• Journal of the Korean Society of Marine Environment & Safety
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• v.15 no.3
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• pp.269-274
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• 2009

Recently, the construction of Liquefied Natural Gas Carriers(LNGC) is being promoted larger and larger depending on long voyage. In 1950 years, $5,000m^3$ class of LNGC had been changed to $71,500m^3$ class in 1973. and to $210,000-266,000m^3$ class in 2007. Especially, the system of main engines and cargo control, Re-liquefaction of natural gases have become possible in LNGC. This research deals with the LNG projects, world markets of energy and developing tendency of liquefied natural gas carriers.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.3
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• pp.333-341
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• 2015

In this paper, a 0.5~4 GHz frequency synthesizer having good phase noise performance is proposed. Wideband output frequencies of the synthesizer were synthesized using DDS(Direct Digital Synthesizer) and analog direct frequency synthesis technology in order to obtain fast settling time. Also in order to get good phase noise performance, 2.4 GHz DDS clock was generated by VCO(Voltage Controlled Oscillator) which was locked by the 100 MHz reference oscillator using SPD(Sample Phase Detector). The phase noise performance of wideband frequency synthesizer was estimated and the results were compared with the measured ones. The measured phase noise of the frequency synthesizer was less then -121 dBc @ 100 kHz at 4 GHz.

• Journal of Digital Convergence
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• v.13 no.6
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• pp.247-256
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• 2015

This study is on kinetic light-emitting object control systems and the methodologies for research. The study explores the methodologies for researching and findings on kinetic light-emitting object control systems, which consist of multiple objects comprising multiple groups; the main control section that transmits the main control signals that correspond to each of the groups in order to display forms using multiple objects; multiple sub control sections that transmit sub control signals in correspondence to each of the objects in the corresponding groups from the above in accord with the main control signal; and multiple driving parts that control the length of the wires connected to each of the multiple objects according to the sub control signal.

• Journal of computational fluids engineering
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• v.20 no.3
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• pp.94-103
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• 2015

The turbulent flow characteristics in the channel flow are investigated using large eddy simulation(LES) of FDS code, built in NIST(USA), in which the near-wall flow is solved by Werner-Wengle wall function. The periodic flow condition is applied in streamwise direction to get the fully developed turbulent flow and symmetric condition is applied in lateral direction. The height of the channel is H=1m, and the length of the channel is 6H, and the lateral length is H. The total grid is $32{\times}32{\times}32$ and $y^+$ is kept above 11 to fulfill the near-wall flow requirement. The Smagorinsky model is used to solve the sub-grid scale stress. Smagorinsky constant $C_s$ is 0.2(default in FDS). Three cases of Reynolds number(10,700, 26,000, 49,000.), based on the channel height, are analyzed. The simulated results are compared with direct numerical simulation(DNS) and particle image velocimetry(PIV) experimental data. The linear low-Re eddy viscosity model of Launder & Sharma and non-linear low-Re eddy viscosity model of Abe-Jang-Leschziner are utilized to compare the results with LES of FDS. Reynolds normal stresses, Reynolds shear stresses, turbulent kinetic energys and mean velocity flows are well compared with DNS and PIV data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1215-1220
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• 2014

Breaking time is an important performance indicator of a circuit breaker. Thus, the operating mechanism of the circuit breaker should be optimized for reducing the breaking time. The operating mechanism in a gas circuit breaker is made up of several latches. Specifically, the geometry and relative positions of latches influence the dynamic behaviors of the operating mechanism. In this study, a three-stage latch operating mechanism is analyzed on the basis of the verified multibody dynamics model constructed using the MSC.ADAMS program. The relative positions and lengths of latches are selected as design variables. The dominant design variables are selected by a design study. Optimization is performed using a genetic algorithm (GA). The study results demonstrate that the performance of the circuit breaker improves by about 22.5.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1112-1115
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• 2006

