• Nuclear Engineering and Technology
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• v.26 no.1
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• pp.108-118
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• 1994

A semi-empirical correlation has been developed for adiabatic interfacial friction factors in a long horizontal air-water countercurrent stratified flow conditions. Using a pipe and duct test sections, a series of experiments hate been conducted varying non-dimensional water depth and flow rates of air. On the basis of simultaneous measurement of the main flow parameters in a horizontal pipe and a duct, a semi-empirical correlation for the interfacial friction factor in a stratified flow regime has been developed employing a new concept of surface roughness in wavy flow. A total of 201 data point, including 15 concurrent pipe flow test data of others, have been used in the present analysis. A comparison between the data and the predictions of the present correlation shows that the agreement is within $\pm$30%.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.438-443
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• 2007

개수로 흐름에 대한 연구는 1700년대 중엽 Chezy에 의해 이론적인 기초를 다졌으며, 광범위하고 조직적인 관측연구는 Darcy(1803-1858)에 의해 약 150년 전에 폭 2m, 길이 600m에 이르는 수로에서 실험관측을 수행하고자 시도하였다. Darcy의 동료이자 후계자인 Bazin은 제한된 조건의 현장관측뿐 아니라 다양한 조건의 수로를 제작하여 실험관측을 수행하였으며 그의 실험자료는 Bazin 자신 뿐만 아니라 Manning이나 Ganguillet와 Kutter 등 여러 연구자들의 경험식 개발에도 이용되었다. Nikuradse(1933)의 균일조도 원형관수로 실험결과로부터 관로 흐름은 층류, 천이층류, 완난류, 천이난류, 전난류 등 다섯 종류의 흐름특성을 가지고 있음을 확인하였고 Bazin(1829-1917)과 varwick(1945)의 실험결과로부터 개수로 흐름에서도 관로 흐름과 마찬가지로 층류, 천이층류, 완난류, 천이난류, 전난류 등 다섯가지의 흐름특성이 존재함을 알 수 있다. 본 연구에서는 기존의 지수형 마찰계수 산정식에서 단순히 조고만의 함수였던 ${\alpha}$에 물의 기본적인 성질인 표면장력, 점성력, 밀도와 자연 하천의 경사, 수심, 수면, 폭, 조고의 영향을 고려한 수심에 관한 무차원수 $Y_h$, 수면 폭에 관한 무차원수 $Y_b$, 조고에 관한 무차원수 $Y_k$를 도입하였다. 따라서 개수로 흐름 해석에 있어서 기존의 마찰계수 산정치보다 여러 영향을 반영하여 정확한 값을 산정할 수 있을 것으로 판단된다.

• Journal of the Korean GEO-environmental Society
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• v.15 no.3
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• pp.21-32
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• 2014

This Research have suggested the new estimation method using parameter estimation algorithm to substitute established velocity and friction factor calculation equation. Established calculation equation has some difficulties for estimation and reflecting exactly flow specification cause parameter uncertainty and material uncertainty governed real phenomenon, so this research has used system modeling method for flow specification estimation and suggested estimation method.

• Nuclear Engineering and Technology
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• v.23 no.4
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• pp.401-409
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• 1991

This work is concerned with the development of an analytical model to predict the friction in longitudinally finned rod bundles. Such bundles are currently considered in KMRR design. The present model assumes the validity of the Law of the Wall over entire flow area. The flow channel area is divided into the interfin region and a number of element channels, and the algebraic form of the Law of the Wall is integrated over each element channel and interfin region to yield an analytic expression for the pressure drop. The model reasonably predicts the 6 fin KMRR data, and overpredicts the 8 fin data about 15 percent.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.61-62
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• 2008

Closed field unbalanced magnetron sputtering 방법을 이용하여 CrZr-Si-N 박막을 증착하였다. Si Target power의 변화에 따라 박막을 증착하여 XRD, SEM, XPS, GDOES, AFM, XPS, Nanoindentation을 이용하여 박막의 미세구조, 성분분석, 표면 조도, 경도를 측정하였다. $500^{\circ}C$에서 annealing한 후 상온에서의 박막의 경도와 비교하였고, 상온과 $500^{\circ}C$에서 마모 실험을 행한 후 마찰 계수를 측정하여 비교하였다. $Cr_{39.4}Zr_{12.3}N_{48.3}$ 박막은 $500^{\circ}C$ annealing 후 경도는 30 GPa에서 24 GPa로 감소하였고 마찰계수는 0.23에서 0.81로 약 4배 증가하였다. $500^{\circ}C$ annealing 후 $Cr_{34.6}Zr_{10.6}-Si_{6.4}-N_{48.4}$ 박막의 경도는 30 GPa로 상온에서의 경도 32 GPa과 비슷하였고 $500^{\circ}C$와 상온에서 수행된 마모시험 결과는 $500^{\circ}C$에서 마찰계수 0.43으로 상온 마모시험 결과와 거의 비슷한 결과를 보였다. 상온의 경우 Si 함량에 따른 기계적 특성 및 마모특성의 변화는 거의 없었다. 그러나 $500^{\circ}C$ annealing 후 CrZi-Si-N 박막의 기계적 특성 및 마모특성은 Si 함량에 따라 큰 차이를 나타내었다. 이러한 결과들을 통해 Si 첨가가 CrZrN 박막의 고온 안정성 향상에 기여함을 확인할 수 있었다.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.181-189
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• 2006

This study analyzes the effects of the curvature friction coefficient, the wobble friction coefficient, and the increased strength of concrete, reinforced tendon on optimum de signs by using the optimum-design program, to minimize the cost of a PSC box girder bridge using the full staging method. The objective of this study is to find a proper tendon for the friction coefficient, and thereafter, to indicate the direction of the study development about tendons and to indicate the direction of a study on the increased strength of used materials. This program used the SUMT procedure and Kavlie's extended-penalty function to allow infeasible design points in the process. Powel's direct method was used in searching design points, and the gradient approximate method was used to reduce the design hours.

