No abstract

To study some of the mechanisms in passive electromagnetic armor (PEA), the pulse current skin effect and the action of the current along the length of a shaped charge jet as it passes through PEA are researched. Considering the different characteristic of the pulse current from the alternating current, a frequency domain analysis method of skin effect is introduced. With the background of PEA, time and frequency characteristics of the pulse current are analyzed based on the equivalent circuit model, and calculation method of the pulse current density distribution in shaped charge jet is obtained. Consequently, the skin depth during the discharge is researched. The validity of the method is approved by contrasting it with the Finite Element Method analysis results. Finally, a distribution of the specific action in the shaped charge jet elements is obtained based on the action time model. The results indicate that pulse current has a broadband, and its skin effect phenomenon is different from that of an alternating current. It shows that current density increases with the decrease in depth not all the time, but declines on the surface of the conductor at the trailing edge of the pulse current. And the specific action is concentrated on the tail of the jet whose velocity is less than 4 km/s. While the action in the radial direction becomes larger, the element gets closer to the surface.Index Terms-Current density, frequency-domain analysis, passive electromagnetic armor (PEA), pulse current, skin effect.

The lateral deviation and bend of shaped-charge jet (SCJ) are generated when the SCJ penetrates the passive electromagnetic armor (EMA). The lateral deviation is caused by the transverse electromagnetic force and the bend is caused by kinking instability and the transverse electromagnetic force, bending and lateral deviating effects coexist and affect the penetration of SCJ together. In this paper, two 3-D simulation models are developed to study bending and deviating effects produced by passive EMA on SCJ. After all, the static analog experiments proceed by copper wire which diameter is 2mm, the bending degree increases with the rising of voltage, when charging pulse voltage exceeds to several kilo-voltage, the breakup of copper wire appears. Besides, the protected experiments of the passive electromagnetic armor against SCJ proceed by armor piercing projectiles, the deviation of SCJ can be seen from the splash on the back plates. The results of simulations and experiments demonstrate that deviating and bending of SCJ can destroy the axial continuity of SCJ remarkably, which decreases the penetration of SCJ and improves the defense performance of passive electromagnetic armor ultimately.

When Shaped-charge Jet (SCJ) penetrates front armor and approach to back armor, powerful pulse current flows it immediately and produces θ magnetic field simultaneously. Due to the effect of electromagnetic force F J B= × , the necking of SCJ occurs and leads to the breakup of SCJ into individual fragments and the penetration capability of SCJ is decreased significantly. In this paper, in order to improve defense capability of the passive electromagnetic armor against SCJ, the necking mechanism of the high-temperature SCJ is studied through Maxwell's equations and elastic-plastic constitutive equations. A 3-D simulation model, supposed to be sine-disturbance and axialsymmetry, is developed to analyze the necking law of SCJ through electromagnetic-structure co-simulation. Take the skineffect of pulse current into account, the distribution of current density, magnetic field, magnetic force and stress field are obtained through electromagnetic-structure co-simulation by finite element software, and the SCJ deformation is also calculated. The results indicate that, a powerful pulse current can accelerate the break-up of SCJ. At last, defense experiments of the passive electromagnetic armor against SCJ with high explosive anti-tank cartridge proceeded. The results demonstrate that, the penetration capability of SCJ with pulse current is lower than that without pulse current, and the penetration capability of SCJ declines remarkably with the increasing of charging voltage.

Abstract. Onboard magnetic flux compression generator (MFCG) would be used widely in new types of projectiles that need huge electric energy, while the inductance variation is significant for onboard MFCG design. In order to achieve the inductance variation, image current model was applied to the circuit parameters calculation of an onboard MFCG. And the inductance variation expression was derived. Subsequently, by simulation software MATLAB, a numerical computation program of onboard MFCG inductance variation was written within deriving process. Curve of inductance change was achieved after substituting design parameters and computing, and next optimum design and experiments benefit from it.