• Journal of Advanced Marine Engineering and Technology
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• 제41권4호
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• pp.310-315
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• 2017

최근 건조되는 선박은 연료소비량을 절감하고 안락한 운항을 위해서 고효율 프로펠러를 부착하고 있다. 이와 같이 고효율 프로펠러가 탑재됨에 따라 이전의 프로펠러 특성을 고려한 프로펠러 감쇠방법을 이용하여 해당 축계의 비틀림진동 해석을 할 경우에는 해석 오차가 많이 발생되고 있다. 이러한 오차는 고효율 프로펠러의 개발이 지속됨에 따라 더욱 커질 것으로 예상된다. 본 논문에서는 비틀림진동 해석에 적용되고 있는 각종 프로펠러 감쇠 적용방법들에 따른 해석 편차를 검토하였다. 또한 고효율 직결식 10MW급 프로펠러를 적용한 선박들을 대상으로 프로펠러 감쇠 적용방법에 따른 해석치와 계측 결과를 비교 검토하여 현 시점에서 사용상 적절한 프로펠러 감쇠방법을 제시하였다.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.3133-3141
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• 2011

The next generation domestic high speed railway system is a power distributed type and uses vector control method for motor speed control. Nowadays, inverter driven induction motor system is widely used. However, recently PMSM drives are deeply considered as a alternative candidate instead of an induction motor drive system due to their advantages in efficiency, noise reduction and maintenance. The next-generation high speed train is composed of 2 converter units, 4 inverter units, and 4 Traction Motor units. Each motor is connected to the inverter directly. In this paper, the effect of IPMSM parameter variations to the system operation characteristics of the multi inverter drive high speed train system are investigated. The parallel connected inverter input-output characteristics are analyzed to the parameter mismatches of IPMSM using the 1C1M control simulator based on Matlab/Simulink.

• ETRI Journal
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• 제38권4호
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• pp.645-653
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• 2016

This paper demonstrates the performance of a metal-substrate power module with multiple fabricated chips for a high current electrical application, and evaluates the proposed module using a 1.5-kW sinusoidal brushless direct current (BLDC) motor. Specifically, the power module has a hybrid structure employing a single-layer heat-sink extensible metal board (Al board). A fabricated motor driver IC and trench gate DMOSFET (TDMOSFET) are implemented on the Al board, and the proper heat-sink size was designed under the operating conditions. The fabricated motor driver IC mainly operates as a speed controller under various load conditions, and as a multi-phase gate driver using an N-ch silicon MOSFET high-side drive scheme. A fabricated power TDMOSFET is also included in the fabricated power module for three-phase inverter operation. Using this proposed module, a BLDC motor is operated and evaluated under various pulse load tests, and our module is compared with a commercial MOSFET module in terms of the system efficiency and input current.

• 전기전자학회논문지
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• 제24권2호
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• pp.586-591
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• 2020

본 논문에서는 인터리브된 전류 주입형 고승압 DC-DC 컨버터가 제안된다. 높은 전압 이득 외에도 인터리빙 방식을 채택하여 낮은 리플 입력 전류가 달성된다. 또한 제안 된 컨버터의 소프트 스위칭 특성은 전력 스위치의 스위칭 손실을 줄이고 변환 효율을 높인다. 변압기의 누설 인덕턴스를 활용하여 다이오드의 전류 변화율을 제어함으로써 출력 정류기의 역 회복 문제도 완화된다. 200W 프로토 타입에서 얻은 실험 결과에 대해 설명한다.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.770-775
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• 2004

Although $High-T_c $superconducting HTS antennas have high efficiency and high gain, narrow bandwidth due to the high Q is the major limitation for application of satellite communication and mobile communication. Defining bandwidth as the frequency range over which standing wave ratio (SWR) is 2:1 or less, HTS antenna bandwidths are typically less than 1 %. Thus considerable effort has been focused on developing HTS antennas for broadband operation. In this work the HTS antenna array, using the bipin antenna which consisted of two triangle-radiation patches, was designed and fabricated using a ${YBa}_2{Cu}_3{O}_7x (YBCO)$ superconducting thin film on a MgO substrate for broadband operation. Also gold antennas with the same dimension as our HTS antennas were fabricated on the MgO substrate for the comparison. Experimental results for both antennas were reported in terms of radiation patterns, return losses, bandwidths and other various characteristics. The center frequency of HTS antennas was 20.28 GHz and the bandwidth obtained was significant 10 %.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.81-86
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• 2005

In this paper, we present an efficiency extension of Doherty power amplifier using LDMOS FET devices with different peak output powers and an unequal power divider. The amplifier is designed by using a MRF21045 with P1 dB of 45 W as the main amplifier biased for Class-AB operation and a MRF21090 with P1 dB of 90 W as the peaking amplifier biased for Class-C operation. The input power is divided into a 1:1.5 power ratio between the main and peaking amplifier. The simulated results of the proposed Doherty amplifier shows an efficiency improvement of approximately 19 % in comparison to the class-AB amplifier at an output power of 42.5 dBm. The fabricated Doherty amplifier obtained a PAE of 33.68 % at 9 dB backed off from P1 dB of 51.5 dBm.

