Simulation of Airborne Electromagnetic Measurements in Three Dimensional Environments

Alumbaugh, David; Newman, Gregory A.

doi:10.4133/1.2922151

Cited by 2 publications

(1 citation statement)

References 8 publications

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“…Previously existing material ABCs are not efficient and often give rise to large reflections. As a result, most researchers avoid using ABCs by increasing the size of the simulation region so that the electromagnetic fields will be attenuated by the lossy medium (Alumbaugh and Newman, 1995;Wang and Hohmann, 1993;Leppin, 1992;Oristaglio and Hohmann, 1984;Goldman and Stoyer, 1983). Obviously, this is only practical for high-loss cases because of limited computational resources.…”

Section: Introductionmentioning

confidence: 96%

Application of perfectly matched layers to the transient modeling of subsurface EM problems

1997

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magnetic field for a pulsed horizontal magnetic dipole embedded in a resistive whole space. The conductivity of the whole space is 0.001 S/m, the relative electric permittivity and relative magnetic permeability are equal to one. The x-directed dipole moment varies in time as where c ϭ 2f max and f max is 300 kHz. These model parameters are chosen to simulate a radio imaging method (RIM)-type transmitter with one or more horizontal wire loops lowered down the boreholes for transmission, reception, or both, operating in a moderately resistive host rock. The x-directed dipole transmitter is placed at the center of a 50 ϫ 50 ϫ 50 cell mesh. The mesh resolution ⌬x is 5 m. For comparison, an analytical solution is obtained by convolving the quasi-static impulse response [8] with the transmitter moment waveform. The model parameters are chosen such that the quasi-static assumption is a good approximation for this case. The comparison of the analytical solution and FDTD solution for the fields as they vary as a function of distance from the source is shown in Figure 1. Moderate agreement is obtained very near the source (1-5 cells), and excellent agreement is obtained further away. This is expected, as the linear representation of the fields in the FDTD algorithm is not consistent with the second-or thirdorder physical variation of the fields very near the source. Although this is a limitation to be noted, it is not a limitation for typical cross-bore surveys, where the transmitters are generally placed further from the target to increase the response they obtain from the target rock. These results are also consistent with those observed in [6] for infinitesimal electric dipoles. DISCUSSION AND CONCLUSIONSSelection and design of accurate numerical modeling techniques is a prerequisite for survey design and for other steps in the interpretation process. A method of accurately simulating the magnetic loop sources that are routinely used in cross-bore EM survey techniques was developed by adapting the standard FDTD algorithm following the method of Buechler et al. [6]. The method was validated by comparison with analytical results for a magnetic source in a resistive whole space. Further validation of the accuracy of the code was demonstrated for PEC plates exposed to realistic cross-bore EM survey tools in a moderately conducting host in [9]. This method was applied to optimization of the designs of well surveys in [9], and the accurate modeling of the sources was critical to the success of the optimization. ACKNOWLEDGMENTSThe authors thank Om Gandhi, Department of Electrical Engineering, University of Utah, for the use of software previously developed under several of his bioelectromagnetic research grants. LARGE-SIGNAL MODELING OF FREQUENCY-DISPERSION EFFECTS IN SUBMICRON MOSFET DEVICES

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Section: Introductionmentioning

confidence: 96%

Application of perfectly matched layers to the transient modeling of subsurface EM problems

1997

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Three‐dimensional wideband electromagnetic modeling on massively parallel computers

Alumbaugh¹,

Newman²,

Prevost³

et al. 1996

Radio Science

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139

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A method is presented for modeling the wideband, frequency domain electromagnetic (EM) response of a three‐dimensional (3‐D) earth to dipole sources operating at frequencies where EM diffusion dominates the response (less than 100 kHz) up into the range where propagation dominates (greater than 10 MHz). The scheme employs the modified form of the vector Helmholtz equation for the scattered electric fields to model variations in electrical conductivity, dielectric permitivity and magnetic permeability. The use of the modified form of the Helmholtz equation allows for perfectly matched layer ( PML) absorbing boundary conditions to be employed through the use of complex grid stretching. Applying the finite difference operator to the modified Helmholtz equation produces a linear system of equations for which the matrix is sparse and complex symmetrical. The solution is obtained using either the biconjugate gradient (BICG) or quasi‐minimum residual (QMR) methods with preconditioning; in general we employ the QMR method with Jacobi scaling preconditioning due to stability. In order to simulate larger, more realistic models than has been previously possible, the scheme has been modified to run on massively parallel (MP) computer architectures. Execution on the 1840‐processor Intel Paragon has indicated a maximum model size of 280 × 260 × 200 cells with a maximum flop rate of 14.7 Gflops. Three different geologic models are simulated to demonstrate the use of the code for frequencies ranging from 100 Hz to 30 MHz and for different source types and polarizations. The simulations show that the scheme is correctly able to model the air‐earth interface and the jump in the electric and magnetic fields normal to discontinuities. For frequencies greater than 10 MHz, complex grid stretching must be employed to incorporate absorbing boundaries while below this normal (real) grid stretching can be employed.

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Simulation of Airborne Electromagnetic Measurements in Three Dimensional Environments

Cited by 2 publications

References 8 publications

Application of perfectly matched layers to the transient modeling of subsurface EM problems

Application of perfectly matched layers to the transient modeling of subsurface EM problems

Three‐dimensional wideband electromagnetic modeling on massively parallel computers

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