Rail Launcher Research Articles

Simulation on temperature field of initial segment of electromagnetic rail launch

The temperature field analysis of electromagnetic rail launcher is an important basis for studying the launching stability and life. Aiming at the rail groove erosion phenomenon, the launching initial segment is selected as the research site. The heat generation mechanism of Joule heat and friction heat is analyzed, the heat source model is established, the three-dimensional finite element simulation model is established and the position, velocity and current waveform of the launching initial section are determined according to the circuit simulation, the finite element simulation results show that the heat in the initial stage of launching mainly concentrates on the contact surface between armature and rail. The friction heat is the main factor affecting the temperature rise of the contact surface, and the uneven distribution of the current density will lead to the uneven temperature distribution of the contact surface.

Research on the inner bore profile detecting system of railgun

In the process of electromagnetic launching, there is much inner damage containing wear, corrosion, gouging, and transition in the rail. After several launchings, the damage has an enormous influence on the accuracy of launching and rail lifetime. In order to protect the rail and research on the damage mechanism, this paper provides an insight into the methods of measuring the inner bore of the electromagnetic rail launcher based on the optical vision measurement principle. Applying this optical method, the apparatus is designed and divided into three subsystems. These three subsystems provide global alignment information, the axial depth information, and inner surface profile information respectively. In this way, the 3D model of the rail can be precisely rebuilt. The feasibility of the method was confirmed in the experiment. And this method may have significant implications for the further research on the on-line measurement of electromagnetic rail launchers.

Comparison and Simulation Analysis of Augmented Electromagnetic Rail Launchers

On the basis of stack augmented electromagnetic rail launcher, using an H type armature to connect the upper and lower two groups of guideways through four contact surfaces to form an electromagnetic rail launcher. By changing the shape of the contact surface of the armature and the guide rail, different launcher models were set up, and compared with the traditional augmented electromagnetic launchers. The simulation analysis was carried out by Maxwell software. The results show that the electromagnetic thrust of the H type armature is obviously greater than that of the double-armature. For the arc shaped contact surface, the current distribution on the contact surface of the double-armature is the most uniform, and the ablation and melting can be well suppressed. The current distribution on the contact surface of the H type armature is more uniform and has the greatest electromagnetic thrust, so it is more suitable electromagnetic rail launch.

Dynamic Response of Interior Ballistic Process and Rail Stress in Electromagnetic Rail Launcher

The dynamic response of interior ballistic process in an electromagnetic (EM) rail launcher (EMRL) directly affect the stress concentration of the rails and the launch performance of the projectile. By simplifying the rail as a Bernoulli–Euler beam fixed on the elastic support under the action of moving loads and acquiring the equivalent stiffness of the elastic support through a static EM-structural coupled model, the critical velocity of the EMRL is captured. Also, the hybrid finite-element/boundary-element method is used to establish a coupled EM-structural-motion model to derive the dynamic contact force between the armature and the rail as well as the stress distribution of the rails. Finally, the measuring data of fiber Bragg grating strain sensors fixed on the back of the rails are used to verify the stress concentration of the rails and analyze the stability of the projectile in the bore. For the typical 30 mm $\times30$ mm rectangular caliber launcher whose critical velocity is less than muzzle velocity, analysis and test results show that the EM extrusion force of the C-type armature exerted on the rail reaches the peak value at the beginning of the flat-top stage and gradually decreases as time goes on; the stress waves aroused by armature passing are easily resonant with the reflected stress waves in the rail in the high-speed stage of the armature, in which the stresses of rails are the severest, and the stress concentration level is about 2.44 times that in the initial low-speed stage; when the armature operates in the high-speed stage, there will be a vibration phenomenon which will lead to the asymmetry of loads on the upper and lower rails. These results have guiding significance to design the EMRL.

Analysis of the Factors Influencing the Dynamic Response of Electromagnetic Rail Launcher

The dynamic response of an electromagnetic rail launcher (EMRL) has a direct influence on launch accuracy. With the Bernoulli–Euler beam located in the elastic support as an object of study, this paper presents an analytical model of the dynamic response of EMRL under the conditions of electromagnetic (EM) repulsive force and armature-and-rail contact force and obtains the analytical solution of the model. The redevelopment of the finite-element software makes it possible to perform a strong coupling transient simulation of the moving EM repulsive force, armature-and-rail contact force, moving thermal power, frictional thermal power, and the structural response in the dynamic launching process. Through the comparison of the results obtained by the analytical method, 2-D finite-element method (2-DFEM), and 3-D FEM (3-DFEM) for the dynamic response of the EMRL, the proposed model proves to be accurate and reliable. It is found that 3-DFEM can more accurately reflect the dynamic response process of the EMRL. On this basis, an analysis is made on the influence of the contact force, structural damping and heat on the dynamic response. The studies show that the contact force and the structural damping have little influence on the dynamic response under the condition of noncritical velocity, but have a great influence under the condition of critical velocity. However, the heat has a great effect on the dynamic response in both the conditions.

