起伏地表下建筑物顶端雷电回击电磁场特性模拟研究

Simulation study on lightning-radiated electromagnetic field characteristics on top of building over complex mountainous terrain

采用时域有限差分(finite-difference time-domain,FDTD)法,分析研究起伏地表下建筑物顶端的雷电回击电磁场特征,给出了锥形山体上的建筑物对雷电回击电磁场的影响,并进一步对真实地形山顶建筑物的雷电回击电磁场的传播特性进行了仿真研究。结果表明:相比于平坦地表,锥形山体的角度和建筑物高度会对雷电回击电磁场产生影响。锥形山体角度越大,垂直电场和水平磁场的峰值越大,且垂直电场峰值呈线性增长,锥形山体引起的电场峰值与平坦地表的电场峰值比为4~8;山顶建筑物的高度越高,垂直电场波形的峰值越大,山顶建筑物高度引起的垂直电场峰值与山顶无建筑物时的垂直电场峰值的比值基本呈对数增长,高度小于100 m时,增幅为100%~150%;随着雷电回击通道与山体之间观测距离的增加,建筑物高度增加引起的垂直电场的峰值先增强再逐渐减弱。以青岛大涧山雷达塔为例的仿真结果表明,建筑物顶端的雷电回击垂直电场的峰值明显大于理想平坦地表的情况,且其峰值增大了3.8倍,但是对水平磁场影响非常小。

In this paper,we present the computed electromagnetic field properties of lightning irradiation on top of buildings over a complex mountainous terrain,using a two-dimensional finite difference time-domain method in cylindrical coordinates.Analyze the effects of lightning-radiated electromagnetic fields on the top of building over a cone-shaped mountain and over real terrain,respectively.It is found that compared with the flat ground,the mountain inclination angle and building height have a significant effect on the lightning-radiated electromagnetic field.The peak values of the vertical electric and azimuthal magnetic fields become larger as the inclination angle of the mountain increases.The peak value of the vertical electric field increases linearly,the ratio of the peak electric field induced by the conical mountain to that induced by the flat surface ranges from 4 to 8.as the building height increases,the peak value of the vertical electric field increases logarithmically,with an increase of 100 to 150 percent when the building height is less than 100 m;as the distance between the return stroke of the lightning and the mountain increases further,the increment of the vertical electric field peak first increases and then decreases due to the increase of the building height;taking the radar tower standing on Dajian Mountain in Qingdao as an example,the peak value of the vertical electric field at the top of the building is significantly larger than that of the ideal flat ground,which is increased by 3.8 times,however,there is a little effect on azimuthal magnetic field.