• International Journal of Fluid Machinery and Systems
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• 제8권3호
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• pp.155-168
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• 2015

No-load speed is an important performance factor for the safe operation of hydropower systems. In turbine design, the manufacturers must conduct several model tests to calculate the accurate value of no-load speed for the complete range of operating conditions, which are expensive and time-consuming. The present study presents steady and unsteady methods for calculating no-load speed of a Francis turbine. The steady simulations are implemented using a commercial flow solver and an iterative algorithm that relies on a smooth relation between turbine torque and speed factor. The unsteady method uses unsteady RANS simulations that have been integrated with a user subroutine to compute and return the value of runner speed, time step and friction torque. The main goal of this research is to evaluate and compare the two methods by calculating turbine dynamic parameters for three test cases consisting of high and medium head Francis turbines. Overall, the numerical results agreed well with experimental data. The unsteady method provided more accurate results in the opening angle range from 20 to 26 degrees. Nevertheless, the steady results showed more consistency than unsteady results for the three different test cases at different operating conditions.

• 한국조경학회지
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• 제34권2호
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• pp.26-35
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• 2006

The purpose of this research is to suggest the planting methods and the reasonable target levels of IGS for promoting green streetscape in Seoul. Using the three dimensional computer simulations, various greening methods were applied to evaluate effectiveness of promoting green streetscape. The results of this study suggest that promoting tree planting on car lane is more effective than on pedestrian side walks. In wide streets, the height of tree has positive effects on promoting green streetscape. In both car lane and pedestrian side walks, the greening effects of tree planting both in zig-zag pattern and in parallel pattern were similarly most high. The width of strip in side strip planting has positive effect on promoting green streetscape. Promoting stratified planting is very effective. Promoting greening wall on pedestrian side walks is more effective than on car lane. Combined the results of IGS survey with the public officials and complex simulations, suggest that the optimal levels of IGS is ranging from 12.0% in alleys to 54.0% in car lanes among arterial roads.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권7호
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• pp.2548-2567
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• 2015

Recently, there has been a clear trend towards the application of ad hoc networking technology in civil aviation communication systems, giving birth to a new research field, namely, aeronautical ad hoc networks (AANETs). An AANET is a special type of ad hoc wireless network with a significantly larger scale and distinct characteristics of its mobile nodes. Thus, there is an urgent need to develop a simulator to facilitate the research in these networks. In this paper, we present a network simulator, Aero-Sim, for AANETs. Aero-Sim, which is based on the freely distributed NS-2 simulator, enables detailed packet-level simulations of protocols at the MAC, link, network, transport, and application layers by composing simulations with existing modules and protocols in NS-2. Moreover, Aero-Sim supports three-dimensional network deployment. Through several case studies using realistic China domestic air traffic, we show that the proposed simulator can be used to simulate AANETs and can reproduce the real world with high fidelity.

• 전력전자학회논문지
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• 제17권3호
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• pp.191-197
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• 2012

This paper proposes a new synthetic test circuit (STC) to confirm the switching operation of thyristor valve in HVDC converter. The proposed STC uses a 6-pulse thyristor converter with 2-phase chopper as a high-current source to provide turn-on current to the test valve. The operation of proposed STC was verified through theoretical analysis and computer simulations. Based on computer simulations, a hardware scaled model was built and tested to confirm the feasibility of implementing a real-size test facility. The proposed system has an advantage of simple structure and operation over the existing system.

• 한국ITS학회 논문지
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• 제17권5호
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• pp.135-142
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• 2018

본 논문은 수중 음향 채널 환경에 따른 CDMA(code division multiple access)와 OFDM(orthogonal frequency division multiplexing) 전송기법의 장단점을 비교 분석한다. 이를 위해서 r.m.s.(root mean square) 지연시간과 도플러 주파수 그리고 다중 경로의 수를 변화시켜가며 다양한 수중 음향 채널에서 전산 모의실험을 수행하였다. r.m.s. 지연시간과 도플러 주파수가 각 전송기법의 설계치 내의 수치이며 동일한 전송률을 갖는 경우 CDMA가 OFDM에 비해 우수한 성능을 갖는 것을 보였다. 그러나 도플러가 설계치보다 큰 경우에는 CDMA의 성능이 저하되어 OFDM이 CDMA보다 우수한 것을 보였다.

