Electromagnetic Rail Research Articles

Simulation Optimization of Body Tube Fastening of Electromagnetic Rail Based on Modal Analysis

Simulation Optimization of Body Tube Fastening of Electromagnetic Rail Based on Modal Analysis

Research on active arc-ignition technology as a possible residual-energy-release strategy in electromagnetic rail launch

In order to solve the problem of the original residual energy release strategy being unsuitable for high-energy and fast-firing electromagnetic rail launch, this work has explored the applicability of active arc-ignition technology (AAT). The results obtained from the comparison of launching experiments show that AAT has no influence on the acceleration of the armature and is capable of quickly releasing the residual energy. Based on the theory of magnetohydrodynamics, this work has also made numerical simulation of the muzzle arc, analyzed the influence of AAT on the muzzle arc flow field, electromagnetic (EM) field and temperature field, and evaluated the performance of AAT according to the projectile initial disturbance, the EM impact on guidance devices and the rail ablation. The results show that AAT is now one of the most practicable strategies for residual energy release.

Combined Fuzzy Time Series Prediction Method for Fault Prediction of EML Pulse Capacitors

Metallized film capacitors are an important part of the electromagnetic rail launch system. It is of great significance to predict its failure. In engineering, the failure law of capacitor is obtained by cyclic pulse accelerated life test of capacitor module with a small number of samples, and is used to predict the actual failure of capacitor in electromagnetic launch (EML) system. This method has the following problems: first, there are few samples of capacitor in life test at affordable cost, which cannot include all capacitor characteristics; second, the time interval of actual EML missions and the voltage of the capacitors are both changing and inconsistent with the conditions used in the life test; third, the statistical law is affected by the measurement and other errors. For these reasons, the prediction accuracy of the existing methods is limited. In this article, a new combined time series prediction method is proposed by using the high-order fuzzy time series prediction theory. Based on the capacitor used in the prototype of an electromagnetic railgun, the life test data of 20 pulse capacitors are used as the prior knowledge input, and the prediction model is obtained. Five groups of capacitor life test data simulating real launch conditions are used as test data to verify that the prediction accuracy of the proposed method is better than that of the traditional method, and the prediction accuracy of capacitor capacitance, which made by different processes, is much higher than that of the traditional method.

The vibration reduction optimization of the body tube fastening of EM rail launcher

In order to further optimize the vibration reduction effect of the body tube fastening of the electromagnetic rail launcher, the vibration reduction optimization scheme of the body tube fastening is determined by the modal superposition method. The electromagnetic rail launcher is simplified to Bernoulli-Euler beam, the vibration equation of the rail is established, and the inherent characteristics of the rail are analyzed. The multi-field coupled finite element model of the electromagnetic rail launcher is established and the complete transient launching process of the launcher is simulated. Based on the modal analysis of the system stiffness at the critical velocity, the optimal position of the tube fastening is determined, and the influence of different fastening positions on the damping effect is analyzed. The results show that the fastening of the body tube can effectively improve the structural stiffness of the electromagnetic rail launcher, and the damping effect of the fastening is affected by the vibration characteristics of the fastening position. The addition of fastening leads to the stress concentration in the adjacent part of the rail, which increases the requirement of rail strength. When the fastening is set in the front part of the rail, the vibration reduction effect is obvious. When it is set in the back part, the resonance range of the critical velocity should be avoided and the priority should be given to the position before the critical velocity.

Current Distribution in Railgun Rails Through Barycenter Filament Model

In this article, we present a novel measurement method to estimate the current distribution in electromagnetic rail launchers. A loop array is magnetically coupled with the railgun to reconstruct the current barycenter position, from which we can argue on the current distribution through the rail cross section. After describing the adopted measurement procedure, we present the results of an experimental analysis performed using the NGL60 rail launcher at the laboratories of the French-German Research Institute of Saint-Louis (ISL). We also compare the experimental results with finite-element simulations, and we show the agreement during the current pulse transient. Finally, we provide a measurement uncertainty analysis performed using Monte Carlo method.