Dynamic Response of Electromagnetic Rail Launcher Due to Projectile Motion

The dynamic response in the dynamic launching process of electromagnetic rail launcher (EMRL) is very important for the design of launchers and armatures. With the Bernoulli–Euler beam located on an elastic support as an object of the study, the analytical model of EMRL dynamic characteristics under the influence of EM repulsive force and contact force between the armature and the rail is obtained, and the corresponding 3-D finite-element simulation model [moving load–rail model (MR model)] is established. On this basis, the 3-D finite-element simulation model [projectile–rail model (PR model)] considering the projection vibration is established to obtain the dynamic response of EMRL due to projectile vibration. Studies show that the calculation results of the analytical model agree well with that of the MR model. When the moving load works at a critical speed and reaches the point of action, the rail will have an increased deformation and then a harmonic vibration, whose amplitude is five or six times than that under the noncritical operating condition. The analysis of the impact of projectile vibration on the rail deformation makes it known that the vibration amplitude of the PR model is four or five times than that of the MR model because of projectile vibration. The greater the gap between the rail and the armature is, the more violent is the projectile vibration and the greater is the vertical deformation of the rail, and the greater the density of the payload with the same volume is, the more intense is the projectile vibration and the greater is the vertical deformation of the rail. When launching reaches the critical speed, the rail deformation of the PR model is less than that of the MR model, which is mainly caused by the vibration of the projectile, but the vibration periods of those two models are the same.

Heat Generation and Thermal Management of a Rapid-Fire Electromagnetic Rail Launcher

The pulse current can raise the bulk temperature of rails in the electromagnetic rail launcher (EMRL) during each shot. Quantifying the energy deposited in the rails and implementing an effective thermal management system are the key to tactical applications of the EMRL. This paper acquired the spatial distribution characteristics of total heat in the rails by using an analytical model and a multiphysics coupled model based on the hybrid finite-element/boundary-element method. The rail segment that produces the most heat is located where the armature arrives near the end time of the rising edge of pulse current. Since the rails suffer the severest stress when the armature passes, the key to the thermal management is to control their residual temperature rise when the armature passes. Therefore, the horseshoe cooling grooves dug on the back of the rails, which have low-stress concentration effect and good engineering feasibility avoiding internal drilling problem, are enough to effectively cool the rails. The experimental data measured by the fiber Bragg grating sensors in the tests of a single shot and a rapid firing of two agree well with the simulation results, which verifies the validity of the thermal management strategy. Furthermore, through prediction, the maximum residual temperature rise is only 2.57 K in the stage of heat balance at a sustained firing rate of 12 shots per minute for the 30 mm $\times30$ mm rectangular caliber launcher presented in this paper. These conclusions are also adaptive to large-scale launchers and have guiding significance to the engineering application of the EMRL.

Analysis of GFRP insulator characteristics under multiphysical fields in electromagnetic rail launchers

The glass fiber-reinforced polymer (GFRP) insulators in electromagnetic rail launchers (EMRLs) work in a complex environment coupling electromagnetic, thermal and structural fields. Ablation, metal deposition, fracture and other destructive forms easily appear in GFRP insulators, which will affect the efficiency and service life of the electromagnetic launcher system. To explore the factors causing insulator performance degradation, a coupling model of multiphysical fields, including electromagnetism, temperature and structure, was established to analyze the physical load on the GFRP insulators in EMRLs. And based on the results of the coupling numerical analysis, delamination or fracture may occur in the middle of insulators. An insulator sample was experimentally analyzed after electromagnetic launch tests to verify the simulation conclusions and to obtain the failure mechanism of GFRP insulators under extreme environments of multiphysical fields. During electromagnetic launching, the rails repeatedly compress the GFRP insulators and cause cracking of the GFRP insulators. High temperature causes carbonization and metal contamination on the surface of the GFRP insulators, which results in a decrease in surface resistivity. In addition, there were pits on the surface of the GFRP insulators, possibly due to the armature planing against the GFRP insulators during electromagnetic launching.

