• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.3
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• pp.306-316
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• 2003

We conducted a time-series analysis of temperature and salinity of sea water around Jeju Island, Korea. Monthly mean temperature and salinity was influenced by precipitation and weather conditions on Jeju as well as by oceanographic conditions of the open sea such as the Tsushima Warm Current and sea water in coastal areas. Salinity of Jeju coastal waters was the highest in April, and it was always over 34.00 psu with tiny fluctuation between December and June. Due to the effects of the Tsushima Warm Current, Jeju coastal waters maintained high salinity and stability. Low salinity and its large fluctuations during summer were closely associated with the China Coastal Water and precipitation in Jeju. The place of the lowest water temperature was the northeast coasts of Jeju (Gimneong, Hado, Jongdalri). In winter, as warmer water of the Tsushima Warm Current appeared in western area of Jeju dwindled flowing along the northern coasts of Jeju area and becoming cool, the lowest water temperature often appeared locally in Gimnyeong and its vicinitly in summer. The Tsushima Warm Current flows into the east entrance of Jeju Strait, but its influence is weak because of geometry and strong vertical mixing due to fast tidal currents.

• Ocean and Polar Research
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• v.37 no.2
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• pp.149-159
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• 2015

The Southern Ocean (SO) plays a primary role in global climate by storing and transporting anthropogenic carbon dioxide through the meridional overturning circulation and the biological pumping process. In this study, we aim to investigate interannual variability of summer chlorophyll concentration in the SO and its relation with the El $Ni{\tilde{n}}o$ Southern Oscillation (ENSO), using satellite ocean color data covering 16 years from 1997 to 2012. During El $Ni{\tilde{n}}o$ periods, chlorophyll concentration tends to increase in the subtropics (north of the subantarctic front). This chlorophyll increase is likely linked to El $Ni{\tilde{n}}o$-induced surface cooling that increases nutrient supply through enhanced vertical mixing in the subtropics. On the other hand, the subpolar gyres show localized chlorophyll changes in response to the ENSO. The localized response seems to be primarily attributed to changes in sea-ice concentrations. Our findings suggest that ENSO contributes interannual variability of chlorophyll in the SO through different mechanisms depending on regions.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.5
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• pp.361-369
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• 1997

In order to investigate the abundance and transboundary fluxes of air pollutants over the Yellow Sea, airborne measurements were made aboard the SF-600 aircraft (Pan-Asia Engineering) in March, 1996. The data presented in this paper are preliminary results and airborne experiment will be carried out until 1999. The vertical profile of relevant meteorological parameters such as temperature, water vapor, wind direction and wind speed were also observed at Taean. Mixing layer height was about 1000~1100m during the flights. The SO$_2$ and NO$_{x}$ concentrations were 3~6 ppb and 5~7 ppb below 1000 m, within 1 ppb and 3~5 ppb at 1000~2000m, respectively. Backward trajectory analyses were also carried out. A mathematical method by Lelieveld et al.(1989) was used to estimate the flux of air pollutants through the planetary boundary layer of Yellow Sea area. Transboundary fluxes were calculated using the measurement results with respect to the pollutants concentration, depth of the planetary boundary layer, wind speed and wind direction. The estimated transboundary flux of SO$_2$through the western boundary of Korea was about 39~42 tons/hour.r.

• Journal of Korean Society for Atmospheric Environment
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• v.27 no.6
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• pp.791-804
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• 2011

Numerical simulations were carried out to investigate the impact of PBL (Planetary boundary layer) scheme implemented in WRF on the result of meteorological fields and CMAQ modeling. 25-day period, representing high ozone concentration, was selected for the simulations. The three WRF domains covered East Asia region, Korean Peninsula and Seoul metropolitan area. The sensitivity of WRF-CMAQ modeling to the various PBL schemes was assessed and quantified by comparing model output and against observation from the meteorological and the air quality monitoring network within the domain. The meteorological variables evaluated included temperature, wind speed and direction over surface sites and upper air sounding sites. The CMAQ variables included gaseous species $O_3$ and $NO_x$ over monitoring stations. Although difference of PBL schemes implemented in WRF, they did not appreciably affect the WRF and CMAQ performance. There are partially differences between non-local and local mixing scheme, but are not distinct differences for the results of weather and air quality. It is suggested that impact of parameterization of vertical eddy diffusivity scheme in CMAQ also need to be researched in the future study.

• Ocean and Polar Research
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• v.32 no.3
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• pp.331-336
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• 2010

The CREAMS (Circulation Research of the East Asian Marginal Sea) survey in 1999 revealed a sharp mid-depth discontinuity of the phosphate:silicate ratio in all basins of the East/Japan Sea. Incidentally, this discontinuity layer corresponds to the oxygen minimum layer. Directly below the discontinuity layer, oxygen concentration is increased. This increase in oxygen concentration is interpreted as a proof of intermediate water formation. Oxygen minimum indicates that the water parcel is old and stable against mixing. So it seems be an efficient barrier to vertical exchange of materials. This means that, once materials enter the lower domain, they rarely return to the upper domain. Therefore, the biogeochemistry of the East/Japan Sea depends heavily on material input through the Korea Strait, and flux is expected to be sensitive to the climate change. As a result, the East/Japan Sea ecosystem seems vulnerable to tipping (regime shift), which occurred on a decadal time scale.

