A multiple bidirectional finite element iterative form-finding analysis method for concave lifting airbags used in aircraft lifting

Abstract

The present invention discloses a multiple bidirectional finite element iterative form-finding analysis method for a concave lift airbag used for aircraft jacking. The method relates to the technical field of aircraft concave lift airbag equipment. The method first performs nonlinear finite element inverse iterative form-finding to determine the airbag's zero-state geometry. The geometry in the designed molding state is used as the zero-state geometry, and a finite element model is established, ultimately obtaining a zero-state geometry that meets the designed molding state. Then, nonlinear finite element forward iterative form-finding is performed to determine the number of airbag layers. The zero-state geometry that meets the design requirements is used as the zero-state geometry of the topmost airbag layer, the first layer. Based on this geometry, the zero-state geometries of the remaining airbag layers, the second to the Nth layers, are established. A finite element model of the entire airbag is constructed, and the zero-state geometries and number of airbag layers of the remaining layers that meet the design force requirements are obtained. The method can obtain an aircraft concave lift airbag that fits the aircraft's outer contour, meeting the design requirements for the geometry, and also obtain a reasonable number of lift airbag layers, meeting the design requirements for the force.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft concave lifting airbag equipment, and in particular to a multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting. Background Art

[0002] Aircraft lifting airbags can play a significant role in areas such as aircraft handling, aircraft maintenance, testing, and emergency rescue. Lifting airbags have the advantages of short manufacturing time, fast molding speed, mass production, low cost, and high safety. In addition, they are foldable when not inflated, highly adaptable, and have low requirements for supporting structures and foundations. The aircraft concave lifting airbag is a flexible structural system that relies on the pressure difference between the inner and outer surfaces formed by the gas filled inside the airbag and the external air pressure to generate prestress on the membrane surface, so that the overall structure has a certain rigidity and can bear the load. During the molding process, the aircraft concave lifting airbag will produce large displacements, internal force redistribution, and exhibit strong geometric nonlinear characteristics. The aircraft concave lifting airbag needs to ensure that its shape after inflation matches the outer contour of the aircraft surface. Therefore, the shape-finding of the aircraft concave lifting airbag is the key to realizing the function of this structural system.

[0003] When analyzing the concave lift airbag of an aircraft, existing form-finding technology can only find the zero-state geometry corresponding to the established target design configuration through finite element analysis and iterative calculations. This means that the top layer of the concave lift airbag of the aircraft fits against the belly of the aircraft, while the shapes of the remaining airbag layers cannot be reasonably determined using existing form-finding technology. Furthermore, the concave lift airbag of an aircraft is a multi-layer composite structure, and its stress characteristics are affected by both the number of airbag layers and the shapes of each layer. Existing form-finding technology cannot simultaneously find a reasonable number of airbag layers and a reasonable zero-state geometry for each airbag layer while meeting the target design configuration and target stress requirements. Therefore, traditional form-finding technology applied to the concave lift airbag of an aircraft cannot meet the design requirements. Summary of the Invention

[0004] The purpose of the present invention is to provide a multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting, so as to solve the problems existing in the above-mentioned prior art. The form-finding analysis method is a multiple bidirectional finite element iterative form-finding method, including a nonlinear finite element inverse iterative form-finding determined by the zero-state geometric configuration of the airbag and a nonlinear finite element forward iterative form-finding determined by the number of airbag layers. Through this form-finding analysis method, it is possible to obtain a concave lifting airbag of an aircraft that fits the outer contour of the aircraft, meeting the design requirements of the aircraft concave lifting airbag for the geometric shape, and to obtain a reasonable number of lifting airbag layers, meeting the design requirements of the aircraft concave lifting airbag for the force.

[0005] In order to achieve the above technical objectives, the technical solution adopted by the present invention is:

[0006] A concave lifting airbag for aircraft lifting is subjected to multiple bidirectional finite element iterations for form-finding analysis. After the concave lifting airbag is inflated, the middle portion of the upper surface is concave, forming an arc that adapts to the shape of the aircraft body. The form-finding analysis method for the concave lifting airbag specifically includes the following steps:

[0007] Step 1: Design a concave lifting airbag. After the concave lifting airbag is inflated, the middle portion of the upper surface is concave, forming an arc that adapts to the shape of the aircraft body. The geometric configuration of the concave lifting airbag in the designed forming state is used as the geometric configuration of the zero state.

