• Journal of Korean Society of Environmental Engineers
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• v.31 no.12
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• pp.1113-1122
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• 2009

In order to find the way to solve the problem of sewage sludge discharge into the ocean, the sludge solubilization by ultrasonic and the improvement methods of wastewater treatment process were studied. In the membrane bioreactor the sludge retention time was stepwise increased from 5.1 day to 442 days where the biomass average concentration has been increased from $c_B$=3.4 $gTSSL^{-1}$ to $c_B$=14.5 $gTSSL^{-1}$ respectively. At the same time, the biomass yield coefficients were reduced from 0.5-0.7 at SRT=5.1 day to 0.005-0.007 at SRT=442 days which means the reduction of sludge production. Oxygen mass transfer coefficients and ${\alpha}$-factor were investigated with changing stirrer speed to find the relation between the high biomass concentration and aeration efficiency in the propeller loop reactor. As a result of sludge solubilization, the solubilization of sludge by ultrasound was increased with increasing energy input and it led to improved anaerobic digestion rate with more biogas production than that of nonsolubilized sewage sludge.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.276-289
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• 2013

In developing offshore wind farms, many environmental issues arise because of the concentration on supply demand and economic logic. Accordingly, community conflict is induced. Especially, recent studies regarding the capacity and location of offshore wind development have been conducted considering wind states and ocean conditions, etc. of coastal seas in Republic of Korea. Nevertheless, studies on the impact of marine environments and ecosystems are very limited so far. Environmental monitoring that follows development projects has been actively done in the offshore wind farms in many developed European countries. In contrast, there is no domestic monitoring data regarding environmental impacts caused by installing and operating offshore wind power. Therefore, the environmental impacts under construction and operation phases as well as the guidelines in the stage of environmental impact assessment suited for domestic coastal seas are well presented in this study by analyzing monitoring cases and references of overseas offshore wind farm. For this reason, this research is ultimately aimed at minimizing the environmental impact in offshore wind farm development and thus simplify administrative procedures in Korea.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.95-100
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• 2006

The COMS(Communication, Ocean and Meteorological Satellite) EPS(Electrical Power Subsystem) is derived from an enhanced Eurostar 3000 version. Eurostar 3000 EpS is fully autonomous operation in nominal conditions or in the event of a failure and provides a high level of reconfigure capability. This paper introduces the COMS EPS preliminary design result. COMS EPS consists of a battery, a solar arrat wing, a PSR(Power Supply Regulator), a PRU(Pyrotechnic Unit), a SDAM(Solar Array Drive Mechanism) and relay and fuse brackets. COMS EPS can offer a bus power capability of 3 kW. The solar array is made of a deployable wing with two panels. One type fo solar cells is selected ad GaAs/Ge triple junction cells. Li-ion battery is base lined with ten series cell module of five cells in parallel. PSR associated to battery and solar array wing generates a power bus fully regulated at 50 V. Power bus os centralized protection and distribution by relay and fuse brackets. PRU provides power for firing actuarors devices. The solar array wing is rotated by the SADM under control of the attitude orbit control subsystem. The control and monitoring of the EPS, especially of the battery, is performed by the PSR in combination with the on-board software.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.1-7
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• 2006

GOCi (Geostationary Ocean Color Imager) is one of the COMS payloads that KARI is currently developing and scheduled to be in operation from around 2008. Its primary objective is to monitor the Korean coastal water environmental condition. We report the current progress in development of the integrated optical model as one of the key analysis tools for the GOCI in-orbit performance verification. The model includes the Sun as the emitting light source. The curved Earth surface section of 2500 km x 2500 km includingthe Korean peninsular os defined as a Lambertian scattering surface consisted of land and sea surface. From its geostationary orbit, the GOCI optical system observes the reflected light from the surfaces with varying reflectance representing the changes in its environmental conditions. The optical ray tracing technique was used to demonstrate the GOCI in-orbit performances such as red tide detection. The computational concept, simulation results and its implications to the on-going development of GOCI are presented.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.6
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• pp.615-623
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• 2020

