Railgun Circuit Research Articles

A Novel Iterative Technique for Interoperability of Real-Time Simulation and Finite Element Simulation Using Railgun Circuit

High-power railgun circuit design and construction is costly and time-consuming. Verifying the behavior and performance of the circuit using a circuit simulator before hardware implementation is faster and more cost-effective. In this brief, a rail type electromagnetic launcher is modeled as a controlled voltage source to the pulse forming circuit and a real-time simulation is performed on that circuit. To validate the developed real-time model of the railgun circuit, the current pulse generated is given as an input to the finite element model developed in LS-Dyna. Obtained results of finite element (FE) simulation and real-time (RT) simulator are compared from a mechanical viewpoint. An iterative procedure is utilized to exactly model the railgun in real-time simulation along with finite element simulation. In the iterative process, the result of the inductance gradient obtained in the finite element simulation is plugged back into the real-time simulator. The current obtained in the real-time simulator is given as an input to finite element simulation. Among the models, the linear fit model of inductance gradient has performed better. A tolerance condition of least approximate error in the muzzle velocity is selected for termination of iterations.

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.

Design and Analysis of Air Core Outer Rotor Halbach Array Compulsator

Conventionally, the capacitor-based pulsed power supply is used for the railgun. However, it cannot create zero current crossings during discharge, which leads to a large muzzle arc. This invariably leads to compulsator as a popular choice for railgun pulsed power supply. Moreover, the size of compulsator is comparatively lower than a capacitor bank of the same energy. A computer-aided design (CAD) of 10-MJ, 4-phase, 4-pole compulsator for achieving desired performance is developed and presented in this article. A six-segment Halbach array is adopted for permanent magnet (PM) excitation to remove the slip ring arrangement and to reduce voluminous design due to external excitation. The designed compulsator is simulated in Ansys electromagnetic (EM) suite for field analysis with practical design considerations along with the inclusion of armature winding impedance, PM demagnetization effects, and eddy current distribution in compensating shield. The railgun circuit analysis is carried out for the designed compulsator co-simulated using Simplorer and Ansys EM. Furthermore, various parametric studies are conducted for designed compulsator to analyze the effects on the acceleration and synchronization of the projectile’s exit from the barrel. Detailed simulation results show that the target specifications are achieved with the new design.

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.

Nonlinear Scaling Relationships of a Railgun

Scaling methods are widely used in railgun technology. But nonlinear problems are seldom studied because of the complexity and uncertainty. To employ the scaling method better, this paper brings the nonlinear drag model to the solid armature railgun circuit. Several drag models are compared including friction drag model (FDM), atmosphere drag model (ADM), and current drag model (CDM). Then, nonlinear scaling relationships of these drag models are discussed. Furthermore, a novel experiment is constructed to compare the drag models at low velocity. At last, the nonlinear scaling method is verified by an example at high velocity. FDM is accurate enough to simulate a railgun system at any condition. Coefficient $\varepsilon$ in FDM should be used considering different test conditions. Scaling relationships of FDM could not be derived at low velocity because of nonlinearity. Although at high velocity, FDM could be simplified to CDM and realize linear scaling method (LSM). Further research indicates that the FDM could use the scaling method directly and realize approximate LSM. CDM is workable which satisfies the conditions of LSM in nature. Due to the work range of the solid armature, usually under 2.5 km/s, nonlinear scaling method could be used in a railgun with FDM. For a solid armature railgun, the $f_{\rm ADM}$ is too small compared with $f_{\rm FDM}$ and it could be ignored in analysis of a railgun, especially at low velocity. What should be noted is that the velocity scaling factor must be controlled above about one-quarter to avoid the nonlinear field.

The Use of Electronic Components in Railgun Projectiles

This paper deals with experiments and calculations performed in order to investigate the influence of the electromagnetic hardening of payloads in a railgun. This is a complex task: besides the large amplitudes of the in-bore magnetic fields due to the pulsed current, the exit of the projectile from the muzzle and the consequences of plasma arcs have to be considered. At the muzzle the magnetic induction can drop from several Teslas to zero within some microseconds, leading to very high induced voltages and electric fields in the metallic parts of the projectile. On the other hand, the electric contact established by solid armatures tends to develop into electric arcs at high velocities during the launch. These plasma arcs as well as the closing switch transients of the railgun circuit are a source of electromagnetic radiation in a broad spectral range. Some electronic devices were selected and tested with static setups corresponding to the previous conditions. In a first phase a series of static railgun experiments (no projectile movement) was performed. In a second phase, static experiments simulating the muzzle exit conditions were carried out. Finally, the influence of electromagnetic waves emitted during railgun experiments on electronic devices was investigated, using a static setup with a conventional spark gap.

