• Journal of Wetlands Research
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• v.6 no.1
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• pp.149-166
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• 2004

Water quality and ecological environment in the Han River estuary was analyzed using the longterm water quality monitoring data from National Fisheries Research and Development Institute (NFRDI) and the existing data collected in this area. Based on the salinity distribution and changes of current direction in the lower Han River and its estuary, boundaries of the estuary were identified and also, distribution patterns of the phyto- and zooplankton, benthos, ichthyoplankton and fish were discussed related with the salinity changes in the macrotidal subestuary of Han River. Seasonal and spatial distribution of salinity suggested that the direct impact of freshwater be limited to the Incheon North Harbour all the year round and even extended to the southern area of Gyunggi Bay near Palmi island during limited time, usually in summer. Upper limit of salt water intrusion through the Han River is likely to be Singok underwater dam located Gimpo, Gyunggi Province, and normally limited to much lower part of the river, Jeonryuri, Gimpo. Biological boundaries of the Han River estuary exceeded the physical boundaries based on the salinity distribution. Many estuarine species in plankton and fish were found at the totally freshwater or saltwater depending on the seasons and tidal cycles. Some estuarine ichthyoplanktons showed extremely limited distributions in the estuary whereas adult fish revealed wide ranges of salinity adaptation. Critical environmental issues in the Han River estuary and its drainage basin are likely to be 1) pressure on development-promoted district for new town in the drainage area of the estuary, 2) reduction of tidal flat by reclamation, 3) pollutant input through river from municipal sewages and industrial wastes, and 4) ecological barrier between river and terrestrial systems by the military wire fence and riverside road.

• Journal of the Korean Society for Marine Environment & Energy
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• v.14 no.2
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• pp.114-120
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• 2011

The characteristics of a helical turbine to be used for tidal stream energy conversion have been numerically studied with varying a few design parameters. The helical turbines were proposed aiming at mitgating the well known poor cut-in characteristics and the structural vibration caused by the fluctuating torque, and the basic concept is introducing some twisting angle of the vertical blade along the rotation axis of the turbine. Among many potential controling parameters, we focused, in this paper, on the twisting angle and the height to diameter ratio of the turbine, and, based on the numerical experiment, We tried to propose a configuration of such turbine for which better performance can be expected. The three-dimensional unsteady RANS equations were solved by using the commercial CFD software, FLUENT with k-${\omega}$ SST turbulence model, and the grid was generated by GAMBIT. It is shown that there are a range of the twisting angle producing better efficiency with less vibration and the minimum height to diameter ratio above which the efficiency does not improve considerably.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.35 no.2
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• pp.129-135
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• 1999

The telemetry system for the current speed and direction, the underwater ambient noise and the distribution ecology of fishes was constructed by the author and his collaborator in order to product and manage effectively in shallow sea culture and setnets fisheries, and then the experiments for the telemetry system carried out at set net fishing ground located Nungpobay in Kojedo from October 1996 to June 1997. As this results, the techniques suggested in the telemetry system gave full display its function even though far away 1.5 km from transmitting part, but with the suggested telemetry system could not be ascertained relationship between physical environment and distribution ecology of fishes.

• Journal of the Korean Society of Marine Environment & Safety
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• v.13 no.2 s.29
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• pp.147-153
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• 2007

In this paper, the authors calculated maneuvering motions of a large container vessel approaching to the newly built container piers to get alongside to her berth in Busan harbour. The motion calculations were done by using fixed coordinate system and the object of the calculations is to check the maneuvering motions are safe or not for berthing the large vessel to her berth. The result of calculations manifested that a large container vessel can get alongside to the piers without any difficulty under normal weather conditions by using 2 Z. Peller tug boats of 4500 H.P. each and also these demonstrated it is difficult to conduct and get her alongside to the piers under rough weather conditions of wind force 16.9m/sec or more. Under rough weather conditions of 6 by Beaufort scale the average wind velocity is about 13.5m and if we add 25% increase of the normal velocity to it, the wind will becomes a gust of 16.9m/sec. So it is advisable to avoid conducting a large container vessel to the pier under the rough weather conditions of 6 or more by Beaufort scale. Also, it is better to use 3 Z. peller tug boats of 4500 H.P. each under the above mentioned rough weather in a case of unavoidable circumstances.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.619-627
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• 2018

As ships become faster, larger and are required to meet higher standards, the importance of flow noise is highlighted. However, unlike in the aeroacoustics field for airplanes and trains (where flow noise is considered in design), acoustics are not considered in the marine field. In this study, analysis procedures for hull-induced flow noise are established to investigate the flow noise characteristics of a wave-piercing hull form that can negate the effect of wave-breaking. The principal mechanisms behind hull-induced flow noise are fluid-structure interactions between complex flows underneath the turbulent boundary layer and the hull. Noise induced by the turbulent boundary layer was calculated using wall pressure fluctuation and energy flow analysis methods. The results obtained show that noise characteristics can be distinguished by frequency range and hull region. Also, the low-frequency range is affected by hull forms such that it is correlated with ship speed.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.2
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• pp.194-199
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• 2017

