• Journal of Plant Biology
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• v.14 no.1
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• pp.15-23
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• 1971

The productivity of summer phytoplankton communities in Lake Hwajinpo, Lake Yongrang and Lake Changja were studied by measuring vertical variation of chlorophyll a amounts. The author also classified the lake types on the basis of the amount of chlorophyll in the lake water. And in Lake Changja, the seasonal changes of stratification of chlorophyll were studies. In Lake Hwajinpo, the productive structure of the phytoplankton community in summer was found to be L-shaped and of the mesotrophic type. In Lake Yongrang, the productive structure of the phytoplankton community in summer was alo L-shaped and of the mesotrophic type. And maximum chlorophyll layer was near the lake bottom below the compensation depth. In Lake Changja, the structure of phytoplankton community in summer was reversed L-shaped and of the eutrophic type, with the maximum chlorophyll layer just below the surface. The vertical distribution of chlorophyll amounts as a measure of the productive structure almost always formed a stratum distribution except in September and sometimes in May, in Lake Changja. In September homogeneous distribution was observed.

• Journal of Plant Biology
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• v.26 no.3
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• pp.119-130
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• 1983

Algal vegetation in the subtidal zone between a small rock output and the Juckdo Island, eastern coast of Korea was investigated at several selected sites. The objectives of the survey were to descirbe the poorly known macroalgae community in this area and correlate the pattern of distribution as well as the change of zonatin with the environmental conditions. The water movement, light intensity and theinclinatin of substrate are considered as the environmental parameters. The upper and mid subtidal zones in sheltered area with less steep rocky surface are dominated by large brown algae Srgassum confusum; in the exposed area are characterised by species of Costaria costata. In the lower subtidal zone, the difference of vegetaton between the sheltered and the exposed areas is not recognized. At this depth the light intensity is an important ecological factor. Six narrow algal zones occur in the sheltered area, whereas two broad belts occur in the exposed area. the biomass value is 4 times greater in the sheltered area than in the exposed area.

• Journal of the korean society of oceanography
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• v.38 no.3
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• pp.101-110
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• 2003

We made intensive observations on the coastal upwelling off the coast of the southern East Sea from June to August in 2001. The upwelling exhibited a weekly waxing and waning. The coastal upwelling of the year 2001 was characterized by abrupt outbreaks and the small local scale. Upwelling occurred more frequently off the coast of Ulsan and Gampo as reported by the earlier observers. The spread of freshly upwelled colder water was varied by each upwelling event. Generally cold waters were carried away northeastward off Pohang province. The upwelled cold waters were saltier than the resident surface waters. The pH and salinity-normalized alkalinity support the idea that the upwelled waters originate from the interior of the East Sea. The extraordinarily high concentration of dissolved oxygen suggests that the upwelled waters are closely connected to the southward flowing North Korea Cold Current. Although a lower primary productivity was reported for the upwelling region, underway surface fluorescence measurement revealed that the recently upwelled waters supported up to an order of magnitude higher algal biomass than the ambient waters. Because thermohaline circulation of the East Sea is so vigorous, with an estimated time scale of less than one hundred years, that the coastal upwelling should be considered not as an anomaly but as a regular component of a circulatory system. A quantitative understanding of upwelling seems to be a key to elucidate material cycling and the associated biological production in the East Sea.

• Journal of Hydrospace Technology
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• v.2 no.1
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• pp.41-54
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• 1996

Sculptured surface structures such as ship hulls are traditionally formed up to the required double curved shape by line heating method. The nature of the line heating process is a transient thermal process, followed by a thermo-elastic-plastic stress field. The permanant shape is dependent on many factors involved in the process, Among them are torch speed and path, supplied heat type and amount , and plate size. Thus, the work is essentially leaded by experts with lots of experiences. However, in order to effectively improve productivity through automation, each factor should be clearly examined how much it affects the final shape. This can not be done only by experiments, but can be achieved by a mechanics-based approach. In this paper, we propose a conceptual configuration for plate forming system, and then present simulations of the line heating process with numerical data in practices and suggest a computerized process of the line heating for practical applications. The modeling of heating torch, water cooling, and the plate to be formed is proposed for the finite element analysis after the mechanics of line heating is studied. Parametric studies are given and discussed for the effects of plate thickness, torch speed and initial curvature in forming a saddle typed surface.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.2
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• pp.22-30
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• 2016