Effect of Nickel–Phosphorus and Nickel–Molybdenum Coatings on Electrical Ablation of Small Electromagnetic Rails

The electromagnetic rail catapult is a device that converts electrical energy into kinetic energy, which means that the strength of electrical energy directly affects the muzzle speed of armature. In addition, the electrical conductivity, electromagnetic rails and armature surface roughness, and the holding force of the rail are influencing factors that cannot be ignored. However, the electric ablation on the surface of the electromagnetic rails caused by high temperatures seriously affects the service life performance of the electromagnetic catapult system. In this study, electrochemically deposited nickel-phosphorus and nickel-molybdenum alloy coatings are plated on the surface of electromagnetic iron rails and their effects on the reduction of ablation are investigated. SEM (scanning electron microscopy) with EDS (energy dispersive spectroscopy) detector, XRD (X-ray diffraction), 3D optical profiler, and Vickers microhardness tester are used. Our results show that the sliding velocity of the armature decreases slightly with the increased roughness of the rail coating surface. On the other hand, the area of electric ablation on the rail surface is inversely related to the hardness of the rail material. The electrically ablated surface areas of the rails are in: annealed nickel–molybdenum < nickel–molybdenum < annealed nickel–phosphorus < nickel–phosphorus < iron material. Heat treatment at 400 and 500 °C, respectively for Ni–P and Ni–Mo alloys, significantly increases hardness due to the precipitation of intermetallic compounds such as Ni3P and Ni4Mo phases. Comprehensive data analysis shows that the annealed nickel–molybdenum coating has the best electrical ablation wear resistance. The possible reason for that might be attributed to the high hardness of the heat-treated nickel–molybdenum coating. In addition, the thermal resistance capability of molybdenum is better than that of phosphorus, which might also contribute to the high wear resistance to electric ablation.

Study of Friction Force in Electrodynamic Rail Accelerator: Experiment and Interpretation Using FEM Modelling

The paper presents experimental data and a model of an electromagnetic rail accelerator. The model includes an equivalent circuit, magnetic field in the system and movement of the projectile (that is solved separately) which is computed numerically. The main results are compared with our experimental data and friction force during acceleration is evaluated.

A multi-field coupling model for the magnetic-thermal-structural analysis in the electromagnetic rail launch

The magnetic-thermal-structural performances (MTSP) in an electromagnetic rail launcher have a significant influence on the successful launch capability. However, it is difficult to explore the MTSP directly through the experimental measurement due to the approximately adiabatic processes in the in-bore environment of the launcher, which further limits us to understand the multi-field properties in the electromagnetic launch process. Considering the interaction between the magnetic field and the thermal field, a transient multi-field coupling model is proposed to investigate the MTSP for the electromagnetic launch based on the finite element method in this paper. The model validation is presented through a comparison of the model prediction with the experimental data of the magnetic flux density and the temperature. The MTSP for an electromagnetic railgun are then analyzed in detail with the effect of the pulse power supply parameter and rail sizes. The results show the pulse power supply parameter has a significant effect on the MTSP near the electromagnetic railgun breech and the rail damage can be decreased with a larger rail size. Moreover, we found the rail was most easily to damage at the rail edge position of the inner sidewall, which is consistent with the groove-shaped damage position in the rail after an experimental test. The results of these investigations will help improve the design of an electromagnetic launcher.

Large-Scale PFN Fault Diagnosis Method Based on Multidimensional Time Series Anomaly Detection Using Convolutional Neural Network

The fast fault diagnosis of large-scale pulse-forming network (PFN) of electromagnetic rail launch system is of great significance. It is an important research direction to diagnose the PFN fault by detecting the anomaly of multidimensional time series in each pulse-formatting unit (PFU). Due to the high sampling rate of time series and the characteristics of aperiodic instantaneous pulse, the current time series diagnosis method is not suitable. Multidimensional coupling aggravates the complexity of the problem. In order to solve the problem, this article proposes a method of multidimensional time series anomaly detection based on convolutional neural network. First, the multidimensional time series is transformed into a gray-scale image, which can reflect the health status of a PFU. Second, a deep convolution neural network is constructed to identify the abnormal images based on the existing data trainers. Finally, a convolution neural network is constructed to locate the fault. The results show that the model can identify 100% of the abnormal PFU waveform, and the fault classification model can also accurately locate the fault, which proves the effectiveness of the proposed algorithm.

