• Journal of the Korean Magnetics Society
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• v.8 no.3
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• pp.161-168
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• 1998

In this paper, a algorithm is proposed, which is applicable to the transient analysis of diffusion equations by combined use of the Laplace transform and the finite element method. The proposed method removes the time terms using the Laplace transform and then solves the associated equation with the finite element method. The solution which is solved at frequency domain is transformed into time domain by use of the Laplace inversion. To verify the proposed algorithm, a heat conduction problem is analysed. And the solution showed a good agreement with analytic solution. Because the time-step method is not needed, the proposed method is very useful in solving various kinds of diffusion equations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.2
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• pp.174-185
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• 1994

This paper presents a modal solution of linear three-dimensional hydrodynamic equations using similarity transform technique. The solution over the vertical space domain is obtained using the Galerkin method with linear shape funtions (Galerkin-FEM model). Application of similarity transform to resulting tri-diagonal matrix equations gives rise 掠 a set of uncoupled partial differential equations of which the unknowns are coefficients of mode shape vectors. The proposed method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.5
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• pp.486-487
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• 1997

This paper presents the pure capacitive lumped element equivalent circuits for several coplanar waveguide(CPW) discontinuities such as an open-end, an open-end with connected ground planes, a gap and an open-end CPW stub and gives their capacitive element values as a function of physical dimensions of the discontinuity and the frequency for a specific substrate. The capacitive element values are determined from the scattering parameters which are obtained using the finite-difference time-domain(FDTD) method. For an open-end, an open-end with connected ground planes and a gap, the numerical results of the FDTD are compared with the quasi-static results which are calculated using the three- dimensional finite difference method(3D-FDM).

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.51-56
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• 2008

The waveform inversion for isotropic media has ever been studied since the 1980s, but there has been few studies for anisotropic media. We present a seismic waveform inversion algorithm for 2-D heterogeneous transversely isotropic structures. A cell-based finite difference algorithm for anisotropic media in time domain is adopted. The steepest descent during the non-linear iterative inversion approach is obtained by backpropagating residual errors using a reverse time migration technique. For scaling the gradient of a misfit function, we use the pseudo Hessian matrix which is assumed to neglect the zero-lag auto-correlation terms of impulse responses in the approximate Hessian matrix of the Gauss-Newton method. We demonstrate the use of these waveform inversion algorithm by applying them to a two layer model and the anisotropic Marmousi model data. With numerical examples, we show that it's difficult to converge to the true model when we assumed that anisotropic media are isotropic. Therefore, it is expected that our waveform inversion algorithm for anisotropic media is adequate to interpret real seismic exploration data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.11
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• pp.2954-2965
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• 1996

In this paper, the electromagnetic field characteristics of leaky caxial cable are anlyzed by using the finite difference-time domain(FDTD) technique. Finite difference equations of Maxwell's equations are definedin cylindrical coordinate systems. To simulate the open boundary problem like a free space, the Mur's Absorbing Boundary condition(Mur-ABC) is also used. After modeling the leaky coaxial cable with the three dimensional grid structure, the transient response of the field distribution and the current distribution, the field pattern, the coupling effect are depicted in the time domain.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1621-1626
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• 2003

This study deals with the heat transfer analysis on phase change optical disc with land/groove recording by means of numerical method. Finite difference time domain(FDTD) method was used to obtain the amount of absorption of light propagating inside disc and finite difference element(FEM) method was used to calculate the temperature distribution. The calculated results present the detailed information of recording characteristics on the phase change optical disc. The temperature profiles are quite different between the land track and the groove track. The recorded mark shape on land track is smaller and more elliptic than that on groove track. It is shown that the thermal problem to the neighboring track takes place due to secondary peaks. It is found that the different write strategy should be applied to land and groove recording, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.8
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• pp.790-796
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• 2002

In our country, historically beautiful and significant wooden architectures are preserved as the cultural properties. For a long time, however, the architectures are often exposed to rough environmental conditions, such as weathering, insect attack, etc. This may lead to deterioration of structural integrity of the architectures. Therefore, it is necessary to diagnose wooden architectures in advance. In this paper, the possibility of a subsurface-penetrating radar(SPR) fur non-destructive testing(NDT) of wooden architectures is investigated by using the three-dimensional finite-difference time-domain(FDTD) simulation and actual laboratory measurement.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.2 s.105
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• pp.158-164
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• 2006

In this paper, we proposed a new algorithm of the inverse scattering for the reconstruction of unknown dielectric scatterers using the finite-difference time-domain method and the design sensitivity analysis. We introduced the design sensitivity analysis based on the gradient information for the fast convergence of the reconstruction. By introducing the adjoint variable method for the efficient calculation, we derived the adjoint variable equation. As an optimal algorithm, we used the steepest descent method and reconstructed the dielectric targets using the iterative estimation. To verify our algorithm, we will show the numerical examples for the two-dimensional $TM^2$ cases.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.326-332
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• 2015

Analyzing electromagnetic properties in plasma medium, it is difficult to numerically solve electromagnetic problem with thin plasma. In this paper, subcell Maxwell-Boltzmann FDTD method was proposed which is combined with Maxwell-Boltzmann FDTD and subcell FDTD method for analyzing plasma and electrically thin materials, respectively. Calculations of reflection coefficient and absorption rate error were performed by using 1D FDTD method. Reflection coefficient computed by applying the proposed method is in agreement with analytic solution. Absorption rate error analyzed by employing the proposed method is 1/10 times less than one by using conventional method.

• Geophysics and Geophysical Exploration
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• v.4 no.2
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• pp.45-54
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• 2001

A three-dimensional finite difference time-domain modeling algorithm based on staggered grid and considering transmitting and receiving antennas has been developed to simulate Ground Penetrating Radar (GPR) survey. This algorithm adopted the subcellular method to simulate the dipole antennas being used in GPR system and added resistors to reduce ringing caused by the reflections at the ends of an antenna. Comparison of the output voltages in the presence of the resistors for half-space said that the ringing and the amplitude of output voltage decreased as the number of resistors increased, and the antenna was designed based upon this result. Radiation patterns were derived to understand the distribution of electric field energy in the planes including or normal to the antenna. The electric field energy concentrated on vertical direction in the plane including antenna more than in normal plane.