• 한국항공우주학회지
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• 제47권7호
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• pp.517-524
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• 2019

진공추력 88톤급 다단연소 사이클 로켓엔진의 시스템 설계를 수행하였다. 엔진 구성품에 대한 성능 평가는 기존의 연구를 활용하였으며 수렴된 엔진 시스템 성능을 구할 수 있는 알고리즘을 제안하였다. 본 연구 방법은 RD-180에 대한 기존의 연구와 비교함으로써 검증하였다. 본 연구는 가격 경쟁력을 고려하면서 성능 개선을 달성하기 위하여 한국형발사체 75톤 엔진의 개발 이력을 최대한 승계하였다. 엔진의 제작 난이도, 비용 그리고 성능 개선을 고려하여 연소압력 12MPa을 적용하였고 결과로써 23.4s의 진공비추력 향상을 얻을 수 있었다.

• 한국인터넷방송통신학회논문지
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• 제10권6호
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• pp.263-268
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• 2010

본 논문에서는 802.11n WLAN 시스템에서 우수한 오류성능을 유지하고 시스템 용량을 개선하기 위해 순환 지연 다이버시티와 블록 대각화 프리코딩 기법을 적용한 다중 사용자 MIMO OFDM 시스템을 제안하였다. 순환 지연 다이버시티(CDD : Cyclic Delay Diversity) 기법은 주파수 다이버시티를 이용하여 OFDM 시스템의 성능을 향상시키는 기법이다. 또한 블록 대각화 프리코딩 기법은 다중 사용자 MIMO 채널 환경에서 만들어진 여러 거지 프리코딩 기법 중 하나로 특이값 분해를 이용하여 zero-forcing을 하는 간단한 방법으로 구성되어 있다. 모의실험 결과를 통해 본 논문에서 제안하는 방법이 기존의 프리코딩을 사용하지 않는 CDD MIMO-OFDM 시스템에 비하여 높은 시스템 용량 성능을 보임을 확인할 수 있다.

• 디지털산업정보학회논문지
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• 제9권4호
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• pp.111-118
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• 2013

Today, universities in Korea give a great effort to complement basic college scholastic ability of freshman. Maybe it could be unnecessary effort from university. However, we cannot just leave students who have poor academic performance about 10 to 30% in a university. Universities have to prepare to solve this problem. Thus government and universities investigate a lot of efforts but there is no guarantee. As a result, e-learning could be the best solution to complement poor academic performance of freshman and it also could be the best way to reduce financial burden of university. So, many universities introduce e-learning system and they also support professors to make e-learning content. We need to promote content usage and to improve overall operations. In this paper, we discuss poor academic performance problems under the current middle and high school education systems and review approaches to solve these problems. From this analysis, we propose the design of an effective e-learning system and a method of operation to complement students who achieve poor academic performance.

• Journal of Advanced Marine Engineering and Technology
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• 제29권4호
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• pp.443-452
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• 2005

The purpose of this study is experimentally to analyze the effects of intake port swirl, injection system and turbocharger on the engine performance and the emission characteristics in a V8 type turbocharger intercooler D.I. diesel engine of the displacement 16.7L, and to suggest the improvement of engine performance. Generally to enhance engine power, TCI diesel engine is put to practically use turbocharged intercooler in order to increase volume efficiency which is cooled boost air. As results of considering the factors of the intake port of swirl ratio 2.25, compression ratio 17.5. re-entrant $8.5^{\circ}$ combustion bowl, nozzle hole diameter ${\phi}0.33{\ast}3+{\phi}0.35{\ast}2$. nozzle protrusion 3.18mm, injection timing BTDC $12^{\circ}CA$ and turbocharger(compressor 0.6A/R+46Trim. turbine 1.0 A/R+57Trim) is the best in the full load in the engine performance and the exhaust characteristics of NOx concentration. Therefore. their factors are appropriated as intake system, injection and turbocharger system.

• 한국항만경제학회지
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• 제39권2호
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• pp.165-178
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• 2023

본 논문은 위수탁제의 주체인 화물자동차 운송회사와 위수탁차주 간의 지속적인 발전과 상생을 위한 경영모델을 제시하였다. 화물자동차 운송시장의 내외적 환경분석 및 운송회사와 위수탁차주 대상의 설문을 진행하여 사업 주체자들의 서로에 대한 인식과 개선 요구 사항 등 경영모델 수립에 필요한 변수를 측정할 수 있는 구조방정식 기반의 설문지를 개발·분석하였다. 분석 결과, 위수탁제도의 합리성은 재무성과나 운송서비스의 수준에 유의한 영향을 미치지 않는 것으로 확인된 반면, 운송 사업의 외부 환경과 보상시스템은 재무성과와 운송서비스 수준에 유의한 영향을 미치는 것으로 분석되었다. 또한 위수탁 제도의 합리성은 사업 주체간 관계 개선에는 영향을 미치지 않으나, 신뢰 수준 향상에는 영향을 미친다. 운송 사업의 외부 환경과 보상시스템은 관계 개선과 신뢰수준 향상 모두에 영향을 미치는 것으로 확인되었다. 신뢰수준은 재무성과에 영향을 미치고, 관계 개선은 재무성과와 운송서비스 수준 모두에 영향을 주지 않는 것으로 나타났다. 운송회사와 위수탁차주가 화물자동차 운송시장에서 지속적으로 발전하고 상생하기 위해 확인된 분석 결과를 토대로 위수탁제를 관리할 필요가 있다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권4호
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• pp.216-223
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• 2006

