• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.248-257
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• 2020

This study presents an initial design for a novel system consisting in a coupled nuclear reactor and a phase change material-based thermal energy storage (TES) component, which acts as a buffer and regulator of heat transfer between the primary and secondary loops. The goal of this concept is to enhance the capacity factor of nuclear power plants (NPPs) in the case of high integration of renewable energy sources into the electric grid. Hence, this system could support in elevating the economics of NPPs in current competitive markets, especially with subsidized solar and wind energy sources, and relatively low oil and gas prices. Furthermore, utilizing a prismatic-core advanced high temperature reactor (PAHTR) cooled by a molten salt with a high melting point, have the potential in increasing the system efficiency due to its high operating temperature, and providing the baseline requirements for coupling other process heat applications. The present research studies the neutronics and thermal hydraulics (TH) of the PAHTR as well as TH calculations for the TES which consists of 300 blocks with a total heat storage capacity of 150 MWd. SERPENT Monte Carlo and MCNP5 codes carried out the neutronics analysis of the PAHTR which is sized to have a 5-year refueling cycle and rated power of 300 MW_th. The PAHTR has 10 metric tons of heavy metal with 19.75 wt% enriched UO₂ TRISO fuel, a hot clean excess reactivity and shutdown margin of $33.70 and -$115.68; respectively, negative temperature feedback coefficients, and an axial flux peaking factor of 1.68. Star-CCM + code predicted the correct convective heat transfer coefficient variations for both the reactor and the storage. TH analysis results show that the flow in the primary loop (in the reactor and TES) remains in the developing mixed convection regime while it reaches a fully developed flow in the secondary loop.

• Journal of Korea Water Resources Association
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• v.44 no.4
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• pp.285-293
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• 2011

This study presents effects of downstream control point by coupled operation of dams and multi function weirs in the Geum River. Geum river basin that study area did authoritativeness high quality data to acquisition possibility. We applied the flow duration curve, flow regime coefficient, impounded flow index analysis to investigate the quantitative changes in natural flow regimes. In sphere that water supply is possible, this study applied believability that satisfy 95% at estimation year. Impounded flow index was calculated 0.292 by dam coupled operation and 0.297 by dam-weir coupled operation. The results indicate that the storage amount is increased by 29.7% as being added. Duration flow of downstream control point was improved because became coupled operation by regulation of dam and weir in the geum river.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.320-329
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• 2021

In this paper, an empirical model of air bubble size to be applied to an air masker for reduction of underwater radiation noise is presented. The proposed model improves the divergence problem under the low-speed flow condition of the existing model derived using Rayleigh's jet instability model and simple continuity condition by introducing a jet flow velocity of air. The jet flow velocity of air is estimated using the bubble size where the liquid is quiescent. In a medium without flow, the size of the bubble is estimated by an empirical method where bubble formation regime is divided into a laminar-flow range, a transition range, and a turbulent-flow range based on the Reynolds number of the injected air. The proposed bubble size model is confirmed to be in good agreement with the Computational Fluid Dynamics (CFD) analysis result and the experimental results of the existing literature. Using the acoustic inversion method, the air bubble population is estimated from the insertion loss measured during the air injection experiment of the air- masker model in a large cavitation tunnel. The results of the experiments and the bubble size model are compared in the paper.

• Journal of Wetlands Research
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• v.21 no.2
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• pp.102-113
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• 2019

Slack-tide sampling was carried out at 6 stations at high and low tide for a tidal cycle during spring tide of the early summer (June) and summer (July, August) of 2016 to determine the difference of water quality according to tide in Masan Bay, Korea. The mixing regime of all the water quality components investigated was well explained through the correlation with SAL. In the early summer and summer, TURB, DSi and NNN which mainly flow into the bay from the streams and SS, COD, AMN and $H_2S$ which mainly indicate the internal sink and source materials have a property of conservative mixing and non-conservative mixing, respectively. The conservative mixing showed a good linear relationship of the water quality between high and low tide, and the non-conservative mixing showed a variation of different pattern each other. Factor analysis performed on the concentration difference data sets between high and low tide helped in identifying the principal latent variables for them. In early summer, multiple effects (tidal action, natural influx and internal sinks and sources etc.) acted in combination for the differences to be distributed evenly in four factors (VF1~4), since there were few allochthonous inputs as a low-water season. On the contrary, in summer, the parameters showing large concentration difference at ST-1 affected by stream water were concentrated in one factor (VF1) and clearly distinguished from the parameters affected by the internal sinks and sources. In fact, there is no estuary (bay) that always maintains steady state flow conditions. The mixing regime of an estuary might be changed at any time due to the change of flushing time, and furthermore the change of end-member conditions due to the internal sinks and sources makes the occurrence of concentration difference inevitable. Therefore, when investigating the water quality of the estuary, it is necessary to take a sampling method considering the tide to obtain average water quality data.

