Cylindrical airbag flat folding model and optimization method for computer simulation

Abstract

This invention discloses a folding model of a cylindrical airbag for computer simulation and its optimization method. The airbag surface consists of two circular surfaces at both ends and a central cylindrical surface. The two circular surfaces at both ends are folded inwards into the cylindrical surface, folding the airbag surface into four planes: the first layer is the first outer plane, the second layer includes the first and second inner planes, the third layer includes the third and fourth inner planes, and the fourth layer is the second outer plane. This invention can completely fold the circular surfaces at both ends of the cylindrical airbag into the cylindrical surface of the airbag, greatly reducing the external dimensions of the folding model. The folding modeling method is simple. By setting the distance between the short top edge of the trapezoidal surface of the four inner planes and the symmetrical horizontal axis of the folding model, the external contour of the folding model of different sizes can be obtained according to the actual engineering situation. By optimizing the height value of the trapezoidal surface, the final folding model can be determined.

Description

Technical Field

[0001] This invention relates to the field of aerospace technology, and in particular to a cylindrical airbag folding model for computer simulation and an optimization method thereof. Background Technology

[0002] In the field of aerospace technology, cylindrical airbags are widely used for impact cushioning and shock absorption during aircraft recovery due to their simple structure and low cost. Before inflating and deploying in the air, the cylindrical airbag is folded and placed inside the airbag chamber. Aircraft design aims to minimize the size of the airbag chamber; therefore, the airbag needs to be folded as small as possible.

[0003] Currently, computer simulation technology is mainly used to simulate the folding and inflation of airbags in order to optimize the design of airbags and aircraft. Airbag folding modeling includes direct folding, initial matrix, nonlinear dynamics, and inverse modeling methods. In computer simulation, the direct folding method establishes a corresponding folding simulation model based on the actual folding behavior of the airbag. However, folding a cylindrical airbag using the initial matrix, nonlinear dynamics, and inverse modeling methods is a complex process. In patent application CN110738004A, a folding model of a cylindrical fabric was established using the direct folding method. However, in this model, the circular surfaces at both ends of the cylindrical fabric are not completely folded into the cylindrical surface. This model cannot achieve a smaller overall outline size after the fabric is laid flat and folded. Therefore, this folding model cannot meet the requirement of minimizing the airbag compartment size in aircraft design. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the deficiencies mentioned in the background art by providing a flat-folding model of a cylindrical airbag for computer simulation and an optimization method thereon.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] The cylindrical airbag folding model used for computer simulation consists of two circular surfaces at both ends and a cylindrical surface in the middle. The two circular surfaces at both ends are folded inwards onto the cylindrical surface, folding the airbag surface into four planes. The first layer is the first outer plane, the second layer contains the first and second inner planes, the third layer contains the third and fourth inner planes, and the fourth layer is the second outer plane.

[0007] The first outer plane and the second outer plane are mirror images. The first and second inner planes are symmetrically folded directly below the first outer plane. The third and fourth inner planes are symmetrically folded directly above the second outer plane. The first and third inner planes are mirror images, and the second and fourth inner planes are mirror images.

[0008] The first outer plane and the second outer plane have the same shape, both consisting of symmetrical arc surfaces at both ends and a rectangular surface in the middle. Both contain two arc sides and two straight sides, and the distance between the two straight sides is equal to half the circumference of the circular surfaces at both ends of the airbag.

[0009] The first to fourth inner planes have the same shape, each consisting of a trapezoidal surface and a circular arc surface. The length of the top edge of the trapezoidal surface is equal to the diameter of the circular surfaces at both ends of the cylindrical airbag, and the length of the bottom edge is equal to half the circumference of the circular surfaces at both ends of the airbag.

[0010] The arc edge of the first outer plane coincides with the arc edges of the first and second inner planes directly below it; the arc edge of the second outer plane coincides with the arc edges of the third and fourth inner planes directly above it; the straight edges of the first and second outer planes coincide.

[0011] The straight edges of the first and third inner planes coincide; the straight edges of the second and fourth inner planes coincide.

[0012] This invention also discloses an optimization method for the flat-folding model of a cylindrical airbag used for computer simulation. The method adjusts the size of the outline of the flat-folding model by setting the distance between the short top edge of the trapezoidal surface of the inner plane and the symmetrical horizontal axis of the folding model. The height value of the trapezoidal surface of the inner plane is obtained through optimization calculation, and the minimum value of the difference between the surface area of ​​the three-dimensional cylinder and the flat-folding area is obtained, thereby determining the optimal flat-folding model.

