Railgun Design Research Articles

Understanding the behaviour of magnetic field distribution of railgun under transient conditions using finite element method

The magnetic field distribution in the rails is a crucial factor in comprehending railgun behaviour. The projectile's rapid movement has a significant impact on the magnetic field. If the dispersion of the magnetic field conclusions regarding the conductors are known suitable methods can be used to sketch the magnetic field distribution. The railgun operates on the premise that a high current flow through the rails and armature will create a strong magnetic field. As a result, before designing magnetic shielding, it is necessary to study the features of the magnetic field distribution. The shape of rail and armature cross section is very essential in rail gun design as it determines the magnetic field distribution over rail and armature. The rail gun geometries with rectangular, convex and concave rail cross-sections are compared and simulated using finite element method (FEM). This method is used to determine the magnetic field distribution over rail and armature by sweeping armature position for different rail cross sections. It is observed that for the different rail/armature shapes like rectangular, convex and concave shapes, the C shaped convex armature possesses strong magnetic fields with minimum current density concentration at the throat and trailing end of the armature. From simulation, it can be shown that the magnetic flux density is a descending function of the central angle. The electromagnetic (EM) rail gun launching mechanism was therefore proven to be compatible with the circular concave armature.

Effects of pulse current waveform on electromagnetic railgun considering the eddy current effects

This paper investigates the effects of pulse current waveform on electromagnetic railgun considering the containment eddy current effects. First, a three-dimensional transient finite element model of the railgun with a metal containment and a pulse current waveform control model with constant feed energy are established. Then, taking the eddy current effect into account, the effects of different waveforms with constant feed energy on the eddy current, the rail current, the armature propulsive force, the rail repulsive force, the eddy current energy consumption, and the muzzle kinetic energy are analyzed. Finally, the simulation shows that reducing the slope of the rising edge of the pulse current can effectively suppress the eddy current and improve the muzzle kinetic energy. When the amplitude and the slope of the rising edge are determined, the excessively long flat top section will lead to more serious eddy current concentration at the ending moment of discharge, more eddy current loss, and less muzzle kinetic energy. Too high or too low amplitude of the pulse current is not conducive to the improvement of the muzzle kinetic energy. The investigation of this paper provides some references for the design of electromagnetic railgun and the selection of pulse current waveform.

A simulation method for the electromagnetic railgun based on equivalent circuit

As a typical electromagnetic launcher, electromagnetic railguns have attracted widespread attention for their broad military application prospects. It is known that skin effects occur during electromagnetic railgun launch. How to quickly and accurately simulate these skin effects is of importance for the application of electromagnetic launch technology. This paper proposes a static two-dimensional finite element model in series with one variable equivalent inductance and three resistances for simulating the dynamic electromagnetic railgun launch. Two skin effects are presented by changing equivalent inductance and resistances. For an electromagnetic railgun including two rails of length of 2 m and width of 0.3 m and square armature of 0.3 m long, after 4.23 ms under a pulse current of a peak of 1 MA, the simulation results based on this proposed static 2D model show that the armature can leave the rails with a velocity and acceleration increasing to 1,464 m/s and 614,876 m/s2, respectively. For an equivalent circuit connected in series, the equivalent inductance, AC resistance, velocity skin effect resistance, and back EMF resistance are 0.49 μH, 2.5 mΩ, 7.1 mΩ, and 4.44 mΩ, respectively, whereas the breech voltage can increase to 1.36 kV. The proposed method simplifies the meshing in the finite element model, saves computational cost, and is conducive to study electromagnetic railgun design and projectile magnetic field shielding. Key words: Electromagnetic railgun, equivalent inductance, equivalent resistance. Tables 1, Figs 7, Refs 10.

Analysis of the Main Factors Affecting the Current Density and Temperature of Electromagnetic Rail

In order to study the influence of different factors on the electromagnetic rail temperature, under the condition of control variables, the variation of current density and temperature in the rail are simulated by COMSOL simulation software under different input current, current waveform, rail geometry, and material. The calculation results show that the peak value of input current has little effect on the distribution of rail current density and temperature, but has a significant effect on the maximum current density and maximum temperature rise on the rail. Shortening the rising time of the input current can quickly increase the armature speed and the rail temperature, but the change of current waveform has little effect on the maximum current density, maximum temperature, and friction heat. Rail conductivity, height, width, armature diameter, and length are negatively correlated with rail maximum current density and maximum temperature. The research conclusion has a certain guiding significance for optimizing the structure design of electromagnetic rail gun and controlling electromagnetic launch conditions.

