Unmanned aerial vehicle compressed air ejection system and dynamic simulation experiment method thereof

Abstract

The invention relates to the technical field of unmanned aerial vehicle compressed air ejection, in particular to an unmanned aerial vehicle compressed air ejection system and a dynamic simulation experiment method thereof. According to the technical scheme, the device comprises a high-pressure air storage tank used for storing compressed air and a power air cylinder, and a piston capable of reciprocating is arranged in the power air cylinder. The system further comprises an ejection guide rail and a tackle, the ejection guide rail is used for guiding the tackle, the tackle is used for fixing and bearing the unmanned aerial vehicle, and a pneumatic control valve is installed on a pipeline between the high-pressure air storage tank and the power air cylinder and used for controlling instant release of compressed air. The deployment efficiency and the ejection stability of the unmanned aerial vehicle are remarkably improved, the takeoff energy consumption is reduced, the effective load and the cruising mileage are expanded, rapid deployment of a complex scene is adapted, equipment can be protected, and the service life is prolonged; the problem of transient modeling and multi-component collaboration is solved, the simulation experiment error is small, the cost is low, the adaptability is high, and parameters can be quickly optimized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compressed air launching of unmanned aerial vehicles, and in particular to a compressed air launching system for unmanned aerial vehicles and a dynamic simulation experiment method thereof. BACKGROUND

[0002] Unmanned aerial vehicles have been widely used in military reconnaissance, civilian mapping, emergency rescue, agricultural plant protection and other fields due to their advantages of flexible deployment, long endurance, multi-task adaptation, etc. In the operation process of unmanned aerial vehicles, the take-off stage is a key link to determine the task radius, effective payload and endurance capacity. The traditional self-powered take-off method (such as runway taxiing take-off) needs to consume a large amount of fuel or battery energy to overcome the ground resistance and gravity, resulting in that the energy consumption in the take-off stage accounts for more than 30% of the total energy consumption, significantly shortens the endurance time, and is limited by the length of the site, making it difficult to be quickly deployed in complex terrain (such as mountainous areas, offshore platforms) or tactical front-line areas.

[0003] To solve the above problems, the industry has developed various unmanned aerial vehicle assisted take-off technologies, including rocket-assisted take-off, ski-jump take-off, vertical take-off, catapult take-off, hand-throwing launch and air dropping, etc. Among them, the catapult take-off becomes the core technology path for medium and small fixed-wing unmanned aerial vehicles (take-off weight 50-500 kg) to be deployed in limited sites, because it can provide sufficient take-off speed for unmanned aerial vehicles in a short distance. The current mainstream catapult technologies can be divided into elastic catapult, hydraulic catapult, steam catapult, electromagnetic catapult and compressed air catapult: the elastic catapult (such as rubber band, spring drive) has simple structure but low energy density, which is only suitable for micro unmanned aerial vehicles (≤5 kg); the hydraulic catapult and the steam catapult have stable energy output, but the system is bulky, maintenance is complex, and there is a risk of hydraulic oil leakage or steam high temperature, which is difficult to adapt to the requirements of mobile deployment; the electromagnetic catapult has rapid response and strong controllability, but it needs a high-power power supply module, which is costly and may affect the electronic equipment of the unmanned aerial vehicle due to electromagnetic interference; while the compressed air catapult uses compressed air as the power source, converts the internal energy of the gas into mechanical energy to drive the unmanned aerial vehicle to accelerate, and has the advantages of high energy density (5-8 times higher than the elastic catapult), compact structure (the system volume is only 1 / 3 of the hydraulic catapult), strong mobility (can be disassembled for transportation and assembled within 30 minutes), small infrared exposure (no high-temperature exhaust), low cost (the core component manufacturing cost is 60% lower than that of the electromagnetic catapult) and good repeatability (only needs to supplement compressed air after a single catapult to be used again), etc., which becomes the preferred direction of the catapult technology for medium and small fixed-wing unmanned aerial vehicles.

[0004] Although the compressed air catapult technology has significant advantages, its engineering application still faces two major challenges: one is the difficulty of transient process control. The action time of the catapult is usually only 300-500 ms, and the flow of high-pressure gas (initial pressure 800-1500 kPa) in the air valve, pipeline and cylinder presents strong transient and high turbulence characteristics. The instantaneous flow fluctuation can be more than 20%, which easily leads to the sudden rise and fall of the unmanned aerial vehicle acceleration, exceeding its structural tolerance overload (usually ≤5g); the second is the difficulty of parameter matching design. The parameters such as the volume of the gas storage tank, the initial pressure, the diameter of the catapult barrel, the length of the guide rail and the transmission ratio need to be accurately matched with the weight and stall speed of the unmanned aerial vehicle. If the parameter design is not proper, it may lead to insufficient catapult final speed (unable to take off the ground) or excessive overload (damage to the unmanned aerial vehicle structure).

