Method for high efficiency constant pressure difference air tightness test of large size airship envelope

Abstract

The application belongs to the technical field of ground test of airship envelope of large-size airship, and relates to a high-efficiency constant pressure difference air-tightness test method for the envelope of large-size airship. The application converts the ground air-tightness test of the envelope of large-size airship into the volume measurement of small-size standard air bags by arranging N small-size standard air bags in the envelope of airship, and the whole air-tightness test process of the envelope of airship is in a constant pressure state, so that the test error of the envelope of large-size airship caused by pressure difference and the error caused by the gradient change of atmospheric pressure in the height direction are eliminated, the air-tightness test error caused by the volume change of the envelope of airship under the action of different pressure differences is reduced to the minimum, the test error caused by the leakage of the standard air bags is eliminated because the standard air bags are arranged in the envelope of airship, the precision of the ground air-tightness test of the envelope of large-size airship is improved, and in addition, the test cycle of the air-tightness test is shortened and the test efficiency is improved due to the implementation of the constant pressure difference method.

Description

Technical Field

[0001] This invention belongs to the field of ground testing technology for airship capsules, specifically relating to an efficient testing method for the constant pressure difference airtightness of large-size airship capsules. Background Technology

[0002] Currently, airship airtightness testing methods are divided into two categories. The first utilizes buoyancy gases, such as hydrogen and helium, to directly determine the leakage rate by measuring the net buoyancy of the airship airtightness in real time. The second method uses the ideal gas law for calculation. The ideal gas law, PV = nRT, describes that for a given mass of an ideal gas, as it changes from one state to another, although P, V, and T may change, the ratio of the product of pressure and volume to the thermodynamic temperature remains constant. Where: P is the absolute pressure of the gas; V is the volume of the gas; n is the amount of substance of the gas, in mol; R is the universal gas constant (proportional constant 8.31), in J / (mol·K); T is the temperature of the system. There are several other forms of change, but the essence remains the same, such as expressing it in terms of gas mass. After substituting, the formula becomes: at this time, This is a constant value related to the type of gas. M is the average molecular weight of the gas, which is related to the type of gas (e.g., 29 for air and 4 for helium).

[0003] The invention patent with patent number CN202210562236.9 proposes a method for rapid verification of the airtightness of airship capsule materials. However, this method is only suitable for airtightness testing of airship materials and is not suitable for testing the airtightness of large airships.

[0004] Patent CN202111670414.1 discloses a system and method for detecting the airtightness and leakage rate of an airship capsule. This invention discloses a "buffer airbag 2," which is placed outside the airship capsule and is susceptible to leakage, affecting the accuracy of leakage rate detection. Furthermore, the method still involves calculation errors related to the large volume of the airship capsule, and the entire airtightness test requires a considerable amount of time to allow the total amount of gas leakage from the airship capsule to increase before it becomes effective.

[0005] The invention patent with patent number CN201811619988.4 provides a device for detecting the leakage rate of airship capsule samples. However, this invention is only suitable for detecting the airtightness of airship capsule samples and cannot detect the airtightness of large-sized airship structures.

[0006] For large-sized airship capsules, the difficulty, cost, and risk of conducting ground-based airtightness tests using buoyancy gas are unacceptable. If hydrogen is used, static electricity on-site could easily trigger an explosion; if helium is used, the experimental cost is too high. For example, for a large airship capsule with a volume of 10,000 cubic meters, the cost of helium is approximately four million. The amount of buoyancy gas used and the measurement of net buoyancy are also difficult to achieve under realistic conditions. Therefore, this method is only suitable for small-sized airship capsules, such as capsules with a volume of less than 100 m3.

[0007] The leakage of the airship capsule is calculated using the ideal gas law. According to the formula, it is necessary to measure the internal and external pressure difference ΔP, the external atmospheric pressure P, the capsule volume V, and the internal temperature distribution T in real time. For large airship capsules, the external atmospheric pressure exhibits an altitude gradient effect. Taking a capsule at an altitude of 40m as an example, the external atmospheric pressure variation is approximately 400Pa-500Pa, leading to errors in the internal and external pressure difference and thus affecting the airtightness test results. Furthermore, measuring the volume of large airship capsules is difficult and the measurement error is hard to control, significantly impacting the accuracy of the airtightness test. Currently, there is no feasible solution. Due to these reasons, the accuracy of ground-based airtightness test results for large airship capsules is low, with significant discrepancies from actual flight test results, severely restricting the development and application of airships.

