Railgun Research Articles

A Multiphase Rail Launcher With Circular Geometry and Modular Design: Development, Construction, and First Experiments

Electromagnetic railguns allow to accelerate payloads to extremely high muzzle speeds ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 2 km/s). Conventionally, the launcher design is based on two rails. The power supply consists of a capacitor bank and a pulse-forming network allowing unipolar operation. In this work, a different system setup is presented. The idea is to use multiphase alternating current instead of direct current to drive a rail launcher. The basic idea had been brought up in the past in connection with the use of compulsators as power supply. Here, it is suggested to connect the launcher to a (noncompensated) multiphase generator. An interesting but not obvious feature of such an approach is that a stationary acceleration force profile can be realized. However, the launcher becomes more complex as more than two rails are required and an appropriate power supply has to be developed. When considering this approach, an important finding is that if one aims at high speeds, several stages are required. It means that a modular or segmented setup is required. As the passage of the armature between the segments is expected to be a critical point, the idea came up to build a three-phase circular geometry, meaning that the armature leaves at the “muzzle” and re-enters at the “breech” of the launcher. This also allows using an electric motor for a preacceleration in order to minimize sliding contact problems during start. As power supply served a redesigned 100-kW high-current transformer, which can be connected directly to the local power grid. Experimental data including electrical parameters (e.g., an armature current of 20 kA) are presented and discussed. For the first time, it can be experimentally shown that stationary acceleration profiles can be realized, in principle.

Numerical Analysis of Aerodynamic Thermal Properties of Hypersonic Blunt-Nosed Body with Angles of Fire

A hypersonic electromagnetic railgun projectile undergoes severe aero-heating with an increase in altitude. The purpose of this study was to investigate the characteristics of the shock layer flow field as well as the thermal environment of the blunt body wall of a hypersonic electromagnetic railgun projectile at different launching angles. The two-temperature model considers the thermal nonequilibrium effect and is introduced into the Navier–Stokes (N-S) equation, and it is solved using the finite volume method (FVM). The reliability of the calculation model in terms of thermal properties and composition production was verified against a blunted-cone-cylinder–flare (HB-2) test case. The surface temperature of the hypersonic blunt projectile was simulated using a radiation balance wall boundary. The thermal characteristics at the emission angles α = 60° and α = 45° were checked within an altitude range of 0–70 km, including the nonequilibrium effect, reaction heat release, aerodynamic heat flux, and wall temperature. The results show that the translational rotational temperature is higher than the vibrational electronic temperature, and the thermal nonequilibrium effect increases with an increase in altitude. Comparing the two launching angles, the nonequilibrium degree and reaction heat release at α = 60° were higher than those at α = 45°. The rates of exothermic reaction decreased with an increase in altitude. The heat flux along the wall of the generatrix decreased sharply from the stagnation point. With an increase in altitude, the heat flux dropped sharply from 7 MW/m2 at H = 0 km to approximately 2 MW/m2 at H = 70 km. The wall temperature distribution was similar to the heat flux distribution; however, the surface temperature decreased less rapidly than the heat flux.

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.

Численный анализ взрывного формирования алюминиевых частиц в диапазоне скоростей 2…16 км/c

Explosive gun launchers are used to test rocket and space systems for their resistance to the impact of meteoroids and fragments of space debris. This work applies numerical simulation within the framework of the two-dimensional axisymmetric problem of continuum mechanics and substantiates design parameters of the shaped charges that form compact aluminum particles weighing up to 1 g and more in a wide range of speeds (from 2 km/s to 16 km/s). Simulation was carried out in relation to the shaped charges of different diameters (from 20 mm to 100 mm) using the ANSYS/AUTODYN, ERUDIT and KOLDUN computer systems. It is shown that charges of larger diameter are required to form faster particles identical in mass. Besides, it is necessary to use segmental cumulative liners of digressive thickness to form particles approaching the lower boundary of the indicated speed range. Wherein, to form faster particles moving at the speeds from 10 km/s to 16 km/s, it is necessary to implement the combined shaped charge liners, where the jet-forming part is shaped as a semi-ellipsoid or a semi-superellipsoid of rotation of the digressive thickness.

