Induction Coilgun Research Articles

Investigation of Synchronous Induction Coilgun With Stepped Coil Launcher and Stepped Armature

Synchronous induction coilgun (SICG) typically includes an array of drive coils and a conductive armature. The structure of the drive coil and armature can greatly affect the launching performance of SICG. The traditional drive coils and armatures have a cylinder-shaped structure for simplicity and ease of fabrication. In this article, a novel structural SICG with stepped drive coil and stepped armature (SA) is proposed and investigated. As a comparison, four structural SICGs are researched by static and transient simulations. The static simulation results show that the stepped drive coil makes the magnetic field larger and the center of the magnetic field moves backward toward the tail end. The transient simulation results indicate that the SA improves the eddy current distribution and the positive propulsion force and weakens the reverse electromagnetic force and the armature capture effect at the same time. As a result of integrating the above characteristics, the new structural SICG with stepped drive coil and SA makes the optimal trigger position of armature move backward by 7 mm and improves the muzzle velocity by 4.79% and the launch efficiency by 9.82%.

Acceleration Mechanism and Experimental Research of Multi-Stage Synchronous Induction Coilgun Based on Magnetic Field Arrangement

Multi-stage synchronous induction coilgun is one of the important research aspects of the electromagnetic launch. Researchers mainly focus on the optimization of the geometrical dimension and parameters for the multi-stage launcher, pulsed power supply, armature, and so on, in order to achieve the best matching between parameters. Based on the basic principle of multi-stage induction coilgun, the acceleration mechanism is investigated in terms of the magnetic field arrangement. First, a field-circuit coupled model for a 15-stage coilgun is built. Through analyzing the velocity profile and the distribution of current density vector on the armature, it is considered that the armature is affected by the magnetic field generated by frontal stages and current stage during the launching process, so the braking force and pushing force both act on the armature. Therefore, the system conversion efficiency is affected. In order to reduce the braking force and increase the variation of the magnetic field, the direction of the magnetic field is changed. The distribution of the current density vector on the armature and transition process for the variation of the magnetic field is analyzed. The simulation results show that the muzzle velocity can be increased significantly by changing the direction of the magnetic field. The acceleration mechanism of the inconsistent direction of the magnetic field is different from that of a consistent direction. The current density on the armature is increased dramatically in the transition area, which is beneficial to increase the magnetic pushing force. A previously built 15-stage coilgun was used to validate the method. The launching experiments are carried out under the condition of the consistent direction and inconsistent direction of the magnetic field. The experiment results show that the system conversion efficiency is improved significantly for the inconsistent direction of the magnetic field. It provides a valuable reference for multi-stage induction coilgun design.

Investigation of the Inner Conical Armature in Synchronous Induction Coilgun

Synchronous induction coilgun (SICG) has attracted more and more attention due to its advantages of simple manufacturing and no physical contact between armature and barrel. The armature, as an important component of SICG, will directly affect the launch speed and energy conversion efficiency. According to the distribution characteristics of eddy current and electromagnetic force, a new structural armature is proposed in this paper. The proposed inner conical armature is characterized by the maximum thickness at the tail end and the minimum thickness at the front end, with a gradual decrease in the thickness along the axial direction. The simulation results reveal that the proposed armature not only increases the mutual inductance between the armature and the drive coil but also enhances the electromagnetic force and weakens the armature capture effect. The experimental results verify that, compared with a traditional armature weighing 56.5 g, the new structure armature weighing 58.0 g enables higher muzzle velocities using the same set of pulsed power supply and drive coil, providing higher efficiency.

