A method for predicting parachute canopy tearing

Abstract

This invention provides a method for predicting parachute canopy tears. Using fluid-structure coupling numerical calculations, the method obtains canopy stress and shape changes under high-speed, unsteady flow fields. Based on the first strength theory, the canopy tear location is automatically determined. Through cyclic calculations that reconstruct the canopy structure and flow field, the method predicts the final tear shape and changes in the canopy's aerodynamic performance. This method can accurately predict the tear location and propagation direction during high-speed parachute deployment, enabling prediction of canopy aerodynamic performance under the influence of tearing. This method reduces the cost of parachute deployment verification testing and improves the efficiency of parachute design and the reliability of recovery systems.

Description

Technical Field

[0001] The present invention relates to the field of airborne airdrop equipment design, and in particular to a method for predicting parachute canopy tearing. Background Art

[0002] Parachutes rely on the aerodynamic forces generated by the inflation of a flexible canopy and are widely used for deceleration during airdrops and spacecraft recovery. During high-speed, high-dynamic-pressure inflation, the canopy's dynamic load increases rapidly, causing the canopy fabric to break due to increased structural stress. This can ultimately lead to extensive tearing and failure, resulting in landing mission failure. Canopy damage caused by excessive dynamic loads has been observed in numerous airdrop tests both domestically and internationally.

[0003] Successful parachute inflation is essential for a safe landing of the payload, so research on the tearing mechanism during parachute operation is essential. However, the canopy is a flexible fabric with large deformation, making it difficult to accurately measure the surface stress of the canopy. Furthermore, canopy damage inevitably damages the test system, making it difficult to study the tearing mechanism during parachute inflation through airdrop tests. Existing test results on parachute tearing during inflation are all from validation tests of different parachute models. Parameters such as canopy structure and deployment conditions vary greatly, making it difficult to directly compare the location and propagation of canopy tears. Therefore, the mechanism of canopy tearing during transient inflation remains a hidden problem.

[0004] The parachute inflation process is essentially the interaction between a flexible canopy and a high-speed flow field. In recent years, fluid-structure interaction computational methods have begun to be used to study transient parachute deployment. By simultaneously modeling and calculating the canopy structure and flow field, the transient changes in canopy shape and stress during inflation can be accurately captured. However, all current inflation process studies assume an ideal canopy that is free of damage or tearing. These studies can only qualitatively predict the location of dangerous canopies and are unable to simulate the development of tears and cracks. This is inconsistent with actual conditions. This is due to the lack of a structural dynamics model that accurately describes the damage and its development when the fabric breaks. Consequently, it is impossible to accurately determine whether a parachute will break and the dynamic loss of aerodynamic drag caused by such damage. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to establish a method for predicting parachute canopy tearing, obtain the transient changes of the canopy's shape and stress in an unsteady flow field through fluid-solid coupling calculation, automatically screen and remove the fabric structural units corresponding to the canopy tearing, accurately predict the occurrence of canopy tearing and the aerodynamic force of the parachute after tearing, and provide a method for studying the mechanism of canopy tearing, improving the efficiency of canopy structure design, and verifying the reliability of the parachute system.

[0006] To solve the above problems, the present invention proposes a method for predicting parachute canopy tearing, comprising the following steps:

[0007] Step 1: Based on the structural parameters and folding shape of the parachute, program or use commercial software to establish a structural calculation model of the canopy fabric folding and parachute opening, and establish a flow field grid mathematical model according to the parachute opening working conditions;

[0008] Step 2: Calculate the unsteady changes of the canopy structure shape and flow field, and calculate the structural stress of the canopy fabric unit (the basic unit of the structural calculation model) in real time;

[0009] Step 3: Automatically determine the occurrence of fabric tearing based on the canopy material stress failure criterion, output the tearing location, and reconstruct the canopy structure calculation model (the structural calculation model corresponding to the canopy's real-time shape) according to the canopy deformation and tearing location;

[0010] Step 4: Reconstruct the flow field grid mathematical model based on the canopy structure calculation model, repeat steps 2 to 3, and output the canopy shape and aerodynamic performance in real time until the parachute aerodynamic load is stable.