[0013] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0014] This invention uses the simplest and most intuitive method to create a flat, folded cylindrical airbag model for computer simulation. By setting the height value of the trapezoidal surface, the size of the flat model's outline can be adjusted. Attached Figure Description

[0015] Figure 1 (a) is a schematic diagram of the fully deployed cylindrical airbag;

[0016] Figure 1 (b) is an exploded view of the cylindrical airbag in its fully deployed state;

[0017] Figure 2 (a) is a schematic diagram of half of a cylindrical airbag in its fully deployed state;

[0018] Figure 2 (b) is a schematic diagram of a symmetrical half of a cylindrical airbag in its fully deployed state.

[0019] Figure 3 This is a schematic diagram of a rectangular plane divided by a semicircle of radius L, with the midpoint of the top edge of the rectangular plane as the center.

[0020] Figure 4 A schematic diagram of a rectangular plane being folded inwards towards the lower semicircle of the paper;

[0021] Figure 5 This is a schematic diagram of the outer fold surface in the first step;

[0022] Figure 6 This is a schematic diagram of the inner plane after folding;

[0023] Figure 7 This is a schematic diagram of the plane below the horizontal axis of the center of symmetry of the rectangular plane after the first fold.

[0024] Figure 8 (a) is a schematic diagram of a flat, folded model of a cylindrical airbag;

[0025] Figure 8 (b) is an exploded view of the flat-folded model of the cylindrical airbag.

[0026] In the diagram, 1-cylindrical airbag, 2-rectangular plane, 3-semicircle, 4-segmentation plane, 5-first step outer folding surface, 6-inner plane, 7-reduced rectangular surface, 8-arc surface, 9-trapezoidal surface, 10-outer plane. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings:

[0028] This invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully express the scope of the invention to those skilled in the art. In the drawings, components are enlarged for clarity.

[0029] It should be understood that although the terms first, second, third, etc., may be used herein to describe various elements, components, and / or parts, these elements, components, and / or parts are not limited by these terms. These terms are merely used to distinguish elements, components, and / or parts from one another. Therefore, the first element, component, and / or part discussed below may be a second element, component, or part without departing from the teachings of this invention.

[0030] This invention discloses a cylindrical airbag folding model for computer simulation. The airbag surface is composed of two circular surfaces at both ends and a cylindrical surface in the middle. The two circular surfaces at both ends are folded inwards onto the cylindrical surface, folding the airbag surface into four planes. The first layer is the first outer plane, the second layer includes the first and second inner planes, the third layer includes the third and fourth inner planes, and the fourth layer is the second outer plane.

[0031] The first outer plane and the second outer plane are mirror images. The first and second inner planes are symmetrically folded directly below the first outer plane. The third and fourth inner planes are symmetrically folded directly above the second outer plane. The first and third inner planes are mirror images, and the second and fourth inner planes are mirror images.

[0032] The first outer plane and the second outer plane have the same shape, both consisting of symmetrical arc surfaces at both ends and a rectangular surface in the middle. Both contain two arc sides and two straight sides, and the distance between the two straight sides is equal to half the circumference of the circular surfaces at both ends of the airbag.

[0033] The first to fourth inner planes have the same shape, each consisting of a trapezoidal surface and a circular arc surface. The length of the top edge of the trapezoidal surface is equal to the diameter of the circular surfaces at both ends of the cylindrical airbag, and the length of the bottom edge is equal to half the circumference of the circular surfaces at both ends of the airbag.

[0034] The arc edge of the first outer plane coincides with the arc edges of the first and second inner planes directly below it; the arc edge of the second outer plane coincides with the arc edges of the third and fourth inner planes directly above it; the straight edges of the first and second outer planes coincide.

[0035] The straight edges of the first and third inner planes coincide; the straight edges of the second and fourth inner planes coincide.

[0036] This invention also discloses an optimization method for the flat-folding model of a cylindrical airbag used for computer simulation. The method adjusts the size of the outline of the flat-folding model by setting the distance between the short top edge of the trapezoidal surface of the inner plane and the symmetrical horizontal axis of the folding model. The height value of the trapezoidal surface of the inner plane is obtained through optimization calculation, and the minimum value of the difference between the surface area of ​​the three-dimensional cylinder and the flat-folding area is obtained, thereby determining the optimal flat-folding model.

[0037] like Figure 1 As shown in (a), this is a schematic diagram of the fully deployed cylindrical airbag 1. Figure 1 (b) shows an exploded view of the fully deployed cylindrical airbag 1. Figure 1 As shown, the surface of the fully deployed cylindrical airbag 1 consists of circular surfaces at both ends and a cylindrical surface in the middle.