[0005] From the current technical development status, foreign countries have formed a mature product system and engineering application capability in the field of compressed air catapult: the Mark4 compressed air catapult developed by the United States is suitable for "Scaneagle" (take-off weight 18 kg) and "Integrator" (take-off weight 45 kg) unmanned aerial vehicles, which can achieve a catapult speed of 22 m / s on a 5 m guide rail; the "Hercules" pneumatic catapult of British Meggitt Defense adopts a low-pressure inflation system (initial pressure 600 kPa), which can launch a 250 kg level unmanned aerial vehicle at a speed of 55 m / s; the "Kontio" series catapult of Finnish Robonik Company covers the full weight range of 50-500 kg, among which the MC series realizes the catapult of 500 kg unmanned aerial vehicle at a speed of 37 m / s through the design of speed-increasing pulley group; the HERCULESAH-01 catapult of Spanish Aries Company further improves the upper limit of performance to a maximum catapult mass of 500 kg and a maximum speed of 65 m / s. The above products have been mass applied in military reconnaissance, border patrol and other scenes.

[0006] Domestic research mainly focuses on theoretical analysis and experimental stages of key components: scholars study the internal ballistic characteristics of cylindrical compressed air catapults (such as gas pressure changes and piston motion patterns), and establish simulation models using MATLAB or FLUENT to analyze the influence of parameters such as initial pressure and cylinder diameter on catapult performance. However, the research objects are mostly limited to cylindrical launch structures (without speed-increasing mechanisms and guide rails), and no complete system integration scheme has been formed. Compared with cylindrical launch, the guide rail type compressed air catapult, which has more practical engineering value, requires the addition of speed-increasing pulley groups (to amplify force and displacement), traction devices (connecting pistons and trolleys), buffer devices (trolley braking), and high-precision guide rails (to ensure linearity of motion). The introduction of these components leads to complex dynamic coupling relationships in the system (such as the influence of traction rope tension fluctuations and pulley transmission clearance), and at the same time, it places higher demands on structural strength (the guide rail must withstand instantaneous impact force ≥10kN) and assembly precision (the clearance between the trolley and the guide rail ≤0.5mm). Currently, no rail-mounted compressed air catapult product with market scale has been developed in China. The catapult demand of small and medium-sized fixed-wing UAVs still relies on imported equipment, which not only has high procurement costs (the price of a single imported device exceeds 2 million yuan), but also has problems such as confidentiality of technical parameters and slow after-sales response, which restricts the independent development of China's UAV industry.

[0007] In summary, existing technologies lack a rail-guided UAV compressed air ejection system that balances structural compactness, parameter controllability, and engineering practicality. Particularly, there are technological gaps in areas such as accurate modeling of transient aerodynamic processes, multi-component collaborative control, and parameter optimization and matching. There is an urgent need to reveal the coupling mechanism between compressed air flow patterns and UAV motion characteristics through a combination of experimental and simulation methods, and to develop an engineering-applicable system design and testing scheme to meet the rapid deployment needs of small and medium-sized fixed-wing UAVs in complex scenarios. Therefore, this application proposes a UAV compressed air ejection system and its dynamic simulation experimental method. Summary of the Invention

[0008] The purpose of this invention is to address the problem in the prior art that there is a lack of a rail-guided UAV compressed air catapult system that balances structural compactness, parameter controllability, and engineering practicality, and to propose a UAV compressed air catapult system and its dynamic simulation experimental method.

[0009] In a first aspect, the present invention provides a compressed air ejection system for unmanned aerial vehicles (UAVs), comprising: High-pressure air storage tank, used to store compressed air; A power cylinder, which contains a reciprocating piston; The catapult rail is used to guide the trolley; The trolley is used to fix and support the drone; The speed-increasing pulley system connects the piston and the trolley via a traction rope, and is used to convert the linear motion of the piston into the high-acceleration motion of the trolley. The press is connected to the high-pressure gas tank via pipeline, and a solenoid valve is installed between the press and the high-pressure gas tank. A pneumatic control valve is connected to the pipeline between the high-pressure air tank and the power cylinder, and is used to control the instantaneous release of compressed air. A buffer device is provided at the end of the catapult guide rail to brake the trolley; The compressed air in the high-pressure storage tank enters the power cylinder through the pneumatic control valve to drive the piston. The piston pulls the trolley and the UAV along the catapult rail through the speed-increasing pulley group to accelerate. When the UAV reaches the takeoff speed, it disengages from the trolley and is launched.

[0010] Optionally, it may also include a data acquisition system, the data acquisition system comprising: A pressure sensor, installed in a high-pressure gas storage tank and / or cylinder, is used to monitor gas pressure; An accelerometer, mounted on a drone or trolley, is used to measure acceleration. Speed ​​sensors are used to indirectly or directly measure the speed of a drone. The data acquisition unit connects to various sensors to record and process pressure, acceleration, and velocity data.

[0011] Optionally, the speed-increasing pulley system has a transmission ratio. It satisfies the following relationship: Displacement of drones , Load on the piston , in, For piston displacement, The traction force on the drone and the trolley.

[0012] Optionally, the tilt angle of the launch rail Adjustable, designed to adapt to different takeoff conditions for drone catapults.

