the limit load by a safety factor of 1.5 is called the ultimate load. And, it is required that the strength of the aircraft component remains within the allowable range even when the ultimate load is applied. That is, a strength margin is provided for each part of the aircraft component. Therefore, whether the strength of the aircraft component is sufficient can be confirmed by calculating the strength margin for each part.
[0004] There are thousands of patterns of loads that can act on an aircraft, and it is necessary to ensure that the strength is sufficient for all cases. However, since it is unrealistic to calculate the strength margin of aircraft components for every single one of a very large number of all cases, the strength margin of aircraft components is calculated by narrowing down to representative cases where a large load is applied.
[0005] In addition, as a technique related to the strength calculation of aircraft components, a device for calculating the load of aircraft components is known (see, for example, Patent Document 1).
Prior Art Documents
Patent Documents
[0006]
Patent Document 1
[0007] The present invention aims to simplify the calculation of the strength of aircraft components. [Means for solving the problem]
[0008] The aircraft component design method according to an embodiment of the present invention comprises the steps of: simulating the aircraft component to be designed with a finite element analysis model consisting of a plurality of elements; and creating design information for the aircraft component by determining the strength of each element by finite element analysis applied to the finite element analysis model so that the strength of each element remains within an acceptable range regardless of the load that may act on each of the plurality of elements. The finite element analysis model is configured such that the load applied to each element can be represented by a combination of three force components, and whether the strength of each element is within the acceptable range is confirmed only when the combination of the three force components representing the load that may act on each element is a critical combination.
[0009] Furthermore, the method for manufacturing an aircraft component according to the embodiment of the present invention involves manufacturing the aircraft component based on the design information of the aircraft component created by the aircraft component design method described above. [Brief explanation of the drawing]
[0010] [Figure 1] A flowchart showing the flow of a design method and a manufacturing method for aircraft parts according to the present invention. [Figure 2] This figure shows an example of modeling an aircraft wing using a two-dimensional (2D) finite element method (FEM) analysis model. [Figure 3] This diagram shows the three component forces (S, M, T) that occur on an aircraft wing when aerodynamic forces act on it. [Figure 4] A diagram plotting the possible combinations of bending moment and shear stress that can occur in the main wing. [Figure 5] A diagram plotting the possible combinations of torque and shear stress that can occur in the main wing. [Figure 6] Figure 2 shows the three components (Nx, Ny, Nxy) acting on the elements of the FEM analysis model. [Figure 7] This figure shows an example of plotting the combinations of the three component forces (Nx, Ny, Nxy) for each load case applied to the element of interest in the FEM analysis model in a three-dimensional (3D) coordinate space. [Figure 8] Figure 7 shows an example of calculating the 3D convex hull of point cloud data with three force components (Nx, Ny, Nxy). [Modes for carrying out the invention]
[0011] A design method and a manufacturing method for aircraft components according to embodiments of the present invention will be described with reference to the accompanying drawings.
[0012] Figure 1 is a flowchart showing the flow of a design method and a manufacturing method for aircraft parts according to an embodiment of the present invention.
[0013] The design method for aircraft components involves determining design parameters that represent the design information of aircraft components such as the main wings, and then creating design information for the aircraft components by confirming safety through strength calculations of the aircraft components specified by the determined design parameters. Furthermore, the manufacturing method for aircraft components involves manufacturing the aircraft components based on the created design information.
[0014] In the following explanation, we will mainly use the example of the main wing of a fixed-wing aircraft, but we may also apply to aircraft parts other than the main wing, such as the tail wing and fuselage, as well as aircraft parts of rotary-wing aircraft.
[0015] First, in step S1, values of a number of parameters representing the design information of aircraft parts are set. The main wing of a fixed-wing aircraft has a box structure in which upper and lower outer plates (panels) are reinforced with reinforcing members such as spars, ribs, and stringers. Therefore, values of various parameters are set, including the plate thickness, position, cross-sectional area, cross-sectional shape, and material of the outer plates and reinforcing members, as well as the presence or absence of a honeycomb structure.
