A fast prediction method for parafoil inflation time

Abstract

The present invention proposes a method for quickly predicting the inflation time of a parafoil, comprising the following steps: according to the structural characteristics of the parafoil with multiple air chambers and spanwise folding and the characteristics of the canopy shape change, the canopy shape change during the parafoil inflation process is decomposed into two stages: wing surface expansion and air chamber inflation. The parafoil inflation time includes the wing surface expansion time and the air chamber inflation time. The wing surface expansion time model is analogous to the inflation time model of a square parachute, and the inflation time correction coefficient is affected by the number of parachute ropes per unit area of ​​the parafoil; the air chamber inflation time is determined by the air chamber full volume and the average air inlet velocity. This method combines the parafoil structure and the inflation shape change, simplifies the complex unsteady nonlinear large deformation fluid-solid coupling behavior of the canopy, and can quickly and accurately predict the parafoil inflation time, which is of great significance for quickly estimating the height loss during the inflation process of the parafoil system, optimizing the design of the parafoil opening condition, and analyzing the opening performance.

Description

Technical Field

[0001] The invention belongs to the field of airborne airdrop and pneumatic deceleration equipment, and specifically relates to parafoil design and analysis. Background Art

[0002] Ramjet paragliders are widely used in sports performances, space recovery, precision airdrops and other fields due to their good gliding performance, strong maneuverability and low landing speed.

[0003] The inflation stage of the parafoil is one of the important links that determine whether the parafoil can work normally. Generally speaking, extending the inflation time can effectively reduce the maximum dynamic load of the parafoil opening, avoid the damage of the parafoil canopy caused by excessive dynamic load of the parafoil opening, and improve the reliability of the parafoil system; shortening the inflation time can reduce the height loss during the inflation process and increase the maximum gliding distance of the parafoil. Therefore, it is very important to analyze and study the inflation process of the parafoil and accurately predict the inflation time of the parafoil to improve the working characteristics of the parafoil.

[0004] The parafoil opening process is essentially a process of violent interaction between the flow field and the canopy structure. It is a highly unsteady nonlinear multi-field coupling problem, which is extremely difficult to calculate and requires a lot of computing power. In addition, the flexible parafoil is a multi-chamber curved surface structure, and the folding modeling is more complicated than that of a conventional parachute. Therefore, it is still very difficult to use fluid-structure coupling numerical calculations to predict the inflation time of the parafoil.

[0005] The dynamic method is widely used in the study of parachute inflation performance, but this method must master the law of aerodynamic characteristics change during the inflation process. Due to insufficient understanding of the parafoil inflation time, it is impossible to establish a model of aerodynamic characteristics change during the parafoil inflation process. Therefore, the dynamic calculation of the parafoil inflation process needs to rely on engineering experience and repeated debugging, and the accuracy is low.

[0006] At present, the inflation time of parafoils is mainly obtained by airdropping or wind tunnel testing. The airdrop test is costly, and because the parafoil opens quickly, it is difficult for ordinary cameras to accurately measure the changes in the shape of the parafoil, and the inflation time measurement error is large. On the other hand, the test results are easily affected by uncertain factors such as weather, and the data has a large discreteness, making it difficult to obtain effective test data. Wind tunnel tests are limited by the size of the wind tunnel, and full-size parafoil tests cannot be carried out. In addition, due to the limitations of the test method, the unfolding process of the parafoil from the folded state cannot be simulated.

[0007] In view of the above problems, the present invention decomposes the parafoil inflation process into two stages based on the canopy shape change characteristics during the parafoil inflation process, and proposes a rapid prediction model for the parafoil inflation time based on theoretical analysis. The model is of great significance for predicting the height loss during the inflation process and analyzing the parafoil opening performance. Summary of the invention

[0008] In order to solve the above problems, the present invention proposes a method for quickly predicting the inflation time of a parafoil, which can quickly and accurately predict the inflation time and help to quickly predict the height loss of the parafoil during inflation.

[0009] A method for quickly predicting the inflation time of a parafoil comprises the following steps:

[0010] Step 1: According to the structural characteristics of the parafoil with multiple air chambers and spanwise folding and the characteristics of the canopy shape change, the canopy shape change during the parafoil inflation process is decomposed into two stages: wing surface expansion and air chamber inflation. The parafoil inflation time consists of two parts: wing surface expansion time and air chamber inflation time.