Nonparametric Modeling and Parameter Optimization of Multistage Synchronous Induction Coilgun

The launching process of multistage synchronous induction coilgun (MSSICG) is a complex process involving multifield coupling, so it is time-consuming to iteratively optimize its structural parameters by stochastic optimization algorithm. A nonlinear regression modeling method of MSSICG based on mainstream machine learning methods is proposed in this paper. Rooted in the current filament model (CFM) verified by prototype experiment, the sample set for training and testing could be obtained by a hybrid experimental design method. The least-squares support vector machine (LSSVM), the kernel extreme learning machine (KELM), and the eco state network (ESN) were employed to learn the training samples. In order to improve the accuracy of the prediction model, the chicken swarm optimization (CSO) was introduced to pretrain the hyperparameters of the LSSVM and the KELM as well as the parameters of the dynamic reservoir of the ESN. The results show that the predictive modeling of MSSICG based on CSO-KELM has better accuracy and generalization performance. Based on the obtained regression model, the CSO algorithm was used to optimize the structural parameters of a five-stage coilgun. It turns out that the optimization based on nonparametric model has higher computational efficiency than the optimization method which requires large-scale iterative calculation. This provides a novel idea for the engineering design of the MSSICG.

Optimal Design and Testing of the Driving Coil on Induction Coilgun

The driving coil, as a key element of synchronous induction coilgun, endures not only the radial expansionary force because of the magnetic flux compression but also the axial force due to the compressive force and counterforce of the armature. Dielectric breakdown and mechanical structure damage occurs frequently. Meanwhile, the driving coil should have high energy conversion efficiency as a pusher to accelerate the armature. Therefore, it is important to choose the appropriate structure and parameters in order to achieve a high launching performance. In this paper, the factors that influence the system efficiency are analyzed first. Different structure designs of the driving coil with the same inductance are evaluated. The effect of different calibers on the system efficiency is analyzed. The simulation result shows that the structure of the driving coil should be chosen according to the practical launching requirement while the magnetic coupling should be increased. Second, the electromagnetic force applied on the coil is calculated and the stress is analyzed. The thickness and displacement of the containment are calculated on the condition of unyielding. In order to validate the accuracy of the theoretical analysis, an electromagnetic-mechanical coupling finite element model is built. Comparing two calculation results, the error is small. Therefore, the method can be used to guide the design of the driving coil. Finally, a driving coil is fabricated according to the calculation results and experimented through static and dynamic tests. The experimental results show that the driving coil performs well and have high conversion efficiency. It provides a theoretical and experimental basis for the future design of multistage induction coilgun.

Development and Experimental Results of a Three-Stage Induction Coilgun

In 2016, Hanwha Defense Systems Corporation commenced an electromagnetic launcher program to develop the next-generation “cold-launching” missile launcher system. This system is based on multistage induction coilguns with advantages such as controllability of energy transfer, reusability, and noncontact between the armature and the stators. The system requirement is to launch missiles to a height of 20 m with weight ranging from hundreds of kilograms to several tons. This paper presents the design, fabrication, and experiment results of a laboratory-scale electromagnetic launcher to demonstrate the feasibility of an electromagnetic launcher for heavy missiles. The effectiveness and performance of an electromagnetic launcher developed to launch heavy missiles have been demonstrated by accelerating a 21.68-kg projectile to 20 m/s.

Development of a Capacitor Bank-Based Pulsed Power Supply Module for Electromagnetic Induction Coilguns

This paper presents some discussions and findings related to the development of the capacitor bank-based pulsed power supply module (PPSM) for an electromagnetic induction coilgun (EIC). Three PPSMs were designed for a three-stage EIC to launch a 21.68-kg projectile at a minimum velocity of 20 m/s. The energy of the PPSM in the first, second, and third stages was 200, 100, and 100 kJ, respectively. Two light-triggered thyristors (LTT) were used as the main switches of the module. The synchronous behaviors of the series LTT, dump circuit, laser diode driver circuit, and protection scheme are analyzed and discussed. The PPSM was built and tested as an EIC system. The simulation results of the PPSM were in agreement with the experimental results. The peak current was about 42 kA at a maximum voltage of 10 kV as in the simulation. The maximum current in the 4-kV launch experiment was 16.47 kA. The velocity of the projectile was more than 25 m/s, which is consistent with the design goal.

Key design parameters and optimum method of medium- and high-velocity synchronous induction coilgun based on orthogonal experimental design**Project supported by the National Natural Science Foundation of China (Grant No. 5140130).