In order to prevent the dangers of major marine accidents, it is very important to be aware of in advance through marine incidents in the background of Heinrich's law, formulated by the safety pioneer who is credited with focusing on workplace safety with emphasis on the human element. At least 11 cases of collision accidents occurred in the Busan VTS area from January 1st to December 31st, 2019, and 24 cases of VTS marine incidents were reported during the same period. According to Heinrich's law, there could be many more potentially risky situations besides the 24 reported cases. In this study, the criteria for VTS marine incidents were established through advanced research and a survey of VTS operators, and analysis of 24 cases of VTS marine incidents in the Busan VTS area. Traffic surveys were conducted for three days to identify potentially hazardous situations. According to the survey, there were 216 cases of VTS marine incidents, and within a year, it is estimated there could be about 26,280 cases. Even if conditions such as "missing VHF communication feedback" which is an important cause of marine incidents, are not reflected, there are many potential risks in the VTS area. Thus, it is vital to strengthen the VTS marine incident reporting system.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.3
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• pp.218-226
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• 2016

Field observations were used to study the characteristics and influence of groundwater level fluctuations on vegetation development on the natural beach of a sandy barrier island, in the Nakdong River estuary. The spatial/temporal fluctuations of the groundwater level and the interactions with the external forces (weather, ocean wave and tide) were analyzed. The results indicated that when it rains the groundwater level rises. During summer, when precipitation intensity is greater than 20 mm/hour, it rose rapidly over 20 cm. Subsequently, it fell gradually during periods of no precipitation. Seasonal characteristics indicated that the groundwater level was high during the summer rainy season and tended to fall in the winter dry season. The time-averaged groundwater level, observed from the four observations over 3 years (2012-2014), was about 1.47 m, higher than mean sea level (M.S.L.). It was shown that the average annual groundwater level rises toward the land rather than showing intertidal patterns observation. Differences in the presence or absence of a coastal sand dunes affected the progress of vegetation. In other words, in environments of saltwater intrusion where the groundwater level varies, dependent on the distance from the shoreline and bottom slope, sand dunes can be provided to affect soil conditions and groundwater, so that vegetation can be grown reliably.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.16 no.4
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• pp.341-348
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• 1983

The Relationship between the distribution of the fishing grounds of anchovy and the oceanographic conditions in the Korean Waters are investigated by using the data of the catch of anchovy by the gill net fishery (Fisheries Research and Development Agency, 1969-1982) and the oceanographic observation data (Fisheries Research and Development Agency, 1979). The main fishing ground of anchovy by the gill net fishery was five fishing areas located in the adjacent seas of Sockcho, Kuryong-po, Kijang, Keoje island and Chungmu, the area of which occupies no more than $20\%$ of all fishing grounds, and it appeared that about $80\%$ of mean catches of fourteen years was concentrated in this area. The main fishing periods were from April to June and October to November. The coefficient of variation of the catch for the main fishing ground were from 0.3 to 0.6 and the condition of all fishing ground was generally stable. The mean CPUE was 81.2 kg/set at the main fishing ground. The annual mean catch of anchovy by the gill net was the smallest in February and the largest in May through a year. It was found that the fluctuation is related to the expansion and reduction of the isothermal line of $10^{\circ}C$.

• The Korean Journal of Malacology
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• v.26 no.1
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• pp.63-78
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• 2010

