• 환경위생공학
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• 제17권4호
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• pp.1-9
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• 2002

In order to define about concern with discharge and water-quality, it is calculated drought flow, low flow, normal flow and wet flow in Chungju watershed from flow duration analysis. Water quality modeling study is performed for forecasting at upstream of Chungju lake. It is devided method of modeling into before and after the equipment of environmental treatment institution. And it is estimated the change of water quality. Before the equipment of environmental treatment, BOD concentration is increased from 23000 to 2006 years at all site and decrease on 2012 years. The rate of increasing BOD concentration is showed height between 2000 years and 2003 years most of all site. And after the equipment of environmental treatment, it is showed first grade of BOD water quality in most of sample site beside Jucheon river. The result of water quality modeling using drought flow showed that a lot of pollution occurred. And water quality using wet flow is good, so much discharge make more improve water quality than little discharge.

• 한국유체기계학회 논문집
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• 제2권1호
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• pp.81-87
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• 1999

This study presents the measurement techniques on the periodic fluctuating flow such as the discharge flow of a centrifugal impeller in an unstable operating region. During rotating stall, the flow at the exit of a centrifugal compressor impeller fluctuates periodically with a lower frequency than that of the blade passing. To observe the blade-to-blade flow characteristics during the rotating stall, the phases of all the sampled data sets should be adjusted to those of the reference signals with two processes, in these processes, DPLEAT (Double Phase-Locked Ensemble Averaging Technique) can be used. From these measurements and data processing techniques, the characteristics illustrated a blade-to-blade flow with high frequency, but also a periodic rotating stall flow with a low frequency at the centrifugal impeller exit which was clearly observed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2658-2663
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• 2008

In the present study, we designed a microfluidic flatform that generates monodisperse droplets with diameters ranging from hundreds of nanometers to several micrometers. To generate fine droplets, T-junction and flow-focusing geometry are integrated into the microfluidic channel. Relatively large aqueous droplets are generated at the upstream T-junction and transported toward the flow-focusing geometry, where each droplet is broken up into the targeted size by the action of viscous stresses. Because the droplet prior to rupture blocks the straight channel that leads to the flow-focusing geometry, it moves very slowly by the pressure difference applied between the advancing and receding regions of the moving droplet. This configuration enables very low flow rate of inner fluid and higher flow rate ratio between inner and outer fluids at the flow-focusing region. It is shown that the present microfluidic device can generate droplets with diameters about 1 micrometer size and standard deviation less than 3%.

• 반도체디스플레이기술학회지
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• 제19권4호
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• pp.51-58
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• 2020

Many types of optical plastic films are essential in optoelectronics display unit fabrication and it is important to develop high precision laser cutting methods of optical films with extremely low level of film surface contamination by fume particles. This study investigates the effects of suction and blowing air motions with air flow misalignment in removing fume particles from laser cut line by employing random particle trajectory simulation and probabilistic particle generation model. The computational results show fume particle dispersion behaviors on optical film under suction and blowing air flow conditions. It is found that suction air flow motion is more advantageous to blowing air motion in reducing film surface contamination outside designated target margin from laser cut line. While air flow misalignment adversely affects particle dispersion in blowing air flows, its effects become much more complicated in suction air flows by showing different particle dispersion patterns around laser cut line. It is required to have more careful air flow alignment in fume particle removal under suction air flow conditions.

• 한국전산유체공학회지
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• 제18권2호
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• pp.49-55
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• 2013

The goal of the research is to evaluate the open source code of OpenFOAM for the use of nuclear plant flow simulation objectively. Of the various incompressible flow solvers, simpleFoam, pimpelFoam are then tested under three validated cases (backward facing step, flow over circular cylinder and turbulent round jet flow). For the evaluation of steady state incompressible laminar flow simulation, low reynolds number of backward facing step flow was solved by simpleFoam. The resultant of the reattached lengths turned out to be similar with the other experimental and simulation results. For transient flow simulation, flow over circular cylinder and turbulent round jet flow were solved by pimpleFoam. The simulation accuracy was evaluated by comparing the resultant flow patterns with the description of the characteristics of the flow over the circular cylinder. The quantitative accuracy was evaluated for no more than 85% by comparing it to the decaying constants of the turbulent round jet velocity.

