• 해양환경안전학회지
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• 제26권4호
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• pp.403-411
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• 2020

본 논문에서는 도서 지역 화물 및 승객 운송을 맡은 연안 항해용 친환경 차도선을 개발하면서, 검토된 주요 결과들에 대해서 논의한다. 시장에서의 경제성을 확보하기 위하여, 폭 19 m를 최종 개발모델 및 갑판면적에 많은 차량이 배치되도록 고려하였다. 조파저항 감소를 위해 선형 형상은 "V"에 선수벌수를 접목하였으며, 수치해석을 통해 개발 선박의 유체역학적 성능을 확인하였다. 선가를 직접 결정짓는 선각 중량을 감소하기 위하여, 최적화 전문 프로그램에 내재된 다목적 최적화 방법인 파레토 시뮬레이트 어닐링을 활용하여 약 3.9 %의 중량 절감을 달성하였다. 본 연구를 통해서 도출된 주요 결과들은 추후 쌍동형 차도선 관련 연구를 수행하는 엔지니어와 관련 산업에 좋은 선례가 될 것으로 기대한다.

• Korean Chemical Engineering Research
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• 제47권2호
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• pp.179-184
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• 2009

최근 전산기술의 발전으로 난류를 비롯한 3차원의 복잡한 전달현상에 대한 전산유체역학(CFD) 해석의 실효성이 제고되고 있다. 본 연구에서는 초음파나 레이저를 이용한 방법보다 저렴하고, 간편하게 좌, 우 입체 화상으로 추출된 입체화상의 변위히스토그램을 이용하여 3차원 화상을 구현하기 위한 윈도우환경하의 모사기 CAMSI(Computer-Aided Management of Stereo Images)를 개발하였다. 본 프로그램에서는 영역기반 방법이 적용되었으며, 좌우 화상의 정합시 대응점을 결정하기 위하여 제곱차거리합계(SSD), 절대거리차합계(SAD), 평균상관계수(NCC)와 동일점세기(MPC)의 방법들이 각각 적용되었다. 구현된 프로그램은 다양한 윈도우 크기와 한계값에 대하여 우수한 해석능력을 보여주었다. 특히, 화상의 잡영이 적은 곳에서는 작은 윈도우 크기의 SSD가 좀더 정확성이 높은 것으로 나타났으며, 일반적으로는 NCC가, 그리고 잡영이 매우 심한 경우에는 MPC 또는 NCC가 SSD보다는 정확성이 높게 나타났다. 본 연구를 통해 구현된 CAMSI는 복잡한 물체의 구현 또는 그 주변에서 다양한 전달현상의 3차원 CFD 해석에 효과적으로 사용될 수 있을 것이다.

• 대한기계학회논문집
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• 제14권6호
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• pp.1621-1628
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• 1990

본 연구에서는 많은 실질적인 시스템에서, 많은 양의 복합된 전도, 대류, 복 사의 열전달 현상이 동시에 일어나기 때문에 복합된 열전달 모드가 다같이 다루어져야 만 한다. Fig.1에서 보는 바와 같이 얇은 원형휜이 튜브 주위에 무수히 부착되어 있 으며, 휜과 튜브주위를 기체가 흐르고 있다. 휜과 휜, 휜과 튜브표면, 휜과 주위환 경, 튜브표면과 주위환경 사이에서 복사 열전달 상호교환이 충분히 다루어졌다. 전 도, 대류, 복사기 동시에 일어나는 열전달 방정식은 비선형 적분-미분 방정식(nonlin- ear integro-differential equation)으로 표현된다. 온도 분포도(temperature dist- ributions), 열전달량(heat transfer rates), 휜효율(fin efficiencies), 휜유효성(f- ineffectivenesses)등이 계산되어졌고, 무차원 형태로 도표에 결과들을 제시하였다.