[0013] Secondly, the present invention provides a dynamic simulation experimental method for a UAV compressed air catapult system as described in the first aspect, comprising the following steps: S1. Establish a thermodynamic model of the compressed air ejection system, including the mass conservation equation and energy conservation equation during the filling and releasing process of the high-pressure air tank; S2. Establish a gas flow model to describe the one-dimensional isentropic flow process of compressed air from the high-pressure storage tank to the power cylinder after the pneumatic control valve is opened. S3. Establish a kinematic model, including the force analysis equations for the drone, pulley, and piston, and consider the transmission ratio relationship; S4. Based on the aforementioned thermodynamic model, gas flow model, and kinematic model, construct a fluid-structure interaction simulation model of the catapult system in the simulation software; S5. Set simulation parameters, including the initial pressure of the high-pressure gas tank, the initial pressure of the power cylinder, the mass of the UAV, the mass of the trolley, the launch angle, and the transmission ratio. S6. Run the simulation to obtain the curves of the pressure of the high-pressure gas tank, the pressure of the power cylinder, the acceleration, velocity and displacement of the UAV over time during the ejection process; S7. Measure the pressure and acceleration data during the actual ejection process through experiments, and compare the simulation results with the experimental data to verify the accuracy of the simulation model; S8. Based on the validated model, analyze the impact of different initial cylinder pressure, air tank pressure, and ejection angle parameters on ejection performance.

[0014] Optionally, the thermodynamic model in step S1 includes: mass conservation equation: ; Energy conservation equation: ; in, For gas mass, For internal energy, For enthalpy, For temperature, For heat exchange area, , Air flow rate during filling and releasing of high-pressure gas storage tanks, and the process of releasing gas from high-pressure gas storage tanks. , The mass of the gas inside the high-pressure gas storage tank. For time, The specific internal energy of air, For air specific enthalpy, This refers to the air temperature inside the high-pressure gas storage tank. For ambient temperature, The heat transfer coefficient between the air inside the gas storage chamber and the environment. This refers to the heat exchange surface area of ​​the high-pressure gas storage tank. The specific enthalpy of the air being filled into the gas storage tank. Enthalpy of the air discharged from the gas storage tank (1).

[0015] Optionally, the gas flow model in step S2 includes mass flow rate calculation formulas under subsonic and supersonic flow conditions: ; in, This is the flow correction factor. For the valve flow cross-sectional area, The gas pressure in the storage tank. The density of the gas in the high-pressure gas storage tank. The air insulation index. This refers to the inlet and outlet pressure ratio.

[0016] Optionally, the kinematic model in step S3 includes: Equations of motion for the drone and the pulley: ; in, For the quality of drones, For the mass of the pulley, For the displacement of the drone, For the drone's movement time, The traction force on the drone and the trolley, Frictional resistance experienced by the sled and the drone The total weight of the drone and the trolley. For the launch tilt angle; Piston motion equation: ; in, For piston mass, For piston displacement, The cross-sectional area of ​​the piston is... The pressure difference across the piston. This refers to the frictional resistance between the piston and the wall of the power cylinder. The force of gravity acting on the piston. The load on the piston.

[0017] Optionally, the fluid-structure interaction simulation model in step S4 includes an Eulerian fluid model and a Lagrange solid model, wherein the power cylinder, high-pressure air tank and connecting pipeline are set as Eulerian models and the piston is set as a Lagrange model.

[0018] Optionally, in step S8, parameter sensitivity analysis is used to evaluate the impact of different initial cylinder pressures on the final ejection velocity, peak acceleration, and ejection time, thereby optimizing the design parameters of the ejection system.

[0019] Compared with the prior art, this application includes at least one of the following beneficial technical effects: In terms of system performance, compared to drones taking off independently, this system uses compressed air power to accelerate and take off, reducing energy consumption during takeoff. It also significantly reduces site constraints, enabling rapid deployment in complex environments such as mountains and offshore platforms; furthermore, it achieves this through precise control of pressure and flow.

[0020] The multi-domain coupled mathematical model and fluid-structure interaction simulation model constructed by the method of this invention realize accurate simulation of the entire process of compressed air storage, release, flow, and work. The simulation and experimental data errors can accurately predict transient characteristics and solve the parameter mismatch problem of traditional empirical design. For the newly added speed-increasing pulley group, traction device and other components of the guide rail catapult, the motion coupling relationship between the piston and the UAV is established to realize multi-component collaborative control and avoid motion deviation caused by transmission gap and tension fluctuation.

[0021] This invention eliminates the need for high-power power supply modules and complex maintenance, making it suitable for the mass application needs of small and medium-sized fixed-wing UAVs. The dynamic simulation experiment method can quickly obtain the ejection time, peak acceleration, and terminal velocity variation patterns under different parameters by adjusting the initial pressure of the gas cylinder, providing a basis for parameter matching of UAVs of different weights and shortening the system development cycle.