[0008] Furthermore, the processing and material manufacturing levels of large-size airship capsules are constantly improving, resulting in very small gas leakage. However, the total errors introduced by instrument errors, algorithm errors, volume errors, etc., exceed the changes in the mass of the gas inside the capsule caused by leakage. In some cases, the mass of the gas inside the capsule gradually increases during the airtightness test. Therefore, it is necessary to extend the test time so that the total mass of gas leakage from the capsule increases continuously with the increase of the test time, which is generally more than 15 days. Summary of the Invention

[0009] In order to solve the above problems, this invention provides a constant pressure difference, low error, and high efficiency testing method suitable for evaluating the ground airtightness performance of large-size airship capsules.

[0010] The technical solution adopted in this invention is: a high-efficiency testing method for the constant pressure difference airtightness of large-size airship bodies, comprising the following steps:

[0011] S1. Prepare N standard airbags;

[0012] S2. Evacuate the standard airbag and place it inside the airship's airbag body;

[0013] S3. The airship capsule and the standard gasbag are connected to an automatic pressure control system and an automatic recording system to inflate the airship capsule to the airtightness test pressure difference ΔP.

[0014] S4. The automatic pressure control system monitors the pressure difference between the inside and outside of the airship in real time. When the pressure difference is lower than ΔP, the automatic pressure control system starts automatically and inflates the standard airship to restore the pressure difference between the inside and outside of the airship to ΔP until the test ends.

[0015] S5. Deflat the standard airbag and remove it. Measure the pressure difference between the standard airbag and the airship body when the airbag is inflated from the outside to the inside of the airship body using volume measurement methods.

[0016] S6. Calculate the mass of gas leaking from the airship's envelope and the equivalent orifice diameter of the leak;

[0017] S7. Complete the airtightness test and obtain the airtightness test results of the large-size airship capsule.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention transforms the ground-based airtightness testing of large-sized airship capsules into a test and calculation related to the volume of the standard gasbags by embedding N small-sized standard gasbags within the airship capsule. Furthermore, the entire airtightness testing process is conducted under constant pressure, eliminating errors caused by pressure difference testing of large-sized airship capsules and atmospheric pressure gradient variations along altitude. This minimizes airtightness testing errors caused by volume changes under different pressure differences. Since the standard gasbags are located inside the airship capsule, testing errors caused by leakage of the standard gasbags are eliminated, improving the accuracy of ground-based airtightness testing of large-sized airship capsules. Additionally, the implementation of the constant pressure difference method shortens the airtightness test cycle (completing the experiment within 5 hours), improving testing efficiency. Attached Figure Description

[0020] Figure 1 This is a flowchart of the invention;

[0021] Figure 2 This is a schematic diagram of the constant pressure difference method for air tightness testing according to the present invention; Detailed Implementation

[0022] To better understand the purpose, structure, and function of this invention, the invention will be described in further detail below with reference to the accompanying drawings.

[0023] Reference Figure 1 , Figure 2 As shown, the present invention provides an efficient method for testing the constant pressure difference airtightness of a large-size airship capsule. The apparatus used in this testing method includes N reusable standard airbags, an automatic test data recording system, and an automatic pressure control system.

[0024] Standard airbags can be prepared by oneself or latex balls can be purchased directly. They are used to adjust the pressure difference ΔP inside and outside the airship under test so that the pressure difference inside and outside the airship is kept constant.

[0025] The airtightness test process records parameters such as the internal temperature T and the internal and external pressure difference ΔP of the airship capsule through an automatic recording system (mature product);

[0026] The automatic pressure control system (a mature product) identifies the pressure difference between the inside and outside of the airship's airbag in real time and automatically performs inflation / deflation operations on the standard airbag.

