• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3114-3119
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• 2008

Relatively high convective flow exists in the under-rib regions of a gas diffusion layer (GDL) when serpentine flow fields are employed in a PEMFC. This under-rib convection is believed to be favorable for the performance of PEMFCs, by enabling more effective use of catalysts in the under-rib regions. From the fact that the under-rib convection in a GDL is directly proportional to the permeability of the GDL, computational fluid dynamics (CFD) simulations were performed to discover the relationship between the GDL permeability and the PEMFC performance. Single-, triple-, and quintuple-path parallel serpentine flow fields for $9\;cm^2$ active cell area were considered while changing the GDL permeability from $1{\times}10^{-12}$ to $5{\times}10^{-11}m^2$. The results showed that higher GDL permeability generally resulted in better performance of PEMFCs, but the degree of performance enhancement became smaller as the parallel path number increased. The effects of the permeability on the local variables were also discussed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.35-36
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• 2010

본 연구는 철근의 마디형상 변화에 따라 상대마디면적비를 달리 하여 콘크리트와 철근의 이음실험을 통해 부착성능을 알아보았다. 그 결과 상대마디면적비가 다른 실험체는 기존 실험체와 유사한 하중-처짐 곡선을 나타내고 있으며 최대 내력과 변위가 증가하는 것으로 나타났다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 추계학술대회 논문집
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• pp.27-28
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• 2009

• Steel and Composite Structures
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• 제35권4호
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• pp.475-494
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• 2020

Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud's strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud's head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

• Journal of Advanced Marine Engineering and Technology
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• 제35권5호
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• pp.616-624
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• 2011

본 연구에서는 사각채널내에 주유속 방향에 가로지르게 배치된 반원 리브의 난류 유동에 대한 유동 특성과 열전달 증대에 관해 수치해석적으로 살펴보았다. 사각채널의 종횡비는 5이고, 수력직경 대비 리브 높이비는 0.07, 사각채널 높이 대비 리브 높이비는 0.117로서 리브 높이 대비 리브 피치비가 8~14인 리브를 주기적으로 배열하여 연구를 수행하였다. 난류 모델의 선정은 실제 현상과 근접한 벽 근처 유동 특성과 열전달을 위해 SST k-${\omega}$ 난류 모델과 v2-f 난류 모델을 이용하였다. 수치해석의 결과는 실험에 의 해 관찰된 난류 유동 특성, 열전달 및 마찰계수의 결과를 잘 예측함을 보여준다. 본 결과에서 난류 운동 에너지가 재순환류 영역의 확산과 밀접한 관련이 있음을 알 수 있고 v2-f 난류 모델이 SST k-${\omega}$ 난류 모델에 비해 실험결과를 더 잘 예측하였다.

• Composites Research
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• 제19권2호
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• pp.13-19
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• 2006

본 논문에서는 미세 방전가공(Electrical Discharge Machining; EDM) 기계를 위한 샌드위치 구조를 설계하기 위해 복합재료의 적층 순서, 두께, 그리고 리브의 형상 등을 고려한 파라메트릭 연구를 수행하였다. 샌드위치 구조는 면재인 섬유강화 복합재료와 심재인 레진 콘크리트 및 고분자 포움으로 이루어졌다. 컬럼은 정적 굽힘강성과 비굽힘강성을 높이기 위해 십자 리브를 가진 형상으로 설계하였으며, 적층 순서와 두께를 조절하였다. 베드의 경우 양방향의 강성을 동시에 향상시키기 위해 적층 순서와 리브 형상을 조절하였다. 최적의 고강성을 얻기 위하여 리브의 두께와 면재의 두께 등 설계 파라메터의 최적치를 제안하였다. 각 설계 파라메터의 변화에 따른 구조의 정적, 동적 강성의 변화를 확인하기 위해 유한요소해석을 수행하였으며, 진동 실험을 통하여 각 요소의 고유진동수와 감쇠비를 측정하여 비교하였다. 이러한 결과로부터 고정밀 미세 방전가공 기계 구조를 위한 최적의 형상조건을 제안하였다.

• 산업기술연구
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• 제24권A호
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• pp.139-155
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• 2004

A room and pillar mining method has been adopting at the Jeungsun limestone mine. To check stability of pillar with multiple and irregular openings, the size, shape and spacing of rib pillar were first designed using some empirical suggestions. The Finite Difference Method(FDM)was used to analyze the pillar stability. Twelve different cases with the variation of K(horizontal/vertical stress)values, different height and different spacing of pillar were used in this study. Finally Mohr-Coulomb criterion was adopted to calculate the safety factors. Horizontal and vertical displacement, maximum and minimum principal stresses, range of plastic zone and safety factors were calculated at each case. As a result of analysis, the size of one block is 160m long, 70m wide, 40m high with 20m wide rib pillar and 20m square column pillar. The overall recovery at this case can be estimated about 40%.

