期刊
GEOPHYSICAL JOURNAL INTERNATIONAL
卷 203, 期 3, 页码 1541-1574出版社
OXFORD UNIV PRESS
DOI: 10.1093/gji/ggv377
关键词
Numerical solutions; Numerical approximations and analysis; Electrical properties; Electromagnetic theory; Marine electromagnetics
资金
- Research Council of Norway through Petromaks program
We have developed an efficient numerical scheme for 3-D electromagnetic (EM) simulations using an exponential finite-difference (FD) method with non-uniform grids. The method uses the set of exponential basis functions {1, exp[+/-(nu(x)x + nu(y)y + nu(z)z)]}, where the exponents nu(x), nu(y) and nu(z) must be chosen carefully depending on the simulation frequency and local node conductivity. The method achieves an approximation of the oscillatory and exponentially decaying EM fields that is better than that obtained via the low-degree polynomial fitting from standard FDs- and hence also leads to more accurate results. An important property of the exponential FD method is that it tends to the standard FD method when the exponents nu(x), nu(y) and nu(z) tend to zero. We applied the standard and exponential FD methods to three marine controlled-source EM modelling scenarios: deep-water, shallow-water and intermediate water depth. For the deep-water scenario, we found that the proposed exponential FD method gave two to three times more accurate results as compared to the standard FD method on the same grid. For the shallow-water and intermediate water depth scenarios, the exponential FD method improved the accuracy of the upgoing fields; it gave 2-2.5 times more accurate results for the upgoing fields than the standard FD method on the same grid. Consequently, the method can achieve the same accuracy with a coarser grid and hence is faster than the standard FD method, as demonstrated using a frequency-domain iterative solver.
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