• Journal of ILASS-Korea
• /
• v.23 no.4
• /
• pp.192-204
• /
• 2018

In this study, a 3D CFD analysis method for the combustion process was established for a low calorific value syngas-diesel dual-fuel engine operating under very lean fuel-air mixture condition. Also, the accuracy of computational analysis was evaluated by comparing the experimental results with the computed ones. To simulate the combustion for the dual-fuel engine, a new dual-fuel chemical kinetics set was used that was constituted by merging two verified chemical kinetic sets: n-heptane (173 species) for diesel and Gri-mech 3.0 (53 species) for syngas. For dual-fuel mode operations, the early stage of combustion was dominated by the fuel burning inside or near the spray plume. After which, the flame propagated into the syngas in the piston bowl and then proceeded toward the syngas in the squish zone. With the baseline injection system and piston shape, a significant amount of unburned syngas was discharged. To solve this problem, effects of the injection parameters and piston shape on combustion characteristics were analyzed by calculation. The change in injection variables toward increasing the spray plume volume or the penetration length were effective to cause fast burning in the vicinity of TDC by widening the spatial distribution of diesel acting as a seed of auto-ignition. As a result, the unburned syngas fraction was reduced. Changing the piston shape with the shallow depth of the piston bowl and 20% squish area ratio had a significant effect on the combustion pattern and lessened the unburned syngas fraction by half.

• Tunnel and Underground Space
• /
• v.29 no.1
• /
• pp.30-37
• /
• 2019

Some leading countries in mining have a very quantitative guideline for underground mine opening design which is useful to minimize mine hazards such as rockfall and collapse. Those hazards sometimes can cause a huge damage on human life and property in the mines. Construction guidelines of underground mines in Korea consist of qualitative and general expressions although the workers' safety rules and guides are well provided. Recently, mining operations in Korea are going underground due to the environmental regulations and resource depletion at shallow depth, and therefore there is a growing demand on a specialized and systematic guideline for mine opening design securing the underground stability. In this paper, current status of mining industry, research trends, and mining guidelines in Korea and overseas have been reviewed to give an insight into developing a new Korean guideline for underground mine design.

• Journal of Wetlands Research
• /
• v.20 no.4
• /
• pp.330-337
• /
• 2018

The Korean Eutrophication Index($TSI_{ko}$) was estimated using water quality monitoring data of eight main sites in the SoOoak River watershed. The environmental characteristics of rivers were classified and evaluated using the $TSI_{ko}$ for each factor calculated by COD, T-P, and Chl-a. There is a good condition for the algae to grow due to shallow water depth, inflow of non-point source pollution during rainfall, influx of sewage treatment effluent and increase of residence time. It shows trophic state more than mesotrophication year round. Especially, in case of Chuso point, which is the inflow point of Daecheong Lake, the water quality deteriorated due to hydraulic characteristics and showed the eutrophic state. Therefore, it is necessary to establish the measures to improve the water quality through the precise monitoring of SoOak River.

• Journal of Korean Society on Water Environment
• /
• v.35 no.2
• /
• pp.165-180
• /
• 2019

Water quality data of 81 lakes in Korea, 2013 ~ 2017 were analyzed. Most water quality parameters showed left-skewed distribution, while dissolved oxygen showed normal distribution. pH and dissolved oxygen showed a positive correlation with organic matter and nutrients, which appeared to be a nonsense correlation mediated by the algae. The ratio of $BOD_5$ and $COD_{Mn}$ to CBOD was 21 % and 52 % in the freshwater lakes, respectively. TOC concentration appeared to be underestimated by the UV digestion method, when salinity exceeds $700{\mu}S\;cm^{-1}$. In terms of nitrogen/phosphorus ratio, the limiting factor for algal growth seemed to be phosphorus in most of the lakes. Chlorophyll ${\alpha}$ increased acutely with decrease of N/P ratio. However, it seemed to be a nonsense correlation mediated by phosphorus concentration, since the N/P ratio depended on phosphorus. The N/P ratio of brackish lakes was lower than that of the freshwater, at the same concentration of phosphorus. It is worth examining denitrification that occurs, in bottom layer and sediment, during saline stratification. $Chl.{\alpha}$ concentration decreased in the form of a power function with increase of mean depth. The primary reason is that deep lakes are mainly at the less-disturbed upstream. However, it is necessary to investigate the effect of sediment, on water quality in shallow lakes. Light attenuation in the upper layer, was dominated by tripton (non-algal suspended solids) absorption/scattering (average relative contribution of 39 %), followed by CDOM (colored dissolved organic matter) (average 37 %) and $Chl.{\alpha}$ (average 21 %).

• The Journal of Engineering Geology
• /
• v.31 no.3
• /
• pp.257-267
• /
• 2021

Constraints on the structure and composition of the active layer are important for understanding permafrost evolution. Soil convection owing to repeated moisture-induced freeze-thaw cycles within the active layer promotes the formation of self-organized patterned ground. Here we present the results of ground penetrating radar (GPR) surveys across a selected sorted circle near King Sejong Station, Antarctica, to better delineate the active layer and its relation to the observed patterned ground structure. We acquire GPR data in both bistatic mode (common mid-points) for precise velocity constraints and monostatic mode (common-offset) for subsurface imaging. Reflections are derived from the active layer-permafrost boundary, organic layer-weathered soil boundary within the active layer, and frozen rock-fracture-filled ice boundary within the permafrost. The base of the imaged sorted circle possesses a convex-down shape in the central silty zone, which is typical for the pattern associated with convection-like soil motion within the active layer. The boundary between the central fine-silty domain and coarse-grained stone border is effectively identified in a radar amplitude contour at the assumed active layer depth, and is further examined in the frequency spectra of the near- and far-offset traces. The far-offset traces and the traces from the lower frequency components dominant on the far-offset traces would be associated with rapid absorption of higher frequency radiowave due to the voids in gravel-rich zone. The presented correlation strategies for analyzing very shallow, thin-layered GPR reflection data can potentially be applied to the various types of patterned ground, particularly for acquiring time-lapse imaging, when electric resistivity tomography is incorporated into the analysis.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.46 no.1
• /
• pp.99-115
• /
• 2022

