• 한국음향학회지
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• 제37권6호
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• pp.451-456
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• 2018

최근 장거리 수중음향통신 연구가 활발하게 진행되고 있다. 장거리 수중음향통신 연구를 위한 해상실험은 해양환경의 영향을 크게 받고 높은 비용과 많은 시간이 소요된다. 따라서 장거리 환경에서 수중음향통신 시스템의 성능을 예측하고 검증하기 위한 시뮬레이터에 대한 연구가 필요하다. 본 논문에서는 장거리 수중음향통신 시뮬레이터의 개발을 목적으로 중장거리 다중송신환경에서 수중음향통신 시뮬레이터로서 VirTEX(Virtual Time series EXperiment)의 성능을 분석하고, 해상 실험 결과와 비교 검증하였다. 송신 신호는 탐침을 위한 Chirp신호와 16QAM 방식으로 변조된 통신 신호를 사용하였다. VirTEX를 통해 수신 신호를 모의하고 다중송신환경에 의해 발생하는 채널 간 간섭을 적응 수동형 시역전을 이용하여 보상하여 통신 성능을 분석하였다. 또한 2005년 7월 이탈리아의 Elba island 북쪽 해역에서 수행한 FAF05(Focused Acoustic Field 2005) 실험 데이터와 비교하여 이를 검증하였다.

• 한국지진공학회논문집
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• 제14권6호
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• pp.55-65
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• 2010

본 실험 연구의 목적은 횡방향 정적가력을 통하여 2층 R.C 전단벽식 구조의 내진성능을 평가하는 것이다. 본 연구의 실험체는 대상 건물의 개구부를 가지는 T자형 벽체 1층과 2층의 일부분을 대상으로 실물크기의 3/5 크기정도로 축소하였고, 인방보의 유 무를 실험변수로한 2개의 실험체를 제작하여 횡방향의 정적가력 실험을 수행하였다. 인방보 유무에 따른 벽체의 구조적 성능 및 거동의 차이를 비교한 결과, 인방보가 있는 실험체가 인방보가 없는 실험체보다 최대내력과 연성능력 등의 내진성능이 우수한 것으로 판단되었다.

• 한국음향학회지
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• 제38권6호
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• pp.678-686
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• 2019

수중에서는 다중 경로로 인한 인접 심볼 간 간섭의 영향으로 통신 성능이 저하되며, 수동형 시역전 처리는 다중 경로를 완화하기 위한 가장 효율적인 기법이다. 수동형 시역전 처리의 성능을 향상시키기 위해 다이버시티 결합기법이 이용되고 있으며, 본 논문에서는 여러 각도로의 빔 조향을 통해 획득한 신호들을 결합하는 빔 다이버시티 결합기법을 이용하여 통신 성능을 분석하였다. 수직 선 배열 센서에 수신된 탐침 신호로부터 추정한 빔-시간 그래프를 통해 음파의 전달 각도들을 추정하였으며, 추정된 각도 중 결합 개수 및 방식에 따른 통신 성능을 분석하였다. 분석을 위해 2018년 10월 포항 동방 해역에서 수행된 Biomimetic Long range Acoustic Communications 2018(BLAC18) 실험 데이터를 활용하였으며, 통신 성능 지표로써 출력 신호 대 잡음비를 이용하였다.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1446-1453
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• 2021

In the past, several experimental investigations aiming at characterizing the natural circulation (NC) behavior in test facilities were carried out. They showed a variety of flow patterns characterized by an inverted U-shape of the NC flow curve versus primary mass inventory. On the other hand, attempts to reproduce such curves using thermal-hydraulic system codes, showed 10-30% differences between the measured and calculated NC mass flow rate. Actually, the used computer codes are generally based upon nodalization using single U-tube representation. Such model may not allow getting accurate simulation of most of the NC phenomena occurring during such tests (like flow redistribution and flow reversal in some SG U-tubes). Simulations based on multi-U-tubes model, showed better agreement with the overall behavior, but remain unable to predict NC phenomena taking place in the steam generator (SG) during the experiment. In the current study, the CATHARE code is considered in order to assess a NC characterization test performed in the four loops PKL facility. For this purpose, four different SG nodalizations including, single and multi-U-tubes, 1D and 3D SG inlet/outlet zones are considered. In general, it is shown that the 1D and 3D models exhibit similar prediction results up to a certain point of the rising part of the inverted U-shape of the NC flow curve. After that, the results bifurcate with, on the one hand, a tendency of the 1D models to over-predict the measured NC mass flow rate and on the other hand, a tendency of the 3D models to under-predict the NC flow rate.

