• International Journal of Fluid Machinery and Systems
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• 제10권2호
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• pp.119-137
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• 2017

Although the stall stagnation phenomena have often been experienced in site and also analytically in numerical experiments in surges in systems of compressors and flow paths, the fundamental causes have not been identified yet. In order to clarify the situations, behaviours of infinitesimal disturbance waves superposed on a main flow were studied in a simplified one-dimensional flow model. A ratio of the amplifying rate of the system instability to the characteristic slope of the compressor element was surveyed as the instability enhancement factor. Numerical calculations have shown the following tendency of the factor. In the situation where both the sectional area ratio and the length ratio of the delivery flow-path to the suction duct are sufficiently large, the enhancement factors are greater in magnitude, which means occurrence of ordinary deep surges. However, in the situation where the area ratio and/or the length ratio is relatively smaller, the enhancement factor tends to lessen significantly, which situation tends to suppress deep surges for the same value of the characteristic slope. It could result in the stall stagnation condition. In the domain of area ratio vs. length ratio of the delivery duct to the suction duct, contour-lines of the enhancement factor behave qualitatively similar to those of the stall stagnation boundaries of a fan analytically obtained, suggesting that a certain range of the enhancement factor values could specify the stagnation occurrence. The significant decreases in the factors are observed to accompany appearances of phase lags and travelling waves in the wave motions, which macroscopically suggests breaking down of the complete surge actions of filling and emptying of the air in the delivery duct. The strength of the action is deeply related with acoustic interferences and is evaluated in terms of the volume-modified reduced resonance frequency proposed by the author. These observations have shown the fundamental cause and the sequence of the stall stagnation in principle.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1437-1446
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• 2000

A numerical analysis on the freeze coating process of a non-isothermal finite dimensional plate with a binary alloy is performed to investigate the growth and decay behavior of the solid and the mushy layer of the freeze coat and a complete procedure to calculate the process is obtained in this study. The continuously varying solid and mushy layers are immobilized by a coordinate transform and the resulting governing differential equations are solved by a finite difference technique. To account for the latent heat release and property change during solidification, proper phase change models are adopted. And the convection in the liquid melt is modeled as an appropriate heat transfer boundary condition at the liquid/mushy interface. The present results are compared with analytic solutions derived for the freeze coating of infinite dimensional plates and the discrepancy is found to be less than 0.5 percent in relative magnitude for all simulation cases. In addition the conservation of thermal energy is checked. The results show that the freeze coat grows proportional to the 1.2 square of axial position as predicted by analytic solutions ar first. But after the short period of initial growth, the growth rate of the freeze coat gradually decreases and finally the freeze coat starts to decay. The effects of various non-dimensional processing parameters on the behavior of freeze coat are also investigated.

• 센서학회지
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• 제3권2호
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• pp.16-23
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• 1994

오염수에서 유기인 화합물을 측정하기 위해 개발된 광섬유 바이오센서의 신호의 분석과 최적설계를 위하여 센서에 사용되어진 AChE효소(acetylcholinesterase)의 반응, 반응기 내의 유체거동 및 물질전달현상의 해석이 필요하다. 사용되어진 센서의 반응기 부분을 해석하고 재설계하기 위하여 효소 반응을 연구하고, 이동현상학적으로 유체 및 물질확산 현상을 해석하여 반응기 모델을 성립하였다. 사용되어진 유기인 화합물에 의해 저해되는 AChE효소의 측정범위인 0-2 ppm 사이에서 저해반응을 실험하였으며, 비가역 저해 효소 반응식을 제안하였다. 반응기를 두상 즉 벌크상과 효소층으로 나누어 유체거동을 해석하였으며, 고정화겔 내의 확산의 영향을 조사하였다. 반응식, 유체거동식 및 확산식을 연계하여 세워진 반응기 전체모델을 제시하였고, 이를 이용하여 신호를 해석하였다. 제시된 모델을 이용하여 효소량, 효소층의 두께의 증가에 따른 센서 신호량의 민감도를 전산모사하였다.

