• 한국전산구조공학회논문집
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• 제30권4호
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• pp.363-370
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• 2017

본 논문에서는 원통형 혼합기를 대상으로 블레이드의 각도, 길이, 개수 및 블레이드와 탱크 바닥과의 간극을 설계변수로 선정하고, 각각의 설계변수가 혼합성능에 미치는 영향을 분석하였다. 이산요소법을 이용하여 임펠러 회전에 의한 고체 입자의 혼합공정을 해석하였으며, 혼합지수를 도입하여 혼합성능을 정량적으로 평가하였다. 다양한 설계변수의 조합을 고려한 실험계획법으로 설계변수의 주효과와 교호작용을 분석함으로써, 블레이드 각도가 입자의 혼합성능에 가장 지배적인 영향을 미치며 간극의 영향은 상대적으로 작다는 결론을 도출할 수 있었다. 또한 가장 우수한 혼합성능을 보이는 설계변수의 조합을 제시하였다.

• 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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.281-285
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• 2002

A new method of dynamic contact force measurement between a pantograph and a contact wire is proposed in this paper The method does not require design modification of an original pantograph in order to install sensors such as load cells. Contact forces can be expressed as the sum of vertical shear forces at the support points and inertial forces. Using specially-designed strain gage rosettes. vertical shear forces at the supported points can be measured without noise mixing and thermal effects. In order to obtain contact forces from shear forces, 3 inertial force compansation methods are proposed and compared in this paper. By validation process, the new proposed measurement method is verified to be applicable to the on-line current collection test.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1221-1228
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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 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 and makes the estimation for safety of vertical roller mill.

• 한국해양학회지
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• 제25권3호
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• pp.151-159
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• 1990

조류에 의한 해수의 혼합이 활발한 연안역에서 동물 플랑크톤이 주야 수직 이동의 능력이 있는지를 파악하기 위하여 채집량의 주야 차이를 살펴 보았다. 상대적으로 크 기가 큰 요각류, Mysid, 모약류, 이매폐 유생 등은 야간에 표층에서 많이 채집되어 주 야 수직이동이 있을 가능성을 시사하고 있었다. 본 연구 결과와 과거의 방법 등을 통 하여 한국 서해 연안역에서 적절한 채집방법에 대하여 살펴 보았다.

• Nuclear Engineering and Technology
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• 제42권4호
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• pp.382-393
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• 2010

Thermal mixing by steam jets in a pool is dominantly influenced by a turbulent water jet generated by the condensing steam jets, and the proper prediction of this turbulent jet behavior is critical for the pool mixing analysis. A turbulent jet flow induced by a steam jet discharged through a vertical upward single hole into a subcooled water pool was subjected to computational fluid dynamics (CFD) analysis. Based on the small-scale test data derived under a horizontal steam discharging condition, this analysis was performed to validate a CFD method of analysis previously developed for condensing jet-induced pool mixing phenomena. In previous validation work, the CFD results and the test data for a limited range of radial and axial directions were compared in terms of profiles of the turbulent jet velocity and temperature. Furthermore, the behavior of the turbulent jet induced by the steam jet through a horizontal single hole in a subcooled water pool failed to show the exact axisymmetric flow pattern with regards to an overall pool mixing, whereas the CFD analysis was done with an axisymmetric grid model. Therefore, another new small-scale test was conducted under a vertical upward steam discharging condition. The purpose of this test was to generate the velocity and temperature profiles of the turbulent jet by expanding the measurement ranges from the jet center to a location at about 5% of $U_m$ and 10 cm to 30 cm from the exit of the discharge nozzle. The results of the new CFD analysis show that the recommended CFD model of the high turbulent intensity of 40% for the turbulent jet and the fine mesh grid model can accurately predict the test results within an error rate of about 10%. In this work, the turbulent jet model, which is used to simply predict the temperature and velocity profiles along the axial and radial directions by means of the empirical correlations and Tollmien's theory was improved on the basis of the new test data. The results validate the CFD model of analysis. Furthermore, the turbulent jet model developed in this study can be used to analyze pool thermal mixing when an ellipsoidal steam jet is discharged under a high steam mass flux in a subcooled water pool.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.389-397
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• 2015