• 한국ITS학회 논문지
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• 제15권6호
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• pp.116-126
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• 2016

본 연구에서는 차로별 주행 궤적 데이터를 기반으로 차로속도역전현상이라는 개념을 이용하여 연속류 도로의 차로별 교통류 특성을 분석하였다. 1차로의 주행속도가 다른 차로보다 느린 경우를 차로속도역전현상이라고 정의하고, 이를 수식화하였다. 서울외곽순환고속도로(자유로IC~장수IC, 총 18.7km)를 대상으로 주중 5일(월~금) 동안의 오전 첨두시간대 차로별 주행 궤적 자료를 활용하여 거시적 측면과 미시적 측면에서 차로속도역전현상을 분석하였다. 실험구간 전체를 대상으로 차로별 주행속도를 비교한 거시적인 측면의 결과에서는 차로속도역전현상이 발생하지 않았으나, 실험구간을 세분화한 후 단위구간별 주행속도를 이용하여 미시적인 분석을 수행한 결과는 거시적인 분석 결과와 다르게 차로속도역전현상이 많이 발생하는 것으로 나타났다. 보다 혼잡한 구간에서 차로속도역전현상이 두드러지게 나타났고, 고속도로 기본구간보다는 연결로 접속부 구간에서 차로속도현상의 강도가 높게 나타났다. 본 연구의 결과는 머지않아 도래할 차로 교통정보 시대를 대비하여 현재의 교통정보 서비스 링크 단위의 적정성 판단, 차로 기반의 최적 경로 안내 서비스의 방향 결정 등에 기초적인 데이터로 활용이 가능하다.

• 자원환경지질
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• 제14권3호
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• pp.111-122
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• 1981

This study is a model analysis for an effective application of the geophysical prospecting to the investigation of geological structures or useful resources, and the purpose of it is to research a property of the electrical resistivity prospecting, especially by using a Three-Point electrode array method. In using the Three-Point electrode array method, it is theoretically assumed to choose the infinite for a distance between the two current electrodes, however it is impossible in applying to the practical field prospecting. Therefore this study was conducted for determination and presentation of a minimum appropriate distance between the two current electrodes by making a study on prospecting effect in the variation of distance between both the electrodes. In case that the ratios of the distance between the two current electrodes to that between the two potential electrodes are respectively chosen for 40, 400, 5,000, the experimental data of this study showed that the minimum appropriate distance between the two current electrodes is forty times as much as that between two potential electrodes. In order to make clear a problem about prospecting depth which is essential to the data processing, it had been chosen equally to the distance between two potential electrodes. As a result of it, it was shown that the anomaly is appeared along the position of an assumed ore body. Consequently it was found out that the prospecting depth of the Three-Point electrode array method is the same as the distance between the two potential electrodes. From the model experiment on the sheeting ore body(or linear structure) of horizontal, dipping of $30^{\circ}$, $60^{\circ}$ and vertical on the basis of above experimental condition, it was found out that the position and dip of assumed ore body could be inferred from the aspects of the equiresistivity curve. In consequence of performing out the simultaneous Normal and Reversal electrode movement, it was shown that the electrode movement of the Reversal forms the anomaly more clearly than that of Normal when the sheeting ore body is situated obliquely, therefore it could be ascertained that the electrode movement have to be performed simultaneously in the manner of Normal and Reversal. It was also exhibited that the aspect of the equiresistivity curve forms symmetrically when an assumed ore body (or linear structure) is situated horizontally or vertically, that is, symmetrically, and moreover that the aspect of the equiresistivity curve forms unsymmetrically when an assumed ore body (or linear structure) is situated obliquely. On the basis of these experimental analysis it is thought that it can be inferred from the aspect of equiresistivity curve whether an assumed ore body is obliquely situated or not.

