A method for determining the breathing frequency spectrum after opening of a parachute in supersonic conditions
By installing an accelerometer on the recovered material to measure the three-component acceleration and performing a Fourier transform, the accuracy problem of obtaining breathing frequency under supersonic conditions of parachutes in the prior art has been solved, and high-precision frequency data acquisition has been achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-30
- Publication Date
- 2026-03-24
AI Technical Summary
Existing technologies struggle to accurately measure the breathing frequency of a parachute under supersonic conditions, resulting in large errors and making quantitative calculations impossible. Furthermore, the error is even greater when the breathing effect does not significantly change the shape of the parachute canopy.
By installing accelerometers on the recovered material, measuring the three-component acceleration data, performing Fourier transform, and extracting the extreme values in the frequency load curve, the respiratory frequency spectrum under supersonic parachute conditions is obtained.
It achieves high-precision acquisition of parachute breathing frequency, avoids the subjective error of image-based methods, and can accurately acquire the primary and secondary frequencies, applicable to various parachute types and opening conditions.
Smart Images
Figure CN116296229B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for determining the breathing frequency spectrum after a parachute opens under supersonic conditions, belonging to the field of aerodynamic deceleration in aviation. Background Technology
[0002] In the aerospace field, parachutes provide effective deceleration or stabilization for recovered materials. Under supersonic conditions, the parachute remains behind the shock wave of the recovered material, and a bow-shaped shock wave also forms in front of the parachute. As the Mach number increases, the spacecraft's wake and the parachute's shock wave interact, causing pulsations in the bow-shaped shock wave in front of the parachute. This results in a continuous, rhythmic filling-contraction-filling action of the parachute. The rapid filling and contraction of the parachute under supersonic conditions causes uneven flow field distribution within the canopy, leading to a decrease in drag area after full filling. Furthermore, this continuous, rapid breathing action can cause fatigue damage at the parachute's contact points, potentially leading to parachute failure. To avoid localized parachute failure due to breathing under supersonic conditions, the duration and frequency of parachute breathing under supersonic conditions should be determined for thorough ground testing.
[0003] The commonly used evaluation method for the breathing effect of supersonic parachutes is the image comparison method. This method uses video footage of parachute deployment under supersonic conditions obtained from airdrop tests to visually compare changes in the parachute's projected area and estimate the frequency of the breathing effect. However, the image method can only provide estimated data and cannot provide quantitative calculations. Furthermore, for breathing effects where the canopy shape does not change significantly, the image comparison method yields large errors. Summary of the Invention
[0004] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a method for determining the respiratory frequency spectrum after parachute deployment under supersonic conditions, thereby obtaining frequency data of respiratory action under supersonic conditions.
[0005] The technical solution to the problem solved by this invention is: a method for determining the breathing frequency spectrum after a parachute opens under supersonic conditions, the method comprising the following steps:
[0006] S1. Obtain the load-time variation curve of the supersonic parachute during its working process.
[0007] S2. Perform a Fourier transform on the parachute load to obtain the load frequency variation curve;
[0008] S3. By extracting the extreme values in the frequency load curve, the frequency spectrum of the respiratory effect under supersonic parachute conditions is obtained.
[0009] Preferably, the extreme values in the frequency load curve in step S3 include at least the maximum value, the second largest value, and the third largest extreme value.
[0010] Preferably, step S1 is specifically implemented as follows:
[0011] S1.1 Connect the parachute to the recovered object so that the aerodynamic load generated by the parachute under supersonic conditions is transferred to the recovered object; the recovered object is selected as a rotating body structure.
[0012] S1.2. Install an acceleration sensor on the reclaimed material to measure three-component acceleration data; the three components include the acceleration a along the central axis of the reclaimed material. x (t), normal acceleration a y (t), lateral acceleration a z (t), the normal acceleration is perpendicular to the central axis of the recovered object, the lateral acceleration is perpendicular to the central axis acceleration and the normal acceleration, and the right-hand rule is satisfied;
[0013] S1.3 Conduct a flight test under supersonic conditions with a parachute, collect data on the three-component acceleration as a function of time during the operation of the parachute, and obtain the data on the composite acceleration of the parachute as a function of time, a(t).
[0014] S1.4 Extract the acceleration data over time corresponding to the parachute opening time under supersonic conditions from the composite acceleration data a(t) of the parachute;
[0015] S1.5. Based on the composite acceleration data of the parachute extracted in S1.4, calculate the composite load change data F(t) of the parachute, and plot the load-time curve of the working process of the supersonic parachute.
[0016] Preferably, the acceleration sensor is installed at the center of mass of the recovered material.
[0017] Preferably, the accelerometer is installed in three directions: along the central axis of the recovered material, the normal direction, and the lateral direction. The normal and lateral directions are perpendicular to the central axis and satisfy the right-hand rule.