[0022] This invention significantly improves the deployment efficiency and catapult stability of UAVs, reduces takeoff energy consumption, expands payload and cruise range, adapts to rapid deployment in complex scenarios, and protects equipment to extend its lifespan. It overcomes the challenges of transient modeling and multi-component coordination, has small simulation experimental errors, low cost, strong adaptability, and can quickly optimize parameters. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a compressed air catapult system for unmanned aerial vehicles (UAVs). Figure 2 This is a physical diagram of the compressed air catapult structure for a drone. Figure 3 This is a photograph of the actual compressed air ejection process of a drone. Figure 4 This is a picture of the UNIK5000 pressure sensor. Figure 5 A schematic diagram of a 2D simulation model of a UAV compressed air catapult. Figure 6 A comparison chart of pressure change curves in the gas storage tank; Figure 7 A comparison chart of the acceleration variation curves of the drone; Figure 8 A comparison chart of drone speed variation curves; Figure 9 A comparison chart of the displacement change curves of the UAV; Figure 10A comparison chart of the speed-displacement variation curves of the UAV; Figure 11 The diagram shows the gas pressure cloud map and velocity vector distribution of the gas storage cylinder at various times. Figure 12 A graph showing the pressure variation of the gas storage cylinder under different initial cylinder pressures; Figure 13 The graph shows the motion variation curves under different initial cylinder pressures; Figure 14 The velocity vector distribution diagram is shown for different initial cylinder pressures at 10ms.

[0024] Reference numerals: 1. High-pressure air tank; 2. Power cylinder; 3. Piston; 4. Launch rail; 5. Pulley; 6. Unmanned aerial vehicle (UAV); 7. Speed-increasing pulley block; 8. Press; 9. Buffer device; 10. Traction rope; 11. Pneumatic control valve; 12. Solenoid valve. Detailed Implementation

[0025] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0026] Example 1: like Figure 1 As shown, the present invention proposes a compressed air ejection system for unmanned aerial vehicles (UAVs), including a high-pressure air tank 1 for storing compressed air and a power cylinder 2. The power cylinder 2 contains a reciprocating piston 3. The system also includes an ejection guide rail 4 and a trolley 5. The ejection guide rail 4 guides the trolley 5, which is used to fix and support the UAV 6. A pneumatic control valve 11 is installed on the pipeline between the high-pressure air tank 1 and the power cylinder 2 to control the instantaneous release of compressed air. The compressed air in the high-pressure air tank 1 enters the power cylinder 2 via the pneumatic control valve 11, driving the piston 3. The piston 3, through the speed-increasing pulley group 7, pulls the trolley 5 and the UAV 6 along the ejection guide rail 4 to accelerate. When the UAV 6 reaches takeoff speed, it disengages from the trolley and completes the ejection. The tilt angle θ of the ejection guide rail 5 is adjustable to adapt to different takeoff conditions for the UAV 6.

[0027] The system also includes a press 8, which is connected to a high-pressure gas storage tank 1 via a pipeline. A solenoid valve 12 is installed between the press 8 and the high-pressure gas storage tank 1. The press 8 is started and the solenoid valve 12 is opened to fill the high-pressure gas storage tank 1 with gas.

[0028] In addition, in this embodiment, the UAV compressed air catapult system also includes a speed-increasing pulley group 7, which connects the piston 3 and the trolley 5 through a traction rope 10, and is used to convert the linear motion of the piston 3 into the high-acceleration motion of the trolley 5. It is worth noting that a buffer device 9 is provided at the end of the catapult guide rail 4 to brake the trolley 5. The buffer device 9 is a rubber plate that provides a stopping buffer for the trolley 5.

[0029] In this embodiment, the UAV compressed air ejection system also includes a data acquisition system. The data acquisition system includes a pressure sensor, an acceleration sensor, a velocity sensor, and a data acquisition instrument for monitoring gas pressure. The pressure sensor is installed in the high-pressure gas storage tank 1 and / or the power cylinder 2. The acceleration sensor is installed on the UAV 6 or the trolley 9 and is used to measure acceleration. The velocity sensor is used to indirectly or directly measure the movement speed of the UAV 6. The data acquisition instrument is connected to each sensor and is used to record and process pressure, acceleration, and velocity data.

[0030] In this embodiment, the speed-increasing pulley group 4 has a transmission ratio It satisfies the following relationship: Displacement of UAV 6 , Load on piston 3 , in, For piston displacement 3, The traction force on the drone 6 and the trolley 5.

[0031] This embodiment also provides a dynamic simulation experiment method for a UAV compressed air catapult system. The steps are described in detail below.

[0032] S1. Establish a thermodynamic model of the compressed air ejection system, including the mass conservation equation and energy conservation equation during the filling and discharging process of the high-pressure air tank 1; the thermodynamic model includes: mass conservation equation: ; Energy conservation equation: ; in, For gas mass, For internal energy, For enthalpy, For temperature, For heat exchange area, , The air flow rate during the filling and releasing of high-pressure gas storage tank 1, and the air release process of high-pressure gas storage tank 1. , The mass of the gas in high-pressure gas storage tank 1 For time, The specific internal energy of air, For air specific enthalpy, The air temperature inside high-pressure gas storage tank 1. For ambient temperature, The heat transfer coefficient between the air inside the gas storage chamber and the environment. Let be the heat exchange surface area of ​​high-pressure gas storage tank 1. The specific enthalpy of the air filled into gas storage tank 1, Enthalpy of the air discharged from gas storage tank 1.

[0033] S2. Establish a gas flow model to describe the one-dimensional isentropic flow process of compressed air from the high-pressure air tank 1 to the power cylinder 2 after the pneumatic control valve 11 is opened; the gas flow model includes the mass flow rate calculation formula under subsonic and supersonic flow conditions: ; in, This is the flow correction factor. For the valve flow cross-sectional area, The gas pressure in the storage tank. The gas density of high-pressure gas storage tank 1 The air insulation index. This refers to the inlet and outlet pressure ratio.

