• Journal of the Korean Society for Marine Environment & Energy
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• v.7 no.2
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• pp.64-69
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• 2004

The results of analyzing the hydrographic observations in the southwestern sea of Jeju Island in the last 10 days of August 1999 to investigate the characteristics of oceanic front area appeared in the East China Sea in August from is summarized as follows: In Line A, a front appears at Station A5 of 124°E and 31°30'N, showing relatively uniform density of 21.4 to 22.1 in the surface layer of 50m depth, which is distinguished from 22.0 shown in the sides of China and open ocean. In Line B, a front also appears at Station B6 of 124°E and 33°N, of which density is distinguished from 20.0 shown in the sides of China and open ocean as In Line A. As a result, the front area caused by fresh water runoffs from the Yangtze River in the East China Sea is formed at 124°E and 124°30'in the direction of east and northeast from Yangtze River, respectively. Nutrient concentrations in the study area are characterized by higher density in the side of China and by clear density difference between the upper and the lower layers in the side of open ocean, while by uniformly lower density concentration between the upper and the lower layers in the front area. Chlorophyll-α concentrations is high in the sides of China and open ocean, while low in the front area. Judging from the above results, the productivity in the front area is lower according to the inactivity of phytoplankton due to increased flow from vertical mixing between the upper layer and the lower layer. Also, the front area in the East China Sea in summer may be moved towards the adjacent sea of Jeju Island by increasing fresh water runoffs from the Yangtze River in summer.

• Journal of the Korean Society of Marine Environment & Safety
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• v.11 no.1 s.22
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• pp.77-82
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• 2005

In order to investigate the initial stage of deep water formation between Vladivostok and the subpolar front in the East Sea, the factors, temperature, salinity, dissolved oxygen, measured by multi-ship surveys in ]969 have been used. Deep water formation in the .cast Sea occurs in essentially two different forms: near continent and open ocean formation. The position of eddy derived from potential vorticity matches well with that of deep water formation. The vertical and horizontal distributions of potential vorticity, geostrophic current, temperature, salinity and dissolved oxygen give clues for the preconditioning phase qf open ocean formation like a doming of isotherm, associated with a cyclonic circulation.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.6
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• pp.23-35
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• 2023

In this study, we developed a method to determine the flood-limited water levels of agricultural reservoirs, considering both their irrigation and flood control functions. Irrigation safety and flood safety indices were defined to be applied to various reservoirs, allowing for a comprehensive assessment of the irrigation and flood control properties. Seasonal flood-limited water level scenarios were established to represent the temporal characteristics of rainfall and agricultural water supply and the safety indices were analyzed according to these scenarios. The optimal scenarios were derived using a schematic solution based on Pareto front analysis. The method was applied to Obong, Yedang, and Myogok reservoirs, and the results showed that the characteristics of each reservoir were well represented in the safety indices. The irrigation safety of Obong reservoir was found to be significantly influenced by the late-stage flood-limited water level, while those of Yedang and Myogok reservoir were primarily affected by the early and mid-stage flood-limited water levels. The values of irrigation safety and flood safety indices for each scenario were plotted as points on the coordinate plane, and the optimal flood-limited water levels were selected from the Pareto front. The storage ratio of the optimal flood-limited water levels for the early, mid, and late stages were 65-70%, 70%, and 75% for Obong reservoir, 75%, 70-75%, and 65-70% for Yedang reservoir, and 75-80%, 70%, and 50% for Myogok reservoir. We expect that the method developed in this study will facilitate efficient reservoir operations.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.115-125
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• 2001

To examine the movement of the freshwater discharged artificially into the estuary during ebbing period in the Keum River dike we observed surface salinity variations in three stations along the estuary channel in May 1998 and July 1997 and surface temperature and salinity along the ferry-route between Kunsan and Changhang during eighteen days in July 1999. Based upon the typical features of observed salinity variation, we analyzed the excursion and decay processes of the discharged water. When freshwater is discharged, the low-salinity water forms strong salinity front over the entire estuary width, which basically moves forth and back by tidal modulation along the channel, producing the sudden change of surface salinity with the front passage. Salinity distribution along the channel, which is deduced from time variation of mean salinity over the estuary width, after one tidal period from gate operation suggests that diluted low-salinity water is trapped to the front and surface salinity increases gradually toward the upstream region. This frontal distribution of salinity is interpreted to be produced by the sudden gate operation supplying and stopping of freshwater within about two hours. Daily repeat of freshwater discharge produces separation (double front) or merge between decaying and new-generated fronts depending on dike-gate opening time, and the front decays with salinity increasing if the freshwater supply is stopped more than two days. In addition, the observed fluctuations and deviations in surface salinity variation is explained in terms of the differences of fronts intensity, their transition time and temporal salinity front running along the channel, which can be generated due to artificial gate-operation for the discharging time and water volume in the estuary dike.