The energy conversion efficiency of a multistage synchronous induction coilgun (MSSICG) has become one of the key factors that restricts its industrialization. To improve the launch efficiency of medium- and high-velocity MSSICG, we propose an optimization design scheme combining orthogonal experimental design (OED) and self-consistent design method in this paper. The OED is introduced to reduce the number of iterations and improve the identification accuracy and efficiency. A self-consistent design model is established to overcome a defect that the parameters that need to be optimized will multiply as the number of coil stages increases. The influence of six factors (radial thickness of armature, axial length of armature, axial length of coil, capacitance, wire diameter, and slip speed) on the launch efficiency are then evaluated by range analysis. This work presents a valuable reference for optimizing medium- and high-velocity MSSICG.

Simulation of Dynamic and Electromagnetic Characteristics of a Superconductor Bulk in a Single-Stage Induction Coilgun

Induction coilgun can accelerate a high-temperature superconductor (HTS) projectile to higher velocity than a conventional projectile, because an HTS projectile can generate greater induced current by the premagnetized process and then obtain larger thrust in the launch process. In this paper, a numerical field model for the dynamic and electromagnetic characteristics of a single-stage induction coilgun is established, using the finite-element method. The electromagnetic force, muzzle velocity, and current density distribution of the aluminum projectile and the HTS projectile are studied, respectively. Then, the effect of magnetization on the characteristics of the HTS projectile during the launch process is considered. The result illustrates that magnetization brings a great improvement in the performance of the coilgun due to the higher induced current value in the HTS projectile. In addition, due to the limitation of the full magnetization state, the magnetization of the HTS projectile should be in a suitable range. The simulation work shows the potential of HTS projectile for future induction coilgun application.

Design of an Attractive Force Circuit of Pulsed Power System for Multistage Synchronous Induction Coilgun

This paper presents a new capacitor bank topology for a pulsed power system to improve the efficiency of multistage synchronous induction coilgun. In the proposed method, a switch, such a gate turn-off thyristor, is inserted in parallel to a crowbar diode and load to generate an attractive force between the next stator and the armature. A mathematical model was developed, and finite-element method simulations were conducted to verify the proposed topology. The results show that the proposed method improves the energy efficiency and launch velocity. The improvement in energy efficiency is confirmed from the simulation results of a three-stage synchronous induction coilgun.

Design of an Electromagnetic Induction Coilgun Using the Taguchi Method

Electromagnetic induction coilgun systems have been receiving great attention, recently, due to the advantage of noncontact between the stator and armature coils. Several studies present the simulation and analysis of the coilgun system by using the finite-element method. However, there are still deficiencies in current modeling studies of the coilgun system. This paper presents a design of a multistage pulsed power induction coilgun system using the Taguchi method to maximize its efficiency and reduce the time and cost of the design process. A coilgun system is analyzed and designed using a state-space equation system. The Taguchi method is applied in order to evaluate and determine the geometric variables, the layer, turn layer numbers for both the stator and armature coils, and the trigger positions of each stage. Then, a 2-D finite-element model of the coilgun system using the MagNet program was developed to compare the design and analysis results. The energy efficiency of the three-stage coilgun system is 31.3% and this is expected to increase with the increase in the number of stages.

WITHDRAWN: An efficiency-improved method of multi-stage induction coilgun based on magnetic field arrangement

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Research on self-consistent control strategy of multistage synchronous induction coil launcher

Trigger control strategy is of vital importance for the multistage synchronous induction coilgun (MSSICG). According to the operating principle of MSSICG, we can theoretically obtain a sustained and steady acceleration which is sufficient to push the projectile to high speed by means of continuously increasing the series of driving coils and matching with the appropriate trigger strategy. However, the transition time between the adjacent coils decreases with the increase of the projectile velocity, which leads to the weakness of the traditional position or time trigger control. In this paper, a self-consistent control strategy of MSSICG was proposed. Its accuracy and flexibility are verified through an illustrative example of a 25 stages synchronous coilgun. The results coincide well with that by finite-element method (FEM), and the error of muzzle velocity is only 3.4%. Based on this method, the influence of slip speed and rise length on the adaptive control effect is calculated and analyzed, and accordingly proposed to use variable slip speed. As far as the capacitive pulsed power supply (CPPS)-based MSSICG is concerned, the research methods and results in this paper have both theoretical and pragmatic value in simplifying the design process and improving energy conversion efficiency (ECE).

