Search Results (18)

The muzzle velocity of electromagnetic rail launchers approaches 1550 m/s, exhibiting typical hypervelocity electrical contact characteristics. During the electromagnetic launching process, extreme conditions, such as high current density, high temperature rise, and strong strain can cause wear on the surfaces of the armature and rail. Electromagnetic launch tests are conducted to study the wear conditions of the rail surface and the relationship between the wear state and contact resistance. After the rail is abraded by hundreds of launching armatures, its surface 2D profile and morphological characteristics are measured and analyzed. Based on fractal theory, the static contact resistance model is developed. Concurrently, the contact resistance at various positions is measured to reveal the evolution of the static contact resistance between the armature and the rail under wear. The research results show that along the direction of the armature launch, the rail surface wear transitions from mechanical wear to electrical wear, the fluctuation range of the 2D profile becomes smoother, and the roughness of the rail surface shows a decreasing trend. When the roughness is greater, the contact resistance is more sensitive to changes in external load. Full article

An electromagnetic launcher is a kind of rail symmetrical distribution launcher. When a symmetrical current is passed between the rails, the strong magnetic field is symmetrically distributed between the two rails. The bore parameters affect the efficiency and accuracy of the launcher. Launching accuracy is an important evaluation content for assessing the technical index of the electromagnetic launcher. In this paper, experiments were carried out to investigate the influence factors of the launching accuracy of a small-caliber electromagnetic launcher. The experimental results show that: (1) The consistency of the muzzle velocity increases with the increase of the rail separation. When the rail separation is 16 mm, the mean deviation of the muzzle velocity is the smallest, at 16.71, 15.72, and 10.77, respectively. When the rail separation is constant, the mean deviation of the muzzle velocity is 10.77, while the convex arc height is 1 mm. Increasing the rail separation and the convex arc height is beneficial to improving the consistency of the initial velocity. (2) When the rail separation is certain, increasing the convex arc height significantly improves the firing accuracy and firing intensity, and when the convex arc height increases from 0 mm to 1 mm, the firing intensity is reduced from 9.6 to 4.41, and the firing intensity decreases from 10.34 to 5.79, which significantly reduces the firing deviation and increases the muzzle consistency of the armature under repeated firing conditions. (3) The muzzle attitude is mainly affected by the effective mass ratio. Within a certain range, adding load can make the muzzle attitude of the integrated projectile more stable. However, when the load mass is too large, it will have a negative impact on the muzzle attitude. The results show that under the two cases of the effective mass ratio of 0.43 and 0.49, the integrated projectile has a better muzzle attitude. Full article

The electromagnetic rail launcher has the advantages of high muzzle velocity, long-range and controllability and has received extensive attention from researchers in various countries. The launcher efficiency reflects the ability of the launcher to convert electrical energy into kinetic energy of the load and is an important parameter of the electromagnetic rail launcher, which includes the launcher effective efficiency and launcher ineffective efficiency. The bore parameters and the effective mass ratio are important factors for the launcher efficiency. Finite element simulations and experiments were carried out to study the effects of rail separation, the convex arc height and the effective mass ratio on the launcher effective efficiency. Three conclusions were obtained. (1) The launcher effective efficiency increased with the growth of the effective mass ratio, the launcher effective efficiency rose from 7.91% to 17.17% when the effective mass ratio was in the range of 0.28~0.56, and the average value of the improvement in the launcher effective efficiency under different conditions of bore parameters is 8.24%. (2) The launcher effective efficiency rose with the increment in the rail separation. As the rail separation increased from 14 mm to 16 mm, the launcher effective efficiency improved by an average of 0.70%, and the increment in the launcher effective efficiency decreased with the growth of rail separation. (3) The launcher effective efficiency increased with the growth in the convex arc height. As the convex arc height rose from 0 mm to 1 mm, the launcher effective efficiency improved by 0.77% on average. Moreover, the muzzle velocity and the acceleration process of the armature in the bore were calculated. The conclusions were the same as the conclusions of the experiments. Full article