[0027] Includes the following steps:

[0028] S1. Prepare N small-sized standard airbags before the test; based on the results of skin leakage test, weld leakage test and accessory leakage test during the manufacturing process of large-sized airships, estimate the gas leakage amount and make a preliminary assessment of the diameter and number of standard airbags.

[0029] The leakage rate of the skin and the sample containing the weld can be tested using a helium permeation instrument. Then, by multiplying the surface area of ​​the airship body and the length of the weld, the leakage rate of the airship can be preliminarily obtained, and thus the preliminary gas leakage amount during the test period can be obtained.

[0030] The testing method proposed in this invention reduces the errors in measuring differential pressure, atmospheric pressure, and capsule volume. However, temperature measurement errors cannot be eliminated, so the test should be conducted during periods of minimal temperature variation, such as 21:00-02:00 at night. During this period, atmospheric pressure initially rises and then falls, while temperature initially falls and then rises.

[0031] S2. Evacuate the standard airbag and place it inside the airship's airbag body; install a temperature sensor inside the airship's airbag body to measure the temperature.

[0032] S3. The airship capsule and the standard gasbag are connected to an automatic pressure control system and an automatic recording system to inflate the airship capsule to the airtightness test pressure difference ΔP.

[0033] S4. After the airbag is inflated to the airtightness test pressure difference ΔP, the pressure difference between the inside and outside of the airship airbag is monitored in real time using an automatic pressure control system. When the pressure difference is lower than ΔP, preferably lower than ΔP-1%ΔP, the automatic pressure control system will start automatically and inflate the standard airbag to restore the pressure difference between the inside and outside of the airship airbag to ΔP, preferably to ΔP+1%ΔP. (In actual inflation and deflation, it is impossible to control precisely, so an inflation and deflation error needs to be reserved. This method initially determines 1% based on experience, and can be adjusted according to the actual situation during the test) until the test ends.

[0034] During the experiment, the experiment was completed when the atmospheric pressure difference and temperature deviation from the initial experimental time were both less than 1%.

[0035] S5. Deflate and remove the standard airbag, and inflate the standard airbag in the outside until the pressure difference is the same as when it is inside the airship body, so that the volume of the standard airbag is the same as when it is inside the airship body. Measure the volume using volume measurement methods and compare it with the thin-shell theory to determine the accuracy of the measured volume. Generally, the difference between the two should not exceed 10%.

[0036] S6. Calculate the mass of gas leaking from the airship's envelope and the equivalent orifice diameter of the leak;

[0037] S7. Complete the airtightness test and obtain the airtightness test results of the large-size airship capsule.

[0038] In step S6, the calculation of the gas leakage mass is as follows:

[0039] Initially, the gas mass inside the airship capsule is m0, the internal and external pressure difference is ΔP, the temperature distribution is T, and the atmospheric pressure is P. The gas mass M inside the standard gas capsule is 0. During the experiment, the internal and external pressure difference ΔP of the airship capsule is kept constant. Since gas leakage is only related to the internal and external pressure difference of the airship capsule and the size of the leakage orifice, and the leakage orifice size of the airship capsule is also constant under the condition of a constant internal and external pressure difference ΔP, that is, the air mass leakage rate inside the airship capsule is constant. Since it is a constant value, the length of the test time will not affect the accuracy of the airtightness test results of the airship capsule.

[0040] During the airtightness test, the initial mass of the gas inside the airship's gasbag is m0, and the initial mass of the gas inside the standard gasbag is M0 = 0. After the test, the mass of the gas inside the airship's gasbag is m1, and the initial mass of the gas inside the standard gasbag is M1. Therefore, the mass of gas leaked from the airship's gasbag during the test is Δm = m0 - m1. According to the ideal gas law, the physical quantities satisfy the following relationship:

[0041]

[0042]

[0043] Therefore, we get:

[0044]

[0045] Since the pressure difference is constant, we have:

[0046] △P0=△P1;

[0047] V0 = V1;

[0048] Furthermore, by selecting time data within the experimental time period Δt that coincides with the initial temperature T0 and initial atmospheric pressure P0, and converting them to the initial state using the ideal gas law, the mass of the airship's leakage can be calculated. This simplifies the formula further to:

[0049]

[0050] A standard airbag is a perfect sphere. According to the thin-shell theory, the relationship between its radius and the pressure difference between the inside and outside is as follows:

[0051]

[0052] Where: v is the Poisson's ratio of the skin material; E is the elastic modulus; This is the initial radius (zero pressure radius).