[0008] Step 2: Establishing a finite element model of the airbag geometry using the zero-state geometry, design material parameters, and design boundary conditions;

[0009] Step 3: Applying the design air pressure and deadweight load to the finite element model of the airbag geometry, performing nonlinear finite element calculations, and obtaining the geometry of the initial state;

[0010] Step 4: Compare the geometric configuration of the designed molding state with the geometric configuration of the initial state to determine whether the deformation of the latter is within an acceptable error range. If so, the geometric configuration of the zero state corresponding to the initial state is the concave lifting airbag geometric configuration that meets the design requirements; if not, the geometric configuration of the zero state is corrected according to the difference between the geometric configuration of the zero state and the geometric configuration of the initial state, and return to step 2 to finally find the geometric configuration in the zero state that meets the geometric configuration of the designed molding state;

[0011] Step 5: The zero-state geometric configuration corresponding to the designed molding state geometric configuration is used as the zero-state geometric configuration of the topmost airbag layer. The thickness h of each airbag layer is determined. Initially, the total number of airbag layers is set to N = 2.

[0012] Step 6: Based on the zero-state geometric configuration of the first layer of airbags, the zero-state geometric configurations of the remaining second to N layers of airbags are sequentially established, and these N layers of airbags are stacked from top to bottom in the order of 1 to N;

[0013] Step 7: Establish a finite element model of each airbag layer based on its geometric configuration and design material parameters. Assemble the finite element models of each airbag layer based on design interactions and design boundary conditions to establish an overall finite element model of the N-layer airbag.

[0014] Step 8: Apply the design air pressure and deadweight load to the overall finite element model, perform nonlinear finite element calculations, and obtain the initial state of the overall airbag;

[0015] Step 9: Apply the designed air pressure, deadweight load, and designed external load to the overall finite element model, perform nonlinear finite element calculations, and obtain the load state of the overall airbag;

[0016] Step 10. Compare the changes in the stress of the airbag membrane surface in the initial state and the loaded state of the overall airbag to determine whether the changes in the stress of the airbag membrane surface meet the design airbag force requirements. If the design airbag force requirements are met, the number of airbag layers N is the number of layers that meet the design airbag force requirements; if the design airbag force requirements are not met, set the number of airbag layers N = N + 1, return to step 6, and finally find the number of layers that meet the design airbag force requirements.

[0017] The above steps 1 to 4 constitute a nonlinear finite element inverse iterative form-finding method for determining the zero-state geometric configuration of the airbag, and the above steps 5 to 10 constitute a nonlinear finite element forward iterative form-finding method for determining the number of airbag layers.

[0018] To optimize the technical solution, further improvements include:

[0019] In step 2, the boundary conditions include the constraint conditions between the concave lifting airbag and the aircraft body and the constraint conditions between the concave lifting airbag and the ground or the ground mat.

[0020] In step 3, step 8 and step 9, the design air pressure includes the external atmospheric pressure and the air pressure filled in the concave lifting airbag structure; the deadweight load refers to the gravity load of the concave lifting airbag structure itself.

[0021] In step 4, the geometric configuration of the designed molding state is compared with the geometric configuration of the initial state to determine whether the deformation of the latter is within the acceptable error range. The specific method is to extract the node coordinates (x aim ,y aim ,z aim ), the node coordinates of the concave lifting airbag in the zero state (x0, y0, z0) and the node coordinates of the concave lifting airbag in the initial state (x p ,y p ,z p ), with (x aim ,y aim ,z aim )-(x p ,y p ,z p ) to obtain the coordinate difference (Δx, Δy, Δz), and by comparing and analyzing the coordinate difference (Δx, Δy, Δz) with the given inverse iterative analysis termination judgment threshold ε1, it is determined whether the geometric configuration of the initial state of the concave lifting airbag is within an acceptable error range.

[0022] In step 4, the specific method for correcting the zero-state geometric configuration is: let the node coordinates of the concave lifting airbag in the state (x0, y0, z0) = (x0, y0, z0) + (Δx, Δy, Δz) to obtain the corrected zero-state geometric configuration.