• 대한가정학회지
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• 제17권4호
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• pp.23-28
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• 1979

In order to measure the change of constructional and some properties of knitted under wears by laundry, constructional properties, such as fabric count , yarn count, loop length and cover, factor, and some properties , such as shrinkage, tearing, strength, air permeability, electrostatic charge of under wears sold in the market were tested. The results of the experiment can be summarized as follows.1. Interlock and rib were increased in wale direction after laundry and decreased in course direction , plain was decreased, in both direction after laundry. 2. Loop form of plain was changed more than those interlock and rib after laundry. 3. Tearing strength was decreased 51% in wale direction, and 70% in course direction after 20 times laundry. Air permeability was generally increased. 4. Electro static charge was increased 9 times after laundry.

• 공학기술논문지
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• 제10권3호
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• pp.285-290
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• 2017

Molding of body with ribs is the most difficult during flow molding process. The rib area is easy to be deformed at the rear side due to wall thickness variation. In this study, relationships between molding condition and deflection of rib-shaped part is investigated during the compression molding of fiber reinforced plastic composites, and the following results are derived. Polypropylene(PP), Polystyrene(PS), and stampable sheet(SS 40wt%) show the increment of deflection along with releasing temperature. For the correlation between incremental holding pressure load and deflection, stampable sheet exhibits lower deflection along with higher holding pressure, while PS shows significant increase of deflection with higher holding pressure, PP shows completely different characteristic, significant reduction of deflection along with higher holding pressure. Regarding to mold temperature and deflection, deflection amount of SS is the biggest, and PS shows the smallest. In addition, all three kinds shows the highest amount of deflection at 173C. Deflection is reduced when mold closing speed is increased. Amount of deflection in SS is larger and is not highly dependent on molding conditions like holding pressure and cooling parameters, compared with single component material like PP. This can be elucidated by anisotropic and inhomogeneous characteristics of glass fiber during filling process of stampable sheet composite.

• 보건행정학회지
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• 제4권1호
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• pp.49-76
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• 1994

Small area variations in health care utilization have long been studied as an important issue related to boto cost containment and quality assurance. This study was conducted to investigate if variations in hospital services across small geographic areas in Korea existed. The claims data of the fiscal year 1992 obtained from the regional health insurance societies were used for the study. Main findings of the research can be summarized as follows : 1. Extremal Quotients(EQ) of hospital expenditure per capita and hospital days per capita varied among diagnosis types. The EQ ranged from 2.05(cataract) to 41.67(pneumonia) in hospital expenditure per capita and from 1.86(cataract) to 45.89(pneumonia) in hospital days per capita. The diagnosis groups which showed high variation were pneumonia, cephalo-pelvic disproportion, gastritis and duodenitis, fracture of rib, and acute bronchitis. Those which showed low variation were acute appendicitis and cataract. 2. The EQ level of admission rate was different in terms of diagnosis types, ranging from 2.57(catarct) to 44.45(pneumonia). The variations were high in medical disorders such as pneumonia, oephalo-pelvic disproportion, gastritis and duodenitis and acute bronchitis, while relatively low in surgical conditions such as acute appendicitis and cataract. 3. As an indicator of service intensity, the EQ of expenditure per admission ranged from 1.67(acute appendicitis) to 31.27(essential hypertension). The diagnoses which had high variation were essential hypertension, gastric ulcer, whereas those which had low variation were cephalopelvic disproportion and acute appendicitis. With regard to hospital days per admission, the EQ ranged from 1.55(acute appendicitis) to 28.13(gastric ulcer) by diagnosis types. The diagnosis groups with showed high variation were gastric ulcer, essential hypertension, and acute bronchitis, whereas those with low variation were cephalo-pelvic disproportion, intervertebral disc disorders, and acute appendicitis. Both the expenditure and hospital days per admission showed lewwer variations than the expenditure per capita, hospital days per capita and admission rate. 4. Comparing patterns of variation in utilization indices, diagnoses such as essential hypertension, gastric ulcer, fracture of rib showed higher variations in expenditure per admission than in admission rates, whereas diagnoses such as pneumonia, cephalo-pelvic disproportion and gastric ulcer showed higher variations in admission rate than expenditure per admission. These findings suggest that wide variations existed in several diagnoses groups across small areas in Korea. Further research should be performed to investigate factors related to small area variations including provider behavior.