Research on the Temperature Field of Multistage Synchronous Induction Coilgun

During coilgun launching, the driving coil and the armature will generate a lot of heat due to pulsed current. Especially in the local area of the armature, temperature may exceed the melting point because of the skin effect, so that the launching performance will be influenced. Therefore, it is very important to investigate the temperature distribution for optimizing the launcher design and improving the system efficiency. In this paper, taking a six-stage induction coilgun for an example, an electromagnetic-thermal coupled simulation model is built using the current filament method. The temperature distribution is calculated under the circumstance of unidirectional coupling and bidirectional coupling for the multiphysics solutions. Comparing the two simulation results, the temperatures of the driving coils are both low and have unconspicuous effect on the system performance. The area of high temperature rise on the armature is located in the outer surface and the rear part. The temperature rise from the unidirectional coupling calculation is higher than that from the bidirectional coupling calculation. The calculation result shows that the temperature rise changes the material conductivity, and the current distribution in the armature is redistributed. So that it leads to the local temperature reduction. The material of the armature may influence the system performance and temperature because the conductivity changes the distribution of the induced current. The armatures made up of copper and aluminum are simulated, respectively. Simulation result shows that the velocity profile is identical, but the temperature rise of the copper armature is lower than that of the aluminum armature for the same mass. Therefore, the material conductivity should be considered for the design of the high-speed launching. In order to validate the simulation results, a six-stage coilgun has been built. Comparing with the test results, the simulation result is validated.

Investigation of Magnetic Field Arrangement on Launching Performance of Multistage Synchronous Induction Coilgun

For the multistage induction coilgun, many researchers pay great attention to improving the system efficiency. The directions of magnetic field generated by the driving coils are consistent for conventional coilgun, because it is convenient to analyze acceleration characteristic and stress status for the armature in the barrel. In this paper, the launching performance of multistage induction coilgun is investigated in terms of different directions of magnetic field in order to improve the system efficiency. A field-circuit coupled model for a 6-stage coilgun is built. The simulation for the consistent direction of magnetic field is calculated. For the same parameter setup, the directions of magnetic field generated by the last three stages current are changed. The simulation results show that the armature endures a large braking force when going through the last three stages, and the velocity drop is obvious. Meanwhile, the currents in the last three stages are very large. The distribution of the current density and the magnetic field during the transition process of magnetic field are analyzed. The reason for velocity drop when changing the direction of magnetic field is discussed. A method that the trigger position is adjusted for the armature is proposed. The simulation results show that the armature can be accelerated to a higher speed on condition of inconsistent direction of magnetic field with adjusting the trigger position. It is feasible to improve the system launching performance through changing the direction of magnetic field. A 15-stage coilgun is built to validate the method. The experimental results show that the velocity and system efficiency are increased dramatically through changing the direction of magnetic field. It provides valuable reference for multistage induction design.

Multiobjective Optimization of Multistage Synchronous Induction Coilgun Based on NSGA-II

The structure and trigger control strategy have become the most important factors that restrict the performance of the multistage synchronous induction coilgun (MSSICG). However, it is still a difficult task to design MSSICG under overload constraint due to coupling between the multiple parameters. In this paper, the maximization of the emission efficiency and acceleration stationarity is treated as a multiobjective optimization problem. By analyzing the relationship between the number of turns and the other structural parameters of the launch, the multiobjective optimization model of MSSICG is established by the current filament method which was verified by the experimental data and finite-element method. And then the second generation nondominated sorting genetic algorithm (NSGA-II) and multiobjective particle swarm optimization (MOPSO) were employed to optimize the model in order to maximize the energy transfer efficiency while achieving the smooth acceleration of the armature. With the formulated optimization model, a five-stage synchronous induction coilgun is optimized as a special case. A decision-making procedure based on the fuzzy membership function is used for obtaining best compromise solution from the set of Pareto-solutions obtained through NSGA-II and MOPSO. In addition, the optimization performance of the proposed multiobjective optimization model and the single-objective optimization model of the MSSICG was compared. The result of optimization shows that the proposed multiobjective optimization model of MSSICG can effectively improve the performance of the coilgun compared with the single-objective optimization model which takes of the launch velocity and overload acceleration as the combination objective function or only the launch velocity.