Modelling and Simulation of a Railgun powered by a Capacitor Bank

A railgun powered by a capacitor bank was developed to launch hypervelocity projectiles. The efficiency of the gun to a large extent will determine its feasibility for weapon applications. A simulation code was developed to predict the performance of the railgun. The railgun has been modelled as a time-varying impedance to determine the currents and the voltages from the power source. In the railgun circuit the currents and the voltages are of the order of hundreds of kiloamperes. Even very low impedances of the order of milli-ohm and micro-henry are substantial sources of energy losses. The measured and simulation currents at peak values agree with in 10%, validating the model. The simulation code accurately predicts the energy distribution in the system. Maximization of the projectile energy leads to improved and efficient designs. The simulation also leads to the optimized launcher pressure and payload velocity.

Heavy-duty explosively operated pulsed opening and closing switches: reducing cost and turnaround time (railgun power supplies)

Improvements to heavy-duty, explosively operated opening and closing switches to reduce component cost, installation cost, and turnaround time without sacrificing reliability are discussed. Heavy-duty opening and closing switches operated by small explosive charges (50 g or less) are essential to operation of the 60 MJ Balcones power supply. The six independent modules can be discharged sequentially. Each delayed inductor must be isolated from the railgun circuit with a heavy-duty closing switch capable of carrying megampere currents of millisecond duration. Similar closing switches are used to crowbar the railgun as the projectile approaches the muzzle. The switches-both opening and closing-are characterized by microhm resistance in the closed state. The opening switches must be structurally and thermally capable of carrying megampere currents for more than 100 ms ( approximately 10/sup 5/ C) and develop 10 kV on opening, stay open for 10/sup -2/ s, and safely and reliably dissipate megajoules of inductive energy in the event of a fault, a failure of the switch to operate, or an attempt to commutate into an open circuit. An example of the severe switching requirements is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The motionally induced back-emf in railguns

Relative motion between armature and rails in the railgun produces induced emf's. The Lorentz force formula correctly predicts the emf present in the armature but it fails to acknowledge the induction of further emf's in the rails which are proportional to the relative velocity. It is easy to confirm the existence of the additional rail emf's behind and ahead of the armature, by voltage measurements across the muzzle and the breech of the railgun. Neumann's forgotten law of induction, which was first proposed in 1845, correctly accounts for the magnitude and position of all motionally induced emf components in the railgun circuit. The velocity dependent back-emf's in the rails coincide with the Ampere recoil forces in the railheads just behind the armature. Electric power extended in overcoming these back-emf's, and associated with the recoil forces, seem to store elastic strain energy in the rails.

Railgun armature plasma-current density from deconvolved B-dot probe signals

It is shown that the spatial distribution of the moving armature current profile in an electromagnetic railgun can be recovered from the recorded signal of a B-dot probe. This approach differs from previous methods in that no a priori assumptions for the functional form of the armature current density are required. From certain simplifying assumptions, a model of the railgun circuit is developed from which the B-dot probe signal can be derived as a convolution of the armature current density with an impulse-response function dependent on the physical parameters of the experimental configuration. Deconvolution of the resulting signal corrupted with measurement noise is performed using a parametric Wiener filter. Simulated and actual numerical examples show that the physical length and overall shape of the armature current profile can be accurately determined using this method. However, the spatial resolution in the deconvolved signal is limited to approximately 1 to 2 cm for practical railgun applications. >

MAGRAC--A railgun simulation program

We have developed and validated a computer simulation code at the Lawrence Livermore National Laboratory (LLNL) to predict the performance of a railgun electromagnetic accelerator. The code, called MAGRAC (MAGnetic Railgun ACcelerator), models the performance of a railgun driven by a magnetic flux compression current generator (MFCG). The MAGRAC code employs a time-step solution of the nonlinear time-varying element railgun circuit to determine rail currents. From the rail currents, the projectile acceleration, velocity, and position are found. We have validated the MAGRAC code through a series of eight railgun tests conducted jointly with the Los Alamos National Laboratory. This paper describes the formulation of the MAGRAC railgun model and compares the predicted current waveforms with those obtained from full-scale experiments.