• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.3
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• pp.373-380
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• 2018

The small coastal vessel registered in Korea, small coastal vessels with a gross tonnage of 10 tons or less account for 94.6 % and among them, aged vessels over 16 years age indicate 40.6 %. In order to reduce GHG emissions from small coast vessels, discussions are underway to replace aging ships' propulsion units with eco - friendly propulsion facilities, and the electric propulsion ship is emerging as one of the measures. The electric propulsion system using the DFE rectifier, which was applied in the conventional large commercial vessel, was effective in reducing the harmonics and improving the DC output voltage of the DC link stage, but it occupied a large volume and caused an increase in the overall system price. Therefore, in this paper, we propose an electric propulsion system using AFE rectifier with a small volume of system that can be applied to a small coastal vessel. In order to analyze the effectiveness of the overall system, the load profile was applied to obtain accurate and rapid speed tracking performance of the propulsion motor affected by the speed load. In addition, the power factor and total harmonic distortion factor of the voltage and current on the improved power output side are derived through simulation.

• Journal of Ocean Engineering and Technology
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• v.37 no.1
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• pp.8-19
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• 2023

In recent years, modular-type floating islands have been considered as a promising option for future ocean space utilization. A modular floating island consists of a number of standardized pontoon-type modules and connectors between them. In this study, the motion responses of a modular floating island in waves was investigated based on frequency-domain numerical analysis. The numerical method is based on the potential flow theory and adopts a higher-order boundary element method with Green's function. First, motion RAOs were directly compared with the model test data by reference to validate the present numerical method. Then, numerical investigations were conducted to analyze the motion characteristics of the floating island by considering various modules shapes and arrangements. It was found that motion responses were reduced in a single central module compared to when divided central modules were used. Finally, the effect of modular arrangement on the motion responses in irregular waves was discussed. It was confirmed that multiple-layer outer modules are more effective in calming the central module than using single-layer outer modules, except under very long period conditions.

• Journal of ILASS-Korea
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• v.28 no.4
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• pp.176-183
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• 2023

Many countries are striving to reduce carbon emissions with the goal of net zero by 2050. Accordingly, vehicles are rapidly being electrified to reduce greenhouse gases in the transportation sector. However, many organizations predict that internal combustion engines of LDV (light-duty vehicle) will exist even in 2050, and it is difficult to electrify aircraft and large ships in a short time. Therefore, synthetic fuel (i.e., e-Fuel) that can reduce carbon emissions and replace existing fossil fuels is in the spotlight. The e-Fuel refers to a fuel synthesized by using carbon obtained through various carbon capture technologies and green hydrogen produced by eco-friendly renewable energy. The purpose of this study is to compare and analyze the injection and spray characteristics of the simulated e-Gasoline. We mixed the hydrocarbon fuel components according to the composition ratio of the synthetic fuel produced based on the FT(Fischer-Tropsch) process. As a result of injection rate measurement, simulated e-Gasoline showed no significant difference in injection delay and injection period compared to standard gasoline. However, due to the low vapor pressure of the simulated e-Gasoline, the spray tip penetration (STP) was lower, and the size of spray droplets was larger than that of traditional gasoline.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.2
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• pp.197-206
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• 2023

Recently, the international community, including the International Maritime Organization (IMO), has strengthened regulations on air pollution emissions of ships, and eco-friendly ships are actively being developed to reduce exhaust gas emissions. Among them, rotor sail (RS), a wind-assisted ship propulsion system, is attracting attention again. RS is a cylindrical device installed on the ship deck, that generates hydrodynamic lift using a magnus effect. This is a next generation eco-friendly auxiliary propulsion technology, and Enercon company, which developed RS-applied ships, announced that fuel savings of more than 30% are possible. In this study, optimal installation conditions such as RS spacing and arrangement type were selected when multiple RSs were installed on ships. AR=5.1, SR=1.0, and D_e/D was fixed at 2.0 according to the RS arrangement, and the wind direction was considered only for the unidirectional +y-axis. Regarding arrangement conditions, five conditions were set at 3D intervals in the +x-axis direction from 3D to 15D and five conditions in the +y-axis direction from 5D to 25D. C_L, C_D and aerodynamic efficiency (C_L/C_D) were compared according to the square(□) and diamond(◇) shape arrangements. Consequently, the effect of RS on the longitudinal distance was not significantly different. However, in the case of RS flow characteristics according to the transverse distance, the interaction effect of RS was the greatest when the two RSs almost matched the wind direction. In the case of the RS flow characteristics according to the arrangement, notably, when the wind blew in the forward (0°) direction, the diamond (◇) arrangement was least affected by the backward flow between RSs.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.207-215
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• 2015

