Direct Time-domain Numerical Simulation Of Quasi-stationary Transient Electromagnetic Field Response In The Conductive Media

With development of electromagnetic field theory and computer performance of growth with rising,computed electromagnetism is getting quiet great progress in recently years.Among them,transient electromagnetic analysis is widely applied in many electronic engineering areas.In this dissertation,we research with the electric earth and use quasi-static characteristic of transient electromagnetic field in surveying for underground objects.To simulate the propagation law of electromagnetic field underground is a very important measure of understanding the respond of underground medium.Moreover,numerical analysis of a two-dimensional time-domain quasi-stationary field is studied by using finite-difference approach directly in time domain which is a effective method.In this paper,we directly make it in time domain,apply DuFort-Frankel format of the FD method and FDTD method to analysis the transient respond underground and interface of a two-dimensional model of line source.To derive the homogeneous diffusion equation of time-domain electric field from Maxwell's equation and do the difference discretion in the investigated region.The source is added as initial condition and the boundary is dealt with upward-continuation. Using difference equation to computer the result of electric field,and it could be shown the entire process of transient electromagnetic fields diffusing with time in the earth.Then we introduce a fictitious displacement current in order to apply FDTD method to simulate the same model,and it can obtain electric field and magnetic field at the same time.So we can have comprehensive understanding of the respond of transient electromagnetic field.Compare the results of numerical and analytical solutions in a half-space model,it indicates that the method which is dealt with boundary condition and source are right,and the precision of numerical compute can meet the need of the exploration project.We take different electromagnetism parameters and different structure to earth and targets,so it makes a great deal of simulation to the transient respond of electromagnetic field.Analysis results indicate,diffusion distance of transient electromagnetic field increases but field density attenuates along with time. Diffusion velocity is influenced by the resistivity of medium;it is slow in the low resistance body and rapid in the high resistance body.Therefore,when low resistance overburden exists,a long time is needed to detecting the same depth while high resistance overburden hardly has any affection to target exploration. Transient electromagnetic field have good resolving power to the low resistance body,but as for high resistance body it needs more identifying techniques.