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고해상도 PIV 기법을 이용한 타원형 제트의 근접 유동장 해석
신대식,이상준,Shin, Dae-Sig,Lee, Sang-Joon 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.3
Flow characteristics of turbulent elliptic jets were experimentally investigated using a single-frame PIV system. A sharp-edged elliptic nozzle with aspect ratio(AR) of 2 was tested and the experimental results were compared with those of circular jet having the same equivalent diameter($D_e$). The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter was about $1{\times}10^4$. The spreading rate along the major and minor axis are different remarkably. The jet half width along the major axis decreases at first and then increases with going downstream. But along the minor axis the jet width increases steadily. The elliptic jet of AR=2 has one switching points at $X/D_e=2$ within the near field. Turbulence properties are also found to be significantly different along the major and minor axis planes.
신대식,김경천,Shin, Dae Sig,Kim, Kyung Chun 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.7
In the fully developed internal flow fields, there are complex transition flows caused by interaction of the cross flow and jet when jet is Injected Into the flow. These interactions are studied by means of the flow visualization methods. An instantaneous laser tomographic method is used to reveal the physical mechanism and the structure of vortices formation in the branch pipe flow. The velocity range of cross flow of the pipe is 0.7m/s and the corresponding Reynolds number $R_{cf}$, based on the duct height is $5.6{\times}10^3$, diameter/height ratios(d/H) 0.14 and velocity ratios 3.0. Oil mist with the size of $10{\mu}m$ diameter is used for the scattering particle. The instantaneous topological features of the vortex ring roll-up of the jet shear layer and characteristics of this flow are studied in detail by performing flow visualization in rectangular duct flow. It is found that the formation and roll-up of ring vortices is a periodic phenomenon. The detailed topology of the vortices in the near field of a cross -flow jet and the mechanism associated with them give enforced hints of vortex breakdown within the vortex system due to the interaction of the jet and the cross-flow.
용융아연 도금공정에서의 SNOUT 내부 유동장 해석 ( I )
신대식,최제호,이상준,Shin, Dae Sig,Choi, Jayho,Lee, Sang-Joon 대한기계학회 1999 大韓機械學會論文集B Vol.23 No.10
PIV(Particle Image Velocimetry) velocity field measurements inside the snout of a1/10 scale model of the Zn plating process were carried out at the strip speed $V_s=1.5m/s$. Aluminum powder particles ($1{\mu}m$) and atomized olive oil ($3{\mu}m$) were used as seeding particles to simulate the molten Zinc flow and deoxidization gas flow, respectively. A pulsed Nd:Yag laser and a $2K{\times}2K$ high-resolution CCD camera were synchronized for the PIV velocity field measurement. From flow visualization study, it is found that the liquid flow in the Zn pot is dominantly governed by the uprising flow caused by the rotating sink roll, with its effect on the steel strip inside the snout largely diminished by installing of the snout. The deoxidization gas flow in front of the strip inside the snout can be characterized by a large-scale vortex rotating clockwise direction formed by the moving strip. In the rear side of the strip, a counter-clockwise vortex is formed and some of the flow entrained by the moving strip impinges on the free surface of molten zinc. The liquid flow in front of the strip is governed by the flow entering the snout, caused by the spinning sink roll. Just below the free surface a counter-clockwise vortex is formed near the snout wall. The moving strip affects dominantly the flow behind the strip inside the snout, and large amount of the liquid flow follows the moving strip toward the sink roll. The thickness of the flow following the strip is very thin in the front side due to the uprising flow, however thick boundary layer is formed in the rear side of the strip. Its thickness is increased as moving downstream toward the sink roll. Inside the snout, the deoxidization gas flow above the free surface is much faster than the liquid flow in the zinc pot. Due to the larger influx of the flow following the moving strip in the rear side of the strip, higher percentage of imperfection can be anticipated on the rear surface of the strip.