Physical model for experimental study of an electromechanical vibration transducer with a spiral closed secondary element

For the first time, a physical model in the form of an electromagnetic gun for the study of electromechanical vibration transducers with a spiral secondary element is proposed. The use of a physical model makes it possible to develop a research stand for determining the mechanical characteristics of an electromechanical vibration transducer (EMVT) with a spiral secondary element based on strain gauges and to obtain the necessary experimental data for further scientific work. Keywords electromagnetic gun, short-circuited coil, vibration transducer, strain gauges, mathematical model

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.

Modular electromagnetic railgun accelerator for high velocity impact studies.

A modular electromagnetic railgun accelerator facility named "RAFTAR" (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000m/s for an 8g solid aluminum-7075 armature projectile. The current fed was 220kA, having a muzzle time of about 1.75ms. It is a single pulse breech-fed rectangular bore (14 × 13mm2) railgun, and its 1.15m long barrel assembly consists of two parallel copper bars with an inter-gap of 13mm that are encased within 50mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.

Effect of active cooling on the thermal effect of electromagnetic rail under single launch mode

In order to investigate the influence of active cooling on the rail thermal effect of electromagnetic gun under single launch mode, characteristics of the peak temperature, cross-section current density and temperature distribution, axial temperature distribution of rail with and without active cooling are simulated. In addition, the time-varying characteristics of the rail axial temperature distribution, the temperature time-varying characteristic in different temperature parts on the rail and the influence of the cooling water flow velocity on the temperature in different temperature parts are experimentally studied. The results show that during the launch, there is almost no difference between the rail peak temperature and its location with and without active cooling, and the peak temperature is basically located at the initial position of the armature. Without active cooling, the rail axial temperature distribution shows a trend of higher at the gun tail and lower at the gun muzzle. The current density and temperature distribution of rail cross-section show a trend of higher on the rail inner side and lower on the rail outer side, and the diffusion of heat lags behind the diffusion of current. Under the action of active cooling, the rail peak temperature will move to the muzzle along the armature moving direction, and there is a “thermal inversion” phenomenon. The rail cross-section temperature drops faster, and the lowest temperature region appears near the middle cooling channel. Active cooling has different effects on rail temperature in different temperature parts. In the high-temperature part, the rail temperature decreases monotonically with the increase of cooling water flow velocity, increasing the water velocity can accelerate the decline of rail temperature. In the middle-temperature parts, the variation trend of rail temperature is different with different water flow velocities. At low water velocity, the rail temperature increases gradually. When the water flow velocity is greater than 0.75 m/s, the phenomenon of “thermal inversion” will occur. i.e., the rail temperature increases first and then decreases. In the low-temperature part, “thermal inversion” will occur at different flow velocities, that is, the rail temperature increases first and then decreases. When the water flow velocity is greater than 1.0 m/s, the improvement of rail cooling effect will no longer be obvious. It is suggested that the appropriate water flow velocity is 0.75–1.0 m/s under the present experimental conditions.

Research on Transient Contact Characteristics of the Hyperbolic Rail Augmented Quadrupole Launcher

The contact surface between the armature and rails of a railgun system is unique for its high-speed sliding and current conduction, which greatly affects the performance of the launcher. In order to study the armature–rail contact characteristics of the electromagnetic railgun, this article simulates the initial contact characteristics, the conducting contact characteristics, the electromagnetic characteristics, and the temperature closely coupled to the contact characteristics based on a hyperbolic rail augmented launcher model. The influencing factors of the contact characteristics are analyzed and compared with the nonaugmented railgun with the same structural configuration, and the evaluation indices of the contact characteristics are established. The research results show that the contact characteristics of the railgun are affected by the electromagnetic force, which changes rapidly with time, which in turn affects the electromagnetic and temperature characteristics of the railgun. This launcher structure can maintain good contact conditions during launching. This study is a preliminary exploration of the contact characteristics of the hyperbolic rail augmented quadrupole launcher, making an improvement to its structural design.

