• Ocean and Polar Research
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• v.35 no.3
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• pp.249-258
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• 2013

Vertical and horizontal mixing processes in the ocean mixed layer determine sea surface temperature and temperature variability. Accordingly, simulating these processes properly is crucial in order to obtain more accurate climate simulations and more reliable future projections using an ocean general circulation model (OGCM). In this study, by using Modular Ocean Model version 4 (MOM4) developed by Geophysical Fluid Dynamics Laboratory, the upper ocean temperature and mixed layer depth were simulated with two different vertical mixing schemes that are most widely used and then compared. The resultant differences were analyzed to understand the underlying mechanism, especially in the Tropical Pacific Ocean where the differences appeared to be the greatest. One of the schemes was the so-called KPP scheme that uses K-Profile parameterization with nonlocal vertical mixing and the other was the N scheme that was rather recently developed based on a second-order turbulence closure. In the equatorial Pacific, the N scheme simulates the mixed layer at a deeper level than the KPP scheme. One of the reasons is that the total vertical diffusivity coefficient simulated with the N scheme is ten times larger, at maximum, in the surface layer compared to the KPP scheme. Another reason is that the zonal current simulated with the N scheme peaks at a deeper ocean level than the KPP scheme, which indicates that the vertical shear was simulated on a larger scale by the N scheme and it enhanced the mixed layer depth. It is notable that while the N scheme simulates a deeper mixed layer in the equatorial Pacific compared to the KPP scheme, the sea surface temperature (SST) simulated with the N scheme was cooler in the central Pacific and warmer in the eastern Pacific. We postulated that the reason for this is that in the central Pacific atmospheric forcing plays an important role in determining SST and so does a strong upwelling in the eastern Pacific. In conclusion, what determines SST is crucial in interpreting the relationship between SST and mixed layer depth.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.05a
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• pp.249-254
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• 2003

분석에 이용된 격자망은 동곡, 고로, 미성, 병천, 효령 및 무성지점에 각각 12개, 30개, 45개, 76개, 46개 및 1265개의 조격자를 구성하였으며 하천의 수로방향 및 경사형태를 세분화하기 위하여 각 지점에 대하여 8개, 24개, 24개, 44개, 12개 및 64개의 세격자로 분할하였다. AGNPS를 이용한 첨두유량의 모의발생 결과치가 동곡, 고로, 미성, 병천, 효령 및 무성지점에서 측정값과 비교하여 각 호우사상별로 상대오차가 1.0~25.0%, 4.0~27.0%, 7.0~29.2%, 2.0~23.9%, 3.0~25.0% 및 3.6~21.0%의 차이를 나타내었다. 분석결과에서 AMCII조건에서는 관측치와 분석결과치가 유사하게 나타났으나 AMCI조건에 대해서는 상대적으로 작은 값을 보였으며 AMCIII조건에서는 다소 큰 값으로 분석되었다. SCS방법에서 제안하는 AMC조건별 CN값을 우리 실정에 적합하도록 수정 보완하기 위한 수정 유출곡선지수 $CN_{m}$ /I과 $CN_{m}$/III을 재구성하였으며, 여기에 적용되는 수정 유출 곡선지수식의 계수 a를 추정한 결과, 기왕에 발표된 연구결과와 거의 일치된 경향을 나타내었다. 제안된 수정 CN식을 이용하여 산정한 결과치와 관측치는 거의 유사하게 나타났다. AGNPS모델에 의한 유출량 산정에 있어 수문학적 토양피복형수(CN)의 결정을 위하여 선행강우량과 토양의 공극율 및 지형인자인 각 셀마다의 유역경사를 이용하여 관계식(CN =f($X_1$, $X_2$, $X_3$))을 유도하였으며, 분석 결과에서 CN이 선행강우량과 가장 밀접한 관계가 있음을 알 수 있었으며 유역경사, 토양의 공극율 순으로 나타났다..88mg/$\ell$~의 범위로 나타났다. 무태교 지점에서의 총인의 농도는 0.52mg/$\ell$~0.99mg/$\ell$~의 범위이었다. 신천에 금호강물을 혼합한 이후에도 부유물질, 생화학적산소요구량, 암모니아태 질소, 총인 등의 농도가 개선되지 않았다. 즉 금호강물의 혼합은 신천수질환경사업소에서 배출되는 방류수에 함유되어 있을 2차 오염물질의 희석이라는 이점외의 수질개선효과는 확인되지 않았다.l years and a new type of transfer crane has been developed. Design concepts and control methods of a new crane will be introduced in this paper.and momentum balance was applied to the fluid field of bundle. while the movement of′ individual material was taken into account. The constitutive model relating the surface force and the deformation of bundle was introduced by considering a representative prodedure that stands for the bundle movement. Then a fundamental equations system could be simplified considering a steady state of the process. On the basis of the simplified model, the simulation was performed and the results co

