• Korean Journal of Ecology and Environment
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• v.41 no.1
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• pp.54-65
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• 2008

The seasonal dynamics of phytoplankton and water quality were evaluated bimonthly at 7 park ponds in the capital region from October 2004 to August 2005. With out the change of water temperature $(0.4\sim26.0^{\circ}C)$, cyanobacteria dominated in park ponds such as Gyungbokgung Gyunghyaeru and Seokchon reservoir. The standing crops of phytoplankton was significant related with cell densities of cyanobacteria (r=0.993), while they did not significant correlation with environmental factors. Almost of all park ponds in the capital region were classified as eutrophic state with high TP concentrations and TN/TP ratios less than 10. Major dominant cyanobacteria were as followed; Anabaena sp., Aphanocapsa elachista, Lyngbya contorta, Merismopedia elegans, Microcystis aeruginosa, M. wesenbergii, Microcystis sp., Oscillatoria sp., Phormidium tenue, and Plectonema sp. To date, although the concentration of chlorophyll-${\alpha}$ and cyanobacterial densities in the capital region was below the 'danger' level of WHO guidelines value, the monitoring of cyanobacterial densities and its toxin (microcystin) in recreational/bath water should be continued.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.1
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• pp.6-13
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• 2012

As ocean resources in shallow water areas are being exhausted, deep sea development is becoming common these days. Therefore floating type offshore structures are more competitive than fixed type structures, and FPSO is the most popular one these days. FPSO's are generally operated in a specific region and positioned to meet mostly head or bow waves in order to reduce roll motions. However this makes these vessels more vulnerable to green water around the bow region, and therefore the bow shape must be properly designed to mitigate green water damage. In the present study, experimental results for three different FPSO bow shapes in regular head waves were analyzed and compared to each other. Also CFD computations were carried out as a sample validation case for the database built for CFD code validation.

• Proceedings of the KIEE Conference
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• 1991.11a
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• pp.435-438
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• 1991

This work is aimed to clarify the effect of only crosslinking of polyethylene on the water tree propagation and thus the crosslinking of LDPE was made by use of $Co^{60}$ $\gamma$-ray irradiation at room temperature. For this purpose, before water tree testing under same test conditions, injection molded samples were made of LDPE using CNRS laboratory model and also some of them were irradiated under different dose rate for crosslinking. Afterwards, the aged specimens were put into microscopic investigation as a mean to compare their different morphological aspects by use of SEM for the fractured surface. The SEM observation points out that the untreed region in the irradiated PE shows the densed structure whereas that in the LDPE is not closely packed. Also in the water treed region of LDPE, the density and the dimension of voids are higher than those in irradiated PE. Based on our results, it seems that the difference in the PE structure could sufficiently contribute to cause the different water tree propagation of these materials.

• Journal of the korean society of oceanography
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• v.36 no.3
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• pp.59-71
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• 2001

In order to investigate the temporal variability of dissolved and particulate trace metals in the Han River, water samples were collected intermittently at two sites for 3 years (August 91 to December 94). Surface seawaters covering the range of salinity were also collected at the estuarine region to evaluate the role of estuary for the riverine fluxes of trace metals within the estuary during October 95 and 96. During the study period, dissolved metal concentrations in riverwaters varied by a factor of 5-10 for Fe, Ni, Co and Cu and 50-100 for Mn, Cd and Pb depending upon the water level; high concentration during the low water and low concentration in high water period except for Fe. The concentration of dissolved Fe increased with increasing water discharge. These concentration-discharge relationships of the studied trace metals are explained by the successive dilution of waters from two different origins, which can be presumably identified as anthropogenic discharges and watershed flushing. Although estuarine waters at early mixing region were not collected due to the difficulty of sampling, mixing behaviors of metals were inferred from the concentration-salinity relationships through the laboratory mixing experiment and field sampling, and distribution coefficients between dissolved and labile particulate phases. It is suggested that the Han River estuary plays a role of accumulating Fe, Mn, Co and Pb from riverine sources due to high turbidity caused by strong tidal current, whereas this system serves as a source of dissolved Cd due to release caused by extended residence time of riverine particles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1406-1415
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• 1996

Several recent studies have revealed that boiling heat transfer may be considerably enhanced in a narrow restricted region. In his study, the narrow restricted region was formed by attaching a perforated plate on top of a boiling surface. Through systematic experiments, effects of the hole size, hole pattern, gap width between the perforated plate and the boiling surface were investigated using water or R-113. Results show that perforated plates considerably enhance the boiling of water or R-113. For water, especially, they have outperformed commercial enhanced tubes, which confirms that boiling enhancement mechanism of the perforated plate (thin film evaporation beneath the elongated bubble) is very effective to the boiling of high surface tension liquids such as water. Optimum configuration was found - 3.0 mm hole diameter, 15 mm * 15 mm hole pattern, 0.3 ~ 0.5 mm gap width for water, and 2.0 mm hole diameter, 3.5 mm * 3.5 mm hole pattern, O.5 mm gap width for R-113. A correlation which correlates most of the data within .+-. 30% was also developed.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.3
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• pp.295-304
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• 2001

