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김동하(D.-H. Kim),함미숙(M.-S. Ham),김민진(M. Kim),유상필(S. P. Yu),엄석기(S. Um),이원용(W.-Y. Lee),김창수(C.-S. Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The fuel cell for a submarine is a closed system and therefore the unreacted hydrogen and oxygen are supposed to be recycled and reused. Generally, the compressors, the blowers, the pumps and the ejectors have been used as the recirculation equipment of a fuel cell system. In case of the vehicle application, the ejector which does not require any parasitic power is good for the performance of the fuel cell system. The ejector has been applied to a solid oxide fuel cell (SOFC) from now on. In case of SOFC, the ejector is designed to maintain the pressure required in fuel cell by compensating the pressure drop in the anode channel. However, the existing research works do not consider about the humidified hydrogen and oxygen which is occurred by electrochemical reaction at proton exchange membrane fuel cell (PEMFC). Unlike dry air, the humidified hydrogen and oxygen shows very complex behaviours in suction chamber and constant-area section. In this study, the ejector for the PEMFC used to the submarine is designed taking into account the property of the gas mixed with vaporized water and hydrogen/oxygen. Consequently, the designed ejector shows the optimal performance within the predefined operating conditions at the PEMFC for a submarine.
도시철도 지하구간에 모바일 핫스팟 네트워크 구현을 위한 연구
김동하(D. H. Kim),유근규(G. G. Yu),이덕규(D. G. Lee) 한국도시철도학회 2014 한국도시철도학회논문집 Vol.2 No.3
Mobile Hotspot Network supports the efficient vehicle group mobile communication that has advantages of mobile cellular communication systems and Wireless Fidelity. This technology acts as a relay between outside base radio station which is linked on the Internet and passengers to establish Access Point with radio interface in vehicles. This paper provides the status of the urban railway wireless communication network and the classification of 18GHz radio communication technology in order to apply Mobile Hotspot Network(MHN) to subway tunnel. Using millimeter wave, MHN serves 100 times faster high-speed data communication than the previous Wireless Broadband Backhaul. It also establishes requirements for metro railway environment and presents business model to study radio-wave propagation characteristics analysis of scattering and reflection electromagnetic waves by subway tunnels structure, optimum antenna arrangement, and handover algorithm.
김동하(D. H. Kim),장조원(J. W. Chang) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
An experimental study was carried out to investigate influence of flow conditions on a boundary layer to the near-wake of a flat plate. The flow condition in the vicinity of trailing edge that is influenced by upstream condition history is an essential factor that determines the physical characteristics of a near-wake. Various tripping wires were used to change boundary layer flow condition of upstream at the freestream velocity of 6.0 m/sec. Measurements of the boundary layer and near-wake according to the change of upstream conditions were conducted by using both I-probe(55P14 for boundary layer) and X-probe(55P61 for wake). Normalized velocity profiles of the boundary layer were shown the flow types such as laminar boundary layer, transition, and turbulent boundary layer at 0.95C from the leading edge. The velocity and turbulence intensity profiles of the near-wake for the case of laminar boundary layer at the flat plate surface exhibited a defect and a double peak showing perfect symmetry, respectively.
커버 형상을 고려한 고속전철 팬터그래프 공력특성의 수치해석적 연구
강형민(H.M. Kang),김철완(C.W. Kim),조태환(T.H. Cho),김동하(D.H. Kim),윤수환(S.H. Yoon),권혁빈(H.B. Kwon) 한국전산유체공학회 2012 한국전산유체공학회지 Vol.17 No.3
The aerodynamic performance of the pantograph on a high speed train was compared for different pantograph covers which are designed to block the aero-acoustic noise from the pantograph. For the study, two types of cover are designed: wedge and cone types. The lift force of pantograph with cover was compared with the force of pantograph only. The comparison clarified that the cone type cover increases the sideslip angle of the flow and decreases the lift force considerably. However, the wedge type cover changes the flow direction upward and increases the lift force of the pan head. This increment of lift force compensates the decrement of lift force caused by the blocking of the flow into the pantograph lower frame due to cover. Therefore, in case of the wedge type cover, the overall lift force changes slightly compared with the cone type cover.
강형민(H.M. Kang),김철완(C.W. Kim),조태환(T.H. Cho),김동하(D.H. Kim),윤수환(S.H. Yoon),권혁빈(H.B. Kwon) 한국전산유체공학회 2011 한국전산유체공학회 학술대회논문집 Vol.2011 No.11
The aero-acoustic analysis around a pantograph of a high speed train is performed. For the grid system, the real shape of the pantograph is utilized and FLUENT is used for the computation of the unsteady flow around the pantograph. Here, large eddy simulation (LES) model is applied for the calculation of the turbulence and aero-acoustic features of the pantograph are estimated by the Ffowcs Williams-Hawkings (FW-H) model. These numerical results are compared with those of experimental results; the aero-acoustic characteristics of the numerical analysis is similar to those of the experimental results and the difference of noise level is about 8dB(A).