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김지영(Ji Young Kim),부닷귀엔(Vu Dat Nguyen),변도영(Do Young Byun) 한국가시화정보학회 2011 한국가시화정보학회지 Vol.9 No.2
The shape of nozzle cross-section plays an important role in stabilizing electrospray jet. The angle of contact line is governed based on the famous Young-Laplace equation. Compared to a round nozzle that has a constant curvature along the orifice, the square nozzle has four square corner edges and four straight edges that hold the meniscus in a different manner and is of interest in this study. By utilizing both square and round capillary nozzle, we examine the effect of nozzle shape in electrohydrodynamic jetting. The ejections were recorded with a high speed camera and analyzed to examine the jetting repeatability based on dynamic movement of meniscus. The result suggests that if the corner edges are not sharp, then its effect on repeatability is also limited.
비회체 열복사 및 검뎅생성을 고려한 액체로켓 엔진의 연소현상 해석
변도영(Do Young Byun),김만영(Man Young Kim),백승욱(Seung Wook Baek) 한국항공우주학회 2004 韓國航空宇宙學會誌 Vol.32 No.1
액체로켓 연소기 내의 연소 및 열전달 특성에 관한 수치 연구를 수행하였다. 기상 및 액상 지배방정식, 케로신 액체연로에 대한 난류연소 모델, 검뎅의 생성, 그리고 비회체 열복사 지배방정식을 도입하였다. 검뎅의 분포를 포함한 액체로켓 연소기 내의 이상연소를 고찰한 후 산소/연료 혼합비, 벽면의 온도, 그리고 방사율이 벽면으로 전달되는 열유속에 미치는 영향을 분석하였다. 이러한 액체로켓 연소 해석에 있어서 검뎅과 열복사의 영향은 결코 무시될 수 없음을 확인하였을 뿐만 아니라 산소/연료 혼합비가 증가할수록, 벽면온도가 감소할수록, 그리고 방사율이 증가할수록 벽면 복사열유속은 증가하였다. Numerical analysis has been carried out to investigate the combustion and heat transfer characteristics in a liquid fuel rocket combustor. Governing gas and droplet phase equations with PSIC model, turbulent combustion model with liquid kerosine fuel, soot formation, and nongray thermal radiative equations are introduced. After confirming two-phase combustion behavior with soot distribution, effects of O/F ratio, wall temperature, and wall emissivity on the wall heat flux are investigated. It is found that effects of soot formation and radiation is important, and as O/F ratio increases, wall temperature decreases, and emissivity increases, the radiative heat flux on the wall increases.
기둥 구조 전극을 내재하는 노즐을 이용한 정전 분무 마이크로 추진기관
이영종(Young Jong Lee),변도영(Do Young Byun),양지혜(Ji Hye Yang),이석한(Suk han Lee),김용재(Yong jae kim),고한서(Han Seo Koh) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.12
본 논문은 기둥 구조의 전극이 내부에 존재하는 노즐을 이용한 정전 분무 마이크로 추진 장치의 새로운 메커니즘을 제시하였다. 기둥 구조의 노즐로 인한 제팅의 효율 증진을 수치적 및 실험적으로 연구하였다. 노즐 상부에 존재하는 전극에 인가된 전압으로 인하여 액면에 형성된 전기장은 액체의 분무를 가능하게 하며 기둥 구조의 전극은 액면의 중앙 부분에 전기장이 집중되도록 하여 제팅을 효율적으로 할 수 있게 하였다. 또한 노즐 크기에 따른 필요한 인가전압의 차이에 대한 연구를 수행하였으며 본 연구로부터 수 마이크로미터의 노즐에 대해서 500V 이하의 전압에서 구동이 가능함을 보였다. This paper presents a novel mechanism of electro-spray micro-thruster featured by a nozzle with a conductive pole inside, referred to here as a pole type nozzle. And the effects of the pole type nozzle on the efficiency of the jetting are numerically and experimentally investigated. The electric voltage signal applied to the upper electrode plate, against the pole as the ground, allows a ejection of spray to take place. It is verified experimentally that the use of the pole type nozzle allows a stable and sustainable jetting mode of ejection for a wider range of applied voltages because it can concentrate the electric field more on the centre of the meniscus. According to results about size effect, experiments indicates that the proposed mechanism allows that operation of micro thruster at less than 500 volts through nanoscale nozzle.
