• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.135-140
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• 2001

The radar method is becoming one of the major nondestructive testing (NDT) techniques for concrete structures. Numerical modeling of electromagnetic wave is needed to analyze radar measurement results and to study the influence of measurement parameters on the radar measurements. Finite difference-time domain (FD-TD) method is used to simulate electromagnetic wave propagation through concrete specimens. In the experiments, three concrete specimens are made with the dimensions of 100 cm (length) x 100 cm (wideth) x 14 cm (depth). Three specimens had a Dl6 steel bar at 8, 10, 12 cm depth.

• Proceedings of the Acoustical Society of Korea Conference
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• 1996.06a
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• pp.9-12
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• 1996

This paper introduces an analysis of the non-axisymmetric mode due to in-plane vibration of an annular type piezoelectric actuator using FEM(Finite Element Method). The actuator is used as stator of ultrasonec motor. The freqrency charecterisrics and non-axisymmetric mode of the annular piezoelectric acruator are considered at a steady-state condition. The non-axisymmetric mode is occured by two sinusodial voltage sources with $\pi$/2 phase difference on the time domain. The resonant frequency of non-axisymmetric of non-axisymmetric mode is 60.358 kHz and 59.880 kHz for calculation and measurement, respectivly. The error was 0.8% between calculation and measurement. The revolution of the non-axisymmetric mode for actuator is analized at a period of exciting voltage sources using annimation. It is confirmed that the actuator has an usefulness as the stator of ultrasonic motor and the preposed method has a properity.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.87-91
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• 2019

As a highly conductive and transparent electrode, ITO/Ag/ITO multilayers are fabricated using an in-line sputtering method. Optimal thickness conditions have been investigated in terms of the optical transmittance and the electrical conductance. Considering the optical properties, in this study, the experimental characteristics are analyzed based on theoretical phenomena, and they are compared with the simulated results. The simulations are based on the finite-difference-time-domain (FDTD) method in solving linear Maxwell equations. Consequently, the results showed that ITO/Ag/ITO multilayer structures with respective thicknesses of 39.2 nm/10.7 nm/39.2 nm are most suitable with an average transmittance of about 87% calculated for wavelengths ranging from 400-800 nm and a sheet resistance of about $7.1{\Omega}/{\square}$.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.4
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• pp.101-112
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• 2004

In this paper, we developed a numerical analysis model by using ADI-FDTD method to analyze three-dimensional interconnect structure. We discretized maxwell's curl equation by using ADI-FDTD. Using ADI-FDTD method, a sampler circuit designed from 3.3 V CMOS technology is simplified to 3-metal line structure. Using this simplified structure, the time delay and signal distortion of complex interconnects are investigated. As results of simulation, 5∼10 ps of delay time and 0.1∼0.2 V of signal distortion are measured. As demonstrated in this paper, the full-wave analysis using ADI-FDTD exhibits a promise for accurate modeling of electromagnetic phenomena in high-speed VLSI interconnect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.2
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• pp.217-224
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• 2002

One of the dominant aspects governing the accuracy of the FDTD method is the size of the spatial increment used in the model. The effect of having reduced cell size is to increase the computational time and memory requirements. To overcome these problems, sub-gridding technique can be used. This implies that the application of a sub-grid cell would provide improved accuracy without increasing the run time and computer resources considerably. In this paper, we describe the three dimensional sub-gridding technique that is applied to model only the fine structure region of interest. The detailed solution procedure is described and some test geometries were solved by both uniform grid and sub-grid models to validate the suggested approach. While keeping the accuracy, the computational time becomes 6 times faster and the memory requirement is reduced by a factor of 2.5 comparing to the conventional FDTD approach.

• Earthquakes and Structures
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• v.5 no.2
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• pp.161-205
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• 2013

We study seismically induced, anti-plane strain wave motion in a non-homogeneous geological region containing tunnels. Two different scenarios are considered: (a) The first models two tunnels in a finite geological region embedded within a laterally inhomogeneous, layered geological profile containing a seismic source. For this case, labelled as the first boundary-value problem (BVP 1), an efficient hybrid technique comprising the finite difference method (FDM) and the boundary element method (BEM) is developed and applied. Since the later method is based on the frequency-dependent fundamental solution of elastodynamics, the hybrid technique is defined in the frequency domain. Then, an inverse fast Fourier transformation (FFT) is used to recover time histories; (b) The second models a finite region with two tunnels, is embedded in a homogeneous half-plane, and is subjected to incident, time-harmonic SH-waves. This case, labelled as the second boundary-value problem (BVP 2), considers complex soil properties such as anisotropy, continuous inhomogeneity and poroelasticity. The computational approach is now the BEM alone, since solution of the surrounding half plane by the FDM is unnecessary. In sum, the hybrid FDM-BEM technique is able to quantify dependence of the signals that develop at the free surface to the following key parameters: seismic source properties and heterogeneous structure of the wave path (the FDM component) and near-surface geological deposits containing discontinuities in the form of tunnels (the BEM component). Finally, the hybrid technique is used for evaluating the seismic wave field that develops within a key geological cross-section of the Metro construction project in Thessaloniki, Greece, which includes the important Roman-era historical monument of Rotunda dating from the 3rd century A.D.