• 에너지공학
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• 제12권1호
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• pp.35-41
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• 2003

본 연구에서는 배가스의 현열회수를 통해 연소기기의 열효율을 향상시키는 축열연소시스템에서 구형축열체를 이용한 축열기내 열유동을 해석할 수 있는 수치해석 코드를 개발하였다. 이를 통해 축열기내 비정상 열유동을 해석하고 축열기 길이를 포함한 축열기 형상과 축열체 구경에 따른 배열회수와 압력손실의 관계를 파악해 보았다. 수치해석은 1차원 2상 유체역학 모델을 도입하여 MacCormack방식으로 해를 얻었으며, 실험적 경향과 일치함을 알 수 있었다. 개발된 수치코드를 통해 얻은 결론은 축열기 길이가 길고 입자구경이 작으며 축열기내 유체 유속이 빠른 경우에 많은 배열을 회수할 수 있으나 압력손실이 커짐을 알 수 있었다.

• Journal of Astronomy and Space Sciences
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• 제21권4호
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• pp.453-466
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• 2004

한국천문연구원에서는 적외선관측기술 개발의 일환으로 지상망원경용 근적외선 카메라인 KAONICS(KAO Near-Infrared Camera System)를 개발하고 있다. 이러한 개발의 선행 연구 과정으로서 우리는 보현산천문대와 소백산천문대의 근적외선($1-5{\mu}m$) 관측 조건을 정량적으로 조사했다. KAONICS의 기본 파장 밴드인 J, H, K, L 에 대해 대기 투과 모델을 사용하여 PWV(Precipitable Water Vapour)에 따른 대기투과율을 계산했으며, 각각의 파장 밴드에서 관측 한계 등급을 계산했다. 계산 결과, 두 천문대 모두 근적외선 영역에서 관측이 가능하며, 서로 비슷한 관측 능력을 가지고 있다는 결론을 얻었다.

• 대한기계학회논문집A
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• 제24권3호
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• pp.613-624
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• 2000

In this study, new design method of prosthetic foot was suggested which can evaluate the performance of prosthetic foot by implementing amputee's gait simulation using the finite element analysis. The basic shape of ESPF(Energy Storing Prosthetic Foot) was designed which is suitable for the below-knee amputee considering mechanical properties and kinematic properties. And, the performance evaluations were performed using the Taguchi method with orthogonal array L25. As a result, average main effect of factors for the ESPF's performance were calculated and then optimum condition of given shape was selected. Essential particulars for the performance evaluation from the simulation result were the quantity of external work needed in stance phase, the quantity of transferred energy from the ESPF through the knee, and the vertical displacement of knee at toe-off. Reasonable optimum condition was obtained from the using performance index. From this study, it was found that it is necessary for the design of ESPF to consider the geometrical data related to the magnitude of load on elastic material.

• 한국식품영양학회지
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• 제20권2호
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• pp.120-124
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• 2007

천연 항산화제로 사용되는 토코페롤은 가열 온도가 높을수록, 가열 시간이 길수록 토코페롤의 분해율이 증가하였으며, 무산소 가열의 경우, 토코페롤은 산소가 있을 때 보다 덜 분해되었다. 알파-, 감마-. 델타- 토코페롤의 무산소 가열 조건을 만들기 위하여 $100{\sim}250^{\circ}C$에서 5${\sim}$60분 가열하는 동안 회화로 속으로 질소를 계속 흘려보내는 실험 방법을 사용하였다. 헥산으로 추출한 토코페롤은 두 종류의 용출 용매와 역상 ${\mu}$-Bondapak C$_{18}$-컬럼을 사용한 HPLC로 분리하였고 토코페롤의 분해 패턴과 잔존량을 조사하였다. 토코페롤의 열분해 키네틱스는 온도와 시간의 함수로 분석되었고 열분해 패턴은 1차 반응으로 나타났다. 무산소 가열시 알파-, 감마-, 델타-토코페롤의 열분해 활성화 에너지는 각각 3.47, 5.85 그리고 6.76 kcal/mole 이었다.

