• Journal of IKEEE
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• v.22 no.4
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• pp.1019-1024
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• 2018

In this paper, we suggest a combined cost function to find out the optimal operation of an envelope tracking system, and evaluated its performance with Quadrature Amplitude Modulation (QAM) waveform, with which envelope tracking coefficients for the peak drain efficiency and the bandwidth of power amplifiers are determined. Based on the classical envelope tracking theory, the operation of the supply modulator, which is a key part of the envelope tracking process, is modeled and analyzed mathematically. Then characteristics of the modulator by setting envelope shaping function as a cubic polynomial and sweeping the coefficients of this function was analyzed. By sweeping the coefficients, efficiency and bandwidth at each condition with 64-QAM signal was used to obtain optimal point of the supply modulator. Compared to the conventional shaping functions, the optimized function showed the bandwidth reduction by 12.7 percent point while the efficiency was maintained.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.3
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• pp.430-440
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• 2022

Shipping companies are key components of the logistics industry, which is extremely significant in enhancing the country's comprehensive national power and promoting global trade development. In the context of the implementation of the new development pattern strategy in China and the impact of the global novel coronavirus (COVID-19), this paper takes 22 Chinese shipping listed companies as the research object and analyses the operational efficiency of them from 2011 to 2020 based on the Super-SBM DEA Model and Window DEA Model. Factors affecting the efficiency are further analyzed with the Tobit model. The research conclude that the operational efficiency of Chinese shipping companies as a whole shows a steady increase from 2011 to 2020. Although most of them are in a relatively ef ective operation state, fewer are absolutely effective companies. Besides efficiency among companies differs obviously, which indicates the potential of further improvement and promotion. What's more, factors such as current economic development level, enterprise size, human resources quality and enterprise turnover speed have significant positive correlation to the operation efficiency of Chinese shipping listed companies, which is significant to improve the operation efficiency of Chinese shipping companies.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.56 no.2
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• pp.126-137
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• 2020

This study collected and analyzed the fishing process of existing fishing boat and newly built fishing boat by using the video observation methods to understand the improvement of fishing operation efficiency and safety according to the scale change of coastal composite fishing boat. The fishing operation efficiency was calculated by analyzing the frequency of movement, the movement distance and the moving time per basket used in the fishing process to derive the improvement of the newly built fishing boat compared to the existing fishing boat. It was confirmed that the mean frequency of movements decreased to 13.9%, the average moving time decreased to 21.8%, the mean movement distance increased to 20.5% and the movement through the top of gunwale did not occur. Movement of frequency, increased and time according to the fishing operation were directly affected by the width of side passages and the presence or absence of walking obstruction such as bulwark stay, hatch coaming and fishing gears on deck. The results of this study are expected to be used as basic data for redesigning into a safe and efficient coastal composite fishing boat in the future.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.4
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• pp.577-585
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• 2010

The Military Tactical Communication technology for effective network-centric warfare is developing. Targeting broadband wireless transmission, core technology for connection, and Transmission technology that secure survivability under High-speed Movement environment. On the one hand, Tactical data communication system that reflects military characteristic is developing on the base of Legacy communication equipment which is used in the field. Because almost every military units in the field have used voice to communicate which lower efficiency of operation, they have made effort to Substitute voice communication which delays military Operation Tempo to digital communication. The Communications environment of troops in Forward edge of battle field area is very poor. Especially in terms of limited frequency allocation and bandwidth. Therefore, improving the efficiency of frequency is essential for Military Tactical Communication. This paper is about The Data Compression Method for increase of Efficiency in Tactical Data Communication over Legacy Radios which are UHF, VHF, HF Radio. I proposed and proved the most efficient Data Compression Method that reflects military characteristic, after analyzing the experimentation, which simulate CAS(Close Air Support mission) data transmission between Pilot and TACP.

