• Nuclear Engineering and Technology
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• 제29권2호
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• pp.167-174
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• 1997

The method that the operating condition of Control Rod Drive Mechanism (CRDM) can be monitored without mounting sensors within CRDM housing was developed, and by using this developed method the closed-loop controller for the CRDM was designed which can optimize the performance and maximize the reliability of CRDM operation. Neural network is utilized as pattern recognition engine in detecting CRDM actuation. In this paper, most problems in previous open loop system are resolved. The control algorithms for closed-loop system ore developed and implemented within the hardware of timing controller based on microprocessor. All functions in the timing controller ore verified by means of real time CRDM simulator. The results show that the timing controller performs its intended functions properly.

• 한국자동차공학회논문집
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• 제14권3호
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• pp.178-185
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• 2006

This paper investigates the steady-state combustion characteristics of the Homogeneous charge compression ignition(HCCI) engine with variable valve timing(VVT) and dimethyl ether(DME) direct injection, to find out its benefits in exhaust gas emissions. HCCI combustion is an attractive way to lower carbon dioxide($CO_2$), nitrogen oxides(NOx) emission and to allow higher fuel conversion efficiency. However, HCCI engine has inherent problem of narrow operating range at high load due to high in-cylinder peak pressure and consequent noise. To overcome this problem, the control of combustion start and heat release rate is required. It is difficult to control the start of combustion because HCCI combustion phase is closely linked to chemical reaction during a compression stroke. The combination of VVT and DME direct injection was chosen as the most promising strategy to control the HCCI combustion phase in this study. Regular gasoline was injected at intake port as main fuel, while small amount of DME was also injected directly into the cylinder as an ignition promoter for the control of ignition timing. Different intake valve timings were tested for combustion phase control. Regular gasoline was tested for HCCI operation and emission characteristics with various engine conditions. With HCCI operation, ignition delay and rapid burning angle were successfully controlled by the amount of internal EGR that was determined with VVT. For best IMEP and low HC emission, DME should be injected during early compression stroke. IMEP was mainly affected by the DME injection timing, and quantities of fuel DME and gasoline. HC emission was mainly affected by both the amount of gasoline and the DME injection timing. NOx emission was lower than conventional SI engine at gasoline lean region. However, NOx emission was similar to that in the conventional SI engine at gasoline rich region. CO emission was affected by the amount of gasoline and DME.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 1999년도 춘계종합학술대회
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• pp.179-184
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• 1999

디지털 시스템을 설계하고 분석할 때, 번지버스와 데이터버스 및 각종 제어 신호들을 타이밍도로 표현하는 경우가 많다. 그러나 디지털 시스템의 동작이 타이밍도로 표현되는 경우, 그 표현이 복잡할 뿐 아니라 동작 분석이 용이하지 못하다. 본 연구에서는 시스템의 타이밍도를 확장된 마크흐름선도(EMFG; Extended Mark flow Graph)로 표현하는 방법을 제안하였다. 시스템의 동작이 EMFG로 표현되는 경우, 각종 신호들에 따라 변화하는 시스템의 상태가 도식적으로 표현되므로 시스템의 동작 분석이 용이해질 뿐 아니라 시스템의 설계에도 유용하게 이용 될 수 있다. 적용 예로 NEC사의 $\mu$PD70320 CPU의 메모리 읽기 사이클 및 MCM60256A의 메모리 동작을 EMFG로 표현하였다.

• 에너지공학
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• 제26권2호
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• pp.32-38
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• 2017

본 연구에서 사용되는 발전기용 커먼레일 디젤엔진은 흡 배기 밸브의 작동을 위해 기계적으로 구동되는 캠축을 이용하고 있으며, 차량 운전조건 알맞게 밸브의 개폐시기가 고정되어 있다. 그러나 발전기용 엔진은 회전속도가 일정하고 부분부하에서 운전된다. 따라서, 발전용 커먼레일 디젤엔진의 최적화 설계를 위해 밸브 타이밍의 변화에 따른 디젤연소와 배출가스의 특성을 고찰하여 연비 측면에서 계산하였다. 디젤엔진의 밸브 타이밍은 흡배기 유동을 변화시킴으로서 연소특성에 영향을 주었으며 발전기의 연비 개선이 가능하다고 판단되었다.