• 한국자동차공학회논문집
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• 제19권5호
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• pp.92-99
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• 2011

To measure the traffic pollutants with high temporal and spatial resolution under real conditions, a mobile emission laboratory (MEL) was designed. The equipment of the mini-van provides gas phase measurements of CO, NOx, $CO_2$, THC (Total hydrocarbon) and number density & size distribution measurements of fine and ultra-fine particles by a fast mobility particle sizer (FMPS) and a condensation particle counter (CPC). The inlet sampling port above the bumper enables the chasing of different type of vehicles. This paper introduces the technical details of the MEL and presents data from the car chasing experiment of diesel bus equipped with aftertreatment system. The dilution ratio was calculated by the ratio of ambient NOx and tail-pipe NOx. Most particles from the diesel bus were counted under 300 nm and the peak concentration of the particles was located between 30 and 60 nm. The total PM number emission from diesel bus equipped with DPF was 10 orders of magnitude lower compared to those emitted from base diesel bus. And the total PM number emission from diesel bus equipped with SCR was comparable to the particle emission from base diesel bus.

• 한국전자파학회논문지
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• 제23권11호
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• pp.1297-1306
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• 2012

본 논문에서는 77 GHz 차량용 레이더 시스템에 필요한 레이더 송신기를 설계하였다. 130 nm RF CMOS 공정을 이용하여 설계한 13 GHz 주파수 합성기로 6 체배기를 내장한 상용의 화합물 전력 증폭기를 구동하여 77 GHz 송신 신호를 발생시켰다. 13 GHz 주파수 합성기는 6 체배용 전력 증폭기를 구동하기 위해 4 dBm 출력을 내는 주입 잠금 버퍼를 내장하고 있다. 제작한 77 GHz 레이더 송신기 모듈은 주파수 조정 범위 내에서 출력 전력이 최소 13.99 dBm이고, 중심 주파수 대비 기준 스퍼의 크기는 -36.45 dBc이다. 또한, 76.5 GHz 중심 주파수의 1 MHz 오프셋에서 -81 dBc/Hz의 위상 잡음 특성을 보인다.

• The Korean Journal of Physiology
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• 제22권1호
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• pp.1-12
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• 1988

The changes in membrane potential and intracellular $Ca^{2+}$ activities along with adenosine triphosphate (ATP) and creatine phosphate (CP) contents of guinea pig hearts were studied during the cardioplegia and recovery phase. The results obtained were summarized as follows: 1) A low concentration of $Ca^{2+}$ in the cardioplegic solution caused significant changes in membrane potential during the cardioplegia and action potential configurations of the first beat after cardioplegia. 2) Intracellular $Ca^{2+}$ activities were decreased significantly during cardioplegia and increased when the cardiac tissue was reperfused with the normal Tyrode solution. The magnitude of increase in intracellular $Ca^{2+}$ activities was larger in the 0.1 mM $Ca^{2+}-cardioplegic$ solution than the 1.8 mM $Ca^{2+}-solution$. 3) ATP and CP contents of cardiac ventricular tissue were decreased during the cardioplegia, regardless of $Ca^{2+}$ concentration in the cardioplegic solutions, and CP contents were recovered with the reperfusion of normal Tyrode solution faster than those of ATP. And, there were no significant differences in the recovery of CP contents with different concentrations of $Ca^{2+}$ in the cardioplegic solutions tested, while the recovery of ATP contents was faster with $15mM\;K^{+},\;0.1mM\;Ca^{2+}$ cardioplegic solution. These results suggest that the $Ca^{2+}$ concentration in the cardioplegic solution is one of major factors influencing the recovery of cardiac tissue from the cardioplegia.