[0011] Step 2: Simplify the wing surface deployment stage into the inflation and opening process of a square parachute. The wing surface deployment time is proportional to the nominal diameter D0 of the parachute and the opening speed v k Inversely proportional, the calculation formula is Where k1 is the wing surface deployment time correction coefficient;

[0012] Step 3: Simplify the air chamber inflation stage into the airbag inflation process. The air chamber inflation time is related to the air chamber filled volume V. qs Proportional to the cutout area A qk and the average velocity at the inlet v p Inversely proportional, the calculation formula is Where k2 is the correction factor for the air chamber inflation time;

[0013] Step 4: Get the parafoil inflation time t m , t m =t1+t2.

[0014] Preferably, the inflation time correction coefficient of the square parachute is referred to, and the wing surface deployment time correction coefficient k1 is determined in combination with the number of parachute ropes arranged per unit area of ​​the parafoil. The more the number of parachute ropes per unit area, the smaller the value of k1.

[0015] Preferably, the air chamber inflation time correction coefficient k2 is determined according to the airflow angle and airfoil structural parameters when the parafoil is inflated, k2=sec(ε+α-90°).

[0016] The present invention has the following beneficial effects:

[0017] This method decomposes the parafoil inflation process into two stages: wing surface expansion and air chamber inflation, based on the characteristics of the canopy shape change during the parafoil inflation process, and obtains the inflation time by using analogy and theoretical analysis methods. This method not only reflects the essence of the canopy shape change during the inflation process, but also avoids the complex nonlinear large deformation fluid-solid coupling calculation. It can quickly and accurately predict the inflation time, and also helps to quickly predict the parachute opening loss height during inflation, which is of great significance for optimizing the design of parachute opening conditions.

[0018] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of a method for quickly predicting the inflation time of a parafoil according to an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the parachute rope configuration of a parafoil according to an embodiment of the present invention;

[0021] Figure 3 is a schematic diagram of the structural parameters of a parafoil air chamber according to an embodiment of the present invention;

[0022] Figure 4 It is a schematic diagram of the airflow direction during the inflation stage of the parafoil air chamber of an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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 creative work are within the scope of protection of the present invention.

[0024] The following is an example of a parafoil system in the literature (Liu Xin. Simulation study of parafoil opening process based on fluid-solid coupling method [D]. Jiangsu: Nanjing University of Aeronautics and Astronautics, 2019: 21-30), and the present invention is further discussed in detail in combination with the accompanying drawings. According to the literature parameters and engineering experience, the parafoil structural parameters and opening conditions of this implementation example are shown in Table 1.

[0025] Table 1

[0026]

[0027] like Figure 1 As shown, a method for quickly predicting the inflation time of a parafoil specifically comprises the following steps:

[0028] Step 1, according to the structural characteristics of the wing parachute with multiple air chambers and span-wise folding and the characteristics of the canopy shape change, the canopy shape change during the wing parachute inflation process is decomposed into two stages: wing surface expansion and air chamber inflation. The wing parachute inflation time consists of two parts: wing surface expansion time and air chamber inflation time.

[0029] Step 2: Simplify the wing surface deployment stage into the inflation and opening process of a square parachute. The wing surface deployment time is proportional to the nominal diameter D0 of the parachute and the opening speed v k Inversely proportional, the calculation formula is Where k1 is the wing surface expansion time correction coefficient.

[0030] Nominal diameter of parafoil According to Table 1, D0 = 4.37 (m). Combined with the parafoil opening speed (Table 1), the wing surface deployment time is:

[0031]

[0032] According to parachute theory, the inflation and deployment time of a square parachute is: The inflation time correction coefficient is generally 5 to 7. The square parachute only has parachute ropes arranged around the periphery, while the paraglider has parachute ropes arranged in both the span and chord directions on the wing surface. Figure 2 As shown, the wing surface unfolds faster. Referring to the inflation time correction factor of the square parachute, the wing surface unfolding time correction factor k1 of the parafoil can be 2 to 3.

