Armature Velocity Research Articles

Study on the Selection of Coil Energization Directions in Multistage Synchronous Induction Coil Launcher

In order to enhance the initial velocity and energy conversion efficiency of multi-stage synchronous induction coil launchers, the direction of coil energization for the drive coils is studied. There are typically two energization methods for multi-stage launching devices: (1) PP (Positive-Positive), where positive current is applied to all drive coils, and (2) PN (Positive-Negative), where currents in opposite directions are alternately applied to the drive coils. A finite element model of a four-stage coil launcher is established in ANSYS2022R2, and the acceleration effects of the armature under different inter-stage distances are analyzed for two energization methods. The study reveals that the PN configuration does not always result in higher armature velocities compared to the PP configuration under different inter-stage distances. The theoretical explanation is provided for the variations in the forces exerted by the previous and next drive coils on the armature during the acceleration process. It is found that the magnitude of the induced current in the previous and next drive coils during the launch process is influenced by the inter-stage distance, which in turn affects the electromagnetic thrust coupled with the armature. Thus, the method of determining the direction of current in the launching device coil is obtained.

Modeling and Verification of Electromagnetic-Thermal Coupling for Electromagnetic Track Launch Considering the Dynamic Conductivity

In order to solve the problems of insufficient precision of the armature velocity and inductance gradient in the process of finite element calculation of the electromagnetic track launcher, an improved dynamic conductivity electromagnetic-thermal coupling model is proposed to make the calculated results closer to the actual working condition. Firstly, the finite element analysis for the electromagnetic-thermal field is carried out. Then, considering the influence of dynamic conductivity on the armature velocity and inductance gradient, an improved dynamic conductivity electromagnetic-thermal coupling model based on finite element analysis is established, whose parameters are identified by the proposed PSO-GA hybrid algorithm. Moreover, the predicted values of armature velocity and inductance gradient are also obtained. Finally, the experimental platform of the electromagnetic track launcher is built to verify the improved model. By comparing the predicted value of the improved model with the experimental test value, it is found that the improved model can further reduce the calculated error from 5.79% to 1.18%, which provides a certain theoretical basis for the full true simulation of the electromagnetic track launch.

Three-dimensional magneto-thermo-mechanical coupling analysis with the influence of velocity skin effect

In this paper, the three-dimensional magnetic diffusion governing equations of an electromagnetic railgun are derived based on Maxwell’s equations and coupled with the energy equations. The finite element method is used to calculate the current density, temperature, and electromagnetic force distribution for armature velocities of 0, 200, 600, and 1200 m/s. The results show that there is a current concentration phenomenon on the rail’s inner surface and the trailing edge of the contact interface; the temperature rise of the rail along the moving direction of the armature tends to decrease, and ablation occurs at the corner of the moving armature’s trailing edge. An increase in the velocity of armature movement results in an increase in the electromagnetic forces on the armature and contact surface. This model can effectively represent the variation of each physical quantity with velocity and provide direction for the optimal design of the rail and armature.

Optimizating the Energy Storage Configuration of a Single Stage Coilgun to Maximize Efficiency

Naval Surface Warfare Center Dahlgren Division (NSWCDD) has been exploring methods of maximizing coilgun electrical-to-kinetic energy transfer efficiency by optimizing the geometries of wire-wound drive coils and armatures. Such optimization permits a reduction in the number of stages for a multistage coilgun, thus decreasing its design complexity and power requirements. NSWCDD applied optimal design trends to the coilgun geometry and its energy storage configuration to build a single stage coilgun capable of launching a 447-g projectile to 144 mph, resulting in an efficiency of 14.47%. To date, this is the highest experimentally achieved efficiency of a single stage coilgun without the use of cooling or initial armature velocity. The efficiency may be determined by the drive coil current measurements with and without the armature, as an alternative to knowing the speed and mass of the armature.

Precision Analysis of Armature Velocity Measurement by Principal Component Analysis Method

Precision Analysis of Armature Velocity Measurement by Principal Component Analysis Method

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.

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.