Research on Ultra-high-speed Armature Nondestructive Recovery Technology of Electromagnetic Railgun

Aiming at the nondestructive recovery of ultra-high-speed armature of electromagnetic railgun, a mathematical model of fluid medium for recovery is established based on fluid damping theory. At the same time, the fluid-solid coupling finite element model is constructed, and then the numerical calculation is carried out. Furthermore, the recovery characteristics of different armature speed under different density medium are analyzed, and then the relationship between the armature initial velocity and the maximum density of medium is given. Additionally, the overload limit of aluminum armature is obtained. Finally, the overall scheme of variable density segments is proposed. The experimental system is built and verification experiments are carried out. The research results show that by using piecewise recovery method, low-density medium is selected for the front part and high-density medium is selected for the rear part, the problem of too long distance or too much overload when a single medium for recovery can be solved. Meanwhile, the nondestructive recovery of armature can be realized, and the appearance of armature can be maintained.

Armature dynamics - an aspect of rail gouging mechanisms in electromagnetic railgun

The purpose of this study is to explore the causes leading to the rail gouging from the perspective of armature dynamics. The axial, lateral motion and rotation equations were derived, and a set of calculations according to the experimental conditions were conducted. The calculated in-bore processes of the armature exhibit apparent non-linear features. Especially with the contact interface of armature being worn rapidly, the armature gradually leans toward one side of the bore, and forms a trend of oblique impact to the rail that may lead to the gouging. This study offered an insight on the transient processes of armature in bore, and helped to better understand the gouging failure mechanism.

О возможности использования кумулятивных зарядов с комбинированными облицовками для получения алюминиевых частиц со скоростями на уровне 16 км/с

Explosive gun launchers are used to test rocket and space technology systems for persistence to the effects of meteoroids and fragments of space debris. Based on numerical simulation in the framework of a two-dimensional axisymmetric problem of continuum mechanics, possibilities of obtaining aluminum particles with speeds of up to 16 km/s were considered using shaped charges with a combined shaped charge liners. A high-speed particle is formed as a result of the “cut-off” by the collapsing cylindrical part of the head section combined liner of the jet flow appearing during the collapse of the liner jet-forming part. Simulation was carried out in regard to a shaped charge with the 100 mm diameter using the ANSYS/AUTODYN and ERUDIT computer systems. To achieve the objective set, the liner jet-forming part was of digressive thickness, and its limiting surfaces had the shape of semi-ellipsoid surfaces or revolution semi super ellipsoid. Based on the calculation results, combined liner geometric parameters were selected making it possible to form an aluminum particle with a speed at the 16 km/s level and its mass of tenths of a gram.

Data Processing Approaches to Measure Velocity of Electromagnetic Gun on Laser Screen in Complex Environment.

The exit velocity of the armature is an important indicator in measuring the launching performance of the electromagnetic gun. The non-contact photoelectric detection technology with the use of a laser screen was applied to the measurement of the armature velocity of the electromagnetic gun. By means of taking the signals that pass through the laser screen obtained by the velocity measurement system as the research object, we solved problems such as the harsh test environment of the launch armature velocity of the electromagnetic gun, the interferences on the armature signal passing through the laser screen unavoidably caused by various factors such as vibration, electromagnetic interference, shock wave, flare, smoke and fragments, and even the non-recognition of the signal passing through the laser screen in severe cases. A data-processing algorithm that combines the Ensemble Empirical Mode Decomposition (EEMD) with Correlation Algorithm (CA) was proposed, with the aim of processing the signals passing through the laser screen, while using the maximum slope point as the time passing through the laser screen so as to calculate the velocity of the armature passing the laser screen. This method can effectively reduce the influence of interference on the test results, and the test results from two sets of velocity measuring systems show that the velocity obtained by the proposed approach is highly consistent.