This paper focuses on improving fire suppression performance through the use of compressed-air launching technology. A launch dynamics calculation model of a compressed-air launcher is presented, developed using VC++ programming, to simulate the acceleration process of a fire-extinguishing bomb in a barrel. By analyzing the influences of various structural and initial parameters on interior ballistics variations, the effectiveness of the calculation model and program in accurately simulating the launching process is demonstrated. The calculation results indicate that the bore pressure follows a similar trend to that of traditional gunpowder launching. Additionally, it is found that specific structural parameters, such as nozzle diameter and gas cylinder volume, have a direct impact on interior ballistics variations. Notably, the nozzle diameter positively affects the peak pressure, muzzle velocity, gas transfer efficiency, and launch efficiency. To ensure an optimal launch effect and efficiency, the nozzle diameter should be selected to be more than half of the launcher caliber. Similarly, the gas cylinder volume positively influences the peak pressure and muzzle velocity while negatively affecting the gas transfer efficiency and launch efficiency. Furthermore, the initial pressure in the gas cylinder exhibits a positive linear relationship with both the peak pressure and muzzle velocity but a negative linear relationship with the gas transfer efficiency and launch efficiency. The loading position minimally impacts the peak pressure and muzzle velocity but slightly enhances the gas transfer efficiency and launch efficiency. Finally, it is observed that launch angles do not affect the interior ballistic process. The research findings provide valuable theoretical guidance for determining the working parameters of compressed-air accelerated fire-extinguishing bombs. Full article

The parameter optimization of a multistage synchronous induction coilgun (SICG) is a time-consuming task. Traditional machine learning methods can accelerate the process by building predictive models, but they require separate modeling for an SICG with different stages, which requires numerous datasets and is a cumbersome process. This paper proposes a method for building a predictive model for an SICG with different stages based on a recurrent neural network (RNN). In this method, the feed time of a 2- to 10-stage SICG is selected from the standard orthogonal design table as the training and test datasets, and the current filament method (CFM) is used to calculate the dataset label. The gate recurrent unit (GRU) neural network is used to study the training dataset, and the predictive model has good accuracy with respect to the test dataset, with an average error of 0.022. The predictive model and a particle swarm optimization (PSO) algorithm are applied to optimize the feed time of the SICG with different stages. The results show that the three-stage SICG can achieve a muzzle velocity of 50 m/s for a projectile, while the maximum muzzle velocity of the three-stage SICG in all datasets is 46.87 m/s. Full article

As a damage element, high-speed fragments have a significant effect on the ammunition safety. The impact from the fragments are also one of the basic problems of ammunition safety tests. To clarify the reaction characteristics of combustion, explosion, detonation, and so on, when hypersonic fragments hit insensitive munitions, it is necessary to carry out corresponding research on the deceleration law of hypersonic fragment in the air. In this paper, a 30 mm caliber gun with large chamber, small caliber, and large aspect ratio is proposed to drive high-speed fragments. According to STANAG 4496 standard, a near-cylinder steel fragment with Brinell hardness HB ≤ 270 and mass of 18.6 g was designed. The test system was composed of zone interception velocity measurement, chamber pressure sensor, trajectory tracking system, high-speed camera, and other equipment were also established to obtain the pressure variations in the chamber, the velocity of the fragment, and its flight orientation. From the video taken by the high-speed camera and trajectory tracking system, the fragment and the projectile sabot achieve effective separation after the fragment travels out of the muzzle. As time goes on, the distance between the fragment and the projectile sabot gradually increases. The fragment is always in the front of the sabot and steadily flies to the target. The muzzle velocity of the fragment is controlled by adjusting the propellant charge, and the flight velocity in the air is measured by the zone interception velocity measuring device in the range of 5 Ma to 7 Ma. The theoretical models of fragment deceleration and the models of flight orientation are also established according to the experimental data. On this basis, F test and least square nonlinear regression fitting were used to analyze experimental data. Finally, the deceleration coefficient of quasi-cylindrical fragments between 5 Ma and 7 Ma stipulated in STANAG 4496 standard is 0.009312, and the average drag coefficient in air is 1.109. Full article

The influence of electromagnetic induction coil launcher (EICL) system parameters on the launch performance was analyzed, and a method for measuring the launch performance of an EICL system with a muzzle velocity and energy conversion efficiency was proposed. The EICL system mainly includes a pulse power supply and launcher. The parameters of the pulse power supply mainly include the discharge voltage and the capacitance value of the capacitor bank. The structural parameters of the launcher mainly include the bore size of the launcher, the air gap length between the armature and the drive coil, the length and width of the drive coil, and the trigger position of the armature. Change in single or multiple parameters in the launch system will influence the launch performance. The influence of single or multiple parameters on the launch performance was summarized, and the physical law as analyzed. The influence law of the EICL system parameters on the launch performance was obtained, which lays a theoretical foundation for the optimization design of EICL. Finally, experimental verification was carried out by a single-stage test platform. Full article

