基于亚网格时域有限差分法的改进雷电电磁脉冲计算模型

在利用均匀网格时域有限差分法(finite-difference time domain, FDTD)计算地闪回击电磁脉冲时，空间步长选取较大会导致计算结果中后期出现震荡，所以为了计算结果的准确必须采用较小的空间步长，导致计算效率低、内存需求大。为了解决这一问题，提出利用惠更斯亚网格技术改进计算模型，改进后的模型可以实现在距离雷电通道近、高频分量多的区域采用较小的空间步长，其余区域仍采用较大的空间步长，从而以较高的计算效率消除计算结果中后期的震荡。首先，分析了空间步长对均匀网格FDTD法的各个场分量计算结果的影响；其次，通过与均匀网格FDTD计算结果对比，深入研究了改进模型对水平电场中后期震荡的消除作用。结果表明：随着步长的增大，水平电场中后期震荡剧烈；在不同地面电导率、地闪回击速度下，改进后的计算模型均能以较高的计算效率得到准确的、无震荡的计算结果。

Improved Computational Model of Lightning Electromagnetic Pulse Based on Subgridding Finite-difference Time-domain Method

The oscillations occur in the middle and late stage of the calculation result when a large space step is used in the uniform grid FDTD to calculate the lightning electromagnetic pulse. Therefore, a smaller space step must be adopted for the accuracy of the calculation result, which will in turn results in low calculation efficiency and large memory requirement. Huygens subgridding technique is used in this paper to improve the calculation model in order to solve this problem. The improved model can adopt a smaller space step in the area close to the lightning channel and with more high-frequency components, and still adopt a larger space step in other areas, thus eliminating the oscillations in the middle and later stages of the calculation results with higher efficiency. Firstly, the influence of space step size on the calculation results of the uniform grid FDTD method is analyzed, and it is found that the horizontal electric field oscillates violently in the middle and late stages with the increase of step size. Then, by comparing with the calculation results of the uniform grid FDTD, the elimination effect of the improved model on the oscillations of the horizontal electric field is studied in-depth. The results show that the improved calculation model can obtain accurate and oscillation-free calculation results with high efficiency under different ground conductivity and return-stroke speed.