• The Journal of Engineering Geology
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• v.28 no.4
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• pp.529-540
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• 2018

Sand dam is a flow barrier commonly built on small or medium size sandy rivers to accumulate sand and store excess water for later use or increase the water table. The effectiveness of sand dam in increasing the water table and the amount of extractable groundwater is tested using numerical models. Two models are developed to test the hypothesis. The first model is to simulate the groundwater flow in a pseudo-natural aquifer system with the hydraulically connected river. The second model, a modified version of the first model, is constructed with a sand dam, which raises the riverbed by 2 m. In both models, the effect of groundwater abstraction is tested by varying the pumping rate. As the model results show the groundwater after the construction of the sand dam has increased significantly and the amount of extractable groundwater is also increased by many folds. Most importantly, in the second model, unlike the pseudo-natural aquifer system, the groundwater abstraction does not have a significant effect on the water table.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2672-2677
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• 2007

An investigation of low Reynolds number flow in nozzles and diffusers which are widely used in the valveless micropump is presented. Flow characteristics in the nozzle and diffuser are explained in view of viscous effect and flow oscillation induced by pumping membrane. These calculation results show that the rectification property of valveless micropump is due to a flow separation in the diffuser and the separation is largely originated from the flow oscillation. Under the assumptions of steady flow velocity profile and flow separation in the diffuser, simplified analytical models are provided to see the dependency of rectification on the micropump geometry. Geometric parameters of channel length, nozzle throat, chamber size, and converging/diverging angle are depicted through the analytical models in low Reynolds number flow, and the prediction and experimental results are compared. This theoretical study can be used to determine the optimum geometry of valveless micropump.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.3
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• pp.240-246
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• 2014

In order to develop a universal cryogenic piston pump of small size for increasing utilization of liquid hydrogen, dynamic compression performance of piston pump were evaluated and improvements were also discussed for piston rod and piston tip. The cryogenic piston pump has crosshead structure and inclined cup shape piston tip. As the results, it was found that i) insulation of heat flow from piston-rod part is required for stable operation ii) improving the self-clearance adjustment effect of piston tip and reducing piston eccentricity were desirable to promote pumping pressure and operating range.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.140-140
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• 2013

3차원 실장을 위한 TSV의 제조 공정 중에 발생할 수 있는 Cu의 돌출 거동에 대해 연구하였다. Cu의 돌출은 반도체를 제조할 때 고온(>$350^{\circ}C$) 공정인 BEOL (back end of line) 중에 발생하는 현상이다. Cu의 돌출은 Si과 Cu의 열팽창계수 차이에 의해 발생하는 현상으로 고온 공정 뿐만아니라 열충격 시험과 같은 열피로에 의해서 발생할 수 있다. 따라서 본 연구에서는 $-65^{\circ}C$에서 15분과 $150^{\circ}C$에서 15분을 1 사이클로 설정하여 0, 250, 500, 1000 사이클의 열충격 시험을 수행하였다. 열충격 시험 후 각 사이클에서의 Cu 돌출 거동과 Cu의 표면 거칠기 변화에 대해 연구하였다.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.04a
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• pp.447-450
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• 2004

This study was conducted to characterize groundwater and river-water fluctuations at a riverbank filtration site in Daesan-myeon adjacent to the Nakdong River, using time series analysis. Water levels from six observation wells from January 2003 to October 2003 were measured. The autocorrelation analysis indicates that the wells are divided into three groups: group 1 represents strong linearity and memory, group 2 intermediate linearity and memory, and group 3 weak linearity and memory. The analysis indicates that groundwater levels in different monitoring wells vary in response to river-water levels, groundwater withdrawal and seasonal rainfall. Cross-correlation was also divided into three groups. Group 1 shows the highest cross-correlation function (0.49 - 0.54) for a lag time of 0 hours, group 2 intermediate cross-correlation function (0.34 - 0.45), and group 3 the lowest cross-correlation function (0.23 - 0.25). Different cross-correlation functions among the 3 groups are interpreted as an effect of tile distance from the river to the pumping wells.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.819-823
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• 2006