• Journal of Microbiology and Biotechnology
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• 제11권5호
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• pp.863-869
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• 2001

A systematic study of microbial fuel cells comprised of alkalophilic Bacillus sp. B-31 has been carried out under various operating conditions. A significant amount of electricity was generated when redox mediators were used. Among the phenothiazine-type redox dyes tested, azure A was found to be the most effective both in maintaining a high cell voltage and for the long-term operation. The maximum efficiency was and for the long-term operation. The maximum efficiency was obtained at ca. $50^{\circ}C$ giving an open circuit voltage of 0.7V. A small change in temperature did not significantly affect the cell performance, but a rapid decrease in performance was observed below $20^{\circ}C$ and above $70^{\circ}C$. It was noticeable that fuel cell efficiency and discharge pattern depended strongly on the carbon source used in the initial culture medium. Regardless of the initial carbon sources, only glucose and trehalose were utilized as substrates. Galactose, however, was not substantially utilized except when galactose was used in the initial medium. Glucose, in particular, showed $87\%$ coulombic efficiency, which was the highest value ever reported, when Bacillus sp. was cultured in a maltose-containing medium. This study demonstrates that highly efficient microbial fuel cells can be constructed with alkalophilic microorganisms by fine-tuning the operating conditions and by carefully selecting carbon sources in the initial culture medium.

• Journal of Advanced Marine Engineering and Technology
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• 제33권6호
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• pp.835-842
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• 2009

The present thesis carried out a research on a compression pressure's reduction phenomenon and its countermeasure according to the thermal efficiency improvement method by a Miller method in 4-cycle low speed diesel engine. In case of retardation of intake valve closing time in a engine, the theoretical heat efficiency shows a remarkably reducing trend when a compression ratio is not compensated. Accordingly, the thermal efficiency showed an increasing trend in case of compensating the compression ratio. Especially, it could be understood that the theoretical heat efficiency at near ABDC $100^{\circ}$ of intake valve closing time in case of compensation of the compression ratio was improved by around 25.1%, and the mean effective pressure was also increased by around 18.6%. Also, as the retardation of intake valve closing time increases, air quantity becomes insufficient due to a backflow phenomenon of intake air and thus thermal efficiency was decreased in a high load operation domain. The solving method of this problem is possible by supercharge. Therefore, in order to improve thermal efficiency by retardation of ntake valve closing time, the thermal efficiency improvement according to low compression is possible when there are a compensation device of a compression ratio and a supercharge device. This is a problem-solving method of low compression and high expansion cycle.

• 한국환경보건학회지
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• 제35권3호
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• pp.214-219
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• 2009

This study examined the removal efficiency of the nitrogen and phosphorus in order to compensate for the combined process of ATAD(Autothermal Thermophilic Aaerobic Digestion) and EGSB(Expended Granular Sludge Bed), which are treatment methods for livestock wastewater, by introducing SBR(Sequencing Batch Reactor) as post-treatment process. The analysis on the treatment efficiency of each operation mode showed that, in the case of T-N, the treatment efficiency were 67.1% and 74.2% for Run-1 and Run-2, respectively, and in the case of T-P, the values were 71.2 and 74.1, respectively, which are indicating that the treatment efficacy is higher in the condition of Run-1, in which the time period of Anoxic and Aerobic segments were increased. In addition, the result of analyzing removal characteristics of nitrogen and phosphorus by Influx load showed that removal efficiency of nitrogen was better in the case of high influx load than in the case of low influx load. Regardless of Influx load, phosphorus showed constant influx concentration, so that removal efficiency of phosphorus was influenced littler by Influx load than that of nitrogen. This study also fed methanol as an external carbon source and performed experiment to induce denitrification under anoxic condition by using nitrate among nitrogen compounds of SBR reactor, and the results showed that intermittent feeding was more effective in Nitrogen Removal than composite feeding.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 추계 학술논문 발표대회
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• pp.125-126
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• 2012

Domestic architect office from a period of high growth from the 1970s to the '80s has been established as some of the large corporations or publicly traded corporation. 1997 IMF has pointed out there is a lot of need for improvement activities in accordance with the construction recession since the 2008 global financial crisis. In order to address these causes, the company's continuous efficient operation for accurate efficiency and competitiveness analysis was required. Leverage financial ratio indicators Study Using Data Envelopment Analysis Data Envelopment Analysis (DEA) model, how to find a benchmark for the improvement of the efficiency of inefficient enterprises in various sectors being. In this study, a comparison of the conventional DEA model and the DEA-AR model is used to analyze the efficiency and domestic architect office is to improve the management efficiency.