Implementing Simulations Of Lightning Electromagnetic Pulse In Grid Computing Environments

Grid computing provides a kind of distributed computing environment, in which implementing real-time calculation and simulation of electromagnetic field is very significant for building rapid flexible distributed simulation platform on Internet/ Intranet. A physical model for nature lightning is built in this paper, analytical and numerical methods for calculating lightning electromagnetic plus (LEMP) are studied, computer program about numerical calculation and simulation is developed and implemented in Grid computing environment. The main contents include the following five aspects. About current models of lightning, the mechanism and characters of nature lightning are described at first, six engineering models about return-stroke current are calculated and discussed, and features of every model are compared. Especially, Diendorfer-Uman (DU) model is studied and discussed, its base current waveform and expression are presented in this paper. About theoretic calculation for lightning electromagnetic field, two analytical methods are raised, which are dipole method in time domain and time-varying field method in frequency domain. By using these two methods, Maxell's equations for vertical channel, oblique channel, tortuous channel and channel branches are solved respectively. By building a dipole model for lightning, differential equations regarding horizontal electric field Er, vertical electric field Ez and tangential magnetic field Bφof any field point in lightning space are derived. For Ez and Bφof field points on ground, analytical formulations are derived directly. By Fourier series expansion of lightning current waveform in time-varying field, analytical formulations in frequency domain are derived. In addition, a calculating formula for LEMP power is also presented. About numerical calculation for lightning electromagnetic field, two numerical methods based on analytical formulas are studied. The numerical method from dipole formula is obtained by scattering lightning current at time and space, and the numerical method from time-varying field formula is obtained by scattering lightning current at time. With finite difference time domain(FDTD) method, lightning space is dispersed and electromagnetic fields for whole free space are solved. Errors between two methods are analyzed and compared, the results indicate values of electric field and magnetic field from two numerical methods are consistent with classical analytical methods. With the proposed dipole method, the effect of channel height, return-stroke speed and ground permittivity on electromagnetic field is analyzed, and some significant conclusions are obtained. At the aspect of Grid computing, application background, infrastructure and popular Grid computing toolkit Globus Toolkit 3 (GT3) are introduced in this paper. With an example of calculating lightning electromagnetic field, methods for GT3 configuration and programming are described in detail. In Grid computing environment, computer programs for calculating and simulating lightning electromagnetic field are developed, and a distributed web-based simulation system with multi-tier architecture and Grid environment is implemented. In addition, results and characters of lightning electromagnetic field are discussed as well. Finally, the work in this paper is summarized and some creative research about the study are indicated, which are methods for calculating oblique channel, tortuous channel and branches are presented; two numerical methods, dipole method and time-varying field method, for calculating electromagnetic field of any point in lightning space are presented; and distributed parallel calculation and simulation are implemented in Grid computing environments. Besides, the further research problems are indicated.