Parachute three-dimensional shape parameterization expression method based on optical measurement

Abstract

The parachute three-dimensional shape parameterization expression method based on optical measurement comprises the steps that the three-dimensional shape dynamic change condition in the parachute opening process of a parachute is obtained through optical measurement, three-dimensional modeling and reconstruction are conducted on the parachute shape, and parachute three-dimensional shape parameters are obtained. The device has the advantages of high measurement efficiency, high measurement accuracy and convenience in data processing, does not damage a parachute product, can be implemented by being carried in a wind tunnel test, and is good in economical efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of parachute design for aerodynamic deceleration of aircraft, and can be used for shape measurement of a parachute when the parachute is fully deployed and during the process of inflation and deployment. BACKGROUND

[0002] A parachute is a flexible deployable aerodynamic deceleration device, which has the advantages of light weight, small packing volume and convenient deployment. After deployment, the parachute can be quickly deployed and generate a large drag surface to generate a large deceleration force. The deployment process of the parachute is the stage at which the maximum load of the parachute is generated, and the deployment load of the parachute is the most important index in the design of the parachute. During the deployment process, the shape size of the parachute changes rapidly, and accurate acquisition of the three-dimensional shape of the parachute during the inflation process is one of the key methods to improve the calculation accuracy of the deployment load of the parachute. The three-dimensional shape of the parachute is generally acquired through simulation calculation, and how to verify the simulation model needs experimental means. At present, there is no public experience on the method for measuring and reconstructing the three-dimensional shape of the parachute during the deployment process. SUMMARY

[0003] The technical problem solved by the present application is to overcome the shortcomings of the prior art, provide a method for acquiring the dynamic changes of the three-dimensional shape of a parachute during the deployment process based on optical measurement, and propose a parameterized expression method for the three-dimensional shape of the parachute to perform three-dimensional modeling and reconstruction on the three-dimensional shape of the parachute, and obtain the three-dimensional shape parameters of the parachute.

[0004] The technical solution of the present application is:

[0005] The parameterized expression method for the three-dimensional shape of the parachute based on optical measurement comprises:

[0006] 1) determining J+M+N parachute measurement marker points; wherein the parachute measurement marker points comprise J radial band position marker points, N canopy bottom edge marker points and M parachute rope intermediate position marker points; wherein the radial band position marker points comprise a canopy top center point;

[0007] 2) fully deploying the parachute, and acquiring data of the three-dimensional space coordinates of the parachute measurement marker points changing with time by optical measurement;

[0008] 3) extracting the coordinates of each parachute measurement marker point at time t;

[0009] 4) fitting the coordinates of the radial band position marker points to obtain a longitudinal section, and fitting the coordinates of the canopy bottom edge marker points to obtain a bottom edge section;

[0010] 5) determining the inflation height H1 by using the canopy top center point and the bottom edge section;

[0011] 6) Select any one of the M paracord midpoint markers, calculate the spatial distance between the coordinates of the midpoints of two adjacent paracord midpoints on the bottom edge of the canopy and the bottom edge tangent, and obtain the outward expansion height B1 of the bottom edge of the canopy.

[0012] 7) Obtain the maximum value between two points among the N umbrella canopy bottom edge markers, and use it as the bottom edge diameter J1;

[0013] 8) Randomly select a marker point at the middle of the paracord, and determine the vertical distance B3 from the center point of the umbrella top to the two bottom edge marker points of the umbrella canopy adjacent to the marker point at the middle of the paracord and the coordinates of the center point of the umbrella top.

[0014] 9) Using the umbrella bottom edge outward expansion height B1 obtained in step 6) and the vertical distance B3 from the umbrella top center point to the two umbrella bottom edge marking points obtained in step 8), determine the umbrella bottom edge outward expansion distance B2;

[0015] 10) The inflation height H1 obtained in step 5), the bottom diameter J1 obtained in step 7), and the outward expansion distance B2 of the bottom edge of the parachute obtained in step 9) are used as the three-dimensional shape expression parameters of the parachute to determine the parachute's projected area and inflation volume.

