Railgun Research Articles

3-D FEM Analysis on Electromagnetic Characteristics of an Air-Core Pulsed Alternator

In pulsed power supply for electromagnetic launchers, air-core pulsed alternators have obvious advantages to enhance the power and energy densities with a compact and lightweight structure, and it is gradually to be the prime candidate for pulsed power supply. Compared with conventional machines, an air-core pulsed alternator will supply large amounts of energy over millisecond time with a huge current as high as 1 MA and a high voltage reached several kilovolts. Since the short history of the air-core pulsed alternator in China, the related theoretical research is not enough and the fabrication experience is absent. At present, research has shown that the performance of the air-core machine cannot be evaluated by the 2-D method due to the nonexistence of ferromagnetic materials, and it is very necessary to carry out the 3-D analysis by a finite-element method (FEM). This paper will present a 3-D model of the machine according to the accurate geometric size, and the model is used to develop electromagnetic analysis by the FEM and a transient simulation about the no-load EMF is carried out too. In order to understand the mechanism and process of electromechanical energy conversion, it is obviously important to figure out the magnetic field distribution in the machine. Meanwhile, in order to evaluate the strength of the windings, the calculation of electromagnetic forces and torques is developed when the machine drives the electromagnetic rail gun with a current of 1 MA.

Thermal Analysis on Electromagnetic Launcher Under Transient Conditions

Since a tactical electromagnetic railgun system is required to fire several times a minute, the thermal load on the rails leads to a higher temperature, which will even result in launch failures and reduce the life span of the launcher. In this paper, the rail temperature was measured during the launch experiment. Furthermore, based on a 3-D transient model with moving armature, mechanically, thermally coupled electromagnetic field analysis using finite-element method is presented. The Joule heating is one of the main heat sources in the rails. Contact resistance and friction force that cause heat between the armature and the rail are also included in the model. The simulation results show that the peak temperature in the rail occurs at the inner surface. Overall, along the direction of armature motion, the temperature of the rail near the breech end is higher than at the muzzle end, and the maximum temperature on the rail appears near the initial position of the armature. The contact resistance contributes much more than friction to the temperature rise in rails.

Flexible Sliding Contact Between Armature and Rails for the Practical Launcher Model

Hypervelocity sliding contact between armature and rails remains a key technology for electromagnetic railgun performance. A U-shaped aluminum armature and two copper alloy rails are widely adopted for those simple railguns nowadays. The advantages of U-shaped aluminum armature and the defects of the corresponding sliding contact were analyzed systematically for simple railgun performance in this paper. Meanwhile, a practical launcher model with complex structure was proposed in 2012. The complex railgun has an opportunity to provide a flexible sliding contact between armature and rails. The flexible sliding contact concept was proposed, and the advantages of flexible sliding contact were analyzed and summarized, which could weaken or eliminate such sliding contact problems for simple railgun as wear and abrasion, transition, discharge and ablation, gouging, velocity skin effect, and grooving. In other words, the flexible sliding contact between armature and rails for practical launcher has much superiority over the rigid and electromagnetic-controlled sliding contact for simple railgun. After the prototypical launcher and relevant armature were fabricated, the flexible sliding contact test and the primary launch experiment were performed. The actual contact interfaces between each armature unit and the relevant rail were lengthened and moved forward from the ends when the contact force was strengthened. The proper contact interface with a length of about 50–60 mm was located in the middle part when the minimum pushing force by a hydraulic machine was recorded about 5.6 kN. A tentative launching experiment with low power was carried out, in which the peak current got 94.67 kA and the corresponding electromagnetic driving force rose to about 32.36 kN.

Research on Elastic Design About Filament Wound Barrel of Railgun

The weight of an electromagnetic railgun can be minimized and pretightening of rails can be realized by using a carbon fiber to reinforce a railgun barrel. In this paper, an elastic design method for the composite material railgun barrel based on the compound theory is introduced. Simple formulas for stress distribution in the fiber laminate are derived in a cylindrical helical coordinate system. A basic flow of elastic design for fiber reinforced layers is established. Ply thickness is first derived according to the limit pressure of the barrel. Second, the initial stress distribution of the fiber is calculated in accordance with the requirements of rail prestressing. Finally, fiber-winding tension for each layer can be designed, considering that the tension of the inner layer was released to a certain extent by the outer layer with a specific tension system. This paper analyzes some additional factors for the design parameters of fiber wraps. Simulation results show heat and dynamic response must be considered in order to control the caliber deformation within a reasonable range.

