• 설비공학논문집
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• 제10권5호
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• pp.619-629
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• 1998

An experimental work was conducted to investigate a feasibility of simultaneous measurement of gas-liquid two-phase flowrates with double orifice plates using air and water. The tests were carried out under the atmospheric pressure and at the ambient temperature using two different tube sizes. Qualities of an air-water flow in the present study have values less than 0.1 and thus the mixed flow showed bubbly, plug, slug flow regimes. The probability density function (PDF) and the power spectral density function (PSDF) of the instantaneous pressure drop traces for the flow regimes were obtained. It is found that some distinctive features exist in the distribution of these functions, depending upon the two-phase flow pattern. The time-averaged value of the instantaneous pressure drop increases with increasing gas and liquid flowrates, showing a single-valued function for the total mass flowrate and the quality. It is also found that the two-phase discharge coefficient exhibits a consistent trend for variation of dimensionless parameters such as the superficial velocity ratio and the gas Reynolds number. The results indicate that simultaneous measurement of two-phase flowrate may be possible based upon a statistical analysis of the instantaneous pressure drop curves monitored using double orifice plates.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4491-4503
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• 2023

This study aimed to verify and validate the transient simulation capability of the hybrid code system RAST-F for fast reactor analysis. For this purpose, control rod (CR) drop experiments involving eight separate CRs and six CR groups in the China Experimental Fast Reactor (CEFR) start-up tests were utilized to simulate the CR drop transient. The RAST-F numerical solution, including the neutron population, time-dependent reactivity, and CR worth, was compared against the measurement values obtained from two out-of-core detectors. Moreover, the time-dependent reactivity and CR worth from RAST-F were verified against the results obtained by the Monte Carlo code Serpent using continuous energy nuclear data. A code-to-code comparison between Serpent and RAST-F showed good agreement in terms of time-dependent reactivity and CR worth. The discrepancy was less than 160 pcm for reactivity and less than 110 pcm for CR worth. RAST-F solution was almost identical to the measurement data in terms of neutron population and reactivity. All the calculated CR worth results agreed with experimental results within two standard deviations of experimental uncertainty for all CRs and CR groups. This work demonstrates that the RAST-F code system can be a potential tool for analyzing time-dependent phenomena in fast reactors.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.28-35
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• 2000

The quality factor and the seismic source parameters such as the $\chi$ corner frequency and the stress drop were estimated from the small-to-medium instrumental earthquake data in south Korea. The Q facter with 95% confidence level ranges from 1519 to 2158. The regression equation of $\chi$in terms of epicentral distance R, is obtained as $\chi$=0.006717+0.00015R. And the stress drop is estimated as 50 bar which is similar to the previous results carried out by independent researchers. Artificial ground motions were simulated using the estimated earthquake parameter values and compared with real earthquake, The simulated response spectrum is very similar to real one.

• 전기전자학회논문지
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• 제11권4호
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• pp.247-251
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• 2007

The recessed gate IGBT has a lower on-state voltage drop compared with the DMOS IGBT, because there is no JFET resistance. But because of the electric field concentration in the corner of the gate edge, the breakdown voltage decreases. This paper is about the new structure to effectively improve the Vce(sat) voltage without breakdown voltage drop in 1700V NPT type recessed gate IGBT with p floating shielding layer. For the fabrication of the recessed gate IGBT with p floating shielding layer, it is necessary to perform the only one implant step for the shielding layer. Analysis on the Breakdown voltage shows the improved values compared to the conventional recessed gate IGBT structures. The result shows the improvement on Breakdown voltage without worsening other characteristics of the device. The electrical characteristics were studied by MEDICI simulation results.

• 한국산업융합학회 논문집
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• 제4권4호
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• pp.395-401
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• 2001

The characteristics of heat transfer and pressure drop through tubes has been investigated experimentally for a compound heat transfer enhancement. The test tubes were spirally indented tubes with wire coil inserts which had a various combinations of pitch and helix angles. Pure water was used as working fluids for the experiments, Heat transfer coefficients and friction factors of the test tubes were evaluated from the values of measured temperatures, flow rates and pressure drops. An performance evaluation was performed to find an optimal combination of spirally indented tubes with wire coil inserts. When the helix angle of wire coil insert are $71^{\circ}-72^{\circ}$, the best heat transfer enhancement was shown. The friction factor was 9 - 13 times higher than those in smooth tubes, and the heat transfer was enhanced a maximum of 500%.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1718-1722
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• 2008

This study explores the influence of volume fraction of nanocrystals of Cu-Zr amorphous alloys on shear band formation. As the number of crystals with very tiny size increases, the strain localization, i.e. shear band, decreases without large drop of flow stress. The DPRs also depict no sudden drop and relatively high values. The strain state during the deformation represents a few shear bands at low volume fraction while there are no distinguishable shear bands at high volume fraction of nanocrystals.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.741-746
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• 2003

The main objective of present study is to obtain information for flow characteristics, such as velocity and wall shear stress, of bifurcation in blood vessel. Branch flows for Newtonian fluids are simulated by using Fluent V.6.0. The numerical simulations are carried out for five cases divided by different values of bifurcation angle and area ratio. As a result of simulation, high wall shear stress is appeared at the bifurcated region. As increasing bifurcation angle, pressure drop is increasing. In addition, as the area is decreasing, pressure drop and wall shear stress is increasing.