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2003.05a
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• pp.292-296
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• 2003

Autoclaving처리를 하지 않은 키토산과 autoclaving처리한 키토산과의 중금속 흡착실험을 해 본 결과 다음과 같은 결과를 도출 할 수 있었다. 1) 먼저 중금속간의 흡착능을 고찰하기 위하여 Langmuir와 Freundlich 흉착등온식에 적용시켜 본 결과 Freundlich 흡착등온식 보다는 Langmuir 흡착등온식이 보다 적합한 것으로 나타났다. 2) 시간에 따라서 autoclaving 처리한 키토산의 중금속 제거 가능성과 그 효율을 검토하기 위하여 각 중금속간의 Langmuir 흡착등온식을 이용하여 $q_{max}$를 나타냈다. 15 min > 60 min > 0 min 순으로 모든 중금속 제거 실험에서 15 min 동안 autoclaving 처리한 키토산의 중금속 흡착량이 가장 높은 것으로 나왔다. 그러므로 기존의 키토산 보다는 15 min동안 autoclaving 처리한 키토산이 중금속 제거에 더 좋은 흡착제로써 역할을 할 수 있을 것으로 판단된다. 3) 키토산을 이용한 중금속 제거에서는 $Pb^{2+}$ > $Cd^{2+}$ > $Cu^{2+}$ > $Cr^{3+}$순서로 제거가 되었다. 여러 연구자들의 실험 결과를 종합해 볼 때 Pb$^{2+}$가 중금속 중에 제거가 잘 된다는 연구 결과가 많이 발표 되었으며, $Cd^{2+}$, $Cu^{2+}$, $Cr^{3+}$의 경우에는 흡착제의 종류에 따라서 제거되는 순서가 다르다는 연구 결과들이 보고 되고 있다. 그러나 어떠한 이유로 중금속의 제거에 차이가 있는지에 대해서는 명확한 결론이 내려져 있지 않는 실정이다. 이러한 중금속간의 경쟁적인 관계에 대해 더 많은 세밀한 연구가 이루어져야 할 것 같다.는 0.52mg/$\ell$~0.99mg/$\ell$~의 범위이었다. 신천에 금호강물을 혼합한 이후에도 부유물질, 생화학적산소요구량, 암모니아태 질소, 총인 등의 농도가 개선되지 않았다. 즉 금호강물의 혼합은 신천수질환경사업소에서 배출되는 방류수에 함유되어 있을 2차 오염물질의 희석이라는 이점외의 수질개선효과는 확인되지 않았다.l years and a new type of transfer crane has been developed. Design concepts and control methods of a new crane will be introduced in this paper.and momentum balance was applied to the fluid field of bundle. while the movement of′ individual material was taken into account. The constitutive model relating the surface force and the deformation of bundle was introduced by considering a representative prodedure that stands for the bundle movement. Then a fundamental equations system could be simplified considering a steady state of the process. On the basis of the simplified model, the simulation was performed and the results could be confirmed by the experiments under various conditions.뢰, 결속 등 다차원의 개념에 대한 심도 깊은 연구와 최근 제기되고 있는 이론