The purpose of this study is to explore the benefits of social capital obtained through the use of social media from the perspective of fashion. The study conducted in-depth interviews with 10 women in their 20s who utilized Instagram and YouTube for fashion-related activities. The results show that bonding social capital was related to Instagram and led increasingly to narrow and deep relationships with acquaintances who had already established offline relationships. The study also finds that informational benefit was derived from people who use Instagram image information for smart fashion consumption; in addition, positive feedback on their posts brought the emotional benefit of psychological satisfaction. On the other hand, bridge social capital developed from YouTube users and subscribers. The study discovers that YouTuber public communication or the exchange of opinions leads to an increase in bridge social capital, which is a wide and shallow relationship. Video-based YouTube brought informational benefits as a specific product description, and there were emotional benefits in terms of entertainment while watching videos that combined fashion and entertainment. This report sheds light on individual fashion activities on social media, which is discussed from the perspective of social capital.

• Ocean and Polar Research
• /
• v.44 no.4
• /
• pp.331-338
• /
• 2022

The high latitude scleractinian coral Alveopora japonica Eguchi, 1965 occurs in high density in the shallow rocky subtidal in Jeju Island, forming coral carpets. Despite its ecological role providing a unique habitat for other benthic organisms, the benthic fauna associated with the A. japonica coral carpet is poorly known. To identify fauna associated with the coral carpet, we explored three sites dominated by A. japonica and one control site on northwestern Jeju Island in May 2013. Using SCUBA, we collected A. japonica and the epibenthic mega-fauna associated with the colonies in 1×1 m² and identified them to the species level. At a depth of 10 to 15 m, A. japonica colonies heavily covered the seafloor, forming a layer called a coral carpet, with a density of 94 (Keumneung-ri), 133 (Biyangdo), and 155 (Gwidok-ri) colonies/m². Thirty-four molluscan species were identified from the four sites, including 20 bivalves and 14 gastropods. The coral carpets were enriched with sessile bivalves compared to the control site, as we identified twenty bivalve and eight gastropod species from the coral carpets. Most bivalve species associated with the coral carpets had tropical-subtropical affinities, while gastropods were mainly subtropical and subtropical-low boreal species. Leiosolenus lischkei M. Huber, 2010, in the family Mytilidae and Barbatia steamsi (Pilsbry, 1895), in the family Arcidae, were the two most abundant bivalve species in the coral carpet, L. lischkei being a borer, and B. stearnsi a nestler. The tropical to subtropical Pacific star shell Astralium haematragum (Menke, 1829)was the most abundant gastropod at the study sites. The bivalves and gastropods associated with the coral carpet were small-sized juveniles or sub-adults, suggesting that the coral carpet provides a micro-habitat for the bivalves and gastropods.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.6
• /
• pp.29-39
• /
• 2022

This study investigates the behavior of a circular vertical shaft wall in the absence and presence of a groundwater table. The effects of wall deflection, backfill settlement, and earth pressure distribution around the circular vertical shaft caused by sequential excavations were quantified. The vertical shaft was numerically simulated for different excavation depths of the bearing layer (weathered soil, weathered rock, soft rock) and transient and steady-state flows in the absence of a groundwater table. The backfill settlements and influential area were much larger under transient flow conditions than in steady-state flow. On the contrary, the horizontal wall deflection was much larger in steady state than in the transient state. Moreover, less settlement was induced as the excavation depth increased from weathered soil to weathered rock to the soft rock layer. Finally, the horizontal stresses under steady- and transient-state flow conditions were found to exceed Rankine's earth pressure. This effect was stronger in the deeper rock layers than in the shallow soil layers.

• Ecology and Resilient Infrastructure
• /
• v.9 no.3
• /
• pp.141-153
• /
• 2022

In this study, a numerical model of debris flow considering driftwood and entrainment erosion is developed. Subsequently, numerical simulations based on the observation data of the 2011 Mt. Umyeon are performed. To develop the debris flow model, the Nays2DFlood model, which is a flooding model based on the shallow water equation, is coupled with the transport diffusion of mixed sediment concentration, debris flow bottom shear stress, and entrainment erosion modules. The simulation closely reproduced the depth, flow velocity, and debris flow volume of Mt. Umyeon. In addition, the reproducibility of the simulation result with driftwood is more accurate than that without driftwood. The results of this study can facilitate in establishing measures to reduce debris disasters, thus alleviating the current increase in debris damage due to climate change.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.34 no.6
• /
• pp.258-265
• /
• 2022

In Korea, the hydraulic model tests for measuring the wave overtopping have been almost conducted with no bottom slope or single slope condition in Korea. In this study, the bottom seabed for the coastal road area was fabricated at the wave flume and the wave overtopping was measured. The overtopping rate was also measured with the numerical modelling by OLAFoam. The measuring data were compared with EurOtop manual. It could be known the the influence of the foreslope in front of the vertical wall was significant and the these effects should be concerned when designing the coastal structures. And also it could be known that OLAFoam could be used to predict the wave overtopping rate for the complex bottom topography.