사각 마이크로채널 내의 2 상 유동 압력강하 상관식의 검증 및 개발

최치웅(Chi-woong Choi),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.1

2 상 유동 압력강하에 대한 모델은 균질유동모델과 분리유동모델 두 가지가 있다. 많은 선행 연구자들은 마이크로채널에서의 2 상 유동 압력강하에 대한 상관식을 제시하였고, 대부분은 분리유동모델에 해당하는 Lockhart-Martinelli<SUP>(27)</SUP>의 수정된 상관식에 기초하고 있다. 본 연구에서는 사각 마이크로채널에서의 압력강하에 대한 연구를 위해서 액상의 물과 기상의 질소를 사용하여 사각 마이크로채널에서의 실험을 수행하였다. 2 상 마찰 압력강하는 2 상 유동양식에 큰 연관성을 가지고 있는 결과를 확인할 수 있었다. 6 가지의 2 상 점성 모델을 포함한 균질유동 모델 (Owen<SUP>(21)</SUP>’s, MacAdams<SUP>(22)</SUP>’s, Cicchitti et al.<SUP>(23)</SUP>’s, Dukler et al.,<SUP>(24)</SUP> Beattie and Whalley,<SUP>(25)</SUP> Lin et al.<SUP>(26)</SUP>)과 6 가지의 분리유동 모델 (Lockhart and Martinelli,<SUP>(27)</SUP> Chisholm,<SUP>(31)</SUP> Zhang et al.,<SUP>(15)</SUP> Lee and Lee,<SUP>(5)</SUP> Moriyama and Inue,<SUP>(4)</SUP> Qu and Mudawar<SUP>(8)</SUP>)에 대한 평가를 실험결과와 비교를 통해 수행하였다. 가장 우수한 2 상 점성 모델은 Beattie and Whalley 의 모델이었고, 가장 우수한 분리유동 모델은 Qu and Mudawar 의 상관식이였다. 균질유동모델과 분리유동모델 모두에 대해서 2 상 유동양식에 종속성을 나타내었다. 그러므로, 본 연구에서는 2 상 유동 양식에 기초한 새로운 상관식을 균질유동모델과 분리유동모델에 대해 각각을 제시하였다. There are two kinds of models in two-phase pressured drop; homogeneous flow model and separated flow model. Many previous researchers have developed correlations for two-phase pressure drop in a microchannel. Most correlations were modified Lockhart and Martinelli’s correlation, which was based on the separated flow model. In this study, experiments for adiabatic liquid water and nitrogen gas flow in rectangular microchannels were conducted to investigate two-phase pressure drop in the rectangular microchannels. Two-phase frictional pressure drop in the rectangular microchannels is highly related with flow regime. Homogeneous model with six two-phase viscosity models: Owen<SUP>(21)</SUP>’s, MacAdams<SUP>(22)</SUP>’s, Cicchitti et al.<SUP>(23)</SUP>’s, Dukler et al.<SUP>(24)</SUP>’s, Beattie and Whalley<SUP>(25)</SUP>’s, Lin et al.<SUP>(26)</SUP>’s models and six separated flow models: Lockhart and Martinelli<SUP>(27)</SUP>’s, Chisholm<SUP>(31)</SUP>’s, Zhang et al.<SUP>(15)</SUP>’s, Lee and Lee<SUP>(5)</SUP>’s, Moriyama and Inue<SUP>(4)</SUP>’s, Qu and Mudawar<SUP>(8)</SUP>’s models were assessed with our experimental data. The best two-phase viscosity model is Beattie and Whalley’s model. The best separated flow model is Qu and Mudawar’s correlation. Flow regime dependency in both homogeneous and separated flow models was observed. Therefore, new flow pattern based correlations for both homogeneous and separated flow models were individually proposed.

세장비 인 초음속 공동유동에서 차원 효과로 인한 유동 진동 주파수 분석

김태욱(T.U. Kim),박수형(S.H. Park),이승수(S. Lee),유동옥(D.O. Yu),유흥철(H.C. You) 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.3

Unsteady turbulent flow simulations were performed to investigate flow oscillation frequency due to three dimensional effect in supersonic cavity flow of length-to-depth ratio of 3, width-to-depth ratio of 1 and Mach 1.5. Two- and three-dimensional unsteady simulations result were compared with experimental data and prediction from the Rossiter equation. Pressure oscillation in three-dimensional cavity and the corresponding frequency were well matched with the empirical data. The flow structure corresponding to each mode was investigated. The results show that two dimensional flow is in the wake mode and three-dimensional flow is mainly in the shear layer mode. The oscillation frequency spectrum clearly indicate the three-dimensional effect due to the sidewall.