In the last decade, increasing national research fund for recycling the waste FRP (fiber reinforced plastics) ships which has caused environmental problems, improves the technology making concrete-reinforcing fibers out of the waste FRP. Furthermore, the concrete with recycled FRP fiber was tested for the structural performance. Experimental strength tests show that use of recycled FRP powder does not reduce the compressive strength of high strength concrete, and does increase the fire resistance performance of high strength concrete significantly. But, the study in investigating the properties of recycled fiber powder from waste FRP has not been completed because of the absence of the method of separation of mat layer from the waste FRP. This study is to propose a new extracting method of the mat layer from waste FRP, which is the efficient and environment friendly system. and thus it is considered to be the useful recycling method for fire resistance high concrete products or structures.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.483-492
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• 2020

In this study, we compared and analyzed the Revealed Comparative Advantage (RCA) and Trade Specialization Index (TSI) based on ballast water management systems (BWMS) trade data, which are related to the International Maritime Organization (IMO) Ballast Water Management Convention to suggest the current status of Korea's industrial competitiveness and suggest future development directions for the BWMS industry. As international interest in eco-friendly vessels is expanding, the IMO is engaged in dramatic discussions and agreement-making related to marine emissions of pollutants from ships. IMO member states that must implement this convention are striving to develop technology and secure industrial competitiveness as major industries in the eco-friendly shipping sector, with the BWMS industry experiencing a high market entry barrier and the possibility of the leading market entrants gaining leadership. The Republic of Korea accounts for 17 (approximately 38 %) of the 45 BWMS that received final approval as of October 2019. Based on trade data relating to product codes HS842219, HS84212, and HS89, the RCA index and TSI were calculated and compared. The findings revealed that the Republic of Korea has relative inferiority compared to countries such as Germany and Denmark. Despite this, Korea's favorable industrial environment, which includes several IMO-approved BWMS technologies and the possession of domestic certification institutions, is likely to strengthen its competitiveness in the BWMS market.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.301-306
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• 2016

During the initial stage of propulsion shaft design, the shaft alignment process includes a thorough consideration of lateral vibration to verify the operational safety of the shaft. However, a theoretical method for analyzing forced lateral vibrations has not been clearly established. The methods currently used in classification societies and international standards can only ensure a sufficient margin to avoid the blade-passing frequency resonance speed outside the range of ${\pm}20%$ of the maximum continuous rating (MCR) for the engine. Typically, in shaft alignment analyses, longer center distances between the support bearings promote affirmative results, but the blade order resonance speed can approach the lower limit for lateral vibration. Therefore, this matter requires careful attention by engineers, and a verification of the theoretical analysis by experimental measurements is highly desirable. In this study, both theoretical and experimental analyses were conducted using strain gauges under two draught conditions of vessels used as 50,000-DWT oil/chemical tankers, introduced recently as eco-friendly ships. Based on the analyses, the influence of the lateral vibration on the shafting system and the system's reliability was reviewed.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.4
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• pp.288-294
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• 2016

In modern ships, the shafting system often becomes stiff owing to the high engine power, whereas the hull structure becomes more flexible owing to optimization using high-tensile-strength thick steel plates; therefore, more sophisticated shaft alignments are required. In this study, strain gauge-based measurement was conducted under five vessel operating conditions and bearing reaction forces and hull deflections affecting shaft alignment were analyzed for a 50,000 dead weight tonnage oil/chemical tanker that has gained repute as an eco-friendly vessel in recent years. Furthermore, the analytical results from each technique-theoretical calculation, jacking ups, and strain gauges-were cross-checked against each other in order to enhance the degree of accuracy and reliability of the calculation.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.47-53
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• 2012

As one of the methods for recycling the FRP from the waste ships, separation of roving layer from the mat has some merits in a sense of the eco-friendly and economical recycling process. Similar characteristics, however, between the roving and the mat even with different ratio of the resin and the glass and the thickness of the roving, much thinner than the mat, make the mechanically automatic differentiation difficult. In this study spectrochemical differentiation between the two layers has been made using boiling concentrated sulfuric acid, methanol and isopropanol solution saturated with KOH, or hydrogen fluoride (HF) solution. Furthermore efficiently coloring water-soluble dye following the HF treatment makes the roving layer more distinguishable photophysically. The layer differentiation and the automatic layer distraction move up the date of simple and automatic separation process for the waste FRP.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.5
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• pp.212-217
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• 2015

Ships and marine structures have a lot of problems in their high maintenance and operating cost by biofouling. A biofouling occurrs by the adhesion of marine microorganism, algae and bacteria. In this study, the aim is to prevent or to reduce the biofouling phenomena through silver nano-particle coating on artificial light-weight aggregates and geopolymer. The antibacterial activity on them is tested according to ASTM E2149-2013a. The test results showed, it is estimated that silver nano-particles removed 99.99 % of bacteria. Specimens were set up in the sea side of field test area in Korea Institute of Ocean Science and Technology (KIOST) and have been observed for five months. The anti-biofouling effect and difference in weight change rate have been detected two months later after the installation. Because silver nanoparticles inhibit bacterial growth and kill the cells by destroying bacterial membranes, silver nano-particle coating on artificial lightweight aggregates is a well-suited and eco-friendly method for preventing biofouling in the sea up to 5 months.