• 한국통신학회논문지
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• 제24권6A호
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• pp.905-912
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• 1999

본 논문에서는 블록부호를 트렐리스상에서 구현하여 블록부호의 연판정 복호 알고리즘인 MAP 복호 알고리즘을 유도하였다. 또한 트렐리스상의 연판정 복호법인 비터비 알고리즘과 MAP 알고리즘을 사용한 모의실험을 통해 그 성능을 분석하였다. 그리고 비교적 간단한 블록부호인 해밍부호를 구성부호로 사용하여 다양한 형태의 직렬연접부호와 병렬연접부호에 대한 성능분석을 수행하였다. 모의실험 결과 블록부호에 연판정 복호 알고리즘을사용한 경우는 경판정 복호 알고리즘에 비해 높은 부호화 이득을 가짐을 알 수 있었다. 또한 구성부호로 블록부호를 사용하는 연접부호의 모의실험을 수행한 결과 반복복호함으로써 우수한 성능을 가진 연접부호를 얻을 수 있음을 검증하였다.

• 한국통신학회논문지
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• 제28권4A호
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• pp.193-199
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• 2003

본 논문에서는 기존의 DS-CDMA 시스템의 성능분석을 위해 사용되는 표준 가우시안 근사법과 간단하고 향상된 가우시안 근사법을 이용하여 3세대 이동통신 시스템인 WCDMA(Wideband Code Division Multiple Access) 시스템의 상향링크에 대한 성능을 분석하였다. 수신된 신호의 신호 대 잡음비를 이용하는 표준 가우시안 근사법과, 다중 사용자 간섭 성분에 대한 통계적 특성을 적용하여 표준 가우시안 근사법을 보완한 간단하고 향상된 가우시안 근사법을 사용하여 대역이 제한된 WCDMA 시스템의 성능을 분석하고 백색 가우시안 채널에 다중 사용자 간섭이 존재하는 상황에서 모의실험을 실시하였다. 신호 대 잡음비가 변하는 환경에서 확산 계수와 롤오프 (roll-off) 계수를 변화시켜가면서 당양한 모의실험을 실시하였고, 이를 바탕으로 해서 간단하고 향상된 가우시안 근사법을 사용한 대역제한된 WCDMA 시스템의 성능 분석이 타당함을 확인할 수 있었다.

• 대한전기학회논문지:전력기술부문A
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• 제53권7호
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• pp.365-374
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• 2004

The relay measures the frequency of the power system in order to detect faults and separate them from the system. Many estimation algorithms for the relay have been proposed to accurately measure the frequency. This paper proposes a new frequency measurement method using the digital phase locked-loop(DPLL) for the relay of the power system. The proposed method is configured with a DPLL scheme and verified through computer simulations and experimental tests. In order to cope with noises in the power system, filters are included in the input signal processing part and the frequency comparator. MATLAB is used for computer simulations and an experimental setup with a CPU and an FPGA(Field Programmable Gate Array) is constructed. The loop filter of the DPLL is run in the CPU software In adjust parameters and others are in the FPGA. Experimental tests are performed lot a function generator and the power system. Results show that the proposed method is appropriate to the frequency measurement for the relay.

• Biomolecules & Therapeutics
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• 제2권1호
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• pp.34-38
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• 1994

In order to investigate the structure-activity relationships of the stereoisomers of angiotensin converting enzyme inhibitors, captopril and its derivatives were selected as model compounds. In vitro enzymatic activities of them depend on the symmetry at the asymmetric carbons. Especially, the alanyl carbon should have the S configuration to be biologically active. But the demethylated captopril having the achiral carbon also shows the activity although it is less active than captopril. Seven stereoisomers of captopril and its derivatives were chosen and their acidic and ionic forms were used for molecular dynamics simulations. Four computer simulations were practiced for each model compound in order to obtain the good condition for simulation to explain the experimental structure-activity relationships. From the computer simulation results, relativistic movements of three well-known pharmacophoric sites, carboxylate carbon, carbonyl oxygen, and sulfur atoms, were analyzed. Good results were obtained from the aqueous solution molecular dynamics simulation with ionic forms of model compounds. Active model compounds have the pharmacophoric areas of 6.08 to 6.38 $\AA$$^2$and the similarity in the geometrical data. But inactive ones have the largely deviated values of 4.51 to 4.87 $\AA$$^2$from those of active ones.

• 한국전자파학회논문지
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• 제8권6호
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• pp.645-655
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• 1997

본 논문에서는 CDMA 시스댐에 적용하기 위해 기저 대역에서 설계된 비동기식 동기 추적 회로의 성능을 이론적으로 분석하고 컴퓨터 시뮬레이션을 통해 검증한다. AWGN 채널 환경에서 지터 분산을 펼스 성형 필터, 타이밍 오프셋, 신호 대 잡음 비, 루우프 필터 계수의 함수로 이론적으로 유도하고 2차 동기 추적 회로를 중심으로 루우프 필터의 설계에 판해 고찰한다. 끝으로, 설계된 동기 추적 회로를 ETRI에서 IMT-2000을 위해 설계한 동기식 CDMA 시스템의 역방향 링크에 적용하여 AWGN과 레일라이 페이딩 환경에서의 성능을 시율레이션을 통해 검증한다.