Performance Evaluation of Electromagnetic Railgun Exterior Ballistics Based on Cloud Model

Exterior ballistics performance evaluation plays a critical role in the design and development of the electromagnetic railgun system. The ballistics performance evaluation can be regarded as a multicriteria decision-making problem, for the reason that various characteristics, also termed criteria, have effects on the overall performance. A sophisticated simulation model, including six-DOF mechanics, railgun configuration, environment, and aerodynamics models are established to compute the exterior ballistics profile. Then a comprehensive framework based on cloud model and analytic hierarchy process method are proposed to evaluate ballistics performance. Eight criteria including ballistics velocity, energy efficiency, flight time, flight range, overload, attack angle, and sideslip angle stability are selected to determine exterior ballistics performance. The proposed approach yields the certainty degree of each criterion and integrates multicriteria into the whole performance. Two scenarios including 32-MJ launch energy and 200-km strike range are taken to generate alternatives for assessing ballistics performance, which demonstrate the proposed approach is feasible. Results show that in the same launch energy 32 MJ, the performance levels of 12- and 16-kg projectiles are I (excellent) and III (medium), respectively. Besides, gaining the projectile’s mass can improve performance in the same strike range 200 km.

Thinking and Study of Electromagnetic Launch Technology

The use of electromagnetic launch (EML) technology in the future launching mode is an inevitable trend. Based on the analysis of the common characters of EML technology, this paper presents the status of three technological branches such as EM aircraft launch, EM rail gun, EM thrust launch, and discusses some concrete problems and related research achievements in detail. Furthermore, clues and important points proposed in this paper will provide valuable reference for developing EML technology.

Metastability of Pulse Power Loads Using the Hamiltonian Surface Shaping Method

Pulse loads on an electric ship are becoming more prevalent as ship component technologies move to more electric power. However, these pulse loads, such as electromagnetic aircraft launch systems, rail guns, lasers, and radar all can have a destabilizing effect on the ships power distribution network. Typically these types of loads are modeled as constant power and are analyzed for stability with small-signal models and techniques. However, small-signal methods are insufficient for pulse power load stability. This paper will present a brief overview of small-signal methods. Then a large signal metastable analysis method based on a Hamiltonian surface shaping and power flow control methodology based on the average-mode model of dc–dc converters will be presented. The results show that the nonlinear time-variant load pulses create nonlinear limit cycles and dynamics. The stability of the limit cycles can be assessed through a comparison of the power generated versus power dissipated in the system. Simulation, hardware-in-the-loop, and hardware experimental results will be presented.

Analysis of the Velocity and Current Measurement Method Based on B-Dot Probes for the Rail Gun

Measuring the velocity and displacement of the armature and current for a rail gun is important. The common method uses B-dot probes to acquire the discrete time points when the armature passes by them. These points can be interpolated into a curve of the armature’s displacement. Actually, the common interpolation method has some disadvantages. Some probes may break down, and the interpolation method is regardless of the process between the discrete points. So it is difficult to get the armature’s position at any time and the exact velocity at any position. Aiming at these disadvantages, this paper presents an improved method, which based on both B-dot points and the main current waveform. A B-dot probe beside the rails easily gives this waveform. The shape of the current waveform helps us to fit the curve with enough physical information. The new method can give a more precise velocity of the armature at an arbitrary position between two B-dot probes’ positions. It is also practical outside of two B-dot probes’ positions too. And it still works when some B-dot probes fail. Moreover, the current waveform with the adjusted amplitude is also calculated out. The launching experimental results and currents measured by Rogowski coils show that the improved method is highly suited for the velocity and current measurement for a rail-gun system.

Energy Transfer Efficiency Optimization in an Electromagnetic Railgun

Electromagnetic railguns (EMRs) launch projectiles by the systematic triggering of current pulse forming units (PFUs), which release stored capacitor energy. Past work has focused on maximizing projectile velocity at the muzzle for given PFU capacitor charge voltages, which maximizes efficiency. However, operators in naval applications need to be able to select the muzzle velocity for a projectile to achieve a desired ballistic path. Thus, there is a demand to maximize efficiency for a given muzzle velocity. As such, this paper investigates maximizing the efficiency of transferring the stored PFU capacitor electrical energy to projectile kinetic energy while minimizing the current value when the projectile exits the rails to reduce damage to them from arcing. This is accomplished by optimizing the choice of the initial capacitor voltage in each PFU and the trigger timing subject to an electrical-mechanical dynamic model of the EMR and projectile and any additional scenario constraints (described shortly). This optimization is solved using numerical programming in the context of a relaxation with the initial capacitor voltages and triggering times as the only explicit variables to the optimizer; additional needed values are obtained from a differential algebraic equation solver. The optimization is successfully demonstrated for three scenarios: operation for a projectile mass and muzzle velocity associated with published operating parameters, operation for several projectile mass-muzzle velocity pairs with both equal and distinct initial capacitor voltages, and operation for several projectile mass-muzzle velocity pairs with a load current bound and equal initial capacitor voltages. Results show improved efficiency in comparison to the use of the published parameters, the independence of efficiency from projectile mass when there is no current bound, virtually identical results for equal and distinct initial capacitor voltages, and decreased efficiency with a current bound.

