Fluid-solid coupling mechanical analysis method for large-span aircraft ground agile protection structure

Abstract

The invention belongs to the technical field of aircraft ground support facilities, and particularly relates to a fluid-solid coupling mechanical analysis method for a large-span aircraft ground agile protection structure. According to the method, on the basis of an arbitrary Lagrange-Euler (ALE) algorithm, by integrating HyperMesh pretreatment and an LS-DYNA solver, high-precision simulation of fluid-structure interaction response of the plane ground agile protection structure under the action of a wind load is achieved. Comprising the following steps: establishing an aircraft ground agile protection structure finite element model and carrying out component division and grid division; constructing a semi-cylindrical air drainage basin and setting fluid material attributes and boundary conditions; and defining a fluid-solid coupling interface, and carrying out explicit dynamic calculation by adopting a bidirectional coupling algorithm. According to the method, the problems of low simulation precision and poor convergence of a flexible large-span structure in a traditional method are effectively solved, the stress, deformation and stability of the plane ground agile protection structure at different wind speeds can be accurately evaluated, and a reliable basis is provided for wind resistance design and safety evaluation.

Description

Technical Field

[0001] This invention belongs to the technical field of aircraft ground support facilities, specifically relating to a fluid-structure interaction mechanics analysis method for agile ground protection structures for large-span aircraft. Background Technology

[0002] Large-span agile aircraft ground protection structures offer significant advantages such as ease of transportation, loading, and rapid erection, leading to their increasingly widespread application. However, the surface of these structures is typically a flexible inflatable membrane. This flexible membrane undergoes significant deformation under wind loads, resulting in drastic changes in the fluid domain boundaries. Conventional Eulerian fluid calculations struggle to accurately capture these aerodynamic boundaries, while Lagrangian solid models are prone to computational instability due to mesh distortion. Furthermore, the nonlinearity, plastic deformation, and viscoelastic behavior of the membrane material itself are further coupled into the dynamic flow field, making conventional unidirectional or weakly coupled methods unable to accurately reflect the real physical processes. This is particularly evident in wind-induced vibration or flutter analysis, where significant simulation distortion and insufficient accuracy are observed. Summary of the Invention

[0003] To address the issues of low accuracy and poor convergence in traditional fluid-structure interaction (FSI) analysis methods for simulating large-span flexible structures such as aircraft ground agile protection structures, this invention provides a FSI mechanical analysis method for large-span aircraft ground agile protection structures. This method can accurately simulate the interaction between the wind field and the aircraft ground agile protection structure, providing an effective technical means for the design optimization and wind resistance safety assessment of aircraft ground agile protection structures.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A fluid-structure interaction (FSI) analysis method for a ground-based agile protection structure for large-span aircraft, comprising the following steps:

[0006] Step S110, Preprocessing of the structural finite element model: Import the geometric model of the aircraft ground agile protection structure into HyperMesh software, and divide the model into three major components: skin, inflatable structure, and end door; mesh the different components separately, using shell element models for the skin, end door, and inflatable structure, and select an appropriate mesh size range; assign material constitutive models to each component; set the element algorithm type, constrain boundary conditions and connection relationships, and set the hourglass control coefficient to suppress zero-energy modes;

[0007] Step S120, Flow Field Modeling and Setup: In HyperMesh, establish a semi-cylindrical air domain fluid model, enclosing the aircraft's ground-based agile protection structure and extending it to a sufficient length to ensure full development of the flow domain; define the fluid material as an ideal gas, and set the density, viscosity, and equation of state parameters; use a hexahedral dominant mesh to divide the fluid domain, refine the mesh in the near-wall region, and set an appropriate overall mesh size; specify inflow, outflow, and non-reflective boundary conditions, and set the wind speed profile and incoming flow direction to simulate wind loads; select the multi-material arbitrary Lagrange-Eulerian (ALE) element algorithm and configure the corresponding hourglass control;

[0008] Step S130, Fluid-structure Interaction Keyword Setting and Solving: Define fluid-structure interaction keywords in HyperMesh, set the surface of the aircraft ground agile protection structure as the coupling interface, and select the ALE algorithm for bidirectional coupling calculation; set the calculation time step, output time interval, and termination time; export the complete K file and submit it to the LS-DYNA solver for explicit dynamic calculation; monitor the solving process, and after completion, import the results into post-processing software to view the structural stress, deformation, flow field pressure distribution, and coupling response, and evaluate the safety and stability of the aircraft ground agile protection structure under different wind speeds.