• International Journal of Railway
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• v.9 no.2
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• pp.41-45
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• 2016

In this paper, a study on the efficiency improvement of the magnetic levitation train using the LIM (Linear Induction Motor) was presented. The maglev train has the advantage of being environmentally friendly since much less noise and dust is produced. However, due to structural limitation, compared to a rotating induction motor, linear induction motor, the main propulsion engine of the maglev train has a relatively greater air gap and hence has the lower operation efficiency. In this paper, the relationship between the operating condition of the train and the slip frequency has been investigated to find out the optimum slip frequency that might improve the efficiency of the magnetic levitation train with linear induction motor. The slip frequency is variable during the operation by this relationship only within a range that does not affect the levitation system of the train. After that, the comparison of the efficiency between the conventional control method with the slip frequency fixed at 13.5[Hz] and the proposed method with the slip frequency variable from 9.5[Hz] to 6.5[Hz] has been conducted by simulation using Simplorer. Experiments of 19.5[ton] magnetic levitation trains owned by Korea Institute of Machinery and Materials were carried out to verify the simulation results.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.4
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• pp.330-335
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• 2017

Increased fossil fuel consumption causes global warming, environmental pollution, and abnormal climate change. Wind-generated power installation is proposed to solve this problem. Recently, the wind power plant construction case encourages the installation of the energy storage system (ESS) to improve the intermittency of wind power. The maximized ESS operation profits connected to wind power are not generated in the simplest operation pattern of charging at night and discharging at day. The battery charging efficiency improvement should be considered to get more profits. Thus, there is a possibility of increasing ESS operation profits by analyzing the battery AC and DC charging/discharging efficiency and the yearly average sealed maintenance free (SMP) in hours. In this paper, the battery impedance characteristic, AC and DC charging/discharging efficiency, and the yearly average SMP are analyzed. The operation scenario to improve the ESS battery charging efficiency connected to wind power is proposed and verified via simulation.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.2297-2302
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• 2010

The status and effectiveness of Bi-modal Tram is analyzed through the comparison of the transport effectiveness and operation cost between the public transportation systems (bus, light rail transit) considering the vehicle and operation characteristic of new transit system Bi-modal Tram. The standard operation schedule is established in consideration of the vehicle specification and operation characteristic of main public transportation modes, and then the annual average operation cost is estimated depending on the volume, speed, analysis length for respective public transportation mode. Through analyzing the operation cost and distribution characteristic of public transportation modes depending on the transport volume and travel speed, the operational efficiency suitable for the city is derived. It is concluded that the operational efficiency of Bi-modal Tram is superior to that of the bus and light rail transit on the aspect of travel volume and operation speed.

• Journal of the Korean Society for Railway
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• v.19 no.3
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• pp.397-407
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• 2016

This study analyzed the efficiency change and the factors affecting productivity change for the six railway operation corporations that are local public enterprises; study was performed with the DEA-CCR Model and Malmquist Productivity Index, using data collected from 2010 to 2014. Since it was not feasible to collect data on the operating expenses and the number of employees of each of the lines, the efficiencies of each operation corporation were analyzed by integrating the operation corporations, and the Malmquist Productivity Index was used to investigate the trend of the periodical productivity change. Average efficiency for urban railway operation corporations was found to be higher in the case of the bigger corporations. In 2014, the Seoul Metro and the Daejeon Metropolitan Express Transit Corporations were analyzed and found to be the most efficient operation corporations. The Malmquist Productivity Index was used to determine the periodical change; the average MPI was 1.06, with a continuous increase of productivity. The analysis showed that changes of technology were generally more obvious than change of technology efficiency for all six operation corporations.

• Journal of Power Electronics
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• v.5 no.3
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• pp.206-211
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• 2005

Conventional switched capacitor converters have an inherent drawback that their efficiency decreases as the output current increases. This inherent drawback is due to a periodical forced charging and discharging operation in the internal switched capacitors accompanied by a large capacitor current. Their efficiency can not be increased by decreasing its internal resistance. As a result, conventional switched capacitor converters have been limited to uses with a very small output current. To solve this problem we presented a novel switched capacitor converter topology that uses a resonant operation instead of the forced charging and discharging operation. Its advantage over a conventional switched capacitor converter is higher efficiency even in a high output current region. In this paper, the operation analysis and steady-state characteristics are described in detail for a half buck type switched capacitor converter, and they are confirmed by experimentation.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.2
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• pp.175-180
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• 2020

The purpose of this study was to clarify precautions during the design and operation phases for energy reduction in a public office building. To check the operation status of the building, we measured the indoor temperature and humidity in the office space of the building installed central heating and cooling systems. And we analyzed these data and annual BEMS data. As a result, we found six problems related to decreasing system efficiency. Based on these, we presented the information to improve the efficiency of the system from the design and operation phase. Also, we present the need for a system to support the decision-making of operational managers in real-time for the energy efficiency of the building.