瞬变电磁法正演计算进展

Progress of forward computation in transient electromagnetic method

详细介绍了瞬变电磁法正演计算的方法、现状和发展趋势.瞬变电磁法一维正演计算需要将电磁场从频率域转换至时间域,转换方法有三种,分别是Gaver-Stehfest算法、余弦变换和Guptasarma算法.在这三种方法中,使用较多的是Gaver-Stehfest算法和余弦变换,Gaver-Stehfest算法速度较快,但精度不及余弦变换.瞬变电磁法的数值模拟主要集中于2.5维和三维,使用的数值计算方法有积分方程法、有限差分法、有限单元法和SLDM法.积分方程法主要在三维数值模拟中使用,现已很少使用;有限差分法和有限单元法是目前瞬变电磁法2.5维和三维数值模拟的主要方法;SLDM法主要应用于三维数值模拟.我国瞬变电磁法正演计算成果主要集中在回线源激发的瞬变电磁场一维数值计算和利用有限单元法进行2.5维和三维数值模拟.瞬变电磁法正演计算的发展趋势有:数值算法的改进、提高计算效率和研究地形对瞬变电磁场的影响规律.

In this paper, the method, current situation and development tendency of TEM forward computation were introduced in detail. Electromagnetic field is transformed from frequency domain to time domain in 1D TEM forward computation. Gaver-Stehfest algorithm, cosine transform and Guptasarma algorithm are three transform methods. Among these three methods, Gaver-Stehfest algorithm and cosine transform are used mostly. Gaver-Stehfest algorithm is faster than cosine transform, and is less accuracy than cosine transform. Numerical simulation of TEM focuses on 2. 5D and 3D, using integral equation method （IEM）, finite difference method （FDM）, finite element method （FEM） and SLDM. IEM, mainly in the use of 3D numerical simulation, has been used very little. At present, FDM and FEM are primary methods in 2. 5D and 3D TEM numerical simulation. SLDM is mainly used in 3D numerical simulation. In China, some influential results of forward computation of transient electromagnetic field excited by loop source have been obtained, for example, 1D numerical computation by G-S algorithm, and 2. 5D and 3D numerical simulation by FEM. Improving numerical algorithm, enhancing efficiency of computing, and studying the impact of terrain on transient electromagnetic field are three development tendencies of TEM forward computation.