• Journal of Korea Water Resources Association
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• v.51 no.10
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• pp.905-916
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• 2018

The purpose of this study is to evaluate the climate change impact on watershed hydrology and flow duration in Geum River basin ($9,645.5km^2$) especially by extreme scenarios. The rainfall related extreme index, STARDEX (STAtistical and Regional dynamical Downscaling of EXtremes) was adopted to select the future extreme scenario from the 10 GCMs with RCP 8.5 scenarios by four projection periods (Historical: 1975~2005, 2020s: 2011~2040, 2050s: 2041~2070, 2080s: 2071~2100). As a result, the 5 scenarios of wet (CESM1-BGC and HadGEM2-ES), normal (MPI-ESM-MR), and dry (INM-CM4 and FGOALS-s2) were selected and applied to SWAT (Soil and Water Assessment Tool) hydrological model. The wet scenarios showed big differences comparing with the normal scenario in 2080s period. The 2080s evapotranspiration (ET) of wet scenarios varied from -3.2 to +3.1 mm, the 2080s total runoff (TR) varied from +5.5 to +128.4 mm. The dry scenarios showed big differences comparing with the normal scenario in 2020s period. The 2020s ET for dry scenarios varied from -16.8 to -13.3 mm and the TR varied from -264.0 to -132.3 mm respectively. For the flow duration change, the CFR (coefficient of flow regime, Q10/Q355) was altered from +4.2 to +10.5 for 2080s wet scenarios and from +1.7 to +2.6 for 2020s dry scenarios. As a result of the flow duration analysis according to the change of the hydrological factors of the Geum River basin applying the extreme climate change scenario, INM-CM4 showed suitable scenario to show extreme dry condition and FGOALS-s2 showed suitable scenario for the analysis of the drought condition with large flow duration variability. HadGEM2-ES was evaluated as a scenario that can be used for maximum flow analysis because the flow duration variability was small and CESM1-BGC was evaluated as a scenario that can be applied to the case of extreme flood analysis with large flow duration variability.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.429-434
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• 2008

최근 하천의 복원과 자연형 하천 조성 사업 등이 활발하게 진행되고 있으며, 하천의 정상적인 상태를 유지하기위한 최소유량의 개념인 하천유지유량의 산정도 정부차원의 사업으로 진행되고 있다. 우리나라 하천복원사업의 주목적은 변형된 수로의 복원, 오염하천의 정화, 생태서식처 조성, 자연 구조물 재료를 이용한 친수공간 확보 등이나, 해외 관련연구사례는 자연상태 혹은 자연상태와 가까운 상태로 하천을 복원, 유지하기 위해서는 과거의 유량 흐름 특성을 복원하는 것이 이에 못지않게 중요함을 시사하고 있다. 본 연구에서는 하천의 유황특성을 세분하여 이들 특성이 하천생태계에 줄 수 있는 영향을 외국의 사례를 통해 고찰하였으며, 금강유역의 유황변동에 가장 큰 영향을 주는 대청댐 및 용담댐의 건설 전 후의 유황특성 변동을 분석하였다. 또한, 과거 관측자료가 부족한 경우, 모형을 통해 산정된 자연유량자료의 활용 가능성을 평가하여 본 연구에 이용하였다. 본 연구의 유황특성 변동 분석은 향후, 하천유지유량의 산정, 자연형 하천 복원 및 하천관리 시 유황의 특성을 복원하기 위한 노력이 필요하다는 방향성을 제시한다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.4
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• pp.587-593
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• 2002