[0011] Preferably, in step 2, the arbitrary Lagrangian Euler method is used to couple the canopy structure and the flow field, and the unsteady change of the canopy structure shape is modeled and calculated using the Lagrangian method. The control equation of the fabric unit in the structural calculation model is:

[0012]

[0013] in, is the time derivative of the displacement of the grid node in the i direction, ρ s is the canopy density, t is the time, σ s ij ,j is the partial derivative of the structural stress tensor in the j direction, f i s is the volume force of the structural unit in the i direction;

[0014] The unsteady changes of the flow field are modeled and calculated using the Euler method. The governing equation of the flow field grid unit (the basic unit in the flow field grid mathematical model) is:

[0015]

[0016] in, is the partial derivative operation, ρ f is the flow field density, v i is the velocity of the structure along the i direction, x i represents the Euler coordinates, w i is the grid node velocity along the i direction, is the stress tensor of the flow field, f i f is the volume force of the flow field, and e is the energy.

[0017] As a preferred embodiment, step 3 includes: calculating the canopy fabric stress using the following formula:

[0018]

[0019] Among them, I1 and I2 are stress invariants, φ is the angle between the principal stress direction and the coordinate axis, and the calculation formula is:

[0020]

[0021] is the structural stress tensor σ s ij Elements corresponding to different directions in .

[0022] As a preference, in step 3, the canopy fabric structure is judged to be torn according to the first strength theory: if the canopy fabric stress If it is failure stress, the fabric structure strength fails to form a tearing point, the canopy fabric unit corresponding to the tearing point will be automatically cleared, and then the tearing position will be output according to the tearing point.

[0023] Preferably, in step 3, the stiffness of the canopy fabric is reduced after tearing, and the stiffness matrix of the structure is obtained by the stiffness matrix of the canopy fabric units constituting the structure:

[0024]

[0025] Where n is the total number of elements in the structure, K is the overall stiffness matrix of the structure after the failure of m elements, K i , K m The stiffness matrix corresponding to unit i and unit m are respectively, and the strain ε of the structure is:

[0026]

[0027] in, Represents the geometric operator matrix; N is the shape function matrix of the element, q is the displacement matrix of the grid node, and P is the external load matrix of the element;

[0028] Stress tensor σ of the fabric unit after damage reconstruction s Expressed as:

[0029]

[0030] Among them, A is the third-order matrix about Poisson's ratio, E is the elastic modulus, v is Poisson's ratio, σ s is the structural stress tensor σ s ij The matrix formed.

[0031] Preferably, in step 3, the reconstruction of the canopy structure calculation model is mainly to remove the failed unit grid, but due to the existence of the failed unit, the stress calculation of the part of the structure where the unit is located is changed, specifically, the stress calculation is changed by changing the stiffness matrix.

[0032] Preferably, in step 4, the flow field boundary conditions are corrected in real time according to the canopy inflation deformation and tearing position, and the grid nodes of the flow field and structure satisfy the following equations:

[0033]

[0034] Where f is the transport function of the flow field, X i are Lagrangian coordinates.

[0035] Preferably, in step 4, the canopy surface pressure is determined based on the calculation results obtained in steps 2 and 3 and the flow field grid node motion equations to obtain the canopy shape and aerodynamic performance.

[0036] Beneficial effects: This method uses transient fluid-solid coupling numerical modeling to simultaneously obtain the unsteady changes in canopy stress and shape. It can quickly and accurately predict the location and expansion direction of the canopy tear during high-speed parachute deployment, thereby accurately predicting the dynamic changes in aerodynamic performance after the canopy tear, saving the cost of parachute verification tests and providing an important reference for parachute structure and strength design. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0038] Figure 1 The present invention is a flow chart of a method for predicting the risk of parachute canopy tearing.

[0039] Figure 2 It is a schematic diagram of the full shape and main geometric dimensions of the hoop parasail.

[0040] Figure 3 It is a schematic diagram of the folding grid model of the ring parasail and the flow field grid model.

[0041] Figure 4 It is a schematic diagram of the structural failure unit.

[0042] Figure 5 It is a schematic diagram comparing the predicted appearance of the present invention and the flight test.

[0043] Figure 6 This is a schematic diagram comparing the canopy projection area predicted by this method with the flight test.

[0044] Figure 7 This is a schematic diagram comparing the parachute opening dynamic load predicted by this method with the flight test. DETAILED DESCRIPTION

[0045] The present invention provides a method for predicting parachute canopy tearing, the specific process is as follows: Figure 1 As shown, in order to show the characteristics and advantages of the present invention, the following Figure 2 Taking the American SSRS (Supersonic Ringsail) supersonic ring sail parachute deceleration system (literature source: O'Farrell, C., Brandeau, EJ, Tanner, C., Gallon, JC, Muppidi, S., & Clark, IG (2016). Reconstructed Parachute System Performance During the Second LDSD Supersonic Flight Dynamics Test. AIAA Atmospheric Flight Mechanics Conference. doi: 10.2514 / 6.2016-3242) as an example, the technical solutions in the embodiments of the present invention are clearly and completely described in combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0046] Step 1. The specific structural dimensions of the SRRS hoop sail canopy are shown in Table 1 (unit: m). According to the hoop sail canopy folding method, the canopy folding and opening structure calculation model is established as follows: Figure 3 The right side shows an enlarged view of the parachute.