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

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

Analysis about Change of the Armature's Average Speed for an Experimental Rail Launcher

In this paper, we measured the armature velocity of an experimental electromagnetic launcher by B‐dot method and analyzed the change of the armature's average speed. The electromagnetic gun launching process was also simulated by Ansoft Maxwell simulation software. The launch current is used as the model's excitation which means that the current in the model is the same as the rail current. Ansoft Maxwell's 3D model can accurately simulate the launching process, in theory. We found that there was an unexpected rise during the real launching process. The phenomenon can be discovered in the following several experiments. We analyzed several possible causes such as the inductive gradient change, rail broken and inaccurate measurement of B‐dot probe. The inductive gradient is an important parameter in the launching process and can affect the armature speed. After checking the measurement problem, we also found that the wave form of the output signal from the probe where the unexpected change occurred was normal but the amplitude was very small. The measurement method was proved correct. The rise of average inductance gradient leads to the unexpected increase in average speed and the small signal. Furthermore, the physical reason for the change of inductance gradient should be the change of current distribution. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Simulation on Side-Ejecting Characteristics of Metal Liquid Film in Electromagnetic Launcher

The Joule heat generated by the pulsed large current and the friction heat of the armature/rail (A/R) contact interface in the electromagnetic launcher causes the surface of the armature's tail melting. A part of the metal liquid film is deposited on the contact interface, a part of it left the barrel together with the armature, and the others was sprayed laterally, which damages the rails and the insulation. In order to lengthen the span of the launcher barrel's life, it is necessary to minimize the side-ejecting of metal liquid film. In this article, we obtained the 2-D Reynolds equation applicable to the metal liquid film. Using the finite-element software LS-DYNA and COMSOL, we have established a 3-D electromagnetic-elastic mechanics-hydrodynamics multiphysics coupling model considering the dynamic changes of magnetic pressure, liquid film's own acceleration, fluid pressure, and film thickness. We use this model to obtain the lateral film thickness, total pressure, and velocity distribution characteristics of the metal liquid film at any time. We have further studied the influence of armature velocity, stiffness of armature's tail, liquid film's own acceleration, and linear current density on the amount of side-ejecting of liquid film.

Dynamic Response and Critical Velocity of Rails in Electromagnetic Rail Launcher Due to Axial Force

The dynamic response and the critical velocity of the rails in electromagnetic rail launcher (EMRL) have a direct influence on launch accuracy and contact between the armature and the rail. In order to analyze the influence of the axial force on the dynamic response of the rails in EMRL during the launching process, the vibration control equation of the rail is established. The analytical solution and the critical velocity of the rail’s vibration under given initial and boundary conditions are derived through the method of separation of variables. On this basis, the influence of the preloaded axial force on the dynamic response and critical velocity of the rail under the typical current excitation and the armature constant velocity motion is analyzed, respectively, by the programming code. Studies have shown that the critical velocity increases with increasing axial force, but as the axial force gradually increases, the increasing trend of the critical velocity gradually becomes slower; the axial tensile force on the rail can suppress the vibration of the rail, especially when the armature velocity is close to the critical velocity; the influence range of the resonance region decreases with increasing axial force. The results can provide guidance for improving the critical velocity of the rail and reduce the amplitude of the vibration during the launch.

Design and Implementation of a High-Speed Real-Time Position Detection System in Electromagnetic Coil Launcher

Electromagnetic coil launcher (ECL) is a specific application of electromagnetic launching technology and has broad prospects in the fields of new weapon systems and launching microsatellites. The acceleration force of the projectile in the ECL depends on the current of the driving coil and the projectile together with the mutual inductance between them, and to maximize the launch coefficient, each drive coil should be energized according to the projectile’s movement position. In order to realize the closed-loop control of the ECL and improve the energy utilization, a new position detection system (PDS) based on fiber optic sensor (FOS) is designed in this article, which can obtain the armature displacement and velocity in real time during the launch process. Then, the main factors influencing the detection results are analyzed and studied. Finally, after experimental verification, the PDS designed in this article has an error of 4.2% and 1.41% in the measurement of the armature position and velocity, respectively. The results are of great significance to the realization of ECL engineering.

