• 한국추진공학회지
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• 제12권2호
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• pp.24-32
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• 2008

마하 1.92 초음속 유동 내에서 평판, 작은 공동, 큰 공동을 사용하여 운동량비(J)에 따른 연료 혼합 실험을 수행하였다. 공동 후면 경사부는 연료의 침투거리를 급격히 증가시키며, 경사부에서 형성되는 이차원 충격파는 후류부의 충격파 구조와 혼합층에 주요한 영향을 미친다. 운동량비가 증가함에 따라(J = 0.9, 1.7, 3.4) 연료의 침투거리가 증가하지만, 후류부에서는 운동량비가 증가하더라도 연료 침투거리는 특정 지점 이상 증가하지 않았다. 큰 공동의 경우 다른 모델에 비해 좋은 혼합 효율을 보이지만 압력 손실 또한 증가하는 경향을 보인다.

• 대한기계학회논문집B
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• 제36권8호
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• pp.839-847
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• 2012

벽면 난류의 항력과 밀접한 관련이 있는 유동구조인 헤어핀 보텍스 패킷의 형성 과정을 파악하기 위해 $Re_{\tau}$ = 180, 395, 590 의 채널유동에서 보텍스의 발달 과정에 대한 전산해석을 수행하였다. 초기 보텍스는 각 레이놀즈 수에 대한 직접수치모사를 수행하여 버퍼층에서 발생하는 Q2 이벤트에 대한 조건부 평균 유동장으로 부과하였다. 초기 보텍스의 발달과정을 시공간적으로 조사하여 ${\Omega}$ 모양의 보텍스의 형성 및 2 차 헤어핀 보텍스의 형성 과정의 시간 척도는 벽단위에 의존함을 확인하였다. 또한, 초기 보텍스가 채널 중심까지 성장한 시점에서는 세 레이놀즈 수 경우 모두 패킷의 경사각이 대략 $12^{\circ}{\sim}14^{\circ}$로 유사하였다. 마지막으로 두 개의 인접한 헤어핀 보텍스가 보텍스 패킷으로 발달하는 경우에 대한 전산해석을 수행하여 보텍스 패킷의 상호작용을 조사하였다.

• 한국수산과학회지
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• 제19권3호
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• pp.274-280
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• 1986

대, 소조기에 마산만에서 연속관측한 자료를 사용하여 만구 단면의 유속 변동특성을 구명하기 위하여 net velocity와 RMS속도의 등양선 및 순 유출입량을 계산하여 검토하였다. 최강유속은 수도 중앙과 서부의 4m 이하의 표층에서 나타나고, 최대 유입속도 24cm/sec 최대 유출속도는 15 cm/sec이다. 최강유속 시간임에도 불구하고 4m 이심에서는 유속이 약하여 $0{\sim}2cm/sec$에 불과하다. 만구 단면의 가장자리의 상층에 역류가 존재한다. net velocity는 비가 오지 않은 대조기의 경우 유출유속은 만구단면 서부에서 나타나며, 유입유속은 단면 동부에서 나타난다. 비온 직후의 소조기에는 이와 정반대로 흐른다. RMS속도의 최대 세기는 대조기에 $11.3{\sim}15.0cm/sec$, 소조기에 $7{\sim}10.3cm/sec$로서 단면 서부의 표층에 있으며, 매 조석주기마다 거의 동일위치에서 계속 존재한다. 순 통과유량은 건기에 $-39.7m^3/sec$, 우기 $-170m^3/sec$로서 유출이 탁월하다. 항유성분은 건기에는 조석잔차류가 우세하지만, 소조기의 강우시에는 밀도류가 우세한 것으로 추리된다.

• Wind and Structures
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• 제23권1호
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• pp.1-18
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• 2016

This work experimentally and numerically analyzes the flow configurations and the dynamic wind loads on panels of rectangular L/h 5:1 cross section mounted on a structural frame of rectangular bars of L/h 0.5:1, corresponding to a radar structure. The fluid dynamic interaction between panels and frame wakes imposes dynamic loads on the panels, with particular frequencies and Strouhal numbers, different from those of isolated elements. The numerical scheme is validated by comparison with mean forces and velocity spectra of a panel wake obtained by wind tunnel tests. The flow configuration is analyzed through images of the numerical simulations. For a large number of panels, as in the radar array, their wakes couple in either phase or counter-phase configurations, changing the resultant forces on each panel. Instantaneous normal and tangential force coefficients are reported; their spectra show two distinct peaks, caused by the interaction of the wakes. Finally, a scaled model of a rectangular structure comprised of panels and frame elements is tested in the boundary layer wind tunnel in order to determine the influence of the velocity variation with height and the three-dimensionality of the bulk flow around the structure. Results show that the unsteady aerodynamic loads, being strongly influenced by the vortex shedding of the supporting elements and by the global 3-D geometry of the array, differ considerably on a panel in this array from loads acting on an isolated panel, not only in magnitude, but also in frequency.

