• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.180-187
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• 2017

항공기 엔진 지상 성능시험을 위한 15만 파운드 급 Test 설비를 구축하기 위해 Test Cell Type, Cell Flow, Cell Bypass Ratio, Approach Velocity, Cell Depression, Front Cell Distortion, Noise 및 Vibration 등의 주요 설계 목표를 설정 하였고, 설비 완공 후 최종 성능검사를 통해 목표 값을 충족하는 성능 데이터를 획득할 수 있었다.

• 한국전산유체공학회지
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• 제14권2호
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• pp.59-67
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• 2009

An accurate prediction of the bypass flow is of great importance in the VHTR core design concerning the fuel thermal margin. Nevertheless, there has not been much effort in evaluating the amount and the distribution of the core bypass flow. In order to evaluate the behavior and the distribution of the coolant flow, a unit-cell experiment was carried out. Unit-cell is the regular triangular section which is formed by connecting the centers of three hexagonal blocks. Various conditions such as the inlet mass flow rate, block combinations and the size of bypass gap were examined in the experiment. CFD analysis was carried out to analyze detailed characteristics of the flow distribution. Commercial CFD code FLUENT 6.3 was validated by comparing with the experimental results. In addition, SST model and standard k-$\varepsilon$ model were validated. The results of CFD simulation show good agreements with the experimental results. SST model shows better agreement than standard k-$\varepsilon$ model. Results showed that block combinations and the size of the bypass gap have an influence on the bypass flow ratio but the inlet mass flow rate does not.

• 한국전기전자재료학회논문지
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• 제21권1호
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• pp.12-17
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• 2008

In this paper, an I-V characteristics of bypass diode has been studied by counting the shading effect in photovoltaic module. The shadow induces hot spot phenomenon in PV module due to the increase of resistance in the current path. Two different types of PV module with and without bypass diode were fabricated to expect maximum output power with an increasing shading rate of 5 % on the solar cell. Temperature distribution is also detected by shading the whole solar cell for the outdoor test. From the result, the bypass diode works properly over 60 % of shading per cell with constant output power. Maximum power generation in case of solar cell being totally shaded with bypass diode decreases 41.3 % compared with the one under STC(Standard Test Condition). On the other hand, the maximum output power of the module without bypass diode gradually decreases by showing hot spot phenomenon with the increase of shading ratio on the cell and finally indicates 95.5 % of power loss compared with the output under STC. Finally the module temperature measured increases around $10^{\circ}C$ higher than that under STC due to hot-spots which come from the condition without bypass diode. It has been therefore one of the main reasons for degrading the PV module and shortening the durability of the PV system.

• Geomechanics and Engineering
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• 제28권2호
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• pp.135-143
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• 2022

Soils are natural granular materials whose mechanical properties differ according to the size and composition of the particles, so soils exhibit an obvious scale effect. Traditional soil mechanics is based on continuum mechanics, which can not reflect the impact of particle size on soil mechanics. On that basis, a matrix-reinforcing-particle cell model is established in which the reinforcing particles are larger-diameter sand particles and the matrix comprises smaller-diameter bentonite particles. Since these two types of particles deform differently under shear stress, a new shear-strength theory under direct shear that considers the stress concentration and bypass phenomena of the matrix is established. In order to verify the rationality of this theory, a series of direct shear tests with different reinforcing particle diameter and volume fraction ratio are carried out. Theoretical analysis and experimental results showed that the interaction among particles of differing size and composition is the basic reason for the size effect of soils. Furthermore, the stress concentration and bypass phenomena of the matrix enhance the shear strength of a soil, and the volume ratio of reinforcing particles has an obvious impact on the shear strength. In addition, the newly proposed shear-strength theory agrees well with experimental values.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 추계 학술대회논문집
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• pp.167-173
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• 1999

An Euler-based CFD tool has been developed for the performance evaluation of a thrust reverser mounted on a high bypass ratio turbofan engine. The computational domain surrounded by the ground and non-reflection boundary includes the whole nacelle configuration with a deployed thrust reverser. The numerical algorithm is based on the modified Godunovs scheme to allow the second order accuracy in both space and time. The grid system is generated by using eleven multi-blocks, of which the total cell number is 148,400. The thrust reverser is modeled as if it locates at the nacelle simply in all circumferential direction. The existence of a fan and an OGV(Outlet Guide Vane) is simulated by adopting the actuator disk concept, in which predetermined radial distributions of stagnation pressure ratio and adiabatic efficiency coefficient are used for the rotor type disk, and stagnation pressure losses and flow outlet angles for the stator type disk. All boundary conditions including the fan and OGV simulation are treated by Riemann solver. The developed solver is applied to a turbofan engine with a bypass ratio of about 5.7 and the diameter of the fan cowl of 83 inch. The computational results show that the Euler-based inviscid method is very useful and economical to evaluate the performance of thrust reversers.

