• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.600-606
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• 2007

3D finite element analyses of a corrugated steel web girder and a steel truss web girder are conducted to investigate the static and dynamic behaviour of the hybrid girders. And the analyses results are compared with those by the equivalent beam theory. The equivalent theory is a theory that all section properties of a truss structure are replaced by section properties of a beam including a shear coefficient. When applying the equivalent beam theory, the shear coefficient of the corrugated steel web girder is estimated as the area ratio of flange section to web section and that of the steel truss web girder is calculated by the equation proposed by Abdel. Static deflections and natural frequencies by 3D finite element analyses and those by the equivalent beam theory are in good agreement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.12
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• pp.3235-3245
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• 1996

A DDFS(Direct Digital Frequency Synthesizer) used in spread spectrum communication systems must need fast switching speed, high resolution(the step size of the synthesizer), small size and low power. The chip has been designed with four parallel sine look-up table to achieve four times throughput of a single DDFS. To achieve a high processing speed DDFS chip, a 24-bit pipelined CMOS technique has been applied to the phase accumulator design. To reduce the size of the ROM, each sine ROM of the DDFS is stored 0-.pi./2 sine wave data by taking advantage of the fact that only one quadrant of the sine needs to be stored, since the sine the sine has symmetric property. And the 8 bit of phase accumulator's output are used as ROM addresses, and the 2 MSBs control the quadrants to synthesis the sine wave. To compensate the spectrum purity ty phase truncation, the DDFS use a noise shaper that structure like a phase accumlator. The system input clock is divided clock, 1/2*clock, and 1/4*clock. and the system use a low frequency(1/4*clock) except MUX block, so reduce the power consumption. A 107MHz DDFS(Direct Digital Frequency Synthesizer) implemented using 0.8.mu.m CMOS gate array technologies is presented. The synthesizer covers a bandwidth from DC to 26.5MHz in steps of 1.48Hz with a switching speed of 0.5.mu.s and a turing latency of 55 clock cycles. The DDFS synthesizes 10 bit sine waveforms with a spectral purity of -65dBc. Power consumption is 276.5mW at 40MHz and 5V.

• Journal of the Korean Society for Marine Environment & Energy
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• v.12 no.4
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• pp.273-278
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• 2009

Overtopping Wave Energy Convertor (OWEC) is an offshore wave energy convertor for collecting the overtopping waves and converting the water pressure head into electric power through the hydro turbines installed in the vertical duct which is fixed in the sea bed. The numerical wave tank based on the commercial computational fluid dynamics code Fluent is established for the corresponding analysis. Several incident wave conditions and shape parameters of the overtopping device are calculated. The straight line type and parabolic type of the sloping arm are compared in the optimal designing investigation of the overtopping characteristics and discharge for OWEC device. The numerical results demonstrate that the parabolic sloping arm is available for wave running up and the overtopping discharge increasing.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.4
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• pp.223-231
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• 2013

This paper presents a time-domain Gauss-Newton full-waveform inversion method for the material profile reconstruction in heterogeneous semi-infinite solid media. To implement the inverse problem in a finite computational domain, perfectly-matchedlayers( PMLs) are introduced as wave-absorbing boundaries within which the domain's wave velocity profile is to be reconstructed. The inverse problem is formulated in a partial-differential-equations(PDE)-constrained optimization framework, where a least-squares misfit between measured and calculated surface responses is minimized under the constraint of PML-endowed wave equations. A Gauss-Newton-Krylov optimization algorithm is utilized to iteratively update the unknown wave velocity profile with the aid of a specialized regularization scheme. Through a series of one-dimensional examples, the solution of the Gauss-Newton inversion was close enough to the target profile, and showed superior convergence behavior with reduced wall-clock time of implementation compared to a conventional inversion using Fletcher-Reeves optimization algorithm.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.7
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• pp.37-45
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• 2002

In this paper, the microwave characteristics of traveling-wave electroabsorption coplanar waveguide modulator have been analyzed and optimized precisely by using the 3-dimensional finite-difference time-domain method (FDTD). Microwave characteristics are affected by the thickness of intrinsic layer, the width of meas, and the distance between signal electrode and ground electrode on traveling-wave type structure. In case that intrinsic layers are composed of InAsP/InGaP (1.3Q), the optimized distance between signal electrode and ground electrode, the optimized intrinsic region thickness and the width of waveguide are founded to be $3{\mu}m,\;039{\mu}m\;and\;2{\mu}m$, respectively, to minimize microwave loss and to obtain velocity and impedance matched structure. By using the FDTD, we could design the traveling-wave electroabsorption modulator more precisely.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.3
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• pp.1-10
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• 2022