[0016] 11) Repeat steps 3) to 10) to obtain the parachute projected area and inflation volume at each moment.

[0017] Preferably, J radial belt position markers are obtained: J markers are evenly distributed along the paracord as radial belt position markers;

[0018] Obtain N bottom edge marking points for the umbrella canopy: Arrange N marking points at the intersection of the bottom edge of the umbrella canopy and the umbrella lines as bottom edge marking points for the umbrella canopy; where N is equal to the number of umbrella canopies, and the N bottom edge marking points for the umbrella canopy are evenly distributed around the perimeter;

[0019] To obtain M paracord midpoint markers: Randomly select M groups of two adjacent paracords and place a marker at the midpoint of the intersection of the two adjacent paracords and the bottom edge of the canopy as the paracord midpoint marker.

[0020] Preferably, the number of M is not less than 2.

[0021] Preferably, the J radial position markers, N canopy bottom edge markers, and M parachute line midpoint markers are sequentially numbered starting from 1 to obtain J+M+N parachute measurement markers; then:

[0022] The J radially marked points are labeled in the range [1, J];

[0023] The labels of the N umbrella canopy bottom edge markers belong to [J+1, J+N];

[0024] The labels of the M paracord midpoints belong to [J+N+1, J+M+N].

[0025] Preferably, the longitudinal section and the bottom section are obtained by least squares fitting.

[0026] Preferably, step 10) determines the parachute's projected area, specifically as follows:

[0027] The parachute's projected diameter is determined to be B2*2+J1, and then the parachute's projected area is determined using the parachute's projected diameter.

[0028] Preferably, step 9) determines the outward expansion distance B2 of the umbrella bottom edge, specifically as follows:

[0029]

[0030] Preferably, step 4) involves obtaining the longitudinal section by fitting the coordinates of the radially marked points, specifically as follows:

[0031] Let the longitudinal section be: z = a0x + a1y + a2;

[0032] The radial band fitting plane coefficients a0, a1, and a2 are determined by the following formula:

[0033]

[0034] Where, x i ,y i ,z i Let i be the coordinates of the radially marked point, where i belongs to [1, J].

[0035] Preferably, step 4) involves using coordinate fitting of the marked points on the bottom edge of the umbrella canopy to obtain the bottom edge cross-section, specifically as follows:

[0036] Let the bottom tangent plane be: z = b0x + b1y + b2;

[0037] The radial band fitting plane coefficients b0, b1, b2 are determined by the following formula:

[0038]

[0039] Where, x i ,y i ,z i Let i be the coordinates of the bottom edge of the umbrella canopy, where i belongs to [J+1, J+N].

[0040] Compared with the prior art, the advantages of the present invention are mainly reflected in:

[0041] This invention proposes a method for acquiring the dynamic changes in the three-dimensional shape of a parachute during its deployment process based on optical measurements. It also proposes a parametric representation method for the three-dimensional shape of the parachute, enabling three-dimensional modeling and reconstruction of the parachute's shape to obtain its parameters. This method offers advantages such as high measurement efficiency, high accuracy, and convenient data processing. It does not damage the parachute product, can be implemented simply by mounting it in a wind tunnel, and is economical. Attached Figure Description

[0042] Figure 1 Top view of the parachute measurement markers;

[0043] Figure 2 This is a schematic diagram of the three-dimensional coordinate data of the parachute marker points in one embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the fitting of the radial section and the bottom section in one embodiment of the present invention;

[0045] Figure 4(a) is a front view of the three-dimensional shape parameters of the parachute of the present invention;

[0046] Figure 4(b) is a bottom view of the three-dimensional shape parameters of the parachute of the present invention. Detailed Implementation

[0047] This invention proposes a method for obtaining the dynamic changes in the three-dimensional shape of a parachute during the opening process based on optical measurement. It also proposes a parametric method for the three-dimensional shape of a parachute, which can perform three-dimensional modeling and reconstruction of the parachute shape to obtain the three-dimensional shape parameters of the parachute.