Numerical Analysis of a Transposed Multiwired Armature in Electromagnetic Rail Launchers

Solid armatures in electromagnetic rail launchers have to undergo severe electromagnetic, mechanical, and thermal stresses. These stresses are unevenly distributed in the armature mainly due to the velocity skin effect. Contrasting this effect reduces the peak to average ratio of the stresses and allows better performance of the device. In this article, the behavior of a transposed multiconductor solid armature is numerically investigated by the research code electric network for electromagnetics (EN4EM) developed at the Department of Energy, System, Territory and Construction Engineering (DESTEC), University of Pisa, Pisa, Italy. The code is based on an integral formulation that reduces the magnetic diffusion problem in the analysis of a time-varying electric network. The code enables a strong electromechanical coupling and allows accounting for currents’ distribution in the rails and in the armature due to the proximity and “ordinary” skin effects, as well as the velocity skin effect. Preliminary computations have shown an improved (more regular) current density distribution in the armature. This allows increasing the total current on the armature without reaching the melting temperature in the armature. Improved performance of the launcher with transposed armature is predicted.

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.

Numerical 3D Simulation of a Full System Air Core Compulsator-Electromagnetic Rail Launcher

Multiphysics problems represent an open issue in numerical modeling. Electromagnetic launchers represent typical examples that require a strongly coupled magnetoquasistatic and mechanical approach. This is mainly due to the high velocities which make comparable the electrical and the mechanical response times. The analysis of interacting devices (e.g., a rail launcher and its feeding generator) adds further complexity, since in this context the substitution of one device with an electric circuit does not guarantee the accuracy of the analysis. A simultaneous full 3D electromechanical analysis of the interacting devices is often required. In this paper a numerical 3D analysis of a full launch system, composed by an air-core compulsator which feeds an electromagnetic rail launcher, is presented. The analysis has been performed by using a dedicated, in-house developed research code, named “EN4EM” (Equivalent Network for Electromagnetic Modeling). This code is able to take into account all the relevant electromechanical quantities and phenomena (i.e., eddy currents, velocity skin effect, sliding contacts) in both the devices. A weakly coupled analysis, based on the use of a zero-dimensional model of the launcher (i.e., a single loop electrical equivalent circuit), has been also performed. Its results, compared with those by the simultaneous 3D analysis of interacting devices, show an over-estimate of about 10–15% of the muzzle speed of the armature.

Interior Ballistic Characteristics of Electromagnetic Rail Launcher Under Continuous Firing

According to the characteristics of an actual electromagnetic rail launcher (EMRL), this article points out defects in the traditional dynamic response model of EMRL, proposes an improved dynamic response model, and analyzes its dynamic and stopping response characteristics. On this basis, it presents a fast and accurate numerical calculation method for three-dimensional transient electromagnetic (EM) force of the EMRL and an order-reduced model of EMRL dynamic response. Furthermore, the second development of commercial software leads to the establishment of an interior ballistic simulation model with EM-structural coupling. The model is used to analyze the interior ballistic characteristics of the EMRL under sequential discharge and continuous firing. The finding is that the dynamic response of the first launching rail will cause a deformation in the second launching rail, in which a greater fluctuation happens. When the time interval between successive launches reaches 1.0 s, the deformation of the second launching rail will no longer be affected by the dynamic response of the first launching rail.

Pulsed-Current Distribution in Electromagnetic Rail Launchers

This article deals with the measurement of current distribution through the rail cross section of an electromagnetic rail launcher. A measurement approach based on a loop system magnetically coupled to the launcher that is placed along the rails is proposed. The estimation of the current distribution in the rail, following the basic rules of the partial-inductance method, is discussed in this article. To test the proposed method, an experimental analysis on an “ad-hoc”-developed multiconductor rail prototype supplied by a high-voltage capacitor bank is presented. The experimental results obtained by the proposed method were compared with the direct-current measurements achieved by a set of Rogowski coils showing good agreement for different current values.

