• 한국유체기계학회 논문집
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• 제13권1호
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• pp.23-28
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• 2010

A draft tube which has impeller to elevate bottom water and spread it over surface of lake water, induces convective circulation of lake water, a Long-Distance Circulation (LDC). Circulation of lake water make stratified water mixed and enhance DO (Dissolved Oxygen) of bottom water. Circulation rate of water is determined by draft rate of the tube, which is dependent on design parameters of the draft tube system, i. e. dimension of impeller and diffuser, inclined angle of impeller, impeller shape, and rotational speed. In this study, change in draft rate and power consumption of circulation equipment was investigated numerically with changing impeller dimension, angle and rotational speed. It was found that flowrate of draft water was increased as the dimensions of draft tube and impeller, and rotational speed and inclined angle of impeller increased. The power consumption was also elevated with increasing parameter values, and final selection of parameter values was made to satisfy target flowrates and power consumption.

• 한국가시화정보학회지
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• 제17권2호
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• pp.25-31
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• 2019

A device that consists of an array of hydrofoils (called a vane deployer) is widely used in ocean engineering. In general, the vane deployer has to spread out efficiently, which is possible by enhancing the lift-to-drag ratio. In the present study, using a computational fluid dynamics, we investigate the effect of hydrofoil arrangement on the lift-to-drag ratio to establish the condition in which a reasonable level of constant lift-to-drag ratio is achieved in a wide range of angle of attack, to avoid a degradation of the hydrodynamic performance. First, the flow around two-dimensional hydrofoil array is examined by varying the size of hydrofoil components, gap between the hydrofoils, and arrangement type. As a result, we determine the optimized hydrofoil array configuration whose lift-to-drag ratio is nearly independent on the angle of attack. Finally, a three-dimensional simulation is performed for the optimized geometry to estimate the performance of actual vane deployer.

• 한국환경과학회지
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• 제30권2호
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• pp.173-184
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• 2021

Ecological disturbance plants distributed throughout the country are causing a lot of damage to us directly or indirectly in terms of ecology, economy and health. These plants are not easy to manage and remove because they have a strong fertility, and it is very difficult to express them quantitatively. In this study, drone hyperspectral sensor data and Field spectroradiometer were acquired around the experimental area. In order to secure the quality accuracy of the drone hyperspectral image, GPS survey was performed, and a location accuracy of about 17cm was secured. Spectroscopic libraries were constructed for 7 kinds of plants in the experimental area using a Field spectroradiometer, and drone hyperspectral sensors were acquired in August and October, respectively. Spectral data for each plant were calculated from the acquired hyperspectral data, and spectral angles of 0.08 to 0.36 were derived. In most cases, good values of less than 0.5 were obtained, and Ambrosia trifida and Lactuca scariola, which are common in the experimental area, were extracted. As a result, it was found that about 29.6% of Ambrosia trifida and 31.5% of Lactuca scariola spread in October than in August. In the future, it is expected that better results can be obtained for the detection of ecosystem distribution plants if standardized indicators are calculated by constructing a precise spectral angle standard library based on more data.

• 대한전자공학회논문지TC
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• 제44권4호
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• pp.88-94
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• 2007

본 논문은 GPS 수신기에서 간섭 제거를 통한 성능 개선을 목적으로 3 차원 배열 안테나를 이용한 DOA ( Direction Of Arrival ) 추정과 빔 형성 성능 분석에 관한 것이다. GPS 수신기에 배열 안테나를 이용하면 신호 도래 방향의 DOA 를 추정한 후, 공간 필터링을 이용하여 원하는 방향으로 주빔과 널을 형성하므로서 재머 ( jammer ) 신호를 제거할 수 있으므로 시스템의 성능을 높힐 수 있게된다. 본 논문에서는 5 가지의 3 차원 배열 안테나 구조를 제안한 후 도래 신호의 DOA 를 추정키위한 MUSIC 알고리즘을 적용할 경우 추정 오차 및 빔 형성의 성능을 제시하였다. DOA 성능 분석을 위하여 DOA 추정 오차를 계산하였으며 빔 형성 성능 분석을 BER 을 사용하였다. 특히 빔 형성 성능 분석에서는 다양한 jammer 전력과 GPS 신호의 존재 및 각도 퍼짐등을 고려하였다. 컴퓨터 시뮬레이션의 결과 제안된 3차원 배열 안테나에서 Curved (B) 7-element 안테나가 DOA 추정, 추정 오차 및 BER 특성과 각도 퍼짐에서 다른 배열 안테나보다 우수한 특성을 얻을 수 있었다.

• 한국통신학회논문지
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• 제30권5C호
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• pp.355-363
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• 2005

이 논문은 옥내와 옥외에 걸친 무선 통신 환경에서 통신 성능을 향상시키는 기술에 관한 것이다. 옥외 무선 통신에서 신호 감쇠는 주로 채널의 페이딩 특성으로 발생되는데, 기존의 다중 안테나 방식과 배열 신호처리 알고리즘을 적용하면 이 문제를 해결할 수 있다. 그러나, 옥내 및 옥외 무선 채널을 가진 통신인 경우, 채널 특성은 페이딩과 각도 퍼짐 특성 모두에 영향을 받으므로, 일반적인 방식으로 채널의 각도 퍼짐 특성을 극복할 수 없다. 이를 해결하기 위해 이 논문에서는 옥내와 옥외에 걸친 채널 특성을 분석하고, 각각에 적합한 채널 모형을 생각한다. 또한, 옥내외 채널의 각도 퍼짐 특성을 극복하고 옥내외 통신 성능을 향상하기 위해, 새로운 평균주사 벡터 개념을 사용한 배열 안테나 처리 알고리즘을 제안하고 성능 분석을 수행한다. 컴퓨터 모의 실험을 통한 성능 분석으로 옥내 전송 신호를 옥외 환경에서 다중 안테나로 수신하는 경우, 기존 방식보다 제안된 방식이 좋은 신호대 간섭 잡음비 특성을 가짐을 보인다.