The Influence of projectile shielding on the internal magnetic field during an electromagnetic launch

Compared with a conventional propulsion system, an electromagnetic railgun is characterized by an in-bore pulsed high magnetic field. However, the dynamic distribution of the magnetic field in the projectile has rarely been experimentally studied. To this end, this paper discusses the possibility of utilizing magnetic field environment information. An equivalent model of an electromagnetic railgun is established by using the finite element method. Based on the magnetic diffusion equation and the Biot-Savart law, the in-bore magnetic induction is determined. The velocity skin effect and projectile shielding are considered in the model. Furthermore, the magnetic measurement method is presented to validate a simulation result. The results obtained from the simulation and experiment show that package shielding affects the pulse width and amplitude of the internal value. The peak magnetic induction of low carbon steel and copper is reduced by 33.6 %, and the pulse width lags by 2.7 ms. Moreover, projectile shielding has a substantial influence on the timing accuracy during launch, and the time error reaches approximately 18 %. Therefore, the in-bore magnetic field is a practical signal for the control module since it considers the influence of different projectile shields.

Development of a low voltage railgun in the context of a swept lightning stroke on an aircraft.

When aircraft are struck by lightning, the aircraft's structural fuselage and components are stressed by electrical and thermo-mechanical constraints, which imposes a need for reliable experimental test benches to design accurate and enhanced lightning protection. In order to reproduce the in-flight conditions of an aircraft in a laboratory, the aim of this work is to design and implement launch equipment able to propel aeronautical test samples at speeds characteristic of an aircraft- from 10m/s for ultra-light gliders to 100m/s for airliners-before striking it with an electric arc within the laboratory dimensions of several meters. After a comparison of several propulsion techniques, the selected solution is an augmented electromagnetic railgun launcher. Since it requires the injection of a high current to be efficient and a low voltage operative point for safety considerations, specific and original electric generator and rail structures have been designed and experimentally implemented. Particular attention has been paid to the experimental problems encountered and mainly the sliding contact, since almost no literature references are available for railgun equipment at this level of performance. Then, based on different experimental implementations, a dynamic and ballistic model of the projectile has been developed to evaluate and characterize friction forces with the aim of predicting launcher performances with different inputs. This serves to control the speed of the material test sample during the lightning strike. Finally, the railgun equipment has been coupled to a lightning generator to reproduce the lightning strike of an aircraft respecting in-flight conditions.

A Novel Technique for Dynamic Analysis of an Electromagnetic Rail Launcher using FEM Coupled with Simplorer

The performance of a rail gun depends on the current density distribution over the rail and armature as it determines the force that accelerates the projectile of the rail gun. A finite element method (FEM) coupled with Simplorer was developed to model and study the performance of the rail gun. The rail gun was modeled using an ANSYS eddy current field solver to determine the current density distribution and equivalent rail gun circuit for the given rail gun geometry. The armature velocity was then calculated using Simplorer by coupling the obtained equivalent rail gun circuit and exciting the rails using a capacitor-based pulsed power supply (PPS) system. The FEM coupled with Simplorer method was verified by numerical calculations for the rectangular rails and also with other researchers’ value, and that showed a good agreement between the results. Further, the current density distribution over rails and armature and velocity of the armature was calculated for different rail cross sections such as circular concave, circular convex, rectangular concave, rectangular convex, T-shaped concave, and T-shaped convex with a C-shaped armature. It was observed that the circular convex rail gun with C-shaped armature showed minimum current density distribution and gives a higher value of armature velocity compared with other rail gun structures. Thus, the circular convex armature was found to be suitable for the electromagnetic (EM) rail gun launchingsystem.