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.3
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• pp.279-285
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• 2011

We perform a numerical study to determine the time of onset of natural convection in a transient hot wire (THW) device for measuring the thermal conductivity of nanofluids. The samples used in this simulation are water-based $Al_2O_3$ nanofluids with volume fractions of 1%, 4%, and 10%, and the properties are calculated by theoretical models and experimental correlations. The THW apparatus using coated wire is modeled by the control-volume-based finite difference method, and the start of natural convection is determined by observing the temperature rise of the wire under a gravity field. The onset time is 11.5 s for water and 41.6 s for water-based $Al_2O_3$ nanofluids predicted by Maxwell thermal conductivity model with a 10% volume fraction. We confirm that the onset time of natural convection of nanofluids in the cylinder increases with the nanoparticle volume fraction. We suggest a correlation for predicting the onset time on the basis of the numerical results. Finally, it is shown that the measurement error due to natural convection is negligible if the measurement using the transient hot wire method is completed before the onset of natural convection in the base fluid.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.1
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• pp.77-82
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• 2010

Our study aims to understand the flow of liquid in an open-top rectangular microchannel that can be used in micro total analysis systems ($\mu$-TAS) because it has advantages in terms of light transmission and energy efficiency. We measured the liquid velocity using particle tracking technique and conducted a simulation with computational fluid dynamics by altering the area of channel cross section and channel length for the capillary-driven flow in the open-top rectangular microchannel. When liquid water drops to an entrance of the fabricated microchannel with a height of 20 μm and a width of 20 ${\mu}m$, it flows along the microchannel by only capillary force. In the wetting behavior of the liquid, important parameters of this flow are channel size, contact angle and liquid properties such as surface tension and viscosity, which are used to control the flow of liquid in the microchannel.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1175-1183
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• 2013

Even if some CFD software developers and its users think that a state-of-the-art CFD software can be used to reasonably solve at least single-phase nuclear reactor safety problems, there remain limitations and uncertainties in the calculation result. From a regulatory perspective, the Korea Institute of Nuclear Safety (KINS) is presently conducting the performance assessment of commercial CFD software for nuclear reactor safety problems. In this study, to examine the prediction performance of commercial CFD software with the porous model in the analysis of the scale-down APR (Advanced Power Reactor Plus) internal flow, a simulation was conducted with the on-board numerical models in ANSYS CFX R.14 and FLUENT R.14. It was concluded that depending on the CFD software, the internal flow distribution of the scale-down APR was locally somewhat different. Although there was a limitation in estimating the prediction performance of the commercial CFD software owing to the limited amount of measured data, CFX R.14 showed more reasonable prediction results in comparison with FLUENT R.14. Meanwhile, owing to the difference in discretization methodology, FLUENT R.14 required more computational memory than CFX R.14 for the same grid system. Therefore, the CFD software suitable to the available computational resource should be selected for massively parallel computations.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.217-226
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• 1998

The anisotropy caused by the fiber orientation, which is inevitably generated by the flow during injection molding of short fiber reinforced polymers, greatly influences dimensional accuracy, mechanical properties, and other quality of the final product. Since the filling stage of the injection molding process plays a vital role in determining fiber orientation, an accurate analysis of flow field for the filling stage is needed. Unbalanced filling occurs when a complex or a multi-cavity mold is used leading to development of regions where the fiber suspension is under compression. It is impossible to make an accurate calculation of the flow field during filling with the analysis assuming incompressible fluid. A mold with four cavities with different filling times was produced to compare the numerical analysis results with the experimental data. There was a good agreement between the experimental and theoretical results when the compressibility of the polymer melt was considered for the numerical simulation. The fiber orientation states for compressible and incompressible fluids were also compared qualitatively as well as quantitatively in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.1005-1012
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• 2011