[0016] In recent years, as materials for aircraft parts, in addition to metals such as aluminum and titanium, FRPs such as glass fiber reinforced plastics (GFRP) and carbon fiber reinforced plastics (CFRP) are often used.
[0017] A typical FRP is composed of a number of fiber reinforcement layers laminated with fiber orientation angles of 0°, 45°, 90°, or -45°. Therefore, for FRPs, there are various lamination configurations, such as unidirectional materials in which the fiber reinforcement layers are laminated so that the fiber orientation angles are all in the same direction, angle-ply laminates in which the fiber reinforcement layers are laminated by combining positive and negative orientation angles, and symmetric laminates in which the fiber reinforcement layers are laminated so that the fiber orientation angles are symmetric in the thickness direction. Therefore, when FRP is selected as at least part of the material, the fiber orientation angle in the fiber reinforcement layer and the lamination order of the fiber reinforcement layers also become one of the design parameters.
[0018] When all the values of the design parameters are set, the provisional design of the aircraft part is completed. When the design of the aircraft part is completed, it is necessary to perform a confirmation operation to check whether the strength of the aircraft part is sufficient by strength calculation. The strength calculation of an aircraft part is an operation to evaluate whether the strength is sufficient under various possible conditions, such as when the aircraft is flying under various flight conditions such as altitude, speed, and acceleration of the aircraft, as well as when the aircraft is receiving a load on the ground.
[0019] In particular, when at least a part of an aircraft component is constituted by FRP having anisotropy in strength, it is necessary to evaluate the strength of each part of the aircraft component. Therefore, the strength calculation of the aircraft component is performed by FEM analysis.
[0020] For this purpose, in step S2, the aircraft component to be designed is simulated by an FEM analysis model composed of a plurality of elements.
[0021] FIG. 2 is a diagram showing an example in which the main wing of an aircraft is modeled in a 2D-FEM analysis model 1.
[0022] As shown in FIG. 2, an aircraft component such as the main wing of an aircraft can be simulated by a 2D-FEM analysis model 1. That is, an aircraft component can be simulated by a 2D-FEM analysis model 1 in which a plurality of elements 2 are arranged in the 2D direction.
[0023] When the division direction of the element 2 in the FEM analysis model 1 is set to an appropriate 2D direction, the load applied to each element 2 can be represented by a combination of three component forces. For example, when simulating the main wing of an aircraft by a 2D-FEM analysis model 1 as illustrated in FIG. 2, the element 2 is not divided in the thickness direction of the main wing, and the element 2 can be divided generally in the length direction D1 of the main wing and in the direction D2 intersecting the length direction of the main wing according to the shape of the main wing. Note that, similar to a typical FEM analysis model, the directions D1 and D2 in which the elements 2 are arranged are not usually straight lines.
[0024] When the FEM analysis model 1 of the aircraft component is a model in which a plurality of elements 2 are arranged in the 2D direction, the load applied to each element 2 can be represented by three component forces including two-directional stress due to pressure received from the elements 2 adjacent in two directions and shear stress due to shear force received from the elements 2 adjacent in the length direction of the main wing. Therefore, it becomes possible to evaluate the strength for each element 2 based on the load represented by the three component forces.
[0025] Next, in step S3, all load cases assumed to be applied to the aircraft and the aircraft component are determined and input into the FEM analysis software.
[0026] Figure 3 shows the three component forces (S, M, T) generated on the main wing 11 of the aircraft 10 when aerodynamic forces act on it.
[0027] As shown in Figure 3, when aerodynamic forces act on the main wing 11 of the aircraft 10, a load corresponding to the aerodynamic force is applied to the main wing 11. The load applied to the main wing 11 can be expressed as a three-component force consisting of shear stress S, bending moment M, and torque T.
[0028] Figure 4 plots the possible combinations of bending moment M and shear stress S that can occur in the main wing 11, and Figure 5 plots the possible combinations of torque T and shear stress S that can occur in the main wing 11.
[0029] As shown in the 2D scatter plots in Figures 4 and 5, the load on the main wing, expressed as a combination of shear stress S, bending moment M, and torque T, changes depending on the aircraft's flight conditions, resulting in thousands of possible load cases.
