• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.832-838
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• 2021

Recently, reports of marine accidents of small fishing vessels less than 10 tons have been increasing. In this study, the characteristics of the motion response in regular waves were analyzed using computations for these ships. Small vessels less than 10 tons are classified by size and used for marine accident investigations. Therefore, the motion response analysis was performed on three small fishing vessels of different sizes. In the case of the head sea, it was confirmed that as the speed of the vessel increased in the long wavelength region, the motion responses of heave and pitch became large. The motion response of the smallest 3-ton fishing vessel was greater than that of the other sizes of fishing vessels. The maximum value of the roll motion shifted to the long wavelength region as the speed gradually increased in the bow sea, regardless of the size of the ship. In all the three small fishing vessels, it was found that the roll motion was the greatest at 15 knots, the highest speed in both bow and beam seas. When sailing in the head sea and bow sea conditions, lowering the speed is one of the effective approaches to reduce the effects of the vertical and lateral plane motions. The roll motion caused by the beam wave showed a tendency to increase rapidly only at a specific wavelength regardless of the speed and the size of the vessel. It was confirmed that the roll motion was significantly reduced with forward speed in the stern wave compared to the bow wave. As there is a specific region where the maximum value of the hull motion response appears depending on the size and speed of the ship, an operation method that can minimize the effect of this motion should be considered and implemented.

• Journal of Korea Water Resources Association
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• v.57 no.9
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• pp.599-613
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• 2024

Unlike other disasters, the water shortage problem caused by drought is characterized by the long-lasting ripple effect of the social and economic sectors in all regions of Korea, and the types and purposes of water mainly used are different depending on the type of region, so the factors and scale of water shortage damage are different. In this study, a methodology to evaluate the risk of water shortage based on socioeconomic characteristics was developed and applied to Gwangju and Jeollanam-do to analyze the results. To this end, 20 impact indicators for risk, exposure, and vulnerability items were selected according to the climate risk concept of IPCC AR6. The results of the water shortage risk evaluation reflecting socioeconomic characteristics were different from the risk results considering only the existing meteorological and hydrological factors. The areas with the greatest risk of water shortage were calculated as Yeonggwang-eup in Yeonggwang-gun, Yeonsan-dong and Haean-dong 4-ga in Mokpo-si, Jeokryang-dong in Yeosu-si and Geumsan-myeon in Goheung-si. Through the evaluation results, risk factors and countermeasures for water shortage were derived in consideration of detailed characteristics of the region, which can be used as data contributing to the establishment of measures to reduce drought damage tailored to the region in the future.

• Korean Journal of Ichthyology
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• v.12 no.2
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• pp.137-145
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• 2000

The embryonic and larval development of Chelon lauvergnii (Eydoux & Souleyet) was surveyed by incubating artificially inseminated eggs with parent fishes obtained at Kang-wha island in the mid-western coastal area of Korea on June, 1997. The fertilized eggs were transparent, spherical in shape, measuring 0.95~1.08 mm in diameter, having a large oil globule, and their perivitelline space narrow, and began to hatch at 40 hrs. in water temperature $22{\pm}1^{\circ}C$. The newly hatched larvae were 2.35~2.68 mm in total length with 23 myomeres, anus opened, mouth closed, preanal length 58.7~61.6% of total length, oil globule located in posterior end of yolk sac. Melanophores, branch in shape, were distributed mainly along the ventro-lateral region of trunk part and a few on the anterior end of caudal part and surface of oil globule. The larvae measuring 3.08~3.36 mm in total length absorbed yolk material completely in 3 days after hatching, in which air bladder began to appear and mouth opened. In 8 days after hatching, the larva was measured 5.09 mm in total length, its posterior end of notochord began to flex upward and the caudal fin rays differentiated as 7, finfold of the second dorsal and anal fins appeared. In this time, melanophores, branch in shape, were concentrated in the anterior half region of the caudal part and a few also distributed on the top of head, snout region, ventral margin of lower jaw and isthmus region. In 12 days after hatching, the larva measuring 8.48 mm in total length completed all the fins (D. IV-9; P1. 16; P2. I, 5; A. II, 9) and reached to the juvenile stage. Melanophores, in this time, were distributed on the mid-lateral region of the caudal part in enlargment than before and a few also found in the dorso-lateral region of the trunk part, and in the cheek region.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.12
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• pp.1166-1176
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• 2011