• Journal of Obesity & Metabolic Syndrome
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• 제27권4호
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• pp.248-253
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• 2018

Background: Sirtuins mediate metabolic responses to nutrient availability and slow aging and accompanying decline in health. This study was designed to assess the expressions of sirtuin1 (SIRT1) and sirtuin3 (SIRT3) in the liver and hypothalamus after duodenal-jejunal bypass (DJB) surgery in rats. Methods: A total of 38 rats were randomly assigned to either sham group (n=8) or DJB group (n=30). DJB group was again divided into three groups according to the elapsed time after surgery (10 weeks, DJB10; 16 week, DJB16; 28 week, DJB28). The mRNA and protein expressions of SIRT1 and SIRT3 in the liver and hypothalamus were measured by reverse transcription polymerase chain reaction, Western blot, and immunohistochemistry analyses. $NAD^+/NADH$ ratio was also measured. Results: We found increased mRNA and protein expression levels of SIRT1 in the liver of DJB16 and DJB28 groups compared with those of sham group. The mRNA and protein expressions of SIRT3 in the liver of DJB group increased proportionally to the elapsed time after DJB surgery. The mRNA expression levels of SIRT1 in the hypothalamus increased in DJB16 and DJB28 groups and protein expression levels of SIRT1 in the hypothalamus increased in DJB10, DBJ16, and DJB28 groups compared with sham group. We observed that mRNA and protein levels of SIRT3 in the hypothalamus of DJB group were not changed. Conclusion: This study proves that DJB increases SIRT1 and SIRT3 expressions in the liver and SIRT1 expression in the hypothalamus. These results suggest the possibility of sirtuins being involved in bypass surgery-induced metabolic changes.

• 대한기계학회논문집B
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• 제33권4호
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• pp.288-297
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• 2009

A serpentine channel geometry often used in a fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from the intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with high aspect ratio of active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compressive forces. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds that of dropwise condensation in cathode channels.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.147-151
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• 2007

A serpentine channel geometry often used in a polymer electrolyte membrane fuel cell has a strong pressure gradient between adjacent channels in specific regions. The pressure gradient helps some amount of reactant gas penetrate through a gas diffusion layer(GDL). As a result, the overall serpentine flow structure is slightly different from intention of a designer. The purpose of this paper is to examine the effect of serpentine flow structure on current density distribution. By using a commercial code, STAR-CD, a numerical simulation is performed to analyze the fuel cell with relatively high aspect ratio active area. To increase the accuracy of the numerical simulation, GDL permeabilities are measured with various compression conditions. Three-dimensional flow field and current density distribution are calculated. For the verification of the numerical simulation results, water condensation process in the cathode channel is observed through a transparent bipolar plate. The result of this study shows that the region of relatively low current density corresponds to that of dropwise condensation in cathode channels.

• 대한토목학회논문집
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• 제31권2B호
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• pp.187-192
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• 2011

질산성 질소는 대표적인 지하수 오염물질로써 우리나라를 비롯한 여러 국가들이 음용수 중의 질산성 질소 농도를 WHO 권고기준인 10 mg/L as N 이하로 규제하고 있다. 본 연구에서는 처리하고자 하는 물질과의 접촉면적을 극대화 시켜줄 수 있는 영가철 충진 복극전해조를 이용하여 지하수 중의 질산성 질소를 처리하기 위해 다양하게 실험조건을 변화시켜 최적의 효율을 얻고자 하였다. 실험결과로서 영가철을 환원제로 사용할 때, 질산성 질소는 산성조건에서 좋은 제거효율을 보여주었으며, 산성조건을 유지시켜주지 않았을 때 암모니아성 질소로 환원되는 과정에서 수산화기 발생으로 pH가 증가하여 환원반응에 필요한 수소이온이 감소함으로 효율이 점차 감소하는 문제가 발생하였다. 복극전해조에서, 영가철과 주문진규사의 충진비는 0.5~1:1에서 제거효율이 가장 좋았으며 이는 각각의 영가철 입자가 미세전극으로 작용했기 때문이라고 판단된다. 충진비 2:1 이상에서는 점진적인 침전물의 형성 및 clogging의 가속화로 제거효율이 감소하였다. 인가전압이 상승할수록 제거효율이 높아졌으나 반응기 내 bypass current가 증가하는 것으로 확인되었으며 소비되는 전력량이 비례 이상으로 증가하였다. 본 실험에서는 최적 인가전압을 50 V로 결정하였고 그 때 질산성 질소를 94.9% 제거할 수 있었다.