[0023] The design material parameters in step 2 and step 7 include the material properties and cross-sectional characteristics of each structural component of the concave lifting airbag.

[0024] The design interactions in step seven include the interaction between the topmost concave lifting airbag and the aircraft body, the interaction between adjacent layers of airbags, and the interaction between the bottommost airbag and the ground or floor mat. The design boundary conditions include the constraints between the airbag and the aircraft body, and the constraints between the airbag and the ground.

[0025] In step nine, the design external load refers to the gravity load from the aircraft body borne by the airbag structure.

[0026] In step 10, the specific method for judging whether the stress change of the airbag membrane surface meets the design airbag force requirements is as follows: according to the initial state of the entire airbag, the stress value σ of each node on the membrane surface of the top airbag structure of the entire airbag is obtained. pj According to the load state of the whole airbag, the stress value of each node on the membrane surface of the top airbag structure of the whole airbag is obtained. qj The ratio μ of the area where the stress change of the membrane surface of the top airbag structure in the initial state and the loaded state exceeds K to the total area of ​​the membrane surface of the top airbag structure in the initial state and the loaded state of the overall airbag structure is compared with the given positive iterative analysis termination judgment threshold ε2 to judge whether the stress change of the overall airbag structure when the number of layers is N meets the design airbag force requirements, where K=(σ qj -σ pj ) / σ pj .

[0027] The value of K is 0.3.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention uses multiple bidirectional finite element iterative form-finding cycles to find a reasonable number of airbag layers and a reasonable zero-state geometry for each airbag layer, while meeting the target design configuration and target load requirements. First, a nonlinear finite element inverse iterative form-finding cycle is performed to determine the zero-state geometry of the airbag. The geometry of the designed molding state is used as the zero-state geometry, and a finite element model is established. The difference between the initial geometry and the designed molding state geometry calculated by finite element analysis is used as the termination criterion for the inverse iterative cycle, ultimately achieving a zero-state geometry that meets the designed molding state. Next, a nonlinear finite element forward iterative form-finding cycle is performed to determine the number of airbag layers. The zero-state geometry that meets the design requirements is used as the zero-state geometry of the topmost airbag layer, the first. Based on this geometry, the zero-state geometries of the remaining airbag layers, the second through the Nth layers, are established. A finite element model of the entire airbag is constructed. The membrane surface stress changes in the initial and loaded states, calculated by finite element analysis, are used as the termination criterion for the forward iterative cycle, ultimately achieving the zero-state geometry and number of airbag layers that meet the design load requirements. Through this form-finding analysis method, we can obtain a concave lifting airbag that fits the outer contour of the aircraft and meets the design requirements of the aircraft's concave lifting airbag for the geometric shape, and we can also obtain a reasonable number of lifting airbag layers to meet the design requirements of the aircraft's concave lifting airbag for the force. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the implementation flow chart of the multiple bidirectional finite element iterative form-finding analysis method for aircraft concave lifting airbags. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative efforts are within the scope of protection of this application.

[0032] like Figure 1 As shown, the present invention provides a multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag for aircraft lifting, which is applied to the form-finding of the concave lifting airbag of the aircraft. The form-finding analysis method includes multiple bidirectional finite element iterative form-finding, and the multiple bidirectional finite element iterative form-finding includes nonlinear finite element inverse iterative form-finding determined by the zero-state geometric configuration of the airbag and nonlinear finite element forward iterative form-finding determined by the number of airbag layers.

[0033] The nonlinear finite element inverse iterative form-finding method for determining the zero-state geometric configuration of the airbag in the present invention comprises the following steps:

[0034] (1) The geometric configuration of the designed molding state is used as the geometric configuration of the zero state;

[0035] (2) Establishing a finite element model based on the zero-state geometry, design material parameters, and design boundary conditions to obtain the zero state;

[0036] (3) Apply the design air pressure and deadweight load to the finite element model, perform nonlinear finite element calculations, and obtain the initial state;

[0037] (4) Compare the geometric configuration of the designed molding state with the geometric configuration of the initial state to determine whether they are within an acceptable error range. If they are within the acceptable error range, the geometric configuration of the zero state corresponding to the initial state is the geometric configuration of the zero state corresponding to the designed molding state; if they are outside the acceptable error range, the geometric configuration of the zero state is corrected according to the difference between the geometric configuration of the designed molding state and the geometric configuration of the initial state, and return to step 2 to finally find the geometric configuration of the zero state that meets the design target requirements.