The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2006년도 Proceedings of ISRS 2006 PORSEC Volume I
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• pp.21-24
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• 2006

Processes controlling the interannual variation of mixed layer temperature (MLT) averaged over the NINO3 domain ($150-90^{\circ}W$, $5^{\circ}N-5^{\circ}S$) are studied using an ocean data assimilation product that covers the period of 1993 to 2003. Advective tendencies are estimated here as the temperature fluxes through the domain's boundaries, with the boundary temperature referenced to the domain-averaged temperature to remove the dependence on temperature scale. The overall balance is such that surface heat flux opposes the MLT change but horizontal advection and subsurface processes assist the change. The zonal advective tendency is caused primarily by large-scale advection of warm-pool water through the western boundary of the domain. The meridional advective tendency is contributed mostly by Ekman current advecting large-scale temperature anomalies though the southern boundary of the domain. Unlike many previous studies, we explicitly evaluate the subsurface processes that consist of vertical mixing and entrainment. In particular, a rigorous method to estimate entrainment allows an exact budget closure. The vertical mixing across the mixed layer (ML) base has a contribution in phase with the MLT change. The entrainment tendency due to temporal change in ML depth is negligible comparing to other subsurface processes. The entrainment tendency by vertical advection across the ML base is dominated by large-scale changes in wind-driven upwelling and temperature of upwelling water. Tropical instability waves (TIWs) result in smaller-scale vertical advection that warms the domain during La Ni? cooling events. When the advective tendencies are evaluated by spatially averaging the conventional local advective tendencies of temperature, the apparent effects of currents with spatial scales smaller than the domain (such as TIWs) become very important as they redistribute heat within the NINO3 domain. However, such internal redistribution of heat does not represent external processes that control the domain-averaged MLT.

• 대기
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• 제17권1호
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• pp.69-86
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• 2007

The characteristics of the dual-Doppler wind retrieval method based on a three dimensional variational (3DVAR) conception were investigated from the following four points of view; the sensitivity of the number of iteration, the effect of the weak constraint term, the effect of the smoothness term, and the sensitivity of the error mixing ratio of the radial velocities. In the experiment, the radial velocities relative to the Gosan and Jindo radar sites of the Korea Meteorological Administration (KMA) were calculated from the forecasting of the WRF (Weather Research and Forecast; Skamarock, 2004) model at 1330 UTC 30 June 2006, which is the one and half hour forecast from the initial time, 1200 UTC on that day. The results showed that the retrieval performance of the horizontal wind field was robust, but that of the vertical wind was sensitive to the external conditions, such as iteration number and the on/off of the weak constraint term. The sensitivity of error mixing ratio was so large that even the horizontal wind retrieval efficiency was reduced a lot. But the sensitivity of the smooth term was not so large. When we applied this method to the real mesoscale convective system (MCS) between the Gosan and Jindo radar pair at 1430 UTC 30 June 2006, the wind structure of the convective cells in the MCS was consistently retrieved relative to the reflectivity factor structure. By comparing the vertical wind structure of this case with that of 10 minutes after, 1440 UTC 30 June 2006, we got the physical consistency of our method.

• 대한토목학회논문집
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• 제30권2C호
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• pp.77-84
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• 2010

연약지반에 지하차도의 기초로서 심층혼합처리공법을 적용하였다. 개량체는 실내배합실험으로 구한 배합비와 강도기준을 만족하는 치환율을 적용하였다. 개량체와 지반의 강성비 및 타설중심거리를 변화시키며 개량체와 지반에 발생한 응력 및 변위를 분석하였으며 지하차도의 부등침하에 미치는 영향을 분석하였다. 구조물의 침하기준과 부등침하를 만족하는 치환율은 10~35%이다. 강성비를 변화시킨 결과 강성비차가 30이상인 경우에는 응력집중 때문에 개량체에 769.2kPa까지 발생하여 기준을 초과한다. C.T.C가 5m인 경우에 지반으로 응력이 전이되어 응력이 커지기 때문에 설치간격을 고려하여야 한다. 복합지반강도 정수를 산정하여 수치해석 한 결과 연직침하는 0.6~1.56cm, 각변위 1/909~1/510이다.