• Journal of Chest Surgery
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• 제37권10호
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• pp.817-826
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• 2004

배경: 심혈관 수술 시 일반적으로 사용하는 저체온 체외순환이 세포의 저체온 손상, 말초혈관계의 비정상적 반응 및 수술 후 높은 출혈 경향을 일으키는데 비해 정상체온 체외순환은 이러한 저체온 체외순환의 유해한 효과들을 예방하고 심장의 빠른 회복을 가져다준다고 한다. 저자들의 연구는 염증 및 혈액학적 반응에 대한 저체온 체외순환과 정상체온 체외순환의 영향을 비교하기 위해 전향적으로 실시되었다. 대상 및 방법: 심장수술이 계획된 34명의 성인 환자들을 연구목적에 따라 무작위로 저체온 체외순환군(비인두 온도 26～28$^{\circ}C$, n=17, 저체온군)과 정상체온 체외순환군(비인두 온도&35.5$^{\circ}C$, n=17, 정상체온군)으로 나누었다. 심근보호는 양 군 모두 비혈액성 냉각심정지법을 적용하였다. 환자들로부터 체외순환 시작 전(Pre-CPB), 체외순환 실시 10분(CPB-10), 체외순환 종료 후(CPB-OFF)에 요골동맥으로부터 혈액을 채취하여 총 백혈구 수, 혈소판 수, interleukin-6 (IL-6)농도의 변화율(백분율로 표시), D-dimer 농도, protein C 활성도 및 Protein S 활성도를 측정하였고 수술 후 24시간 출혈량, 혈액제제 사용량도 조사하여 양 군 간에 비교 평가하였다. 결과: Pre-CPB에 비해 CPB-OFF의 경우 정상체온군의 총 백혈구 수(10,032$\pm$65/mm$^3$) 및 IL-6 증가율(353$\pm$7.0%)이 저체온군의 총 백혈구 수(7,254$\pm$$48/mm^3$) 및 IL-6 증가율(298$\pm$7.3%)보다 유의하게 높았다(p=0.02 및 p=0.03). 그러나 정상체온군의 protein C activity (32$\pm$3.8%) 및 protein S activity (35$\pm$4.1%)는 저체온군의 protein C activity (45$\pm$4.3%) 및 Protein S activity (51$\pm$3.8%)보다 유의하게 낮았다(p=0.04 및 p=0.009). 체외 순환 중 혈소판 수와 D-dimer농도의 변화는 양 군 간에 유의한 차이가 없었다. 정상체온군의 수술 후 24시간 출혈량(850$\pm$23.2 mL) 및 수혈을 위한 농축적혈구(1,402$\pm$20.5 mL), 신선냉동혈장(970$\pm$20.8 mL), 농축 혈소판(252$\pm$6.4 rnL) 사용량은 저체온군의 수술 후 24시간 출혈량(530$\pm$21.5 mL) 및 수혈을 위한 농축적혈구(696$\pm$15.7 mL), 신선냉동혈장(603$\pm$18.2 mL), 농축혈소판(50$\pm$0.0 mL) 사용량보다 유의하게 더 높았다(p=0.04 및 p=0.01, p=0.04, p=0.01). 결론: 정상체온 체외순환은 저체온 체외순환에 비해 더 높은 염증반응, 수술 후 더 많은 출혈 및 혈액제제 사용량의 증가를 유발하므로, 저자들은 심장수술시 정상체온 순환법을 일상적으로 사용하기 위해서는 더 많은 연구가 필요할 것으로 생각한다.