[0018] Preferably, the aerodynamic load of the parachute is:
[0019] F(t)=Ma(t)·
[0020] Where M is the total mass of the recovered material and the parachute, and a(t) is the resultant acceleration of the parachute over time.
[0021] Preferably, the parachute deployment time under supersonic conditions starts at the point when the aerodynamic load exceeds 5% of its peak value and ends when the Mach number is less than 1.5.
[0022] Preferably, the frequency of the accelerometer measurement is not less than 2000Hz.
[0023] Preferably, the connection between the recovered material and the parachute is as follows: the parachute and the recovered material are connected by slings, with the centerline of each sling passing through the central axis of the recovered material.
[0024] The advantages of this invention compared to the prior art are:
[0025] (1) In this invention, the aerodynamic load during the parachute operation is directly measured by an accelerometer. The accelerometer has high accuracy and can well characterize the load changes of the parachute under various supersonic conditions, reflecting the parachute's breathing phenomenon.
[0026] (2) The breathing frequency of the parachute of the present invention is obtained by Fourier transform of high-precision load time data, avoiding the error caused by subjective judgment in the image method.
[0027] (3) Because the load data sampling rate is very high, the Fourier transform can obtain the breathing frequency over a large range, and will not fail to capture the rapid breathing of the parachute.
[0028] (4) By taking the extreme value of the frequency load curve, the present invention can not only obtain the main frequency of parachute breathing action, but also the secondary frequency with a larger secondary load. The obtained parachute breathing action frequency data under supersonic conditions is richer, and the method is more accurate and universal.
[0029] (5) This invention can calculate the breathing frequency of all parachutes, without any restrictions on parachute type or opening conditions. Attached Figure Description
[0030] A fuller understanding of the invention can be obtained from the accompanying drawings, which form part of this application, and the following detailed description.
[0031] Figure 1 This invention provides a method for calculating the wind field during the operation of a parachute.
[0032] Figure 2 This is a schematic diagram of parachute load measurement according to an embodiment of the present invention;
[0033] Figure 3 This is the load-time curve of the parachute under supersonic conditions according to an embodiment of the present invention;
[0034] Figure 4 This is the load frequency distribution of the parachute breathing effect in an embodiment of the present invention. Detailed Implementation
[0035] The present invention will be further described below with reference to the embodiments.
[0036] like Figure 1 As shown, this invention provides a method for determining the breathing frequency spectrum after a parachute opens under supersonic conditions. This method comprises three parts: acquiring the parachute load in an airdrop test, performing a Fourier transform of the load data, and calculating the time and frequency of the breathing effect. It is a method for inverting the horizontal wind field of a parachute in an airdrop test, specifically including the following steps:
[0037] S1. Obtain the load-time variation curve of the supersonic parachute during its operational process; specifically implemented as follows:
[0038] S1.1 Connect the parachute to the recovered object so that the aerodynamic load generated by the parachute under supersonic conditions is transferred to the recovered object; the recovered object is selected as a rotating body structure. In the airdrop test, the parachute is connected to the recovered object, and the aerodynamic load generated by the parachute under supersonic conditions is transferred to the recovered object. In order to obtain the aerodynamic load of the parachute and avoid measurement errors caused by the attitude of the recovered object, an acceleration sensor is installed at the center of mass of the recovered object. The connection method between the recovered object and the parachute is as follows: the parachute and the recovered object are connected by slings, and the centerline of each sling passes through the central axis of the recovered object.
[0039] S1.2. Install an acceleration sensor on the reclaimed material to measure three-component acceleration data; the three components include the acceleration a along the central axis of the reclaimed material. x (t), normal acceleration a y (t), lateral acceleration a z (t), the normal acceleration is perpendicular to the central axis of the recovered object, the lateral acceleration is perpendicular to the central axis acceleration and the normal acceleration, and the right-hand rule is satisfied;
[0040] S1.3 Conduct a flight test under supersonic conditions with a parachute, collect data on the three-component acceleration as a function of time during the operation of the parachute, and obtain the data on the composite acceleration of the parachute as a function of time, a(t).
[0041] S1.4 Extract the acceleration data over time corresponding to the parachute opening time under supersonic conditions from the composite acceleration data a(t) of the parachute;
[0042] S1.5. Based on the composite acceleration data of the parachute extracted in S1.4, calculate the composite load change data F(t) of the parachute, and plot the load-time curve of the working process of the supersonic parachute.
[0043] The accelerometer is installed in three directions: along the central axis of the recovered object, the normal direction, and the lateral direction. The normal and lateral directions are perpendicular to the central axis and satisfy the right-hand rule. The accelerometer's measurement frequency is no less than 2000Hz. Due to the high sampling rate of the payload data, the Fourier transform can obtain a wide range of breathing frequencies, ensuring that the rapid breathing of the parachute is not missed.
[0044] The aerodynamic load of the parachute is:
[0045] F(t)=Ma(t)·
[0046] Where M is the total mass of the recovered material and the parachute, and a(t) is the resultant acceleration of the parachute over time.
