• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.1
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• pp.13-21
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• 2023

As problems such as difficulties in securing stable energy resources and global warming due to the emission of greenhouse gases due to the use of fossil fuels have emerged, interest in the development of renewable energy is increasing. Since the tidal phenomenon has a regularity that occurs regularly with a certain period, it is possible to predict accurately in advance, which has a advantage in terms of energy recovery. Therefore, various methods have been devised to utilize the tide as an energy source. Tidal power using barrages is a representative method that is widely operated, but the promotion of tidal power generation projects is being delayed or stopped due to the decrease in the level of water in the tidal basin, changes in water quality and in the ecosystem. In this study, a field experiment was conducted to develop and verify the performance of a tidal power device applicable to sea areas where dykes are already installed. As a result of carrying out four cases of experiments using two water tanks, pipe lines, open channels, weirs, and water turbine and generator, the possibility of developing a power generation system capable of 10 kW output or more and 60% efficiency or more was confirmed. These research results can be used for small-scale tidal power by utilizing the existing dykes.

• Journal of Marine Life Science
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• v.2 no.1
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• pp.27-33
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• 2017

The effects of starvation on the growth, survival and hepatocyte nuclear size of the just hatched grass puffer, Takifugu niphobles larvae were studied. The total length of the larvae showed increase up to 3 days after hatching (DAH), however, 3th to 6th DAH, the starved group grew, slower than the fed group, significantly. The body weight of the fed group grass puffer showed increase steadily during experimental period. The body weight of the starved group showed increase until 3th DAH, however, after 3th DAH the growth of body weight showed minute decrease. The survival of starved group decreased more significantly lower than that of the fed group and all the larvae died on the 6th DAH (p < 0.05). The nuclear area of the hepatocytes in the starved group were not significantly different from those of the hepatocyte nuclei in the fed group to 3th DAH, however, the starved group showed histological differences with smaller hepatocyte nuclear size compared with the fed group from the 4th to 6th DAH. Results form this study can be used as an indicator of the nutritional status of grass puffer larvae.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.35 no.6
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• pp.138-145
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• 2023

A study using numerical analysis techniques was conducted to examine the scour effect of pier-type dolphin structures installed in the domestic marine environment, and the effect of scour on horizontal bearing capacity was examined. In this study, we designed the berthing structures, taking into account the environmental and ground conditions of the target maritime area, and after calculating the predicted scour area, stability evaluation was performed by removing the ground elements of the area. The increase in scour depth was found to induce a direct decrease in horizontal bearing capacity due to soil loss in contact with the foundation, establishing a relationship that increases horizontal displacement. However, in the foundation designed to withstand the design load by reflecting the safety rate, the increase in horizontal displacement formed by possible scour is not large, which did not have a dominant effect on the horizontal bearing capacity of the foundation. In the future, research is required to analyze the impact of each factor and formalize evaluation and design techniques to evaluate the scour safety of marine foundations and pier-type structures installed in various ground conditions and structural formats.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.653-658
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• 2023

In systems like the combat management system of a naval ship or smart city of civilians, where many sensors and actuators are connected, the middle-ware DDS (Data Distribution Service) is mainly used to transmit large amounts of data. It is scalable and can effectively respond to the increase in sensors or equipment connected to the system in the future. The engineering control system (ECS), which plays an important role similar to the combat management system of a naval ship, still uses Server-Client model with industrial protocols such as Modbus and CAN (Controller Area Network) bus, to transmit data, which is unfavorable in terms of scalability. However, as automation and unmanned systems advance, more sensors and actuators are expected to be added, necessitating substantial program modification. DDS can effectively address such situations. The purpose of this study is to confirm the development possibility of an integrated monitoring and control system of a ship by using OpenDDS, which follows the OMG (Object Management Group) standard among the middle-ware DDS used in the combat management system. To achieve this goal, field equipment simulators and an ECS server were configured to perform field equipment data input/output and simulation using DDS was performed. The ECS prototype successfully handled data transmission, confirming that DDS is capable of serving as the middle-ware for the ECS of a ship.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.666-671
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• 2023

As international environmental regulations on ship emissions are gradually strengthened, interest in electric propulsion and hybrid propulsion ships is increasing, and various solutions are being developed and applied to these ships, especially stabilization of the power system and system efficiency. The direct current distribution system is being applied as a way to increase the power. In addition, verification and testing of safety and performance of marine DC distribution systems is required. As a result of establishing a DC distribution test bed, verifying the performance of the DC distribution (variable speed power generation) system, and analyzing fuel consumption, this study applied a variable speed power generation system that is applied to DC power distribution for ships, and converted the power output from the generator into a rectifier. A system was developed to convert direct current power to connect to the system and monitor and control these devices. Through tests using this DC distribution system, the maximum voltage was 751.5V and the minimum voltage was 731.4V, and the voltage fluctuation rate was 2.7%, confirming that the voltage is stably supplied within 3%, and a variable speed power generation system was installed according to load fluctuations. When applied, it was confirmed through testing that fuel consumption could be reduced by more than 20% depending on the section compared to the existing constant speed power generation system.