The prospect in opening the arctic trade transportation route on a year-round basis offers vast opportunity of exploring untapped resources and shortened navigational routes. In addition, the environment's remoteness and lack of technical experiences remains a big challenge for the maritime industry. With this, engine designers and makers are continually investigating, specifically optimizing propulsion shafting system design, to meet the environmental and technical challenges of the region. The International Association of Classification Society, specifically machinery requirements for polar class ships(IACS UR13), embodies the propulsion shafting design requirements for ice class vessels. However, the necessity to upgrade the various features of the unified rules in meeting current polar requirements is acknowledged by IACS and other classification societies. For the polar class propulsion shafting system, it is perceived that the main source of excitation will be the propeller - ice load interaction. The milling - and the impact load, in addition to the load cases interpreted by IACS, contribute greatly to the overall characteristic of the system and due considerations are given during the propulsion design stage. This paper will expound on the excitation load estimation factors affecting the dynamic response of the different propulsion shafting system design. It is anticipated that detailed understanding of these factors will have a significant role during propulsion shafting design in the future.

• Journal of Korea Water Resources Association
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• v.45 no.3
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• pp.291-300
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• 2012

We conducted a three-dimensional numerical simulation by using the FLOW-3D, with RANS as the governing equation, in an effort to track the dam-break wave.immediately after a dam break.in areas surrounding where the dam break took place as well as the bed change caused by the dam-break wave. In particular, we computed the bed change in the movable bed and compared the variation in flood wave induced by the bed change with our analysis results in the fixed bed. The analysis results can be summarized as follows: First, the analysis results on the flood wave in the L-shaped channel and on the flood wave and bed change in the movable-bed channel successfully reproduce the findings of the hydraulic experiment. Second, the concentration of suspended sediment is the highest in the front of the flood wave, and the greatest bed change is observed in the direct downstream of the dam where the water flow changes tremendously. Generated in the upstream of the channel, suspended sediment results in erosion and sedimentation alternately in the downstream region. With the arrival of the flood wave, erosion initially prove predominant in the inner side of the L-shaped bend, but over time, it tends to move gradually toward the outer side of the bend. Third, the flood wave in the L-shaped channel with a movable bed propagates at a slower pace than that in the fixed bed due to the erosion and sedimentation of the bed, leading to a remarkable increase in flood water level.

• Journal of Korean society of Dental Hygiene
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• v.9 no.3
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• pp.282-293
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• 2009

The purpose of this study was to examine the degree of infection control implemented at dental offices and factors affecting it in an attempt to help promote the health of dental health care workers. The subjects in this study were 180 medical personnels who worked at dental offices in the region of South Jeolla Province. A self-administered survey was conducted from April 1 to May 30, 2008, and the collected data were analyzed. The findings of the study were as follows: 1. As for the implementation of infection control at the dental offices, what the health care workers investigated did the most was post-treatment hand washing(95.0), a constant separation of infectious wastes(94.4), wearing rubber gloves all the time during medical instrument cleansing(92.8) and pre-treatment hand washing(91.7). 2. In regard to the implementation of infection control at the dental offices, what the dental personnels did the least was drying their hands with air(5.0), wearing goggles in times of treatment(23.3), receiving regular education on infection control(26.7) and putting sterilizers to a performance test on a regular basis(43.9). 3. The dental health care workers were significantly different according to age in the management of contagious diseases(p=0.005). Their career made a significant difference to the management of contagious diseases(p=0.000) and instrument cleansing/sterilization(p=0.043). The service area made a significant difference to wearing and managing personal protective clothes (p=0.040) and waste management(p=0.040). 4. Concerning the relationship between the acquisition of dental hygienist certificate and the practice of infection control, whether the dental health care workers were certified or not made no significant difference to that. 5. As to the correlation among the factors affecting the prevention and management of contagious diseases, there was a positive correlation among hand washing(r=0.379), wearing and managing personal protective clothes(r=0.349), instrument cleansing/sterilization(r=0.323) and waste management(r=0.388). All the factors made a statistically significant difference to the prevention and management of contagious diseases(p<0.01).