Analysis of the Melt Erosion Patterns at Rail-Armature Contact of Rail Launcher in Current Range of 10–20 kA/mm

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. This current melt erosion (CME) has been experimentally studied in the current range of 10–20 kA/mm with a 20-mm caliber lab-scale rail launcher, and payload separated method was used to keep the recovered armatures intact. Thus, the onset behavior and erosion patterns of CME can be successfully observed in such relatively low current densities. In this paper, we will further our study to analyze the patterns of CME with the increasing current densities under the effect of different initial mechanical contact force. Results show that CME all start at the side edge, and then spreading longitudinally and transversely with the increase of current. It is found that the starting position of CME appears near the trailing edge at small mechanical contact force and moves to the leading edge with larger mechanical contact force. At the same current magnitude, erosion amounts are much more under small mechanical contact force. Stationary mechanical contact pressures and current distribution of armature surface are simulated to investigate the effect of initial mechanical contact force on starting position of CME. Current distributes at the edges of actual contact zone and the maximum of current density appears at the side edges of armature. As the initial mechanical contact force increases, actual contact zone and current density move toward to the leading edge from trailing edge. It can be confirmed that the erosion starting position is at the side edge along actual contact zone and will move toward to the leading edge from trailing edge with the increase of initial mechanical contact force. Smaller initial mechanical contact force will cause more erosion at the same current magnitude because of larger current density. Furthermore, an average friction coefficient calculation method is proposed to evaluate the melt lubrication effect of CME. The result shows that the lubrication effect becomes better with larger current densities.

Simulations, Experiments, and Launch Characteristics of a Multiturn Series–Parallel Rail Launcher

In order to markedly improve the inductance gradient of electromagnetic (EM) railgun and current-carrying capacity of the armature, and enhance the ability to launch large mass projectiles, a system simulation analysis and preliminary experiments were carried out for the multiturn series-parallel rail launcher (MSPRL). First, the Simulink simulation model of the rail launcher system based on the circuit model was established, and the changing rules of current waveforms and armature velocities under different contact resistances were obtained. Then, an EM-structural multiphysics fields coupling model is constructed, with the supplied currents obtained earlier, the EM propelling force on the armature as well as contact force between the armature and rails were analyzed. In view of those analyses, the inductance gradient and armature velocity in bore were calculated. Finally, the test platform of the MSPRL was built to carry out preliminary verification experiments of relevant parameters. During the test, the muzzle impedance and muzzle velocity were measured, and the validities of the simulation models were verified.

Modeling for the Calculation of Interior Ballistic Velocity of Electromagnetic Rail Launch Projectile

Interior ballistics is of great importance to the study of gun barrels and projectiles. One of its important characteristics is velocity, which determines the firing capability of projectiles. Aiming at the interior ballistic velocity (IBV) of projectiles launched from electromagnetic (EM) rail, this paper has analyzed the differences in the mechanism between the EM rail gun and the traditional cannon. Based on some assumptions, the calculation formula of projectile EM force was gained with the time-frequency analysis method. Then, it built a simulation calculation model of IBV of the projectile. In addition, the use of the positioned data of the magnetic probe (B-dot probe), to obtain the displacement fitting matrix, leads to the establishment of an experimental fitting model of IBV of the projectile. With the plane EM rail launcher in our laboratory as an example, the above-mentioned two models are applied to analyzing the accelerated motion of the projectile in the chamber. The experimental fitting results are compared with the measured data and simulation results of the B-dot probe, which are basically consistent. Thus, it shows that the IBV's simulation model and the experimental fitting model have high reliability.

Compact Energy Storage Device for Electromagnetic Launchers of Solids

Numerical study has been performed to investigate the operating characteristics and modes of an energy storage device based on a pulsed magnetohydrodynamic generator and a step-up transformer with a stored energy of 25 and 50 MJ and a secondary winding current of 250 kA at the final stage of operation. The operating parameters of such storage devices with rail launchers operating in the mode of rapid-fire launching of several projectiles were calculated.