• 한국양식학회지
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• 제15권2호
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• pp.87-93
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• 2002

양어용수 재순환을 위한 생물여과상의 처리효율을 향상시키기 위하여 상향류식 연속역세여과장치를 이용하여 다양한 조건하에서 실험하였는데, 기존의 연속역세여과장치와 이를 개량한 연속역세여과장치를 가지고 실험하였다. 개량역세여과장치는 기존에 이용되고 있는 DynaSand 여과장치를 유체역학 및 물리,화학적 개념을 응용한 장치로 개조하여 역세기능의 향상, 산소전달 능력의 향상, 여과 처리수 인출부의 개량에 의한 처리수 탁도제거 기능 향상 및 연속적인 수두손실 감지에 의해 폐수성상에 따른 여과장치운전의 자동화를 도모하는데 중점을 두었고, 또한 여과사의 표면을 특정물질로 코팅함으로 여과사 표면전하를 변화시켜 여과능력의 향상과 생물막 형성력의 증대를 꾀하는데 실험의 목적을 두었다. 본 실험에서 사용 한 여과장치의 크기는 전체 용적이 약 70 L이고 working volume은 35 L이었다 이번 연구에서 양어장사육용수 처리를 위해 조사된 개량형 상향류식 연속역세여과장치의 효율은 부유물 제거 효율이 평균 71% 이었고, NH$_4$$^{+/-N}$ , T-P및 SRP의 제거효율은 84%, 85% 및 88%로 각각 나타나서 그 효과가 인정되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.666-669
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• 2008

Droplet in miniaturized microfluidic systems have received much focused attention recently. In this work, electrical charging phenomenon of a conducting water droplet on the electrode under the dc electric field is studied and using this phenomenon droplet actuation method for microreactor applications is experimentally demonstrated. To find effects of key factors, the effects of electric field, medium viscosity, and droplet size are investigated. A scaling law of charging for the conducting droplet is derived from the experimental results. Unlike the case of a perfect conductor, the estimated amount of electrical charge ($Q_{est}$) of a water droplet is proportional to the 1.59 power of the droplet radius (R) and the 1.33 power of the electric field strength (E). (For a spherical perfect conductor, Q is proportional to R2 and E.) It is thought that the differences are mainly due to incomplete charging of a water droplet resulted from the combined effect of electrochemical reaction at electrode and the relatively low conductivity of water. Using this phenomenon, we demonstrate the transport of the charged droplet and fusion of two oppositely-charged droplets. When electric field is subjected sequentially on the electrode, the charged droplet is transported on the electrode. For the visualization of fusion of charged droplets, the precipitation reaction is used. When subjected to a DC voltage, two droplets charged are moving and merging toward each other due to the Coulombic force and chemical reaction is simultaneously occurred by coalescence of droplets. It may be due to the interchange effect of charge. It is shown that the droplet can be used for microreactor where transporting, merging etc. of reagents constitute unit operation.

• Asian Journal of Atmospheric Environment
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• 제12권1호
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• pp.47-58
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• 2018

The aim of this work is to investigate the effect of atmospheric stability on near-field pollutant dispersion from rooftop emissions of a single cubic building using computational fluid dynamics (CFD). This paper used the shear stress transport (here after SST) k-${\omega}$ model for predicting the flow and pollutant dispersion around an isolated cubic building. CFD simulations were performed with two emission rates and six atmospheric stability conditions. The results of the simulations were compared with the data from wind tunnel experiments and the result of simulations obtained by previous studies in neutral atmospheric condition. The results indicate that the reattachment length on the roof ($X_R$) obtained by computations show good agreement with the experimental results. However, the reattachment length of the rooftop of the building ($X_F$) is greatly overestimated compared to the findings of wind tunnel test. The result also shows that the general distribution of dimensionless concentration given by SST k-${\omega}$ at the side and leeward wall surfaces is similar to that of the experiment. In unstable conditions, the length of the rooftop cavity was decreased. In stable conditions, the horizontal velocity in the lower part around the building was increased and the vertical velocity around the building was decreased. Stratification increased the horizontal cavity length and width near surface and unstable stratification decreased the horizontal cavity length and width near surface. Maintained stability increases the lateral spread of the plume on the leeward surface. The concentration levels close to the ground's surface under stable conditions were higher than under unstable and neutral conditions.

