• 한국분무공학회지
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• 제28권4호
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• pp.198-206
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• 2023

In this study, visualization of in-cylinder spray behavior and spark channel stretching by air flow characteristics depending on engine operating conditions were investigated. For in-cylinder spray behavior, increase in engine rpm did not alter the counter-clockwise air flow direction and location of in-cylinder dominant air flow but increased average air flow velocity, which hindered spray propagation parallel to the piston surface. When injection timing was retarded, direction of in-cylinder dominant air flow was changed, and average air flow velocity was reduced resulting in an increase in spray penetration length and change in direction. For spark channel stretching, increase in air flow speed did not affect spark channel stretch direction but affected length due to increase in spark channel resistance and limitation of energy ignition coil can handle. Change in air flow direction affected spark channel stretch direction where the air flow was obstructed by ground electrode which caused spark channel direction to occur in the opposing direction of air flow. It also affected spark channel stretch length due to change in air flow speed around the spark plug electrode from the interaction between the air flow and ground electrode.

• 한국항공우주학회지
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• 제36권8호
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• pp.728-733
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• 2008

경계요소법을 이용하여 비평면 지면 위를 움직이는 공압부양 고속 지상운송체의 비정상 공력해석을 수행하였다. 비정상 공력해석을 위하여 시간전진법과 이에 연계한 자유후류를 도입하였다. 공압부양 고속 지상운송체가 채널 내를 움직일 때, 채널에 갇힌 공기에 의해 지면효과가 증가하여 운송체의 양력계수와 피칭모멘트 계수가 더욱 증가한다. 즉, 채널과 같은 비평면 지면은 운송체의 종방향 불안정성을 증가시킨다. 반면, 채널과 같은 비평면 지면에 의한 양력상승이 운송체 탠덤날개의 왼쪽과 오른쪽에 동일하게 발생하기 때문에 채널과 같은 비평면 지면효과가 운송체의 횡방향 안정성에 미치는 영향은 크지 않다.

• 한국통신학회논문지
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• 제41권11호
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• pp.1528-1538
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• 2016

영상정보용 데이터링크는 장거리의 공중-지상 환경에서 영상과 신호정보를 전송하도록 설계된 통신 시스템이다. 본 논문은 장거리 공중-지상 채널환경의 신호 분석에 적합한 곡면지구 2-Ray 모델을 사용하여 영상정보용 데이터 링크의 통신거리에 따른 수신전력 변화 폭을 분석하고 지면 반사파에 의한 수신전력의 변화폭을 경감할 수 있는 수신 안테나의 최적 고각 제어방법을 제안한다. 제안된 방법은 추가적인 하드웨어 성능 향상 없이도 기존의 고각 제어 방법에 비하여 추가적인 링크마진을 확보할 수 있다.

• 한국통신학회논문지
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• 제42권4호
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• pp.703-715
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• 2017

본 논문은 장거리 공중-지상 가시선 링크에서 대용량 영상정보용 데이터링크의 무선채널 특성을 분석하고 공중-지상 채널의 협대역 및 광대역 간섭이 대용량 데이터링크의 수신 신호에 미치는 영향을 수학적으로 분석하는 방법을 제안한다. 제안된 성능분석 방법을 이용하여 통신거리에 따른 수신성능을 분석하였고 지면 반사파의 협대역 및 광대역 간섭에 의해 통신거리가 제한됨을 확인하였다. 또한 수신 안테나를 상향으로 제어하는 방법의 성능분석 결과, 협대역뿐만 아니라 광대역 간섭도 효과적으로 제거함으로써 별도의 등화기를 포함하지 않은 기존 대용량 데이터링크 장비로도 통신거리를 증가시킬 수 있음을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.43.2-43.2
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• 2005

• 한국컴퓨터정보학회논문지
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• 제23권1호
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• pp.1-7
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• 2018

The Korean Air Force FA-50 aircraft currently operating in the Air Force is using Ultra High Frequency (UHF) frequency communications for navigation communications with ground control stations or other aircraft. The pilot communicates by changing frequency at any time during flight, and performs communication by directly inputting from the Integrated Up-Front Controller installed in the cockpit. The frequency is designated as secret, and the pilot receives the task with the frequency channel number (001~xxx) and finds the frequency of the channel in the list of 4,000 frequency channels and inputs it manually. This reduces the safety and convenience of pilots' operations and exposes them to hazards that may occur especially during night flight missions. In this paper, we propose a function to embed the frequency corresponding to the frequency channel list in IMDC, the aircraft mission computer, and to automatically change the frequency when the pilot only inputs the channel number.

