• Transactions of the Korean hydrogen and new energy society
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• v.35 no.3
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• pp.300-309
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• 2024

Hydrogen utilization in the transportation sector, which relies on fossil fuels, can significantly reduce greenhouse gas by using to hydrogen fuel cell vehicles, and its adoption depends performance of hydrogen refueling station. The present study developed a model to simulate the back-to-back filling process of heavy duty hydrogen fuel cell vehicles at hydrogen refueling stations using a cascade method. And its quantitatively evaluated hydrogen refueling station performance by simulating various mass flow rates and storage tank capacity combinations, analyzing vehicle state of charge (SOC) of vehicles. In the cascade refueling system, the capacity of the high-pressure storage tank was found to have the greatest impact on the reduction of filling time and improvement of efficiency.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.638-644
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• 2012

In this study, we numerically estimated available and unavailable time of conventional railway by examining 60% which is known as average range of track utilization efficiency. We also estimated track repair time for maintenance which is the main factor of making track utilization change and analyzed appropriate estimated time. The railway's safety should be guaranteed by appropriate railway operating plan and by adequate rail facilities maintenance. At the same time, daily railway train 'Dia's recovery power should be reflected to the management plan. Considering these factors, we examined mechanical equipment and the national rail network in order to rationally estimate track repair time of the maintenance and to secure spare time in case of train delays. It was found that track utilization efficiency was more or less 60%.

• Journal of Korean Society of Transportation
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• v.27 no.3
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• pp.49-58
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• 2009

Four alternative plans for the bus network in Daejeon metropolitan city, which have different hierarchical structure, were proposed : Alternative 1 represents a bus network without hierarchical structure, and Alternative 2, 3, and 4 represent bus networks with primary, intermediate, and advanced hierarchical structures, respectively. Efficiency of the alternative plans were evaluated based on the evaluation index including travel time cost, waiting time cost, and transition penalty cost. The travel time cost was decreased as the level of hierarchical structure gets higher until it reaches the extremely high level. As the level of hierarchical structure get higher, the waiting time cost significantly decreased while the transition penalty cost increased. Collectively, a bus network with hierarchical structure was shown to be more efficient than without it in the light of total travel cost. For the bus network with hierarchical structure, total travel cost shows a concave curve, which implies that there exists an optimal level of hierarchical structure in a bus network.

• Journal of Korean Society of Transportation
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• v.28 no.3
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• pp.109-117
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• 2010

The purpose of advanced traffic information system(ATIS) is to help drivers save time and energy in getting to their destinations by providing traffic information through variable message sign(VMS), internet, traffic broadcasting and mobile phones. ATIS does not just provide drivers with benefits in terms of time and energy, but it provides them with psychological benefit as well, i.e., the drivers can relieve their anxiety by getting provided with traffic information. In this study, the efficiency of traffic information system is evaluated and degree of satisfaction of drivers with the system is analyzed by building satisfaction models of various media of traffic information. Each medium has different factors for satisfaction and each factor has different degree of influence, but in general, the efficiency of traffic information in helping drivers choose routes and in providing drivers with peace of mind is considered to have the highest influence on satisfaction of drivers with the system.

• Journal of Korean Society of Transportation
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• v.26 no.5
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• pp.7-16
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• 2008

There are unique aspects of truck vehicle movements compared with the personal travel in trip chaining. This paper reports an analysis on the truck vehicle trip chaining which intercity/metropolitan/intraregional trips are classified. Data collected from the travel dairy survey is used the truck trip-chaining analysis. The pattern of trip chaining classes is classified by the GIS mapping based on orgin-destination trip information. The physical index and efficiency index for each trip diary is used to the truck vehicle activity. Truck trips lengths and time differs from its truck type, service type and travel patterns. It is shown that the efficiency of the truck trip chaining depends on vehicle types and its delivery patterns. There are many other topics for research on trip chaining modeling such as the classification of trip chain, time use and mode choice by trip chaining.

