• Korean Journal of Remote Sensing
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• v.37 no.5_2
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• pp.1307-1315
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• 2021

The Changjiang Diluted Water (CDW) spreads over the East China Sea every summer and significantly affects the sea surface salinity changes in the seas around Jeju Island and the southern coast of Korea peninsula. Sometimes its effect extends to the eastern coast of Korea peninsula through the Korea Strait. Specifically, the CDW has a significant impact on marine physics and ecology and causes damage to fisheries and aquaculture. However, due to the limited field surveys, continuous observation of the CDW in the East China Sea is practically difficult. Many studies have been conducted using satellite measurements to monitor CDW distribution in near-real time. In this study, an algorithm for estimating Sea Surface Salinity (SSS) in the East China Sea was developed using the Geostationary Ocean Color Imager (GOCI). The Multilayer Perceptron Neural Network (MPNN) method was employed for developing an algorithm, and Soil Moisture Active Passive (SMAP) SSS data was selected for the output. In the previous study, an algorithm for estimating SSS using GOCI was trained by 2016 observation data. By comparison, the train data period was extended from 2015 to 2020 to improve the algorithm performance. The validation results with the National Institute of Fisheries Science (NIFS) serial oceanographic observation data from 2011 to 2019 show 0.61 of coefficient of determination (R²) and 1.08 psu of Root Mean Square Errors (RMSE). This study was carried out to develop an algorithm for monitoring the surface salinity of the East China Sea using GOCI and is expected to contribute to the development of the algorithm for estimating SSS by using GOCI-II.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.27 no.1
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• pp.17-32
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• 2022

The buffer capacity of southern Korean waters in summer was quantified using data set of temperature, salinity, dissolved inorganic carbon, total alkalinity obtained from August 2020 cruise. The geographical distribution and variability of six buffer factors, which amended the existing Revelle factor, are discussed their relationship with the hydrological parameters of temperature and salinity. The calculated results of six buffer factors showed the spatial variations according to the distributions of various water masses. The buffer capacity was low in the East Sea Surface Mixed Water (ESMW) and South Sea Surface Mixed Water (SSMW) where upwelling occurred, and showed an intermediate value in the Yellow Sea Surface Water (YSSW). In addition, the buffer capacity increased in the order of high temperature Tsushima Warm Current (TWC) and Changjiang Diluted Water (CDW). This means that the Changjiang discharge water in summer strengthens the buffer capacity of the study area. The highest buffer capacity of CDW is due to its relatively higher temperature and biological productivity, and a summer stratification. Temperature showed a good positive correlation (R²=0.79) with buffer capacity in all water masses, whereas salinity exhibited a poor negative correlation (R²=0.30). High temperature strengthens buffer capacity through thermodynamic processes such as gas exchange and distribution of carbonate system species. In the case of salinity, the relationship with buffer capacity is reversed because salinity of the study area is not controlled by precipitation or evaporation but by a local freshwater input and mixing with upwelled water.

• Korean Journal of Environmental Biology
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• v.41 no.1
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• pp.89-100
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• 2023

We investigated the spatial distribution of heterotrophic bacteria associated with different water masses in the northern East China Sea(ECS) in summer. The surface water masses were divided into the Changjiang Diluted Water (CDW) and high salinity water (HSW). In the CDW region, the concentrations of dissolved inorganic nitrogen (DIN) and chlorophyll-a (Chl-a), and micro Chl-a contribution were high; and bacterial abundance (BA) and ciliate abundance (CA) were also high. In the HSW region with relatively low DIN concentrations, Chl-a concentration and micro Chl-a contribution were low, but pico Chl-a contribution was increased compared to those in the CDW region. BA did not show any significant difference from the CDW region, but CA was decreased. BA showed a positive correlation with Chl-a concentration in the CDW region; however, it did not show a significant correlation with Chl-a concentration in the HSW region. The ratio of bacterial carbon biomass/phytoplankton carbon biomass was exponentially increased with a decrease in the Chl-a concentration. Compared to the past (1990-2000s), the surface phosphate concentrations and the size of dominant phytoplankton have recently decreased in the ECS. Considering this trend of nutrient decrease and miniaturization of the phytoplankton, our results indicate that changes in the strength of the oligotrophic water mass could alter the function of the microbial food web.

• Wind and Structures
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• v.25 no.5
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• pp.415-432
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• 2017

The nonlinear aerodynamic instability of a tensioned plane orthotropic membrane structure is theoretically investigated in this paper. The interaction governing equation of wind-structure coupling is established by the Von $K\acute{a}rm\acute{a}n's$ large amplitude theory and the D'Alembert's principle. The aerodynamic force is determined by the potential flow theory of fluid mechanics and the thin airfoil theory of aerodynamics. Then the interaction governing equation is transformed into a second order nonlinear differential equation with constant coefficients by the Bubnov-Galerkin method. The critical wind velocity is obtained by judging the stability of the second order nonlinear differential equation. From the analysis of examples, we can conclude that it's of great significance to consider the orthotropy and geometrical nonlinearity to prevent the aerodynamic instability of plane membrane structures; we should comprehensively consider the effects of various factors on the design of plane membrane structures; and the formula of critical wind velocity obtained in this paper provides a more accurate theoretical solution for the aerodynamic stability of the plane membrane structures than the previous studies.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.5 no.4
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• pp.357-362
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• 2000