Durability and Stiffness Estimation for the Composite Overwrap Electromagnetic Rail Launcher Barrel

One of the ways to decrease electromagnetic rail launcher (EMRL) barrel mass is to utilize composite material overwrap. Design of novel light, stiff, and durable EMRLs requires accurate computational prediction of barrel strength. This paper presents numerical model and corresponding computer code for the calculation of stresses in composite overwrap EMRL barrel. The computer code named, NDSPDE, based on the finite-element method for stresses analysis in complex geometric shapes designs in a plane strain. The code allows carrying out numerical structural studies of EMRL barrels under various electromechanical loads accounting for the orthotropic properties of utilized constructive materials. Depending on the requirements for EMRL barrel stiffness and durability the results of numerical studies allow to select suitable construction materials to optimize both the barrel design and the barrel electromechanical loading conditions. The safety margin evaluation of the side insulators and the overwrap was carried out by classical criterion of maximum tensile stress. Note that in durability assessing of other launcher elements the above safety margin is not applicable, since the stress is not unixial in the most loaded parts of those elements. In case of nonuniaxial stress, evaluation of the launcher structural elements durability requires utilization of more complex criteria, which account for the type of the stress state arising in the launcher elements. This paper presents the numerical results of the EMRL barrel cross-sectional parameter estimation including the glass fiber overwrap, rails, and insulators. Estimations were carried out both for stresses and for durability of the EMRL barrel structural elements.

An Electromagnetic Rail Launcher by Quadrupole Magnetic Field for Heavy Intelligent Projectiles

This paper presents a new rail launcher based on a rupole magnetic field. This novel propulsion concept is adopted for launching heavy intelligent projectile. The interaction between the magnetic field and the armature current results in the generation of a large thrust. The thrust acts on the armature where the intelligent projectile is loaded without magnetic shielding, and pushes it forward. The configuration of the rails is given in this paper. Numerical analysis and the finite-element model are adopted to validate the properties of the magnetic field in the launch tube. The current and magnetic field distribution in the armature are simulated in ANSYS Maxwell 3-D and based on which the armature’s structure is designed. The thrusts as function of the rail distance and current are presented. The results show that the proposed rail launcher can project sensitive devices because of its magnetic field features and it can provide abundant thrust for heavy projectile, as well as good stability in launch process.

Experimental Studies on Melt Erosion at Rail-Armature Contact of Rail Launcher in Current Range of 10–20 kA/mm

Sliding electrical contact between rail and armature in rail launchers is characterized by high speed and large current. Melt erosion is caused by the current concentration on the contact surface of armature. Because the current melt erosion (CME) was considered to be a main mechanism of armature-rail contact failure, it was experimentally and theoretically studied in the early years using current density of 30–40 kA/mm, which is the exact driving current of rail launches. However, the critical behavior at the onset of CME cannot be observed due to the serious melt erosion at such high current densities. In this paper, the CME of armatures has been experimentally studied in the current range of 10–20 kA/mm with a lab-scale rail launcher. A payload separated method was used to keep the recovered armatures intact. The critical process for the onset of melting was observed and the erosion spreading patterns on the contact surface was analyzed. It is found that the current melt-wave model postulated in early years cannot describe the development of CME in our experiments. The result shows that current erosion mostly occurs at the static and the low-velocity stage of armature. The CME begins at the point of maximum contact pressure provided by armature-rail interference fit, and then, the melt erosion spreads longitudinally and transversely. The current erosion is affected by both current distribution and the movement of liquid aluminum. In longitudinal direction, the flow of liquid aluminum results in erosion propagation to leading edges. The transverse width of erosion zone expands with increasing current magnitude along the edge of interference fit.

A New Finite-Element Method to Deal With Motion Problem of Electromagnetic Rail Launcher

In dynamic launching processing of the electromagnetic rail launcher (ERL), the armature is sliding along the rail while the pulse current flows through the interface between the armature and rails. The distribution of physical fields at the interface of the rail and the armature is quite complex, and meanwhile they may be phenomena like abrasion, melt, erosion, and cutting, which are typical problems of rapid electrical contact sliding. For numerical analysis of ERL considering the movement of armature at the velocity of v, a new method has been introduced in this paper, which has used $v\cdot A = 0$ as a gauge condition by tree technique in Whitney elements. By this method, the interface condition of E has been satisfied while the continuity of the electric scalar potential $\varphi $ and the magnetic vector A across the interface of two conductor region has also been ensured. Finally, the 2-D and 3-D finite-element model has been built by the edge element method. The results of the model have been analyzed and compared with EMAP3D code’s, which have verified the described methods.

