RESEARCH ON INFLUENCE OF DIFFERENT SOIL TYPES AND MOISTURE ON LIGHTNING ELECTROMAGNETIC FIELD BASED ON FDTD
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摘要: 为深入研究土壤类型和土壤湿度对雷电电磁场传播效应的影响, 首次将工程勘察领域研究得出的土壤湿度和电导率计算关系应用到雷电电磁场模拟计算中。基于Heidler雷电通道基电流函数模型和MTLL回击模型, 在Mur一阶边界条件下, 利用2D-FDTD计算粘土、粉土和砂土这三种具有代表性土壤在不同土壤湿度和观测距离下的雷电电磁场。研究结果表明: 相比于粉土和砂土, 雷电电磁场沿粘土地表传播过程中产生的水平电场更容易受土壤湿度的影响, 特别是土壤湿度较低时, 即土壤湿度从5%到6%变化过程中, 水平电场峰值的波动幅度达39.86%;当土壤类型为粘土时, 水平电场Er、垂直电场Ez和磁场Hφ受土壤湿度影响等级为Ez > Hφ; 随着闪电电磁辐射传播距离和土壤湿度的增大, 场幅值减小, 波形的波头上升沿时间变慢。研究结果为准确评估和量化不同土壤类型和土壤湿度对雷电电磁场传播的影响以及优化闪电站网定位提供了重要的科学依据。Abstract: To investigate the influence of soil type and soil moisture on the propagation effect of lightning electromagnetic field(LEMF), the present study applies the relationship between soil moisture and conductivity obtained in engineering surveys to the study of LEMF. Bases on the Heidler function, MTLL model and Mur Absorbing Boundary, the present study uses 2D-FDTD to calculate the LEMF of clay, silt and sand under different moisture conditions and observation distances. The main results are as follows: Compared with those of silt and sand, Er generated by the propagation of LEMF along clay surface is more susceptible to soil moisture. When soil moisture changes from 5% to 6%, the attenuation of the peak of Er is 39.86%. When the soil is clay, the influence of soil moisture on Er is the strongest, followed by Ez and H∅. As the propagation distance of lightning electromagnetic radiation and soil moisture increase, the attenuation of electromagnetic field intensifies, and the rise time of field waveform also increases. The results provide an important scientific basis for accurate evaluation and quantification of the influence of soil type and soil moisture on the propagation of LEMF and the optimization of the positioning of lightning station network.
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Key words:
- lightning electromagnetic field /
- FDTD /
- soil type /
- soil moisture /
- soil conductivity
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图 1 闪电通道底部基电流波形[14]
图 3 土壤电导率拟合曲线[23]
表 1 继后回击各电流参数取值
参数 数值 参数 数值 i01 10.7 kA i02 6.5 kA τ11 0.25 μs τ21 2 μs τ12 2.5 μs τ22 230 μs 表 2 电磁场分量节点
电磁场分量 r轴取样 z轴取样 时间轴取样 Er i+1/2 j n Ez i j+1/2 n Hφ i+1/2 j+1/2 n+1/2 表 3 各土壤湿度对应的电导率
电导率 p=5% p=6% p=10% p=15% p=25% σclay 0.003 5 0.009 2 0.032 2 0.060 8 0.118 1 σsilt 0.021 8 0.024 9 0.037 3 0.052 9 0.084 0 σsand 0.004 8 0.006 3 0.012 0 0.019 2 0.033 6 表 4 粘土的水平电场峰值与土壤湿度关系
土壤湿度 p=5% p=6% p=10% p=15% p=25% 峰值 118.10 V/m 71.02 V/m 33.18 V/m 20.95 V/m 12.33 V/m Δp 1% 4% 5% 10% Δ 47.08 V/m 9.46 V/m 2.45 V/m 0.86 V/m 表 5 粉土的水平电场峰值与土壤湿度关系
土壤湿度 p=5% p=6% p=10% p=15% p=25% 峰值 42.87 V/m 39.35 V/m 29.93 V/m 23.27 V/m 16.28 V/m Δp 1% 4% 5% 10% Δ 3.52 V/m 2.36 V/m 1.33 V/m 0.699 V/m 表 6 砂土的水平电场峰值与土壤湿度关系
土壤湿度 p=5% p=6% p=10% p=15% p=25% 峰值 100.20 V/m 87.44 V/m 71.02 V/m 46.38 V/m 32.21 V/m Δp 1% 4% 5% 10% Δ 12.760 V/m 4.105 V/m 4.928 V/m 1.417 V/m 表 7 垂直电场和磁场峰值差(V/m)
观测点高度 50 m 100 m 200 m 1 km ΔEz1 130 70 33 2.7 ΔEz2 90 30 14 1 ΔH1 0.03 0.03 0.019 0.06 ΔH2 0.02 0.01 0.012 0.03 表 8 各土壤湿度对应的水平电场峰值(V/m)和波头上升沿时间(μs)
湿度 50 m峰值/时间 100 m峰值/时间 200 m峰值/时间 1 km峰值/时间 p=5% 611.4/0.81 271.2/0.95 118.1/1.18 17.29/2.72 p=15% 103.4/1.18 46.82/1.35 20.95/1.65 2.974/3.22 p=25% 59.66/1.30 27.23/1.51 12.33/1.83 1.765/3.50 -
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