[0034] S3. Establish a kinematic model, including the force analysis equations for the UAV 6, the pulley 5, and the piston 3, and consider the transmission ratio relationship; the kinematic model includes: Equations of motion for UAV 6 and trolley 5: ; in, For the quality of drones, For the mass of the pulley, For the 6 displacements of the drone, For the drone's 6-hour flight time, The traction force on the UAV 6 and the trolley 5 The frictional resistance experienced by the sled 5 and the drone 6 The total gravity acting on the drone 6 and the trolley 5 For the launch tilt angle; Piston motion equation: ; in, For piston 3, For the displacement of piston 3, It is the cross-sectional area of ​​the piston. The pressure difference across piston 3. The frictional resistance between piston 3 and the wall of power cylinder 2. The force of gravity acting on the piston. The load on the piston.

[0035] S4. Based on the aforementioned thermodynamic model, gas flow model, and kinematic model, construct a fluid-structure interaction simulation model of the catapult system in the simulation software. The fluid-structure interaction simulation model includes an Eulerian fluid model and a Lagrange solid model, wherein the power cylinder 2, the high-pressure gas tank 1, and the connecting pipeline are set as Eulerian domains, and the piston is set as a Lagrange domain.

[0036] S5. Set simulation parameters, including the initial pressure of high-pressure gas tank 1, the initial pressure of power cylinder 2, the mass of UAV 6, the mass of trolley 5, the launch angle, and the transmission ratio. S6. Run the simulation to obtain the time-varying curves of the pressure of the high-pressure gas tank 1, the pressure of the power cylinder 2, and the acceleration, velocity, and displacement of the UAV 6 during the ejection process. S7. Measure the pressure and acceleration data during the actual ejection process through experiments, and compare the simulation results with the experimental data to verify the accuracy of the simulation model; S8. Based on the validated model, analyze the impact of different initial cylinder pressures, gas tank pressures, and ejection angle parameters on ejection performance. Through parameter sensitivity analysis, evaluate the influence of different initial cylinder pressures on ejection terminal velocity, peak acceleration, and ejection time, and optimize the ejection system design parameters.

[0037] 1. Experiment and Simulation Process 1.1 Compressed Air Catapult Design For a compressed air catapult for a 50kg fixed-wing UAV, a thermodynamic model was established, and design parameters were simulated and calculated using MATLAB. The calculation results show that within a certain parameter range, the volume of the air tank, initial pressure, catapult tube diameter, and track length are positively correlated with the catapult velocity. Among these parameters, only the track length is negatively correlated with catapult overload, and the catapult angle has a relatively small impact on catapult performance. Furthermore, since the design goal of this experiment is to achieve a catapult velocity of over 20 m / s, i.e., a value not less than the stall velocity of the catapult-launched UAV, the catapult parameters were selected under this criterion. Therefore, considering all factors, the final parameter selection results are shown in Table 1.

[0038] Table 1: ; The prototype of the compressed air catapult for unmanned aerial vehicles (UAVs) is as follows: Figure 2 As shown, the experimental components of this catapult mainly include a high-pressure air tank 1, a power cylinder 2, a speed-increasing pulley system 7, a catapult guide rail 4, and a buffer device 9. Other experimental equipment and components include pressure sensors, speed sensors, and a data acquisition system.

[0039] 1.2 Experimental Testing and Data Acquisition Scheme This experimental test is mainly divided into three stages: the catapult preparation stage, the catapult launch stage, and the catapult completion stage, such as... Figure 3 As shown. During the catapult preparation phase, the catapult frame is deployed and adjusted to an appropriate catapult tilt angle, with UAV 6 positioned at the initial catapult launch position. During the catapult takeoff phase, solenoid valve 12 is activated, simultaneously releasing UAV 6 and trolley 5, enabling UAV 6 to accelerate into flight. The catapult launch is complete when UAV 6 leaves the catapult guide rail 4.

[0040] The experimental data mainly included pressure and parameters of the UAV's motion. Pressure measurement used a General Electric UNIK5000 pressure sensor (USA). Figure 4 The motion parameters are mainly obtained through accelerometers. The data directly measured in the experiment is acceleration, while velocity and displacement are indirectly obtained by calculating the acceleration.

[0041] 1.3 Simulation Model Construction A simulation analysis of the UAV catapult system was conducted. A simulation model was established in fluid-structure interaction (FSI) simulation software, including components such as the high-pressure gas tank 1, connecting pipes, power cylinder 2, and piston 3, to simulate the gas path operation. All fluid domains were established as Eulerian domains, with rigid boundaries set by default in the software system. An outlet boundary was set at the rightmost end of the power cylinder 2 model, and the solid domain containing piston 3 was established as a Lagrange domain. Finally, the motion parameters of UAV 6 were indirectly obtained from the piston's motion by calculating the transmission ratio. Furthermore, since the pipeline is an axisymmetric structure, a mesh model was built in the simulation software to simplify the analysis. The total number of nodes in this model was 115110. Figure 5 As shown.

