• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1098-1105
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• 2021

The International Maritime Organization has steadily strengthened environmental regulations on nitrogen oxides and carbon dioxide emitted from marine vessels. Consequently, the demand for electric propulsion vessels based on eco-friendly elements has increased. To this end, research and development has been steadily conducted for various vessels. In electric propulsion systems, a redundancy configuration is typically adopted to increase reliability and facilitate the onboard arrangement. Furthermore, studies have been actively conducted to ensure the safety of electric propulsion systems through the combination with digital twin technology. A digital twin can be used to predict outcomes in advance by implementing real-world equipment or space in a virtual world like twins, integrating real-world information and data with the virtual world, and performing computer simulations of situations that can occur in a real environment. In this study, we perform failure modes and effects analysis (FMEA) to validate the electric power management system (PMS) redundancy scheme for the digital twin technology development of electric propulsion vessels. Then, we propose the role and algorithm of PMS as a compensation function for preventing primary and secondary damages caused by a single equipment failure of the PMS and preventing additional damages by analyzing the impact on the entire system under real vessel operating conditions based on the redundancy FMEA suggested for the ship classification and certification. We verified the improvement in propulsion conservation through tests.

• Journal of the Korean Institute of Landscape Architecture
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• v.42 no.6
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• pp.60-71
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• 2014

In this study, on the assumption that the urban park originally is imbued with a public welfare ideology, said public welfare ideology and its characteristics were attended to among the various social roles that the urban park currently fulfills. Aspects of welfare meaning in urban parks were attempted to be identified with the former history of urban parks and the movements of the connections between modern parks and welfare territories. The ideologies, benefits and practices regarding the welfare role that the urban park has played from the past to the present were examined and the backgrounds and contexts within which the welfare ideologies have been expressed in the urban park were examined. In order to examine the implicated public welfare ideologies of the urban park, case studies were conducted to identify how they are expressed and practiced in the present times and the facilitation of these parks and public welfare both in the U.S. and the South Korea. The study results of the cases show that expressions of public welfare in urban parks are composed of more specific and visible programs and strategies in the present times, which are different from the simple proclamatory ways in the past. Particularly, in order to visibly practice a public welfare ideology, many-sided integrated designs are conducted along with various public welfare institutions and programs inside and outside of the urban park. The conclusions from this study are as follows. First, the urban park plays a role as a space to realize public welfare ideology, to create welfare benefits and to realize social welfare. Modern urban parks are used as an indicator to measure the actual conditions of social welfare and are a social environmental commodity that can offer universal benefits to urban residents. Second, many-sided integrated designs are tried along with various public welfare institutions at urban parks, which visibly practice public welfare ideologies in the present. In addition, public welfare institutions greatly influence the consistent development of the resources in the urban park. Third, if the detailed utilization of the regional facilities infrastructure could be brought along with multidimensional approaches about the resources in the urban park, it could be much closer to the lives of residents and could secure a space for increasing resident quality of life.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.517-534
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• 2021

Hydrogen fuel is emerging as an new energy source to replace fossil fuels in that it can solve environmental pollution problems and reduce energy imbalance and cost. Since hydrogen is eco-friendly but highly explosive, there is a high concern about fire and explosion accidents of hydrogen fueled vehicles. In particular, in semi-enclosed spaces such as tunnels, the risk is predicted to increase. Therefore, this study was conducted on the applicability of the equivalent TNT model and the numerical analysis method to evaluate the hydrogen explosion pressure in the tunnel. In comparison and review of the explosion pressure of 6 equivalent TNT models and Weyandt's experimental results, the Henrych equation was found to be the closest with a deviation of 13.6%. As a result of examining the effect of hydrogen tank capacity (52, 72, 156 L) and tunnel cross-section (40.5, 54, 72, 95 m²) on the explosion pressure using numerical analysis, the explosion pressure wave in the tunnel initially it propagates in a hemispherical shape as in open space. Furthermore, when it passes the certain distance it is transformed a plane wave and propagates at a very gradual decay rate. The Henrych equation agrees well with the numerical analysis results in the section where the explosion pressure is rapidly decreasing, but it is significantly underestimated after the explosion pressure wave is transformed into a plane wave. In case of same hydrogen tank capacity, an explosion pressure decreases as the tunnel cross-sectional area increases, and in case of the same cross-sectional area, the explosion pressure increases by about 2.5 times if the hydrogen tank capacity increases from 52 L to 156 L. As a result of the evaluation of the limiting distance affecting the human body, when a 52 L hydrogen tank explodes, the limiting distance to death was estimated to be about 3 m, and the limiting distance to serious injury was estimated to be 28.5~35.8 m.