[0053] This transforms the airtightness test of large-sized airship capsules into a calculation related to the volume of standard airship capsules, eliminating the influence of volume errors in large-sized airship capsules.

[0054] Leakage equivalent orifice diameter: (Based on the fluid dynamics formula for viscous flow in porous media)

[0055]

[0056] Where d is the equivalent aperture, η is the gas dynamic viscosity coefficient, ΔP is the pressure difference between the inside and outside of the airship capsule, and h m The thickness is the material thickness.

[0057] With a volume of 10,000 m³ 3 Taking the airship capsule as an example, it is estimated that under a pressure difference of 1000 Pa, the total volume of gas leakage within 3 hours would be 50 m³. 3 The following method involves placing two 4m diameter spherical standard gasbags inside the airship. During the test, the pressure difference between the inside and outside of the airship is maintained at 1000Pa by inflating and deflating the standard gasbags. After the test is completed, the standard gasbags are removed and their volume is measured under the same pressure difference. The gas leakage mass and leakage equivalent orifice diameter of the airship can then be calculated.

[0058] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A highly efficient method for testing the constant pressure difference airtightness of a large-size airship capsule, characterized in that: Includes the following steps: S1. Prepare N standard airbags; S2. Evacuate the standard airbag and place it inside the airship's airbag body; S3. The airship capsule and the standard gasbag are connected to an automatic pressure control system and an automatic recording system to inflate the airship capsule to the airtightness test pressure difference ΔP. S4. The automatic pressure control system monitors the pressure difference between the inside and outside of the airship in real time. When the pressure difference is lower than ΔP, the automatic pressure control system starts automatically and inflates the standard airship to restore the pressure difference between the inside and outside of the airship to ΔP until the test ends. S5. Deflat the standard airbag and remove it. Measure the pressure difference between the standard airbag and the airship body when the airbag is inflated from the outside to the inside of the airship body using volume measurement methods. S6. Calculate the mass of gas leaking from the airship's envelope and the equivalent orifice diameter of the leak; S7. Complete the airtightness test and obtain the airtightness test results of the large-size airship capsule.

2. The efficient testing method for constant pressure difference airtightness of large-size airship capsules according to claim 1, characterized in that: The airtightness test will be conducted between 21:00 and 02:00 at night.

3. The efficient testing method for constant pressure difference airtightness of large-size airship capsules according to claim 1, characterized in that: The selection criteria for the number of standard airbags in S1 are based on the estimated gas leakage amount, and a preliminary assessment of the diameter and number of standard airbags, based on the results of skin leakage tests, weld leakage tests and accessory leakage tests during the manufacturing process of large-size airships.

4. The efficient testing method for constant pressure difference airtightness of large-size airship capsules according to claim 1, characterized in that: During the S4 test, the test is completed when the atmospheric pressure difference and temperature deviation from the initial test time are both less than 1%.

5. The efficient testing method for constant pressure difference airtightness of large-size airship capsules according to claim 4, characterized in that: In step S4, when the pressure difference between the inside and outside of the airship capsule is lower than △P-5Pa, the automatic pressure control system is automatically activated to inflate the standard airbag inside the airship capsule until the pressure difference between the inside and outside of the airship capsule reaches △P+5Pa.

6. The efficient testing method for constant pressure difference airtightness of large-size airship capsules according to claim 1, characterized in that: In step S6, the gas leakage mass and equivalent orifice diameter of the airship capsule under a pressure difference of ΔP during the time interval Δt are calculated using the gas leakage mass formula: Where d is the equivalent aperture, η is the gas dynamic viscosity coefficient, ΔP is the pressure difference between the inside and outside of the airship capsule, and h m The thickness is the material thickness.

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