Bin Lei

Analysis on Thermal Character of Interface Between Rail and Armature for Electromagnetic Railgun

The thermal character of the interface between rail and armature significantly affects the launch performance of electromagnetic railguns. In this paper, the friction coefficient μ between brass and aluminum is discussed; it is found that, under hypervelocity and electrical contact conditions, μ maintains an order of magnitude of 10-2 or less, which is smaller than that under normal conditions. A 2-D simulation model is developed to analyze the temperature character of armature contact surface caused by friction, and the simulated results concretely demonstrate the order of magnitude of μ when armature is launching in bore. Another 3-D simulation model is also developed to obtain the temperature distribution on the armature contact surface under high current. According to simulation results of interface temperature distribution, the thermal effect on armature wear and contact performance is analyzed. For an electromagnetic railgun with hypervelocity and high current, it is concluded that the heat generated by friction and high current can cause armature surface film to melt and cause armature edges of ends to be damaged. The aluminum film is helpful to improve the contact performance.

Analysis of Parameter Sensitivity of Induction Coil Launcher Based on Orthogonal Experimental Method

There are many parameters that can affect the launching efficiency of the induction coil launcher (ICL), but which parameter is the most important factor to the launching efficiency still needs further study. Taking the 82-mm caliber ICL, for instance, eight parameters of the ICL were chosen to analyze based on orthogonal experimental method, and then the tables of the parameter level and orthogonal experiment were built, respectively. After that a simulation model of the ICL was built and each experiment scheme in the orthogonal table was analyzed by simulation, and then the launching efficiency of each experiment scheme was obtained. Furthermore, the range analysis method was used to analyze the parameter sensitivity of the ICL. The research results show that the parameter sensitivity of the ICL from high to low for the analysis instance above is as follows: external radius of driving coil, trigger position, capacitance, driving coil turns, armature length, charge voltage of capacitor, driving coil length, and armature inner radius, which is useful to the parameter optimization and the design of the ICL. After that, four ICLs with different parameters were designed, with which the experiments were taken and the research results obtained from the orthogonal experimental method were verified.

Analysis of Transient Current Distribution in Copper Strips of Different Structures for Electromagnetic Railgun

A railgun is a kind of new-concept kinetic energy weapon. To overcome the local aggregation of the high pulse current on the surface of the railgun conductor, a method was introduced to abate the skin effect. On the basis of theoretical analysis, three kinds of methods were adopted to increase the current uniformity coefficient. Then, the copper strips, whose thicknesses were 40, 20, 15, and 10 mm, respectively, were simulated with a typical half-period sine waveform that had a 10-ms pulsewidth and a 2-MA peak current. The best current uniformity coefficient in the copper strips is more than 83%. Three conclusions are drawn in this paper. First, under the same conditions, the current distribution will become more uniform as the copper strips become thinner. Second, the current distribution can be improved to a certain extent by rounding strip edges. Third, the added tungsten sheaths or iron sheaths on both sides of the copper strips can further improve the current distribution. The results of this paper have great significance for improving the pulse current-carrying capability of the railgun conductors.

Design and Experiment of Reluctance Electromagnetic Launcher With New-Style Armature

In order to analyze the launching efficiency and firing accuracy of the reluctance electromagnetic launcher (REML) with different armatures, the working principle of the REML was introduced in brief at first. The effect of different armature structures to launching efficiency and firing accuracy was analyzed in theory. After that, this paper demonstrated a five-stage REML and three kinds of armatures: cylindrical armature (CA), CA with notch (CAN), and CA with tail fin (CATF). The muzzle velocity and the circumradius of projectile impact position for different armatures were got by experiment with the five-stage REML. The experiment results show that the maxim launching efficiency is 2.87% for the CAN, and the minimum circumradius of projectile impact position is 68 mm for the CATF. It can draw the conclusions that the notch in the cross section of armature can weaken or even eliminate the formation of eddy current in the armature, which is beneficial to the improvement of the launching efficiency. It can improve the firing accuracy by furnishing a tail fin at the rear of the armature.

Magnetic Flux Compression Generator as Future Military Pulsed Power Supply

As a kind of maneuverable pulsed power supply (PPS), the Magnetic Flux Compression Generator (MFCG) can be used in many military fields, but the MFCG concept has not been explored systematically. The definitions of MFCG were given in two ways: the electric circuit model and the magnetic field model, and the latter was indispensable to resolve many technical difficulties. According to the field model, the working principles of the MFCG with perfect solenoid were shown as the magnetic flux conservation or the magnetic flux linkage conservation. The inherent coherence of the two definitions was also outlined. The names of MFCGs were discussed, and the distinguishing features of MFCG from other pulsed generators were summarized. According to the different forms of the windings and the different moving modes of the armatures, 14 kinds of MFCGs were classified systematically, and their characteristics were generalized respectively. The most useful kinds of MFCGs were the piston type, the explosive one, and the rotary one. The key technology of the piston type MFCG was analyzed and the conclusion is that the conical armature without any longitudinal slits on its surface is necessary. The working process of the two stages explosive MFCG for the microwave bomb was reviewed: the first stage as a magnetic energy accumulator, and the second as an ordinary pulsed generator. The CPA, as a kind of rotary MFCG, was developed as a kind of drum alternator in the big ship to power the EM launcher. The essential work was important for MFCG concept, theory research, technology development, and military applications.