[0038] like Figure 2 As shown in (a), this is a schematic diagram of half of the cylindrical airbag 1 in its fully deployed state. Figure 2 (b) shows a schematic diagram of the symmetrical half of the fully deployed cylindrical airbag 1. Figure 1 and Figure 2 As shown in (a), the cylindrical airbag 1 has a symmetrical structure, so only one half needs to be modeled by folding it flat to obtain the other half's model by mirroring it. Figure 2As shown in (b), after the semi-cylindrical surface is laid flat, it becomes a rectangular plane 2, and two semicircles 3 are laid symmetrically on top of each other. Assuming D is the diameter of the semicircle 3 and L is the length of the cylindrical airbag 1, then the side length l01 of the rectangular plane 2 is equal to half the circumference of the circular surfaces at both ends of the cylindrical airbag, and the side length l02 of the rectangular plane 2 is equal to the length of the cylindrical airbag 1. The areas of the rectangular plane 2 (i.e., the area S01 of the semi-cylindrical surface) and the areas S02 of the semicircles 3 can be calculated using the following formulas:

[0039]

[0040] l02=L

[0041] S01=l01*l02

[0042]

[0043] like Figure 3 The diagram shows a semicircle of radius L, centered at the midpoint of the top edge of rectangular plane 2. Figure 2 (b) and Figure 3 As shown, point c is the midpoint of the upper edge of rectangular plane 2, and point g is the midpoint of the lower edge of rectangular plane 2. Rectangular plane 2 is divided into dividing plane 4. The lengths of the lines from point b to point c, l_bc, l_ac, and l_ab on dividing plane 4 can be calculated using the following formulas:

[0044] l_ac=L

[0045]

[0046]

[0047] like Figure 4 The diagram shows a folding of the lower semicircle 3 of the rectangular plane 2 towards the inward direction. Figure 5 The diagram shows the first step of the outer folding surface 5, which consists of a reduced rectangular surface 7 and an arc surface 8. Figure 6 The diagram shows the folded inner plane 6, which consists of a trapezoidal surface 9 and a circular arc surface 8. Figure 4 , Figure 5 as well as Figure 6 As shown, the outer folded surface 5 and the inner plane 6 have the same arc shape in the first step.

[0048] like Figure 2 (b) and Figure 4 As shown, assuming that during modeling, after the semicircle 3 is flipped and folded, the distance between its diameter side and the horizontal axis of the center of symmetry of the rectangular plane 2 is Δl, and the range of Δl is 0≤Δl≤0.5(LD). Figure 2(b) Figure 3 , Figure 4 , Figure 5 as well as Figure 6 As shown, after the lower semicircle 3 of rectangular plane 2 is folded inwards towards the paper, point g moves inwards to point i. The lower part of rectangular plane 2 will then fold inwards into a circular arc fold line containing points e, h, and m, a straight fold line connecting point e to point j, and a straight fold line from point m to point k, thus obtaining the first step outer fold surface 5 and inner plane 6. Figure 4 As shown, point d is the point on line ab projected from point j; the length of line af is equal to the length of line gh; point e is any point between lines df. The lengths of the lines between these points can be calculated using the following formula:

[0049]

[0050] l_cg=L

[0051]

[0052] l_gi=l_cg-l_ci

[0053]

[0054] l_ch=l_ci+l_hi

[0055] l_af=l_gh

[0056] l_ad=l_ab-l_bd

[0057] l_df=l_ad-l_af

[0058] l_be=l_bd+l_de 0<l_de<l_df

[0059] like Figure 2 (b) Figure 4 as well as Figure 6 As shown, the height of trapezoidal surface 9 is equal to the length of line de, l_de; the length of the shorter apex of trapezoidal surface 9, l_jk, is equal to the diameter of the two circular surfaces at both ends of the cylindrical airbag; and the length of the longer base, l_em, is equal to half the circumference of the two circular surfaces at both ends of the cylindrical airbag. r represents the arc. The radius of the arc, θ is the radius of the arc. The area S03 of the reduced rectangular surface 7, the area S04 of the arc surface 8, and the area S05 of the trapezoidal surface can be calculated using the following formulas:

[0060] l_em=l01

[0061] l_jk=D

[0062]

[0063]

[0064] S03=l_em*l_be

[0065]

[0066]

[0067] like Figure 2 (b) and Figure 4 As shown, the surface area of ​​the airbag before and after folding is equal. Therefore, the total area S01+S02 of rectangular plane 2 and semicircle 3 is equal to the total area S03+S04+S04+S05 of the outer folding surface 5 and inner plane 6 in the first step. This allows us to calculate l_de, thus determining the position of point e during modeling. However, directly calculating l_de using the above formula is very difficult. By setting l_de as a design variable, the function f(l_de)=S01+S02-[S03(l_de)+2*S04(l_de)+S05(l_de)] can be transformed into a very simple single-objective optimization problem. Solving for l_de yields the value used to determine the position of point e during modeling.

