• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.288-296
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• 2003

Generally, application of steel pipe pile as deep foundation member needs special requirement for the connection method between steel pipe pile and concrete footing. Even though two types of connection method are suggested in the related specification, type B-method is provident. To investigate real structural behavior of type B connection, several load tests are done with carefully designed experimental system. The purpose of this experiment is mainly focused on the understanding of actual behavior which can be predicted by design theory. At this research stage, vertical and lateral loading test are done for three types of specimen to review stress concentration, formation and behavior of imaginary RC column in the footing and effect of non-slip device installed in the steel pipe pile. The load resistance mechanism in these specific connection method is predicted based on both experimental results. The three-dimensional finite element modeling is also done for the purpose of comparison between numerical and experimental result. With all the results gained from experiment the structural behavior of imaginary RC column in the design concept is confirmed. The role of non-slip device is very important and it affects the resistance capacity with help of composite action of concrete and steel pipe pile.

• Membrane Journal
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• v.22 no.5
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• pp.369-380
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• 2012

A one-dimensional numerical model based on the energy and mass equations have been developed to predict the trans membrane water vapor flux and thermal efficiency under various operating conditions in Direct Contact Membrane Distillation (DCMD) process. The model validation have been carried out by experimental data from literature and showed good agreement. The effect of operating parameters such as brine inlet temperature and velocity, and distillate inlet temperature and velocity to increase water vapor flux and thermal efficiency were predicted by the steady-state model. The results showed that the inlet temperature and velocity in brine side are dominant factors to control the water vapor flux and thermal efficiency because the effect of inlet temperature and velocity in brine side showed the higher water vapor flux and thermal efficiency than that of inlet temperature and velocity in distillate side. The water vapor flux was increased 3.4 times in the range of 21.22 $kg/m^2h$ to 71.26 $kg/m^2h$ and the thermal efficiency was increased 37.5% in that of 0.556 to 0.765 with increasing brine inlet temperature from $60^{\circ}C$ to $95^{\circ}C$. Meanwhile, the water vapor flux was increased 30% in that of 27.91 $kg/m^2h$ to 36.33 $kg/m^2h$ and thermal efficiency increased 7.5% in that of 0.6 to 0.646 as the brine inlet velocity was increased from 60 m/h to 300 m/h.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.265-281
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• 2017

For shallow tunnel constructions, settlement of the ground surface is a main issue. Recent technical developments in shield TBM tunneling technique have enabled a decrease in such settlements based on tunneling with ground deformation controls. For this objective, the tail void grouting is a common practice. Generally surface settlements in a soil of low permeability occur during a tunnel construction but also during a long period after completion of the tunnel. The long-term settlements occur mainly due to consolidation around the tunnel. The consolidation process is caused and determined by the tail void grouting which leads to an excess pore water pressure in the vicinity of the tunnel. Because of this, the grouting pressure has a strong effect on the long-term settlements in the shield tunneling. In order to investigate this effect, a series of coupled hydro-mechanical 3D finite element simulations have been performed. The results show that an increase in grouting pressure reduces the short-term settlements, but in many cases, it doesn't lead to a reduction of the final settlements after the completion of consolidation. Thereby, the existence of a critical grouting pressure is identified, at which the minimal settlements are expected.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.69-74
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• 2015

The study investigated numerically the heat transfer and chemical reaction characteristics of a methane-steam reforming by using a 3-dimensional computational fluid dynamics (CFD) code (Fluent ver. 16.1). The fuel temperature and its species mole fractions were estimated for various Reynolds number in the reformer tube at different burner temperatures. The catalysts were modeled as the porous medium of nicrome in the reformer tube. We considered radiation effect as well as conduction and convective heat transfer because the methane-steam was reformed at very high temperature condition above 1000 K. For two different Reynolds numbers of 49,000 and 88,000 and the burner temperatures were in the range from 1,100 K to 1,300 K. At a low Reynolds number, the fuel temperature increased, leading to increase in hydrogen reforming. However, fuel temperature and hydrogen reforming decreased because of higher convective heat transfer from relatively low fuel temperature. Moreover, the hydrogen reforming also increased with burner temperature.

• Journal of the Institute of Convergence Signal Processing
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• v.11 no.1
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• pp.32-40
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• 2010

In this work, the method of acquiring the pupil function of optical system is proposed. The wavefront aberration and the intensity distribution of pupil can be analysed with the pupil function. This system can be adopted to the manufacturing line of optical pickup directly and also has good performance to analysing various property of optical instrument. It is one kind of inverse problem to get pupil functions by 3D beam data. The extended Nijboer-Zernike(ENZ) approach recently proposed by Netherlands research group is adopted to accompany to solve these inverse problem. The ENZ approach is one of a aberration retrieval method for which numerous approaches are available. But this approach is new in the sense that it use the highly efficient representation of pupil functions by means of their Zernike coefficients. These coefficients are estimated by using matching procedure in the focal region the theoretical 3D intensity distribution and measured 3D intensity distribution. The algorithm that can be applied more general circumstance such as high-numerical aperture instrument is developed by modifying original ENZ approach. By these scheme, MS windows based GUI program is developed and the good performance is verified with generated 3D beam data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.8
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• pp.717-724
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• 2013

Urea-SCR technology is known as one of the powerful NOx reduction systems for vehicles as well as stationary applications. For its consistent and reliable operation in vehicle applications, however, the freezing and melting of the urea solution in cold environments have to be resolved. In this study, therefore, a numerical study of three-dimensional unsteady problems was analyzed to understand the urea freezing and heating phenomena and heat transfer characteristics in terms of urea liquid volume fraction, temperature profiles, and phase change behavior in urea solutions with time by using the commercial software Fluent 6.3. As a result, it was found that the freezing phenomenon proceeds with a phase change from the tank wall to the center, whereas the melting phenomenon occurs faster in the upper part of the storage tank by natural convection and in the adjacent part of the coolant pipe than in other parts. Furthermore, approximately 190 s were required to obtain 1L of urea solution using a 4-coiled coolant heater under conditions of $70^{\circ}C$ and 200 L/h.

