Research on Compressed Air Ejection Interior Ballistics Based on AUTODYN

The ultra-short-range defensive weapon system is a kind of attacking ammunition weapon system used for striking the last sensitive and submunitions within the range of 20~200m from the protected target. The compressed air ejection method adopted avoids the gas jet impact problem caused by the ammunition propellant combustion when the self-propelled emission mode is used, which does not generate large infrared characteristics, and improves the initial velocity and payload of the ammunition, and also satisfies the super near The defensive requirements of the infrared defense feature are small and the response speed is fast.

Health, research direction is compressed air ejection.

The compressed air ejection system was first applied to the launch of torpedoes. After World War II, with the development of ballistic missiles and over-the-horizon air-to-air missiles, it was gradually applied to the launch of strategic missiles and medium-range air-to-air missiles. Currently, people are using compressed air ejection systems. Ballistic research has achieved a lot of research results. Qiao Wei proposed the estimation method of torpedo motion parameters in the torpedo launcher tube using compressed air emission. 3 Xu Bin used the joint simulation of SIMULINK and ADAMS to study the ejection force of airborne missile. Learning behavior 4, Liao Zhenqiang established a mathematical simulation model of the ejection device under high-pressure nitrogen driving, and analyzed the separation parameters and separation posture of the missile. 5. Based on the previous research, this paper uses compressed air emission for the ultra-short-range defense system. The device is the application background. Under the condition that the muzzle initial velocity requirement is 120 m/s, the internal ballistic model of the compressed air launching device is established by using the AUTODYN software. The compressed air pressure, the structural parameters of the launching device and the projectile ejection are studied according to the numerical simulation of the model. The relationship between the initial velocity provides a basis for the structural design of the launcher

1 The structure of the launching device and the internal ballistic model are shown. The device uses an electromagnet lock mechanism to control the launch. The principle is that the ammunition is pressed against the membrane diaphragm at the discharge port of the compressed gas cylinder under the action of the lock body to control the high voltage. gas. At the time of launch, the electromagnet is energized, the armature moves to the left, the handle and the latch body lose the armature restraint and move upwards. At this time, the lock body cannot continue to restrain the ammunition, the compressed air breaks through the diaphragm, enters the inner ballistic portion of the launch tube, and pushes the ammunition movement. .

Taking into account the need for maintenance and re-use, the design of the program is designed as follows: the rear part of the launch tube is the space for storing compressed air. When normal, the compressed air is not stored. When entering the combat readiness state, first attach it to the discharge port. The membrane is then filled with ammunition so that the ammunition is placed against the membrane membrane, the handle is pressed to close the ampoule to the ammunition, the electromagnet armature is pressed against the handle, the locking force begins to act, and the ammunition is restrained. At this point, the compressed air storage area at the rear of the launch tube is started to be inflated. After the inflation is completed, the system enters the standby state. 1.1 Determination of the relevant parameters of the ballistic model in the launching device On the basis of the above device, the known ammunition quality: 4kg; muzzle initial velocity: 120m/s; energy utilization coefficient n: 0.15; constant volume specific heat capacity: 717 kgK); After the air temperature: 266K. The compressed air mass required to launch the ammunition is calculated as follows: If the initial pressure of the cylinder is selected to be 35 MPa, the compressed air cylinder temperature is 300 IK, then the volume of the compressed air cylinder is: and the air is Constant, and = 287 kg-K). Calculated: VB0 assumes that the high-pressure gas cylinder is a cylindrical tank, the diameter of the tank diameter D is compressed, and the approximate size range is determined. This data can be used as the initial data for the ballistic estimation in AUTODYN. H. 1.2 Analysis of the impact of internal ballistic performance In order to verify the effect of high pressure air pressure on the performance of the internal ballistics, model 1 was established in the AUTODYN software to verify the effect of high pressure air at different pressures on the internal ballistic performance of the muzzle initial velocity. 7. In order to verify the discharge area of ​​the high pressure gas cylinder Ballistic performance impact, model 2 was established in the AUTODYN software to verify the effect of high pressure air on the internal ballistic performance of the muzzle initial velocity under different discharge areas.

The characteristics of Model 1 are many considerations, except that the compression of the air filled in the model should be considered. In actual cases, the high-pressure air is compressed by the emission cylinder through the channel with smaller diameter and flows into the ballistic portion of the launch tube, and the launch tube is also considered. Friction with ammunition. Model 2 mainly considers leakage, which is relatively simple.

The difference is that in the high-pressure air region of the model 1, a high-pressure air of 34 MPa is filled on the basis of a discharge diameter of 20 mm. On the basis of the high-pressure air of 35 MPa, the model 2 has a discharge diameter of 20 on the elastic tube clearance. Due to the different launching systems of the compressed air launching device and the artillery and rocket launcher, there is no high temperature in the rocket engine combustion chamber under field conditions. The induced radial elastic deformation of the projectile, the temperature difference between the barrel and the ammunition, and the accumulation of carbon during the continuous shooting process, etc., so that the factor that can significantly affect the elastic tube clearance of the compressed air launching device is the geometric error of the ammunition. Ammunition geometry error is mainly subject to the concentricity of the connecting threads of the various components constituting the ammunition and the axis bending of the various components of the ammunition. 8. In the various components of the ammunition, the warhead often has a large wall thickness, a large rigidity, and is not easy to generate geometry. Bending, while the ultra-short-range defensive weapon system uses compressed air launching. There is no rocket engine or other thin-walled structure on the ammunition. Therefore, the ammunition used in the ultra-short-range defensive weapon system tends to be stiff, and the elastic tube clearance can be set. Significantly smaller than the bullet clearance of rockets and other weapons. The model flare clearance is set to by comparing the bullet clearance of the associated weapon. The establishment of the 1mm. 1.3 fluid-solid model involves the interaction of fluids and solids, and therefore involves fluid-solid coupling, which can be implemented in the AUTODYN software. The establishment process of the model: six component models are established, namely the launch tube model, the ammunition model, the upper boundary model of the launch tube, the lower boundary model of the launch tube, the upper boundary model of the discharge channel, and the lower boundary model of the discharge channel. The model built is as shown.