갑상선전절제술 및 부갑상선 자가이식 후 갑상선암 재발로 오인된 부갑상선기능항진증 1례

유동만,김태용 대한내과학회 2020 대한내과학회 추계학술대회 Vol.2020 No.1

반도체 Burn-In 공정용 장비 개발

유동상(劉同相) 대한전기학회 1997 전기의 세계 Vol.46 No.10

Comparative study on deformation and mechanical behavior of corroded pipe: Part I-Numerical simulation and experimental investigation under impact load

유동만,Lei Wang,김슬기,이제명 대한조선학회 2017 International Journal of Naval Architecture and Oc Vol.9 No.5

Experiments and a numerical simulation were conducted to investigate the deformation and impact behavior of a corroded pipe, as corrosion, fatigue, and collision phenomena frequently occur in subsea pipelines. This study focuses on the deformation of the corrosion region and the variation of the geometry of the pipe under impact loading. The experiments for the impact behavior of the corroded pipe were performed using an impact test apparatus to validate the results of the simulation. In addition, during the simulation, material tests were performed, and the results were applied to the simulation. The ABAQUS explicit finite element analysis program was used to perform numerical simulations for the parametric study, as well as experiment scenarios, to investigate the effects of defects under impact loading. In addition, the modified ASME B31.8 code formula was proposed to define the damage range for the dented pipe.

광역-협력적 거버넌스 구축을 통한 지방의회 의원의 전문성 강화에 관한 연구

유동상(劉東相),강인호(姜仁皓) 한국지방정부학회 2016 지방정부연구 Vol.20 No.1

본 연구는 기존의 지방의회 전문성 강화와 관련된 대안들이 현재의 상위법령의 제약, 재정건전성 악화 우려, 그리고 이로 인한 주민의 사회적 합의 도출의 어려움 등으로 인해 실현가능성이 낮다는 점에서 출발하였다. 이로 인해 본 연구는 현실적인 대안이 될 수 있는 광역-협력적 거버넌스의 이론적 근거 하에 ‘(가칭)광역정책지원단’ 설립을 제시하고 있다. ‘광역정책지원단’은 그 성격상 일정 권역내의 기초지방자치단체들이 공동부담으로 설립할 수 있기 때문에 재정 건전성 악화 우려를 불식시킬 수 있다는 장점이 있다. 또한 지방자치단체가 공동으로 출자 혹은 출연하여 공동의 광역연구기관을 설립하기 때문에 법적 문제가 제기될 가능성이 매우 낮다. 이러한 공동의 투자는 지역주민들로 하여금 연구기관의 설립에 동의를 구할 수 있는 원동력이 될 것이다. 오늘날 지방자치단체의 당면한 문제는 더욱더 복잡해지고 다양화되고 있다. 이러한 문제해결을 위해서 지방의회는 전문성을 구비하고, 문제해결을 위한 정책대안을 개발 · 제시해야 할 것이다. 이를 위한 현실적인 전문성 제고 방안이 ‘(가칭)광역정책지원단’ 설립이라고 판단된다. This study starts from the fact that the previous literature have provided nonrealistic alternatives to enhance local councils" expertise. Even though all of the alternatives have been justified, they could not be feasible because of the constraints of parent laws, deteriorated local financial health, and the difficulties of deriving social consensus. So, based upon the regional-cooperative governance, this study tries to provide a feasible alternative that can avoid the previous problems, tentatively named “Regional Policy Support Group.” “Regional Policy Support Group” can be more feasible than the previous alternatives. Since it is jointly established by local governments, it could reduce the concerns about local government financial health. In addition, legal issues regarding the establishment of a new organization would not be raised since it is financed and jointly owned by local governments. Finally, those advantages would be a driving force to get social consensus from local residents. The problems that local governments face have become complex and changed day to day. Local councils, as a policy decision making body, should enhance their expertise to address those problems effectively. One of feasible way to support and enhance it should be the establishment of a “Regional Policy Support Group.”

비정렬 적응격자 기법을 이용한 HART Ⅱ 로터 BVI 예측 및 동체 영향 예측 연구

유동옥,권오준 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.4

본 연구에서는 비정렬 격자를 기반으로 한 유동해석 프로그램을 이용하여 HART II 로터 형상에 대한 비정상 점성 유동해석을 수행하였다. 블레이드-와류 간섭 현상을 효과적으로 포착하기 위해 적응 격자기법을 적용하였으며, 블레이드의 탄성 변형은 HART II 실험데이터를 이용하여 모사하였다. 단일 로터형상과 로터-동체 형상에 대한 해석 결과들을 비교함으로써 동체가 로터의 공력 특성 및 와류 구조에 미치는 영향을 분석하였다. 동체를 포함한 로터 트림 해석 후 블레이드 조종 피치각의 예측 정확도가 향상되었으며, 블레이드 공력 예측 정확도 역시 향상된 것을 확인할 수 있었다. 격자 적응이 진행됨에 따라 블레이드 수직력의 고주파 성분이 더욱 정확하게 예측되었으며, 반면 저주파 성분은 크게 변화하지 않는 것을 확인할 수 있었다. In the present study, viscous flow simulations of the HART II rotor were conducted using a flow solver based on unstructured meshes. To capture the blade-vortex interaction (BVI) phenomena efficiently, a series of solution-adaptive mesh refinements was carried out. The blade deformation was prescribed from the HART II test data. Calculations were made for two configurations, isolated rotor and rotor-fuselage configuration, to investigate the fuselage effect on the blade loading and the rotor wake structure. It was found that inclusion of fuselage makes significant improvement in the trim control prediction, and this improved trim control also leads to an improvement in the blade loading prediction for the rotor-fuselage configuration. It was also found that the high frequency blade loading caused by BVI can be obtained more accurately as the mesh is further refined, whereas the low one is mostly independent to the mesh resolution.