Electromagnetic Compatibility and Current Pulse of Railgun

Electromagnetic (EM) interference and its suppression are one of the major issues in most current systems design. The electric device such as railgun generates the EM fields that unintentionally propagate away from the structure. Railgun that have significant amounts of radiated emissions may interfere with the normal operation of other devices in close proximity. Also during the accelerating run of rail launchers, and particularly during the ignition of the armature, the radiated EM fields can compromise the life of electronic devices, can influence the signal to noise ratio, and can generate electrical shock hazard. The short duration pulse signal, such as current pulse of railgun, switching and arcing between components of railgun is typically rich in frequency spectral contents. It should be noted that the propulsive force of current pulse in each time push the armature in motion direction and change the propagation parameters of railgun as a time varying antenna and can affect on the radiation pattern in the various frequency ranges. Furthermore, in each component of current pulse, armature is in special position in direction of motion along the barrel and the impedance of railgun that power source see in front is different with previous stage and radiation pattern is different too. In this paper, the relationship between pulse form of input current and electric field around railgun are analyzed and simulated with finite-element method, then by attention of the armature position in each time it will be investigated the radiation pattern of railgun.

Research on Insulation Problems Under Multishot Experiments in Electromagnetic Rail Launcher

Insulators between conductive rails assume a leading role in electrical insulation and support fixation. Failure of insulating materials during continuous repetitive launches has been found in experiments, the performance changes of insulators will directly affect efficiency and lifetime in repetitive electromagnetic launcher system. Many factors may influence the insulating performance because of complicated working condition, such as strong pulse stress and high temperature. A multishot minor-caliber launcher was designed for the study of the insulating performance. The length of the launcher is 890 mm with a caliber size of 10 mm × 10 mm. C-shaped aluminum alloy armatures and glass-reinforced polymer insulator G10 are used. The muzzle speed is above 2 km/s. After the multishot experiments, the surface topography and surface resistivity of the insulators were measured by megger and digital microscope. The experimental and testing results show that the surface resistivity of G10 reduces gradually with the increase of experiment times, also the surface resistivity of different locations changes. Some pits and cracks appear at individual locations on the G10 surface, the phenomena of resin wear and fiber exposed are observed. Metal deposition is also found on the insulator surface by different types at different positions. Surface flashover voltage is measured after ablation.

The Dynamic Performance and Thermal Computation of Electromagnetic Rail Launcher Considering Parameters Variation

For the electromagnetic rail launcher, the parameters variation has obvious effect on the dynamic performance and efficiency. This paper constructs the system simulation model of the electromagnetic rail launcher by using of Simulink software, and then analyzes the influences on the system dynamic performance for main devices. Based on the parameters and large current condition, the launching efficiency model is constructed, and the energy distribution characteristics are obtained. The loss of rail, armature, and feeder equipment is 38.7%, and the loss of arc extinguishing equipment is about 4.76%, so the heat loss is about 43.46% of total loss. When considering that the other loss is 33.37%, the system energy efficiency is 23.17%. Based on the design of the small prototype, the energy loss characteristics of the full prototype in launch rail and its temperature features are discussed in detail. The peak temperature is 276 °C after 11 continuous shots with converting coefficient being 5000 W/( $\text{m}^{{{2}}}\cdot \text {K}$ ), and it can decrease 58 °C if the better convection boundary condition is achieved, which means the rail can meet the requirement of the thermal management.

Design of a Superconducting Self-Supplied Electromagnetic Launcher Proof of Concept Using HTS REBCO Conductor

A superconducting magnetic energy storage (SMES) is an attractive power supply for electromagnetic rail launchers (EMRL), which require pulse currents to launch projectiles at very high speeds. Moreover, the accelerating force in an EMRL may be enhanced by adding a background field, a principle known as launcher S3EL concept (Superconducting Self-Supplied Electromagnetic Launcher) consists in using the SMES both as a power supply and for background field generation. The challenge is to reach the operating current and peak magnetic field of such launchers, which can be up to hundreds of kA and up to 10 T. The use of a high-temperature superconductor is mandatory to maintain superconducting operation during a launch, though operation at 4.2 K is foreseen to benefit from the RareEarth-BaCuO (REBCO) tape high critical current densities. The aim of this work is to derive a practical design for a 1-m-long small-scale S3EL proof of concept using REBCO coated conductor, with a reduced output velocity (100 m/s). After preliminary sizing studies, the spatial constraints for the SMES-Launcher integration is presented. A parametric joint analytical and Finite Element Method (FEM) study is conducted to refine the design and maximize the operation margins while maintaining the launch performances. Finally, cable design and discharge method suitable to reach the required operating current are presented.