[0047] Table 1

[0048]

[0049] The mathematical model of flow field grid is as follows Figure 3 The nominal area and geometric porosity of the canopy, as shown in the square area on the left, are consistent with those of the hoop-sail canopy used in the experiment. The canopy, line, and fluid unit type settings are shown in Table 2.

[0050] Table 2

[0051]

[0052] Step 2. Use the arbitrary Lagrangian Euler method to couple the unsteady changes of the canopy structure shape and flow field.

[0053] The canopy structure is calculated using the Lagrangian method, and the governing equation is:

[0054]

[0055] Where, is the time derivative of the displacement of the grid node in the i direction, ρ s is the canopy density, t is the time, σ s ij,j is the partial derivative of the structural stress tensor in the j direction, f i s is the volume force of the structural unit in the i direction.

[0056] The flow field is calculated using the Euler method, and the governing equation is:

[0057]

[0058] Where, ρ f is the flow field density, vi is the velocity of the structure along the i direction, x i represents the Euler coordinates, w i is the grid node velocity along the i direction, is the stress tensor of the flow field, f i f is the volume force of the flow field, and e is the energy.

[0059] Step 3. Determine the maximum principal stress of the canopy fabric unit based on transient coupling calculation.

[0060] The calculation formula of canopy fabric stress σ1 is:

[0061]

[0062] Where I1 and I2 are stress invariants, φ is the angle between the principal stress direction and the coordinate axis, and the calculation formula is:

[0063]

[0064] According to the first strength theory, the tear of the canopy fabric structure is judged, that is, the principal stress of the fabric unit The fabric strength fails and a tear point is formed, and the corresponding unit is automatically cleared. is the failure stress and is the property of the fabric material.

[0065] After the canopy is torn, the stiffness of the fabric unit decreases, and the stiffness matrix of the structure is obtained by assembling the stiffness matrices of the units that make up the structure, such as Figure 4 As shown, unit 3 is a stress-failed fabric unit, and K is the overall stiffness matrix of the structure after unit 3 fails, which can be expressed as:

[0066]

[0067] Where, represents the stiffness between nodes i and j in unit k. The strain ε of structural unit k is:

[0068]

[0069] Where, Represents the geometric operator matrix. N is the shape function matrix of the unit, P is the external load matrix of the unit, q is the displacement matrix of the structure, and the stress tensor σ of the fabric is s It can be expressed as:

[0070]

[0071] Where A is the third-order matrix about Poisson's ratio, E is the elastic modulus, and v is the Poisson's ratio.

[0072] Step 4. Calculate the transient deformation and motion of the canopy according to the flow field pressure. Based on the motion and tearing position of the canopy fabric, modify the flow field calculation boundary conditions. The grid node motion equation is:

[0073]

[0074] Where, X i is the Lagrangian coordinate, x i is the Euler coordinate.

[0075] Repeat steps 2 and 3 to carry out unsteady coupling calculations to obtain the canopy shape and structural tearing of the hoop sail parachute during supersonic inflation. Figure 5 As shown in the comparison diagram of the canopy shape change, this method accurately predicts the transient change law of the canopy tearing shape during the inflation process, which is basically consistent with the experimental observation results. However, the traditional fluid-structure coupling method does not consider the failure problem of the fabric material and is therefore unable to analyze the canopy tearing problem, which may overestimate the safety of the canopy.

[0076] This method can predict the effect of canopy tearing on aerodynamic performance through fluid-structure coupling calculation, such as Figure 6 、 Figure 7 As shown in the figure, the transient changes in the canopy projected area and dynamic load are basically consistent with the experimental measurements. Compared with traditional methods, this method can accurately predict the sudden drop in canopy aerodynamic force after canopy damage (t>0.4s). The peak analysis results of the canopy projected area and dynamic load are shown in Table 3. The prediction errors of this method are all less than 7%, which is significantly lower than that of traditional methods.

[0077] Table 3

[0078]

[0079] The comparison of the above results shows that the method of the present invention can quickly and accurately determine the location and direction of the tear in the canopy fabric material when the parachute is opened at high speed, thereby accurately predicting the change in aerodynamic force after the canopy is torn, saving the cost of parachute verification tests, and providing an important reference for parachute structure design.