Electromechanical coupled nonlinear dynamics of euler beam rails for electromagnetic railgun

The electromagnetic field can cause an essential change of the dynamic behavior of the railgun. The evaluation of the dynamics performance of railgun is a mandatory task. Here, a nonlinear electromagnetic force equation of the railgun is given in which the clearance, the thickness and the width of the rail are considered. Based on it, the nonlinear electromechanical coupled dynamics equations of Euler beam rails for the railgun are proposed. Using the equations, the nonlinear free vibration frequency of the railgun is investigated and the effects of the system parameters on the frequency are analyzed. The nonlinear forced responses of the rail to the electromagnetic excitation are investigated as well. The results show that as the nonlinearity of the railgun system is considered, the vibration frequencies of the railgun system increase; as the current in the rail increases, the difference between the natural frequencies and the nonlinear vibration frequencies increases significantly; the nonlinearity of the railgun system is more obvious for smaller distance between the two rails, smaller rail thickness, and smaller stiffness of the elastic foundation; the unstable dynamics state of the rail system occurs when the armature runs to the exit of the railgun. The results are useful for design and application of the railgun system.

Design and experimental analysis of magnetic shielding of electronic-magnetic rail gun ammunition fuse

Design and experimental analysis of magnetic shielding of electronic-magnetic rail gun ammunition fuse

Study on interaction characteristics between multi gas jets and water during the underwater launching process

To further understand the mechanism of new submerged water piercing gun launcher, the simulation device of an imitated projectile is designed with using multi combustion gas jets to drain off the water in gun tube. The expansion characteristic of multi gas jets and generation mechanism of the gas-curtain in the liquid medium are experimental observed by a high speed camera. The experiment shows that, with the mixing process between the multi combustion gas jets and the liquid medium, the gas-curtain is generated, which provides a gas path for the projectile motion. On the base of experimental observation result, the influences of injection pressure and sprayer structure on projectile motion are discussed. Experiment result indicates: increasing injection pressure, both axial expansion velocities of gas-curtain and projectile moving speed increase; magnifying the center nozzle cannot enhance the drainage performance of the gas-curtain and will restrain projectile motion in the later stage; with enlarging the oblique plane nozzles, the axial velocity of gas-curtain tend to rise after converging and projectile kinematic performance is also improved.

Investigation the Effect of B Dot Probe Positions in 500kJ Pulsed Power Supply System using MATLAB Simulation

In a rail gun a small sensing coil named B dot probe is kept over the path of armature which generates the signal from an induced voltage based on faraday's law. The output signal which is generated from the B dot probes consist of a positive and negative elements. The zero-crossing point in the output signal is hypothetical to be the time of passage for the centroid of the armature current, and the zero-crossing times from different probes kept along the length of the rails are on the whole employed to find out the velocity of the projectile. Pulsed power supply system has got a significant role in rail gun system as it gives an enormous electrical energy in a short duration of time to accelerate the movable armature with higher velocity. Pulsed power supply system which is generally capacitor based are the most well-known form of pulsed power supplies system used in rail gun investigation for the past several years. In India for surface fire support, 500-kJ capacitor module pulsed power system design which is capable to accelerate the projectile with a velocity of 1km/s to 1.5km/s, is currently under investigation. In this paper an effort is made to design a 500kJ PPS using MATLAB in order to predetermine the gun parameters such as acceleration of the projectile, muzzle velocity, peak current, current at exit, and also effective barrel length. In general the capacitors are grouped into modules and they are triggered at different time to get desired parameters of rail gun. In this work the capacitors are grouped in five modules and modules are triggered by using projectile positions and projectile position is being identified by using B dot probes positions.

A new advanced railgun system for debris impact study

Abstract: The growing quantity of debris in Earth orbit poses a danger to users of the orbital environment, such as spacecraft. It also increases the risk that humans or manmade structures could be impacted when objects reenter Earth's atmosphere. During the design of a spacecraft, a requirement may be specified for the surviv-ability of the spacecraft against Meteoroid / Orbital Debris (M/OD) impacts throughout the mission; further-more, the structure of a spacecraft is designed to insure its integrity during the launch and, if it is reusable, during descent, re-entry and landing. In addition, the structure has to provide required stiffness in order to allow for exact positioning of experiments and antennas, and it has to protect the payload against the space environment. In order to decrease the probability of spacecraft failure caused by M/OD, space maneuver is needed to avoid M/OD if the M/OD has dimensions larger than 10cm, but for M/OD with dimensions less than 1cm M/OD shields are needed for spacecrafts. It is therefore necessary to determine the impact-related failure mechanisms and associated ballistic limit equations (BLEs) for typical spacecraft components and subsys-tems. The methods that are used to obtain the ballistic limit equations are numerical simulations and la-borato-ry experiments. In order to perform an high energy ballistic characterization of layered structures, a new ad-vanced electromagnetic accelerator, called railgun, has been assembled and tuned. A railgun is an electrically powered electromagnetic projectile launcher. Such device is made up of a pair of parallel conducting rails, which a sliding metallic armature is accelerated along by the electromagnetic effect (Lorentz force) of a cur-rent that flows down one rail, into the armature and then back along the other rail, thanks to a high power pulse given by a bank of capacitors. A tunable power supplier is used to set the capacitors charging voltage at the desired level: in this way the Rail Gun energy can be tuned as a function of the desired bullet velocity. This facility is able to analyze both low and high velocity impacts. A numerical simulation is also performed by using the Ansys Autodyn code in order to analyze the damage. The experimental results and numerical simulations show that the railgun-device is a good candidate to perform impact testing of materials in the space debris energy range.