Stable isotope ratios of oxygen and hydrogen were investigated in southern Yellow Sea in August 1997. Salinity showed good positive correlation with ${\delta}^{18}$O and ${\delta}$. The correlation between ${\delta}^{18}$O and ${\delta}$D is good. From the relationship between these parameters, we obtained two lines of conclusion: 1) seawater of study area I in summer is a mixture of Changjiang Water and modified Kuroshio Water; 2) stable isotopes are very useful tracers in studying property and behavior of water masses in the study area. In case when water masses can not be easily distinguished by T-S analysis, the stable isotopes seem to be powerful tools for this purpose.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.2
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• pp.207-218
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• 2017

Seawater with salinity of 32.5 psu or less is observed in the southern Japan/East Sea (JES) every autumn. It is confined to a surface layer 30-45 m in depth that expands to cover the entire JES in October. Two sources of "autumn low-salinity water" have been identified from historical hydrographic data in the western JES: East China Sea (ECS) water mixed with fresh water discharge from the Yangtze River (Changjiang) and seawater diluted with melted sea ice in the northern JES. Low-salinity water inflow from the ECS begins in June and reaches its peak in September. Low-salinity water from the northern JES expands southward along the coast, and its horizontal distribution varies among years. A rare observational study of the entire JES in October 1969 indicated that water with salinity less than 33.0 psu covered the southwestern JES; the lowest salinity water was found near the Ulleung Basin. In October 1995, the vertical distribution of salinity observed in a meridional section revealed that water with salinity of 33.6 psu or less was present in the area north of the subpolar front.

• Ocean and Polar Research
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• v.31 no.2
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• pp.219-229
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• 2009

In order to establish annual variations in the marine ecosystem of the East China Sea, suspended solids (SSs) and particulate organic carbon (POC) were extensively investigated in the northern part of the East China Sea from August 2003 to April 2008. Surface SS concentrations showed large spatial variations in spring and fall, but not in summer. Surface SS concentrations in spring were lower than those in summer and fall. In summer, SSs discharged from Changjiang were mostly deposited in the coastal areas and did not reach our study area which was located about 260 km from the river mouth. High SS concentrations were observed near the bottom, which resulted from resuspension of bottom sediments by the bottom currents. Surface POC concentrations did not exhibited large seasonal variations. Phytoplankton biomass was a main factor controlling surface POC concentrations. POC/chlorophyll ratios showed large seasonal variations, with maximum numbers in summer. POC/PON ratios were higher in summer than the Redefied ratio (6.6), while they were lower in spring and fall. In summer, higher POC/chlorophyll and POC/PON ratios were probably attributed to the high phytoplankton mortality caused by nutrient depletion in surface waters.

• Structural Engineering and Mechanics
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• v.57 no.6
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• pp.1085-1105
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• 2016

The drainage problem in bifurcations causes pecuniary losses when hydropower stations are undergoing periodic overhaul. A new design philosophy for Y-typed bifurcations that are flat-bottomed is proposed. The bottoms of all pipe sections are located at the same level, making drainage due to gravity possible and shortening the draining time. All fundamental curves were determined, and contrastive analysis with a crescent-rib reinforced bifurcation in an actual project was conducted. Feasibility demonstrations were researched including structural characteristics based on finite element modeling and hydraulic characteristics based on computational fluid dynamics. The new bifurcation provided a well-balanced shape and reasonable stress state. It did not worsen the flow characteristics, and the head loss was considered acceptable. The proposed Y-typed bifurcation was shown to be suitable for pumped storage power stations.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.645-655
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• 2017

To determine the seismic applicability of a long-span railway concrete upper-deck arch bridge with concrete-filled steel-tube (CFST) rigid skeleton ribs, some fundamental principles and seismic approaches for long-span bridges are investigated to update the design methods in the current Code for Seismic Design of Railway Engineering of China. Ductile and mixed isolation design are investigated respectively to compare the structural seismic performances. The flexural moment and plastic rotation demands and capacities are quantified to assess the seismic status of the ductile components. A kind of triple friction pendulum (TFP) system and lead-plug rubber bearing are applied simultaneously to regularize the structural seismic demands. The numerical analysis shows that the current ductile layout with continuous rigid frame approaching spans should be strengthened to satisfy the demands of rare earthquakes. However, the mixed isolation design embodies excellent seismic performances for the continuous girder approaching span of this railway arch bridge.

• Journal of the korean society of oceanography
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• v.35 no.2
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• pp.65-77
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• 2000

A simple but effective method has been developed for estimating diurnal and semi-diurnal tidal currents from trajectories of satellite-tracked drifters. The estimation method consists of separation of tidal current signals contained in the drifter trajectories, computation of undulations by diurnal and semi-diurnal currents, and correction of dominant diurnal and semi-diurnal tidal constituents. M$_2$ tidal currents estimated from drifter trajectories in the Yellow Sea are well consistent with those observed by moored current meters and this supports the validity of this method. We have constructed M$_2$ tidal current chart in the Yellow Sea by applying this method to available drifter trajectories collected during 1994-1998. According to this chart, M$_2$ current in the Yellow Sea rotates in the clockwise direction south of 35$^{\circ}$ 30'N but in the counterclockwise one to the north. Also it is found that the M$_2$ current is strong in the bank area northeast of the Changjiang River mouth and in the Korean coastal area, while it is weak in the deep central trough.