본 연구는 SWAT-MODFLOW에 포함된 양수모듈 (MODFLOW의 well package와 SWAT의 결합)을 경안천 유역에 시험적으로 적용한 것이다. SWAT-MODFLOW 모형에서 SWAT 모형의 대수층과 MODFLOW 모형의 Well Package의 연계는 함양우물과 배출우물 모두 사용이 가능하며 이 중 얕은 대수층에서의 배출우물에 관한 적용을 수행하였다. 물이동의 목적지는 하천, 저수지일 수도 유역외일 수도 있는데 양수된 물이 유역 밖으로 소비되는 경우로 국한하였다. 이를 위해서 소유역내 MODFLOW의 셀에 배출정을 위치시키고 두 가지 경우의 양수량에 대해 지하수위 변화와 물수지 변화를 살펴보았다. 양수 후 일정기간이 지난 시점에서 양수정 영향권내 유역 단면(남-북방향)에서의 지하수위 변화를 살펴본 바 개선된 양수모듈은 유역내 물이동을 효과적으로 묘사하고 있으며 지하수 유출량의 감소분은 하천으로 옮겨져 지표수 증가분으로 계산되고 있음을 물수지 변화를 통해 확인할 수 있었다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.647-650
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• 2001

In case of bent axis type axial piston hydraulic pump or motor, hydrostatic bearing used to achieve the lubrication effect on the mechanical sliding contact areas between the following pairs ; piston shoe and swash plate, valve plate and cylinder block, piston and cylinder block, etc. In this research, we designed two pairs of spherical ball joint in witch connecting rod piston end. The one is not hydrostatic bearing, the other is designed with spherical hydrostatic bearing in point of view minimum pumping power loss. By varying supply pressure on the piston, we can know that it is possible to reduce the friction torque by using hydrostatic bearing designed one. Finally, by comparing the results of driving torque between the two models, it was verified that the spherical hydrostatic bearing is well designed.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.81.1-81.1
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• 2014

We utilized a 2-D PDR code developed by Lee et al. (2014) to explore the observed OH line fluxes toward embedded protostars. This 2-D PDR code combines self-consistently the FUV radiative transfer, gas-energetics, chemistry, and line radiative transfer. We modeled two sources, GSS30-IRS1 and Elias29, which show conspicuous line emission in the Herschel/PACS wavelength range. The physical and chemical structure for a given embedded source was derived by fitting the PACS CO line fluxes. After exploring various parameter spaces, we conclude that IR-pumping effect either by the central IR source and dust in-situ is insignificant for OH emission, unlike previous studies. We here present a possible solution for the observed OH fluxes, which require a high OH abundance and temperature at the inner-part of the UV heated cavity wall.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.112.2-112.2
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• 2014

We propose simultaneous monitoring observations of 22 GHz $H_2O$ and 43/86/129 GHz SiO masers toward ~15 evolved stars in order to investigate spatial structure and dynamical effect from SiO to $H_2O$ maser regions including mass-loss process and development of asymmetry in circumstellar envelopes. We also aim at investigating mutual association and difference between SiO and $H_2O$ masers for establishing SiO and $H_2O$ maser models coupled to hydrodynamical model of circumstellar envelope. In addition, the correlation and difference of SiO maser properties among J=1-0, J=2-1, and J=3-2 transition masers are traced according to different type of stars for constraining SiO pumping models. These scientific goals and target sources were determined based on KVN single dish and VLBI feasibility test observations at 4 bands. As a total observing time of every 2 month monitoring, about 90 and 360 hours (in average per year) are required for single dish and VLBI observations, respectively. From the 2014B observing season, these monitoring observations will be derived as one of KVN key science programs.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.125-129
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• 2004

Hydrating concrete pavement is typically subjected to temperature-induced stresses that drive cracking mechanisms at early concrete ages. Undesired cracking plays a key role in the long-term performance of concrete pavement systems. The loss of support beneath the concrete pavement due to curling caused by temperature changes in the pavement may induce several significant distresses such as punch out pumping, and erosion. The effect of temperature on these distress mechanisms is both significant and intricate. Because thermal conductivity dominates temperature flow in hydrating concrete over time, this material property is back-calculated by transforming governing equation of heat transfer and test data measured in laboratory. Theoretically, the back- calculated thermal conductivity simulates the heat movements in concrete very accurately. Therefore, the back- calculated thermal conductivity can be used to calibrate concrete temperature predicted by models.