[0030] Next, in step S4, a 2D-FEM structural analysis is performed on the 2D-FEM analysis model 1 for each assumed load case. To this end, the distribution of air pressure loads applied to aircraft components such as the main wing, which are simulated in the FEM analysis model 1, is calculated for each load case using computational fluid dynamics (CFD) analysis as needed. This makes it possible to determine the loads applied to each part of the aircraft components, such as the main wing, when the aircraft is in various flight conditions.
[0031] Specifically, the amount of deformation in the FEM analysis model 1, along with the load applied to each element 2, can be determined for each load case. Since the FEM analysis model 1 is 2D, as mentioned above, the load applied to each element 2 is represented by a three-component force consisting of three stress components.
[0032] Figure 6 shows the three force components (Nx, Ny, Nxy) acting on element 2 of the FEM analysis model 1 shown in Figure 2.
[0033] As shown in Figure 6, the load acting on each element 2 of the FEM analysis model 1 as a three-component stress can be expressed as a three-component force consisting of Nx, a load acting from adjacent elements 2 in the x-axis direction; Ny, a load acting from adjacent elements 2 in the y-axis direction; and Nxy, a load acting in the shear direction from adjacent elements 2 in the xy-plane, assuming that the local 2D arrangement direction for the element 2 of interest is the x-axis and y-axis.
[0034] When FEM analysis is performed, thousands of load cases, as illustrated in Figures 4 and 5, are calculated, corresponding to the number of element 2s in FEM analysis model 1. Therefore, it is impractical to perform strength calculations for all element 2s for all conceivable load cases.
[0035] Therefore, strength calculations are performed to select critical load cases that need to be verified from all possible load cases. However, even by referring to 2D scatter plots as exemplified in Figures 5 and 6, it is not easy to quickly and comprehensively select all critical load cases.
[0036] Therefore, in step S5, the three component forces (Nx, Ny, Nxy) acting on each element 2 of the FEM analysis model 1 are plotted in 3D coordinate space.
[0037] Figure 7 shows an example of plotting the combinations of the three component forces (Nx, Ny, Nxy) applied to element 2, the focus of the FEM analysis model 1, for each load case in 3D coordinate space.
[0038] As shown in Figure 7, when the load Nx acting on element 2 in the x-direction, the load Ny acting in the y-direction, and the shear load Nxy acting in the xy-plane are plotted in a 3D coordinate space with thousands of combinations of the three component forces (Nx, Ny, Nxy) for each load case, a 3D scatter plot is obtained. In other words, 3D point cloud data consisting of thousands of points representing the combinations of the three component forces (Nx, Ny, Nxy) is obtained.
[0039] However, even if aircraft component designers refer to 3D scatter plots and 3D point cloud data, it is still not easy to quickly and comprehensively select all critical load cases.
[0040] Therefore, in step S6, the 3D convex hull of the 3D point cloud data is determined. The 3D convex hull is the smallest convex polyhedron that encompasses all the points included in the 3D point cloud data. The algorithm for determining the 3D convex hull is publicly known, and solutions are commercially available.
[0041] Figure 8 shows an example of obtaining the 3D convex hull of the point cloud data of the three force components (Nx, Ny, Nxy) shown in Figure 7.
[0042] As shown in Figure 8, calculating the 3D convex hull allows us to identify the points located in the outermost layer of the 3D point cloud data. In other words, the points located at each vertex of the 3D convex hull can be extracted as points located in the outermost layer of the 3D point cloud data.
[0043] Each vertex of the 3D convex hull, that is, each point on the outermost shell of the 3D point cloud data, corresponds to a point where one of the three components of the force (Nx, Ny, Nxy) is constant, i.e., the maximum or minimum value in a one-dimensional scatter plot.
[0044] Therefore, if a point representing a combination of three force components (Nx, Ny, Nxy) is a vertex of the 3D convex hull, then at least one of the three force components (Nx, Ny, Nxy) can be considered a critical value that distinguishes whether a load case is critical or not. In other words, a combination of three force components (Nx, Ny, Nxy) that is a vertex of the 3D convex hull can be considered a critical load case.