[0038] In step (1), the node coordinates (x aim ,y aim ,z aim ).

[0039] The design material parameters in step (2) include the material properties and cross-sectional characteristics of each structural component of the airbag; the boundary conditions include the constraints between the airbag and the aircraft body, and the constraints between the airbag and the ground or the floor mat.

[0040] In step (2), the node coordinates (x0, y0, z0) of the airbag structure in the zero state are extracted according to the zero state of the airbag structure.

[0041] The designed air pressure in step (3) includes the external atmospheric pressure and the air pressure filled into the airbag structure; the deadweight load refers to the gravity load of the airbag structure itself.

[0042] In step (3), the node coordinates (x p ,y p ,z p ).

[0043] In step (4), the node coordinates (x aim ,y aim ,z aim ) and the node coordinates of the initial state of the airbag structure (x p ,y p ,z p) to obtain the coordinate difference (Δx, Δy, Δz), and by comparing and analyzing the coordinate difference (Δx, Δy, Δz) with the given inverse iterative analysis termination judgment threshold ε1, it is judged whether the geometric configuration of the initial state of the airbag meets the requirements of the geometric configuration of the designed molding state.

[0044] In step (4), the geometric configuration of the zero state is adjusted according to the coordinate difference (Δx, Δy, Δz), so that the node coordinates of the airbag structure in the zero state are (x0, y0, z0) = (x0, y0, z0) + (Δx, Δy, Δz), and the corrected geometric configuration of the zero state is obtained.

[0045] The nonlinear finite element forward iteration form-finding method for determining the number of airbag layers in the present invention comprises the following steps:

[0046] (5) The zero-state geometric configuration that meets the design requirements found by the nonlinear finite element inverse iterative form-finding is used as the zero-state geometric configuration of the topmost layer of the airbag. The thickness h of each layer of the airbag is determined, and the total number of layers of the airbag is initially set to N = 2;

[0047] (6) Based on the zero-state geometric configuration of the topmost layer of airbags, the zero-state geometric configurations of the remaining layers from the second to the Nth layer of airbags are sequentially established;

[0048] (7) Establishing finite element models of each layer of airbags according to their geometric configurations and design material parameters;

[0049] (8) Assembling the finite element models of each layer of the airbag according to the design interaction and design boundary conditions to establish an overall finite element model of the N-layer airbag;

[0050] (9) Applying the design air pressure and deadweight load to the overall finite element model, performing nonlinear finite element calculations, and obtaining the initial state of the overall airbag;

[0051] (10) Apply the design air pressure, deadweight load, and design external load to the overall finite element model, perform nonlinear finite element calculations, and obtain the load state of the overall airbag;

[0052] (11) Compare the changes in the membrane stress of the entire airbag in the initial state and the loaded state to determine whether the designed airbag stress requirements are met. If the designed airbag stress requirements are met, the number of airbag layers N is the number of layers that meet the designed airbag stress requirements; if the designed airbag stress requirements are not met, set the number of airbag layers N = N + 1, return to step 6, and finally find the number of layers that meet the designed airbag stress requirements.

[0053] Step (5) According to the geometric configuration of the topmost first layer of airbag, the control starting point coordinates (x s1 ,y s1 ,z s1), control the midpoint coordinates (x m1 ,y m1 ,z m1 ), control the end point coordinate (x f1 ,y f1 ,z f1 ).

[0054] The control starting point coordinates (x si ,y si ,z si )=(x s1 ,y s1 ,((Ni) / N)*(z s1 -z m1 )+z mi ), control the midpoint coordinates (x mi ,y mi ,z mi )=(x m1 ,y m1 ,z m1 -(i-1)*h), control the end point coordinate (x fi ,y fi ,z fi )=(x f1 ,y f1 ,((Ni) / N)*(z f1 -z m1 )+z mi ).

