Railgun System Research Articles

Electromechanical Coupled Parametric Vibrations for Electromagnetic Railgun

In the rail gun system, the current fluctuation occurs which causes the changes of the electromagnetic stiffness and forms disturbance to the dynamics system. It may lead to disturbances of the projectile trajectory. This is an electromechanical-coupled parametric vibration problem and should be investigated. Rails in electromagnetic railgun are assumed to be elastic foundation beams. The current flowing through the rail causes an electromagnetic repulsive force between the two rails. The fluctuation of rail current causes mechanical vibration and stiffness change of the rails. The wave current is assumed to vary in the cosine function. Considering the current fluctuation in the railgun system, an electromechanical-coupled parametric vibration equation is proposed. Using Poincare method, the coupled parameter vibration equation is resolved. As the dynamic current amplitude, the static current, and distance of the armature to the entrance of the gun increase, the unstable region of the railgun system vibrations increases. As the distance between the two rails, the rail thickness and the rail width, and the stiffness of the elastic foundation increases, the unstable region of the railgun system vibrations decreases. In this paper, the unstable regions of the railgun system are determined and their changes as the function of the system parameters are analyzed. Results can be used to increase the stability of electromagnetic railgun.

Real-Time System-on-Chip Emulation of Electrothermal Models for Power Electronic Devices via Hammerstein Configuration

Real-time emulation of device-level power electronics plays an essential role in many industrial applications for design and hardware-in-the-loop testing of system components and controllers. Due to the complexity and heavy computational burden of the real-time hardware implementation of the analytical and the numerical models, this paper proposes dynamic electrothermal behavioral models for diode, thyristor, and insulated-gate bipolar transistor based on the Hammerstein configuration. The power electronic device model parameters are extracted from the known device datasheets and implemented in Zynq System-on-Chip platform with accelerated processing for real-time application. An electromagnetic rail gun system has been employed as the study case to compare the performance of the proposed electrothermal behavioral models with that of off-line simulation models on SaberRD software.

Modeling and Simulation of Railgun System Driven by Multiple HTSPPT Modules

In the rail-type electromagnetic launching system, the equivalent load of pulsed-power supplies (PSs) varies with the launching process, while it has a certain influence on the discharge of pulsed PS. However, in the analysis and design of pulsed PS, researchers usually use the fixed resistance and inductance to simulate the load, which is impossible to accurately study the characteristics of the pulsed PS. The electromagnetic launching needs high-amplitude current pulse. Therefore, in this paper, a mathematical model of electromagnetic launching system driven by multiple superconducting inductive pulsed PS modules is established. In this model, the fixed resistance and inductance load are replaced by the dynamic load model of the railgun; the effects of dynamic load and fixed load on the discharge characteristics are analyzed; the parallel discharge characteristics of multiple high-temperature superconducting pulsed-power transformer (HTSPPT) modules are studied; and the characteristics of the simple rail-type electromagnetic launching driven by multiple HTSPPT modules are analyzed. The simulation results show that a high amplitude of current pulse can be produced using synchronous parallel discharge of multiple HTSPPT modules. The simulation results show that when the resistance and inductance of load are fixed at 2 $\text{m}\Omega$ and 0.5 $\mu \text{H}$ , respectively, the current amplification factor is 15.666, and the maximum voltage of the auxiliary capacitor is 1079 V. In the dynamic load model, the current amplification factor is 17.174, and the error is 9.6%. The maximum voltage of the auxiliary capacitor is 983 V, and the error is 8.9%. Therefore, the discharge characteristics of pulsed PS can be more accurately studied using dynamic models.

Some Key Parameters of Different Caliber Solid-Armature Railgun Related to Linear Current Density

By introducing current carrier margin coefficient named $\alpha $ , ratio of armature thickness to armature width named $\beta $ , and ratio of armature height to armature width named $\gamma $ , equations of some key parameters of rectangular caliber railgun system, which is related to linear current density, are proposed. Then, some key parameters for different caliber railgun system are studied. Based on the analysis of electromagnetic contact pressure between armature and rail, $+ di/dt$ skin effect, velocity skin effect, and melt wear of armature, it can be obtained that current density of rail/armature interface is directly proportional to the linear current density. Thus, in order to decrease rail/armature interface current density, it is necessary to reduce linear current density. It can also be obtained that current density of rail/armature interface in current ramp-up is inversely proportional to the root of current rise time. Thus, it is necessary to increase current rise time to decrease rail/armature interface current density. Average melt wear rate of armature is directly proportional to the square of linear current density.