Coilgun Velocity Optimization With Current Switch Circuit

An inductive coil gun is a solenoid surrounding a cylindrical metallic armature (the projectile), both electromagnetically coupled. One or more capacitors discharge a stored voltage quickly through the coil, configuring a kind of RLC circuit, with the pulse-shaped current generating a magnetic field inside the coil that accelerates the projectile. Once the projectile crosses an equilibrium point inside the coil, the existing magnetic field pulls the armature back, therefore reducing the final muzzle velocity and decreasing the efficiency-defined as the ratio between the available capacitor electrostatic versus the slug kinetic energies. This paper describes a system that monitors the armature position inside the coil, with a laser beam, and automatically cuts the current when the projectile reaches the equilibrium point. The system, named current switch circuit, enables higher velocities using the same set of coilgun and projectiles, providing a higher efficiency.

Two fluxes multistage induction coilgun

This paper presents a brand new induction electromagnetic launcher, which uses two magnetic fluxes in order to accelerate a projectile. One magnetic flux induce a current in the armature and the second magnetic flux is creating a radial magnetic field. This aproach offer multiple advantages over single flux designs. First we are able to control the induced current in armature because we use the coil just to induce current inside the ring with a great efficiency. Second advantage is the angle of 900 between magnetic field density B and the ring. We used the induction to avoid contact between armature and accelerator. In order to create the magnetic field radial we used four coils perpendicular on armature. This approach alove us to control the phase difference between induced current in armature and current in magnetic field coils for a maximum force. The phase difference is obtained by changing the frequency of magnetic field coils power source. We used simulation software to analyze, and simulate a multistage induction coilgun design with two fluxes. The simulation results demonstrated the theoretical results.

Asymmetric Multistage Synchronous Inductive Coilgun for Length Reduction, Higher Muzzle Velocity, and Launching Time Reduction

This paper discusses a study made for good asymmetric three-stage electromagnetic coilgun launching medium-weight projectile. Different lengths, number of turns, and switching times are chosen for each individual coil to get better results. Two detailed investigated models have been presented, including the effect of the switching time. Medium-caliber projectile of $\text {weight} = 0.5$ kg is employed in this paper. The results confirm that the second model asymmetric coilgun has 16.96% higher output speed, 63.92% lower length, and 57.5% lower launching time than the first model asymmetric coilgun. The obtained results have been recorded using the transient time electromagnetic simulations.

Optimization analysis study of a multi-stage SICG based on OED

This paper analyzes the influences of the factors in a capacitor-driven multi-stage synchronous induction coilgun (SICG) and optimal combination of the design parameters based on orthogonal experiment design (OED). Finite element transient solver is used to calculate the motion characteristics of a multi-stage SICG. The muzzle speed is set to be the target of the optimization. System parameters (factors), levels and orthogonal array (OA) are determined by the order. Three optimization schemes are compared, including stage-by-stage optimization, section optimization and full optimization. Optimal combination of the three-stage SICG is obtained, as well as important order of factors. It shows that a set of comparatively better parameters and relatively higher efficiency could be achieved through orthogonal optimum. Wire diameter and coil diameter are the most important factors that influence the system efficiency of the launcher. Besides them, length of coil, trigger position and number of turns have less influence for the system in the important order. Section optimization could reduce the amount of computations compared to full optimization and a set of comparatively better parameters and relatively higher efficiency could be achieved. It is suggested to optimize a multi-stage SICG. How to choose the factors from lots of parameters is according to the engineering practice. Improper choices of the value in levels may cause unable to reach an optimum. The conclusion will be useful for coilgun design.