신대식(Dae Sik Shin),조종철(Jong Chul Cho),김용현(Yong Hyun Kim),신미영(Mi Young Shin),한상설(Sang Sul Han),박찬식(Chansik Park),전향식(Hyang-Sig Jun),남기욱(Gi-Wook Nam),이상정(Sang Jeong Lee) 한국항공우주학회 2007 韓國航空宇宙學會誌 Vol.35 No.12
본 논문에서는 GPS, GPS 현대화, Galileo, SBAS 및 GBAS등의 항법 시스템을 모두 고려하여 한국 지역에서의 GNSS 무결성 감시의 가용성을 분석하였다. 현대화된 GPS, Galileo 및 SBAS를 사용하면 Cat. Ⅰ에 근접한 성능을 얻을 수 있음을 시뮬레이션을 통해 확인 하였다. 그러나 여전히 수직오차의 영향으로 Cat. Ⅱ 및 Ⅲ를 만족시키지 못하므로 GBAS와 같은 보다 개선효과가 큰 보강 항법 시스템이 필요함을 확인하였다. 본 논문의 연구 결과는 보강 시스템의 구축뿐 아니라 지역 위성항법시스템 구축을 위한 기초 자료로 활용될 수 있다. In this paper, integrity analysis in Korean region using GPS, modernized GPS, Galileo, SBAS and GBAS is given. The simulation results show that Cat. Ⅰ requirement can be met using modernized GPS and Galileo alone, however, Cat. Ⅱ and Ⅲ are not met even augmenting SBAS because of VPL. A more efficient augmentation such as GBAS reduces VPL to meet Cat. Ⅱ and Ⅲ requirements in Korean region. This result will be used to design and implement not only an augmentation system but also regional satellite navigation system.
고해상도 CCD카메라를 이용한 Single-Frame PIV 속도장 측정기법 개발
이상준,신대식,Lee, Sang-Joon,Shin, Dae-Sig 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.1
Although commercial PIV systems have been widely used for the non-intrusive velocity field measurement of fluid flows, they are still under development and have considerable room for improvement. In this study, a single-frame double-exposure PIV system using a high-resolution CCD camera was developed. A pulsed Nd:Yag laser and high-resolution CCD camera were synchronized by a home-made control circuit. In order to resolve the directional ambiguity problem encountered in the single-frame PIV technique, the second particle image was genuinely shifted in the CCD sensor array during the time interval dt. The velocity vector field was determined by calculating the displacement vector at each interrogation window using cross-correlation with 50% overlapping. In order to check the effect of spatial resolution of CCD camera on the accuracy of PIV velocity field measurement, the developed PIV system with three different resolution modes of the CCD camera (512 ${\times}$ 512, lK ${\times}$ IK, 2K ${\times}$ 2K) was applied to a turbulent flow which simulate the Zn plating process of a steel strip. The experimental model consists of a snout and a moving belt. Aluminum flakes about $1{\mu}m$ diameter were used as scattering particles for the liquid flow in the zinc pot and the gas flow above the zinc surface was seeded with atomized olive oil with an average diameter of 1-$3{\mu}m$. Velocity field measurements were carried out at the strip speed $V_s$=1.0 m/s. The 2K ${\times}$ 2K high-resolution PIV technique was significantly superior compared to the smaller pixel resolution PIV system. For the cases of 512 ${\times}$ 512 and 1K ${\times}$ 1K pixel resolution PIV system, it was difficult to get accurate flow structure of viscous flow near the wall and small vortex structure in the region of large velocity gradient.
분지관 혼합기의 난류혼합에 대한 유동가시화 연구(III)
김경천,신대식,박기영,Kim, Kyung Chun,Shin, Dae Sig,Park, Kee Young 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.11
A flow visualization study was carried out for the branch pipe mixing flow in which a jet was issued normally to the fully developed pipe flow. An instantaneous laser tomographic method was used for cross flow Reynolds numbers based on the cross flow diameter D ranged $Re_{cf}=5.26{\times}10^3{\sim}1.13{\times}10^4$, diameter ratios d/D = 0.1 ~ 0.2 and velocity ratios R = 0.5 ~ 10. Oil mist with the size of about $10{\mu}m$ diameter was used for the scattering particle. The main purpose of this study was to reveal the physical mechanism and the structure of vortices formation with varying the velocity ratios and diameter ratios in the branch pipe flow. It was found that the physical mechanism and the structures of vortices formation were quite different depending on the velocity ratios. Particularly in the case of R < 1, the typical vortex shows single loop shape and that for the case of R > 1 depicts mushroom-like structure in the cross flow jet.
가정용 냉장고의 응축기 적용을 위한 판형 핀-관 열교환기의 성능실험
손영우(Young-Woo Son),이장호(Jang-Ho Lee),김무환(Moo Hwan Kim),신대식(Dae-Sig Shin) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Experimental performance of plate fin-tube heat exchanger is studied to check the possibility of applying to the condenser of household refrigerator. It has lighter weight and lower price of 30% than the conventional circular-fin condenser which has been used. In this experimental study, the refrigerant supplying system instead of the hot water supplying system was used to test condenser in the similar condition with real bousehold refrigerator. It has following test conditions: inlet air temperature of 3 2℃, inlet air velocity of 0.63 ㎧, inlet refrigerant temperature of 60℃, and saturation temperature of 44.5℃. Totally, four kinds of heat exchanger are tested, and heat transfer rate, pressure drop, are evaluated for each test sample.