[0045] Therefore, in step S7, load cases corresponding to each vertex of the 3D convex hull, i.e., points located in the outermost shell of the 3D point cloud data, are selected as critical load cases for which strength calculations should be performed.
[0046] Furthermore, since the 3D convex hull is calculated for each element 2 of the FEM analysis model 1, critical load cases will also be selected for each element 2. Therefore, if a combination of the three force components (Nx, Ny, Nxy) in at least one element 2 corresponds to a point in the outermost layer of the 3D point cloud data, that is, if at least one of the three force components (Nx, Ny, Nxy) reaches a critical value, it will be considered a critical load case. Also, if the point in the outermost layer of the 3D point cloud data can be identified, it is not necessary to derive the formula for the 3D convex hull or to display the 3D convex hull as an image on a display.
[0047] Thus, when plotting multiple combinations of values for the three components of force (Nx, Ny, Nxy), representing multiple loads that can act on each element 2 of the FEM analysis model 1, in a 3D coordinate space where the direction in which the values of the three components of force (Nx, Ny, Nxy) change is defined as the three axis directions, the combination of values for the three components of force (Nx, Ny, Nxy) corresponding to the point plotted in the outermost layer of the point cloud formed in the 3D coordinate space can be considered a critical combination.
[0048] Furthermore, by selecting critical load cases by extracting points located on the outermost layer of the point cloud data using 3D convex hull calculations from load cases assumed for the main wing of an aircraft, it was confirmed that approximately 100 critical load cases could be selected from approximately 2000 possible load cases.
[0049] Once the selection of critical load cases is complete, in step S8, strength calculations for each element 2 are performed, limited to the critical load cases.
[0050] Aircraft components are required to have sufficient strength to withstand the ultimate load, which is the maximum load expected to be applied to the aircraft components during aircraft operation, multiplied by a safety factor of 1.5. In other words, each part of the aircraft component must be given the necessary strength margin by setting a safety factor. Therefore, by calculating the strength margin of each element 2 in FEM analysis model 1, it is possible to evaluate whether the strength of each element 2 is sufficient.
[0051] Therefore, the strength margin in each element 2 of the FEM analysis model 1 is calculated. The strength of each part of an aircraft component is expressed by multiple evaluation parameters such as compression buckling load, shear buckling load, load that causes crunching failure (local buckling), Euler buckling load (long column buckling load), and material strength, except in cases of special designs such as post-buckle designs that allow buckling of FRP under loads below the ultimate load. Note that buckling load is the load that causes buckling. Furthermore, material strength can be expressed as the yield stress of the material in compression, tension, shear, and surface pressure.
[0052] Therefore, the strength margin in each element 2 is calculated for each evaluation parameter. That is, the strength margin is calculated between the load represented by the three force components (Nx, Ny, Nxy) corresponding to the critical load case and the value of the strength evaluation parameter applied to each element 2.
[0053] Then, in step S9, it is determined whether the strength margin of each element 2 in the FEM analysis model 1 is within the acceptable range, specifically whether the safety factor is above the lower limit for all critical load cases. In other words, whether the strength of each element 2 in the FEM analysis model 1 is within the acceptable range is checked only when the combination of the three force components (Nx, Ny, Nxy) representing the load that can act on each element 2 is a critical combination.
[0054] Furthermore, if the strength margin of at least one element 2 is insufficient for at least one critical load case, a design change is required to increase the strength of that element 2. In this case, the design parameters are reset in step S1. Then, the work and processing, including FEM structural analysis, from step 2 to step 8 is performed again.
[0055] On the other hand, if it is confirmed that the strength margins of all element 2 are sufficient for all critical load cases, then in step S10, the set design parameters are finalized as design information for the aircraft component. In other words, the design information for the aircraft component is finalized.
[0056] Thus, by performing FEM analysis on FEM analysis model 1 to create design information and calculate the strength of aircraft parts, it is possible to determine the strength of each element 2 such that the strength of each element 2 remains within an acceptable range regardless of the loads that may act on each of the multiple elements 2 of FEM analysis model 1.