Lab-scale impact test to investigate the pipe-soil interaction and comparative study to evaluate structural responses

유동만,이치승,최광호,구본용,송준규,김명현,이제명 대한조선학회 2015 International Journal of Naval Architecture and Oc Vol.7 No.4

This study examined the dynamic response of a subsea pipeline under an impact load to determine the effect of the seabed soil. A laboratory-scale soil-based pipeline impact test was carried out to investigate the pipeline deformation/strain as well as the interaction with the soil-pipeline. In addition, an impact test was simulated using the finite element technique, and the calculated strain was compared with the experimental results. During the simulation, the pipeline was described based on an elasto-plastic analysis, and the soil was modeled using the Mohr-Coulomb fail-ure criterion. The results obtained were compared with ASME D31.8, and the differences between the analysis results and the rules were specifically investigated. Modified ASME formulae were proposed to calculate the precise structural behavior of a subsea pipeline under an impact load when considering sand- and clay-based seabed soils.

다른 세장비의 사각 마이크로채널 내의 기포 거동에 관한 연구

최치웅(Chi-woong CHOI),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.5

다른 세장비에 따른 단일 사각 마이크로 채널 내의 이상유동연구를 수행하였다. 본 연구에서는 대략 넓이가 500 ㎛ 이며 수력직경이 각각 490, 322, 143 ㎛ 인 사각 마이크로채널 내에서의 물-질소 유동에 대한 실험이 수행되었다. 또한, 고속카메라와 장거리 현미경을 통해 이상유동양식을 가시화하였다. 본 연구는 이상유동 중 기포류에 중점을 두었으며 가시화 결과를 통해 기포의 속도, 기포의 길이, 관 내 기포의 개수, 기공률을 산출하였고 단위 셀 모델을 기반으로 늘어진 단일 기포의 압력강하를 해석하였다. 실험을 통해 기포의 속도, 기공률, 단일 기포의 압력강하가 각각 겉보기 속도와 체적건도, 세장비와 연관이 있음을 확인하였으며, 사각 마이크로 채널 내 늘어진 단일 기포의 압력강하에 대한 상관식을 개발하였다. The adiabatic two-phase flow in single rectangular microchannels was studied for different aspect ratios. The working fluids were liquid water and nitrogen gas. The hydraulic diameters of the rectangular microchannels were 490, 322, and 143 ㎛, and the widths of the microchannels were around 500 ㎛. The two-phase flow pattern was visualized using a high-speed camera and a long-distance microscope. This study was focused on bubble flow regimes. From the visualized images, the bubble velocity, bubble length, number of bubbles, and void fraction were evaluated. Further, the pressure drop in a single bubble was evaluated by using a unit cell model. The bubble velocity is proportional to the superficial velocity. Further, the relationship between the void fraction and the volumetric quality is linear. The pressure drop in a single elongated bubble is strongly related to the aspect ratio. Finally, the new correlation about the pressure drop of a single elongated bubble in the rectangular microchannel was proposed.

사각 마이크로채널 내의 2 상유동 압력강하와 유동양식에 대한 젖음성의 영향에 대한 연구

최치웅(Chi-woong CHOI),유동인(Dong In Yu),김무환(Moo Hwan Kim) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.12

Wettability is a critical parameter in micro-scale two-phase system. Several previous results indicate that wettability has influential affect on two-phase flow pattern in a microchannel. However, previous studies conducted using circular microtube, which was made by conventional fabrication techniques. Although most applications for micro thermal hydraulic system has used a rectangular microchannel, data for the rectangular microchannel is totally lack. In this study, a hydrophilic rectangular microchannel was fabricated using a photosensitive glass. And a hydrophobic rectangular microchannel was prepared using silanization of glass surfaces with OTS (octa-dethyl-trichloro-siliane). Experiments of two-phase flow in the hydrophilic and the hydrophobic rectangular microchannels were conducted using water and nitrogen gas. Visualization of twophase flow pattern was carried out using a high-speed camera and a long distance microscope. Visualization results show that the wettability was important for two-phase flow pattern in rectangular microchannel. In addition, two-phase frictional pressure drop was highly related with flow patterns. Finally, Two-phase frictional pressure drop was analyzed with flow patterns.