Electromechanical Performance of Rails With Different Cross-Sectional Shapes in Railgun

Railgun is a kind of electromagnetic launcher that can accelerate masses in the range from milligrams to tens of kilograms to velocities more than several kilometers per second. The cross-sectional areas moment of inertia is one of the most important mechanical properties of the rails, affecting the critical velocity and launch performance. The current distribution in the railgun determines its efficiency and contact performance of rail/armature sliding. Factors that affect the electromechanical performance of the rails include geometry and material. To improve the electromechanical performance, two types of rails with convex and concave cross sections are designed by adding and removing arch forms to/from the conventional flat rails. Modified C-shaped armatures are constructed for each rail geometry. This paper presents the results on mechanical performance on the basis of structural analysis and current distribution from coupled EM-structural simulations. The results show that the moments of inertia of convex and concave rails are larger than those of flat rails for a given cross-sectional area and rail width, but the differences in mechanical performance among the three geometries are not significant, and the advantage of rails with larger moments of inertia for a given cross-sectional area is limited. The inductance gradient of the flat railgun is larger than those of the others, and the concave railgun has the smallest; consequently, the concave railgun is the least efficient. Compared with the flat and concave rails, the current density of the convex rail is smaller at the bore-side rail surface, but greater at the contact interface, especially at the trailing edge of the armature.

On velocity skin effect — Part I: Physical principle analysis and equivalent models simulation

Velocity skin effect (VSE) is a kind of current clustering phenomenon, which occurs at the sliding contact interfaces between the high-speed armature and the stationary rails of electromagnetic railgun launchers. Serious current clustering may lead to local conductor melting, deforming, and discharge erosion, which are disadvantageous to the launching performance, but the physical principle of VSE has not been extracted and summarized so far. The typical current clustering phenomena in static conductors are classified, and the physical principle of VSE is analyzed for rail and armature respectively in this paper. The physical principle in rails is just Skin Effect because of the short risetime of the accepted pulse current, and the physical principle in armature is Clustering Near Small Source (CNSS) and Clustering Along Short Path (CASP) of steady current owing to the continuity characteristic or the voltage drop. An equivalent steady 3-dimension model has been proposed and adopted, and the quantitative distributions of current for U-shaped and cuboid armatures are simulated contrastively by Maxwell 14.0. The simulation results reveal that the current in the interface trends to cluster along the rear perimeter, and the U-shaped armature is superior to the cuboid armature. The physical principle of VSE has importance for restraining VSE.

MFCG as Future Military PPS

As a kind of mobile pulsed power supply (PPS), the magnetic flux compression generator (MFCG) can be used in many military fields, but the MFCG concept has not been explored systematically. The definitions of MFCG were given in two ways: the electric circuit model and the magnetic field model, and the latter was indispensable to resolve many technical difficulties. According to the field model, the working principles of the MFCG with perfect solenoid were shown as the magnetic flux conservation or the magnetic flux linkage conservation. The inherent coherence of the two definitions was also outlined. The names of MFCGs were discussed, and the distinguishing features of MFCG from other pulsed generators were summarized. According to the different forms of the windings and the different moving modes of the armatures, 14 kinds of MFCGs were classified systematically, and their characteristics were generalized respectively. The most useful kinds of MFCGs were the piston type, the explosive one, and the rotary one. Their technical aspects were reviewed. The key technology of the piston type MFCG was analyzed and the conclusion is that the conical armature without any longitudinal slits on its surface is necessary. The working process of the two stages explosive MFCG for the microwave bomb was analyzed: the first stage as a magnetic energy accumulator, and the second as a pulsed generator. The CPA, as a kind of rotary MFCG, was developed as a kind of drum alternator in the big ship to power the EM launcher. All those essential work was important for MFCG concept, theory research, technology development, and military applications.

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.

Essential launching characteristics of four typical electromagnetic railguns launchers models

The essential launching characteristics of four typical electromagnetic railguns models were comparatively reviewed referring to the current distribution in conductors. Such four models were as a small conductive simple railgun, the large resistive simple one, the large conductive simple one, and the large conductive complex one. First, according to strict physical theories, a small conductive copper-and-aluminum simple railgun and the proportionally-enlarged large simple railgun with deliberately-designed resistive materials could satisfy the same equations, the similar forms of current distributions, the same temperatures distributions at the corresponding positions, and the same launch velocity, etc. The small model can absolutely express the large one and vice versa. Second, the large resistive simple railgun and a conductive copper-and-aluminum simple railgun with the same structures could launch approximate projectiles to the same velocity, with the same temperature distribution on the surfaces at the corresponding positions. On the one hand, the large conductive approximate railgun is a little excellent than the large resistive one because of the less Ohmic loss; on the other hand, the resistive one has merely a little higher induction gradient than the conductive one. Third, the large conductive simple railgun carried a mal-distributed current and had a limited launching ability, while, the large conductive complex railgun carried a much evenly-distributed current and had a more powerful launching ability. The conclusions reached were: according to the large resistive simple model as a key reference lever, the small conductive simple railgun was an economic experimental facility to research the launching characteristics of both small and large conductive railguns; the large conductive complex model was a practical railgun model deserving investments for research.