[0057] Therefore, even if at least a portion of an aircraft component is made of FRP, by simulating the aircraft component, which is at least partly made of FRP, with FEM analysis model 1 and selecting an appropriate critical load case for each element 2, it is possible to determine the anisotropic strength for each element 2 that simulates the FRP portion. In other words, by dividing the aircraft component into multiple elements 2, it is possible to appropriately select a critical load case even if part of the material is FRP.
[0058] Once the design information for the aircraft component is finalized, in step S11, the aircraft component can be manufactured based on the design information.
[0059] The aircraft component design method described above involves performing strength calculations for each element 2 using FEM structural analysis, and by calculating the 3D convex hull, etc., the load cases subject to strength calculations are limited to critical load cases where the three component forces acting on element 2 are in a critical combination. Furthermore, the manufacturing method for the aircraft component involves manufacturing the aircraft component based on the design information created using the design method described above.
[0060] (effect) Therefore, according to the design method and manufacturing method for aircraft components, it is possible to eliminate the need for strength calculations of aircraft components for unnecessary load cases. In particular, by calculating the 3D convex hull of 3D point cloud data representing a large number of load cases, critical load cases for which strength calculations of aircraft components should be performed can be selected with high accuracy and efficiency. In other words, the minimum necessary critical load cases can be identified quickly through calculation. As a result, the safety of aircraft can be easily ensured.
[0061] In addition, instead of using 3D point cloud data of the three component forces (S, M, T) acting on the aircraft parts to select critical load cases, we used point cloud data of the three component forces (Nx, Ny, Nxy) acting on each element 2 arranged in a 2D array in the 2D-FEM analysis model 1. This makes it possible to quickly calculate the strength margin of each element 2 from the values of the three component forces (Nx, Ny, Nxy).
[0062] (Other embodiments) Although specific embodiments have been described above, these embodiments are merely examples and do not limit the scope of the invention. The novel methods and apparatus described herein can be embodied in various other forms. Furthermore, various omissions, substitutions, and modifications can be made in the forms of methods and apparatus described herein, without departing from the spirit of the invention. The attached claims and equivalents include such various forms and modifications as being encompassed within the scope and spirit of the invention. [Explanation of symbols]
[0063] 1. FEM Analysis Model 2 elements 10 aircraft 11 Main wing S shear stress M Bending moment T Torque Nx,Ny,Nxy Load (3 component force)
Claims
1. The steps include: simulating the aircraft component to be designed using a finite element analysis model consisting of multiple elements; The steps include creating design information for the aircraft component by determining the strength of each element by performing a finite element analysis on the finite element analysis model, such that the strength of each element remains within an acceptable range regardless of the load that may act on each of the aforementioned elements; In a design method for aircraft components having, A design method for aircraft parts, wherein the finite element analysis model is configured such that the load applied to each element can be represented by a combination of three force components, and the determination of whether the strength of each element is within the allowable range is limited to cases where the combination of three force components representing the load that can act on each element is a critical combination.
2. The method for designing aircraft components according to claim 1, wherein the critical combination is defined as the case in which at least one of the three force components reaches a critical value in at least one of the elements.
3. The method for designing an aircraft component according to claim 1, wherein when multiple combinations of the values of the three components of force, representing multiple loads that can act on each element, are plotted in a three-dimensional coordinate space with the direction in which the values of the three components of force change as three axes, the combination of the values of the three components of force corresponding to the point plotted on the outermost shell among the point cloud formed in the three-dimensional coordinate space is defined as the critical combination.
4. A method for designing an aircraft part according to claim 1, wherein the aircraft part is composed of at least a portion of fiber-reinforced plastic having anisotropy in strength, the aircraft part is simulated using the finite element method analysis model, and the strength of each element simulating the portion composed of fiber-reinforced plastic is determined to have anisotropy.
5. A method for manufacturing an aircraft component, comprising manufacturing the aircraft component based on design information of the aircraft component created by the aircraft component design method according to any one of claims 1 to 4.