• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.2
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• pp.53-58
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• 1998

Ekman layer equation with rough-bottom boundary condition has been solved to determine the effect of roughness on the magnitude of Ekman veering. The bottom boundary condition and the flow field were expanded in a power of roughness (h) which is always smaller than the Ekman layer thickness (${\delta}_E$). By changing the magnitude of roughness parameter (h/${\delta}_E$), the magnitude of the veering, which rotates counterclockwise from the interior geostrophic flow, has been computed. At a fixed depth within the Ekman layer, the magnitude of veering increases as the roughness parameter increases. However, the cross-isobar flux turns out to decrease with increasing roughness. To verify the analytic solution, laboratory experiments were carried out. Rough-bottom cylinderical container filled with homogeneous fluid was sit on a rotating table. The flow pattern during the period of steady spin-up shows that the degree of veering coincides well with the analytic results for various roughness parameters.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.3 no.4
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• pp.228-233
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• 1998

This study presents a close-range photogrammetry that is applicable to beach profile estimation using a non-metric camera. Based on the analysis of oblique video image in which the video camera was installed on a horizontal plane and the field of view was fixed, a new equation to analyze a photograph was developed considering the following aspects: (1) camera is allowed to be rotated about its optical axis and (2) a simple error model is adopted to correct lens distortion and other systematic errors associated with the non-metric camera, which improves accuracy of non-metric imageries. To test the modified technique, photographs of the beach were taken near the Donghae City in February, 1998. In addition, beach profiles were surveyed with conventional dumpy level and surveying staff. RMS error between the estimated and measured beach profiles is less than 10 cm in elevation.

• Journal of Welding and Joining
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• v.28 no.1
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• pp.66-71
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• 2010

With large specific strength and outstanding corrosion resistance and erosion resistance in sea water, titanium and titanium alloy are widely used in heat exchanger production. In particular, pure titanium demonstrates outstanding molding performance and may be considered optimal for production of heat exchanger. Since titanium is very vulnerable to oxidation and embrittlement during welding, processes with less heat input are widely used, and laser welding is widely applied by considering production performance and shield etc in atmosphere. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through oxygen and nitrogen quantitative analysis and hardness measurement, and evaluated welding performance and mechanical properties of butt welding. This study evaluated field applicability of lap welding to heat exchange plate of LPG re-liquefaction device for ships through tensile stress test, hardness test and internal pressure test etc after deducing optimal weding condition and applying to actual heat exchange plate. In bead overlap area, the experiment produced sound welds with no porosity or defect by increasing and decreasing laser power, and tensile-shear test results indicated virtually the same tension and yield strength as base metal. As a result of measuring hardness at lateral cross section and bead overlap zone of actual heat exchanger welds, hardness difference within 20Hv was produced at base metal, HAZ and weldment, and as a result of pneumatic and hydraulic pressure test, no leakage occurred.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.1
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• pp.18-24
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• 1999

The satellite image acquired by RADARSAT SAR on August 15, 1996 reveals internal waves in north coastal waters of Cheju Island. It is indicated from the image data, the tidal elevation data, and the bottom topography data, the internal waves seem to be generated by interaction between shallow bottom and tidal currents travelling in the stratified water in the summer time during the tidal changeovers from ebb to flood. The internal waves generated in such condition show patterns of trains of solitons. Probable amplitude of observed solitons is calculated using estimation of the soliton wave length from SAR image data and K-dV equation. Detection of the internal waves is very significant not only to military strategist for underwater maneuvers such as operation of submarines, but also to physical and biological oceanographers. Temporal and spatial variation of the internal waves are needed to be measured by simultaneous in-situ field study together with SAR to examine the nature of these internal waves.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.1
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• pp.41-52
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• 2014

The impact of freshwater discharge on plankton was investigated in a semi-closed Cheonsu Bay during the rainy season. Field observations for environmental factors (seawater temperatures, salinities, chlorophyll a concentrations and nutrient concentrations) and zooplankton sampling were carried out from June 27 to September 1, 2012 at about 10 days interval. The relationship between the measured parameters and estimated values of zooplankton abundance were examined. After freshwater discharge, nutrient concentrations increased up to about twice and resultant increase of chlorophyll a followed within about 10 days. Both positive and negative impacts on zooplankton were observed. Positive one was the numerical response of zooplankton on this increased food supply, and negative one was the increased mortality caused by sudden changes in salinity. Maximum mortality of copepods was found to be up to 40%, although fast sinking of carcass made it difficult to estimate reliable mortality caused by salinity shock.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.2
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• pp.96-102
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• 2014

A three-dimensional beach evolution model was presented to predict morphodynamics around a river mouth. The presented model was based on the depth-averaged (2DH) and quasi three-dimensional (Q-3D) nearshore current modules, and the model took into account shoreline changes, the effect of advection diffusion of suspended load and discharged sediments from the river. First, the 3D beach evolution model was applied to the formation of sand spits and terrace at the river mouth in order to investigate the performance of the model. Secondly, the model was applied to the river mouth at the Ara River, facing the Sea of Japan. The formation of sand spit at the Ara River in winter season was reproduced. The computed result showed qualitatively agreement with field site observation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.350-360
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• 2016