[0033] According to the design specifications of parafoils, the larger the canopy area, the lower the number of parachute ropes required per unit area. 2 ~300m 2 , the number of parachute ropes per unit area in this example is relatively large, so k1=2. Then the wing surface deployment time in this example is:

[0034]

[0035] Step 3: Simplify the air chamber inflation stage into the airbag inflation process. The air chamber inflation time is related to the air chamber filled volume V. qs Proportional to the cutout area A qk and the average velocity at the inlet v p Inversely proportional, the calculation formula is Where k2 is the correction coefficient of the air chamber inflation time.

[0036] According to parachute theory, the average air inlet velocity is: (n is 0.85~1), n ​​is affected by the deceleration speed of the inflation process. The larger the wing load per unit area, the slower the deceleration, and the larger the value of n. In this example, 0.95 is taken. Figure 3 As shown, it can be seen that the wing parachute air chamber is filled with volume V qs =bcd p , cutting area A qk =be. Where b is the span, c is the chord length, d p is the average thickness of the airfoil, and e is the size of the cut. According to the parafoil structure design theory, the ratio of the average thickness of the airfoil to the maximum thickness of the airfoil is Relative height of airfoil cutout is about 0.5, then the air chamber inflation time is:

[0037]

[0038] According to the parameters in Table 1, the calculation formula for the air chamber inflation time in this example is: t2 = 0.152k2.

[0039] According to the posture and airflow direction of the parafoil chamber during inflation, Figure 4 , ∠1=ε-β, ∠2=α, ∠3=180°-∠1-∠2=180°-ε+β-α, then the angle between the inlet normal and the airflow velocity ∠4=90°-∠3=ε-β+α-90°, where α is the airflow angle, ε is the incision angle, and β is the geometric angle. β is small and can be ignored. According to the parameters in Table 1, it can be obtained that the airflow velocity angle ∠4=ε+α-90°=30°, and the correction coefficient is:

[0040]

[0041] The air chamber inflation time in this example is: t2 = 0.152 × 1.155 = 0.176 (s).

[0042] In summary, the total inflation time of the parafoil in this example is t m =t1+t2=0.429(s).

[0043] According to the average speed and trajectory angle during inflation, the parachute opening loss caused by the inflation process is approximately H = v p t m cosθ≈10.78(m).

[0044] Compared with the parafoil inflation time t of reference m =0.404(s), the error of this prediction method is 6.19%, and the prediction accuracy is higher.

[0045] The specific embodiments described above are further explanations of the purpose, technical solutions and beneficial effects of the present invention and should not be construed as limitations of the present invention. Any modifications, improvements, equivalent substitutions, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for quickly predicting the inflation time of a parafoil, characterized in that The process includes: Step 1: According to the structural characteristics of the wing parachute with multiple air chambers and spanwise folding and the characteristics of the canopy shape change, the canopy shape change during the wing parachute inflation process is decomposed into two stages: wing surface expansion and air chamber inflation; Step 2: Simplify the wing surface deployment stage into the inflation and opening process of a square parachute, determine the wing surface deployment time correction coefficient k1 and the wing surface deployment time t1, specifically, refer to the inflation time correction coefficient of the square parachute, and determine the wing surface deployment time correction coefficient k1 in combination with the number of parachute ropes arranged per unit area of ​​the parachute, wherein the more the number of parachute ropes per unit area, the smaller the value of k1; Where D0 is the nominal diameter of the parafoil, v k is the parachute opening speed; Step 3, simplifying the air chamber inflation stage into the inflation process of the airbag, determining the air chamber inflation time correction coefficient k2 and the air chamber inflation time t2, specifically, determining the air chamber inflation time correction coefficient k2 according to the airflow angle and airfoil structural parameters during the wing parafoil inflation, k2 = sec (ε + α - 90°), where ε is the cutout angle and α is the airflow angle; Among them, V qs is the volume filled with air chamber, A qk is the cutout area, v p is the average velocity at the air inlet; Step 4: Based on Step 2 and Step 3, the parafoil inflation time t is obtained. m , t m =t1+t2.

2. A method for quickly predicting the inflation time of a parafoil according to claim 1, characterized in that: The air chamber fills a volume V qs It can be calculated from the span b, chord length c, and average airfoil thickness d p Indicates that V qs =bcd p The average air inlet velocity is Where n is the coefficient affected by the deceleration speed of the inflation process, v k is the parachute opening speed, and the air chamber inflation time is

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