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.

Some Key Parameters of Monolithic C-Type Armature in Rectangular Caliber Railgun

Monolithic C-type armature is one of the most important armatures in electromagnetic railgun. Some key parameters of monolithic C-type armature in rectangular caliber railgun system—width of armature X, height of armature Y, thickness of armature’s throat $d_{0}$ , length of armature’s tail $d_{1}$ , thickness of trailing edge of armature’s tail $d_{2}$ , and angle of armature’s tail $\theta $ —are studied in this paper. By introducing current carrier margin coefficient named $\alpha $ , ratio of armature thickness to armature width named $\beta $ , ratio of armature height to armature width named $\gamma $ , and ratio of length of armature’s tail to armature height named $\kappa $ , equations of some key parameters of monolithic C-type armature in rectangular caliber railgun system are proposed. Based on analysis of mass of armature, electromagnetic contact force between armature and rail, mechanical strength of armature’s tail, and inductance gradient, relationship of some key parameters of monolithic C-type armature in rectangular caliber railgun system are proposed. Conclusion can be drawn that increase of $\theta $ can reduce mass of armature and improve mechanical strength of armature’s tail, but electromagnetic contact pressure between armature and rail will be decreased. Decrease of $\gamma $ could be a considerable way to remarkably increase inductance gradient, and then increase launch system efficiency.

Research of a Modular Pulsed Alternator Power System

This paper investigates a modular pulsed alternator power system (MPAPS) composed of multiple pairs of counter-rotating alternators. This design provides benefits of torque management, machine manufacturing, current pulse shape flexibility, and fault tolerance, especially in powering long-range railguns. For a practical railgun system powered by MPAPS, one issue is determining the number of modules. Due to the complex nature of pulsed alternators and system, this paper presents a design methodology based on scaling laws of pulsed alternators and system. A variety of physical scaling laws are investigated. The implemented scaling laws are able to predict the system performances as a function of the number of modules including specific energy, alternator temperature, reliability, and efficiency. Finally, taking into account all factors, the proper number of modules is determined. This method can save time and provide the theoretical guideline for the practical design and optimization.

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.

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.

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.

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.

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.

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.

Design Considerations of an Air-Core Pulsed Alternator in an Electromagnetic Railgun System

An air-core pulsed alternator is extremely attractive for driving the electromagnetic launchers. The reason is that the machine can offer high voltage and current performance in a single-element energy storage device, a smooth pulse profile, and naturally cycled current zeros, which can allow for extremely low muzzle currents and simplifies switching requirements. But because of the short history of the air-core pulsed alternator in China, the relevant theoretical research is not enough and the experience in fabrication is absent. It is really necessary to summarize a preliminary design method in order to rapidly determine the size and approximately evaluate the electrical performance of the machine. The optimization will be based on this first-stage design scheme. In this paper, based on the requirements of the railgun, some important design considerations of a seven-phase and six-pole air-core pulsed alternator are presented in detail. In addition, it is significant to obtain the analytical formulas for the first-stage design requiring less costs; these formulas intuitively allow us to expedite the design process and optimize the design scheme. Finally, some basic output parameters of the machine are given for the preliminary design; the designed pulsed alternator will generate 1.4 kV and drive a train of 1-MA pulses into a 5-m railgun, accelerating 200-g masses at 2 km/s.