Investigation on the Spatial-Temporal Distribution of Electromagnetic Gun Rail Temperature in Single and Continuous Launch Modes

In order to study the spatial-temporal distribution characteristics of electromagnetic rail gun temperature, based on moving grid processing method and mod function method, a 3-D geometric model of electromagnetic rail gun under single launch mode, a 2-D geometric model of electromagnetic rail gun under continuous-fire mode, and the corresponding transient electromagnetic field-temperature field coupling model are established by using the finite element analysis software COMSOL Multiphysics, and the temperature spatial-temporal distribution characteristics in the rail-armature contact area, cross section of rail, and along the rail axis is simulated under single launch and continuous launch. The results show that, under the conditions of single launch and natural cooling, the high temperature area in the rail-armature contact surface is located at the rear of the armature due to the skin effect. The temperature distribution along the axial inner side of rail tends to be higher near the tail and lower near the muzzle, it increases with time, but the peak temperature does not exceed the melting point of copper. Under the continuous launch and natural cooling, after five launches, the peak temperature of the rail increases to 709 °C, which is close to the melting point of copper. Continued launching will cause rapid accumulation of heat in the rail and a rapid increase of peak temperature, resulting in shortened life of the launcher and even launch failure. Therefore, without active cooling measures, the electromagnetic rail gun cannot be used in actual combat. The results of the study are an important guide for the design and thermal management of the cooling system of electromagnetic rail gun.

Technical Paper on Electromagnetic Railgun

The paper has the information about the model and working of electromagnetic rail gun. The basic idea of study is Lorentz Principle and applications of this principle. The model can be translated as the simple model of a loop which is made from a current carrying wire and studying the loop properties in an external magnetic field. Although applying this idea on a practical system has its own difficulties and necessities. These necessities and difficulties are discussed in this paper. The concept of launching the projectile using the electromagnetic field under the influence of external magnetic conditions is a new concept. this type of concept is a future development concept but however It has been demonstrated how this concept is effective.

Calculation Method of Projectile Movement Characteristics for Complex Structure Railgun

Electromagnetic railgun is a launcher that relies on electrical energy to do work to propel a projectile to high speed. In the military application of railgun, the acquisition and adjustment of projectile movement characteristics, including acceleration and velocity, are very important. In order to realize the rapid calculation of the projectile movement characteristics and the precise adjustment of the thrust, the force and projectile movement characteristics for a complex structure railgun, augmented quadrupole hyperbolic railgun, were studied by the method of field-circuit coupling. Based on Biot-savart Law and accurate fitting of current distribution, the electromagnetic characteristics and force characteristics of the launcher are analyzed, and the iterative method is used to realize the coupling between the pulse forming network and the calculation of the force on launcher and finally solve the movement of the launcher projectile characteristic. Comparing the calculation and experiment, the error of speed calculating with this method is small in the low speed stage.

A damage detection system for inner bore of electromagnetic railgun launcher based on deep learning and computer vision

The inner bore damage affects the launch performance and service life of electromagnetic railgun launcher. Detection and observation of railgun inner bore damage contribute to the study on mechanism and development rules of railgun damage. This paper analyzes five types of typical railgun inner bore damage. Based on the detection requirement for the damages, this paper proposes an automated damage detection system for the inner bore of electromagnetic railgun launcher consisting of data acquisition device and detection algorithms. The proposed device can step inside the inner bore of the railgun launcher to take photos of the inner bore surface automatically. We use the images obtained by the proposed device to build a data set for the training and verification of the detection algorithms. The object detection algorithm You Only Look Once v5 (YOLOv5) is utilized to achieve the rapid detection of railgun inner bore damages. We introduce the adaptive data augmentation and the focal loss to balance out the uneven category distribution of our data set. The result proves that our YOLOv5 model reaches the state-of-the-art level in the railgun inner bore damage detection task, with its mean Average Precision (mAP) of 0.659 and detection speed of 47.6 frames per second (fps). We choose Segmenting Objects by Locations v2 (SOLOv2) to extract the shape of the damage, with the Average Precision of 0.631. We further achieve damage statistics and the model visualization of damage distribution. The experimental results show that the proposed detection system meets the requirements of rapid detection and accurate feature extraction. It provides researchers with an approach for the study of railgun inner bore damage mechanism.