This research carried out a 3-dimensional simulation using computerized fluid dynamics (CFD) for the flow characteristics, temperature distribution, velocity distribution and residence time, etc. in a reactor in order to derive the optimal combustion conditions of an innovative combustion system. The area-weighted average temperature of the outlet of a furnace during combustion at a condition of fuel input rate 1.5 ton/hr, residence time 1.25 sec and air/fuel ratio 2.1 was $1,077^{\circ}C$, which is a suitable temperature for energy recovery and treatment of air pollutants. Exhaust gas is discharged through a duct at a 40~50 m/s maximum speed along strong vortexes at the center of a combustion chamber, so strong turbulence is created at the center of a combustion chamber to enhance the combustion speed and combustion efficiency. In this system, the optimum operation conditions to prevent incomplete combustion and suppress the formation of thermal NOx were air/fuel ratio 1.9~2.1 and fuel input rate 1.25~1.5 ton/hr.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.260-265
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• 2002

Microbiologically influenced Corrosion (MIC) is one of the most deleterious effects of metal microbe interactions. When a fresh metal surface comes in contact with a non-sterile fluid, biofilm formation is ensued. This might result in the initiation of corrosion. The sites and materials where MIC is implicated are versatile. Industries such as shipping, power generation, chemical etc are reported to be affected. The rapid and unexpected failure of AISI type 304 stainless steel was investigated in the laboratory by simulation studies for a period of 4 months. Slime and water samples from the failure site were screened for corrosion causing bacteria. Both aerobic and anaerobic nora were enumerated and identified using PCR techniques. Pseudomonas sp. and Bacillus sp. were the most common aerobic bacteria isolated from the water and slime samples, whilst sulfate reducing bacteria (SRB) were the major anaerobic bacteria. The aerobic bacteria were used for the corrosion experiments in the laboratory. Coupon exposure studies were conducted using a very dilute (0.1%V/V) nutrient broth medium. The coupons after retrieval were observed under a Scanning Electron Microscope (SEM) for the presence of MIC pits. Compared to sterile controls, metal coupons exposed to Pseudomonas sp and Bacillus sp. showed the initiation of severe pitting corrosion. However, amongst these two strains, Psudomonas sp. caused pits in a very short span of 14 days. Towards the end of the experiment, severe pitting was observed in both the cases. The detailed observation of pits showed they vary both in number and shapes. Whilst the coupons exposed to Bacillus sp. showed widely spread scales like pits, those exposed to Pseudomonas sp. showed smaller and circular pits, which had grown in number and size by the end of the experiment. From these results it is inferred that the rapid and unexpected failure of 304 SS might be due to MIC. Pseudonwnas sp. could be considered as the major responsible bacteria that could initiate pits in the metallic structures. As the appearance of pits was different in both the tested strains, it was thought that the mechanisms of pit formation are different. Experiments on these lines are being continued.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.373-386
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• 2017

This study simulated water quality item and flow rate of subbasin for Saemangeum watershed using Soil and Water Assessment Tool (SWAT) model and Environmental Fluid Dynamics Code (EFDC) model which simulate hydraulic and water quality in three-dimensions. The simulated values corresponded to observed value well. The result of simulation for floodgate operations at the M3 and M5 points, it exceeds water quality standard and at the M3 and D3 points, change of range for concentration is too wide, and upstream of Saemangeum reservoir is sensitive to inflow flow rate. Compared to the annual average concentration for observed station according to the discharge conditions, improvement of water quality for upstream was apparently compared to the downstream. Range of influence for change of water quality presented that maximum discharge condition, the influence range is 22 km in the direction of the Saemangeum downstream from the Mankyung bridge, and 15 km in the downstream direction of saemangeum in the Dongjin bridge. This study result demonstrated that floodgate operating at upstream has significant influence on water quality management of Saemangeum reservoir and it needs to be considered in plans of water quality management for Floodgate operation on Saemangeum reservoir.