• 한국전자통신학회논문지
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• 제15권1호
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• pp.21-30
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• 2020

본 논문에서는 국제전기통신연합에서 권고하는 경로손실 예측모델을 이용하여 지상통제소와 무인 항공기 사이의 공대지 채널에 대한 경로손실을 예측하고, 이를 공대공 채널로 확장하여 중고도급 무인 항공기를 기반으로 하는 공중중계 시스템에 대한 네트워크 커버리지를 분석한다. 대기에 의한 경로손실 예측을 위해 한반도의 기후 및 지리적 인자를 활용하였다. 특히 국내의 강우량 및 유효지구반경 인자는 한국정보통신기술협회에서 공시한 실측 데이터를 활용하여 정확도를 높였다. 또한, 공중중계 송수신기는 현재 국내에서 개발 완료된 공용데이터링크 시스템의 주요지표를 활용하였다. 예측 결과로부터 임무 고도가 높아질수록 공중중계 시스템의 네트워크 커버리지가 넓어짐을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권8호
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• pp.2666-2687
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• 2022

As a new alternative communication scheme in 5G, unmanned aerial vehicle (UAV) is used as a relay in the remote base station (BS) for assistant communication. In order to ameliorate the quality of the backhaul link, a UAV backhaul transmission scheme based on improved Nash equilibrium (NE) strategy is proposed. First, the capacity of air-to-ground (A2G) channel by the link preprocess is maximized. Then, the maximum utility function of each UAV is used as the basis of obtaining NE point according to the backhaul channel and the backhaul congestion. Finally, the improved NE strategy is applied in multiple iterations until maximum utility functions of all the UAVs are reached, and the UAVs which are rejected by air-to-air (A2A) link during the process would participate in the source recovery process to construct a multi-hop backhaul network. Simulation results show that average effective backhaul rate, minimum effective backhaul rate increases by 10%, 28.5% respectively in ideal A2G channel, and 11.8%, 42.3% respectively in fading channel, comparing to pure NE strategy. And the average number of iterations is decreased by 5%.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 춘계학술대회 논문집
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• pp.550-553
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• 2008

In this paper, experiments of air-breathing proton exchange membrane fuel cell (PEMFC) for mobile devices were carried out according to the cathode conditions. These conditions are defined by the cathode flow field plate type (the channel type, the open type) and the cathode surface direction. Single cell and 6-cell stack were used in this experiments. The experimental results showed that the open type cathode flow field plate gave better performance for small size PEMFCs because the open type cathode plate allowed better air convection than the channel type cathode plate. In the experiments related to the direction of the slits on the cathode flow field plate, the horizontal slit cell was better than the vertical slit cell. With respect to the cathode surface direction, when the cathode surface is placed in the direction normal to the ground, PEMFC generated more stable power in the mass transport loss region.

• Wind and Structures
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• 제25권4호
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• pp.397-413
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• 2017

When bridges are constructed with lower heights from the ground, the formed channel between the deck and the ground will inevitably hinder or accelerate the air flow. This in turn will have an impact on the aerodynamic forces on the deck, which may result in unexpected wind-induced responses of bridges. This phenomenon can be referred to "ground effects." So far, no systematic studies into ground effects on the wind-induced responses of closed box girders have been performed. In this paper, wind tunnel tests have been adopted to study the ground effects on the aerodynamic force coefficients and the wind-induced responses of a closed box girder. In correlation with the heights from the ground in two ground roughness, the aerodynamic force coefficients, the Strouhal number ($S_t$), the vortex-induced vibration (VIV) lock-in phenomena over a range of wind velocities, the VIV maximum amplitudes, the system torsional damping ratio, the flutter derivatives, the critical flutter wind speeds and their variation laws correlated with the heights from the ground of a closed box girder have been presented through wind tunnel tests. The outcomes show that the ground effects make the vortex-induced phenomena occur in advance and adversely affect the flutter stability.