• 한국지하수토양환경학회지:지하수토양환경
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• 제15권2호
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• pp.1-9
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• 2010

Estimations of porosity and bulk density, particle size analysis of soli samples, tracer test and slug test were performed in a petroleum contaminated area of Kangwon for understanding characteristics of the aquifer. Porosities of the samples were estimated 0.158~0.257, and bulk densities were estimated as $1.73\sim2.10\;g/cm^3$. Majority proportion of the soil samples was 0.5~1.0 mm size. In the soil texture triangle, all samples were distributed at sand area. Uniformity coefficients were estimated as 7.71~10.39, and thus all samples were poorly-sorted. In the tracer test, Darcy velocity was estimated to $4.8\times10^{-6}$ cm/day, effective porosity was 0.175, and longitudinal dispersivity was 0.1 m. According to the slug test, hydraulic conductivities of the test wells were estimated as $2.243\times10^{-2}\sim1.634\times10^{-2}$ cm/sec. These hydrogeologic parameters can be used for efficient remediation design of the petroleum contaminated area.

• Journal of Advanced Marine Engineering and Technology
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• 제34권8호
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• pp.1084-1093
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• 2010

화염 전파 특성을 나타내는 G 방정식에 기초한 Sub-grid Scale연소 모델을 이용하여 보염기 주위의 난류 예혼합 연소 해석에 관한 대 와동 모사를 수행하였다. Dynamic SGS 모델이 G방정식에 도입되었으며, 삼각형의 보염기 배면의 예혼합 연소 유동에 의해 검증되었다. 해석결과는 실험결과와의 비교를 통해 속도와 온도분포를 잘 예측하고 있음을 확인하였다.

• Wind and Structures
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• 제22권6호
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• pp.663-684
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• 2016

Conical vortices generated at the corner regions of large-span flat roofs have been investigated by using the Particle Image Velocimetry (PIV) technique. Mean and instantaneous vector fields for velocity, vorticity, and streamlines were measured at three visual planes and for two different flow angles of $15^{\circ}$. The results indicated that conical vortices occur when the wind is not perpendicular to the front edge. The location of the leading edge corresponding to the negative peak vorticity and maximum turbulent kinetic energy was found at the center of the conical vortex. The wind pressure reaches the maximum near the leading edge roof corner, and a triangle of severe suctions zone appears downstream. The mean pressure in uniform flow is greater than that under turbulent flow condition, while a significant increase in the fluctuating wind pressure occurs in turbulent streams. From its emergence to stability, the shape of the vortex cross-section is nearly elliptical, with increasing area. The angle that forms between the vortex axis and the leading edge is much smaller in turbulent streams. The detailed flow structures and characteristics obtained through FLUENT simulation are in agreement with the experimental results. The three dimensional (3-D) structure of the conical vortices is clearly observed from the comprehensive arrangement of several visual planes, and the inner link was established between the vortex evolution process, vortex core position and pressure distribution.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1777-1783
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• 2012

본 논문에서는 DC모터의 출력특성을 개선할 수 있는 새로운 구조의 DC모터 구동회로를 설계하였고 이 회로를 이용한 콘트롤러를 개발하였다. 설계된 구동 회로에 의하여 콘트롤러는 자체발진회로의 스위칭 신호를 갖는 트랜스포머를 이용하여 연속적으로 DC모터를 구동할 수 있다. 또한 최대속도시, 제어회로의 기준전압 값을 삼각파보다 높게 유지할 수 있고 모터 구동 FET를 항상 온 값을 가지도록 하여 최대출력을 얻을 수 있도록 한다. 제안된 구동회로를 활용하여 24V-500W급 DC모터속도 컨트롤러를 개발하였고 소형전동차를 제작하고 구동시험을 실시하였다. 구동테스트 및 특성 측정결과, 구동전류 12A로써 DC모터의 전진 및 후진 속도를 연속 가변 할 수 있음을 보였다. 그 밖에 과전류 감시기능, 모터과열 감시기능의 정상동작을 확인하였으며, 배터리 잔량이 20~100%까지 6단계로 표시할 수 있음을 확인하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권6호
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• pp.615-624
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• 2014

핀-튜브 열교환기는 산업용 보일러, 라디에이터, 냉동기 등에 많이 사용되고 있어 열교환기의 성능향상을 위한 다양한 연구가 진행되고 있다. 본 연구에서는 Plain형 핀-튜브 열교환기에 대해 가로피치, 와류발생기위치, 튜브표면의 돌기형상 및 돌기개수 등의 변화에 따른 열전달 및 압력강하 특성을 이론적으로 해석하였다. CFD 해석시 경계조건으로는 SST 난류모델을 적용하였으며, 튜브표면의 온도는 333 K이고, 입구측 공기의 온도와 속도는 423~438 K, 1.5~2.1 m/s로 가정하였다. 해석결과로는 열전달계수는 가로피치에 대한 영향은 큰 차이가 없으며, 열전달특성은 와류발생기 설치가 튜브 전방부에 위치할수록 양호한 것으로 나타났다. 또한 튜브표면의 돌기형상은 열전달 및 압력강하 특성에서 원형이 톱니형과 삼각형보다 적절하였으며, 16개 원형 돌기형상이 가장 양호하였다.

• 한국운동역학회지
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• 제26권1호
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• pp.115-126
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• 2016

Objective: The purpose of this study was to investigate plantar foot pressure and static balance according to the type of insole in the elderly. Methods: Thirteen elderly (mean age: $67.08{\pm}2.25years$, mean height: $159.63{\pm}9.64cm$, mean body weight: $61.48{\pm}9.06kg$) who had no previous injury experience in the lower limbs and a normal gait pattern participated in this study. Three models of insoles of the normal, 3D, and triangle types were selected for the test. The Pedar-X system and Pedar-X insoles, 3.3 km/h of walking speed, and a compilation of 20 steps walking stages were used to analyze foot-pressure distribution. Static balance test was conducted using Gaitview AFA-50, and balance (opening eyes, closing eyes) was inspected for 20 s. One-way ANOVA was conducted to test the significance of the results with the three insoles. p-value of less than .05 was considered statistically significant. Results: The mean foot pressure under the forefoot regions was the lowest with the 3D insole during treadmill walking (p<.05). The mean value under the midfoot was the highest with the 3D insole (left: p<.05, right: p<.01). The mean value under the rearfoot was the lowest with the 3D insole (p<.001). The maximum foot pressure value under the foot regions was the lowest on both sides of the forefoot with the 3D insole. A statistically significant difference was seen only in the left foot (p<.01). The maximum value under the midfoot was the highest with the 3D insole (p<.001). No statistically significant difference was detected on the values under the rearfoot. In the case of vertical ground reaction force (GRF), statistically significant difference was seen only in the left side rearfoot (p<.01). However, static balance values (ENV, REC, RMS, Total Length, Sway velocity, and Length/ENV) did not show significant differences by the type of insole. Conclusion: These results show that functional insoles can decrease plantar pressure and GRF under the forefoot and rearfoot. Moreover, functional insoles can dislodge the overload of the rearfoot and forefoot to the midfoot. However, functional insoles do not affect the static balance in the elderly.