• Journal of Korean Port Research
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• v.14 no.4
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• pp.451-461
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• 2000

The design and maintenance of navigation channel and water facilities of an harbor which is located at the mouth of river or at the estuary area are difficult due to the complexity of estuarial water and sediment circulation. Effects of deepening navigable waterways, of changing coastline configurations, or of discharging dredged material to the open sea are necessary to be investigated and predicted in terms of water quality and possible physical changes to the coastal environment. A borad analysis of the transport mechanism in the estuary area was made in terms of sediment property, falling velocity, concentration and flow characteristics. In order to simulate the transport processes, a two-dimensional finite element model is developed, which includes erosion, transport and deposition mechanism of suspended sediments. Galerkin’s weighted residual method is used to solve the transient convection-diffusion equation. The fluid domain is subdivided into a series of triangular elements in which a quadratic approximation is made for suspended sediment concentration. Model could deal with a continuous aggregation by stipulating the settling velocity of the flocs in each element. The model provides suspended sediment concentration, bed shear stress, erosion versus deposition rate and bed profile at the given time step.

• Current Optics and Photonics
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• v.1 no.1
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• pp.65-72
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• 2017

We propose a nearly lossless, compact, electrically modulated vertical directional coupler, which is based on the controllable evanescent coupling in a previously proposed graphene-assisted total internal reflection (GA-FTIR) scheme. In the proposed device, two single-mode waveguides are separate by graphene-$SiO_2$-graphene layers. By changing the chemical potential of the graphene layers with a gate voltage, the coupling strength between the waveguides, and hence the coupling length of the directional coupler, is controlled. Therefore, for a properly chosen, fixed device length, when an input wave is launched into one of the waveguides, the ratio of their output powers can be controlled electrically. The operation of the proposed device is analyzed, with the dispersion relations calculated using a model of a one-dimensional slab waveguide. The supermodes in the coupled waveguide are calculated using the finite-element method to estimate the coupling length, realistic devices are designed, and their performance was confirmed using the finite-difference time-domain method. The designed $3{\mu}m$ by $1{\mu}m$ device achieves an insertion loss of less than 0.11 dB, and a 24-dB extinction ratio between bar and cross states. The proposed low-loss device could enable integrated modulation of a strong optical signal, without thermal buildup.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.4
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• pp.343-351
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• 2019

Green water impact may sometimes cause some structure damages on ship's bow deck. Prediction of proper design pressure against the green water impact is an essential task to prevent the possible damages on bow deck. This paper presents a computational method of the bow deck's design pressure against the green water impact. Large heave and pitch motions of ship are calculated by the time domain nonlinear strip method. Green water flow and pressure on bow deck are simulated by the predictor-corrector second kind upstream finite difference method. This green water simulation method is based on the shallow water wave equations expanded for moving bottom conditions. For various kind of ships such as container ship, VLCC, oil tanker and bulk carrier, the green water design pressures on bow deck are computed and discussed. Also, the obtained results of design pressure on bow deck are compared with those of the classification society rules and discussed.

• Journal of the Korean Geotechnical Society
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• v.27 no.5
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• pp.85-92
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• 2011

The dynamic behavior of piles becomes very complex due to soil-pile dynamic interaction, soil non-linearity, resonance phenomena of soil-pile system and so on. Therefore, the proper numerical simulation of the pile behavior needs much effort and calculation time. In this research, a new modeling method, which can be applied to the conventional finite difference analysis program FLAC 3D, was developed to reduce the calculation time. The soil domain in this method is divided into a near-field region and a far-field region, which is not influenced by the soil-pile dynamic interaction. Then, the ground motion of the far-field is applied to the boundaries of the near-field instead of modeling the far-field region as finite meshes. In addition, the soil non-linearity behavior is modeled by using the hysteretic damping model, which determines the soil tangent modulus as a function of shear strain and the interface element was applied to simulate the separation and slip between the soil and pile. The proposed method reduced the calculation time by as much as one third compared with a usual modeling method and maintained the accuracy of the calculated results. The calculated results by the proposed method showed a good agreement with the prototype pile behavior, which was obtained by applying a similitude law to the 1-g shaking table test results.