• 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.

• Nuclear Engineering and Technology
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• v.27 no.3
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• pp.281-291
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• 1995

The objective of this work is to obtain the experimental data for the heat transfer processes occurring both on the inside and outside surfaces of containment steel wall with dry and wet outer surface conditions in the passive containment cooling system. The test model represented a 60$^{\circ}$ section of a containment vessel based on the AP 600 geometry. Major linear dimensions of the test model ore reduced tv a factor of ten. To simulate the decay heat a steam generator heated by electricity was placed in the test model. The maximum heat flux was 8.91 kW/$m^2$. Two types of tests were performed. The one was the tort on the natural convection of air without water film flow. The other was the evaporative heat transfer test with the falling water film flow and natural air draft. no test result shooed that the heat transfer capability by the natural convection from the containment to the air without oater film flow was limited at about 1.48 kW/$m^2$ heat flux. It was found that the heat removal capability was remarkably enhanced in the tests with the waster film flow and air draft. The obtained heat transfer data ore compared with the existing correlations.

• Journal of Korea Water Resources Association
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• v.42 no.11
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• pp.897-909
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• 2009

The relative contribution of between hillslope-flow and stream-flow by heterogeneity of drainage path are quantitatively assessed in the present study with GIUH model based on grid of GIS. Application watersheds are selected Pyeongchang, Bocheong and Wi river basin of IHP in Korea. The mean and variance of hillslope and stream length are estimated and analyzed in each watershed. And coupling with observation storm events, estimate hillslope and stream characteristic velocity which dynamic parameters of GIUH model. The mean and variance of distribution of travel time (i.e. IUH) calculate using estimated pass lengths and characteristic velocities. And the relative contributions are assessed by heterogeneity of drainage path. As a result, the effect of the variance that determine shape of IUH dominate with hillslope's effect in the small watershed area (within 500 $km^2$). Thus, GIUH in the small watershed area must consider hillslope-flow.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.237-237
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• 2020

수도계량기(이하 "수량계")는 액체용 적산부피계로 물 사용량을 적산 계량하기 위한 기계기구 또는 장치이며 수량계 검정기준에 의해 검사기준 합격제품을 사용하서 수도요금을 징수합니다. 사실상 국내계량에 관한 법률에 의거하여 전이유량비가 6.3배수(2014년) > 4.0배수(2016년) > 1.6배수(2017년)로 점점 향상되며 2017년 기준으로 국제법정계량기구(OIML)의 성능과 같은 1.6배수까지 향상되어 국내의 수량계 기술기준이 많은 부분 향상되었습니다. 그러나 국제법정계량기구(OIML)는 현재 1.6배수의 80배수까지 검사기준에 합격에 반하여 현제 국내의 검사기준은 1.6배수의 100배수까지만 합격기준을 가지고 있습니다. 이러한 기준은 점차 발전해가고 있는 후발국가에 속하는 자국의 검사기준이 너무 갑작스럽게 국제법정계량기구(OIML)의 기준보다 높은 검사기준을 시행하며 많은 문제가 발생한 것 같습니다. 위와 같은 문제를 해결하기 위하여 여러 복합적인 부품으로 이루어진 수량계의 유량 및 유속에 영향력이 있다고 보여지는 특정 부품 혹은 부위의 개선 및 개발로 해결할 수 있지 않을까 하는 의구심에 연구를 시작되었습니다. 유량 및 유속에 영향을 끼치는 유입부의 스트레이너, 내부 임펠러의 변경으로 성능검사에서 영향을 끼치는지를 유체역학 및 유동해석 등을 통하여 테스트 후 각각 단계 및 상황별 목업금형을 제작하여 현재 국내검사기준으로 진행되는 성능테스트인 기차테스트를 진행하였습니다. 먼저 수량계의 특성상 수량계 내부의 유량을 유체역학 및 유동해석으로 정확히 뽑아내는 것이 불가능하여 유입부 유출부의 유량의 흐름을 기준으로 유체역학 및 유동해석을 진행하였습니다. 테스트 후 그 결과 값으로 유입부의 스트레이너의 삽입 각도를 0°, 90°, 135°, 180°, 270°로 각각 제작하여 테스트를 진행하였으며, 내부 임펠러는 straight, SR, SL, SL R70, SL R60, R75, SR R65 형상으로 각각 제작하여 테스트를 진행하였습니다. 전반적으로 기존의 수량계보다 높은 성능을 보여주었으며, 특정 스트레이너의 삽입각도 및 임펠러의 형상에서는 기존보다 훨씬 유수율이 절감되는 결과값이 나왔습니다. 그로 인해 검사기준에 쉽게 부합할 수 있으며 물 사용량을 보다 정확히 계측하여 정확한 수도요금을 부과하여 국세 낭비로 인한 경제적 손실을 감소할 수 있을 것 같습니다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.12 no.3
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• pp.130-138
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• 2000

The friction factor equation of open channel flow is developed by using Prandtl's mixing length theory and considering the flow characteristics of smooth or rough turbulent flow. BYO model considers vertical velocity profile for the (:omputation of bottom friction of surface waves and current flow. The model computes the mean bottom friction of combined wave-current flow by the vectorial summation of wave velocity and current velocity at Bijker point. The near bottom flow is discriminated by three flow regimes; smooth, transitional and rough turbulent flow. The model, BYO, has been further refined considering the combination of smooth turbulent flow and rough turbulent flow.

