Study On Simulation Of The Process Of Tall Structures Struck By Lightning Based On Stochastic Lightning Model

Considering the observed fact that most upward connecting leaders (UCL) does not branch during downward negative cloud-to-ground (CG) strikes, we modified the simulation scheme of upward positive leaders based on the existing two-dimensional (2D) stochastic lightning model so that the upward positive leader does not branch during development. In addition, we simulated two connecting behaviors, i.e., the "tip-to-tip" connecting and the "tip-to-lateral" connecting (lateral strike) between the downward leader and the UCL during the process in which lightning strikes tall buildings. For example, for a building with a height of 440 m, we simulated the connecting process between the leaders during the process of lightning striking a tall building by altering the horizontal distance (d) between the initiation point of the downward leader (at a height of 1,000 m) and the tall building. The results indicate that when the value of d increases from 0 to 700 m, the probability of a lateral strike for the UCL generally exhibits a trend of first increasing and then decreasing; it reaches a maximum of 58% when d is 500 m. As the value of d increases, the length of the UCL exhibits an increasing trend, and the ratio of the part of the UCL above the connecting point accounting for the entire length of the UCL upon the lateral strike generally exhibits an increasing trend.In order to study the height of the structure on the influence of the connection process of lightning, this paper simulates the situations for structures with different heights (100m,200m,300m,400m,500m). It shows a positive correlation between the length of UCL initiating from the top of the tall structure and the height of the structure.The higher the height of the buildings, the longer the length of the UCL starting from the top of the structure, and with the increase of d, the higher the height of the buildings the greater the increase of the length of the UCL start initiating from the top of the tall structure. When the structure is very high, the interaction of the long UCL initiating from the top of the tall structure is very high, the branch phenomenon downward stepped leader is more obvious.Presume the ratio of speed of downward leader and upward leader change with the distance between the downward leader and upward leader, rather than 4:1 before. Simulation lightning process of the 440 m high structure again. The results show that: The length of the UCL starting from the top of the structure increases obviously. The length is 1.5～2.8 times than before, and more closer to the observed the actual length of UCL. On this basis, the paper simulate the lightning connection process on the tall structures of different shapes. The results show the probability of getting struck by lightning and the length of the UCL received the influence of the shape of structure to a certain extent.