• Water for future
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• v.29 no.4
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• pp.187-198
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• 1996

A numerical model for unsteady dispersion of horizontal line source in turbulent shear flow is developed. A fractional step finite difference method is used which splits the unsteady two-dimensional advective diffusion equation into the longitudinal advection and the vertical diffusion equations, and solves them alternately for half time intervals by the Holly-Preissmann scheme and the Crank-Nicholson scheme, respectively. The developed numerical model is verified using a semi-analytic solution for steady dispersion in turbulent shear flow. Dispersion of an instantaneous plane source in turbulent shear flow is analyzed using the model. The degree of mixing at the same dimensionless time is almost the same regardless of the friction factor, and the travel distance required to reach a certain degree of mixing is inversely proportional to the square root of the friction factor.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.137-137
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• 2019

돌출줄눈은 산지하천의 만곡부의 빠른 유속을 감소시키기 위하여 활용된다. 본 연구에서는 친환경 디자인의 나무줄기 돌출줄눈(Tree Trunk Rip, TTR)과 사다리꼴 돌출줄눈(Trapezoid Rip, TR)의 흐름저항을 비교 분석하기 위하여 개수로 수리실험을 수행하였다. 실험은 길이 9m, 폭이 0.6m이며 경사가 0.0035로 고정된 개수로의 한쪽 측벽에 돌출줄눈을 설치하여 진행하였다. 사다리 꼴 돌출줄눈의 형상은 밑변 각이 $63^{\circ}$이며 무차원 설치간격 ${\lambda}_{nv}$가 6, 9, 12인 경우이다. 나무줄기 돌출줄눈의 기본 형상은 사다리꼴이고 표면은 나무껍질 무늬이며 ${\lambda}_{nv}$가 약 10이다. 나무줄기 돌출줄눈의 간격은 사다리꼴 돌출줄눈의 최적 설치 간격 9~12배 범위에 해당되고 평균 마찰계수는 사다리꼴 돌출줄눈의 9~12배의 평균 마찰계수 범위에 포함되었다. 사다리꼴 돌출줄눈의 ${\lambda}_{nv}$가 9, 12일 때의 전체 저항에 대한 형상저항의 비는 평균 $69.4{\pm}5.8%$였으며 나무줄기 돌출줄눈은 $70.2{\pm}2.1%$로 사다리꼴 돌출줄눈과 유사하다. 산지하천 흐름저항을 위한 돌출줄눈 설치에 있어 친환경적 디자인을 고려한 나무줄기가 사다리꼴 돌출줄눈보다 활용도가 클 것으로 기대된다.

• Journal of Korea Water Resources Association
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• v.44 no.7
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• pp.553-563
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• 2011

According to the improvement of computer's performance, the development of Geographic Information System (GIS), and the activation of offering information, a distributed model for analyzing runoff has been studied a lot in recently years. The distribution model is a theoretical and physical model computing runoff as making target basin subdivided parted. In the distributed model developed by this study, the volume of runoff at the surface flow is calculated on the basis of the parameter determined by landcover data and a two-dimensional diffusion wave equation. Most of existing runoff models compute velocity and discharge of flow by applying Manning-Strickler's mean velocity equation and Manning's roughness coefficient. Manning's roughness coefficient is not matched with dimension and ambiguous at computation; Nevertheless, it is widely used in because of its convenience for use. In order to improve those problems, this study developed the runoff model by applying not only Manning-Strickler's equation but also Chezy's mean velocity equation. Furthermore, this study introduced a power law of exponential friction factor expressed by the function of roughness height. The distributed model developed in this study is applied to 6 events of fan-shape basin, oblong shape test basin and Anseongcheon basin as real field conditions. As a result the model is found to be excellent in comparison with the exiting runoff models using for practical engineering application.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.689-695
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• 2012

The friction factor in a rod bundle and the loss coefficient at a spacer grid were examined. As a test section, 25 smooth rods, 9.5 mm in diameter and 2000 mm in length, were prepared and installed in a $5{\times}5$ square array in a square channel. In this case, the P/D (Pitch-to-Diameter ratio) was 1.35. In this work, plain (i.e., no mixing vanes), split-vane, and hybrid-vane spacer grids were tested. In a bare rod bundle (i.e., no spacer grid), the measured friction factors were in good agreement with the previous correlations. Among the spacer grids tested, the hybrid-vane spacer grid presented the largest friction factor in the rod bundle and loss coefficient. This may be because of the flow pattern change induced by large relative plugging of the flow cross section and mixing vane geometry. At Re=$5{\times}10^5$, the predicted loss coefficients of plain, splitvane, and hybrid-vane spacer grids were approximately 0.79, 0.80, and 0.88, respectively.