• Structural Engineering and Mechanics
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• 제43권3호
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• pp.287-309
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• 2012

Precast segmental bridge columns (PSBC) are alternatives for monolithic cast-in-situ concrete columns in bridge substructures, with fast construction speed and structural durability. The analytical tool for common use is demonstrated applicable for seismic performance prediction of PSBCs through experiment conducted earlier. Then the analytical program was used for parameter optimization of PSBC configurations under reversal cyclic loading. Shear strength by pushover analysis was compared with theoretical prediction. Moreover, seismic response of PSBC with energy dissipation (ED) bars was compared with its no ED bar counterpart under three history ground acceleration records. The investigation shows that appropriate ED bar and post-tensioned tendon arrangement is important for higher lateral bearing capacity and good ductility performance of PSBCs.

• 한국가시화정보학회지
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• 제9권3호
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• pp.16-23
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• 2011

Experiment and numerical investigation are performed on swirling water flow in a vertical circular tube. This kind of flow is used in heat exchangers, combustion chambers, thermal power plants, and other mechanical equipment to move slurries or to convey materials. However, limited information on swirling flow in vertical circular tubes is available. In the current paper, the three-dimensional particle image velocimetry(PIV) technique is employed to compare the measured velocity profiles of water along the vertical circular tube with those of non-swirl flow. In addition, computational fluid dynamics(CFD) code was applied to calculation of the flow velocities with swirl.

• 대한기계학회논문집
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• 제19권7호
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• pp.1675-1683
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• 1995

A numerical study of the fluid flow and heat transfer characteristics of the two-dimensional impingement jet with a confinement plate has been carried out. The fluid flow was calculated by solving the full Navier-Stokes equation. In doing that, the well known SIMPLER algorithm was used and the trouble making convection term was discretized according to QUICKER scheme. The energy equation was simply solved by using the SOR method. For the Reynolds number of 10000, two channel heights, say 1.5 and 3.0 times the jet exit width, and two thermal boundary conditions constant wall temperature and constant wall heat flux were considered. Discrete heat sources were flush mounted along the impingement plate at a distance of 0, 2, 3, 4, 5, 6, 10, 12, times the jet exit width from the stagnation point. The length of each heat source is 4 times the jet exit width long. The Nusselt number averaged over each heat source was compared with experiment. Comparison shows that both calculations and experiment have the secondary peak of Nusselt number at downstream of stagnation point, even though there is a little quantitative difference in between. The difference is believed due to abscure thermal boundary condition in experiment and also accuracy of turbulence model used. The secondary peak is shown to be caused by rigorous turbulent flow motion generated as the wall jet flow is retarded and developes into the channel flow without flow reversal.

• Journal of Magnetics
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• 제9권2호
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• pp.60-64
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• 2004

In this paper calculations of magnetisation and magnetoresistance characteristics of the Spin Valve (SV) and Pseudo Spin Valve (PSV) spintronics structures are reported and compared with the experimental data. The magnetisation reversal process was analysed with respect to the Stoner- Wohlfahrt model of total surface energy in terms of uniaxial anisotropy, exchange coupling between ferromagnetic layers, unidirectional exchange anisotropy of pinned layer (modelled by exchange coupling between magnetisation of pinned layer and net magnetisation of antiferromagnetic layer with high anisotropy). The numerical simulation of the model to the experimental magnetisation data yielded the above parameters for SV and PSV structures. These parameters were used to more sophistically micromagnetic modelling tool originating from the project called Object Oriented Micromagnetic Framework. Influence of the shape anisotropy of the Magnetic Tunnelling Junction cell used in MRAM was simulated by means of micromagnetic simulations. Results were compared to those obtained from the spot Kerr measurements.