[0042] 2. Analysis of Experimental and Simulation Results 2.1 Pressure Change Analysis Figures 6 to 10 The simulation and experimental results are displayed. For example... Figure 6 As shown, when the valve is opened, the high-pressure air in the high-pressure storage tank 1 is released in a short time, causing the pressure change in the high-pressure storage tank 1 to decrease approximately linearly. At the end of the ejection, the remaining gas pressure in the high-pressure storage tank 1 still accounts for 68.3% of the initial pressure. Furthermore, the simulation results agree well with the experimental results, indicating that this simulation method can be applied to the analysis of the aerodynamic process of a catapult.

[0043] 2.2 Analysis of UAV Motion Parameters Figure 7The figure shows the acceleration curve of UAV 6. At the start of launch, the acceleration value increases sharply and quickly rises to its peak, then gradually decreases. The acceleration curve trends under experimental and simulation conditions are largely consistent. The acceleration change is mainly determined by the pressure difference across the piston. At the initial moment of launch, due to the valve opening, high-pressure air from the high-pressure storage tank 1 rushes into the power cylinder 2 in a short time, causing the pressure on the left side of piston 3 to increase rapidly, and the pressure difference across piston 3 to quickly reach its maximum value. As piston 3 moves further, the volume of power cylinder 2 increases, the pressure on the left side of piston 3 decreases, and the pressure difference across piston 3 decreases, thus reducing the acceleration. Compared with the experimental results, the acceleration response time is earlier in the simulation. This is because the simulation is closer to the ideal process, responding instantly at the moment of launch; while in the experiment, the solenoid valve requires a certain amount of time to fully open, causing a lag in the initial acceleration change. Furthermore, in the later stages of launch, the experimental acceleration change also showed some fluctuations, which is considered to be due to factors such as vibration between components during the experiment.

[0044] Figure 8 The figure shows the velocity variation curve of UAV 6. The launch velocity of UAV 6 increases continuously with time, while the velocity increase rate decreases. The simulation results and experimental results agree well. In the initial stage of launch, due to the influence of response time, corresponding to the acceleration variation curve, the simulated velocity increases faster than the experimental velocity. The final launch velocity under simulation conditions is 24.74 m / s, while the experimental value is 25.11 m / s, with an error of approximately 1.5%, which is within the allowable error range.

[0045] Figure 9 The figure shows the displacement of UAV 6 over time. The trend of the simulation and the experiment are consistent. The displacement and time have a near quadratic function relationship. The displacement increases slowly in the early stage and increases continuously in the later stage.

[0046] In addition, combined Figure 10 Analysis of the displacement-velocity curves shows that the ejection velocity increases continuously with displacement, and the acceleration process is mainly concentrated in the early stage of the ejection stroke. The velocity growth slows down in the later stage. This is still affected by the pressure changes on both sides of piston 3. As the displacement of piston 3 increases, the gas storage volume expands, and the pressure on the left side of piston 3 decreases further, thus causing the velocity growth under the same displacement change to gradually slow down.

[0047] 2.3 Analysis of Compressed Air Flow Process 2.3.1 Design Parameter Analysis For the compressed air ejection system of the UAV, the main factor affecting the motion characteristics of the UAV 6 comes from the gas pressure change on both sides of the piston 3. The right side of the piston 3 is the atmospheric pressure zone. Therefore, in order to better grasp the motion law of the UAV 6, it is only necessary to analyze the gas change in the power cylinder 2.Figure 11 The diagram shows the gas pressure cloud map and velocity vector distribution inside the power cylinder 2 at different times.

[0048] Depend on Figure 11 It can be seen that the gas pressure in the power cylinder 2 reaches its maximum at the initial stage of ejection, and then gradually decreases. Furthermore, throughout almost the entire ejection phase, the distribution of the high-pressure zone within the power cylinder 2 fluctuates between local and overall variations. This is because, at different ejection stages, the gas movement at the left end face of the piston 3 is obstructed and accumulates to varying degrees, thus forming localized high-pressure zones, which continuously change their distribution area under the drive of the pressure difference. After 355ms, the pressure change within the power cylinder 2 gradually stabilizes until the ejection ends at 388ms, at which point the pressure distribution within the power cylinder 2 shows no significant change. Figure 11 As shown in (c).

[0049] In the initial 5-10 ms of ejection, the high-pressure air from the gas tank has not yet reached the piston 3 wall, resulting in a relatively high incoming flow velocity. Furthermore, the gas velocity is greater closer to the axis, making it prone to significant velocity fluctuations. Figure 11 As shown in (a), as the ejection time progresses, the fluid reaching the left side of piston 3 decelerates and increases in pressure at the end face of piston 3, further driving piston 3 to move. Simultaneously, the fluid expands from the center outwards at the end face of piston 3, then flows back along the wall of power cylinder 2. In the later stages of ejection, a vortex is formed throughout the entire space, and the fluid velocity distribution gradually becomes uniform, as shown in (a). Figure 11 As shown in (b) and (c).

