|Title:||Lightning-caused surface charge/current density on metallic roof of structure|
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Building Services Engineering|
|Pages:||x, 70,  leaves : ill. (chiefly col.) ; 30 cm.|
|Abstract:||In previous lightning research, there are few discussions on the prediction of lightning and the effects of downward leader on building structures before lightning strike. These are the main motivation to implement the current research project. The research purpose is to establish a lightning model with numerical and graphical simulations and evaluate the existing standard of lightning protection methods in International Electrotechnical Commission Standard (IEC) 62305. In this study, lightning phenomenon factors from lightning models by previous researchers has been compared and summarized. Fundamental electrostatic theories including Poisson's equation and Coulomb's Law are employed to develop a lightning model with reasonable lightning factors such as 10 kV/m, ambient electric field and 10m diameter of downward leader. COMSOL Multiphysics software by using Finite Element Method (FEM) is also applied to simulate a series of 3D lightning models on the computation of the strength of electric field and the surface charge density on the metallic roof under thundercloud conditions with and without downward leader. The results of the investigations have demonstrated (i) the strength of electric field and surface charge level, (ii) the intensification factors of electric field and surface charge density intensified by varied structure height and the shielding effect of adjacent structures and (iii) the evaluation of the collection area applied on lightning protection system in IEC 62305. By the numerical analysis in this research, the current induced on the metallic roof by time-varying change of induced charges under different velocity of downward leader is achieved and thus a possible prediction method such as current sensing equipment could be developed to give an approaching lightning warning for "Active" lightning protection.|
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