• Journal of Korean Society of Transportation
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• v.25 no.5
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• pp.7-14
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• 2007

The purpose of this study is to investigate the differences between the service providers and the users of 3PL services, in their perceptions about the qualities. The results of analysis identified five elements of the quality of 3PL services: reliability, efficiency, tangibility, responsiveness, and timeliness. The perceived importance and satisfaction showed the significant differences between 3PL service providers and the clients for all of the five elements. With respect to importance, efficiency showed the largest cognitive difference. Timeliness appeared to be the most important element perceived by both the service providers and the users. In terms of satisfaction, responsiveness indicated the biggest cognitive difference. In addition, it was noticed that the clients' satisfaction levels were particularly low, with respect to responsiveness and efficiency. It must be a strategic task of the 3PL service provider to improve customer satisfaction by reducing those cognitive differences.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.41 no.3
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• pp.120-128
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• 2018

OLED Display fabrication system is one of the most complicated discrete processing systems in the world. As the glass size grows from $550{\times}650mm$ to $1,500{\times}1,850mm$ in recent years, the efficiency of Automated Material Handling System (AMHS) has become very important and OLED glass manufacturers are trying to improve the overall efficiency of AMHS. Aiming to meet the demand for high efficiency of transportation, various kind of approaches have been applied for improving dispatching rules and facility layout, while simultaneously considering the system parameters such as glass cassettes due date, waiting time, and stocker buffer status. However, these works did not suggest the operational policy and conditions of distribution systems, especially for handling unnecessary material flows such as detour. Based on this motivation, in this paper, we proposed an efficient algorithm for improving detour transportation in OLED FAB. Specifically, we considered an OLED FAB simplifying OLED production environment in a Korean company, where four stockers are constructed for the delivery of Lot in a bay and linked to processing equipments. We developed a simulation model using Automod and performed a numerical experiment using real operational data to test the performance of three operation policies under considerations. We showed that a competitive policy for assigning alternative stocker in case of detour was superior to the current dedicated policy using a specified stocker and other considered policies.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.6
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• pp.843-851
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• 2009

Much work has already been done to control and regulate the worldwide problems caused by climate change, particularly the issues on greenhouse gas (GHG) emissions. Carbon dioxide ($CO_2$), having the highest form of concentration among GHGs composed around 1.0 billion tons of emission, and comprises about 98% of the total emissions from the shipping industry. Korean trade mainly rely on the sea transportation. Korean ship tonnages that was brought about by shipbuilders all over the country, continues to grow annually due to the prevailing demands on goods or material supplies and depicting only a small part of the global maritime activity. Nowadays, new build ships coming from the Korean Shipbuilders are being optimized by hull, structure and appendages design, The operational capability of the propulsion and auxiliary machineries in its maximum capacity to achieve the highest possible efficiencies for energy and onboard power use to mitigate $CO_2$ emissions are continually being done through the help of research and development. In this paper, the energy efficiency design index and anboard power capacity of Korean new build ships have been analyzed with response to data collected by ship types, and its respective fuel consumption in relation to $CO_2$ emission results. In response to climate change convention outcome proposals, the best way for the new build ships to become energy efficient is by lowering its operational speed thru adopting the state of the art diesel propulsion engines, patronizing the best sailing practice to lower the transportation cost on the different sea trade routes also helps in $CO_2$ mitigation.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.8 no.11
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• pp.523-530
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• 2018

It has been studied over the long time for the high efficiency and high power density of the power converter. It is possible to obtain higher power conversion efficiency and small volume by increasing switching frequency, however, the switching loss is also increased. The soft switching technique can overcome of the above deficiency. The design and analysis method for ZVS(Zero Voltage Switching) Phase Shifte Full bridge converter is presented in this paper. The power transfer depends on the phase difference between two legs of the power stage and the maximum power conversion efficiency is achieved by the optimum leakage inductance value. The waveform of the current and voltage of the operational mode is analysed and the corresponding switch status is plotted as on/off status. A ZVS full bridge converter for a communication rectifier with 2kW output power is implemented and its performance are verified through PSIM software simulation and experimental results.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.163-170
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• 2006

This paper presents a approach to the measurement of efficiency. Data envelopment analysis(DEA), as it is called, has particular applicability in the service sector. Applying mathematical programming techniques, DEA enables relative efficiency ratings to be derived within a set of analysed units. This paper investigates the efficiency employing DAE-CCR Model and DEA-BCC Model on data for 15 container terminals covering 1998$^{\sim}$2005 in Korea Results of this paper, suggests to some plan for operation strategy in Container terminals.