This present work suggests a charge technique to produce a super high-velocity fragment (≥2350 m/s) using a 30 mm launching system. The steel cylindrical fragments with Brinell hardness HB ≤ 270 are designed according to STANAG 4496 in the experiment, and a test system including interval speed measuring device, pressure measurement and high-speed camera is employed to obtain the information on the velocity, pressure and muzzle field of the fragment. The flame characteristics presents an increasing area, and the fragment escapes the control of the muzzle field when the high-velocity fragment is flying out of the muzzle. Moreover, the projectile sabot can timely be separated from the fragment in the range of the first interval velocity measuring device. Based on this, the mathematic models on the interior ballistic process of the fragment movement are established to analyze the effects of various charge structures on the motion characteristic of the fragment. Comparisons of fragment velocity and chamber pressure of computational results are performed with experimental studies. A reasonable match has been obtained in these comparisons. Further, a discussion on the choice of charge parameters is performed by the optimization design for this super high-velocity fragment. Full article

The gas-curtain launch is designed to address the shortcomings of conventional underwater launchers, such as poor dependability and low muzzle velocity. In this paper, the influence of jet structures on the propulsion performance and internal flow field of an underwater gas-curtain launcher is investigated. To conduct the experiment on a small-aperture underwater launcher, three projectiles with different jet structures were designed. The experimental results show that a projectile with a central nozzle is more conducive to gas-curtain formation than one with four sidewall grooves. Additionally, the central nozzle can reduce launch resistance and improve propulsion performance more effectively. Furthermore, increasing the diameter of the central nozzle aids in gas-curtain formation and propulsion performance. Following the experiment, a numerical model of the internal flow field for gas-curtain launch is built in order to develop numerical simulations under three jet structures. The calculation results show that the three gas-curtain projectiles can likewise acquire good propulsion performance. Different jet structures have significant impacts on the launching resistance of a gas-curtain launcher, thereby affecting its propulsion performance. The launch resistance is lower when the central nozzle jet structure is utilized; however, the muzzle velocity is also lower because more gas is consumed for drag reduction and the projectile force area is smaller. This study reveals the effect of jet structure on the propulsion performance and flow field evolution of a gas-curtain launcher. Full article

Numerical and experimental investigations of armament systems are an important part of modern design processes. The presented paper reports problems that were encountered on the theoretical analysis of the performance of 35 mm anti-aircraft cannon and the way in which they were solved. The first problem concerns the application of results of closed vessel tests of used propellant in interior ballistics simulations. The use of a nonstandard form of the gas generation rate equation solved this problem. The second problem concerned the assessment of projectile–barrel interaction. The barrel resistance was estimated making use of finite element analysis. The third problem arose from the need to determine the heat transfer from propellant gases to the barrel. The employed formula for the heat exchange coefficient and 2D modelling of the heat conduction in the barrel provided the solution. Selected elements of the theoretical model were validated by shooting range experiments and data provided by the ammunition producer. Using the considered approach, crucial ballistic parameters (maximum propellant gas pressure and muzzle velocity) were estimated with an error of less than 6.0%, without application of additional fitting coefficients. The numerical estimation of the barrel external surface temperature provided a relative discrepancy with the experimental data lower than 6% and enabled the estimation of the critical burst length, equal to 14 shots. Full article

Excessive recoil severely restricts the loading of high-power traditional guns on modern vehicles. To reduce the recoil without breaking the continuous firing mode and reducing the projectile velocity, a recoil reduction method that controls the lateral ejecting of propellant gas by a piston was proposed. The recoil reduction device is symmetric about the barrel axis. First, a one-dimensional two-phase flow model of interior ballistic during the gun firing cycle was established. Next, the MacCormack scheme was used to simulate, and the piston motion was gained. Then the propagation of the rarefaction wave in the barrel was presented. Finally, the propulsion difference between the piston-controlled gun and the traditional gun was discussed. The results showed that the recoil momentum was reduced by 31.80%, and the muzzle velocity was decreased by just 1.30% under the reasonable matching of structural parameters. Full article