• The Korean Journal of Quaternary Research
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• v.17 no.2
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• pp.129-133
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• 2003

Water is critically important for Tricholoma matsutake(Tm) growth because it is the major component of the mushroom by over 90%. The mushroom absorbs water through the below ground hyphal colony. Therefore, the objectives of our study were to investigate spatio-temporal water changes in Tm colonies. This study was carried out at Tm fruiting sites in Sogni Mt National Park, where the below-ground mushroom colonies have been irrigated. To identify spatial water status within the Tm soil colony soil moisture and ergosterol content were measured at six positions including a mushroom fruiting position on the line of the colony radius. To investigate temporal soil moisture changes in the soil colony, Time Domain Reflectometry(TDR) sensors were established at the non-colony and colony front edge, and water data were recorded with CR10X data logger from late August to late October. Before irrigation, whereas it was 12.8% at non-colony, the soil water content within Tm colony was 8.0% at 0-5cm from the colony front edge, 6.2% at 10-15cm and 6.5-7.5% at 20-40cm. And the content was 12.1% at 80cm distance from the colony edge, which is similar to that at the non-colony. In contrast, ergosterol content which is proportional to the live hyphal biomass was only 0.4${\mu}g$/g fresh soil at the uncolonized soil, while 4.9 $\mu\textrm{g}$/g fresh soil at the front edge where the hyphae actively grow, and 3.8 ${\mu}g$/g fresh soil at the fruiting position, l.1${\mu}g$/g at 20cm distance and 0.4${\mu}g$/g in the 40cm rear area. Generally, in the Tm fungal colony the water content changes were reversed to the ergosterol content changes. While the site was watered during August to October, the soil water contents were 13.5∼23.0% within the fungal colony, whereas it was 14.5∼26.0% at the non-colony. That is, soil water content in the colony was lower by 1.0∼3.0% than that in the non-colonized soil. Our results show that Tm colony consumes more soil water than other parts. Especially the front 30cm within the hyphal colony parts is more critical for soil water absorption.

• Journal of the Korean Geosynthetics Society
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• v.10 no.4
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• pp.71-79
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• 2011

In this study, the variation of wetting front and ground water level at the embankment constructed in the Saemangeum area were predicted considering rainfall duration times and the slope stability analysis of the embankment was carried out according to prediction results of wetting front and ground water level. The embankment was formed by dredging soils. A suction stress, a cohesion and a frictional angle of dreding soils measured by soil tests were applied to estimate the unsaturated soil properties. According to the analysis results of the wetting front and the ground water level for various rainfall duration time, the wetting front began to descend from the upper part of embankment at the beginning time of rainfall and after 1 hour of rainfall duration time. After that, the ground water level continued to ascend as the rainfall duration time was getting longer. After rainfall, the ground water level was distributed at a certain depth, and the ground water level was gradually descending as time goes by. According to the slope stability analysis of the embankment considering the variation of the wetting front and the ground water level, the safety factor of slope was rapidly reduced as the rainfall began to infiltrate into the ground, and the minimum safety factor of slope was estimated after 24 hours of rainfall duration time. Meanwhile, the safety factor of slope was increased with regaining the matric suction in the ground after rainfall.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.193-200
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• 1999

Since Broms and Bennermark(1967) suggested the face stability criterion based on laboratory extrusion tests and field observations, the face stability of a tunnel driven in cohesive material has been studied by several authors. And recently, more general solution for the tunnel front is given by Leca and Panet(1988). They adopted a limit state design concept to evaluate the face stability of a shallow tunnel driven into cohesionless material and showed that the calculated upper bound solution represented the actual behavior reasonably well. In this study, two factors are simultaneously considered for assessing tunnel face stability: One is the effective stress acting on the tunnel front calculated by upper bound solution; and the other is the seepage force calculated by numerical analysis under the condition of steady state ground water flow. The model tests were performed to evaluate the seepage force acting on the tunnel front and these results were compared with results of numerical analysis. Consequently, the methodology to evaluate the stability of a tunnel face including limit analysis and seepage analysis is suggested under the condition of steady state ground water flow.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.502-513
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• 2007

This paper describes the rainfall-induced slope failures caused by infiltration due to prolonged rainfall. The emphasis was on quantifying the effect of fine-grained contents which are influencing on the infiltration rate in the wetting front of initially unsaturated slopes during rainfall. Suction tests by tensiometer were performed for five mixture specimens with varying fine-grained contents and then, numerical analyses for the stability of unsaturated slopes are carried out for different relative densities and mixture portions based on the soil water characteristic curves obtained by GCTS pressure plate. It is shown that the fines are highly influenced on wetting front suction of unsaturated soil slopes. Based on the results, it is found that until 15% fine content is the limit showing different wetting front suction, beyond which the wetting band depth do not affect considerably the stability of unsaturated slopes.

• 어항어장
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• s.13
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• pp.87-93
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• 1990

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.237.1-237.1
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• 2010

Recent developments such as concern over global warming, depletion of fossil fuels and increase in energy demands by the increasing world population has eventually lead to mass production of electricity using renewable sources. Ocean contains energy in form of thermal energy and mechanical energy: thermal energy from solar radiation and mechanical energy from the waves and tides. The current paper looks at generating power using waves. The primary objective of the present study is to maximize the primary energy conversion (first stage conversion) of the base model by making some design changes. The model entire consisted of a numerical wave tank and the turbine section. The turbine section had three components; front guide nozzle, augmentation channel and the rear chamber. The augmentation channel further consisted of a front nozzle, rear nozzle and an internal fluid region representing the turbine housing. Different front guide nozzle configuration and rear chamber design were studied. As mentioned, a numerical wave tank was utilized to generate waves of desired properties and later the turbine section was integrated. The waves in the numerical wave tank were generated by a piston type wave maker which was located at the wave tank inlet. The inlet which was modeled as a plate wall which moved sinusoidally with the general function, $x=asin{\omega}t$. In addition to primary energy conversion, observation of flow characteristics, pressure and the velocity in the augmentation channel, rear chamber as well as the front guide nozzle are presented in the paper. The analysis was performed using the commercial code of the ANSYS-CFX. The base model recorded water power of 29.9 W. After making the changes, the best model obtained water power of 37.1 W which represents an increase of approximately 24% in water power and primary energy conversion.