• 한국항공우주학회지
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• 제37권8호
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• pp.744-750
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• 2009

본 논문에서는 압전 작동기로 구동되는 무밸브 마이크로 펌프의 펌프 성능을 계산하였다. 선행연구에서 개발된 마이크로 펌프는 4층의 경량 압전 복합재료 작동기, PDMS로 된 챔버와 2개의 디퓨져로 이루어져 있다. 유한요소 해석은 압전 영역, 구조 영역 및 유체 영역을 완전 연성하여 수행되었다. 구조 및 압전 영역의 해석은 ANSYS를 사용하였으며, 유체영역의 해석은 ANSYS CFX를 사용하여 수행하였다. 작동 주파수가 10 Hz와 40 Hz인 경우에 대한 해석을 수행하여 작동 주파수가 유동 특성에 미치는 영향을 고찰하였다. 또한 300 Hz까지의 유동 해석을 통하여 작동 주파수에 따른 유량을 계산하였다.

• Corrosion Science and Technology
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• 제20권6호
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• pp.373-383
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• 2021

The effect of Cr addition to high Mn steel on flow-accelerated corrosion (FAC) behavior in a neutral aqueous environment was evaluated. For comparison, two types of conventional ferritic steels (API X70 steel and 9% Ni steel) were used. A range of experiments (electrochemical polarization and impedance tests, weight loss measurement, and metallographic observation of corrosion scale) were conducted. This study showed that high Mn steel with 3% Cr exhibited the highest resistance to FAC presumably due to the formation of a bi-layer scale structure composed of an inner Cr enriched Fe oxide and an outer Mn substituted partially with Fe oxide on the surface. Although the high Mn steels had the lowest corrosion resistance at the initial corrosion stage due to rapid dissolution kinetics of Mn elements on their surface, the kinetics of inner scale (i.e. Cr enriched Fe oxide) formation on Cr-bearing high Mn steel was faster in dynamic flowing condition compared to stagnant condition. On the other hand, the corrosion scales formed on API X70 and 9% Ni steels did not provide sufficient anti-corrosion function during the prolonged exposure to dynamic flowing conditions.

• 대한방사성의약품학회지
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• 제8권2호
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• pp.95-101
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• 2022

Microfluidic radioimmunoassay (RIA) platform called µ-RIA spends less reagent and shorter reaction time for the analysis compared to the conventional tube-based radioimmunoassay. This study reported the design of µ-RIA chips optimized for the gamma counter which could measure the small samples of radioactive materials automatically. Compared with the previous study, the µ-RIA chips developed in this study were designed to be compatible with conventional RIA test tubes. And, the automatic gamma counter could detect radioactivity from the ¹²⁵I labeled anti-PSA attached to the chips. Effects of the multi-layer microchannels and two-phase flow in the µ-RIA chips were investigated in this study. The measured radioactivity from the ¹²⁵I labeled anti-PSA was linearly proportional to the number of stacked chips, representing that the radioactivity in µ-RIA platform could be amplified by designing the chips with multi-layers. In addition, we designed µ-RIA chip to generate liquid-gas plug flow inside the microfluidic channel. The plug flow can promote binding of the biomolecules onto the microfluidic channel surface with recirculation in the liquid phase. The ratio of liquid slug and air slug length was 1 : 1 when the ¹²⁵I labeled anti-PSA and the air were injected at 1 and 35 µL/min, respectively, exhibiting 1.6 times higher biomolecule attachment compared to the microfluidic chip without the air injection. This experimental result indicated that the biomolecular reaction was improved by generating liquid-gas slugs inside the microfluidic channel. In this study, we presented a novel µ-RIA chips that is compatible with the conventional gamma counter with automated sampler. Therefore, high-throughput radioimmunoassay can be carried out by the automatic measurement of radioactivity with reduced radiowaste generation. We expect the µ-RIA platform can successfully replace conventional tube-based radioimmunoassay in the future.