When sea tide and wave velocity change, the behavior of silt protectors underwater changes, and a hydraulic force exceeding the anchor wave force is applied. In this study, the movement mechanism of a silt protector has been analyzed using the mass-spring method. The initial position of the silt protector was in the Jindo area near Gwangpo Port (742-1, Gyupori, Chongdo-myeon, Jindo-gun, Jeonnam, Korea). The tension required to exceed the holding power of the anchor was 0.05 m/s at 318 sec., 0.15 m/s at 77 sec., 0.25 m/s at 43 sec., and 0.3 m/s at 37 sec.. As the anchor started to move from the sea floor and the tide speed increased to 0.01 m/s, anchor movement start time shortened by an average of 11.2 sec.. Compared with when tide was the only affecting factor, the silt protector and anchor were found to have moved 19.7 % at 0.1 m/s, 7.6 % at 0.15 m/s, 5.8 % at 0.2 m/s, 4.3 % at 0.25 m/s and 2.8 % at 0.3 m/s, showing an increase. When wave effect was added to the tide, anchor movement started when the flow rate was slow 7.6 % of the time. With a high flow velocity, anchor movement started without any significant difference less than 4.3 % of the time. When tide speed exceeded 0.13 m/s and the direction of the waves matched, the silt protector was not able to perform due to collisions with surrounding sea structures. When installing a silt protector, the fluid flow situation and the silt protector situation must be carefully analyzed using the mass-spring method to apply the result found in this study.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.7
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• pp.930-938
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• 2018

Underwater noise radiated from submarines is directly related to the probability of being detected by the sonar of an enemy vessel. Therefore, minimizing the noise of a submarine is essential for improving survival outcomes. For modern submarines, as the speed and size of a submarine increase and noise reduction technology is developed, interest in flow noise around the hull has been increasing. In this study, a noise analysis technique was developed to predict flow noise generated around a submarine shape considering the free surface effect. When a submarine is operated near a free surface, turbulence-induced noise due to the turbulence of the flow and bubble noise from breaking waves arise. First, to analyze the flow around a submarine, VOF-based incompressible two-phase flow analysis was performed to derive flow field data and the shape of the free surface around the submarine. Turbulence-induced noise was analyzed by applying permeable FW-H, which is an acoustic analogy technique. Bubble noise was derived through a noise model for breaking waves based on the turbulent kinetic energy distribution results obtained from the CFD results. The analysis method developed was verified by comparison with experimental results for a submarine model measured in a Large Cavitation Tunnel (LCT).

• Korean Journal of Environment and Ecology
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• v.35 no.3
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• pp.285-293
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• 2021

This study was conducted to elucidate spawning period characteristics and early life development of eight barbel loach, Lefua costata (Balitoridae) at the Jusucheon stream, Okgye-myeon, Gangneung-si, Gangwon-do, Korea between January and December in 2018. The spawning period was estimated to be from May to August, considering the change in the gonad-somatic index, the appearance of young fry, and frequency distribution in egg diameter. It was a multi-spawning type. The gender ratio was 1:0.79 with 1,117 females and 879 males collected. The egg size was 0.24-0.93 mm, with mature and immature eggs found during the spawning period. The size of mature eggs was 0.71±0.02 mm, and the average number of fecundity was 1,786±818 (n=31). Observation of the egg development showed that the fertilized eggs were the sticky, gray, segregated, and demersal type with 0.76±0.03 mm in diameter. The hatching of the embryos began at about 34 hours (hatching rate 50%) after fertilization underwater temperature of 25℃. The average length of the newly hatched pre-larvae was 2.7±0.11 mm. The average length of pre-larvae at 4 days after hatching was 4.5±0.16 mm, and the yolk sac was completely absorbed and entered the post-larvae stage. At 20 days after hatching, the average length of post-larvae was 11.5±0.67 mm, and their fin rays were formed before they transitioned to the juvenile stage. At 100 days after hatching, the average length reached 49.8±2.60 mm, and the appearance and the lateral sideband patterns were similar to those of the adult fish.

• The Journal of the Korea Contents Association
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• v.22 no.10
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• pp.733-741
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• 2022

Among the various evidence found in maritime crimes, fingerprints and DNA are very important in that they can identify a suspect. In this study, 5 types of non-porous surfaces (plastic, stainless, glass, ceramic, FRP), which are often found as evidence in the actual marine environment, were selected, and latent and blood fingerprints were passed down and immersed at the Donghae Maritime Police Station's exclusive pier for about 7 days. After that, DNA extraction, quantification, and STR profile were analyzed after fingerprint developing CA fumming method and 4 powder methods (Swedish black powder, Concentrated black powder, Supranano red powder, Dazzle orange powder). Among the fingerprint developing methods, when Supranano red powder was applied, a relatively high amount of DNA was found. As a result of STR profile analysis, an average of 16.8 to 9 loci were secured, and all 20 were confirmed in glass and ceramic materials. As a result of the study, it was possible to secure the STR profile by extracting and quantifying DNA after applying the fingerprint developing method to virtual evidence immersed for about 7 days, and further research is needed to secure the STR profile by analyzing DNA after applying various fingerprint developing methods such as VMD and SPR.

• The Journal of the Acoustical Society of Korea
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• v.43 no.1
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• pp.78-88
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• 2024

Ship-radiated noise received by passive sonar that can measure underwater noise can be identified and classified ship using Detection of Envelope Modulation on Noise (DEMON) analysis. However, in a low Signal-to-Noise Ratio (SNR) environment, it is difficult to analyze and identify the target frequency line containing ship information in the DEMONgram. In this paper, we conducted a study to extract target frequency lines using semantic segmentation among deep learning techniques for more accurate target identification in a low SNR environment. The semantic segmentation models U-Net, UNet++, and DeepLabv3+ were trained and evaluated using simulated DEMONgram data generated by changing SNR and fundamental frequency, and the DEMONgram prediction performance of DeepShip, a dataset of ship-radiated noise recordings on the strait of Georgia in Canada, was compared using the trained models. As a result of evaluating the trained model with the simulated DEMONgram, it was confirmed that U-Net had the highest performance and that it was possible to extract the target frequency line of the DEMONgram made by DeepShip to some extent.