Laboratory modelling of an active space experiment using railgun as a launch device

Laboratory modelling of active space experiments is described. To accelerate an impactor, a specially developed electromagnetic railgun capable of accelerating 10-mg cubic impactors to velocities of up to 5.5km/s was used. As targets, different materials, such as ice and moon-like regolith, were employed. To simulate a collision with a comet, a hypervelocity impact on water ice targets with different densities was performed. To simulate an impact on the Moon's surface, a special method for preparation of regolith targets with the compositions corresponding to the Moon's surface materials was developed. The impact experiments with regoliths of different densities were carried out.

Magnetic and conductive shielding for air‐core pulsed alternators in railgun systems

Magnetic and conductive shielding are the alternative choices for air‐core pulsed alternators (air‐core CPAs) in electromagnetic railgun systems. Because of the absence of ferromagnetic materials in the air‐core alternators, the flux density inside can be 3–5 T. Electromagnetic shielding is needed to protect the surrounding electronic devices and humans from exposure to high oscillating magnetic fields. Electromagnetic shielding changes the distribution of the magnetic field and the corresponding winding inductance, as well as the output performance of the powering the railgun. This paper mainly concentrates on a GW‐scale, four‐phase air‐core CPA‐based railgun system. The magnetic and conductive shielding are adopted correspondingly. The effectiveness of shielding and electric performance are investigated in detail. Using the co‐simulation method, an instructive comparison is made between the magnetic shield and the conductive shield, which is meaningful to the design of the electromagnetic shielding of air‐core CPAs for railgun systems. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Coupled Oscillation of an Electric System for Electromagnetic Railgun

AbstractThe railgun system is an electromechanical coupled system. In this paper, electromechanical coupled dynamics equations of the electrical system in the railgun are proposed. The free oscillation of the electrical system in the railgun is investigated, changes in the natural frequency and the damping coefficients of the electrical system, along with the time and related parameters, are analyzed, the forced responses of the current to the voltage fluctuation are discussed, and the dynamic electromagnetic forces in the railgun are determined. The results show that a small voltage fluctuation of the electrical system in the railgun can cause a large dynamic magnetic force on the rails under some conditions.

Numerical modeling of electromagnetic railgun rail temperature field

Electromagnetic railgun temperature field characteristics are important basis for rail design and thermal management. This paper carries out numerical modeling of electromagnetic railgun rail temperature field and studies the temperature field characteristics during and after launch of armature. Fi rstly, the thermodynamics environment of rails during and after armature launch is analyzed; Then, on the basis of rail conducting contact heat model and rail 3D finite element model we have built, the rail temperature field is simulated by finite element software ANSYS. The temperature field of rail at each moment is obtained. The research results show that: The maximal temperature rise of rail is near the armature initial position; the rail temperature rise gradually decreases from the armature initial position to the muzzle; under the condition of parameters setting in this paper, the temperature rise of each shot near the armature initial position is approximately 8.945°C.

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.

Performance Analysis and Parameter Optimization of CPPS-Based Electromagnetic Railgun System

A fast solving method for the launching process of the electromagnetic railgun and an automatic assignment method for the trigger strategy of the capacitive pulsed power supply (CPPS) are proposed. The accuracy of the solving method and the feasibility of the assignment method are verified through an illustrative example with a 1.8-MJ initially stored energy. On the basis of these methods, parameter optimization in design phase and performance analysis in operation phase are conducted around the projectile muzzle kinetic energy $E_{k}$ and the system energy transfer efficiency $\eta $ . To be specific, the single-objective optimal solutions of $E_{k}$ and $\eta $ and the biobjective Pareto front of $E_{k}$ – $\eta $ are acquired by evolutionary computation. And the influence relations of certain system parameters on $E_{k}$ and $\eta $ are acquired by parameter sweep. The research methods and results in this paper have both theoretical and pragmatic values in improving the performance of the CPPS-based electromagnetic railgun system.