[0009] The present invention has the following beneficial effects:

[0010] 1. This invention proposes a fluid-structure interaction mechanics analysis method for agile ground protection structures for large-span aircraft. By integrating HyperMesh preprocessing and LS-DYNA's ALE algorithm solution technology, it effectively solves the problems of insufficient simulation accuracy and difficulty in convergence of traditional methods for flexible large-span structures, and significantly improves the reliability and engineering applicability of the simulation.

[0011] 2. By dividing the components into meshes, setting material parameters differently, and modeling the flow field in detail, a high-fidelity simulation of the complex interaction between the aircraft ground agile protection structure and the wind field was systematically achieved, providing detailed data support for the wind-resistant design of the structure.

[0012] 3. The method described in this invention is both versatile and practical, and can be extended to the analysis of wind-induced response and stability of other inflatable flexible space structures, with good prospects for scientific research and engineering applications. Attached Figure Description

[0013] Figure 1 This is a flowchart of a fluid-structure interaction mechanics analysis method for a large-span aircraft ground agile protection structure according to the present invention;

[0014] Figure 2 This is a schematic diagram of displacement changes during penalty function processing;

[0015] Figure 3The aircraft ground-based agile protection structure model used for simulation;

[0016] Figure 4 Finite element model of aircraft ground agile protection structure;

[0017] Figure 5 For fluid finite element model;

[0018] Figure 6 The results of stress calculations for the ground-based agile protection structure for an aircraft operating at 0°C in a Force 10 wind. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] This invention provides a fluid-structure interaction analysis method for large-span aircraft ground agile protection structures, which can accurately simulate the interaction between wind field and aircraft ground agile protection structures, providing an effective technical means for the design optimization and wind resistance safety assessment of aircraft ground agile protection structures. Figure 1 A schematic flowchart of the method is shown. (e.g.) Figure 1 As shown, the method includes the following steps:

[0021] Step S110: Preprocessing of the finite element model of the aircraft ground agile protection structure: Import the geometric model of the aircraft ground agile protection structure into HyperMesh software, and divide the model into three major components: skin, inflatable structure, and end door; mesh the different components separately, using shell element models for the skin, end door, and inflatable structure, and select an appropriate mesh size range; assign material constitutive models to each component; set the element algorithm type, constrain boundary conditions and connection relationships, and set the hourglass control coefficient to suppress zero-energy modes;

[0022] Step S120, Flow Field Modeling and Setup: In HyperMesh, establish a semi-cylindrical air domain fluid model, enclosing the aircraft's ground-based agile protection structure and extending it to a sufficient length to ensure full development of the flow domain; define the fluid material as an ideal gas, and set the density, viscosity, and equation of state parameters; use a hexahedral dominant mesh to divide the fluid domain, refine the mesh in the near-wall region, and set an appropriate overall mesh size; specify inflow, outflow, and non-reflective boundary conditions, and set the wind speed profile and incoming flow direction to simulate wind loads; select the multi-material arbitrary Lagrange-Eulerian (ALE) element algorithm and configure the corresponding hourglass control;

[0023] Step S130, Fluid-structure Interaction Keyword Setting and Solving: Define fluid-structure interaction keywords in HyperMesh, set the surface of the aircraft ground agile protection structure as the coupling interface, and select the ALE algorithm for bidirectional coupling calculation; set the calculation time step, output time interval, and termination time; export the complete K file and submit it to the LS-DYNA solver for explicit dynamic calculation; monitor the solving process, and after completion, import the results into post-processing software to view the structural stress, deformation, flow field pressure distribution, and coupling response, and evaluate the safety and stability of the aircraft ground agile protection structure under different wind speeds.

