雷击锥形山体对近距离电磁场影响的模拟研究

Simulation Study on the Influence of Lightning Striking to a Cone-Shaped Mountain on the Close Distance Electromagnetic Field

为研究雷击锥形山体对近距离电磁场的影响,提出了一种二维时域有限差分(FDTD)共形网格算法。利用该算法对锥形山体进行精确模拟,并具体讨论了不同山体倾角情况下回击电磁场的传输特性。相比于平坦地表(倾角为0°),雷击锥形山体时水平电场幅值随山体倾角增加而增大,当达到45°后,继续增加倾角对幅值影响较小,如土壤电导率为0. 001 S/m时,45°倾角对应的幅值为0°倾角的2. 30倍,60°倾角对应的幅值为2. 31倍;垂直电场和水平磁场幅值均随倾角增加持续显著地增大,如30°、45°和60°倾角对应的水平磁场幅值分别为0°倾角的1. 39、1. 62和1. 78倍。通过进一步分析雷电回击电磁场的时空演变情况,发现这是由于其在山体和平地之间的过渡处产生反射造成的,且倾角越大,反射越强,相应的幅值也越大。另外,锥形山体附近的垂直电场(主要是静电场分量)因山体的静电屏蔽效应而明显小于周围区域。

In order to study the influence of lightning striking to a cone-shaped mountain on the close distance electromagnetic field,a two-dimensional finite-difference time-domain(FDTD)with conformal grid algorithm is proposed.Using this method,we have accurately simulated the cone-shaped mountain and specifically discussed the propagation characteristics of the lighting electromagnetic field for different mountain inclinations.Compared with the flat ground(the inclination is 0°),the amplitude of the horizontal electric field generated by lightning striking to mountain will increase as the inclination of the mountain increases,when the inclination is larger than about 45°,it has no or little effect on the field,for the soil conductivity of 0.001 S/m,the field value for inclination 45°is 2.30 times larger than that for inclination 0°,and the field value for inclination 60°is 2.31;the amplitudes of the vertical electric field and the horizontal magnetic field will always increase with the increase of the mountain inclination,for example,the amplitude of the horizontal magnetic field corresponding to inclination 30°,45°and 60°is respectively 1.39,1.62,and 1.78 times larger than that for inclination 0°.Through further analyzing the temporal and spatial evolution of the lightning electromagnetic field,it is found to be due to reflections at the transition between the mountain and the land,and the larger the inclination is,the stronger the reflections will be,resulting in a larger amplitude.In addition,the vertical electric field(mainly the electrostatic field component)near the cone-shaped mountain is significantly smaller than the surrounding area on account of the electrostatic shielding effect of the mountain.