• Tunnel and Underground Space
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• v.33 no.5
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• pp.399-413
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• 2023

The present study conducted a numerical modeling of CO₂ injection at the Janggi Basin using the TOUGH-FLAC simulator, and examined the hydro-mechanical stability of the aquifer and the fault. Based on the site investigations and a 3D geological model of the target area, we simulated the injection of 32,850 tons of CO₂ over a 3-year period. The analysis of CO₂ plume with different values of the aquifer permeability revealed that assuming a permeability of 10^-14 m² the CO₂ plume exhibited a radial flow and reached the fault after 2 years and 9 months. Conversely, a higher permeability of 10^-13 m² resulted in predominant westward flow along the reservoir, with negligible impact on the fault. The pressure changes around the injection well remained below 0.6 MPa over the period, and the influence on the hydro-mechanical stability of the reservoir and fault was found to be insignificant.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.15 no.4
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• pp.192-202
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• 2010

Submarine groundwater discharge (SGD) has been recognized as a provider for freshwater, nutrients, and dissolved constituents from continents to the oceans and paid more attention with regard to the mass balance of water or dissolved constituents on local and global scales. The submarine discharge of fresh groundwater (fresh SGD) through seepage or springs in coastal ocean may be especially important in aspects of water resource and marine environment managements in the future. Based on the worldwide compilations of observed fresh SGD, our review reveals that fresh SGD occurs in various marine environments along most shoreline of the world and the global estimates of fresh SGD were approximately 0.01-17% of surface runoff. In addition, the input of fresh SGD calculated and investigated in this study were about 50%, 57%, 89%, and 420% of total river discharge in Jeju Island, Yeongil Bay, Masan Bay, and Yeoja Bay, respectively. These inputs from fresh SGD along the shoreline of Korea Peninsula are much higher than those of the whole world, greatly vary with the region. However, since these estimates are based on the water balance method mainly used in coastal ocean, we have to perform continuous monitoring of various parameters, such as precipitation, tide, evapotanspiration and water residence time, which have an impact on the water balance in a lot of areas for evaluating the precise input of fresh SGD. In addition, since the method estimating the input of fresh SGD has brought up many problems, it is required to make an intercomparison between various methods such as hydrogeological assumption, numerical modeling, and seepage meter.

• Journal of Navigation and Port Research
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• v.47 no.6
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• pp.401-409
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• 2023

This study compared and analyzed the performance of a distributed area search algorithm and a distributed probability search algorithm based on information exchange between ships. The distributed algorithm is a method that can search for an optimal avoidance route based on information exchange between ships. In the distributed area search algorithm, only a ship with the maximum cost reduction among neighboring ships has priority, so the next expected location can be changed. The distributed stochastic search algorithm allows a non-optimal value to be searched with a certain probability so that a new value can be searched. A circular-based ship collision avoidance model was used for the ship-to-ship collision avoidance experiment. The experimental method simulated the distributed area search algorithm and the distributed stochastic search algorithm while increasing the number of ships from 2 to 50 that were the same distance from the center of the circle. The calculation time required for each algorithm, sailing distance, and number of message exchanges were compared and analyzed. As a result of the experiment, the DSSA(Distributed Stochastic Search Algorithm) recorded a 25%calculation time, 88% navigation distance, and 84% of number of message exchange rate compared to DLSA.

• Journal of Navigation and Port Research
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• v.48 no.3
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• pp.200-205
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• 2024

This paper examines the impact of ESG activities of domestic shipping companies on the cost of debt. It is known that companies with large information asymmetry tend to have high costs of debt. Corporate ESG activities have been identified as an effective means of reducing information asymmetry. By actively engaging in ESG activities, companies can lower the cost of debt by reducing information asymmetry. Therefore, this study aims to investigate whether these mechanisms, which have been observed in previous studies, also apply to domestic shipping companies. Multiple regression analysis is conducted on KOSP I-listed shipping companies from2010 to 2022. The cost of debt is set as the dependent variable, while the ESG rating is used as the explanatory variable. The analysis reveals that companies with a high level of ESG activities generally have a lower cost of debt. However, it is important to note that ESG activities of shipping companies do not seem to have a significant impact on their cost of debt. In fact, the level of ESG activities among domestic shipping companies is not particularly high (Hong, 2024). Despite these findings, domestic shipping companies should still strive for sustainable management to adapt to the rapidly changing business environment and meet the demands of the modern era. ESG management is a representative method for achieving sustainability. Therefore, shipping companies should not only focus on reducing the cost of debt but also on opening up the closed industry culture and communicating with capital market participants for sustainable growth. It is crucial for these companies to listen to the voices of stakeholders and embrace a holistic approach to sustainability.

• Journal of Navigation and Port Research
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• v.48 no.1
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• pp.55-61
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• 2024

Environmental, Social, and Governance (ESG) management may be one of the recent hot topics in corporate management. The purpose of this paper was to study the level of ESG activities of shipping companies. The shipping industry is known to have low transparency and low favorability (Yun, 2022). This study determined whether ESG activities of shipping companies known to the public or studied qualitatively were consistent with objective facts through quantitative analysis. Analysis was conducted on 8,009 firm-year KOSP I listed companies from 2010 to 2022 using ESG ratings evaluated and published by KCGS. As a result of the analysis, it was found that shipping companies had a lower level of ESG activities than non-shipping companies. Although many research studies have been done on companies' ESG activities, research on corporate social responsibility activities and ESG activities of domestic shipping companies is limited. This paper is significant in that it is the first study to quantitatively analyze ESG management status of domestic shipping companies. Shipping companies should make efforts to improve their images, improve their business performances, and increase corporate sustainability by taking the lead in proactive ESG activities rather than performing passive ESG activities due to external regulations such as IMO 2020 and IMO 2050.