It is very important to obtain the net shape of the product to maximize the shear cutting surface of fine blanking. In this paper, the fine blanking die was manufactured to achieve part characteristics, such as flatness and a fully sheared surface. The V-ring in the fine blanking die was designed to prevent lateral movement of the material. The fine blanking experiment was conducted with the fine blanking die. The material usage rate was increased by over 5.7% and that of the water-soluble lubricant was decreased by over 33% when the 2-cavity die technology was applied to fine blanking. The capacity of the existing press could lead to productivity improvement and cost reduction. Thus, 2-cavity die technology for fine blanking with a minute module of an accurate gear for producing seat recliner parts was developed.

• Journal of Ship and Ocean Technology
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• v.12 no.1
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• pp.16-27
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• 2008

The interaction between advancing ships and the waves generated by them plays important roles in wave resistances and ship motions. Wave breaking phenomena near the ship bow at different speeds are investigated both numerically and experimentally. Numerical simulations of free surface profiles near the fore bodies of ships are performed and visualized to grasp the general trend or the mechanism of wave breaking phenomena from moderate waves rather than concentrating on local chaotic irregularities as ship speeds increase. Navier-Stokes equations are differentiated based on the finite difference method. The Marker and Cell (MAC) Method and Marker-Density Method are employed, and they are compared for the description of free surface conditions associated with the governing equations. Extra effort has been directed toward the realization of extremely complex free surface conditions at wave breaking. For this purpose, the air-water interface is treated with marker density, which is used for two layer flows of fluids with different properties. Adaptation schemes and refinement of the numerical grid system are also used at local complex flows to improve the accuracy of the solutions. In addition to numerical simulations, various model tests are performed in a ship model towing tank. The results are compared with numerical calculations for verification and for realizing better, more efficient research performance. It is expected that the present research results regarding wave breaking and the geometry of the fore body of ship will facilitate better hull form design productivity at the preliminary ship design stage, especially in the case of small and fast ship design. Also, the obtained knowledge on the impact due to the interaction of breaking waves and an advancing hull surface is expected to be applicable to investigation of the ship bow slamming problem as a specific application.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.5
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• pp.721-734
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• 2022

This study analyzed the spatio-temporal variation characteristics of major environmental factors such as primary productivity (PP), chlorophyll a, nutrients, sinking particle matters, and organic contamination and biochemical composition of surface sediment on a monthly basis for approximately 2 years around shellfish mariculture in Jaran Bay, Korea. In addition, PP in Jaran Bay was compared with that in other coastal areas and related policy plans were proposed. The average PP of the study area was high in summer and autumn with 6.43~115.43 mgC m^-2 hr^-1 range. This was lower than that in Gamak Bay and Masan Bay, whereas higher than that in Garorim Bay and the West Sea. The PP in coastal waters, where many aquaculture farms were distributed, significantly fluctuated. The different size compositions of phytoplanktons constituting chlorophyll a slightly varied by month, and little restriction existed on the productivity of phytoplanktons owing to the depletion of nutrients. Typically, the Redfield ratio was less than 16, indicating that nitrogen was the limiting factor for the growth of phytoplanktons. The biochemical composition of particulate organic matters in the water column showed the highest carbohydrates, but lipids and protein contents were high in surface sediments. The concentration of TOC and AVS of the surface sediments was high at inside of bay, and sometimes, exceeded the environmental criteria of fishing grounds. The organic C:N ratio of sediments ranged from 8.1 to 10.4 on average. PP had the highest correlation with chlorophyll a, nitrogen and protein of particle organic materials. Recently, chlorophyll a, DIN, and DIP of water column trends tended to decrease, however, the contamination of sediments increased. Considering the annual PP of 125.9 gC m^-2 yr^-1 and mariculture area (oyster) of 4.97 km², the annual carbon production from phytoplanktons was estimated to be about 625 tons, and the annual total wet weight of shellfish (oyster) was estimated to be about 6,250 tons.