The fracture failure of a high-speed long rod has historically been a challenge. Since the flying plate and flying rod have a relatively low velocity, it is challenging to achieve a multi-stage fracture of the high-speed long rod within the range of existing technology. In this paper, the linear explosively formed penetrators (LEFPs) sequence with a stable flight velocity of 850 m/s were used to cut a high-speed long rod. We investigated the deformation and fracture of Φ10 mm tungsten alloy long rods having different length-diameter ratios (20, 26, 35) and different speeds (1200, 1400, 1600 m/s) by employing the LEFPs sequence with different spacings (0–40 mm) and different interception angles (30°, 60°). In the meantime, the fractured rods movement pattern was recorded with a high-speed camera to elucidate the change law of the length, speed, linear momentum, and angular momentum of fractured rods. It was found that the length loss rate of the fractured rods is as high as 27%. The fractured rods rotated around the center of mass, and the vertical speed change could reach up to 18% of the muzzle velocity of the long rod, and the greatest reduction of horizontal speed and momentum could reach 37%. The longer the interaction time between LEFPs sequence and the long rod, the more beneficial the failure of the long rod. The application of LEFPs sequence solved the difficult problem of disabling the high-speed long rod, and the quantitative analysis of the fracture failure of the long rod had an important sense for studying the terminal penetration effect of the fractured rods. Full article

The electromagnetic rail catapult is a device that converts electrical energy into kinetic energy, which means that the strength of electrical energy directly affects the muzzle speed of armature. In addition, the electrical conductivity, electromagnetic rails and armature surface roughness, and the holding force of the rail are influencing factors that cannot be ignored. However, the electric ablation on the surface of the electromagnetic rails caused by high temperatures seriously affects the service life performance of the electromagnetic catapult system. In this study, electrochemically deposited nickel-phosphorus and nickel-molybdenum alloy coatings are plated on the surface of electromagnetic iron rails and their effects on the reduction of ablation are investigated. SEM (scanning electron microscopy) with EDS (energy dispersive spectroscopy) detector, XRD (X-ray diffraction), 3D optical profiler, and Vickers microhardness tester are used. Our results show that the sliding velocity of the armature decreases slightly with the increased roughness of the rail coating surface. On the other hand, the area of electric ablation on the rail surface is inversely related to the hardness of the rail material. The electrically ablated surface areas of the rails are in: annealed nickel–molybdenum < nickel–molybdenum < annealed nickel–phosphorus < nickel–phosphorus < iron material. Heat treatment at 400 and 500 °C, respectively for Ni–P and Ni–Mo alloys, significantly increases hardness due to the precipitation of intermetallic compounds such as Ni₃P and Ni₄Mo phases. Comprehensive data analysis shows that the annealed nickel–molybdenum coating has the best electrical ablation wear resistance. The possible reason for that might be attributed to the high hardness of the heat-treated nickel–molybdenum coating. In addition, the thermal resistance capability of molybdenum is better than that of phosphorus, which might also contribute to the high wear resistance to electric ablation. Full article

Multiphysics problems represent an open issue in numerical modeling. Electromagnetic launchers represent typical examples that require a strongly coupled magnetoquasistatic and mechanical approach. This is mainly due to the high velocities which make comparable the electrical and the mechanical response times. The analysis of interacting devices (e.g., a rail launcher and its feeding generator) adds further complexity, since in this context the substitution of one device with an electric circuit does not guarantee the accuracy of the analysis. A simultaneous full 3D electromechanical analysis of the interacting devices is often required. In this paper a numerical 3D analysis of a full launch system, composed by an air-core compulsator which feeds an electromagnetic rail launcher, is presented. The analysis has been performed by using a dedicated, in-house developed research code, named “EN4EM” (Equivalent Network for Electromagnetic Modeling). This code is able to take into account all the relevant electromechanical quantities and phenomena (i.e., eddy currents, velocity skin effect, sliding contacts) in both the devices. A weakly coupled analysis, based on the use of a zero-dimensional model of the launcher (i.e., a single loop electrical equivalent circuit), has been also performed. Its results, compared with those by the simultaneous 3D analysis of interacting devices, show an over-estimate of about 10–15% of the muzzle speed of the armature. Full article

In an electromagnetic rail launcher, a metal liquid film is created at the armature/rail (A/R) contact interface. It has a significant impact on electromagnetic launch performance. In this paper, an electromagnetic-elastic mechanics-hydrodynamics multi physics coupling model is established in consideration of the metal liquid film’s own acceleration, magnetic pressure and dynamic changes in film thickness. Based on this model, the lubricating characteristics of magnetic pressure and fluid pressure distribution, film thickness distribution and velocity distribution of the metal liquid film were studied. When the velocity of the metal liquid film is very fast, and the magnetic pressure is reduced, it may fail to maintain stability and rupture, which may be an important reason for the transition. Finally, this paper analyzes the lubrication effect of the metal liquid film, and points out that when we want strictly to control the muzzle velocity, the lubrication effect of the metal liquid film must be considered. Full article