[0048] The main steps include:

[0049] a) Determine J+M+N parachute measurement marker points.

[0050] The parachute measurement markers include: J radial zone position markers, N canopy bottom edge markers, and M parachute line midline position markers;

[0051] Obtain J radially positioned marker points: such as Figure 1 As shown, J marker points are arranged along two radial bands symmetrical about the center of the parachute. The radial band position markers include: the coordinates of the parachute top center point (x...). d ,y d ,z d ).

[0052] Obtain N marking points on the bottom edge of the umbrella canopy: Place N marking points at the intersection of the bottom edge of the umbrella canopy and the umbrella lines, where N is equal to the number of umbrella canopies (i.e. the number of umbrella lines).

[0053] To obtain M marker points at the midpoint of the paracord: Randomly select M groups of two adjacent paracords and place marker points at the midpoint of the intersection of the two adjacent paracords and the bottom edge of the canopy. The specific number M can be determined as needed, but to ensure measurement accuracy, it is generally no less than 2.

[0054] The J radial position markers, N canopy bottom edge markers, and M parachute line midpoint markers are numbered sequentially from 1, resulting in J+M+N parachute measurement markers. Then:

[0055] The labels of the J radially marked points belong to [1, J]; Figure 1 (Middle green dot).

[0056] The labels of the N umbrella canopy bottom edge markers belong to [J+1, J+N]; Figure 1 (Middle red dot).

[0057] The labels of the M parachute rope midpoints belong to [J+N+1, J+M+N]; Figure 1 (Middle purple dot).

[0058] b) Experimental Measurement: With the parachute fully deployed, optical measurements are used to obtain data on the three-dimensional spatial coordinates of the marked points as a function of time. For time t, the coordinates (x, y, t) of each marked point are obtained. i ,y i ,z i )(i=1,2,...,J+N+M).

[0059] c) Experimental Data Processing: By processing the three-dimensional coordinates of the marked points and performing fitting calculations, the three-dimensional shape parameters of the parachute inflation process (base diameter J1, parachute base outward expansion distance B2, inflation height H1) are obtained as the three-dimensional shape expression parameters of the parachute, used to calculate the parachute's projected area and inflation volume. Specifically:

[0060] 1) Using the coordinates of J radially marked points, a longitudinal section is obtained by fitting the coordinates. Assume the fitted longitudinal section is:

[0061] z = a0x + a1y + a2

[0062] Using the least squares method to fit the plane, we have:

[0063]

[0064] Take the derivatives of the coefficients separately:

[0065]

[0066] After extracting the coefficients:

[0067]

[0068] When arranged in matrix form, the following are available:

[0069]

[0070] Where i belongs to [1, J].

[0071] The solution yields the radial band fitting plane coefficients (a0, a1, a2).

[0072] 2) Using the coordinates of N marked points on the bottom edge of the umbrella canopy, fit the bottom edge sectional surface to obtain the sectional surface. The fitting method is the same as in step 1). Solve for the fitting plane coefficients (b0, b1, b2) of the bottom edge of the umbrella canopy to obtain the expression for the bottom edge sectional surface z = b0x + b1y + b2.

[0073]

[0074] Where i belongs to [J+1, J+N].

[0075] 3) Calculate the angle θ between the longitudinal section in step 1) and the bottom section in step 2):

[0076]

[0077] θ should be around 90° (in this embodiment of the invention, θ is between 89-91°), indicating that the measurement and fitting method is accurate. Otherwise, outliers need to be removed and the experimental measurement in step b) needs to be repeated.

[0078] 6) Calculate the coordinates of the center point of the umbrella top (x d ,y d ,z d The spatial distance from the bottom edge tangent plane (i.e., the bottom edge fitting plane) z = b0x + b1y + b2 is taken as the inflation height H1, specifically:

[0079]

[0080] 7) Select any one of the M paracord midpoint markers and calculate the spatial distance between the coordinates of the midpoints of two adjacent paracord midpoints on the bottom edge of the canopy and the bottom edge tangent plane (i.e., the bottom edge fitting plane) z = b0x + b1y + b2, which is the outward expansion height B1 of the bottom edge of the canopy. The method is the same as step 6).