[0068] min f(l_de)

[0069] st0 < l_de < l_df

[0070] After calculating the position of point e during modeling using the above formula, the shapes of the arc surface 8 and the trapezoidal surface 9 can be determined, thus obtaining the shapes of the first-step outer fold surface 5 and the inner plane 6, which are used to establish the final flat folding model.

[0071] like Figure 7 The image shows a schematic diagram of the plane below the horizontal axis of the center of symmetry of rectangular plane 2 after the first fold. Figure 8 As shown in (a), this is a schematic diagram of the flat-folded model of the cylindrical airbag 1. Figure 8 (b) shows an exploded view of the flat-folded model of the cylindrical airbag 1. With the horizontal axis of the center of symmetry of the rectangular plane 2 as the axis of symmetry, [the following diagram is shown]. Figure 7 As shown, the planar symmetry allows us to obtain a flat, folded model of half of the cylindrical airbag 1, including one outer plane 10 and two symmetrical inner planes 6. Mirroring this model towards the inside of the paper yields the final result. Figure 8 The cylindrical airbag 1 shown is a flat, folded model. Figure 8As shown, the flat-folding model of the cylindrical airbag 1 is divided into 6 planes, including 2 outer planes 10 and 4 inner planes 6; the 2 inner planes 6 are symmetrically folded directly below the top outer plane 10, and the other 2 inner planes 6 are symmetrically folded directly above the bottom outer plane 10. The 4 inner planes 6 are mirror images of each other. Figure 4 and Figure 8 As shown, the arc edge of the top outer plane 10 coincides only with the arc edge of the inner plane 6 directly below it, and the arc edge of the bottom outer plane 10 coincides only with the arc edge of the inner plane 6 directly above it; the straight edges of the two outer planes 10 coincide, and the straight edges of the two mirrored inner planes 6 coincide, thus making the folded model a closed model; the size of the outline of the folded model is adjusted by setting the distance between the short top edge of the trapezoidal surface 9 of the inner plane 6 and the symmetrical horizontal axis of the folded model; after optimizing the calculation to obtain the height value of the trapezoidal surface 9, the final folded model can be determined.

[0072] This invention can completely fold the circular surfaces at both ends of a cylindrical airbag into the cylindrical surface of the airbag, greatly reducing the external size of the flat folding model. The flat folding modeling method is simple. By setting the distance between the short top edge of the trapezoidal surface of the inner plane and the symmetrical horizontal axis of the folding model, the external outline of the flat folding model of different sizes can be adjusted according to the actual engineering situation.

[0073] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0074] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optimization method for a flat-folding cylindrical airbag model for computer simulation, wherein the surface of the airbag is composed of two circular surfaces at both ends and a cylindrical surface in the middle, and the two circular surfaces at both ends are flat-folded inward to the cylindrical surface, folding the airbag surface into four planes, the first layer being the first outer plane, the second layer including the first and second inner planes, the third layer including the third and fourth inner planes, and the fourth layer being the second outer plane; The first outer plane and the second outer plane are mirror images. The first and second inner planes are symmetrically folded directly below the first outer plane. The third and fourth inner planes are symmetrically folded directly above the second outer plane. The first and third inner planes are mirror images, and the second and fourth inner planes are mirror images. The first outer plane and the second outer plane have the same shape, both consisting of symmetrical arc surfaces at both ends and a rectangular surface in the middle. Both contain two arc sides and two straight sides, and the distance between the two straight sides is equal to half the circumference of the circular surfaces at both ends of the airbag. The first to fourth inner planes have the same shape, each consisting of a trapezoidal surface and a circular arc surface. The length of the top edge of the trapezoidal surface is equal to the diameter of the circular surfaces at both ends of the cylindrical airbag, and the length of the bottom edge is equal to half the circumference of the circular surfaces at both ends of the airbag. The arc edge of the first outer plane coincides with the arc edges of the first and second inner planes directly below it; the arc edge of the second outer plane coincides with the arc edges of the third and fourth inner planes directly above it; the straight edges of the first and second outer planes coincide. The straight edges of the first and third inner planes coincide; the straight edges of the second and fourth inner planes coincide. Its features are, The specific steps of the optimization method for the flat-folding model of the cylindrical airbag used for computer simulation are as follows: The size of the outline of the folded model is adjusted by setting the distance between the short top edge of the trapezoidal surface of the inner plane and the symmetrical horizontal axis of the folded model; the height value of the trapezoidal surface of the inner plane is obtained through optimization calculation, and the minimum difference between the surface area of ​​the three-dimensional cylindrical shape and the folded area is obtained, thus determining the optimal folded model.

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