The hydrodynamic impact problem was studied from 1929 to recent. Especially, Impact pressure is important for the design of the ships and offshore structure and spacecrafts, and under weapons. A ship traveling at high speed or in heavy sea has its bow and bottom damaged by high pressure caused by impact with and detachment from the water surface. Considerable impact may also occur when large waves hit the cross member or deck plate of an offshore structure within the splash zone. Many engineering cases require consideration of impact pressure, the movement of objects and change of the flow field. This study was obtained the pressure distribution of a falling body that is deadrise angle $0^{\circ}$ and deadrise angle $5^{\circ}$ upon a water surface by the experiment with the impact machine. The theoretical equation was obtained the air region and the interface and the water region which devide 3 parties between the body and the water surface for an investigation of the complete phenomena. Pressure distributions and histories compare favorably with available experimental data. The numerical results are similar to the experimental results for the impact force type with Fo(1+$cos{\pi}t/tc$).

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.559-565
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• 2005

As the wave impinges on and overtops the structure, a large highly aerated region is created in front of the structure and water splashs on top of the structure. The broken wave in front of the structure and associated green water on top of the structure are highly aerated containing not only a large number of bubbles but also very large sizes of bubbles. In this paper, the velocity field of the highly aerated region and the splashing water on the top is measured using a modified PIV method incorporating the traditional PIV method with the shadowgraphy technigue by correlating the ' texture ' of the bubble images. The velocity fields of a plunging wave impacting on a structure in a two-dimensional wave flume is measured. It is found that the maximum fluid particle velocity in flout of the structure during the impinging process is about 1.5 times the phase speed of the wave, while the maximum horizontal velocity above the top is less than the phase speed, It is also found that the dam breaking solution does not work well in predicting the green water velocity.

• International Journal of Ocean System Engineering
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• v.3 no.2
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• pp.68-76
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• 2013

In this study, a 3D numerical model was used to predict nonlinear wave forces on a cylindrical pile installed in a shallow water region. The model was based on solving the viscous and incompressible Navier-Stokes equations for a two-phase flow (water and air) model and the volume of fluid method for treating the free surface of water. A new application was developed based on the cut-cell method to allow easy installation of complicated obstacles (e.g., bottom geometry and cylindrical pile) in a computational domain. Free-surface elevation, water particle velocities, and inline wave forces were calculated, and the results show good agreement with experimental data obtained by the Danish Hydraulic Institute. The simulation results revealed that the proposed model can, without the use of empirical formulas (i.e., Morison equation) and additional wave analysis models, reliably predict non-linear wave forces on an offshore wind turbine foundation installed in a shallow water region.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.215-220
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• 1996

Seasonal and interannual variations of the oceanic condition in the surface layer of the northwestern East Sea are described. The seasonal variation shows two types in the water circulation. In the first type the East Korean Warm Current (EUC) Water are dominant in the East Korean Bay in spring, while in summer the cold water region develops as the North Korean Cold Current (NKCC) becomes strong. In the second type the cold water appears in the East Korean Bay from spring, but in summer the EKWC comes close to the coast, thus influencing the coastal cold water region. The characteristics of the interannual variation can be classified into 4 types according to the relative strength between the EKWC and the NKCC, and the paths of these currents. In each case various sizes of cyclonic cold eddies and/or anti-cyclonic warm eddies are formed frequently in the East Korean Bay.

• Journal of Korean Society of Water and Wastewater
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• v.36 no.5
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• pp.275-287
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• 2022

In order to overcome the small scale of Korea waterworks and to achieve comprehensive improvement and innovation transformation, the waterworks integration was reviewed. The effect of consolidation was confirmed by the integration of the water supply business in the southern Gangwon region and the western Gyeongnam region in Korea, such as an increase in the flow rate and a decrease in the production unit cost. After facing management and service limitations overseas, more than 1,000 small-scale waterworks projects in the UK were integrated into 27 waterworks providers, and Japan also revised the Waterworks Act in December 2019 and is in the process of integrating waterworks. It is considered appropriate to promote the integration of waterworks projects in Korea by respecting the autonomy of local governments, but using a participatory method, a win-win method, and a linkage method. For the integration of waterworks projects, three strategies are proposed: First creating a national foundation for integration (revision of the Waterworks Act), Second establishing a waterworks integration strategy led by local governments, Third forming an external consensus and providing incentives for participation.