[0081] 8) Obtain the maximum value between any two points among the N bottom edge markers of the umbrella canopy, and use this value as the bottom edge diameter J1; that is, use the coordinates of any point (x, y) of the bottom edge markers of the umbrella canopy. i ,y i ,z i (i = J+1, ..., J+N), calculate (x i ,y i ,z i(i = J+1, ..., J+N) and (x j ,y j ,z j The distance between (j = J+1, ..., J+N; j ≠ i) points is taken as the maximum value and denoted as D. i .

[0082]

[0083] 9) Randomly select a marker point at the middle of the paracord, and based on the two adjacent marker points at the bottom edge of the canopy, and the coordinates of the center point of the canopy top (x... d ,y d ,z d Determine the vertical distance B3 from the center point of the umbrella top to the two marked points on the bottom edge of the umbrella canopy; that is, for M umbrella canopy bottom edges, mark points are arranged at the midpoint between the two umbrella ropes, with coordinates denoted as (x... i ,y i ,z i (i = J + N + 1, ..., J + N + M), the coordinates of the two umbrella canopy bottom edge markers near this point are (x k ,y k ,z k ), (x p ,y p ,z p ), calculate the distance from the point to the line:

[0084]

[0085] 10) Calculate the outward expansion distance of the umbrella canopy bottom edge due to aerodynamic load, i.e., the outward expansion distance B2 of the umbrella bottom edge:

[0086]

[0087] 11) Calculate the projected diameter of the umbrella canopy as B2*2+J1, and determine the projected area;

[0088] 12) Determine the parachute inflation volume using the inflation height H1 and the parachute projection area.

[0089] Parachute measurement marker distribution scheme as follows Figure 1 As shown, one marker is placed at the center of the umbrella top, and J-1 markers are placed along two symmetrical radial sections. N markers are placed along the umbrella lines at the bottom edge of the canopy, where N is the number of canopy flaps (number of umbrella lines). A marker M is placed between the two umbrella lines at the bottom edge of the canopy; the exact number can be determined as needed, but generally no less than two are used to ensure measurement accuracy. A total of J+N+M markers are used. The experiment measures the three-dimensional spatial coordinates of the marker positions as a function of time. For time t, the coordinates (x, y, y) of each marker are obtained. i ,yi ,z i (i = 1, 2, ..., J + N + M) such as Figure 2 As shown. The coordinates of J radially positioned marker points and N umbrella canopy bottom edge marker points are fitted to a plane, as follows: Figure 3 As shown in Figure 4(a) and Figure 4(b), the inflation height H1, the outward expansion height B1 of the umbrella bottom edge, the outward expansion distance B2 of the umbrella bottom edge, the vertical distance B3 from the center point of the umbrella top to the two bottom edge marking points of the umbrella canopy, and the bottom edge diameter J1 are obtained through data processing.

[0090] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make possible variations and modifications to the technical solutions of the present invention using the disclosed methods and techniques without departing from the spirit and scope of the invention. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall fall within the protection scope of the present invention. Where there is no conflict, the embodiments of this application and the technical features thereof can be combined with each other.

