• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.309-318
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• 2001

A zero-dimensional simple model is presented to predict the currents in the opening channel of tide embankment and the sea-level response of the interior basin to ocean sea level. In general, a tidal embayment has wide tidal flats so that the effect of tidal flats has been taken into account by formulating the volute variation vs. depth. The model has been verified through the comparison with the 2-dimensional depth-integrated model which can resolve the small area by using the multigrid method. As the results applied to the storage of dredged material of Incheon North Harbour, the results indicate that both models adequately describe the sea-level and current fluctuations in the storage.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.251-256
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• 2008

The experimental analysis on a ducted fan for the propulsion system of a small UAV were performed. To investigate the aerodynamic characteristics of the ducted fan, flow fields at inlet and outlet were measured using a hot-wire anemometry. Thrusts were measured with the six-component balance with due regard to the cross wind. To reproduce the cross wind effect, the ducted fan was aligned to $90^{\circ}$ rotated direction against flow direction in the wind tunnel. In this paper, the variation of the flow fields and thrust according to the cross wind were analyzed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.82-85
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• 2008

A Helmholtz resonator is applied to control high frequency combustion instability in liquid rocket engine. Damping characteristics of the Helmholtz resonator are investigated by the flow characteristic and its design. To simulate combustion instability, resonance in a test section(with fixed volume) is made by a pressure pulsator, and then damping characteristics are investigated. Its orifice length and diameter are selected as the design parameters and flow rates are varied to reveal the effect on damping characteristics. The experimental results show that a Helmholtz resonator is also working with flows. When length and diameter of an orifice are small, the tuning frequency increases as the flow velocity increases.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.4
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• pp.255-262
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• 2012

Numerical simulations were performed to evaluate the dispersion characteristics of the pollutant around a Wolsung coastal area at located nuclear power plants. Numerical experiments by using EFDC(Environmental Fluid Dynamics Code) showed good agreements by comparison with the time series and harmonic analysis of the tidal elevations. The released pollutants moved in north direction at flood tide and in south direction at ebb tide. The calculated salinity and temperatures showed good agreements with the observed results by NFRDI(National Fisheries Research & Development Institute). The water circulation due to the variations of the temperature, salinity and tidal components were analyzed to estimate the dispersion characteristics of the pollutant.

• 한국해양학회지
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• v.29 no.2
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• pp.83-94
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• 1994

Two-dimensional tidal and tidal residual currents in Chinhae Bay are investigated by field observations, hydraulic and numerical experiments. The results of hydraulic and numerical model experiments roughly coincide with the field measurements. Maximum tidal currents during the spring and neap tides in Kaduk and Kyunnaeryang channel and the central channel of Chinhae Bay are strong as 90 to 110 and 30 to 40 cm/s respectively, and strong tidal residual currents having numerous eddies take place. Maximum tidal currents during the spring and neap tides in the western and northern parts of the bay are weak as below 30 and 10 cm/s respectively, and also tidal residual currents are relatively weak. Tidal residual currents in the northern part of Kajo-do go toward the north, whereas the currents in the southern part move down the bay, and the currents rotating clockwise occur around Bu-do. The surface currents in the bay depend strongly on the wind and river inflow, and such phenomena are more remarkable during he neap tide than the spring tide.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.2
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• pp.145-156
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• 2020

The climate change occurring all over the world increases the risk, specially in urban area, Accordingly, rainwater pumping station expansion is required than before. In order to increase the efficiency of the rainwater pumping station, the analysis of flow characteristics in the pump sump is needed for vortex control. Many efforts have been made to illuminate the vortex behavior using PIV, but any reliable results have not been obtained yet, because of the limitations in image capturing and dependency of measured velocity values on the interrogation area and time interval used for velocity calculation. In this study, therefore, experiments were carried out to find out the limitation of PIV and estimate the validation of the velocity values associated with the analysis parameters such as interrogation area, time interval, grid size. For the experimental condition used in this study, the limitation of PIV and the effects of parameters on the velocity estimation are presented.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.4
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• pp.253-266
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• 2014