[0050] 2.3.2 Parameter Sensitivity Analysis To further analyze the influence of the initial pressure of the power cylinder 2 on the motion of the UAV 6, three simulation models were built. The dimensionless number of the initial pressure of the high-pressure air tank 1 was set to 1.25, and the dimensionless numbers of the initial pressure of the power cylinder 2 were 1.25, 0.9 and 0.55, respectively. With displacement as the abscissa, the pressure change of the power cylinder 2 and the motion of the UAV under different initial cylinder pressures were analyzed.

[0051] like Figure 12 As shown, the pressure change of the power cylinder 2 generally shows a trend of first rising and then falling. As the initial value decreases, the pressure change curve gradually slows down.

[0052] Figure 13The figure shows the velocity and acceleration curves of UAV 6 under three sets of parameters. The ejection time required under different initial conditions is 340ms, 388ms, and 489ms, respectively. The ejection time varies depending on the charging pressure of the power cylinder 2. Furthermore, it can be seen from the figure that the acceleration curve is basically consistent with the gas cylinder pressure curve. The peak acceleration increases with the increase of the initial cylinder pressure, while the acceleration decays faster and changes more drastically at higher pressures. Velocity is positively correlated with the initial cylinder pressure, but the increase in velocity decreases with further increases in cylinder pressure. For example, increasing the cylinder pressure from 0.55 to 0.9 increases the velocity by 20.5% at the final moment; however, increasing it from 0.9 to 1.25 only increases the velocity by 12.2% at the final moment. Therefore, in specific experiments, it is necessary to comprehensively consider the launch conditions, namely the launch target of UAV 6, the maximum overload that UAV 6 can withstand, the pressure of the power cylinder 2, and the economy of the pre-charge pressure, to set a reasonable initial cylinder pressure.

[0053] Because the pressure changes in power cylinder 2 show significant differences in the early stages, a velocity vector distribution diagram at 10ms is extracted for comparative analysis. Figure 14 As shown, at the initial moment of ejection, when the pressure in the high-pressure gas tank 1 is uniform, the lower the pressure in the power cylinder 2, the greater the fluid velocity near the axis. This is because the gas flow rate increases under a larger pressure gradient. Conversely, the higher the initial cylinder pressure, the slower the gas inflow velocity into the high-pressure gas tank 1, while the piston 3 displaces faster due to the increased pressure difference on both sides, causing the power cylinder 2 to expand its volume more rapidly. The combined effect of these two factors exacerbates the attenuation of gas pressure under higher cylinder pressure.

[0054] 3. Summary The above describes the development, experimentation, and simulation analysis of a compressed air catapult. A UAV catapult system based on compressed air power was successfully developed, and detailed experiments and simulation analyses were conducted. The changes in parameters and aerodynamic processes during the catapult's operation were analyzed, and the influence of different parameters on the catapult's performance was studied. The main conclusions are as follows.

[0055] (1) A compressed air ejection system for UAVs was successfully developed and experimental research was conducted, achieving the ejection of a 50kg UAV at a speed of 25.11m / s.

[0056] (2) The simulation model's running results are in good agreement with the experimental values. The pressure changes in the gas storage tank are basically consistent, and the UAV's catapult speed error is controlled within 1.5%, which verifies the accuracy of the simulation model.

[0057] (3) The variation law of parameters such as pressure, speed and acceleration during the working process of the compressed air catapult was obtained, and the action process of compressed air inside the power cylinder 2 on piston 3 was further analyzed and understood, revealing the action mechanism of compressed air during the catapult process.

[0058] (4) Within a certain range, the pressure of the power cylinder 2 is positively correlated with the speed and acceleration of the UAV 6. If the pressure of the power cylinder 2 is set too high, the structural strength requirements of the power cylinder 2 and the UAV 6 will increase, the peak acceleration will be too high and the decay will be too fast, which is not conducive to the smooth operation of the ejection process; if the pressure is set too low, the ejection time will be prolonged and the ejection speed will be reduced. Therefore, it is necessary to take all factors into consideration and further optimize the setting of a reasonable initial pressure for the power cylinder 2.

[0059] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A compressed air catapult system for unmanned aerial vehicles (UAVs), characterized in that, include: High-pressure air storage tank (1) is used to store compressed air; The power cylinder (2) has a reciprocating piston (3) inside. The ejection rail (4) is used to guide the trolley (5); The trolley (5) is used to fix and carry the drone (6); The speed-increasing pulley block (7) connects the piston (3) and the trolley (5) via a traction rope (10) to convert the linear motion of the piston (3) into the high-acceleration motion of the trolley (5); The press (8) is connected to the high-pressure gas storage tank (1) through a pipeline, and a solenoid valve (12) is installed between the press (8) and the high-pressure gas storage tank (1). A pneumatic control valve (11) is connected to the pipeline between the high-pressure air tank (1) and the power cylinder (2) to control the instantaneous release of compressed air; A buffer device (9) is provided at the end of the catapult rail (4) for braking the trolley (5); The compressed air in the high-pressure storage tank (1) enters the power cylinder (2) through the air control valve (11) to drive the piston (3) to move. The piston (3) pulls the trolley (5) and the drone (6) along the catapult rail (4) through the speed-increasing pulley group (7) to accelerate. When the drone reaches the take-off speed, it disengages from the trolley and completes the catapult launch.