In order to investigate characteristics of waves and currents varying in space in the Haeundae coast in winter, numerical simulations by using a 2-D spectral wave model(SWAN) and 2-DH hydrodynamic model(Delft3D) were carried out in this study. The results of numerical simulations were validated with the field data collected at several different locations in the study area in February, 2014. From the numerical simulations, it was found that waves and currents were significantly influenced in terms of direction and magnitude by bottom topography characterized by straggling rock crops covered with sea grasses. The coupling of SWAN and Delft3D models also revealed that alongshore currents directing from the east to the west were developed in the nearshore, due to the influence of larger waves with the main incident direction from the east.

• Economic and Environmental Geology
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• v.18 no.1
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• pp.55-63
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• 1985

Studies based on field observation and laboratory analysis of the littoral sands of beaches in Jeju Island indicate that the shores exhibit a great variation in both the beach geometry and the composition in terms of geological agents. Most of the beaches around the Island are developed in relatively small patches and discontinuous, as the result of intervening sea cliffs and rocky headlands. The sand quality and the dimensions of the beaches in the Island are relatively poor; for example, these beaches are 220~2,780m in length, 41~313m in width, and $7^{\circ}$ steepness in average foreshore slope. According to the textural parameters analysis, the beach sediments in study portion shows medium grained ($average\;1.42{\phi}$), moderately well sorted ($average\;0.65{\phi}$) and negative skewed ($average\;0.34{\phi}$), which seems to reflecting a high energy marine depositional environment. The heavy and light minerals of te beach sediments are composed of quartz, volcanic fragments, Na-Ca feldspar, olivine, augite as major constituents, along with apatite, biotite and other minor components, which originates from the adjacent geology. The content of CaO-MgO in shell fragments of the littoral sands ranged from 4.69~51.96%, suggesting that the high CaO-MgO content in some of the Island's beaches is attributable to geologic environments conducive to the growth of shell organisms and sediments migration. The provenance of the sediments studied are derived predominantly from adjacent continental shelves and/or terrigenous older river portion, Which sediments were transported mostly by rolling or bottom suspension. The depositional environments of the Jeju beaches can be divided into two types: beaches distributed in the North and the Northeastern parts of the Island are dominated by marine enviroment, whereas beaches in the Southwestern portion are characterized by terrigenous agencies.

• Journal of fish pathology
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• v.9 no.2
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• pp.137-145
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• 1996

A specific disease syndrome, which led to massive mortality on larve of rockfish(Sebastes schlegeli) in marine hatcheries at Chungnam area during the period 1995~1996 was studied. The causative agent isolated from the diseased or dead larvae was identified as Vibrio ordalii on the basis of biochemical and biological characteristics. In the experimental challenges aganist 0 and 1 summer fish conducted at two different temperatures as $18^{\circ}C$ and $25^{\circ}C$, Vibrio ordalii showed higher virulence to no summer fish at $18^{\circ}C$ than 1-summer fish at $25^{\circ}C$. These results were consistent to field data obtained during epizootic outbreaks in the farms. Moribund and died larvae presented telangiectasis of secondary gill lamella and brain, dissecting of respiratory epithelium, atrophy of hepatic cells and necrosis of kidney associated with the presence of the bacteria. But the digestive tissue of these fish showed no significant change.

• Fisheries and Aquatic Sciences
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• v.16 no.3
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• pp.159-164
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• 2013

The mouse bioassay and high performance liquid chromatography (HPLC) post-column oxidation method are different methods of quantifying paralytic shellfish poisoning toxins. In this study, we compared their ability to accurately quantify the toxicity levels in two types of field sample (oysters and mussels) with different toxin profiles for routine regulatory monitoring. A total of 72 samples were analyzed by both methods, 44 of which gave negative results, with readings under the limit of detection of the mouse bioassay ($40{\mu}g/100g$ saxitoxin [STX] eq). In 14 oysters, the major toxin components were gonyautoxin (GTX) 1, -2, -3, -4, -5, decarbamoylgonyautoxin-2 (dcGTX2), and decarbamoylsaxitoxin (dcSTX), while 14 mussels tested positive for dcSTX, GTX2, -3, -4, -5, dcGTX2, neosaxitoxin (NEO), STX, and dcSTX. When the results obtained by both methods were compared in two matrices, a better correlation ($r^2=0.9478$) was obtained for mussels than for oysters ($r^2=0.8244$). Additional studies are therefore needed in oysters to investigate the differences in the results obtained by both methods. Importantly, some samples with toxin levels around the legal limit gave inconsistent results using HPLC-based techniques, which could have a strong economic impact due to enforced harvest area closure. It should therefore be determined if all paralytic shellfish poisoning toxins can be quantified accurately by HPLC, and if the uncertainties of the method lead to doubts regarding regulatory limits.