Three-dimensional Simulation Study Of Multi-lead Connection Process Of Tall And Short Buildings

A large number of optical observation showed that in the lightning attachment process,with the propagation of downward leader,multiple upward leaders were usually initiated.In order to deepen the scientific understanding of the near ground multiple upward leaders attachment process,a three-dimensional multiple upward leaders model has been used to carry out CG lightning simulation sensitivity tests with high and low buildings as the underlying surface.By changing the height of the high building to discusses the different situations and influencing factors of the attachment process in the case of multiple upward leaders.In addition,in view of the limitations of the previous model,we improved it,and conducted the same sensitivity test as the original model to explore the behavior characteristics of downward leader selection connection,and compared it with the original model.Finally,three groups of sensitivity tests under the same spatial configuration were carried out by using the new model to explore the effects of the height of the high building,the horizontal spacing of the high and low building and the initial potential of downward leader on the initiation of multiple leaders and strike points distribution in the lightning attachment process.The main conclusions are as follows:1.The probability of initiating upward leader on a low building is small,but once it initiates upward leader,it is more likely to be struck.The height difference between buildings is the main factor affecting the lightning attachment process.When the height difference between buildings is small,if the downward leader channel is biased towards the low building,the low building can give priority to initiate upward leader and have a high probability of being struck;With the increase of the height difference between buildings,when the downward leader channel is obviously biased towards the low building and keeps approaching them,the low building may initiate upward leader later and have a certain probability to be struck;When the height difference between buildings exceeds a certain threshold,the spatial form of the downward leader has little effect on the lightning attachment process.The low building will neither initiate upward leader nor be struck.2.At different heights of the high building,the times that the low building initiate upward leader first and has been struck is less than that of the high building.The times that the downward leader connects with the first upward leader is greater than that with the subsequent upward leader,and the gap becomes larger with the increase of the height of the high building.However,in the case of multiple buildings with multiple upward leaders,the number of connections between the downward leader and the first upward leader is less than that with the subsequent upward leader.The initial position of downward leader,the development of subsequent branches,the induced distance and initiated time of multiple upward leaders will affect the selective connection of downward leader.3.The effects of various parameters on the upward leader initiation and strike points distribution in the attachment process of the high and low buildings are as follows: the higher the high building is,the less likely the low building is to be struck,and the more difficult it is to initiate upward leader.The protective effect of the high building on the low building increases with the increase of the high building.The horizontal distance between the high and low buildings mainly has a great impact on the initiation of upward leader of the low building.The greater the horizontal distance between the high and low buildings,the more times the low building is struck and the more the number of initiated upward leaders.At this time,the factors affecting the attachment process on the high and low buildings are mainly the height of the building itself and the initial potential of downward leader.The initial potential of the downward leader has a great influence on the initiation of upward leader in the attachment process.The stronger the initial potential of the downward leader is,the more the total number of upward leaders initiated from buildings.The proportion of the number of upward leaders initiated from the low building to the total number of upward leaders decreases with the increase of the initial potential of the downward leader,resulting in the decrease of the strike number.