[0055] In step (6), the control starting point coordinates (x si ,y si ,z si ), control the midpoint coordinates (x mi ,y mi ,z mi ), control the end point coordinate (x fi ,y fi ,z fi ), and obtain the zero-state geometric configuration of the i-th layer airbag.

[0056] The material parameters designed in step (7) include the material properties and cross-sectional characteristics of each structural component of the airbag.

[0057] Step (8) designing interactions includes the interaction between the topmost airbag and the aircraft body, the interaction between adjacent airbag layers, and the interaction between the bottommost airbag and the ground or floor mat. Designing boundary conditions includes the constraint conditions between the airbag and the aircraft body, and the constraint conditions between the airbag and the ground.

[0058] The designed air pressure in step (9) includes the external atmospheric pressure and the air pressure filled into the airbag structure; the deadweight load refers to the gravity load of the airbag structure itself.

[0059] Step (9) According to the initial state of the whole airbag, the stress value σ of each node on the membrane surface of the top airbag structure is obtained. pj .

[0060] The design air pressure in step (10) includes the external atmospheric pressure and the air pressure filled into the airbag structure; the deadweight load refers to the gravity load of the airbag structure itself; and the design external load refers to the gravity load from the aircraft body borne by the airbag structure.

[0061] Step (10) According to the load state of the entire airbag, the stress value σ of each node on the membrane surface of the top airbag structure is obtained. qj .

[0062] Step (11) is based on the stress value σ of each node on the membrane surface of the topmost airbag structure in the initial state of the overall airbag structure. pj and the stress value of each node on the membrane surface of the top airbag structure under the load state of the entire airbag structure σ qj The area of ​​the membrane surface stress change exceeding K on the top airbag structure in the initial state and the loaded state of the overall airbag structure is obtained, where the recommended value of K is 0.3.

[0063] Step (11) determines whether the stress change of the overall airbag structure when the number of layers is N meets the design airbag force requirements by comparing and analyzing the ratio μ of the area where the stress change of the membrane surface on the top airbag structure in the initial state and the loaded state exceeds K to the total area of ​​the membrane surface on the top airbag structure in the initial state and the loaded state of the overall airbag structure.

[0064] In step (11), the number of layers N of the overall airbag structure is adjusted based on the comparative analysis between the ratio μ and the given positive iterative analysis termination judgment threshold ε2, so that the number of layers N of the overall airbag structure is N=N+1, and the corrected number of layers of the overall airbag structure is obtained.

[0065] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting, characterized in that: The following steps are involved: Step 1: Design a concave lifting airbag. After the concave lifting airbag is inflated, the middle portion of the upper surface is concave, forming an arc that adapts to the shape of the aircraft body. The geometric configuration of the concave lifting airbag in the designed forming state is used as the geometric configuration of the zero state. Step 2: Establishing a finite element model of the airbag geometry using the zero-state geometry, design material parameters, and design boundary conditions; Step 3: Applying the design air pressure and deadweight load to the finite element model of the airbag geometry, performing nonlinear finite element calculations, and obtaining the geometry of the initial state; Step 4: Compare the geometric configuration of the designed molding state with the geometric configuration of the initial state to determine whether the deformation of the latter is within an acceptable error range. If so, the geometric configuration of the zero state corresponding to the initial state is the concave lifting airbag geometric configuration that meets the design requirements; If it is outside the acceptable error range, the geometric configuration of the zero state is corrected according to the difference between the geometric configuration of the zero state and the geometric configuration of the initial state, and the process returns to step 2 to finally find the geometric configuration of the zero state that satisfies the geometric configuration of the designed molding state. Step 5: The zero-state geometric configuration corresponding to the designed molding state geometric configuration is used as the zero-state geometric configuration of the topmost airbag layer. The thickness h of each airbag layer is determined. Initially, the total number of airbag layers is set to N = 2. Step 6: Based on the zero-state geometric configuration of the first layer of airbags, the zero-state geometric configurations of the remaining second to N layers of airbags are sequentially established, and these N layers of airbags are stacked from top to bottom in the order of 1 to N; Step 7: Establish a finite element model of each airbag layer based on its geometric configuration and design material parameters. Assemble the finite element models of each airbag layer based on design interactions and design boundary conditions to establish an overall finite element model of the N-layer airbag. Step 8: Apply the design air pressure and deadweight load to the overall finite element model, perform nonlinear finite element calculations, and obtain the initial state of the overall airbag; Step 9: Apply the designed air pressure, deadweight load, and designed external load to the overall finite element model, perform nonlinear finite element calculations, and obtain the load state of the overall airbag; Step 10. Compare the changes in the stress of the airbag membrane surface in the initial state and the loaded state of the overall airbag to determine whether the changes in the stress of the airbag membrane surface meet the design airbag force requirements. If the design airbag force requirements are met, the number of airbag layers N is the number of layers that meet the design airbag force requirements; if the design airbag force requirements are not met, set the number of airbag layers N = N + 1, return to step 6, and finally find the number of layers that meet the design airbag force requirements.

2. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 1 is characterized in that: In step 2, the boundary conditions include the constraint conditions between the concave lifting airbag and the aircraft body and the constraint conditions between the concave lifting airbag and the ground or the floor mat.

3. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 1 is characterized in that: In step 3, step 8 and step 9, the design air pressure includes the external atmospheric pressure and the air pressure filled in the concave lifting airbag structure; the deadweight load refers to the gravity load of the concave lifting airbag structure itself.

4. The method for multiple bidirectional finite element iteration form-finding analysis of a concave lifting airbag for aircraft lifting according to claim 1, characterized in that: In step 4, the geometric configuration of the designed molding state is compared with the geometric configuration of the initial state to determine whether the deformation of the latter is within the acceptable error range. The specific method is to extract the node coordinates (x aim ,y aim ,z aim ), the node coordinates of the concave lifting airbag in the zero state (x0, y0, z0) and the node coordinates of the concave lifting airbag in the initial state (x p ,y p ,z p ), with (x aim ,y aim ,z aim )-(x p ,y p ,z p ) obtains the coordinate difference (Δx, Δy, Δz), and by comparing and analyzing the coordinate difference (Δx, Δy, Δz) with the given inverse iterative analysis termination judgment threshold ε1, it is determined whether the geometric configuration of the initial state of the concave lifting airbag is within an acceptable error range.

5. The method for multiple bidirectional finite element iteration form-finding analysis of a concave lifting airbag for aircraft lifting according to claim 4 is characterized in that: In step 4, the specific method for correcting the zero-state geometric configuration is: let the node coordinates of the concave lifting airbag in the state (x0, y0, z0) = (x0, y0, z0) + (Δx, Δy, Δz) to obtain the corrected zero-state geometric configuration.

6. The method for multiple bidirectional finite element iteration form-finding analysis of a concave lifting airbag for aircraft lifting according to claim 1, characterized in that: The design material parameters in step 2 and step 7 include the material properties and cross-sectional characteristics of each structural component of the concave lifting airbag.

7. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 1 is characterized in that: The design interactions in step seven include the interaction between the topmost concave lifting airbag and the aircraft body, the interaction between adjacent layers of airbags, and the interaction between the bottommost airbag and the ground or floor mat. The design boundary conditions include the constraints between the airbag and the aircraft body and the constraints between the airbag and the ground.

8. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 1 is characterized in that: In step nine, the designed external load refers to the gravity load from the aircraft body borne by the airbag structure.

9. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 5, characterized in that: In step 10, the specific method for judging whether the stress change of the airbag membrane surface meets the design airbag force requirements is as follows: according to the initial state of the entire airbag, the stress value σ of each node on the membrane surface of the top airbag structure of the entire airbag is obtained. pj According to the load state of the whole airbag, the stress value of each node on the membrane surface of the top airbag structure of the whole airbag is obtained σ qj The ratio μ of the area where the stress change of the membrane surface of the topmost airbag structure in the initial state and the loaded state exceeds K to the total area of ​​the membrane surface of the topmost airbag structure in the initial state and the loaded state of the overall airbag structure is compared and analyzed with the given positive iterative analysis termination judgment threshold ε2 to judge whether the stress change of the overall airbag structure when the number of layers is N meets the design airbag force requirements, wherein K=(σ qj -σ pj ) / σ pj .

10. The multiple bidirectional finite element iterative form-finding analysis method for a concave lifting airbag used for aircraft lifting according to claim 9, characterized in that: The value of K is 0.3.

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