For the composite section of corrugated steel sheet and concrete, which is often used in soil structures, a conservative design method based on the ultimate strength state is still applied due to the difficulty of the analysis of compatibility condition. In this study, plastic analysis was performed on the flexural and axial strength of the composite section using two limit state design methods, LRFD and LSD. As a result of the analysis of the experimental results, the LRFD analysis value was interpreted as a conservative results for compressive strength, and it was analyzed that the effect of the concrete compressive strength was greater than the steel ratio of the steel plate. The flexural strength was analyzed to be in good agreement with the experimental results by the LSD analysis. From the parametric analysis on the design variables, the hogging moment, which is affected by the tensile strength of the steel plate, slightly decreased the increasing rate of the strength due to the influence of the bolts connection, but the sagging moment linearly increased according to the increment of steel reinforcement ratio.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1997.11a
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• pp.115-118
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• 1997

주어진 채널에 대하여 원하는 성질을 갖는 통신신호 파형을 설계하는데 있어 본 논문에서는 발생하는 잡음과 간섭의 효과를 최소화해주는 신호 셀을 생성하기 위해 시간-주파수제안된 WPM 변조 기법을 현재 사용되고 있는 QAM 방식과 비교하여 광범위한 간섭 환경에 적응적으로 대처할 수 있는 융통성있는 구조를 제공해줌을 보였다.

• Journal of the KSME
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• v.16 no.4
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• pp.12-18
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• 1976

기계 및 구조물들이 등진폭하중만을 받는 경우는 극히 드물어서 대부분이 진폭과 주파수가 불규 칙하게 변하는 하중을 받는다. 실하중이력이 불규칙(random)한 모양을 갖는 것은 비행기, 자동차, 선박 등의 많은 기구물들이 공기의 터블런스, 거치론 도로표면 및 대양의 파도와 같이 random한 주위환경에 접하기 때문이다. 이 random한 환경과 구조물의 탄성성질들로 인해서 구조물로부터 측정된 하중응답신호들(응신율,변위 혹은 가속도)은 건폭과 주파수가 random하게 변하는 특정한 형태의 파형을 갖는다. 현금 우리나라에 이 방면의 연구가 활발하지 못하여 complex load history가 피로에 미치는 영향과 이에 관련된 피로시험들을 간략히 소개한다.

• Proceedings of the KIEE Conference
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• 2008.05a
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• pp.197-198
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• 2008

지파도파관의 분산관계를 구하기 위해서는 마이크로파 발생장치의 발진구조 원리에 대한 정확한 분석이 필요하다. 이것은 파를 지연시키는 지파구조와 도파관을 이론적으로 분석 성가해야 하는데 이는 매우 어렵다. 본 연구에서는 이론과 실험을 병행하여 분석하였으며 이는 공진점을 측정하여 분산관계를 확인하는 방법을 통하여 톱니파형 도파관의 전자계특성을 평가하였다.

• 전기의세계
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• v.46 no.5
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• pp.3-10
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• 1997

뇌파, 즉 뇌전도는 뇌에서 일어나는 전위의 변화를 기록하는 것이다. 이는 두개골의 두피에 전극을 부착하거나 뇌 표면 또는 뇌속에 전극을 삽입하여 기록할 수 있다. 종래에는 뇌파는 활동전위의 동기화와 통합의 결과로서, 어떤 피질 영역에서의 뉴론의 활동을 직접 반영하는 것이라고 생각되어 왔다. 그러나 EEG 활동에서 상당한 부분은 뉴론의 막전위에 기인하며, 특히 느린 시냅스 후 전위의 가중에 기인한다고 할 수 있다. 그렇지만 활동전위가 EEG에 전혀 공헌하지 않는 것은 아니다. EEG는 그 파형에 따라 동기화 또는 비동기화로 나눌 수 있는데, 그 근간을 이루는 뇌 구조물은 상이하다. 그리고 피질의 활동에서 유래한 EEG는 피질하 구조물에 의해서도 영향을 받는다. 이러한 EEG를 활용한 연구는 인간 정신 과정을 이해하는데 이바지하는 바가 클 것이다.