• 한국지리정보학회지
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• 제17권3호
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• pp.160-174
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• 2014

본 연구의 목적은 광역의 일단위 수문순환을 모의할 수 있는 격자기반의 분포형 모델을 구축한 후, 이를 미래 기후변화에 따른 광역적 수문영향을 평가하는데 있다. 격자별로 지표 유출층, 지표하 불포화 및 포화 토양층의 3단으로 구성하여 일별 물수지를 계산하며, 증발산량은 Penman-Monteith방법을 사용하였고, 지표 및 지표하유출은 지체계수(lag coefficient)와 감수곡선 계수(recession curve slope)를 적용하였다. 모델의 검보정을 위하여 한강유역의 충주댐과 소양강댐을 대상으로 9개년(2001-2009)의 댐유입량 자료를 이용하여 모델의 6개 주요매개변수를 보정하였으며, Nash-Sutcliffe 모델효율 (NSE)은 각각 0.57, 0.71의 값을 보였으며, 결정계수($R^2$)는 각각 0.65, 0.72의 값을 보였다. 5개의 IPCC SRES A1B 기후변화 시나리오자료(CSIRO MK3, GFDL CM2_1, CONS ECHO-G, MRI CGCM2_3_2, UKMO HADGEMI)를 적용한 결과, 미래 유출량의 변화는 강수량과 비슷한 경향을 보이면서 전체적으로 7.0%~27.1% 증가하였고, 증발산량도 미래 기온의 증가경향으로 일부 경우를 제외하고 증가하는 경향을 나타내었으며, 이들의 공간적 변화를 제시하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.2-11
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• 2006

In the processes of hydrological cycle, when precipitation reaches the ground surface, water may become surface runoff or infiltrate into soil and then possibly further percolate into groundwater aquifer. A part of the water is returned to the atmosphere through evaporation and transpiration. Soil moisture dynamics driven climate fluctuations plays a key role in the simulation of water transfer among ground surface, unsaturated zone and aquifer. In this study, a one-layer canopy and a four-layer soil representation is used for a coupled soil-vegetation modeling scheme. A non-zero hydraulic diffusivity between the deepest soil layer modeled and groundwater table is used to couple the numerical equations of soil moisture and groundwater dynamics. Simulation of runoff generation is based on the mechanism of both infiltration excess overland flow and saturation overland flow nested in a numerical model of soil moisture dynamics. Thus, a comprehensive hydrological model integrating canopy, soil zone and aquifer has been developed to evaluate water resources in the plain region of Huaihe River basin in East China and simulate water transfer among precipitation, surface water, soil moisture and groundwater. The newly developed model is capable of calculating hydrological components of surface runoff, evapotranpiration from soil and aquifer, and groundwater recharge from precipitation and discharge into rivers. Regional parameterization is made by using two approaches. One is to determine most parameters representing specific physical values on the basis of characterization of soil properties in unsaturated zone and aquifer, and vegetations. The other is to calibrate the remaining few parameters on the basis of comparison between measured and simulated streamflow and groundwater tables. The integrated modeling system was successfully used in the Linhuanji catchment of Huaihe plain region. Study results demonstrate that (1) on the average 14.2% of precipitation becomes surface runoff and baseflow during a ten-year period from 1986 to 1995 and this figure fluctuates between only 3.0% in drought years of 1986, 1988, 1993 and 1994 to 24.0% in wet year of 1991; (2) groundwater directly deriving from precipitation recharge is about 15.0% t of the precipitation amount, and (3) about half of the groundwater recharge flows into rivers and loses through evaporation.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.235-235
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• 2003

The development of a buffer layer is an important issue for the second -generation wire, YBCO coated metal wire. The buffer layer demands not only on the prohibition of the reaction between YBCO and metal substrate, but also the proper lattice match and conductivity for high critical current density (Jc) of YBCO superconductor, In order to satisfy these demands, we suggested CaRuO3 as a useful candidate having that the lattice mismatches with Ni (200) and with YBCO are 8.2% and 8.0%, respectively. The CaRuO3 thin films were deposited on Ni substrates using various methods, such as e-beam evaporation and DC and RF magnetron sputtering. These films were investigated using SEM, XRD, pole-figure and AES. In e-beam evaporation, the deposition temperature of CaRuO3 was the most important since both hi-axial texturing and NiO formation between Ni and CaRuO3 depended on it. Also, the oxygen flow rate had i[n effect on the growth of CaRuO3 on Ni substrates. The optimal conditions of crystal growth and film uniformity were 400$^{\circ}C$, 50 ㎃ and 7 ㎸ when oxygen flow rate was 70∼100sccm In RF magnetron sputtering, CaRuO3 was deposited on Ni substrates with various conditions and annealing temperatures. As a result, the conductivity of CaRuO3 thin films was dependent on CaRuO3 layer thickness and fabrication temperature. We suggested the multi-step deposition, such as two-step deposition with different temperature, to prohibit the NiO formation and to control the hi-axial texture.