[0091] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A parametric representation method for the three-dimensional shape of a parachute based on optical measurement, characterized in that, include: 1) Determine J+M+N parachute measurement markers; wherein, the parachute measurement markers include: J radial band position markers, N canopy bottom edge markers, and M parachute line midpoint markers; wherein, the radial band position markers include the parachute top center point; 2) Fully deploy the parachute and use optical measurements to obtain data on the three-dimensional spatial coordinates of the parachute measurement markers as a function of time; 3) For time t, extract the coordinates of each parachute measurement marker point; 4) Obtain the longitudinal section by fitting the coordinates of the radial position markers, and obtain the bottom section by fitting the coordinates of the bottom edge markers of the umbrella canopy. 5) Determine the inflation height H1 using the center point of the umbrella top and the tangent of the bottom edge; 6) Select any one of the M paracord midpoint markers, calculate the spatial distance between the coordinates of the midpoints of two adjacent paracord midpoints on the bottom edge of the canopy and the bottom edge tangent, and obtain the outward expansion height B1 of the bottom edge of the canopy. 7) Obtain the maximum value between two points among the N umbrella canopy bottom edge markers, and use it as the bottom edge diameter J1; 8) Randomly select a marker point at the middle of the paracord, and determine the vertical distance B3 from the center point of the umbrella top to the two bottom edge marker points of the umbrella canopy adjacent to the marker point at the middle of the paracord and the coordinates of the center point of the umbrella top. 9) Using the umbrella bottom edge outward expansion height B1 obtained in step 6) and the vertical distance B3 from the umbrella top center point to the two umbrella bottom edge marking points obtained in step 8), determine the umbrella bottom edge outward expansion distance B2; 10) The inflation height H1 obtained in step 5), the bottom diameter J1 obtained in step 7), and the outward expansion distance B2 of the bottom edge of the parachute obtained in step 9) are used as the three-dimensional shape expression parameters of the parachute to determine the parachute's projected area and inflation volume. 11) Repeat steps 3) to 10) to obtain the parachute projected area and inflation volume at each moment.

2. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 1, characterized in that, Obtain J radial band position markers: Distribute J markers evenly along the paracord as radial band position markers; Obtain N bottom edge marking points for the umbrella canopy: Arrange N marking points at the intersection of the bottom edge of the umbrella canopy and the umbrella lines as bottom edge marking points for the umbrella canopy; where N is equal to the number of umbrella canopies, and the N bottom edge marking points for the umbrella canopy are evenly distributed around the perimeter; To obtain M paracord midpoint markers: Randomly select M groups of two adjacent paracords and place a marker at the midpoint of the intersection of the two adjacent paracords and the bottom edge of the canopy. These markers will serve as the paracord midpoint markers.

3. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 2, characterized in that, The number of M is no less than 2.

4. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 3, characterized in that, Number the J radial position markers, N canopy bottom edge markers, and M parachute line midpoint markers sequentially from 1 to obtain J+M+N parachute measurement markers; then: The J radially marked points are labeled in the range [1, J]; The labels of the N umbrella canopy bottom edge markers belong to [J+1, J+N]; The labels of the M paracord midpoints belong to [J+N+1, J+M+N].

5. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to any one of claims 1-4, characterized in that, The longitudinal section and the bottom section were obtained by least squares fitting.

6. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 5, characterized in that, Step 10) Determine the projected area of ​​the parachute, specifically: The parachute's projected diameter is determined to be B2*2+J1, and then the parachute's projected area is determined using the parachute's projected diameter.

7. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 6, characterized in that, Step 9) Determine the outward expansion distance B2 of the umbrella bottom edge, specifically:

8. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 7, characterized in that, Step 4) The method of obtaining the longitudinal section by fitting the coordinates of the radially marked points is as follows: Let the longitudinal section be: z = a0x + a1y + a2; The radial band fitting plane coefficients a0, a1, and a2 are determined by the following formula: Where, x i ,y i ,z i Let i be the coordinates of the radially marked point, where i belongs to [1, J].

9. The parametric representation method for the three-dimensional shape of a parachute based on optical measurement according to claim 8, characterized in that, Step 4) The method of obtaining the bottom edge sectional plane by fitting the coordinates of the marked points on the bottom edge of the umbrella canopy is as follows: Let the bottom tangent plane be: z = b0x + b1y + b2; The radial band fitting plane coefficients b0, b1, b2 are determined by the following formula: Where, x i ,y i ,z i Let i be the coordinates of the bottom edge of the umbrella canopy, where i belongs to [J+1, J+N].

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