[0024] Specifically, step S110 includes:

[0025] Step S110-1, Model Import and Processing:

[0026] Import the geometric model of the inflatable aircraft ground agile protection structure into HyperMesh software, and divide the model into three main components: skin, inflatable structure and end gate, so as to facilitate mesh generation and attribute assignment respectively.

[0027] Step S110-2, Finite element mesh generation:

[0028] The three components defined in step S110-1 were meshed using quadrilateral shell elements as the primary element. The baseline mesh size for the skin and end doors was set to 50mm, while the inflatable structure, due to its greater curvature, used a finer mesh with a size of 30mm. Local mesh refinement was performed in the junction areas between the components, reducing the mesh size to 20mm to ensure the accuracy of force transmission between components.

[0029] Step S110-3, Definition of Material Constitutive Model:

[0030] The skin, inflatable structure, and end doors are all considered as flexible fabric composite materials, which are created in HyperMesh. The `MAT_FABRIC` keyword is used to define its material model. This model can effectively simulate the nonlinear and large deformation behavior unique to fabric materials. Assuming the material is isotropic, its density is set to 830.2 kg / m³. 3 With an elastic modulus of 1 GPa, a Poisson's ratio of 0.3, and a yield stress of 106 MPa, the material model is assigned to the corresponding component.

[0031] Step S110-4, Feature creation settings:

[0032] Create for all shell unit components The `SECTION_SHELL` keyword is used to define characteristic attributes. The section type is selected as ALE multi-material algorithm, and `ELFORM` is set to 5 for subsequent fluid-structure interaction calculations. The shell element thickness is uniformly set to 0.0007m. To control hourglass distortion, the hourglass control coefficient is set to 0.1.

[0033] Step S110-5, Boundary conditions and connection relationships are defined:

[0034] pass The BOUNDARY_SPC_SET keyword defines the fixed connection between the aircraft's ground-based agile protective structure and the ground: all nodes of the skin and end doors that are in contact with the ground are selected, and all their translational degrees of freedom are constrained. For the mechanical connection between the skin, inflatable structure, and end doors, a node coupling method is used to ensure that the load can be effectively transferred between different components, simulating the effect of actual stitching or bonding connections.

[0035] Further, step S120 includes:

[0036] Step S120-1, Creation of the flow field geometry model:

[0037] Create a semi-cylindrical air domain fluid model in HyperMesh. This fluid domain should completely enclose and be larger than the aircraft-ground agile protection structure model. The length of the fluid domain should be aligned with the axis of the aircraft-ground agile protection structure. Its inlet end should be at least twice the length of the aircraft-ground agile protection structure's end gate, and its outlet end should be at least three times the length of the aircraft-ground agile protection structure's tail end. Its diameter should be at least three times the width of the aircraft-ground agile protection structure to ensure sufficient flow field development and effectively reduce boundary effects, thereby simulating infinite-domain airflow.

[0038] Step S120-2, Definition and Setting of Fluid Materials:

[0039] Air material in HyperMesh The `MAT_NULL` keyword is used for definition, and the card name can be selected as `MATL9`. This material model is used in conjunction with the equations of state and is specifically designed for simulating fluid materials such as gases and liquids. A linear polynomial equation of state is employed. The pressure-volume-energy relationship of air is described using EOS_LINEAR_POLYNOMIAL. The parameters of the equation of state are set as follows: C0=0, C1=0, C2=0, C3=0, C4=0.4, C5=0.4, C6=0. The initial internal energy per unit reference volume is 253089 J, and the initial relative volume is 1.

[0040] Step S120-3, Flow field mesh generation:

[0041] The fluid domain is meshed using hexahedral solid elements. This is then performed in HyperMesh. The SECTION_SOLID keyword defines fluid characteristic attributes. The card name is selected as SectSld_ALE, and the algorithm type ELFORM is set to 11, meaning it's a single-point integration unit suitable for the multi-material ALE algorithm. The overall mesh size is controlled at approximately 50mm, consistent with the mesh size of the aircraft's ground-based agile protection structure. The divided fluid domain hexahedral solid elements are categorized into an air domain solid element set for subsequent element association at the fluid-structure interaction interface.