In this paper, a methodology for the efficiency improvement of the photovoltaic system without adding some elements or increasing the cost comparing with the conventional system is discussed. It is suggested the optimal photovoltaic module configuration through its performance analysis, and also the suitable maximum power point tracking (MPPT) voltage considered the system cost and the efficiency of the converter. The high efficiency photovoltaic system by using the parallel power transfer (PPT) based MPPT converter is proposed and analyzed theoretically comparing with the conventional Buck type MPPT converter. Finally, it is designed and implemented the proposed photovoltaic system for supplying DC 48V by using the PPT based MPPT converter. And the effect of the efficiency improvement and the usefulness of the proposed system is proved through some preliminary simulation and experiment results.

• 한국건축시공학회지
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• 제9권2호
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• pp.63-68
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• 2009

Construction Performance measurement and management has been interested by construction practitioners. However, current construction project management practices are related to short-term improvement plans rather than long-term and systematic approaches based upon performance analysis. AR a result, there is a need for developing of a collaborative plan over project life cycle. Therefore, this paper reviews extensive literature and proposes the construction performance estimating model using a system dynamics. The paper proposes casual maps for planning, design, procurement, and construction phases. Each casual map includes all performance indicators and factors that impact on performance directly or indirectly. These casual maps that were developed by system thinking will enhance the understanding of the relationships among performances and factors. After further data gathering, these models can be used to estimate construction performance and eventually these will save project costs and shorten project schedule.

• 농업과학연구
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• 제40권4호
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• pp.385-394
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• 2013

Short-term agricultural machinery rental system has been operated by agricultural extension organization of local government (agricultural technology center) and sponsored by Ministry of Agriculture, Food, and Rural Affairs, to improve utilization efficiency and save agricultural production cost through joint utilization of agricultural machinery. This study was conducted to analyze current status of the rental system operation and provide recommendations for future direction. Question survey was conducted for officers in charge of the rental system in the technology center, and strategic improvement was suggested through importance performance analysis (IPA). Survey results showed that 11 issues should be reformed or improved by 2015, which is not practically feasible. IPA analysis resulted that administration and manpower support, cooperation between federal and local organizations, and cooperation with other organizations should be focused for successful operation of the rental system. Issues that seem to happen after 2015 need to be handled as future research.

• Journal of information and communication convergence engineering
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• 제14권4호
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• pp.227-232
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• 2016

In this study, the performance of a 32-quadrature amplitude position modulation (QAPM) system is analyzed under a Rician fading channel condition when the maximal ratio combining (MRC) diversity technique is used in the receiver. The fading channel is modeled as a frequency non-selective slow Rician fading channel corrupted by additive white Gaussian noise (AWGN). QAPM is available to improve BER performance without amplifying transmit power, and MRC diversity makes the performance improvement of QAPM system even bigger by intentionally maximizing SNR. Error performances are shown for the 32-QAPM system and a 32-phase silence shift keying (PSSK) system in order to examine the effects of fading severity, for various values of the Rician parameter, K. The dependence of error rates on MRC diversity is also analyzed. The simulation results show that the BER performance of the 32-QAPM system is better than that of the 32-PSSK system under the above mentioned conditions.

• 한국정밀공학회지
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• 제22권6호
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• pp.192-198
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• 2005

Recently, Automobile manufacturers regarding stability, economic environmental-friendly problems by the development of automobile. This reason is increasingly strict environmental regulations to lower fuel consumption and reduce emission. Designing more efficient and low emission control exhaust system results in more efficient Performance, reduced back Pressure and higher convert efficiency. Also to reduce the noise and the vibration of the automobile. According to develop variable type muffler, dual muffler and active intelligence exhaust system unit. Improvement in engine performance and fuel consumption rate, higher conversion efficiency demand information of pressure fraction and heat characteristics. To be able to determine these factor fur we experiment on each case of exhaust system unit. In this study, how back pressure is distributed in flow-through in exhaust system and how to design exhaust system flexibleness, efficiency, lower back pressure and optimal performance. This study furnish basic data for engineers, technicians.