• International Journal of Automotive Technology
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• 제8권5호
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• pp.555-562
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• 2007

The Variable Valve Timing(VVT) system for high performance is a key technology used in newly developed engines. The system realizes higher torque, better fuel economy, and lower emissions by allowing an additional degree of freedom in valve timing during engine operation. In this study, a model-based control method is proposed to enable a fast and precise VVT control system that is robust with respect to manufacturing tolerances and aging. The VVT system is modeled by a third-order nonlinear state equation intended to account for nonlinearities of the system. Based on the model, a controller is designed for position control of the VVT system. The sliding mode theory is applied to controller design to overcome model uncertainties and unknown disturbances. The experimental results suggest that the proposed sliding mode controller is capable of improving tracking performance. In addition, the sliding mode controller is robust to battery voltage disturbance.

• 한국분무공학회지
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• 제15권1호
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• pp.1-7
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• 2010

As world attention has focused on global warming and air pollution, high efficiency diesel engines with low $CO_2$ emissions have become more attractive. Premixed diesel engines in particular have the potential to achieve the more homogeneous mixture in the cylinder which results in lower NOx and soot emission. Early studies have shown that the operation conditions such as the EGR, intake conditions, injection conditions and compression ratio are important to reduce emissions in a PCCI (Premixed Charge Compression Ignition) engine. In this study a modified cam was employed to reduce the effective compression ratio. While opening timing of the intake valve was fixed, closing timing of the intake valve was retarded $30^{\circ}$. Although Atkinson cycle with the retarded cam leads to a low in-cylinder pressure in the compression stroke, the engine work can still be increased by advanced injection timing. On that account, we investigated the effects of various injection parameters to reduce emission and fuel consumption; as a result, lower NOx emission levels and almost same levels of fuel consumption and PM compared with those of conventional diesel engine cam timing could be achieved with the LIVC system.

• Journal of Positioning, Navigation, and Timing
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• 제8권1호
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• pp.19-29
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• 2019

This paper analyzes the design factors for GNSS anti-jamming receiver system in which the adaptive beamforming algorithm is applied in GNSS receiver system. The design analysis factors used in this paper are divided into three: antenna, beamforming algorithm, and operation environment. This paper analyzes the above three factors and presents numerical simulation results on antenna and beamforming algorithm.

• 한국항행학회논문지
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• 제13권3호
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• pp.337-343
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• 2009

본 논문에서는 D8PSK 변조 방식을 이용하는 VDL Mode-2 수신기에 적용 가능한 버스트 모드 심벌 타이밍 복원기를 제안하고 성능 분석과 연동실험을 실시하였다. IIR 루프필터를 사용하여 심볼 타이밍 에러를 최소화 하는 방식은 수렴 속도가 늦기 때문에 버스트 모드에 적용하기 곤란하다. 즉 빠른 수렴 특성이 중요시 된다. 본 논문에서 제안한 방식은 프리앰블을 이용하여 초기 동기가 이루어진 후 최대 심벌 전력을 갖는 방향으로 한 샘플 빠르게 또는 한 샘플 느리게 샘플 클럭을 이동하여 최적의 심벌을 취하는 방식이다. 제안된 방식을 적용한 수신기와 호주 ADS사 송신 장비와 연동 시험한 결과 100 ppm 이상에서도 잘 동작함을 확인하였다.

• 정보통신설비학회논문지
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• 제10권4호
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• pp.135-142
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• 2011

This paper proposes a performance evaluation method for power consumption of set-top box (STB) stand-by mode transition schemes. A stand-by mode transition scheme characterizes the timing of mode transition. The timing of mode transition affects the duration of stand-by mode operation, and the power consumptions of STB as well. Recently a fast stand-by mode transition scheme (FMT) has been proposed based on user input for selecting the device to be connected to TV. In this paper, we evaluate power consumption of FMT and a conventional mode transition scheme. For the computation of the duration of stand-by mode operation, the user input events are modeled as Poisson process. Simulation results based on the modeling reveals that the proposed scheme is more effective in power saving than the conventional scheme by up to 30%.

• 한국자동차공학회논문집
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• 제6권6호
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• pp.259-266
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• 1998

In the SI engine, the improvement of combustion stability is important not only for the fuel consumption rate but also for the emission control at idling of engine. Thus the engine speed fluctuation at idle operation mainly comes from cyclic variation of combustion in the SI engine. In this syudy, the improvement of combustion stability for the SI engine at idle condition by the cooling water temperature, duty ratio of ISC, spark ignition timing as well as the reducement of the harmful exhaust gas emission was discussed.