[0042] Step S120-4: Setting the flow field boundary conditions and initial conditions:

[0043] Through HyperMesh The BOUNDARY keyword series defines the boundary conditions of the flow field. The inlet section is defined as the velocity inlet boundary, setting the amplitude and direction of the incoming airflow velocity. The incoming flow direction is set to be perpendicular to the inlet section and pointing inwards into the flow field. The outlet section is defined as the pressure outlet boundary to allow fluid to flow out of the computational domain without reflection. The top and bottom surfaces of the semi-cylindrical flow field are set as non-reflective boundary conditions to simulate free-slip walls and eliminate unreasonable reflections of pressure waves at the boundaries. The `INITIAL_VELOCITY_GENERATION` keyword assigns an initial velocity consistent with the inlet to the entire flow field, thereby improving stability during the initial stages of computation.

[0044] Step S120-5, Flow field algorithm and control parameter settings:

[0045] In HyperMesh The `CONTROL_ALE` keyword sets the control parameters for the multi-material ALE algorithm. To ensure computational stability, appropriate hourglass control needs to be configured. The HOURGLASS keyword defines the hourglass control coefficient for the flow field solid element. Setting it to 0.1 prevents the element from entering a zero-energy mode.

[0046] Further, step S130 includes:

[0047] Step S130-1, Definition of Fluid-Structure Coupling Interaction Keywords:

[0048] Creating fluid-structure interaction control keywords in HyperMesh is central to enabling the interaction between the wind field and the aircraft's ground-based agile protection structure. The `CONSTRAINED_LAGRANGE_IN_SOLID` keyword defines the coupling relationship. Within this keyword, the set of shell elements for all components of the aircraft ground agile protection structure defined in step S110 is set as a Lagrangian structure, and the set of solid elements for the air domain defined in step S120 is set as an Eulerian fluid. The coupling direction is set to bidirectional to simultaneously calculate the effect of fluid pressure on the structure and the influence of structural deformation on the flow field. The penalty function method is chosen as the coupling algorithm to ensure accurate transmission of coupling forces and computational stability.

[0049] Furthermore, the arbitrary Lagrange-Euler method employed in this invention is a numerical simulation technique widely used to solve fluid-structure interaction problems in flexible materials, particularly suitable for engineering problems involving large deformations, moving boundaries, and significant changes in material interfaces. This method effectively combines the advantages of the Lagrange description in accurately tracking structural motion with the Euler description's strong adaptability to large fluid deformations by introducing an arbitrary reference coordinate system independent of the motion of material points and the spatially fixed frame.

[0050] In the ALE framework, the computational mesh can move independently of the material, neither constrained by material deformation nor completely fixed in space. This allows for maintaining computational accuracy while avoiding mesh distortion caused by large structural deformations. The basic idea is to reconstruct the mesh based on the boundaries of the material region after every few computational steps, and then map historical variables onto the new mesh through interpolation, achieving mesh optimization and adaptation during the computation process.

[0051] set up Using Lagrange coordinates, Using Euler coordinates, Using ALE reference coordinates, the mesh movement speed is The velocity of the material point relative to the grid is... ,in It is the velocity of matter. Based on the ALE description, for any physical quantity Its total time derivative can be expressed as:

[0052] ,

[0053] Applying this to the governing equations of fluid motion, we obtain the ALE form of the fluid mass and momentum conservation equations. The mass conservation equation is:

[0054] ,

[0055] The momentum conservation equation is:

[0056] ,

[0057] in, For fluid density, For Cauchy stress tensor, For volume forces, It is the Hamiltonian operator.

[0058] In this invention, the air-domain fluid is described using the aforementioned ALE (Air-to-Earth) description to accommodate the significant movement and deformation of the inflatable aircraft ground-based agile protection structure under wind loads; while the aircraft ground-based agile protection structure is described using a Lagrangian description, and its equation of motion can be written as:

[0059] ,

[0060] in, The structural displacement vector. For structural density, This represents the structural stress tensor. The fluid-structure interaction interface conditions must satisfy both displacement compatibility and force equilibrium.

