• 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.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• Structural Engineering and Mechanics
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• v.48 no.5
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• pp.711-736
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• 2013

In this paper new implicit time integration called N-IHOA is presented for dynamic analysis of high damping systems. Here, current displacement and velocity are assumed to be functions of the velocities and accelerations of several previous time steps, respectively. This definition causes that only one set of weighted factors is calculated from the Taylor series expansion which leads to a simple approach and reduce the computational efforts. Moreover a comprehensive study on stability of the proposed method i.e., N-IHOA compared with IHOA integration which is performed based on amplification matrices proves the ability of the N-IHOA in high damping vibrations such as control systems. Also, wide range of numerical examples which contains single/multi degrees of freedom, damped/un-damped, free/forced vibrations from finite element/finite difference demonstrate that the accuracy and efficiency of the proposed time integration is more than the common approaches such as the IHOA, the Wilson-${\theta}$ and the Newmark-${\beta}$.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.163-166
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• 2000

The design, numerical simulation, and an experimental implementation of two-element cross-shaped microstrip line-fed printed slot array antenna for IMT-2000 at the 2.0 GHz band is presented in this paper. The proposed antenna with relative permittivity 4.3 and thickness 1.0mm is analyzed by the Finite-Difference Time-Domain (FDTD) method. It was shown that the measured 2.0 VSWR bandwidth of one-element microstrip slot antenna is from 1.42 GHz to 2.69 GHz, which is approximately 61.8% and that of two-element microstrip slot array antenna is from 1.42 GHz to 2.56 GHz, which is approximately 57.3% And it was shown that the measured gain of one-element microstrip slot antenna is 2.75 dBi and that of two-element microstrip slot antenna is 4.75 dEi. The antennas were fabricated and tested. The measured results are in good agreements with the FDTD results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.6
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• pp.605-611
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• 2002

A simple and efficient analysis method of the suspended stripline using the finite-difference time-domain (FDTD) method is presented. New FDTD equations are derived using the contour path FDTD concept for the Yee cell which contains a dielectric sheet. The characteristic impedance and the effective dielectric constant of the suspended stripline are calculated using our proposed FDTD method. Using the calculated results, a 5-element lowpass filter is designed and fabricated. Our proposed FDTD method is validated by the measured data of the fabricated lowpass filter.

• Journal of Biosystems Engineering
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• v.28 no.4
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• pp.305-314
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• 2003

The ROPS of an agricultural tractor is designed to protect its driver when the tractor overturns. Although the current OECD tests to determine whether the ROPS meets the requirements of the OECD regulation are desirable, they need long time to test. We experimental time and effort by using CAE. We conducted a finite element analysis for the ROPS design of a Dae-Dong tractor cabin in an attempt to reduce the design and manufacturing time. This study shows the interpretative skill using MARC(v.2000) for designing ROPS and difference between the results of testing and FEA. Design process is generally divided into two phases: a concept and a detail design. The concept design uses simple analysis to predict structural behavior, whereas the detail design involves a finite element analysis performed by the results of the concept design. This study focused on the detail design and used Patran(v.2000r2) and MARC(v.2000) of the MSC software corporation. The model consisted of 4812 elements and 4582 nodes. Four tests. specified in the OECD standards, were performed: (1) longitudinal loading test (2) rear crushing test (3) side loading test (4), and front crushing test. Independent analyses were also performed for each test, along with a sequential analysis. When compared, the results of the independent and sequential analyses were found to be similar to the test results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.700-703
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• 1999

Thls paper describes the process of corona discharge in $SF_6$ gas. The discharge characteristm such as electric field distribution, electron density, ion density and current denslty distribution are considered as time go by, The result show that difference between electronegative gas and nonelectronegative gas.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.518-523
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• 1993

A computer program has been developed for analyzing the two-dimensional unsteady conservation equations for transport phenomena in the ool region of direct rolling with semi-solid metal in order to describe the velocity and temperature, and the solidification process of the semi-solid metal. The energy equations of cooling roll is solved simultaneously with semi-solid metal in order consider heat transfer through the cooling roll. The FDM(finite difference method) and FEM(finite element method) are used in region of pool and roll, respsctively, to reduce computing time and to improve accuracy of calculation. In the present study, influence of solid fraction and casting speed are investigated in a point of view of strip formability with semi-solid metal.

• Journal of the Semiconductor & Display Technology
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• v.3 no.3
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• pp.19-21
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• 2004

This paper presents a 3-dimensional diffusion simulation with adaptive solution strategy. The developed diffusion simulator VLSIDIF-3 was designed to re-refine areas. Refine scheme was calculated by the difference of doping concentration between any of two nodes. Each element is greater than tolerance and redo diffusion process until error is tolerable. Numerical experiment in low doping diffusion problem showed that this adaptive solution strategy is very efficient in both memory and time, and expected this scheme would be more powerful in complex diffusion model.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.3
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• pp.237-245
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• 2003

Since the velocity is dependent on the fiber orientation in anisotropic composites, the application of traditional acoustic emission (AE) source location techniques based on the constant velocity to composite structures has been practically impossible. The anisotropy makes the source location procedure complicated and deteriorates the accuracy of the location. In this study, we have divided the region of interest(ROI) into a set of finite elements, taken each element as a virtual source, and calculated the arrival time differences between sensors by using the velocities at every degree from 0 to 90. The calculated and the experimentally measured values of the arrival time difference aye then compared to minimize the location error. The results from two different materials, namely AA6061-T6 and CFRP(uni-directional; UD, $[0]_{32}4$) laminate confirmed the practical usefulness of the proposed method.