• 한국도로학회논문집
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• 제10권1호
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• pp.87-95
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• 2008

형상이 일정하지 않은 구조에 충돌하는 차량의 탑승자 안전을 확보하기 위해서 그 구조물의 앞에 공간이 허용하는 한도의 깊이만큼 충격을 흡수하는 재료로 만든 모듈을 쌓아두는 방법을 생각할 수 있다. 충격흡수모듈로 사용되기 위해서는 재료가 충분한 에너지 흡수능력을 가져야 하고 동시에 탑승자의 안전을 확보할 수 있어야 한다. 본 논문에서는 에너지 흡수능력과 더불어 탑승자의 안전을 보장하기 위하여 충격흡수재료가 가져야 할 조건을 설명하고 auard-Guard 시스템 모듈, 샌드백, 재활용 타이어, 지오컨테이너, 지오셀 그리고 EPS 블록에 대한 정적압축실험을 실시하여 그 결과를 분석하였다. 이로부터 $30kg/m^{3}$의 밀도를 갖는 EPS 블록이 쿠션모듈로 사용되기 적합한 재료임을 보였다. 한편 시속 35.6km/h까지의 충돌조건으로 Drop Test를 실시하여 EPS블록의 정적특성과 동적특성간 큰 차이가 없음을 보여 주었으며 쿠션모듈로서의 성질을 개선시키기 위한 방안으로 EPS 블록에 공극을 두는 방안을 제안하고 공극이 있는 EPS블록에 대하여 Drop Test를 실시하여 EPS 블록을 이용한 충격흡수시설의 설계에 필요한 재료적 특성치를 제시하였다.

• 마이크로전자및패키징학회지
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• 제29권3호
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• pp.49-53
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• 2022

초박형 유리(Ultra-Thin Glass, UTG)는 디스플레이 보호용 커버 윈도우로 폴더블(foldable) 디스플레이에 사용되고 있으며, 향후에는 롤러블(rollable) 디스플레이나 다양한 플렉시블(flexible) 전자기기에 확대 적용될 것으로 예상되고 있다. 폴더블 디스플레이의 경우, 사용자들에 의해 굽힘과 터치 펜에 의해 충격을 받게 되고, 이 외에도 낙하 등 다른 외부충격에 쉽게 노출되어 있다. 초박형 유리는 100 ㎛ 이하로 두께가 얇고 취성하여 여러 외부 충격에 의해 쉽게 균열이나 파단이 발생할 수 있고, 이러한 균열이나 파단은 폴더블 디스플레이에 심각한 신뢰성 문제를 야기한다. 따라서, 본 연구에서는 초박형 유리의 내충격 신뢰성을 평가하는 펜 낙하 실험을 유한 요소 모델로 구성하고, 초박형 유리의 내충격 신뢰성을 향상시키기 위한 기계적 모델링을 진행하였다. 초박형 유리층 상부 혹은 하부에 보강층을 삽입했을 때, 펜 낙하에 의해 초박형 유리층에 작용하는 응력 메커니즘을 분석하였고, 그에 따라 신뢰성 향상을 위한 최적의 구조를 제시하였다. 또한 초박형 유리의 강도에 따른 최대 펜 낙하 높이를 예측할 수 있도록 펜 낙하 높이에 따라 초박형 유리층에 작용하는 최대 주 응력 값을 분석하였다.

• 한국지역사회생활과학회지
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• 제19권3호
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• pp.419-429
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• 2008

This study was conducted to analyze the characteristics of women's body somatotypes by direct measurements. Through the classification of degree of obesity and silhouette, women in their 20s who have a great interest in body somatotype can grasp their real somatotype and recognize their obesity rate and silhouette easily. The results are as follows: 1. Average sizes of subjects for this study were: height 160.3cm, weight 52.2kg, bust 83.7cm, waist 65.7cm, hips 91.1cm. And average values of each body mass index were: BMI 20.3, Rohrer Index 1.27, Vervaeck Index 84.8. 2. For the BMI value, the Average Numeric Index of normal somatotype was the highest, 76.9%. The Rohrer Index of underweight somatotype was 34.3% and the Average Numeric Index was 1.12. In the Vervaeck Index, underweight somatotype was 35.7%, and the average Numeric Index was 79.1, while the overweight somatotype was 7.4% of the Vervaeck Index and 100.8 of the Average Numeric Index. So the index which had the largest range of normal values from the same subjects, was the BMI, then the Rohrer Index, and finally, the Vervaeck Index in that order. 3. In the result of sorting bodies with silhouettes, when drop value were used to sort, N type (normal somatotype) was 69.4%, H type (one has similar sizes in waist size and hips) was 20.4% and A type (one has big hips) was 10.2% in that order. Among people in their early 20s, A type was 12.1%. H type was high, 22.8%, among women in their late 20s. When Sinozaki's method of classifying body types was used, ideal somatotype was 86.6%, A type was 7.4%, I type was 5.6% and X type was 0.5%. Women in their late 20s showed higher rates of ideal somatotype, the rates of A type and I type were lower than women in their early 20s.