[0080] In a specific implementation, the present application provides a computer storage medium and a corresponding data processing unit. The computer storage medium is capable of storing a computer program that, when executed by the data processing unit, executes the invention disclosure of a method for predicting parachute canopy tearing provided by the present invention, as well as some or all of the steps in each embodiment. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

[0081] Those skilled in the art can clearly understand that the technical solutions in the embodiments of the present invention can be implemented by means of computer programs and their corresponding general hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, in essence or in other words, the part that contributes to the prior art, can be embodied in the form of a computer program, i.e., a software product. The computer program software product can be stored in a storage medium and includes several instructions for enabling a device including a data processing unit (which can be a personal computer, a server, a single-chip microcomputer, a MUU, or a network device, etc.) to execute the methods described in various embodiments of the present invention or certain parts of the embodiments.

[0082] The present invention provides a method for predicting parachute canopy tears. There are numerous methods and approaches for implementing this technical solution. The above is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for predicting parachute canopy tearing, characterized in that: The following steps are involved: Step 1: Based on the structural parameters and folding shape of the parachute, a structural calculation model of the canopy fabric folding and opening is established, and a flow field grid mathematical model is established according to the opening condition; Step 2: Calculate the unsteady changes of the canopy structure shape and flow field, and calculate the structural stress of the canopy fabric unit in real time; Step 3: Automatically determine the occurrence of fabric tearing based on the canopy material stress failure criterion, output the tearing location, and reconstruct the canopy structure calculation model based on the canopy deformation and tearing location; Step 4: Reconstruct the flow field grid mathematical model based on the canopy structure calculation model, repeat steps 2 to 3, and output the canopy shape and aerodynamic performance in real time until the parachute aerodynamic load is stable; In step 2, the arbitrary Lagrangian Euler method is used to couple the canopy structure and flow field. The unsteady changes in the canopy structure shape are modeled and calculated using the Lagrangian method. The control equation of the fabric unit in the structural calculation model is: in, is the time derivative of the displacement of the grid node in the i direction, ρ s is the canopy density, t is the time, σ s ij,j is the partial derivative of the structural stress tensor in the j direction, f i s is the volume force of the structural unit in the i direction; The unsteady changes of the flow field are modeled and calculated using the Euler method. The governing equation of the flow field grid unit is: in, is the partial derivative operation, ρ f is the flow field density, v i is the velocity of the structure along the i direction, x i represents the Euler coordinates, w i is the grid node velocity along the i direction, is the stress tensor of the flow field, f i f is the volume force of the flow field, and e is the energy.

2. The method according to claim 1, characterized in that Step 3 includes: calculating the canopy fabric stress using the following formula Among them, I1 and I2 are stress invariants, φ is the angle between the principal stress direction and the coordinate axis, and the calculation formula is: is the structural stress tensor σ s ij Elements corresponding to different directions in .

3. The method according to claim 2, characterized in that In step 3, the canopy fabric structure is judged to be torn according to the first strength theory: if the canopy fabric stress If it is failure stress, the fabric structure strength fails to form a tearing point, the canopy fabric unit corresponding to the tearing point will be automatically cleared, and then the tearing position will be output according to the tearing point.

4. The method according to claim 3, characterized in that In step 3, the stiffness of the canopy fabric decreases after tearing, and the stiffness matrix of the structure is obtained by the stiffness matrix of the canopy fabric elements that make up the structure: Where n is the total number of elements in the structure, K is the overall stiffness matrix of the structure after the failure of m elements, K i , K m The stiffness matrix corresponding to unit i and unit m are respectively, and the strain ε of the structure is: in, Represents the geometric operator matrix; N is the shape function matrix of the element, q is the displacement matrix of the grid node, and P is the external load matrix of the element; Stress tensor σ of the fabric unit after damage reconstruction s Expressed as: Among them, A is the third-order matrix about Poisson's ratio, E is the elastic modulus, v is Poisson's ratio, σ s is the structural stress tensor σ s ij The matrix formed.

5. The method according to claim 4, characterized in that In step 4, the flow field boundary conditions are corrected in real time according to the canopy inflation deformation and tearing position, and the grid nodes of the flow field and structure satisfy the following equations: Where f is the transport function of the flow field, X i are Lagrangian coordinates.

6. The method according to claim 5, characterized in that In step 4, the canopy surface pressure is determined based on the calculation results obtained in steps 2 and 3 and the flow field grid node motion equations to obtain the canopy shape and aerodynamic performance.

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