The ECOM3D is used to study the circulation characteristics and density current from the Sumjin River runoff in the Kwangyang Estuarine System, South Sea, Korea. Annual mean value of $120m^3/s$ was imposed from the Sumjin River. The numerical model results in terms of tidal height, current and salinity field show satisfactory with skill scores over 90%. The current velocity showed the range of 1~2.5 m/s during flood and ebb phases. In particular, very strong flow occur in the narrow Channels of Noryang, Daebang and Changson exceeding over 2.0 m/s. The tidal residual currents in the various locations in the Kwangyang Estuary showed the range of 1~21 cm/s, The density-driven current through the Yeosu and Noryang Channels are about 12 cm/s and 4 cm/s, respectively. The current path through the Yeosu Channel is deflected toward west Bank. Based on budget analysis of the volume flux, the volume flux through the Yeosu Channel and the Noryang Channel were estimated to be 97.4 and $22.1m^3/s$ accounting for the 81.5% and 18.5% of total flux, respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.853-857
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• 2009

2차원 흐름해석 모형인 SMS(Surface-Water Modeling System)와 RAMS(River Analysis Modeling System)를 이용한 유속장 모의를 통해 Manning 조도계수와 와점성계수에 대한 민감도 분석을 수행하여 흐름특성은 Manning 조도계수에 큰 영향을 받음을 알 수 있었다. 본 연구에서는 Manning 조도계수의 변화를 통하여 실측치에 근사한 유속 분포의 모의결과를 도출하고자 현장실측을 통해 취득한 자료를 이용하여 2차원 수치모형의 모의결과와 비교하였다. 국가하천 형산강 본류 중 안강수위관측소에서 부조수위관측소 사이 약 4.3 km 의 구간을 모의구간으로 선정하였으며, $2006{\sim}2007$년에 걸쳐 취득된 현장실측자료를 바탕으로 매개변수 추정 및 모의결과와 비교하였다. 대상구간에 대한 모의결과의 정확도를 개선하기 위하여 하도의 지형특성 등을 고려하여 모의구간을 다수의 구획으로 구분한 후 수심 및 하도 평면선형을 고려한 Manning 조도계수를 차등적으로 할당하여 모의하였다. 이상의 과정을 통해 모의결과의 정확도 제고가 가능함을 관찰할 수 있었다.

• Nuclear Engineering and Technology
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• v.29 no.6
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• pp.49-59
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• 1997

본 기술 보고는 임계 열유속(Critical Heat Flux; CHF)을 예측하기 위해 사용되고 있는 상관식의 형태와 적용 방법, 이에 따른 예측 오차와 여유도의 변화 등을 종합적으로 분석한다. CHF 현상에 대해서는 지난 반 세기 동안 발생 메커니즘, 예측 모델, 설계에의 적용 방법 등에 대한 연구가 광범위하게 수행되어 대부분의 운전 조건에 대해 신뢰할만한 예측 모델들이 확립되어 있다. 그러나 예측 모델의 이용에서 가장 중요한 기준이 되는 예측 오차의 의미가 잘못 이해되는 경우가 많으므로, 이 글에서는 예측 모델의 형태 및 적용 방법에 따라 예측 오차가 달라지는 원인을 명확하게 해석하고, 실제 계산을 통하여 예시하였다. 그리고 상관식 형태 및 이용 방법에 따라 임계 열유속비(Critical Heat Flux Ratio: CHFR)와 임계 출력비(Critical Power Ratio; CPR)가 어떠한 관계를 갖는가를 논의하였다.

• Membrane Journal
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• v.14 no.3
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• pp.207-217
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• 2004

In this study, we prepared nanofiltration membrane by applying the interfacial polymerization method as a way of manufacturing composite membranes. We have examined the effects of various preparation factors such as monomer concentration and composition, thermal curing condition, post treatment condition. In addition to preparation conditions, we also monitored the effects of operation conditions such as feed solution concentration and operation pressure on the permeation properties of the resulting nanofiltration membrane. We intended to increase the permeation rate of nanofiltration membrane by the enlargement of effective surface area using additives during interfacial polymerization step. With increasing the monomer concentration, membrane permeation rate are decreased with maintaining almost constant rejection. With respect to curing condition, with increasing the curing temperature both permeation rate and rejection are decreased. With increasing the ratio of MPD in amino monomer composition, permeation rate decreased drastically with high rejection. With increasing the feed solution concentration, both permeation rate and rejection decreased. Both permeation rates and rejection increased with increasing the operating pressure. Nanofiltration membrane have higher surface roughness with increasing additive concentration in the case of using MPD contained amine composition than using piperazine alone. Permeation rates are much lower than the nanofiltration membrane prepared by piperazine.