Interior Ballistic Characteristics of Electromagnetic Rail Launcher Considering the Dynamic Characteristics of Real Launcher

In this article, we have presented a three-dimensional transient electromagnetic (EM) force calculation model of the electromagnetic rail launcher (EMRL), which could quickly calculate the transient EM force of the armature and the rail through combining the finite-element method with experiment and proposed the model of structural stiffness nonlinearity of EMRL. To study the interior ballistic characteristics of the EMRL, through the self-programming and the development of commercial finite-element software for the second time, the article presents the first time that an interior ballistic simulation model (IBSM) of the EMRL with EM and structural coupling considering the structural stiffness nonlinearity of EMRL. The correction function is proposed to improve the prediction accuracy of armature dynamic parameters by IBSM and the calculation errors of displacement of IBSM can be guaranteed not to exceed 1% compared with the test results of magnetic probes array. A strain test platform with a demodulation frequency of 8000 Hz was established to verify the IBSM's ability to calculate dynamic characteristics of the armature and the rail. After considering the structural stiffness nonlinearity of EMRL, the simulation accuracy of IBSM has been greatly improved compared with that of linearity. The experimental test results show that the IBSM is ease of application and, meanwhile, performs satisfactorily in terms of high accuracy and low computation.

An initial velocity model study of electromagnetic railgun based on back propagation neural network

The velocity of launch has been the key factor restricting the application of electromagnetic rail. For electromagnetic launch system, the structural parameters change directly or indirectly affect the Launching velocity of the electromagnetic launch system. In order to improve the initial velocity of the electromagnetic railgun. The mathematical model of electromagnetic rail gun launch was set up, the structure parameters of armature and the size of the pretension force between armature and orbital were variables, based on the target function, The equivalent model of rail gun BP neural network is established by using the calculation results of mathematical model, and the model of rail gun BP neural network was optimized by electromagnetic emission test data. The error of rail gun BP neural network model optimized by experimental data is 18.5% lower than that before optimization and 6.5% lower than that of experimental data. The results show that the launch speed of the optimized rail gun BP neural network model is closer to the actual speed.

Study on Lubrication Characteristics of Metal Liquid Film Based on Electromagnetic-Elastic Mechanics-Hydrodynamics Multiphysics Coupling Model.

In an electromagnetic rail launcher, a metal liquid film is created at the armature/rail (A/R) contact interface. It has a significant impact on electromagnetic launch performance. In this paper, an electromagnetic-elastic mechanics-hydrodynamics multi physics coupling model is established in consideration of the metal liquid film’s own acceleration, magnetic pressure and dynamic changes in film thickness. Based on this model, the lubricating characteristics of magnetic pressure and fluid pressure distribution, film thickness distribution and velocity distribution of the metal liquid film were studied. When the velocity of the metal liquid film is very fast, and the magnetic pressure is reduced, it may fail to maintain stability and rupture, which may be an important reason for the transition. Finally, this paper analyzes the lubrication effect of the metal liquid film, and points out that when we want strictly to control the muzzle velocity, the lubrication effect of the metal liquid film must be considered.

Thermal Analysis in Electromagnetic Rail Launcher Taking Friction Heat into Account Under Active Cooling Condition

A high-efficiency thermal management system is one of the key points in the practical application of electromagnetic rail launcher (ERL). In this paper, the thermal characteristics in ERL with the section of rectangle, convex, and concave rails by active cooling under different friction coefficient condition are investigated. By two cooling approaches, at two launch rates, with four friction coefficients, peak temperature in convex rails at the same moment is minimum in three types rails. Joule heat dominates in three shapes rail by channel or surface/channel cooling approach, but friction heat is a nonnegligible part under multiple launching mode. The spatial and temporal distribution features of peak temperature of three shapes rail with different friction coefficient under active cooling condition are compared. The mathematical relations between friction coefficient, time and temperature rising caused by friction at pulse end time and shot end moment in ERL with the three types rail are obtained, respectively. In terms of obtaining lower maximal temperature in rail, the ERL with convex rails is the best one.

Electromagnetic plasma rail accelerator for surface analysis and modification in solids

In this study we investigate the possibility of using plasma rail accelerator as a dense plasma jet generator for scientific and technological purposes. It was found that plasma railgun can generate supersonic plasma jets, both pure and saturated with solid and liquid microparticles. Such jets can cause thermal and mechanical erosion of the target surface, sputtering material of the railgun channel and transferring it to the surface being treated. We studied working regimes of the plasma railgun. SEM and optical micrographs of the treated samples were obtained.

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.