Simulational analysis on electromagnetic field evolution in launching process of a series enhanced electromagnetic railgun based on the moving-window method
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摘要: 简要介绍了Railgun3D程序的主要控制方程，使用Railgun3D程序对串联增强型轨道炮发射过程进行了模拟，详细分析了一复杂构型的电枢在梯形驱动电流加载外轨道/电枢上电磁场的演化过程，对电流涡结构、电流趋肤效应进行了讨论。计算中观察到了不同于普通单轨的现象，由于增强轨道的存在，驱动电流在增强轨道上产生了较大的磁场，由于电磁感应，在内轨道炮口一端上有显著的磁场和电流分布，感应电流的大小依赖于驱动电流的变化率。计算给出了多个时刻电枢附近电流涡结构的演化过程，并在电流下降段，电枢后表面上电流出现反向，指出该效应可能是导致电枢与轨道接触应力不足、甚至出现电枢转捩的重要因素。通过中心对称面上电流密度云图，模拟结果显示出磁扩散与速度趋肤效应在整个过程中的相互竞争决定了电流的分布形态。Abstract: It is very important to simulate and analyze the evolution of the electromagnetic field on the armature/rail in the electromagnetic emission process for optimizing and improving the design of the rail and armature, which is the main basis for controlling the temperature rise of the rail, armature and armature transition. Series enhanced trajectory design is an effective way to improve projectile initial velocity and launch efficiency under the condition of inherent energy storage. In this design, the magnetic field strength on the armature is increased through the series current of the circuit, thus improving the emission ability. A mathematical and physical model is established for the series enhanced orbit. The main control equations of the Railgun3D program are briefly introduced in this paper. The moving window FE/BE Hybrid simulation method is adopted to simulate the series reinforced railgun. This method can make more efficient use of computer resources and focus the simulation on the vicinity of the rail/armature interface. The evolution process of the electromagnetic field of a complex rail/armature under trapezoidal driving current is analyzed in detail. Due to the existence of the enhanced orbit, the driving current produces a large magnetic field on the enhanced orbit. Due to electromagnetic induction, the corresponding induced current will be generated on the inner orbit, that is, there are significant magnetic field and current distribution on the orbit at one end of the muzzle. The magnitude of the induced current depends on the change rate of the driving current. The distribution of current direction near the armature at several times is given, and the evolution process of the current vortex structure is observed. In the current drop section, the results of current reversal on the surface behind the armature are given. It is pointed out that this effect may be an important factor leading to insufficient contact stress between the armature and the track, and even the occurrence of armature transition. Through the current density nephogram on the central symmetry plane, the simulation results show the competition mechanism between magnetic diffusion and velocity skin effect in the whole process.
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图 1 串联增强型轨道炮的轨道和电枢设计示意图（四分之一模型）
Figure 1. Schematic diagram of rail and armature design for a series enhanced railgun (1/4 model)
图 3 48 ns时刻磁场与电流密度分布
Figure 3. Distributions of magnetic field and current density at 48 ns
图 4 108 ns时刻磁场与电流密度分布
Figure 4. Distributions of magnetic field and current density at 108 ns
图 5 204 ns时刻磁场与电流密度分布
Figure 5. Distributions of magnetic field and current density at 204 ns
图 6 348 ns时刻磁场与电流密度分布
Figure 6. Distributions of magnetic field and current density at 348 ns
图 7 两个不同时刻的电流密度分布与电流方向
Figure 7. Current density distributions and current directions at two different moments
图 8 348 ns时刻电流密度分布与电流方向
Figure 8. Current density distribution and current direction at 348 ns
图 9 348 ns时刻电流密度分布与洛伦兹力方向
Figure 9. Current density distribution and Lorentz force direction at 348 ns
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