• Korean Journal of Environmental Biology
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• v.34 no.1
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• pp.30-36
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• 2016

We investigated the diversity pattern of spring moths across two regions of South Korea, Yongin city (middle part) and Muan gun (southern part) and the effects of climatic variables on moth species richness and abundance. Moths were weekly collected using UV light trap in April from 2013 to 2015. Climatic factors included growth degree day with base temperature 8 (GDD8), average temperature, precipitation, duration of sunshine, wind speed, and snow cover. The climatic effects on moth species richness and abundance were analyzed by short (0~3 weeks before collecting) and long (4~12 weeks before collecting) time periods, respectively. The diversity of spring moths showed the similar pattern of species composition at family level. However the dominant family differed depending on the region: Geometridae at middle part and Noctuidae at southern part. In addition the dominant species of Noctuidae occurred early in April and that of Geometridae moths occurred later in April. Three short-term climatic factors, GDD8, duration of sunshine, and precipitation one week before collecting were significant on moth species richness and abundance, while only one long-term climatic factor, temperature four weeks before collecting was significantly affected on moth species richness. We found that both Geometridae and Noctuidae were dominant in spring moth fauna across South Korea and they were different in the dominance and flying time in April. The occurrences of spring moths were largely affected by warmness and precipitation. The current global warming could affect the occurrence of spring moths and this should be monitored consistently.

• Korean Journal of Environmental Biology
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• v.24 no.1 s.61
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• pp.7-18
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• 2006

Samples were collected from five stations monthly from October 2003 to September 2004 to investigate seasonal variation of size structure of phytoplankton and relationship between size-fractionated phytoplankton and environmental factors in the Asan Bay. The contribution of large cells (microphytoplankton, $>20\;{\mu}m$) to total concentrations of chlorophyll $\alpha$ was higher than small cells (nanophytoplankton, $3\sim20\;{\mu}m$; picophytoplankton, $<3\;{\mu}m$) during the sampling period. Especially, large cells contributed 80% to the total chlorophyll a from February, 2004 to April 2004 when chlorophyll $\alpha$ concentrations were high. The size structure of phytoplankton shifted from micro-size class to nano-size class and picophytoplankton rapidly increased when phytoplankton biomass decreased in May 2004. Microphytoplankton exhibited a high biomass in the upper region during winter-spring season whereas nano- and picophytoplankton showed two peaks in the middle-lower regions (Station 3,5) during spring and summer. Microphytoplankton are most likely controlled by water temperature and nutrient supply during the cold season whereas nano- and picophytoplankton may be affected by stratification, light exposure during the warm season.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.13-23
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• 2008

In coastal region, eutrophication, Do deficit and red tide are frequently occurred by influx of fresh water. When the fresh water containing pollutants is discharged into the sea, the surrounding water is contaminated by dispersion of freshwater flowing into coastal waters. The prediction and analysis about the dispersion process of the discharged fresh water should be conducted. A modeling system using GUI was developed to simulate hydrodynamic flow and fresh water dispersion in coastal waters and to analyze the results efficiently. The modeling module of the system includes a tide model using a finite element method and a fresh water dispersion model using a particle-tracking method. This system was applied to predict the tidal currents and fresh water dispersion in Mokpo coastal zone. To verify accuracy of the hydrodynamic model, the simulation results were compared with observed sea level and time variations of tidal currents showing a good agreement. The fresh water dispersion was verified with observed salinity distribution. The dispersion model also was verified with analytic solutions with advection-diffusion problems in 1-dimensional and 2-dimensional simple domain. The system is operated on GUI environment, to ease the model handling such as inputting data and displaying results. Therefore, anyone can use the system conveniently and observe easily and accurately the simulation results by using graphic functions included in the system. This system can be used widely to decrease the environmental disaster induced by inflow of fresh water into coastal waters.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.6
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• pp.721-730
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• 2021

Maritime air pollutants around port cities have gained a great deal of attention due to their direct impacts on regional air quality. This study aims to determine the geographical properties of sea/land breezes in different areas to discover overall ranges of maritime emission dispersion. The HOTMAC-RAPTAD modeling program was used to simulate regional-scale air dispersion considering non-linear and unsteady states during the general summer period for the target areas of the Yellow Sea (Incheon Port and Pyeongtaek·Dangjin Ports), archipelago region (Mokpo Port), South and East Sea (Busan and Masan Ports) and East Sea with mountainous area (Donghae·Mukho Ports). The resulting dispersion lengths of vessel emissions into the onshore regions around the target ports shed light on portal air quality management, because vessel emissions from the Incheon, Mokpo, Busan, and Donghae·Mukho ports were transported 27-31km (Western Seoul), 21-24km (Southern Muan), 20-26km (Gimhae and Yangsan), and 22-25km (Taebeak Mountains), respectively. Therefore, the results of this study provide useful data for regional air quality management and marine air pollution mitigation to improve the sustainability of port cities.