[0061] ,

[0062] in, and These represent the displacements of the fluid and the structure at the interface. For the interface normal vector, This is the stress tensor of the fluid at the fluid-structure interaction interface.

[0063] To achieve the numerical implementation of the above coupling conditions, this invention employs the penalty function method to apply fluid-structure interaction constraints, such as... Figure 2 As shown: The left side of the figure presents the initial coupling state, including fluid elements marked with hollow dots and structural elements interacting with the fluid elements. The integral coupling points marked within the fluid elements are key nodes for integrating physical quantities such as force and displacement in fluid-structure interaction calculations, and for transmitting fluid-structure interactions. The fluid elements also contain corresponding material points within the fluid, i.e., fluid material particles participating in fluid-structure interaction and interacting with structural elements, used to track the interaction behavior between fluid materials and structures. The right side of the figure presents the coupled state, demonstrating the effect of applying a restoring force through a penalty function after slight interface penetration. This method approximately satisfies interface compatibility conditions by allowing slight interface penetration and applying a restoring force proportional to the penetration amount at the penetration node. The penetration distance is defined. Then the coupling force exerted by the penalty function can be expressed as:

[0064] ,

[0065] in, For the penalty stiffness coefficient, The damping coefficient is... Penetration distance The rate of change of time. This coupling force acts simultaneously on the fluid and the corresponding nodes of the structure, achieving a two-way coupling effect.

[0066] For time integration, an explicit time-progression scheme combined with the Galerkin discretization scheme is employed to transform the continuous control equations into a discrete system for iterative solution. Within each time step, the fluid field, structural field, and mesh position are updated sequentially, and interaction forces are transferred through a coupling algorithm until convergence. The final coupled system can be expressed as:

[0067] ,

[0068] in, Subscript and The subscripts represent structure and fluid respectively. This represents the coupling effect between the fluid and the structure. For the quality matrix, Here is the damping matrix. Here is the stiffness matrix. For external load vector, For fluid pressure, The structure velocity vector, The structure's acceleration vector. This is the fluid velocity vector.

[0069] Step S130-2, Solve for control parameter settings:

[0070] Create a series in HyperMesh The CONTROL keyword is used to configure the operating parameters of the LS-DYNA solver. Parameters such as total computation time, time step, energy control, and result output settings are set.

[0071] Step S130-3, K-file export and solution calculation:

[0072] After completing all preprocessing settings, the entire model is exported as a complete LS-DYNA input K file using HyperMesh's export function. The computation task is then submitted using the LS-DYNA solver, and the solution process is monitored in real time.

[0073] Step S130-4, Post-processing and Safety Assessment:

[0074] After the calculations are completed, the result file is opened using the post-processing software LS-PrePost to view the stress and deformation contour maps of the aircraft ground agile protection structure, pinpointing the locations of maximum stress and maximum displacement and their changes over time. The maximum stress is compared with the material's yield stress to determine whether the structure has experienced yield failure, thus conducting a safety assessment of the aircraft ground agile protection structure.

[0075] The following uses the method proposed in this invention to conduct fluid-structure interaction simulation analysis on the ground agile protection structure of a certain type of aircraft and evaluate its safety.

[0076] This embodiment uses an aircraft ground agile protection structure model, such as... Figure 3 The facility features a shell-type frame-style wind-resistant inflatable structure door at the front and a progressive wind-resistant inflatable wall at the rear, integrated with the main structure. Finite element mesh generation was performed on the aircraft ground agile protection structure model, and the fluid finite element model is as follows: Figure 4 finite element model of structure, such as Figure 5 .

[0077] This analysis simplifies the structure appropriately, identifying the airbag module as the primary load-bearing structure. The main dimensional parameters of the analyzed structure are: internal height 13500 mm, internal span 36500 mm, and air rib diameter 2400 mm. In the model, length is expressed in meters (m), force in N, weight in kg, and pressure in Pa. The structure is composed of a high-strength, airtight membrane material, whose material constants are shown in Table 1.