• Proceedings of KOSOMES biannual meeting
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• 2017.11a
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• pp.162-163
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• 2017

해양 HNS(Hazardous and Noxious Substances)의 유출 사고 시, 막대한 인명 피해와 환경 훼손을 피하기 위해 유출 사고 조기 예측과 정확한 확산 경로를 예측하는 것이 필수적이다. 본 연구의 최종목적은 전산유체역학을 이용하여 HNS사고가 발생하였을 때 위험구역을 적절히 예측할 수 있는 수치해석기법을 개발하고, 다양한 해양사고조건과 환경영향을 고려하여 근접역에서의 2차원 확산 특성을 고찰하고 확산 현상을 예측하기 위한 모델을 개발하는 것이다. 본 연구에서는 상용코드인 ANSYS FLUENT(V. 17.2)을 사용하여 근접역에서의 2차원 확산특성을 모사하고 분석하였다. 특히, 누출된 HNS의 위치별 농도를 예측하기 위해 종수송방정식(Species Transport Equation)을 이용하였으며 RANS(Reynolds-Averaged Navier-Stokes) 방정식과 표준 $k-{\varepsilon}$ 모델을 이용하여 난류유동을 모사하였다. 해석된 결과는 문헌에서 얻어진 실험데이터와 상호비교하였으며 해수의 유속, HNS의 밀도에 따른 유층 두께, 해수면 HNS 평균 농도 그리고 HNS 전파 속도를 분석하였다. 유층 두께는 해류 유속에 따라 변화하며 변화 경향에 따라 두 구간으로 나눌 수 있다. 해류 전파 속도는 대체로 해류 유속과 선형적 비례관계를 갖는 것으로 나타났다. 해수면 평균 HNS 농도는 해류 유속에 선형적으로 비례하여 감소하며, HNS 밀도가 큰 경우 해수면 평균 HNS 체적 농도는 더 빠르게 감소하게 된다. 이러한 결과는 HNS 확산 특성을 분석하고 관련된 예측모델을 개발하는 데에 기여할 수 있다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1313-1320
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• 1993

Flow patterns inside the riser section and the effects of the heater inlet-and exit-restrictions, liquid charging level and the heater inlet subcooling on the flow characteristics inside an open two-phase natural circulation loop were studied experimentally. Three basic circulation modes were observed ; periodic circulation (A)(flow oscillations with incubation(no boiling) period), continuous circulations(stable operation mode with no flow oscillations), and periodic circulation (B) (flow oscillations with continuous boiling). The circulation rate increases and then decreases with the increase of the heating rate and the maximum circulation rate appears with the continuous circulation mode. The decrease of the inlet-restriction or the increase of the exitrestriction destabilizes the system. When the liquid charging level or the inlet subcooling decreases, the continuous circulation mode starts at the lower heating rate and the system is stabilized.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.2
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• pp.15-22
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• 2003

Computational study using the 2-dimensional, compressible, Navier-Stokes equations is performed to predict the discharge coefficient of air flow through a film-cooling hole. In order to investigate the effect of internal/external flows on discharge coefficient, the present computational results which are obtained for three flow cases, only external flow, only internal flow, and no flow, are compared with experimental ones. It is found that the computational results predict the discharge coefficient of the film-cooling hole in a reasonable accuracy and the external crossflow reduces the discharge coefficient, while the internal crossflow increases the discharge coefficient in a range of momentum flux ratio $I_{c-jet}$ > 1 due to the total pressure loss and boundary layer effect.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.70-78
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• 2014

A numerical study has been conducted to investigate flow and heat transfer characteristics of supersonic second throat exhaust diffusers for high altitude simulation. By changing pressure and configuration, flow and cooling characteristics of the diffuser have been studied. At the normal operation of the diffuser, there were high temperature regions over 3,000 K without cooling, especially near wall and in subsonic diffuser part. If the cooling system of the diffuser is added, flow velocity is increased due to the cooled wall temperature.

• Clean Technology
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• v.25 no.2
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• pp.153-160
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• 2019

As air pollution becomes more serious due to the increased number of diesel vessel operations, ship regulations on harmful emissions strengthen. Therefore, the development of a diesel exhaust after-treatment system for ships is required, and the higher the flow uniformity of the exhaust treatment system, the higher the treatment efficiency. With the computer software ANSYS Fluent, pressure drop and flow uniformity were used in this study to simulate flow rate with and without a baffle in both a Diesel Oxidation Catalyst (DOC) and Diesel Particulate Filter (DPF) system. The system pressure drop was found to be 38 to 40 mbar in the existing system condition, and the flow uniformity was approximately 84 to 92% at the inlet and outlet of the DOC. When the baffle was installed inside the system, the pressure increased and the flow uniformity was lowered due to an increase in flow rate. When the exhaust gas flow was reduced by 50% from $7,548kg\;h^{-1}$ to $3,772kg\;h^{-1}$, the flow uniformity at the inlet and outlet of the DOC increased by approximately 1 to 3% due to the low flow rate. In the case of DPF, the flow uniformity of exhaust gas was 98 to 99% because the uneven flow proceeded after uniformly flowing from the DOC.