Design and Performance Analysis of an Electromagnetic Railgun

A railgun is a launcher that accelerates projectiles to super-velocity. In this paper, FEM-BEM coupling simulation method is used to study the electromagnetic characteristics, force and contact state of the railgun and an augmented hyperbolic quadrupole railgun structure is proposed. Compared with the traditional railgun and the non-augmented quadrupole railgun, it is found that the proposed railgun structure has excellent performance in electromagnetic compatibility, thrust on the armature, and the contact state between the armature and the rail. The research of this paper can provide a reference for the structural design of railguns.

A Modeling and Measuring Method for Armature Muzzle Velocity Based on Railgun Current

In this article, the circuit model and the dynamic model of railgun launching process are established by analyzing the Lorentz force, air resistance, and friction force of the armature in the gun bore. Based on the armature dynamic model, a muzzle velocity model of armature can be simulated by utilizing MATLAB, which takes the launching current and loading force of railgun as the main input parameters. Through those two input parameters, the variation curve of armature velocity is measured and calculated by using the armature muzzle velocity model. Moreover, we can read the armature muzzle velocity from the armature variation curve. The influencing factors of the muzzle velocity of armature in this model are also calculated and analyzed, respectively. Comparing with the armature muzzle velocity measured by net target and B-probe, the result shows that the armature muzzle velocity model can accurately estimate the armature muzzle velocity, and can be used to calculate the muzzle velocity in the railgun launching experiment. This method provides reference for the performance optimization design of railgun.

Dynamic response of electromagnetic railgun under time-dependent electromagnetic moving loads

The rail vibration of an electromagnetic railgun can affect the contact status between the armature and rails, even causing rail damage. To reveal the dynamic characteristics of a railgun, we investigated the rail vibration of an electromagnetic railgun under different armature motions. The rail is assumed to be a Euler–Bernoulli based beam, and the time-dependent electromagnetic moving loads applied on the rail are considered. By considering the reaction of the magnetic pressure to the rail deformation, a nonlinear finite element model is proposed to study the dynamic characteristics of the railgun rail. The model validation is presented through a comparison of the model predictions with the analytical solution of the rail deflection, and the experimental result of the rail strain. The differences between the dynamics of rail beam under different moving loads are then compared. Moreover, rail vibration features are discussed in detail. The results indicate that the probable fatigue areas of the rail are located where the pulse current reaches its maximum or where the armature approaches its critical speed. The results of these investigations will help improve the design of railguns.

Comparative study on longitudinal momentum characteristics of L-type and I-type breech in railgun

The position and magnitude of the longitudinal force during launch are very important to the design of electromagnetic railgun. This problem has become a hot topic of research for a long time. Previous experiments showed that most of the recoil force of the electromagnetic railgun locates at the breech. In order to study the stress distribution and momentum characteristics of the breech during launch. Based on Maxwell’s stress tensor, the momentum conservation equations for electromagnetic railgun were derived. Depending on whether the direction of the source current is perpendicular to the current direction in the rails, the breech is simplified and summarized into I-type and L-type structures. Then, the 3-d models of the two breeches were established and the launch process was simulated by finite element method. Some results such as the current density, magnetic field intensity and electromagnetic stress of the current injector plates and coaxial power connector under both models were obtained. The simulation results show that the longitudinal force on the breech is concentrated on the current injector plates. The longitudinal force on the power connector of L-type breech is much bigger than that of the I-type breech, up to nine times. Besides, different structures of the breech will not affect the launch performance of the railgun.

Linear electromagnetic accelerator

Over time, the weapons have been based on mechanical energy (bows, catapults) and chemical energy (guns, missiles), however, at the moment, more and more weapons are designed using electromagnetic energy (railgun, coilgun). The focus of this paper is to obtain the desired muzzle velocities of a projectile according to the existent current. In the first part of the paper, the railgun and coilgun design are presented along with their most important advantages. Based on these observations, a new design of an electromagnetic launch system is presented. Next, Maxwell interactive software package was used that applies the finite element method (FEM) to analyze and solve 3D electromagnetic field problems in order to analyze the variation of acceleration force, speed in time. All simulation data shows that this design has a great potential, because of the adaptability to different applications.

Research on the Dynamic Properties of Electromagnetic Railgun Launch System

Electromagnetic railgun launch system is the part designed for launching projectile. The dynamic properties of the launch system contribute to the firing accuracy. This paper models the finite element model of a square-shaped railgun. The Ansys ACP module is used to design the layer of carbon fibre barrel of the railgun. Modal analysis of the launch system is performed using Ansys. On this basis, the modal superposition method is used to calculate the dynamic response of the launch system caused by the electromagnetic expansion force during launching. This paper analyses the steel encapsulation barrel as a comparison and verifies the rationality of using the composite material. The results provide support for the engineering design of electromagnetic railgun.