[0078] Table 1 Material constants

[0079]

[0080] The design value for the aircraft's ground-based agile protective structure against wind loads of 28.4 m / s (level 10) and 504 Pa is determined according to GJB50068-2018 "Unified Standard for Reliability Design System of Building Structures," which sets the structural importance factor of this structure at 1. (Based on:)

[0081] ,

[0082] in, This is the structural load-bearing design value. The required structural load-bearing value, As a structural importance coefficient, the required load-bearing capacity of this structure is determined to be equal to the design value, i.e., the wind pressure is required to withstand a wind speed of 10 on the Beaufort scale and a wind speed of 504 Pa. In the structural calculations, the wind load is calculated using the wind pressure obtained from fluid dynamics calculations, the internal pressure of the inflatable module, and the structure's self-weight. The output wind pressure from the fluid dynamics calculations and the output deformation of the structure are iterated until convergence, with the internal pressure of the inflatable module reaching 4200 Pa. The wind load structural calculation results are as follows: Figure 6 As shown, the maximum stress is generated at the 0° windward position, with a maximum stress of 11.9 MPa and a maximum deformation of 0.57 m. The structure is stable and has not become unstable.

[0083] In summary, this invention employs the Arbitrary Lagrange-Euler (ALE) method for fluid-structure interaction simulation modeling. It effectively addresses mesh distortion in large deformation regions through mesh reconstruction and slip boundary techniques. While retaining the advantages of the Euler framework in efficiently describing the flow field, it incorporates the precise capture of structural motion by the Lagrange description. Combined with a nonlinear viscoelastic-plastic constitutive model, it achieves accurate characterization of membrane material pretension, plastic elongation, and creep behavior. The ALE method significantly improves the simulation confidence and computational accuracy of inflatable membranes under strong dynamic wind loads, providing a basis for performance evaluation and optimization of flexible inflatable structures.

[0084] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fluid-structure interaction mechanical analysis method for a large-span aircraft ground-based agile protection structure, characterized in that, The method includes the following steps: Step S110: Preprocessing of the finite element model of the aircraft ground agile protection structure: Import the geometric model of the aircraft ground agile protection structure into HyperMesh software, and divide the model into three major components: skin, inflatable structure, and end door; mesh the different components separately, using shell element models for the skin, end door, and inflatable structure, and select an appropriate mesh size range; assign material constitutive models to each component; set the element algorithm type, constrain boundary conditions and connection relationships, and set the hourglass control coefficient to suppress zero-energy modes; Step S120, Flow Field Modeling and Setup: In HyperMesh, establish a semi-cylindrical air domain fluid model, enclosing the aircraft's ground-based agile protection structure and extending it to a sufficient length to ensure full development of the flow domain; define the fluid material as an ideal gas, and set the density, viscosity, and equation of state parameters; use a hexahedral dominant mesh to divide the fluid domain, refine the mesh in the near-wall region, and set an appropriate overall mesh size; specify inflow, outflow, and non-reflective boundary conditions, and set the wind speed profile and incoming flow direction to simulate wind loads; select the multi-material arbitrary Lagrangian-Eulerian ALE element algorithm and configure the corresponding hourglass control; Step S130, Fluid-structure Interaction Keyword Setting and Solving: Define the fluid-structure interaction keyword in HyperMesh, set the surface of the aircraft ground agile protection structure as the coupling interface, select the ALE algorithm for bidirectional coupling calculation; set the calculation time step, output time interval and termination time; Export the complete K file and submit it to the LS-DYNA solver for explicit dynamic calculations; Monitor the solution process, and after completion, import the results into post-processing software to view the structural stress, deformation, flow field pressure distribution, and coupling response, and evaluate the safety and stability of the aircraft ground agile protection structure under different wind speeds.

2. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 1, characterized in that, Step S110 includes: Step S110-1, Model Import and Processing: Import the geometric model of the aircraft ground agile protection structure into HyperMesh software, and divide the model into three main components: skin, inflatable structure and end door, so as to facilitate mesh generation and attribute assignment respectively; Step S110-2, Finite element mesh generation: The three components divided in step S110-1 are meshed using quadrilateral shell elements as the main element. Step S110-3, Material Constitutive Model Definition: The skin, inflatable structure, and end gate are all considered as flexible fabric composite materials, which are defined in HyperMesh by creating... The MAT_FABRIC keyword is used to define its material model; Step S110-4, Feature Creation Settings: Create for all shell unit components The SECTION_SHELL keyword is used to define feature attributes; Step S110-5, Boundary conditions and connection relationships definition: through The BOUNDARY_SPC_SET keyword defines the fixed connection between the aircraft's ground agile protective structure and the ground: select all nodes of the skin and end door bottom that are in contact with the ground, and constrain all their translational degrees of freedom; for the mechanical connection relationship between the skin, inflatable structure and end door, the node coupling method is used to achieve the connection, ensuring that the load can be effectively transferred between different components, simulating the actual stitching or bonding effect.

3. The fluid-structure interaction mechanical analysis method for large-span aircraft ground agile protection structures according to claim 2, characterized in that, In S110-2, the base grid size for the skin and end gate is set to 50mm, and the grid size for the inflatable structure is set to 30mm; local grid densification is performed in the junction and connection areas between components, and the grid size is reduced to 20mm.

4. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 2, characterized in that, In step S110-3, assuming the material is isotropic, its density is set to 830.2 kg / m³. 3 With an elastic modulus of 1 GPa, a Poisson's ratio of 0.3, and a yield stress of 106 MPa, the material model is assigned to the corresponding component.

5. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 2, characterized in that, In step S110-4, the section type is selected as ALE multi-material algorithm, and ELFORM is set to 5 for subsequent fluid-structure interaction calculations; the shell element thickness is uniformly set to 0.0007m; and the hourglass control coefficient is set to 0.

1.

6. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 2, characterized in that, Step S120 includes: Step S120-1: Creation of the flow field geometry model: Create a semi-cylindrical air domain fluid model in HyperMesh. This fluid domain completely encloses and is larger than the aircraft ground agile protection structure model. The length direction of the fluid domain is consistent with the axis of the aircraft ground agile protection structure. Its inlet end is at least twice the length of the aircraft ground agile protection structure from the end gate, and its outlet end is at least three times the length of the aircraft ground agile protection structure from the tail end. Its diameter is at least three times the width of the aircraft ground agile protection structure to ensure that the flow field is fully developed and effectively reduce boundary effects, thereby simulating infinite domain airflow. Step S120-2, Definition and Setting of Fluid Materials: The air material in the flow field is defined in HyperMesh through... The MAT_NULL keyword is used for definition, and the card name is selected as MATL9; this material model is used in conjunction with the equation of state and is specifically designed for simulating gases and liquids; a linear polynomial equation of state is employed. EOS_LINEAR_POLYNOMIAL is used to describe the pressure-volume-energy relationship of air; Step S120-3, Mesh Generation of the Flow Field: The fluid domain is meshed using hexahedral solid elements; in HyperMesh, through... The SECTION_SOLID keyword defines fluid characteristic attributes. The card name is selected as SectSld_ALE, and the algorithm type ELFORM is selected as 11, which is a single-point integration unit suitable for multi-material ALE algorithm. The overall mesh size is controlled at about 50mm, which is consistent with the mesh size of the aircraft ground agile protection structure. The divided fluid domain hexahedral solid elements are classified into air domain solid element sets for subsequent element association at the fluid-structure interaction interface. Step S120-4, Setting the flow field boundary conditions and initial conditions: This is done through HyperMesh. The BOUNDARY series of keywords defines the boundary conditions of the flow field; the inlet section is defined as the velocity inlet boundary, setting the amplitude and direction of the incoming air velocity; the incoming flow direction is set to be perpendicular to the inlet section and pointing inwards into the flow field; the outlet section is defined as the pressure outlet boundary to allow fluid to flow out of the computational domain without reflection; the top and bottom surfaces of the semi-cylindrical flow field are set as non-reflective boundary conditions to simulate free-slip walls and eliminate unreasonable reflections of pressure waves at the boundaries; settings The `INITIAL_VELOCITY_GENERATION` keyword assigns an initial velocity consistent with the inlet to the entire flow field, thereby improving stability during the initial stages of computation. Step S120-5, Flow field algorithm and control parameter settings: In HyperMesh, through... The CONTROL_ALE keyword sets the control parameters for the multi-material ALE algorithm; through... The HOURGLASS keyword defines the hourglass control coefficient for the flow field solid element, set to 0.