• Advances in concrete construction
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• v.10 no.3
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• pp.221-236
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• 2020

To reduce the CO₂ emissions associated with the manufacture of portland cement (PC), an efficient alternative like an alkali-activated binder (AAB) is the requirement of the industry. To promote the use of AAB in construction activities, a practically implementable mix proportion is required. Owing to the several raw ingredients of AAB concrete and their associated uncertainties, partial replacement of PC by AAB may be adopted instead of complete replacement as per industrial requirements. Hence, the present study aims to determine an optimal proportion for partial replacement of PC with AAB and recommend a technique for it based on site conditions. Three modes of partial replacement are followed: combining all the dry ingredients for AAB and PC followed by the addition of the requisite liquids (PAM); combining the PC and the AAB concrete in two horizontal layers (PAH); and two vertical layers (PAV). 28-day old specimens are exposed to 10% v/v solutions of HCl, H₂SO₄, and HNO₃ to evaluate changes in mechanical, physical, and microstructural characteristics through compressive strength, corrosion depth, and microscopy. Based on deterioration in strength and integrity, PAH or PAV can be adopted in absence of acid attack, whereas PAM is recommended in presence of acid attack.

• Journal of The Korean Society of Agricultural Engineers
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• v.64 no.1
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• pp.91-98
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• 2022

Multi-layered geotextile tubes may have problems on its stability when used as cofferdam. This study presents the shear strength characteristics at the interface between geotextiles and a cementitious binder material to improve the stability of the multi-layered geotextile tubes. In this study, two different types of geotextiles are used. After mixing with a rapid setting cement, fly ash, sand, accelerator, and water, the cementitious binder material is prepared at the interface between two geotextile samples and cured under water for a desired period. The specimen is placed on upper and lower direct shear boxes by using clamping systems. A series of direct shear tests for two different geotextiles are performed along the curing time under three vertical stresses. Experimental results show that the shear strength at the interface between the cementitious binder material and geotextiles is greater than that at the interface between two geotextiles. For two types of geotextiles, apparent cohesion occurs at the interface between the cementitious binder material and geotextiles. In addition, the friction angles for any curing time are improved, compared to the interface between two geotextiles. The cementitious binder material suggested for the interface between two geotextiles may be useful for the reinforcement of multi-layered geotextile tubes.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.265-274
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• 2024

The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

• Structural Engineering and Mechanics
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• v.92 no.1
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• pp.89-97
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• 2024

Discarded cigarette butts in the environment have caused significant pollution. Therefore, providing solutions to address these environmental issues is of great importance. Concrete is known as one of the most widely used materials around the world. Hence, this study investigates the feasibility of using cigarette butts to product concrete. For this purpose, cellulose acetate fibers obtained from cigarette butt filters were added to silica fume concrete in 10 different volume ratios. Then, the mechanical properties of the concrete samples, including compressive strength, Brazilian tensile strength, and flexural tensile strength, were examined. Based on the results, adding fibers to silica fume concrete improved the mechanical properties of the concrete. Among the 10 mixing designs, adding 0.2% by volume of fibers to silica fume concrete yielded the highest compressive and tensile strengths. In other words, adding 0.2% by volume of fibers resulted in a 16% and 34% increase in compressive strength and a 70% and 38% increase in Brazilian tensile strength at 7 and 28 days, respectively, compared to the state without cellulose acetate fibers. Additionally, the flexural tensile stress capacity increased by 56%. Furthermore, the vertical deformation tolerance in beam specimens increased by 287%, and the energy absorption capacity of the concrete beam also significantly increased. Consequently, along with the significant improvement in the mechanical properties of concrete, this study proposes a new and practicalstrategy to addressthe environmental issues caused by waste cigarette butts.

• Atmosphere
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• v.28 no.1
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• pp.99-112
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• 2018

In this study, the accuracy of ocean analysis data, which are produced from the Korea Meteorological Administration (KMA) Nucleus for European Modelling of the Ocean/Variational Data Assimilation (NEMO/NEMOVAR, hereafter NEMO) system and the HYbrid Coordinate Ocean Model/Navy Coupled Ocean Data Assimilation (HYCOM/NCODA, hereafter HYCOM) system, was evaluated using various oceanic observation data from March 2015 to February 2016. The evaluation was made for oceanic thermal environments in the tropical Pacific, the western North Pacific, and the Korean peninsula. NEMO generally outperformed HYCOM in the three regions. Particularly, in the tropical Pacific, the RMSEs (Root Mean Square Errors) of NEMO for both the sea surface temperature and vertical water temperature profile were about 50% smaller than those of HYCOM. In the western North Pacific, in which the observational data were not used for data assimilation, the RMSE of NEMO profiles up to 1000 m ($0.49^{\circ}C$) was much lower than that of HYCOM ($0.73^{\circ}C$). Around the Korean peninsula, the difference in RMSE between the two models was small (NEMO, $0.61^{\circ}C$; HYCOM, $0.72^{\circ}C$), in which their errors show relatively big in the winter and small in the summer. The differences reported here in the accuracy between NEMO and HYCOM for the thermal environments may be attributed to horizontal and vertical resolutions of the models, vertical coordinate and mixing scheme, data quality control system, data used for data assimilation, and atmosphere forcing. The present results can be used as a basic data to evaluate the accuracy of NEMO, before it becomes the operational model of the KMA providing real-time ocean analysis and prediction data.