• Journal of Korea Water Resources Association
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• v.41 no.1
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• pp.75-85
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• 2008

The pale chub (Zacco platypus) is a dominant species that migrates locally and inhabits in rivers in Korea. The fish movement at confluences or hydraulic connections is very important especially for the life of small fish as pale chub. If main stream and off-channel habitats are connected with culverts, they would restrict the fish movement due to the high flow velocities and low depths. In foreign conturies, design flow conditions of fish friendly culvert, including flood flow capacity and fish-passage flow capacity, were assigned. Installation of culvert fishways is one way to improve the fish-passing capacity of culverts. On the contrary, in Korea, the design flow of culvert contains only the flood flow capacity. The effect of the fish passage with offset baffles was tested with the fixed velocity method in an experimental flume. As a result, An occasion velocity 1.2m/s, proportional success of pale chubs pass is maximum 20% improve than without baffle flume for energy dissipate. Offset baffle fishway(baffle height 5cm) provides that resting areas and/or a continuous channel of low velocity water in culverts. Especially, short baffle areas are domain where the pale chubs pass. And, FLOW-3D, a three dimentional numerical model, was used in order to evaluate detailed hydraulic characteristics and application possibility in a culvert fishway design.

• Journal of Environmental Science International
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• v.16 no.4
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• pp.523-532
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• 2007

This study utilized the 1/25,000 topographic map of the upper area from the Geum-ho watermark located at the middle of Geum-ho river from the National Geographic Information Institute. For the analysis, first, the influence of the size of critical area to the hydro topographic factors was examined changing grid size to $10m{\times}10m,\;30m{\times}30m\;and\;50m{\times}50m$, and the critical area for the formation of a river to $0.01km^2{\sim}0.50km^2$. It is known from the examination result of watershed morphology according to the grid size that the smaller grid size, the better resolution and accuracy. And it is found, from the analysis result of the degree of the river according to the minimum critical area for each grid size, that the grid size does not affect on the degree of the river, and the number of rivers with 2nd and higher degree does not show remarkable difference while there is big difference in the number of 1st degree rivers. From the results above, it is thought that the critical area of $0.15km^2{\sim}0.20km^2$ is appropriate for formation of a river being irrelevant to the grid size in extraction of hydro topographic parameters that are used in the runoff analysis model using topographic maps. Therefore, the GIUH model applied analysis results by use of the river level difference law proposed in this study for the explanation on the outflow response-changing characters according to the decision of a critical value of a minimum level difference river, showed that, since an ogival occurrence time and an ogival flow volume are very significant in a flood occurrence in case of not undertow facilities, the researcher could obtain a good result for the forecast of river outflow when considering a convenient application of the model and an easy acquisition of data, so it's judged that this model is proper as an algorism for the decision of a critical value of a river basin.

• Explosives and Blasting
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• v.26 no.2
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• pp.38-44
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• 2008

Recently, planning road construction in South Korea is focused on upgrading of the existing road by rerouting or restructuring. For this, roads under current construction in Korea go for more straight in its alignments and routing. Straight routing makes it all the more required to construct many mountain tunnels and bridges in Korea where mountains are so widely spread. Some portal of mountain tunnel is not rarely planed at high steep slope of mountain valley where it is not easy to secure working space for tunnel excavation. Reverse excavation is an alternative measure for excavation of tunnel portal at high steep slope. Construction in reverse excavation method has three important points requiring careful consideration: 1)planning of pilot tunnel in proper width, height, and length etc., 2)measure against the effect of one-side earth pressure to the direction of tunnel portal, 3)securing tunnel safety against shallow ground condition at portal zone. This paper intends to suggest applicable range of pilot tunnel for reverse excavation at the portal zone located at high steep slope, and shows result of study on the appropriateness of a reverse excavation by means of 3D numerical analysis. Result of 3D numerical analysis for reverse excavation at high steep slope shows that pilot tunneling will be applicable to start from the point $20{\sim}25m$ before the portal from inside the tunnel.

• The Journal of Engineering Geology
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• v.9 no.3
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• pp.187-206
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• 1999

A computer program to numerically predict the permeability tensor of fractured rocks is developed using information on discontinuities which Borehole Televiewer and Borehole Image Processing System (BIPS) provide. It uses orientation and thickness of a large number of discontinuities as input data, and calculates relative values of the 9 elements consisting of the permeability tensor by the formulation based on the EPM model, which regards a fractured rock as a homogeneous, anisotropic porous medium. In order to assess feasibility of the program on field sites, the numerically calculated tensor was obtained using BIPS logs and compared to the results of pumping test conducted in the boreholes of the study area. The degree of horizontal anisotropy and the direction of maximum horizontal permeability are 2.8 and $N77^{\circ}CE$, respectively, determined from the pumping test data, while 3.0 and $N63^{\circ}CE$ from the numerical analysis by the developed program. Disagreement between two analyses, especially for the principal direction of anisotropy, seems to be caused by problems in analyzing the pumping test data, in applicability of the EPM model and the cubic law, and in simplified relationship between the crack size and aperture. Aside from these problems, consideration of hydraulic parameters characterizing roughness of cracks and infilling materials seems to be required to improve feasibility of the proposed program. Three-dimensional assessment of its feasibility on field sites can be accomplished by conducting a series of cross-hole packer tests consisting of an injecting well and a monitoring well at close distance.