모바일 GIS를 홍수재해관리 시스템에 도입하기 위한 목적은 홍수에 대비한 신속한 상황대처 통해 인명 및 재산피해를 최소화하는데 있다. 모바일 GIS 시스템 구축의 기본 방향은 하천유역에 대한 행정업무 및 정보화 업무의 효율성을 높여 현장업무에서 실시간으로 제공되는 수문정보 및 지형정보에 대한 다양한 컨텐츠를 주민들이 쉽게 접근하여 서비스를 제공받을 수 있도록 하고 현장 실무자가 하천 수위 및 유량을 관리하는 데 있어 즉각적인 조치를 가능하도록 하기 위한 것이다. 본 연구에서 이동 클라이언트와 홍수재해관리시스템 서버간의 무선통신채널은 AP(Access Point)를 통한 WLAN이나 CDMA망의 모바일 네트워크 또는 차세대 휴대인터넷 망을 대상으로 하였다. 홍수재해관리시스템은 ArcIMS, HTML, Java Script를 이용하여 구축하고 웹 서비스를 위해 마이크로소프트사의 IIS(Internet Information System) 사용하며, ArcIMS의 정상적인 구동을 위해 JRE(Java Runtime Environment)를 설치하도록 하였다. 주요 GIS 기능은 줌인, 줌아웃, 팬, 속성정보 검색, 거리측정, 버퍼링 기능 등이고 Layer는 침수위험건물, 대피건물, 침수지역 건물용도, 건물, 도로, 수계, 침수예상지역(100, 200년 빈도), 위성영상, DEM, 행정경계 등이 포함되도록 하였다. 시스템 구축에 사용될 데이터는 수리수문학적 데이터(유출량, 강우강도, 대상지역의 면적, Manning 계수 등)와 대상지역의 수치지도, DEM, 고해상 위성영상, 문헌조사와 현장조사를 통해 얻은 자료를 바탕으로 구성하도록 하였으며, 수리수문학적 데이터와 DEM 데이터를 바탕으로 침수지역 데이터를 생성하고 문헌조사와 현장조사를 통해 얻은 속성정보와 디지털 지도인 공간정보를 연결하기 위해 디지털 지도에서 건물 Layer, 도로 Layer, 등고선 Layer, 수계 Layer를 추출하여 ArcGIS에서 Coverage로 변환하여 위상관계를 설정한 후 다시 Shape 파일로 변환하여 속성정보와 연결시키도록 데이터베이스 구축방안을 제시하였다. 이와 같이 본 연구에서는 홍수재해 관리시스템에서 모바일 GIS를 적용하기 위하여 Pocket PC를 탑재한 이동 클라이언트인 PDA에 GPS 모듈을 확장하여 GPS 위성으로부터 위치정보를 획득하고 지리정보를 제공하는 모바일 GIS 서버간에 XML 기술을 이용하여 수문정보 및 지형정보 서비스를 제공하는 방안을 제시하였다.

• The Transactions of the Korea Information Processing Society
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• v.3 no.1
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• pp.118-126
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• 1996

Memory hierarchy is a useful mechanism for improving the memory access speed and making the program space larger by layering the memories and separating program spaces from memory spaces. However, it needs at least two memory accesses for each data reference : a TLB(Translation Lookaside Buffer) access for the address translation and a data cache access for the desired data. If the cache size increases to the multiplication of page size and the cache associativity, it is difficult to access the TLB with the cache in parallel, thereby making longer the critical timing path in the processor. To achieve such parallel accesses, we present the hybrid mapped TLB which combines a direct mapped TLB with a very small fully-associative mapped TLB. The former can reduce the TLB access time. while the latter removes the conflict misses from the former. The trace-driven simulation shows that under given workloads the proposed TLB is effective even when a fully-associative mapped TLB with only four entries is added because the effects of its increased misses are offset by its speed benefits.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.5
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• pp.231-236
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• 2008

This paper proposes a cost-efficient and flexible FPGA-based logic circuit emulation platform. By improving the performance and adding more features, this new platform is an enhanced version of our LAPG. It consists of an FPGA-based hardware engine and software element to drive the emulation and monitor the results. It also provides an interactive verification environment which uses an efficient communication protocol through a bi-directional serial link between the host and the FPGA board. The experimental results show that this new approach saves $55%{\sim}99%$ of communication overhead compared with other methods. According to the test results, the new LAPG is more area efficient in complex circuits with many I/O ports.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.347-350
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• 2006

The rocket grade hydrogen peroxide has been widely used as a monopropellant in propulsion systems. In the present paper, we described an experimental study of a catalytic reactor that employs two stage catalyst beds to enhance the low temperature performance of the reactor. $K_2MnO_4$ was chosen as the catalyst for the initial stage of the reactor bed for its superior behavior in the low temperature regime. LSC was used for the catalyst of the second stage of the reactor. The gas generator with combined catalyst beds was built and tested to exhibit high decomposition efficiency over 90% and successful cold-start characteristics.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.3C
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• pp.314-322
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• 2007

This paper proposes a new optimization algorithm named by GBNSGA(Goal-Pareto Based Non-dominated Sorting Genetic Algorithm) which determines the best configuration for CR(Cognitive Radio) communication systems. Conventionally, in order to select the proper radio configuration, genetic algorithm has been introduced so as to alleviate computational burden along the execution of the cognition cycle proposed by Mitola. This paper proposes a novel optimization algorithm designated as GBNSGA for cognitive engine which can be described as a hybrid algorithm combining well-known Pareto-based NSGA(Non-dominated Sorting Genetic Algorithm) as well as GP(Goal Programming). By conducting computer simulations, it will be verified that the proposed method not only satisfies the user's service requirements in the form of goals. It reveals the fast optimization capability and more various solutions rather than conventional NSGA or weighted-sum approach.