1.

7. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground-based agile protection structure according to claim 6, characterized in that, Step S130 includes: Step S130-1, Definition of Fluid-Structure Coupling Interaction Keywords: Through The `CONSTRAINED_LAGRANGE_IN_SOLID` keyword defines the coupling relationship; within this keyword, the set of shell elements for all components of the aircraft ground agile protection structure defined in step S110 is set as a Lagrangian structure, and the set of solid elements for the air domain defined in step S120 is set as an Eulerian fluid; the coupling direction is set to bidirectional to simultaneously calculate the effect of fluid pressure on the structure and the influence of structural deformation on the flow field; the penalty function method is selected as the coupling algorithm to ensure the accurate transmission of coupling forces and the stability of the calculation; Step S130-2, Solving the control parameter settings: Create a series of... The CONTROL keyword is used to configure the operating parameters of the LS-DYNA solver; it sets the total computation time, time step, energy control, and result output settings. Step S130-3, K-file export and solution calculation: After completing all preprocessing settings, export the entire model as a complete LS-DYNA input K-file using the HyperMesh export function, submit the calculation task using the LS-DYNA solver, and monitor the solution process in real time. Step S130-4, Post-processing and Safety Assessment: After the calculation is completed, open the result file using the post-processing software LS-PrePost, view the stress cloud map and deformation cloud map of the aircraft ground agile protection structure, locate the location of the maximum stress and the maximum displacement and their change over time; compare the maximum stress with the yield stress of the material to determine whether the structure has yielded and failed, and conduct a safety assessment of the aircraft ground agile protection structure.

8. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 7, characterized in that, In S130-1, the air domain fluid is described using ALE: Let Using Lagrange coordinates, Using Euler coordinates, Using ALE reference coordinates, the mesh movement speed is The velocity of the material point relative to the grid is ,in It is the velocity of matter; based on the ALE description, for any physical quantity Its total time derivative is expressed as: ， Applying this to the governing equations of fluid motion, we obtain the ALE-form equations for the conservation of fluid mass and momentum. The mass conservation equation is as follows: ， The momentum conservation equation is: ， in, For fluid density, For Cauchy stress tensor, For volume forces, It is the Hamiltonian operator; The aircraft's ground-based agile protection structure is described using a Lagrangian approach, and its equation of motion is written as: ， in, The structural displacement vector. For structural density, For structural stress tensor; The fluid-structure interaction interface conditions satisfy both displacement compatibility and force equilibrium: ， in, and These represent the displacements of the fluid and the structure at the interface. For the interface normal vector, This is the stress tensor of the fluid at the fluid-structure interaction interface.

9. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 8, characterized in that, In S130-1, the penalty function method is used to apply fluid-structure interaction constraints: the penetration distance is defined. The coupling force exerted by the penalty function is expressed as: ， in, For the penalty stiffness coefficient, The damping coefficient is... Penetration distance The rate of change of time; the coupling force acts simultaneously on the corresponding nodes of the air domain and the aircraft ground agile protection structure, realizing a two-way coupling effect.

10. The fluid-structure interaction mechanical analysis method for a large-span aircraft ground agile protection structure according to claim 8, characterized in that, In S130-1, for time integration, an explicit time-progression combined with the Galerkin discrete scheme is used to transform the continuous control equations into a discrete system for iterative solution. Within each time step, the air domain fluid field, the aircraft ground agile protection structure field, and the mesh position are updated sequentially, and the interaction forces are transferred through a coupling algorithm until convergence. The final coupled system is expressed as: ， in, Subscript and The subscripts represent structure and fluid respectively. This represents the coupling effect between the fluid and the structure. For the quality matrix, Here is the damping matrix. Here is the stiffness matrix. For external load vector, For fluid pressure, The structure velocity vector, The structure's acceleration vector. This is the fluid velocity vector.

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