• Computers and Concrete
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• 제13권6호
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• pp.781-798
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• 2014

Estimating the workability of self-compacting concrete (SCC) is very important both in laboratories and on construction site. A method using visual information during the mixing process was proposed in this paper to estimate the workability of SCC. First, fourteen specimens of concrete were produced by a single-shaft mixer. A digital camera was used to record all the mixing processes. Second, employing the digital image processing, the visual information from mixing process images was extracted. The concrete pushed by the rotating blades forms two boundaries in the images. The shape of the upper boundary and the vertical distance between the upper and lower boundaries were used as two visual features. Thirdly, slump flow test and V-funnel test were carried out to estimate the workability of each SCC. Finally, the vertical distance between the upper and lower boundaries andthe shape of the upper boundary were used as indicators to estimate the workability of SCC. The vertical distance between the upper and lower boundaries was related to the slump flow, the shape of the upper boundary was related to the V-funnel flow time. Based on these relationships, the workability of SCC could be estimated using the mixing process images. This estimating method was verified by three more experiments. The experimental results indicate that the proposed method could be used to automatically estimate SCC workability.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.240-240
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• 2015

As Simpson et al. (1990) emphasized the importance of the straining process in the stratification and mixing in the estuarine circulation process, various researches have investigated on the relative contribution of each process to the overall potential energy anomaly dynamics. However, many numerical works have done only for two dimensional modeling along channel or the short distance cross sectional three dimensional simulations as Burchard et al. (2008) and the estuarine channel was not simulated so far. But, in the study on the physics of shallow coastal seas, spatial dimension in the three dimensional way affects significantly on results of a particular numerical model. Therefore, the comparison of two and three dimensional models is important to understand the real physics of mixing and stratification in an estuary. Also, as Geyer and MacCready (2013) pointed out that the lateral process seems to be important in determining the periodic stratifications, to study such process the three dimensional modeling must be required. The present study uses a numerical model to show the signification roles of each term of the time-dependent dynamic equation for the potential energy anomaly (PEA) in controlling along and lateral channel flows and different stratification structures. Moreover, we present the relationships between the ${\Phi}$-advection, the depth mean straining, vertical mixing and vertical advection can explain well how water level, salinity distribution and across velocity 2D model are slightly different from 3D.

• 대기
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• 제30권1호
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• pp.91-102
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• 2020

MERRA-2 ozone and atmospheric data are utilized to test the usefulness of reanalysis-based tracer transport analysis for ozone in the tropical tropopause layer (TTL). Transport and mixing processes related to the seasonal variation of TTL ozone are examined using the tracer transport equation based on the transformed Eulerian mean, and the results are compared to previously proposed values from model analyses. The analysis shows that the seasonal variability of TTL ozone is mainly determined by two processes: vertical mean transport and horizontal eddy mixing of ozone, with different contributions in the Northern and Southern Hemispheres. The horizontal eddy mixing process explains the major portion of the seasonal cycle in the northern TTL, while the vertical mean transport dominates in the southern TTL. The Asian summer monsoon likely contributes to this observed difference. The ozone variability and related processes in MERRA-2 reanalysis show qualitatively similar features with satellite- and model-based analyses, and it provides advantages of fine-scale analyses. However, it still shows significant quantitative biases in ozone budget analysis.

• 한국환경과학회지
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• 제25권3호
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• pp.405-415
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• 2016

We analyzed the micro-meteorological characteristics during typical steam fog over the Gumi Reservoir of Nakdong river with the field observation data for recent 2 year(1 April 2013~31 March 2015) collected by the national institute of meteorological research, KMA. Steam fog occur when the cold drainage flows over the warm water surface. As the sensible and latent heat from water are provided to the air, the instability of lower atmosphere is increased. The resultant vertical mixing of warm, moist air near water surface and cold air aloft causes the formation of status cloud. The convection strengthened by radiative cooling of the upper part of the stratus causes the fog to propagate downward. Also, the temperature at the lowest atmosphere is increased rapidly and the inversion near surface disappear by these processes when the fog forms. The increase of wind speed is observed because the downward transportation of momentum is caused by vertical mixing.