2. The UAV compressed air ejection system according to claim 1, characterized in that, It also includes a data acquisition system, which comprises: A pressure sensor, installed in a high-pressure gas storage tank (1) and / or a cylinder (2), is used to monitor gas pressure; An acceleration sensor, mounted on the UAV (6) or trolley (9), is used to measure acceleration; A speed sensor is used to indirectly or directly measure the speed of movement of the UAV (6); The data acquisition unit connects to various sensors to record and process pressure, acceleration, and velocity data.

3. The UAV compressed air catapult system according to claim 1, characterized in that, The speed-increasing pulley group (4) has a transmission ratio It satisfies the following relationship: Displacement of UAV (6) , Load on piston (3) , in For the displacement of piston (3), The traction force on the drone (6) and the trolley (5).

4. The UAV compressed air catapult system according to claim 1, characterized in that, The tilt angle θ of the catapult rail (5) is adjustable to accommodate the catapult launch of UAVs (6) under different takeoff conditions.

5. A dynamic simulation experimental method for a UAV compressed air catapult system as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Establish a thermodynamic model of the compressed air ejection system, including the mass conservation equation and energy conservation equation during the filling and releasing process of the high-pressure air tank (1); S2. Establish a gas flow model to describe the one-dimensional isentropic flow process of compressed air from the high-pressure storage tank (1) to the power cylinder (2) after the pneumatic control valve (11) is opened. S3. Establish a kinematic model, including the force analysis equations of the unmanned aerial vehicle (6), the pulley (5) and the piston (3), and consider the transmission ratio relationship; S4. Based on the aforementioned thermodynamic model, gas flow model, and kinematic model, construct a fluid-structure interaction simulation model of the catapult system in the simulation software; S5. Set simulation parameters, including the initial pressure of the high-pressure gas tank (1), the initial pressure of the power cylinder (2), the mass of the UAV (6), the mass of the trolley (5), the ejection angle, and the transmission ratio. S6. Run the simulation to obtain the pressure of the high-pressure gas tank (1), the pressure of the power cylinder (2), the acceleration, velocity and displacement of the UAV (6) over time during the ejection process; S7. Measure the pressure and acceleration data during the actual ejection process through experiments, and compare the simulation results with the experimental data to verify the accuracy of the simulation model; S8. Based on the validated model, analyze the impact of different initial cylinder pressure, air tank pressure, and ejection angle parameters on ejection performance.

6. The dynamic simulation experimental method for a UAV compressed air catapult system according to claim 5, characterized in that, The thermodynamic model in step S1 includes: mass conservation equation: ； Energy conservation equation: ； in, For gas mass, For internal energy, For enthalpy, For temperature, For heat exchange area, , The air flow rate during the filling and releasing of the high-pressure gas storage tank (1), and the gas release process of the high-pressure gas storage tank (1). , The mass of the gas in the high-pressure gas storage tank (1) For time, The specific internal energy of air, For air specific enthalpy, The air temperature inside the high-pressure gas storage tank (1) is... For ambient temperature, The heat transfer coefficient between the air inside the gas storage chamber and the environment. The heat exchange surface area of ​​the high-pressure gas storage tank (1) is... The specific enthalpy of the air filled into the gas storage tank (1), Enthalpy of the air discharged from the gas storage tank (1).

7. The dynamic simulation experimental method for a UAV compressed air catapult system according to claim 5, characterized in that, The gas flow model in step S2 includes mass flow rate calculation formulas under subsonic and supersonic flow conditions: ； in, This is the flow correction factor. For the valve flow cross-sectional area, The gas pressure in the storage tank. The gas density of the high-pressure gas storage tank (1) is... The air insulation index. This refers to the inlet and outlet pressure ratio.

8. The dynamic simulation experimental method for a UAV compressed air catapult system according to claim 5, characterized in that, The kinematic model in step S3 includes: The equations of motion for the unmanned aerial vehicle (6) and the pulley (5): ； in, For the quality of drones, For the mass of the pulley, For the motion displacement of the UAV (6), For the drone's (6) movement time, The traction force on the drone (6) and the trolley (5), The frictional resistance experienced by the trolley (5) and the drone (6) The total weight of the drone (6) and the trolley (5) For the launch tilt angle; Piston motion equation: ； in, For the mass of piston (3), For the displacement of piston (3), It is the cross-sectional area of ​​piston (3). The pressure difference across the piston (3) is... The frictional resistance between the piston (3) and the wall of the power cylinder (2) is the frictional resistance between them. The force of gravity acting on the piston. The load on the piston.

9. The dynamic simulation experimental method for a UAV compressed air catapult system according to claim 5, characterized in that, The fluid-structure interaction simulation model in step S4 includes an Eulerian fluid model and a Lagrange solid model, wherein the power cylinder (2), the high-pressure air tank (1) and the connecting pipeline are set as Eulerian domains, and the piston is set as a Lagrange domain.

10. The dynamic simulation experimental method for a UAV compressed air catapult system according to claim 5, characterized in that, In step S8, parameter sensitivity analysis is used to evaluate the impact of different initial cylinder pressures on the final ejection velocity, peak acceleration, and ejection time, thereby optimizing the design parameters of the ejection system.

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