雷击建筑物的先导连接过程模拟

Simulation of Lightning Leaders and Connection Process with Structures

为了研究闪电先导与地物的相互作用,该文建立了一个闪电先导的二维模式以模拟雷击建筑物的先导连接过程。模拟得到梯级长度在13.8～51.5 m的范围内,下行先导的感应电荷为0.03×10^(-4)～1.2×10^(-4) C/m,梯级长度和感应电荷量均随着先导离地高度的下降而增加,模拟结果与观测值相吻合。下行先导最后一跳之前的转向并不明显,但最后一跳,下行先导向避雷针产生的上行先导偏转一定角度。模式模拟了下行先导与40 m宽度的建筑之间的相互作用和连接过程,得到建筑物拐角也具有一定的吸引半径,避雷针和拐角之间存在竞争关系。因此,在雷电防护设计中需要考虑拐角等复杂结构尖端对闪电的吸引作用,简单地采用理想情况(如地面孤立高耸尖端)下避雷针的吸引半径等参数进行复杂建筑物的防雷设计会存在问题和隐患。

Lightning is a kind of long-distance discharge phenomenon,and it often causes a variety of disasters which become more serious by the extensive use of electronic devices particularly.With deep understanding on physical processes of lightning occurrence and development,lightning leader model is established based on observational facts to study development of lightning leader and its interaction with structures and provide reference for lightning protection.In order to study the interaction of lightning leaders and structures, the connection process of leaders is simulated.A 2-dimension model of lightning leader is developed by simulating ambient potential distribution using an over relaxation method.In the model,the direction of next leader step depends on the position of a maximum potential gradient.Attractive radius in the model is defined by horizontal distance between initial axis of downward leader and connection point（such as lightning rod,the corner of building）.The distance of final jump is defined by the distance between the tip of downward leader before final jump and connection point.Simulation results show that the length of stepped leader ranges from 13.8 m to 51.5 m.The induced charge of downward leader is about 0.03×10^（-4）—1.2×10^（-4） C/m.The length of stepped leader and the induced charge of downward leader increase with the propagation of downward leader.These simulated results are consistent with the observation.Before the final jump,the turning of downward leader is not obvious.In the final jump,downward leader turns some direction towards the upward leader initiated from lightning rod.Simulation results are accord- ant with the previous simulation results. The interaction and connection process between downward leader and a structure with a width of 40 meters are simulated using this model.The corner of structure has some attractive radius and can compete with lightning rod on structure.In the design of lightning protection,attractive effect of corner to lightning leader can＇t be neglected.The design of lightning protection based on attractive radius of lightning rod under perfect conditions（such as isolated tip on the ground） is problematic and risky.