Causes of Damage at Electromagnetic Railgun’s Initial Position and Corresponding Improvement Measures

Damage at an electromagnetic railgun’s initial position during launch affects the life of the rail and launcher as well as the launch speed and efficiency. Therefore, this study investigated such damage through electromagnetic railgun experiments. Analyses of metallographic specimens and surface composition as well as 3-D scanning and reconstruction of damaged parts indicate that the damage is a thermal effect mainly caused by transition ablation. Transition ablation problems caused by insufficient initial contact pressure, large rail spacing, and insufficient rail strength are analyzed and corresponding improvement measures are suggested. Finally, the effectiveness of these measures is verified through experiments to guide the design, manufacture, and application of electromagnetic railguns.

The NGL-60 Railgun

At the French-German Research Institute (ISL), several railgun setups are used to investigate different military scenarios. One compelling scenario for a railgun application is the long-range artillery. For this, it is required to be able to handle multimegaampere currents to accelerate heavy launch packages of velocities above 2 km/s and to do so as efficient as possible. The NGL-60 is a 6-m-long open-barrel breech-fed railgun with a square caliber of 60 mm. With this railgun, it will be possible to fully utilize the currently available 10-MJ capacitor-based power supply unit (PSU). To validate the concept of the NGL-60 design, a 2-m-long prototype was installed. Subsequent tests showed that the railgun design is able to handle currents above 2 MA without structural damages or electrical failures. After the successful test series with the prototype, the construction of the full NGL-60 started and is finished by now. In this report, results from the prototype tests are reported, and the first experiments with the 6-m-long NGL-60 are presented.

Research on Segmentation Evaluation Model of Sliding Electrical Contact Performance of Electromagnetic Railgun

The sliding electrical contact performance of the electromagnetic railgun is the main factor affecting the launch accuracy, launch efficiency, and working life of the electromagnetic railgun. The objective evaluation of the sliding electrical contact performance of the electromagnetic railgun is crucial for the research of the electromagnetic railgun theory and engineering design. Because the sliding electrical contact process of the electromagnetic rail gun is complex, the mechanism and performance requirements of the launcher in different phases are different, so it is difficult to evaluate according to the unified standard. In this paper, the whole launch process is divided into three phases: dry friction, liquefaction layer, and high-speed instability. The sliding electrical contact mechanism of these three phases is analyzed separately, and the evaluation model is established, respectively. Then, the theoretical analysis, expert evaluation, and experimental data statistics are used to comprehensively determine the weight system of the three phases. Finally, the comprehensive evaluation model of the three phases is established. The validity of the above-mentioned model is verified by the actual launch test. The evaluation method of this model has practical significance for the scientific research, engineering design, and model development of the electromagnetic rail gun.

Research on proximity effect of electromagnetic railgun

Abstract The rails of electromagnetic railgun can be ablated by the temperature rise due to current concentration. The current distributions on the rails and armature are not only affected by the skin effect, but also influenced by the proximity effect which is rarely mentioned. This paper illustrated the difference between skin effect and proximity effect, and the influencing factors of proximity effect were investigated. Results show that the current is concentrated on the surface around rails due to the skin effect, and the proximity effect exacerbates the current density on the inner surfaces of rails. Decrease in distance from rails enhances the proximity effect, but has nothing to do with the skin effect, which also augments the rail resistance, resulting in temperature rise. It can explain the reason why the ablation is often detected in the small caliber railgun. Research results in this paper can provide support for design and optimization of electromagnetic railgun.

Experimental and Numerical Investigations of Vibrations at a Railgun with Discrete Supports

Within the French-German Research Institute of Saint-Louis (ISL) railgun design, discrete supports in the form of steel bolts uniformly distributed along the length of the railgun counteract the repelling magnetic forces acting on the rails. In the past, numerical simulations on the structural mechanics of these setups have been performed. However, the establishment of the displacement amplitude during an experiment is the final goal. The first task to manage in this respect is the application of a sensor capable of sensing vertical rail displacements. Experimental investigations started at the ISL at a short-circuited railgun employing an optical (noncontact) method. However, this sensor turned out to be nonsuitable for the job due to its lack of a preferred axis. This became clear when comparative measurements with an accelerometer (a single-axis measurement device) were carried out. Consequently, in further experimental investigations, accelerometers were used, and the first experimental results were reported. Finally, the validity of the experimental results was proven by comparing with numerical calculations based on the 1-D and the 3-D models.