The purpose of this study was to investigate the effect of tributyltin (TBT) on histopathological and ultrastructural changes in the digestive gland structure of the equilateral venus, Gomphina veneriformis. Experimental period was 36 weeks. Experimental groups consist of control condition and 3 TBTCl exposure conditions (0.4, 0.6, $0.8\;TBTC\;{\mu}g\;L^{-1}$). Outer envelop of the visceral mass of G. veneriformis exposed to TBTCl was observed disappearance of microvilli and cilia, decrease of mucous cell and partially destruction of epithelium. In the digestive gland showed an increase of number of hemocyte and mucopolysaccaride near the digestive tubule at early time of the exposure. Especially, in $0.8\;TBTC\;{\mu}g\;L^{-1}$ group, collapse of digestive tubule with modification of epithelium was observed. TEM observation revealed the numerous glycogen granules in epithelium of the outer envelop and connective tissue. In the ciliated cell of the primary duct formed the cilia in cytoplasm. Basophilic cell was observed destruction of the rough endoplasmic reticulum and mitochondria. Also, nucleus in the epithelium of the digestive tubule was disappeared heterochromatin and nucleolus, and condense. As the concentration of TBTCl increased, the accumulation of lipofucin increased in the digestive gland, but the collapse of digestive tubule induced a decrease of accumulation of lipofuscin.

• Ocean Systems Engineering
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• v.6 no.3
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• pp.245-264
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• 2016

The iterative boundary element method (IBEM) developed originally before for cavitating two-dimensional (2-D) and three-dimensional (3-D) hydrofoils moving under free surface is modified and applied to the case of 2-D (two-dimensional) airfoils and 3-D (three-dimensional) wings over water. The calculation of the steady-state flow characteristics of an inviscid, incompressible fluid past 2-D airfoils and 3-D wings above free water surface is of practical importance for air-assisted marine vehicles such as some racing boats including catamarans with hydrofoils and WIG (Wing-In-Ground) effect crafts. In the present paper, the effects of free surface both on 2-D airfoils and 3-D wings moving steadily over free water surface are investigated in detail. The iterative numerical method (IBEM) based on the Green's theorem allows separating the airfoil or wing problems and the free surface problem. Both the 2-D airfoil surface (or 3-D wing surface) and the free surface are modeled with constant strength dipole and constant strength source panels. While the kinematic boundary condition is applied on the airfoil surface or on the wing surface, the linearized kinematic-dynamic combined condition is applied on the free surface. The source strengths on the free surface are expressed in terms of perturbation potential by applying the linearized free surface conditions. No radiation condition is enforced for downstream boundary in 2-D airfoil and 3-D wing cases and transverse boundaries in only 3-D wing case. The method is first applied to 2-D NACA0004 airfoil with angle of attack of four degrees to validate the method. The effects of height of 2-D airfoil from free surface and Froude number on lift and drag coefficients are investigated. The method is also applied to NACA0015 airfoil for another validation with experiments in case of ground effect. The lift coefficient with different clearance values are compared with those of experiments. The numerical method is then applied to NACA0012 airfoil with the angle of attack of five degrees and the effects of Froude number and clearance on the lift and drag coefficients are discussed. The method is lastly applied to a rectangular 3-D wing and the effects of Froude number on wing performance have been investigated. The numerical results for wing moving under free surface have also been compared with those of the same wing moving above free surface. It has been found that the free surface can affect the wing performance significantly.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.2
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• pp.219-226
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• 2020

Nondestructive testing is one of the most commonly used quality inspection methods for evaluating ship structures. However, accurate evaluation is dif icult because various composite materials, such as reinforcements, resin, and fiber-reinforced plastics (FRPs), are used in hulls, and manufacturing quality differences are likely to exist owing to the fabrication environment and the skill level of workers. This possibility is especially true for FRP ships because they are significantly thicker than other structures, such as automobiles and aircraft, and are mainly manufactured using the hand lay-up method. Because the density of a material is a critical condition for ultrasonic inspection, in this study, a hull plate was selected from a vessel manufactured using e-glass fiber, which is widely used in the manufacture of FRP vessels with the weight fraction of the glass content generally considered. The most suitable ultrasonic testing conditions for the glass FRP hull plate were investigated using a pulse-echo ultrasonic gauge. A-scans were performed with three probes (1.00, 2.25, and 5.00 MHz), and the results were compared with those of the hull plate thickness measured using a Vernier caliper. It was found that when the probe frequency was higher, the eco-pulse velocity of the receiver had to be lowered to obtain accurate measurement results, whereas fewer errors occurred at a relatively low probe frequency.