• Journal of Korea Water Resources Association
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• v.56 no.11
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• pp.721-728
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• 2023

Agricultural drought is triggered by a depletion of moisture content in the soil, which hinders photosynthesis and thus increases carbon dioxide (CO₂) concentrations in the atmosphere. The aim of this study is to analyze the relationship between soil moisture (SM) and vegetation activity toward quantifying CO₂ concentration in the atmosphere. To this end, the MODerate resolution imaging spectroradiometer (MODIS), an optical multispectral sensor, was used to evaluate two regions in South Korea for validation. Vegetation activity was analyzed through MOD13A1 vegetation indices products, and MODIS gross primary productivity (GPP) product was used to calculate the CO₂ flux based on its relationship with respiration. In the case of SM, it was calculated through the method of applying apparent thermal inertia (ATI) in combination with land surface temperature and albedo. To validate the SM and CO₂ flux, flux tower data was used which are the observed measurement values for the extreme drought period of 2014 and 2015 in South Korea. These two variables were analyzed for temporal variation on flux tower data as daily time scale, and the relationship with vegetation index (VI) was synthesized and analyzed on a monthly scale. The highest correlation between SM and VI (correlation coefficient (r) = 0.82) was observed at a time lag of one month, and that between VI and CO₂ (r = 0.81) at half month. This regional study suggests a potential capability of MODIS-based SM, VI, and CO₂ flux, which can be applied to an assessment of the global view of the agricultural drought by using available satellite remote sensing products.

• Ocean and Polar Research
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• v.26 no.2
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• pp.255-263
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• 2004

This study was conducted to investigate the community structure and distributional pattern of meiobenthos in the deep-sea bottom of the Clarion-Clipperton Fracture Zone of the northeastern Pacific during July 2003. The samples were collected using the multiple corer at 13 stations along the transects fiom $5^{\circ}N\;to\;17^{\circ}N$. The most abundant meiobenthos was nematodes and followed by sarcomastigophorans; these two taxa comprised more than 70% of the total abundance at all stations. For size distribution analyses showed that animals which fit into the sieve mesh size of 0.063mm were abundant. The maximum density of meiobenthos was $147inds./10cm^2$ at station located in $7^{\circ}N$, and the minimum density was $6 inds./10cm^2$ at station located in $14^{\circ}N$. More than 60% of meiobenthos were distributed at surface sediment layer within 1.0cm, and the peak abundance was found at $0{\sim}0.25cm$ layer. The latitudinal distribution pattern of meiobenthos in the study area seemed to be related with the primary productivity of the surface water that is also connected to the water circulation pattern of the Pacific Ocean near the Equator, diverging at latitude of $8^{\circ}N$ and conversing at $5^{\circ}N$.

• Journal of Korean Society of Rural Planning
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• v.24 no.2
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• pp.47-58
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• 2018

Protected horticultural complexes would increase crop productivity but would adversely affect the groundwater recharge function in the area because the impervious area would increase. Further, they would limit the movement of living beings, affecting biodiversity. Therefore, this study evaluated the groundwater ecosystem services provided by protected horticultural complexes in terms of consistent utilization of water. The estimated amounts of groundwater loss obtained through quantitative assessment of groundwater infiltration showed that a higher impervious area results in higher losses. We, therefore, predict a much higher loss if similar changes in land use are realized on a nationwide scale. A plan to promote groundwater recharge in impervious areas is actively being discussed for urban areas; however, this plan is not yet applicable to farming areas. We consider it is essential to develop groundwater infiltration facilities for horticultural complexes, infiltration trenches, permeable pavements, surface water storage facilities, water purification facilities, etc. Further research and development of groundwater infiltration facilities is important for consistent utilization of water and the improvement of ecosystem services.