Optimization of Launched Parameters of the Railgun with Internal Penalty Function Method

The launched speed of projectile is one of the most important parameters in the design of railgun, in order to explore the influence of the launched speed of projectile by the length of rail and the driving current. Therefore, it is meaningful that gets the optimum speed of projectile. In this paper, main resistances (plasma viscous drag, inertial drag and air drag) was full considered in the motion process of plasma armature, and the optimization model includes the speed of the armature,driving current and the length of rail were build,then it was optimization calculated with internal penalty function method. The optimization result shows that the launched speed of projectile is maximum when the driving current and the length of rail are fixed value. The purpose lies in adjusting the width and the length of the rail and the distance between two rails so as to adjust the launched speed of projectile. The result of research laid a theoretical foundation for designing and manufacture of the railguns.

Effect of Rail Tapering on the Inductance Gradient Versus Armature Position by 3D-FEM

The increasing of projectile final velocity and the uniformity of current density in the special regions of the armature and rail such as the root of the armature which is in melting are some of the purposes of the railgun design. In railgun, the applied force to run an armature is resulted from the interaction of the current passing from the armature with the magnetic field in that place. Therefore, to increase the running force and gain bigger projectile velocities, we have to increase the input current or the magnetic field between two rails per a constant current. The increasing of input current can cause more heat losses in the structure of the railgun and may cause failing of the projectile procedure because of the melting of some points of the armature or rail. High magnetic fields between rails without input stimulation increasing are possible with the application of the geometrical and structural variations in rails. The current paths in rails will be closer to each other (increasing the amount of magnetic fields between them), and so, narrowing the rail using a constant current, the current density will be bigger in the cross section of the rail. We will evaluate the effect of rail narrowing in the projectile path length with consideration of a rail length of 1 m. The narrowing procedure of the rail is defined as decreasing its cross section in the projectile path length until, in the output gate, its amount reaches zero (the height of the rail is constant). The result of simulation shows that the gradient inductance will be increased with the narrowing of the cross section of the rail in the projectile path length, and this will increase the amount of the final projectile velocity.

Design of Low-Current High-Efficiency Augmented Railguns

Properly designed augmented railguns (ARGs) can operate at significantly lower currents and higher efficiency than conventional non-ARGs. This paper analyzes the performance of a two-turn and a three-turn ARG showing the design parameters that are needed to achieve low-current high-efficiency operation. The ARG of this paper has a 40-mm square bore and is 820 mm long. Typical operating currents are from 150 to 300 kA with pulsewidths of approximately 6 to 8 ms. Projectile mass is typically in the range of 130 to 400 g. Projectile velocity is variable from 50 to 250 m/s. Experimental performance is compared with the theoretical predictions of the recently developed electromagnetic launcher (EML) equation. There is a good agreement between measured efficiency and theoretical predictions providing further confirmation of the EML equation. Deviations between measured efficiency and theoretical predictions are attributed to a poor sliding contact. The data also provide further evidence of the recently reported velocity-skin-effect in the contact.

Phenomenological Electromagnetic Modeling of Laminated-Containment Launchers

Electromagnetic launchers typically feature a containment structure around the rails that is fabricated using high-strength stainless steel laminations. Eddy currents induced in these laminations reduce the propulsive force in the launcher, leading to a reduction in incremental inductance-a fundamental railgun design parameter. Thus, designers need a method to simulate the effect of the laminated containment structure on this parameter. Using finite-element (FE) analysis to model individual laminations is likely to be counterproductive; an impossibly large number of elements would be required to model the laminations, and the insulating layers between them, for the entire railgun. Instead of modeling the physical structure of the laminated containment, it is more productive to model the effect it has on magnetic fields around the armature. The basic idea is to replace the laminated containment material with anisotropic material with different properties in the longitudinal and transverse directions. Both electrical conductivity and magnetic permeability of the containment structure will affect the magnetic field around the armature, and both these properties can be represented by an anisotropic model for the bulk. The phenomenological model discussed in this paper is designed to find the magnetic fields and currents at the sliding armature, so that L' can be calculated using readily available commercial FE codes

Design Considerations for Electromagnetic Railguns

Electromagnetic (EM) railguns are similar to powder guns in that both provide an accelerative force to the projectile, while accepting the resulting recoil impulse. They are designed to contain lateral and axial pressure. They must be capable of surviving the thermal environment to which they are exposed. Although there are similarities, there are also striking differences. Both are explored in the present paper with emphasis placed on EM railgun design.