• Journal of mucopolysaccharidosis and rare diseases
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• 제2권1호
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• pp.19-22
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• 2016

Purpose: Mucolipidosis type II (ML II), also known as I-cell disease is an autosomal recessive inherited disorder of lysosomal enzyme transport caused by a deficiency of the uridine diphosphate (UDP)-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase). Clinical manifestations are skeletal abnormalities, mental retardation, cardiac disease, and respiratory complications. A severely and rapidity progressive clinical course leads to death before 10 years of age. Methods/Results: In this study we diagnosed three cases of prenatal ML II in two different at-risk families. We compared two procedures -biochemical analysis and molecular analysis - for the prenatal diagnosis of ML II. Both methods require an invasive procedure to obtain specimens for the diagnosis. Biochemical analysis requires obtaining cell cultures from amniotic fluid for more than two weeks, and would result in a late diagnosis at 19 to 22 weeks of gestation. Molecular genetic testing by direct sequence analysis is usually possible when mutations are confirmed in the proband. Molecular analysis has an advantage in that it can be performed during the first-trimester. Conclusion: Molecular diagnosis is a preferable method when a prompt decision is necessary.

• 한국전산유체공학회지
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• 제18권1호
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• pp.58-62
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• 2013

Personal Rapid Transit (PRT) is the emerging personal transport vehicle operating on the loop automatically. The PRT system utilize the electrical power from super capacity or battery, it is important to manage the power or energy. In this regards, the management of high temperature occurred by the operation of system is significantly important to prevent from serious damage of component. In this study, we studied the adequate shape of underbody which can reduce the heat accumulation by pickup coil and condenser using natural air cooling. We suggested the additional air pathway, air inlet and flow separator to decrease the temperature of the heat source components. It was found that suggested system can decrease the temperature of PRT under body by 16% during the static mode and by 10% during the running mode at 30km/h. It is expected that the findings of this study will feed into final design of newly built Korean PRT vehicle.

• 대한기계학회논문집B
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• 제26권12호
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• pp.1646-1654
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• 2002

A two-phase closed thermosyphon was one of the most effective devices in the removing heat because of its simple structure, thermal diode characteristics, wide operating temperature range and so on. In this study, a two-phase closed thermosyphon(working fluid PFC(C6F14), container copper(inner grooved surface)) was fabricated with a reservoir which can change the fill charge ratio. The experiments were performed in the range of 50~600W heat flow rate and 10~70% fill charge ratio. The results were compared with some correlations that were presented by Rohsenow and Immura et al. in the evaporator, by Nusselt, Gross and Uehara et al. in the condenser and by Cohen and Bayley, Wallis, Kutateladze and Faghri et al. in heat transfer limitation etc.. The heat transfer coefficient at the evaporator increased with the input power. However the effect of the fill charge ratio was nearly negligible. At the condenser, it showed an opposite trend to the evaporator and with increase of the fill charge ratio, showed some enhancement of heat transfer. The heat transport limitation was occurred by the dry-out limitation for small fill charge ratio(10%) and presented about 100W. For the case of large fill charge ratio(Ψ$\geq$40%), it was occurred by the flooding limitation at about 500W.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1209-1219
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• 2003

The dynamic behaviors of the single vortex interacting with $CH_4-Air$ jet diffusion flame are investigated numerically. The numerical method is based on a predict-corrector scheme for a low Mach number flow. A two-step global reaction mechanism is adopted as a combustion model. Studies are conducted in fixed initial velocities for the three cases according as where $CO_2$ is added; (1) without dilution, (2) dilution in fuel stream and (3) dilution in oxidizer stream. A single vortex is generated by an axisymmetric jet, which is made by an impulse of a cold fuel when a flame is developed entirely in a computational domain. The simulation shows that $CO_2$ dilution in fuel stream results in somewhat larger vortex radius, and greater amount of entrainment of surrounding fluid than in other cases. Thus, the dilution of $CO_2$ in fuel stream enhances the mixing in single vortex and increases the stretching of the flame surface. The budgets of the vorticity transport equation are examined to reveal the mechanism of vortex formation when $CO_2$ is added. It is found that, in the case of $CO_2$ dilution in fuel stream, the vortex destruction due to volumetric expansion and the vortex production due to baroclinic torque are more dominant than in other cases.