• 한국환경과학회지
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• 제11권3호
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• pp.191-199
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• 2002

In this study, water protection reservoir is selected as the target which is located at the estuary of Taehwa river to analyze and examine the effects of hydraulic structure on river environment. This study aims at the definition of factors which cause the change of ecological environment of river due to the effects of the sediment protection reservoir, and the proposal of the direction of environmental friendly river space development through the analysis and examination of stream variation conditions and riverbed variation characteristics among many effects of hydraulic structure on river environment before and after removal of the sediment protection reservoir when design flow is yielded. Firstly, in case of removal the existing sediment protection reservoir, the hydraulic variation characteristics like depth drop due to removal of the sediment protection reservoir are thought of little because it is examined that depths drop with about 0.01m and 0.01~0.56m when low flow is yielded and design flood yielded, respectively. Nextly, as the examination result of the variation characteristics of flow velocity in case of removal the existing sediment protection reservoir, it is thought that the concern about riverbed erosion is not serious according to the analyzed result as the mean velocity of the channel section where the velocity varies in case of removal the sediment protection reservoir is about 0.07~1.36m/s when low flow is yielded, and is about 1.02~2.41m/s when design flood is yielded despite riverbed erosion is concerned as it is examined that flow velocity is getting increase as about 0.01m/s when low flow is yielded and about 0.01~0.44m/s when design flood is yielded. Lastly, from the prediction result of riverbed variation for each flow amount condition before and after removal the sediment protection reservoir, it is known that the variation range of riverbed is nearly constant when flow amount of the channel exceeds a specific limit as it is analyzed that the more flow amount, the more erosion and sediment in the channel section of down stream part of the sediment protection reservoir and the sediment protection reservoir~Samho-gyo, and the variation ranges according to flow amount between flood condition and design flood condition have little difference in the channel section of the upstream of Samho-gyo.

• Advances in aircraft and spacecraft science
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• 제9권5호
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• pp.415-431
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• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제21권2호
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• pp.89-107
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• 2017

In this paper, we have proposed a modified Marker-And-Cell (MAC) method to investigate the problem of an unsteady 2-D incompressible flow with heat and mass transfer at low, moderate, and high Reynolds numbers with no-slip and slip boundary conditions. We have used this method to solve the governing equations along with the boundary conditions and thereby to compute the flow variables, viz. u-velocity, v-velocity, P, T, and C. We have used the staggered grid approach of this method to discretize the governing equations of the problem. A modified MAC algorithm was proposed and used to compute the numerical solutions of the flow variables for Reynolds numbers Re = 10, 500, and 50000 in consonance with low, moderate, and high Reynolds numbers. We have also used appropriate Prandtl (Pr) and Schmidt (Sc) numbers in consistence with relevancy of the physical problem considered. We have executed this modified MAC algorithm with the aid of a computer program developed and run in C compiler. We have also computed numerical solutions of local Nusselt (Nu) and Sherwood (Sh) numbers along the horizontal line through the geometric center at low, moderate, and high Reynolds numbers for fixed Pr = 6.62 and Sc = 340 for two grid systems at time t = 0.0001s. Our numerical solutions for u and v velocities along the vertical and horizontal line through the geometric center of the square cavity for Re = 100 has been compared with benchmark solutions available in the literature and it has been found that they are in good agreement. The present numerical results indicate that, as we move along the horizontal line through the geometric center of the domain, we observed that, the heat and mass transfer decreases up to the geometric center. It, then, increases symmetrically.

• 간호행정학회지
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• 제19권1호
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• pp.87-94
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• 2013

Purpose: The purpose of this study was to provide a basis for non-humidified low flow oxygen by nasal cannula and to provide a guide for consistent care in nursing practice. Methods: A methodological study on the development of guidelines with experts' opinions on collected items, framing PICO questions, evaluating and synthesizing texts which were searched with the key words (low flow oxygen, nasal cannula, humidification of oxygen, guideline) from web search engines. Results: Of the 45 researched texts on the web, 9 texts relevant to the theme were synthesized and evaluated. All patients with humidified or non-humidified oxygen therapy reported that they had no discomfort. Conclusion: The results indicate that there are no tangible grounds for patients' perceived differences between the humidified and non-humidified oxygen under 4L/min supplied by nasal cannula. with oxygen. Therefore, non-humidification oxygen therapy is strongly advised when suppling under 4L/min oxygen by nasal cannula (recommended grade A).

• 대한토목학회논문집
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• 제29권3B호
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• pp.311-317
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• 2009

원주천 수환경과 어류군의 조사연구를 기초로 하여 표본 집단 사이의 유사지수를 파악하고 UPGMA 분류법을 사용한 어류군집의 cluster분석을 실시하였다. 원주천의 상류, 중류, 하류의 복원을 위한 지표어종으로 독중개, 갈겨니, 피라미를 선택하였다. 서식환경 향상으로 하수관거의 재정비와 유역관리를 분석을 통한 갈수유량 증대와 그에 따른 수질향상을 분석하였다. 원주천 중류의 복원목표 어종으로 갈겨니를 선택하여 복합 서식적합도를 분석하였다. 갈수유량의 증가는 서식적합도 향상에 매우 중요한 것으로 나타났다. 저수로의 변경에 따른 수심과 유속의 변화가 복합서식적합도의 향상을 가져오지만 지배적인 변수는 아닌 것을 확인하였다. 갈수유량의 증가와 더불어 저수로 폭을 10%씩 줄인 결과는 초기 복합서식적합도 0.1~ 0.25에서 0.37~ 0.78로 약 3배 이상의 향상을 가져와, 이를 원주천 어류군집의 서식 적합한 하천구조 개선방안으로 제시하였다.