• 한국화재소방학회논문지
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• 제30권3호
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• pp.86-93
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• 2016

드렌처 헤드의 형상이 화재확산 차단을 위한 수막의 유동특성 및 복사 감쇠에 미치는 영향에 관한 실험적 연구가 수행되었다. 헤드의 형상인자로서 오리피스 출구와 반사판의 거리(h) 그리고 반사판의 직경(D)이 변화되었으며, 오리피스의 직경(d)은 고정되었다. 주요 결과로서, h의 증가는 방수량과 분사각의 증가를 가져오지만, D의 증가에 따라 분사각의 변화는 감소한다. D의 증가는 방수량 증가에 매우 작은 영향을 미치며, 분사각의 큰 감소를 초래한다. 또한 D의 증가는 보다 편평한 수막 패턴을 생성시킬 수 있지만, 분사각 내의 더 낮은 액적 균일도를 가져온다. 작동압력의 증가에 따라 평균 액적직경은 크게 감소하지만, 일정한 압력 조건 하에서 헤드 형상변화는 액적직경 변화에 큰 영향을 주지 않는다. 마지막으로 일정한 작동압력의 조건에서 드렌처 헤드의 복사 감쇠효과는 h 및 D의 변화에 따른 방수량과 액적 균일도에 의해 각각 영향을 받는 것으로 확인되었다.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.92-96
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• 2019

In the presence of ${\mu}-tip$ embedded in a slot-die head for stripe coatings, there arises the capillary flow that limits an increase of the stripe density, which is required for the potential applications in organic light-emitting diode displays. With an attempt to suppress it, we have employed a computational fluid dynamics software and performed simulations by varying the ${\mu}-tip$ length and the contact angles of the head lip and ${\mu}-tip$. We have first demonstrated that such a capillary flow phenomenon (a spread of solution along the head lip) observed experimentally can be reproduced by the computational fluid dynamics software. Through simulations, we have found that stronger capillary flow is observed in the hydrophilic head lip with a smaller contact angle and it is suppressed effectively as the contact angle increases. When the contact angle of the head lip increases from $16^{\circ}$ to $130^{\circ}$, the distance a solution can reach decreases sharply from $256{\mu}m$ to $44{\mu}m$. With increasing contact angle of the ${\mu}-tip$, however, the solution flow along the ${\mu}-tip$ is disturbed and thus the capillary flow phenomenon becomes more severe. If the ${\mu}-tip$ is long, the capillary flow also appears strong due to an increase of flow resistance (electronic-hydraulic analogy). It can be suppressed by reducing the ${\mu}-tip$ length, but not as effectively as reducing the contact angle of the head lip.

• International Journal of Internet, Broadcasting and Communication
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• 제12권3호
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• pp.1-8
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• 2020

This paper studied a method of estimating target information using a radar in wireless communication. Position information on the target can be estimated angle, distance and velocity. The velocity information can be estimated since the Doppler frequency is changed in the moving target. The signal incident on the receiving array antenna is multiplied by the delay time and the reference signal to represent the output signal. This output signal is estimated by applying FFT (Fast Fourier Transform) after calculating signal correlation through correlation integrator. Since the output signal must be calculated within the correlator, it should be processed with the Dwell time. The correlation signal of the correlation integrator outside this Dwell time is indicated by the velocity measurement error. The FFT is applied to the signal that has passed through the correlated integrator in order to estimate the distance of the signal. The Doppler resolution must be improved because the FFT estimates target information using the Doppler information. The Doppler resolution decreases with increasing the integration time. The velocity information estimation should have no spread of the velocity. As a result of the simulation, there was no spread of the target velocity in this study.

• 한국대기환경학회지
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• 제12권5호
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• pp.529-540
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• 1996

Dispersion experiment using SF$_{6}$ tracer was performed in the flat field of Chunchon Basin during four nights from August 29 to September 2, 1991. The purpose of this study is to analyze toe horizontal distribution of tracer concentration under the strong stable conditions and to evaluate the results calculated by INPUFF model. Incase of high wind speed, plume spread of SF$_{6}$ concentration appeared in narrow area of the downwind and the standard deviation of the horizontal wind angle (.sigma.$_{a}$) was amall. However, the SF$_{6}$ was spread widely in cases of low wind speed because of the large .sigma.$_{a}$. The result of the INPUFF model was similar to the observed distribution of the SF$_{6}$ concentration. It is proved that the Gaussian puff model is useful when wind direction varies significantly.tly.tly.tly.

• KIEE International Transactions on Electrophysics and Applications
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• 제4C권1호
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• pp.26-30
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• 2004

Orientation control of a polyoxometalate (POM) nanoparticle in its two-dimensional arrangement was attempted by Langmuir-Blodgett (LB) technique. For their uniorientation, two carboxyl groups were introduced on one side of the POM particle, and hydrophobic long chains were attached by esterification with the carboxyl groups (C18-POM). The C18-POM layer spread on water surface showed stability against surface pressure up to 60 mN/m. The pattern of the C18-POM isotherm was quite different from stearyl alcohol (C18-OH), while the POM itself did not show any development of surface pressure on water surface. The AFM images of C18-POM LB films showed some microcrystalline structures that were noticed as dot structures by Brewster angle microscopy. The microimages for C18-POM did not completely spread out as a monolayer on the water surface. The XPS spectra indicated the presence of POM structures and stearyl ester bonds formed from about 65% of the total carboxyls. The XRD spectra showed that the unioriented POMs were not positioned with the same lattice distance but rather in a wavy surface state.