서울전파천문대(SRAO) 6M 망원경의 ON-THE-FLY 관측 시스템 구축
강현우,변도영,박용선,Kang, Hyun-Woo,Byun, Do-Young,Park, Yong-Sun 한국천문학회 2005 天文學論叢 Vol.20 No.1
On-The-Fly (OTF) observation method is developed for the efficient use of 6 M radio telescope at Seoul Radio Astronomy Observatory (SRAO). This technique, in which data and information of antenna position are recorded synchronously while driving a telescope regularly and rapidly across a field, provides more efficient use of telescope time and better calibration of the acquired data than the traditional point-to-point observation method does. For the realization of the method, we (1) added RT-Linux modules to the existing operating system, (2) replaced digital voltmeter with voltage-to-frequency converter, and (3) modified many SRAO observation programs. By observing Moon and G78.2+2.7 using this method and comparing them with previous observations, we verify the successful operation and efficiency of the OTF observation mode.
김만영,변도영,백승욱,Kim, Man-Young,Do, Young-Byun,Baek, Seung-Wook 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.1
The convergence of finite volume method (FVM) or discrete ordinate method (DOM) is known to degrade for optical thickness greater than unity and large scattering albedo. The present article presents a convergence acceleration procedure for the FVM based on a full approximation storage (FAS) multigrid method. Among a variety of multigrid cycles, the V-cycle is used and the full multigrid algorithm (FMG) is applied to an analysis of radiation in irregular two-dimensional geometry. Solution convergence is discussed for the several cases of various optical thickness and scattering albedo. At small scattering albedo and optical thickness, there is no advantage to using the multigrid method for calculation CPU time. For large scattering albedo greater than 0.5 and optical thickness greater than unity, however, the multigrid method improves the convergence and the solution is rapidly obtained.
고진환,변도영,Ko, Jin-Hwan,Byun, Do-Young 한국전산구조공학회 2007 한국전산구조공학회논문집 Vol.20 No.6
대수학 부구조법은 대형 문제들의 고유치 계산에 최고 성능을 지닌 방법이지만 근본적으로 최소 고유치만을 계산하기 위해 설계되었다. 본 논문에서는 이동값을 이용하여 특정범위 안의 내부 고유치를 계산하기 위해 대수학 부구조법의 갱신된 버전을 제안하고, 이를 이동 대수학 부구조법이라 명명한다. 그리고 구조문제의 유한요소모델에 대한 수치실험을 통해 제안된 방법이 다수의 내부고유치를 계산하는데 란쵸스방법보다 월등한 효율성을 가지고 있음을 보였다. Algebraic substructuring (AS) is a state-of-the-art method in eigenvalue computations, especially for large size problems, but, originally, it was designed to calculate only the smallest eigenvalues. In this paper, an updated version of AS is proposed to calculate the interior eigenvalues over a specified range by using a shift value, which is referred to as the shifted AS. Numerical experiments demonstrate that the proposed method has better efficiency to compute numerous interior eigenvalues for the finite element models of structural problems than a Lanczos-type method.
송민규,변도영,김현구,오세진,한석태,노덕규,이보안,Song, Min-Gyu,Byun, Do-Young,Kim, Hyun-Goo,Oh, Se-Jin,Han, Seog-Tae,Roh, Duk-Gyoo,Lee, Bo-Ahn 한국천문학회 2005 天文學論叢 Vol.20 No.1
e-VLBI was invented to enhance the efficiency of VLBI (Very-Long-Baseline Interferometry) system by transmitting the data via high speed network. Korean VLBI Network (KVN) has a plan to construct e-VLBI system named e-KVN. High speed backbone network and efficient network model are essential to implement successful e-VLBI system. This paper introduces a network model based on PC cluster technology. The present status of high speed backbone network in Korea is overviewed. We suggest that the network link via Korea Advanced Research Network (KOREN) is one of feasible way for e-KVN. We also describe the principles of e-VLBI and protocol for network transmission such as VSI-E (VLBI Standard Interface - Electronic), RTP (Real-Time Transport Protocol) and RTCP (Real-Time Transport Control protocol).
MOGABA: Monitoring of Gamma-ray Bright AGN with KVN 21-m radio telescopes at 22, 43 and 86GHz
이상성,변도영,백준현,한명희,양지혜,손봉원,Lee, Sang-Sung,Byun, Do-Young,Baek, Junhyu,Han, Myounghee,Yang, Jihae,Sohn, Bong Won 한국천문학회 2012 天文學會報 Vol.37 No.2
We report preliminary results of MOGABA project for monitoring total flux density, linearly polarized flux, and polarization angle at 22, 43 and 86GHz of Gamma-ray bright AGN (Active Galactic Nuclei) with KVN (Korean VLBI Network) 21-m radio telescopes. The project has been conducted in one year since May 2011 with an effective monitoring cycle of 1 week, observing four main objects (3C 454.3, BL Lac, 3C 273, and 3C 279). More objects were included in the source list when they had flared in Gamma-ray. Especially, we included a compact radio source at the Galactic center, SgrA* since Jan. 2012. In this paper, we report the current status of the project and preliminary results for the monitoring observations.