• 대한토목학회논문집
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• 제13권2호
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• pp.191-199
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• 1993

정상 2차원 이송확산(移送擴散) 방정식의 수치해석에 의하여 난류전단(亂流剪斷) 흐름에서의 정상(定常) 수평(水平) 선오염원(線汚染源)의 확산(擴散)을 모의하였다. 유속과 난류확산계수(亂流擴散係數)의 수심에 따른 변화가 없을 경우에 대한 해석해와 비교한 결과, 일정 유속 및 난류확산계수(亂流擴散係數)를 가정할 경우 수심방향 확산(擴散)을 과대평가하는 것으로 나타났다. 무차원화된 지배방정식에 따르면 수심방향 확산(擴散)을 지배하는 물리적 변수는 마찰계수(摩擦係數)뿐이다. 마찰계수(摩擦係數)에 대한 확산과정의 민감도(敏感度) 분석(分析)으로부터 수심방향 확산속도(擴散速度)는 대략 마찰계수(摩擦係數)의 제곱근에 비례함을 알 수 있었다. 오염원(汚染源)의 초기 방류위치에 따른 민감도(敏感度) 분석(分析) 결과, 가장 신속한 수심 방향 확산(擴散)을 가져오는 최적의 방류위치는 수심의 중간정보다 위쪽이며, 마찰계수(摩擦係數)가 커질수록 그 위치가 수면쪽에 가까와지는 것으로 나타났다.

• 대한토목학회논문집
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• 제33권2호
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• pp.495-506
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• 2013

본 연구에서는 전단류 분산이 이송과 난류에 의한 확산의 결합에 의해 발생한다는 Taylor (1954)의 가정을 바탕으로 개념적 모형을 구성하고, 이를 3차원 개수로에 적용하여 오염물질의 혼합과정을 재현할 수 있는 시간분리 혼합모형(Time-split Mixing Model; TMM)을 개발하였다. 개발된 모형은 연산자 분리 기법(operator split method)과 유사하게 혼합과정을 종방향 혼합과 횡방향 혼합으로 분리하고, 유속 연직편차에 의한 농도분리과정과 난류확산에 의한 연직방향 혼합과정을 순차적으로 반복 계산함으로써 2차원 이송-분산을 재현한다. 수치모의 결과, 제안된 모형은 수로벽면에 의한 농도중첩 효과를 잘 반영하고 있으며, Taylor 구간 내에서 2차원 이송-분산 모형의 해석해와 거의 일치하고 있음을 확인하였다(Chatwin, 1970). 본 모형은 하상경사, 하폭 대 수심 비, 혼합시간 등의 변화에 따라 분산 정도를 달리 재현하고 있으며, 산정된 종분산계수는 Elder(1959)가 제안한 상수값과는 달리 혼합시간에 따라 변화하는 양상을 나타냈다. 횡분산계수의 경우, Sayre와 Chang(1968), Fischer 등(1979)이 실험을 통해 제시한 값과 유사한 범위를 나타냈다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.236-239
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• 2003

The spent fuel slitting device is an equipment developed in order to feed UO$_2$pellet to the dry pulverizing/mixing device. In this study, we have compared and analyzed the handling method of the slitting and that of the pellet and hull, processing time, separating time for 20kgHM, the number of blades, on the existing slitting device using in DUPIC, and spent fuel management technology research and test facility. Also, we have compared and analyzed about an advantage and weak point, designing and producing, processing, establishment, operation, maintenance about the vertical and horizontal slitting device. Based on these results, we have developed the vertical slitting device. By using the results, we have enhanced the slitting processing time(over 40%)in comparison with DUPIC device, and it will is effectively applied to available data for designing and producing of the hot test facility.

• 한국정밀공학회지
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• 제21권8호
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• pp.97-105
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• 2004

The vertical roller mill is the important machine grinding and mixing various crude materials in the manufacturing process of portland cement. Table liner is one of grinding elements of vertical roller mill and is subjected to the cyclic bending stress by rollers and the centrifugal force by rotation of table. It demands $4{\times}10^7$ expense of life but has $4{\times}10^6~-8{\times}10^6$ cycle. It fractures at the edge of grinding path of outside roller The repair expense fur it amounts to 30% of total maintenance of vertical roller mill. Therefore, this study shows the fracture mechanism of table liner of vertical roller mill using HDM and fatigue analysis

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.163-169
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• 2003

The vertical roller mill is the important machine grinding and mixing various crude materials in the manufacturing process of portland cement. Table liner is one of grinding elements of vertical roller mill and is subjected to the cyclic bending stress by rollers load and the centrifugal force by rotation of table. It demands $4{\times}10^7$ cycle but has $4{\times}10^6{\sim}8{\times}10^6$ cycle. It fractures at the edge of grinding path of outside roller. The repair expense for it amounts to 30% of total maintenance of vertical roller mill. Therefore, this study shows the fracture mechanism of table liner for vertical roller mill using HDM and fatigue analysis

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1130-1135
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• 2004

The vertical roller mill is the important machine grinding and mixing various crude materials in the manufacturing process of portland cement. Vertical roller mill is subjected to the cyclic bending stress by rollers load. It demands $4{\times}10^7$ cycle but has $4{\times}10^6{\sim}8{\times}10^6$ cycle. It fractures at the edge of grinding path of outside roller. The repair expense for it amounts to 30% of total maintenance. Therefore, this study shows optimal design for vertical roller mill using DOE and neural network.