[0047] To avoid interference from measurement data, the starting point of the parachute opening time under supersonic conditions is set at the point when the aerodynamic load exceeds 5% of its peak value, and the ending point is when the Mach number is less than 1.5.
[0048] S2. Perform a Fourier transform on the parachute load to obtain the load frequency variation curve;
[0049] S3. By extracting the extreme values in the frequency load curve, the frequency spectrum of the respiratory effect under supersonic parachute conditions is obtained.
[0050] The extreme values in the frequency load curve include at least the maximum value, the second largest value, and the third largest extreme value.
[0051] In the parachute load acquisition section of this invention, a high-precision accelerometer is used to acquire load-time data during the parachute's operation, ensuring timely acquisition of parachute load changes caused by breathing. In the Fourier transform section of the load data, by taking the extreme values of the frequency-load curve, not only the dominant frequency of parachute breathing can be obtained, but also the secondary frequencies with larger secondary loads. This results in richer acquisition of parachute breathing frequency data under supersonic conditions, making the method more accurate and versatile.
[0052] This invention can be used to obtain the respiratory rate under supersonic conditions of parachutes, thereby providing a basis for accurate and sufficient experimental verification on the ground.
[0053] In a specific embodiment of the present invention, the specific implementation steps are as follows:
[0054] The load time data of parachute breathing effect are obtained by the load measurement equipment in the airdrop test, with at least 200 data points per second and a duration of more than 5 seconds;
[0055] Perform a Fourier transform on the parachute load to obtain the load frequency curve;
[0056] Extract the three extreme values fmax1, fmax2, and fmax3 of the peak in the frequency load curve, and then the breathing frequencies under supersonic parachute conditions are fmax1, fmax2, and fmax2, respectively.
[0057] The parachute load measurement, load-time curve, and load-frequency curve involved in this embodiment are shown in the following figures. Figure 2 , Figure 3 , Figure 4 As shown.
[0058] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present 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 technical solutions of the present invention.
Claims
1. A method of determining the breathing frequency spectrum after parachute opening in supersonic conditions, characterized in that The method comprises the following steps: S1, obtaining a load-time curve of a working process of a parachute under supersonic conditions; S2, performing Fourier transform on the load of the parachute to obtain a load-frequency curve; S3, extracting extreme values in the load-frequency curve to obtain a frequency spectrum of breathing action of the parachute under supersonic conditions; The specific implementation of the step S1 is as follows: S1.1, connecting the parachute with a recovery object, so that the aerodynamic load generated by the parachute under supersonic conditions is transmitted to the recovery object; the recovery object is a gyroid structure. S1.2, mounting an acceleration sensor on the recyclate for measuring three-component acceleration data; the three components comprising a central axis direction acceleration of the recyclate , a normal acceleration , a lateral acceleration , the normal acceleration being perpendicular to the central axis direction of the recyclate, the lateral acceleration being perpendicular to the central axis direction acceleration and the normal acceleration, and satisfying the right-hand rule; S1.3, conducting a parachute supersonic speed condition flight test, collecting three-component acceleration data varying with time during parachute operation, and obtaining parachute synthetic acceleration data varying with time ; S1.4, extracting acceleration over time data corresponding to the opening time period of the parachute under supersonic conditions from the synthetic acceleration over time data of the parachute extracting acceleration over time data corresponding to the opening time period of the parachute under supersonic conditions from the synthetic acceleration over time data of the parachute S1.5, according to the synthetic acceleration data of the parachute extracted in S1.4, the synthetic load change data of the parachute is calculated and the working process load-time curve of the parachute under supersonic condition is plotted accordingly.
2. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The extreme values in the load-frequency curve in the step S3 at least include a maximum value, a second maximum value and a third maximum value.
3. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The acceleration sensor is installed at a center of mass position of the recovery object.
4. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The installation direction of the acceleration sensor is that three directions of the acceleration sensor are along a central axis direction, a normal direction and a lateral direction of the recovery object, the normal direction and the lateral direction are perpendicular to the central axis direction and satisfy a right-hand rule.
5. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The aerodynamic load of the parachute is: wherein, Mtot is the total mass of the recovery and parachute, is the time derivative of the resultant acceleration of the parachute.
6. A method of determining the post-opening breath frequency spectrum of a parachute under supersonic conditions according to claim 1, characterized in that The opening time period of the parachute under supersonic conditions is from a time point at which the aerodynamic load exceeds 5% of a peak value of the aerodynamic load to a time point at which a Mach number is less than 1.
5.
7. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The frequency of the acceleration sensor during measurement is not less than 2000 Hz.
8. A method of determining the breathing frequency spectrum of a parachute after opening in supersonic conditions according to claim 1, characterized in that The connection mode of the recovery object and the parachute is that the parachute and the recovery object are connected through harnesses, and center lines of the harnesses pass through the central axis direction of the recovery object.