Transient Response of an Oscillating Heat Pipe by a Pulsed Heating in a High Magnetic Field Environment

An experimental investigation of a compact, triple-layer oscillating heat pipe (OHP) has been conducted to determine the fast-transient heating effect on the heat transport capability of an OHP in a high magnetic field environment. The OHP has dimensions of 1.3 cm thick, 22.9 cm long, and 7.6 cm wide embedded with two-independent closed-loops forming three layers of channels. The OHP was directly clamped to a railgun system in a medium caliber launcher (MCL) and subjected to high current electric discharges occurring over several microseconds. The experimental results show that the OHP is capable of significantly reducing peak temperatures during a pulsed heating event over pure copper, even in the presence of relatively high magnetic fields.

Influences of Electric Parameters of Pulsed Power Supply on Electromagnetic Railgun System

To analyze the electric parameters of a pulsed power supply (PPS) system and their influence on muzzle velocity, a stable and reliable 200-kJ compact PPS system used for electromagnetic railgun system has been developed. The PPS system consists of ten modules, and each module is comprised of a high energy density capacitor (3270 $\mu $ F/3.5 kV), 4-in thyristor, a pulse shaping inductor (1.5 $\mu $ H), and a crowbar diode. At the same time, a railgun circuit model for simulation was established. In this model, velocity skin effect, current skin effect, and friction were taken into consideration. Some electromagnetic launching experiments were carried out to verify the correctness of the railgun circuit model. Influence of different electric parameters of PPS on muzzle velocity was analyzed by the computer aided circuit design program PSPICE based on this model. The parameters include capacitance, equivalent series resistance (ESR) of the capacitor, inductance, and jitter time of the thyristor. The simulation results show that the ESR is the most critical influencing factor (the deviation of velocity is −4.286% when the ESR is 5 m $\Omega $ ). The following is the change of the capacitance (the deviation of velocity is −3.827% when the capacitance decreases to 95%C0). In the meantime, the changes of the resistance of inductor do have an influence on muzzle velocity (the deviation of velocity is −0.908% when the resistance of inductor is 1 m $\Omega $ ). However, the changes of inductance and the jitter time of the thyristor impose no significant effect on muzzle velocity. The conclusions provide reference to the overall optimization of PPS design and quality control of the manufacturing process.

Rail electromagnetic accelerators with an external magnetic field

The main problems of using electromagnetic rail accelerators to accelerate solid bodies of the millimeter range are outlined in the paper. A modernized system of biasing a rail gun is presented, its operating principle is described. Mathematical modeling of the rail gun system with and without bias for accelerated bodies of different mass is carried out. The influence of the bias system on the basic parameters of electromagnetic rail accelerators is analyzed. The acceleration forces acting on the object from the main loop and the bias circuit are plotted, as well as armature velocities and magnetic field induction in the object accelerated. The limits of applicability of the model described are given. Several variants of the design of rail gun bias systems including a multi-stage one are presented. The effect of some of the initial conditions on the acceleration of an object in the channel of the rail electromagnetic accelerator is analyzed. The effectiveness of introducing an external magnetic field in the channel of the accelerator making it possible to increase the speed of the lifter more than twice, while maintaining the resource of rail electrodes, is shown.

On electric warship power system performance when meeting the energy requirements of electromagnetic railguns

This paper investigates the ability of a gas turbine alternator to provide power to an electromagnetic (EM) railgun in surface combatants whilst simultaneously maintaining acceptable levels of power quality for other consumers. Following the justification of the investigation and a description of the research methods, which includes a proposed EM railgun charging control system, this paper discusses simulated results obtained from a validated power system model for both single shot and salvo operations and identifies factors that limit the rates of fire in each case. The findings from the investigations suggest that a large gas turbine alternator is able to maintain quality of power supply within acceptable limits for the majority of EM railgun operations. However, the transient quality of power supply limits was found to be exceeded for heavy firing rates but would remain within tolerable limits as defined for exceptional loads by North Atlantic Treaty Organization (NATO) standardization agreement (STANAG) 1008 Edition 9. A method to increase the maximum rate of fire whilst maintaining the quality of the power supply within acceptable limits is investigated by increasing the size of the energy storage device and retaining a residual charge. The paper concludes by suggesting that the EM railgun system could be integrated into the ship's electrical system without the need for any additional prime movers to achieve rates of fire commensurate with a surface combatant's requirements.