The present research proposes a pressure based approach along with Langmuir slip condition for predicting microscale fluid flows. Using this method, gaseous slip flows in 2 -dimensional microchannels are numerically investigated. Compared to the DSMC simulation, statistical errors could be avoided and computing time is much less than that of the aforementioned molecular approach. Maxwell slip boundary condition is also studied in this research. These two slip conditions give similar results except for the pressure nonlinearity at high Knudsen number regime. However, Langmuir slip condition seems to be more promising because this does not need to calculate the streamwise velocity gradient accurately and to calibrate the empirical accommodation coefficient. The simulation results show that the proposed method using Langmuir slip condition is an effective tool for predicting compressibility and rarefaction in microscale slip flows.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.2
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• pp.48-55
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• 2003

The effects of pressure charge on combustion stability and emissions have been analyzed using a GDI single cylinder engine. A late injection mode of stratified condition at the air-fuel ratio of 40:1 for 1200∼2400 rpm was tested while the boosted pressure ratio was increased up to 1.5:1. In-cylinder CFD analysis was also performed for better understanding of in-cylinder flow and fuel spray behavior. With a higher boosted pressure ratio the IMEP was increased greatly due to the increased engine load, and the ISFC was improved by more than 10% at all engine speeds. The regime of stable stratified combustion was extended to a higher engine speed, but the spark ignition angle had to be more advanced for stable combustion. The emissions of ISHC and ISNOx did not show a particular trend for the increased engine speed but a general trend of lower ISHC and higher ISNOx for a gasoline engine.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.199-211
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• 2010

The objectives for this study were to evaluate spatial and temporal characteristics of water quality, based on long-term water quality monitoring data during 1993~2008. We found that physico-chemical and ecological conditions in the Daecheong Reservoir (DR) were modified by the construction of upper dam (i.e., Yongdam Reservoir). total phosphorus (TP), Secchi depth (SD), and chlorophyll-a (CHL) in the DR showed significant longitudinal decreases along the headwater-to-the downlake, indicating a large spatial variation, and this gradient was more intensified during the high-flow season (monsoon). Nutrient-rich water containing high nitrogen and phosphorus in the monsoon season (July~August) passed through the reservoir as a density current in the metalimnetic depth, and also high suspended solids increased in the metalimnetic depth, especially during the monsoon. According to the deviation analysis of Trophic State Index (TSI), >50% of TSI (CHL)-TSI (SD) and TSI (CHL)-TSI (TP) values were negatives, so that inorganic suspended solids (non-votatile solids) influenced the underwater light regime against phytoplankton growth. Also, ratios of CHL:TP after the dam construction evidently increased, compared to the values before the upper dam constructions, indicating a greater yield of phytoplankton in the unit phosphorus. Overall data showed that ecological and functional changes in Daecheong Reservoir occurred after the construction of upper dam (Yongdam Reservoir).

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.1365-1369
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• 2010

본 연구에서는 자연하안 조성을 위한 공법 설계시 공법의 적용 위치, 규모, 제원 등을 선정하기 위한 수문학적 정보 및 하천의 수문학적 특성에 적합한 식생을 선정하기 위한 수심, 침수기간 정보를 제공하기 위한 기법을 제시하였다. 이를 위해 장기 유출모형인 SWAT 모형을 적용하였으며, 자연하안 조성 공법 중 하나인 방틀이 시험 적용된 평창강을 대상으로 수문학적 특성을 분석하기 위한 유황 분석을 실시하였다. 평창강의 상안미 수위관측소 상류부에 위치한 방틀 시험지점의 유황을 분석하기 위해 상안미 수위관측소 상류유역을 대상유역으로 하여 상안미 수위관측소의 관측유량과 비교를 통해 신뢰성 있는 검보정을 마친 모형을 이용, 1989년부터 2008년까지 20년간의 유출분석을 실시하였다. 모의된 20년간의 일유출자료를 토대로 방틀 시공 단면의 유황곡선을 도시하여 유량특성을 분석하였으며, 유량을 수심으로 환산하여 대상 단면의 침수기간별 수심분포를 산정하였다. 또한 대상 단면의 하안을 침수기간별로 구분하여 하안의 높이에 따라 적정한 식생의 종류를 선정할 수 있는 자료를 생성하였다. 이와 같은 정보의 제공은 공법 설계에 필수적으로서 본 해석기술의 주요한 성과 및 활용성이라고 판단된다.