Study on the Characteristics of Magnetic-Field Arrangement of Synchronous Induction Coilgun

Energy-conversion efficiency directly determines the scale of the synchronous induction coilgun, which is an important index to evaluate the launch system. Therefore, the method of improving the energy-conversion efficiency is one of the hot spots in the electromagnetic launch research. By changing the direction of the magnetic field, the acceleration mechanism of the armature has changed. This article focuses on the characteristics of the magnetic field arrangement of the multistage synchronous induction coilgun in order to obtain the design method of the magnetic field. First, the acceleration mechanism of the armature is analyzed for the consistent and inconsistent directions of the magnetic field. The feasibility of changing the magnetic field direction to improve the energy-conversion efficiency and the correctness of the simulation model is verified by the experimental results. The variation in the armature velocity and the single-coil efficiency is investigated when the direction of the magnetic field changes once, twice, and thrice. The prediction model of the magnetic field arrangement is established. Based on this model, the magnetic field arrangement of the coils is predicted when the direction of the magnetic field changes twice or thrice and the parameters of the pulsed-power supply are changed. The predicted results are in good agreement with the simulation results. The influence of the caliber on the prediction result is analyzed. Finally, the prediction model of the magnetic field arrangement based on the armature velocity and the discharge-loop parameters under the efficiency threshold related to the launcher caliber is established. The prediction model proposed in this article can effectively improve the energy-conversion efficiency and provide a valuable reference for the design of the magnetic field of the multistage synchronous induction coilgun.

Research on Armature Recovery of a Coil Launcher

At present, the boost payload of electromagnetic coil launcher mainly adopts integrated launching mode; that is, the armature and payload are integrated into a projectile to shoot out of the bore together. There are some problems with this kind of launching form, such as high parasitic mass and low efficiency of payload launching. In this article, a payload projection scheme of armature–load separation launching is proposed. When the armature and payload reach the peak velocity, the armature is separated from the payload by electromagnetic capture force, and the armature can be recovered and reused under certain conditions. A model of five-stage coil launcher is established and the interior trajectory characteristics of armature under the integrated launching and separation launching modes are compared by simulation. It is shown that the mass of armature will exaggerate the launching performance. The armature–load separated launching mode can effectively improve the launching efficiency. Then the armature recovery method is further proposed. The armature velocity is related to many factors such as mass ratio of armature and payload, driving voltage, and turns of the last coil stage. The study proves that under certain conditions, the armature can be recovered, which could improve the safety of launch.

Influence of Armature Movement Velocity on the Magnetic Field Distribution and Current Density Distribution in Railgun

In a railgun, the velocity of the armature has an important effect on the magnetic field distribution and current density distribution of the launch system. However, the calculation models established by scholars were mostly models under static conditions. They could not effectively reflect the velocity skin effect (VSE). This article uses the finite-element softwares COMSOL and LS-DYNA to establish a calculation model that considers the influence of the armature movement velocity on the magnetic field distribution and current density distribution. The calculation results show that when considering the armature movement, the magnetic field distribution of the rail side is very different from the static calculation result. Under the influence of the VSE, the current of the armature/rail (A/R) interface is mainly concentrated on the end of the armature's tail. When considering the armature movement, the values of maximum current density of the rail side doubled. Also, as the armature velocity increases, its range of influence also increases. However, it tends to saturate after reaching a certain velocity. Considering the influence of the armature velocity on the magnetic field distribution and current density distribution can make our results closer to the actual launch situation.

Dynamic Mechanical Properties in Electromagnetic Rail Launcher With Cooling Channels

An electromagnetic rail launcher (ERL) is essentially a high-speed linear motor, which can accelerate projectiles from milligrams to several kilograms and the velocities of which can reach more than several kilometers per second. In this article, the dynamic electromechanical characteristics of an ERL with the cross-section of plane, convex, and concave rails under different conditions of frictional coefficient and channel cooling are investigated. The kinematic characteristics of armatures and the stress distribution of three types of rails are compared. The mathematical relation between the frictional coefficient, the sliding time, and the armature speed in an ERL with three types of rails is obtained. The equations for the frictional coefficient, the sliding time, and the displacement of armature in an ERL with three types of rails are obtained. Under the same frictional coefficient condition, the velocity and displacement of armature in an ERL with a convex rail are the largest. The peak stress in a plane rail during one shot period is the greatest. In light of obtaining a higher armature velocity and moderate stress in a rail, the ERL with convex rails is the best one.