The launch tube model is built by the Euler unit, filled into the air, filled with high-pressure air in the high-pressure air cylinder area, and set the outflow boundary at the muzzle. The ammunition model is built by the Lagrange unit and is filled with the same material density as the ammunition. The upper and lower boundary models of the launch tube are established by the Lagrange unit and placed on the upper boundary of the launch tube. During the simulation, the ammunition is restrained due to the movement of the elastic tube gap in the +Y direction.

The upper boundary model of the discharge passage and the lower boundary model of the discharge passage are both established by the Lagrange unit and placed on both sides of the simulated discharge passage, which is used to restrain the air flow during the simulation process and simulate the effect of the discharge passage.

Coupling and Euler-Lagrange coupling. In the simulation model, Lagrange-Lagrange coupling is mainly used for contact and friction analysis of ammunition and launch tube boundary. Euler-Lagrange coupling is mainly used for fluid-solid coupling analysis of high-pressure air-driven ammunition movement. 9. In the setting of Lagrange coupling, The friction coefficient of the ammunition model and the upper and lower launch tube models was set to /=0.15 to simulate the frictional force of the ammunition from the wall surface of the launch tube in the launch tube.

Lagrange-Lagrange coupling requires that the minimum distance between two parts be no less than 1/10 of the minimum mesh size. In this model, the elastic tube gap is 0.1mm and the single side distance is 0.05mm, so the mesh must be split. The minimum mesh size is set to less than 0.5 mm. - In the setting of the Lagrange coupling type, the Euler-Lagrange coupling is set to fully automatic coupling.

2 Numerical simulation results and analysis 2.1 Simulation results of model 1 For the effects of high pressure air with different pressures on the internal ballistic performance of the muzzle initial velocity, the velocity-time and velocity-displacement curves of model 1 are obtained as shown.

The acceleration process of compressed air of 35MPa pressure is not stable, the initial velocity of the muzzle can not meet the requirements of the initial velocity of 120m/s muzzle, and the compression air acceleration process of 36MPa pressure is stable, which can make the initial velocity of ammunition muzzle reach 116m/s.2.2 Simulation result of model 2 According to the influence of the discharge area of ​​different high-pressure gas cylinders on the internal ballistic performance, the speed-time and speed-displacement curves of the model 2 are obtained as shown.

The process is unstable, the initial velocity of the muzzle can not meet the requirement of 120m/S. When the diameter of the discharge is increased from 20mm to 24mm, the acceleration process becomes obviously stable. The initial velocity of the muzzle increases from less than 100m/s to 119m/s. When the diameter is increased from 24mm to 28mm, the initial velocity of the muzzle increases from 119m/s to 121m/s. 2.3 Speed-displacement relationship extracted from the simulation results Based on the analysis of the above results, in order to obtain the appropriate barrel length, the displacement of the appropriate model is selected. A speed curve is shown.

In the case of a discharge diameter of 28 mm and a compressed air pressure of 35 MPa, the ammunition can reach a speed of 120 m/s at a displacement of 800 mm.

3 Test comparison According to the simulation data, the experimental model was established. Since 35MPa gas is difficult to obtain, this test uses 20MPa test gas as a comparison, only for software simulation and experimental comparison.

Through the test and test, the time-acceleration data map is obtained, and then the same model simulation is made in the software, and the results of the test data and the software simulation on the same size data are compared.

By comparison, it is found that the software simulation data is too large, and there is a certain error with the test, but the overall trend is consistent, and the error is within the acceptable range. Therefore, the software has certain credibility and is acceptable in the preliminary design stage.

4 Conclusions By establishing the internal ballistic model of the compressed air launcher in the AUTODYN software, the relationship between compressed air pressure, launch tube discharge diameter, ammunition displacement, and muzzle velocity is obtained. The following conclusions are obtained: Under the condition of 20mm, the accelerated air acceleration process of 34MPa and 35MPa pressure is not stable. Increasing the discharge diameter of compressed air can solve the problem that the acceleration process of the ammunition is not stable; the compressed air pressure is 35MPa, when the discharge diameter is increased from 20mm to 24mm, The acceleration process became apparently stable. The initial velocity of the muzzle increased from less than 100 m/s to 119 m/s. When the discharge diameter was changed from 20 mm to 24 mm, the muzzle initial velocity increased sharply.

When the diameter of the discharge increases from 24mm to 28mm, the initial velocity of the muzzle increases from 119m/s to 121m/s, and the lifting is not high; in the case of a discharge diameter of 28mm and a compressed air pressure of 35MPa, the ammunition can be displaced at 400mm. At a speed of 100m/s, the compressed air discharge diameter of the launching device can be set to 35MPa for compressed air pressure and 800mm for the length of the launch tube.

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