• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1199-1213
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• 2011

Slurry type shield would be very effective for the tunnelling in a sandy ground, but low slurry pressure could cause a tunnel face failure or a ground settlement in front of the tunnel face. Thus, the stability of tunnel face could be maintained by applying an excess slurry pressure that is larger than the active earth pressure. However, the slurry pressure should increase properly because an excessively high slurry pressure could cause the slurry flow out or the passive failure of the frontal ground. It is possible to apply the high slurry pressure without passive failure if a horizontal impermeable layer is located in the ground in front of the tunnel face, but its location, size, and effects are not clearly known yet. In this research, two-dimensional model tests were carried out in order to find out the effect of a horizontal impermeable layer for the slurry shield tunnelling in a saturated sandy ground. As results, larger slurry pressure could be applied to increase the stability of the tunnel face when the impermeable layer was located in the ground above the crown in front of the tunnel face. The most effective length of the impermeable grouting layer was 1.0~1.5D, and the location was 1.0D above the crown level. The safety factor could be suggested as the ratio of the maximum slurry pressure to the active earth pressure at the tunnel face. It could also be suggested that the slurry pressure in the magnitude of 3.5~4.0 times larger than the active earth pressure at the initial tunnel face could be applied if the impermeable layer was constructed at the optimal location.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.361-368
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• 2010

In this paper, the parallel algorithm using MPI(Message-Passing Interface) library is introduced in order to improve numerical efficiency for the staggered method for nearly incompressible and impermeable porous media which was introduced by Park and Tak(2010). The porous media theory and the staggered method are also briefly introduced in this paper. Moreover, we account for MPI library for blocking, non-blocking, and collective communication, and propose combined the staggered method with the blocking and nonblocking MPI library. And then, we present how to allocate CPUs on the staggered method and the MPI library, which is related with the numerical efficiency in order to solve unknown variables on nearly incompressible and impermeable porous media. Finally, the results comparing serial solution with parallel solution are verified by 2 dimensional saturated porous model according to the number of FEM meshes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.2
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• pp.61-68
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• 2018

This study was conducted to propose the optimum minimum requirement of cutoff system composed of the impermeable soil layer and vertical barrier in offshore landfill for prevention pollution leakage by seepage, advection, and dispersion numerical analyses under steady state. According to the study results, the minimum requirement of impermeable soil layer is below $1{\times}10^{-6}cm/s$ of hydraulic conductivity with more than 500 cm thickness or a system with equivalent cutoff effect. The minimum requirement of vertical barrier is below $1{\times}10^{-6}cm/s$ of hydraulic conductivity with more than 50 cm thickness or a system with equivalent cutoff effect. In addition, the vertical barrier should be embedded enough to seal securely with the impermeable soil layer for working cutoff effect.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.12
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• pp.1635-1643
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• 2000

The present work investigates a heat transfer phenomenon at the interface between a porous medium and an impermeable wall. In an effort to appropriately describe the heat transfer phenomenon at the interface, the heat transfer at the interface between the microchannel heat sink, which is an ideally organized porous medium, and the finite-thickness substrate is examined. From the examination, it is clarified that the he heat flux distribution at the interface is not uniform for the impermeable wall with finite thickness. On the other hand, the first approach, based on the energy balance for the representative elementary volume in the porous medium, is physically reason able. When the first approach is applied to the thermal boundary condition, and additional boundary condition based on the local thermal equilibrium assumption at the interface is used. This additional boundary condition is applicable except for the very th in impermeable wall. Hence, for practical situations, the first approach in combination with the local thermal equilibrium assumption at the interface is suggested as an appropriate thermal boundary condition. In order to confirm our suggestion, convective flows both in a microchannel heat sink and in a sintered porous channel subject to a constant heat flux condition are analyzed. The analytically obtained thermal resistance of the microchannel heat sink and the numerically obtained overall Nusselt number for the sintered porous channel are shown to be in close agreement with available experimental results when our suggestion for the thermal boundary conditions is applied.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.193-198
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• 2011

This study aimed to provide basic data for permeable pavement application upon design and installation stages by analyzing the effect of permeable pavement used on the facility area rather than using non-point pollutants treatment facility upon development business in accordance with recent trend. To perform this study, the area of development target was separately applied as impermeable and permeable developments so as to compare and analyze the economics of cut pollution load and installation construction cost. Consequently, the processing amount and cut load of non-point pollutant sources are influenced much by permeable and impermeable developments, and it was turned out to be better to develop target river area as permeable area rather than installing non-point pollutants treatment facility of equipment type or natural type upon development to yield smaller discharge load. If we can prepare a countermeasure regulating impermeable area ratio to certain level to manage non-point pollutants upon development based on this result, we can minimize the source of pollution caused by the development.

• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.44-51
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• 2008

The planning and design of coastal structures against wave attack is required to accurately predict wave transformation, wave run-up, and fluid. particlevelocities an a slope. On tire other hand, in tire swash and surf zones of a natural beach, where coastal erosion and accretion occur at tire land-sea boundary, hydrodynamic analysis is essential. In this study, a RBREAK2 numerical model was created based on the nonlinear shallow water equation and laboratory measurements were carried out in terms of tire free surface elevations and velocities for tire cases of regular and irregular waves on 1 : 10 and 1 : 5 impermeable slopes. The data were used to evaluate tire applicability and limitations of tire RBREAK2 numerical model. The numerical mode1 could predict tire cross-shore variation of the wave profile reasonably well, but showed more accurate results for slopes that were steeper than 1 : 10. Except near tire wave crest, tire computed depth averaged velocities could represent tire measured profile below tire trough level fairly well.

• Journal of Ocean Engineering and Technology
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• v.30 no.6
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• pp.484-497
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• 2016

In order to understand the characteristics of the topography change in front of an impermeable breakwater, a coupled model for a two-way analysis of the existing LES-WASS-2D and newly developed morphodynamic model was suggested. A comparison to existing experimental results revealed that the results computed using the 2-D hydro-morphodynamic model were in good agreement with the experimental results for the wave form, pore water pressure in the seabed, and topographical change in front of a submerged breakwater. It was shown that the two-way model suggested in this study is applicable to a morphological change in the seabed around a submerged breakwater. Then, using the numerical results, the topographical changes in front of an impermeable submerged breakwater were examined in relation to partial standing waves. Moreover, the characteristics of the local scour depths in front of them are also discussed in relation to incident wave conditions, sediment qualities, and submerged breakwater shapes.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.4
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• pp.347-370
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• 2011

Slurry type shield would be very effective for the tunnelling in a sandy ground, when the slurry pressure would be properly adjusted. Low slurry pressure could cause a tunnel face failure or a ground settlement in front of the tunnel face. Thus, the stability of tunnel face could be maintained by applying an excess slurry pressure that is larger than the active earth pressure. However, the slurry pressure should increase properly because an excessively high slurry pressure could cause the slurry flow out or the passive failure of the frontal ground. It is possible to apply the high slurry pressure without passive failure if a horizontal impermeable layer is located in the ground in front of the tunnel face, but its location, size, and effects are not clearly known yet. In this research, two-dimensional model tests were carried out in order to find out the effect of a horizontal impermeable layer for the slurry shield tunnelling in a saturated sandy ground. In tests slurry pressure was increased until the slurry flowed out of the ground surface or the ground fails. Location and dimension of the impermeable layer were varied. As results, the maximum and the excess slurry pressure in sandy ground were linearly proportional to the cover depth. Larger slurry pressure could be applied to increase the stability of the tunnel face when the impermeable layer was located in the ground above the crown in front of the tunnel face. The most effective length of the impermeable grouting layer was 1.0 ~ 1.5D, and the location was 1.0D above the crown level. The safety factor could be suggested as the ratio of the maximum slurry pressure to the active earth pressure at the tunnel face. It could also be suggested that the slurry pressure in the magnitude of 3.5 ~4.0 times larger than the active earth pressure at the initial tunnel face could be applied if the impermeable layer was constructed at the optimal location.

• Proceedings of the Korean Fiber Society Conference
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• 2003.04a
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• pp.191-194
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• 2003

In this study, permeability tensor is computed for a three dimensional braided preform by applying a FVM to a unit cell. It is evident that resin will flow through the inter-tow and the intra-tow regions when pressure gradient is applied to the resin. The intra-tow region in the braided preform is regarded as not only an impermeable solid but also a permeable porous media. When the intra-tow region is excluded from domain of flow analysis in the case of the impermeable solid, the Stokes equation is computer for only inter-tow region. (omitted)

• Journal of applied mathematics & informatics
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• v.30 no.3_4
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• pp.499-510
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• 2012

Here we consider the inertial effect in a horizontal mushy layer during solidification of a binary alloy. Using perturbation technique, we obtain two systems, one of zero order and the other of first order. We consider a mushy layer with an impermeable mush-liquid interface and of constant permeability. The analysis reveals that the effect of inertial parameter is stabilizing in the sense that the critical Rayleigh number at the onset of motion increases by the inertial effect.