A Closed-Loop Velocity Control System for Electromagnetic Railguns

The electromagnetic railguns possess the characteristics of active and accurate control of the muzzle velocity. As to our understanding, the muzzle velocity control has two levels. One is to design the triggering strategy of the pulsed power supplies before the launching process, while the other is to adjust the triggering strategy during the launching process. The objective of the first one is to realize the desired muzzle velocity with ideal system parameters, and the target of the second one is to design a closed-loop adjusting system for the precalculated triggering strategy, so as to keep the actual muzzle velocity equal or closed to the desired value when the launching process has some kind of turbulences, e.g., nonideal charging voltage and errors of the armature mass. This paper proposes a closed-loop velocity control system and four different methods to adjust the actual muzzle velocity in real launching time. The core idea of this system is to detect the armature velocities at key points along the rails and adjust the following triggering pulsed forming unit (PFU) number of the pulsed power supplies. In simulations, the desired muzzle velocity is 2000 m/s, the capacitance of the energy storage capacitors $C_{\mathrm {PFU}}$ is 2 mF, the precharged voltage $U_{0}$ is 5 kV, and the armature mass ${m}$ is 0.15 kg. Without the closed-loop adjusting, if $U_{0}$ , $C_{\mathrm {PFU}}$ , and ${m}$ simultaneously and randomly change within [−2%, 2%] in actual operations, the muzzle velocity relative errors are within [0%, 2.1346%]. However, after using this closed-loop system, the results show that the muzzle velocity errors can be less than 1%, even when there is ±0.5% detection error.

Design and Development of 4-MJ Capacitor Bank-Based Pulsed Power System for Electromagnetic Launcher

A capacitor-based pulsed power system of 4 MJ was designed and developed to propel projectiles of mass above 100 g to hypervelocites. The system used the modular approach, by integrating ten 400-kJ capacitor bank modules. A number of simulation studies were carried out viz., performance analysis of the system using Microcap simulation package, design of various pulsed power subsystems using ANSYS Maxwell simulation tool, and finite element transient analysis for current diffusion through the in-house developed software. Power transfer lines, coaxial cables, and pulse-shaping inductor were designed and fabricated. Various electromagnetic (EM) launchers were designed, developed, and fabricated. Modules are arranged on various racks and are integrated with the EM launcher. Launchers are initially test fired with four modules and then with ten modules. The data acquisition system was developed to measure module currents, in-bore position, velocity, and acceleration of armature. The pulsed power system was experimented up to 1.1-MA current pulse and was successfully test fired to accelerated 120-g mass projectile at a muzzle velocity of 2024 m/s.

Simulations, Experiments, and Launch Characteristics of a Multiturn Series–Parallel Rail Launcher

In order to markedly improve the inductance gradient of electromagnetic (EM) railgun and current-carrying capacity of the armature, and enhance the ability to launch large mass projectiles, a system simulation analysis and preliminary experiments were carried out for the multiturn series-parallel rail launcher (MSPRL). First, the Simulink simulation model of the rail launcher system based on the circuit model was established, and the changing rules of current waveforms and armature velocities under different contact resistances were obtained. Then, an EM-structural multiphysics fields coupling model is constructed, with the supplied currents obtained earlier, the EM propelling force on the armature as well as contact force between the armature and rails were analyzed. In view of those analyses, the inductance gradient and armature velocity in bore were calculated. Finally, the test platform of the MSPRL was built to carry out preliminary verification experiments of relevant parameters. During the test, the muzzle impedance and muzzle velocity were measured, and the validities of the simulation models were verified.

Armature Velocity Control Strategy and System Efficiency Optimization of Railguns

This paper at first proposes a method to calculate a trigger strategy before launching in order to control the muzzle velocity of railguns. Five triggering points are set equidistantly and six pulsed forming unit (PFU) groups are triggered in total. First, given a desired muzzle velocity, the expected uniformly accelerated rectilinear motion of the armature is calculated. Second, the module number of each PFU group is obtained according to the principle of minimizing the absolute relative error between the actual and the expected velocity at each triggering point. The results show that, when the desired muzzle velocity is within [1500, 2000] m/s, the absolute muzzle velocity relative error $\delta $ is less than 0.5%. In order to achieve a better control performance, the places of the five triggering points are then optimized by a genetic algorithm (GA). The objective function is the sum of absolute $\delta $ , when the desired muzzle velocities are 1500, 1600, $\ldots $ , 2000 m/s. After the optimization, $\delta $ is reduced to less than 0.05%. At last, based on this velocity control method, the railgun system is optimized to pursue the highest system efficiency $\eta $ by GA. The independent variables are the armature mass, the precharged voltage, and the places of the five triggering points. The constraints are that the desired muzzle velocity is 1800 m/s and the absolute $\delta $ is within 1%. The results show that $\eta $ increases from 6.57% to 25.37%.