• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.19-27
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• 2018

Terzaghi proposed a 2D formula for arching based on the assumption of a vertical sliding surface induced in the upper part due to the downward movement of a trapdoor. The formula was later expanded to consider 3D tunnel excavation conditions under inclined sliding surfaces. This study further extends the expanded formula to consider the effects of different ground properties and inclined sliding conditions in the transverse and longitudinal directions considering anisotropic ground conditions, as well as 3D tunnel excavation conditions. The 3D formula proposed in this study was examined of the induced vertical stress under various conditions (ground property, inclined sliding surface, excavation condition, surcharge pressure, earth pressure coefficient) and compared with the 2D Terzaghi formula. The examination indicated that the induced vertical stress increased as the excavation width and length increased, the inclination angle increased, the cohesion and friction angle decreased, the earth pressure coefficient decreased, and the surcharge pressure increased. Under the conditions examined, the stress was more affected at low excavation lengths and by the ground properties in the transverse direction. In addition, The comparison with the 2D Terzaghi formula showed that the induced vertical stress was lower and the difference was highly affected by the ground properties, inclined sliding conditions, and 3D tunnel excavation conditions. The proposed 3D arching formula could help to provide better understanding of complex arching phenomena in tunnel construction.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1318-1327
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• 2008

Geotechnical sites in urban areas may have embedded structures such as utility lines and underground concrete structures, which cause difficulties in site investigation. This study is a preliminary research to establish knowledge base for developing an optimal technique for site investigation in urban areas. Surface-wave method and resistivity survey, which are frequently adopted for non-destructive site-investigation for geotechnical sites, were investigated to characterize effects of adjacent structures. In case of surface wave method, patterns of wave propagation were investigated for typical sets of multi-layered geotechnical profiles by numerical simulation based on forward modeling theory and field experiments for small-size model tests and real-scale tests in the field. In case of resistivity survey, 3-D finite element analyses and field tests were performed to investigate effects of adjacent concrete structures. These theoretical and experimental researches for surface-wave method and resistivity survey resulted in establishing physical criteria to cause interference of adjacent structures in site investigation at urban areas.

• Journal of the Korean institute of surface engineering
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• v.23 no.2
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• pp.24-29
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• 1990

The TiN filmms were deposited on the stainless steel substrates by BARE techinique in order to investigate the effects of process parameters such as source-to-substate distance (15-35cm), N2 pressure(4$\times$10-10 -1$\times$10-3mb)and bias voltage(O-2000V), on the deposition rate, the concentration ratio [N/Ti] and the surface color of the films. The deposition rate was deduced from the weight measurement, the [N/ti] ratio by ESCA. The deposition rate decreased with a relationship of=40.2/D2 where D was source-to-substrate distance. The effect of the bias voltage and the N2pressure on the deposition rate, however, appeared negligble. The [N/Ti] ratio was in the narrow range of 0.7 tp 0.8 It increased slightly with the N2 partial pressure and deceased with the source-to-substrate distance. It was confired by ESCA that a significant amount of oxygen and carbon was contaminated after deposition in the top surface of TiN films. The surface color of TiN film was changed from light gold yellow to reddish gold yellow with increasing [N/Ti] ratio.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.27-34
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• 2002

3-D numerical studies are performed to investigate the effect of the air dam height and approaching air velocities on the pressure distribution of notchback road vehicle. For this purpose, the models of test vehicle with four different air dam heights are introduced and PHOENICS, a commercial CFD code, is used to simulate the flow phenomena and to estimate the values of pressure coefficients along the surface of vehicle. The standard $k-{\varepsilon}$ model is adopted for the simulation of turbulence. The numerical results show that the height variation of air dam makes almost no influence on the distribution of the value of pressure coefficient along upper and rear surface but makes strong effects on the bottom surface. That is, the value of pressure coefficient becomes smaller as the height is increased along the bottom surface. Approaching air velocity makes no differences on pressure coefficients. Through the analysis of pressure coefficient on the vehicle surface, one tries to assess aerodynamic drag and lift of vehicle. The pressure distribution on the bottom surface affects more on lift than the pressure distribution on the upper surface of the vehicle does. The increase of air dam height makes positive effects on the lift decrease but no effects on drag reduction.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.6
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• pp.178-186
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• 2002

3-D numerical studies are performed to investigate the effect of the trunk height and approaching air velocities on the pressure distribution of notchback road vehicle. For this purpose, the models of test vehicle with four different trunk heights are introduced and PHOENICS, a commercial CFD code, is used to simulate the flow phenomena and to estimate the values of pressure coefficients along the surface of vehicle. The standard k-$\xi$ model is adopted for the simulation of turbulence. The numerical results say that the height variation of trunk makes almost no influence on the distribution of the value of pressure coefficient along upper surface but makes very strong effects on the rear surface. That is, the value of pressure coefficient becomes smaller as the height is increased along the rear surface and the bottom surface. Approaching air velocity make no differences on pressure coefficients. Through the analysis of pressure coefficient on the vehicle surfaces one tried to assess aerodynamic drag and lift of vehicle. The pressure distribution on the rear surface affected more on drag and lift than pressure distribution on the front surface of the vehicle does. The increase of trunk height makes positive effects on the lift decrease but negative effects on drag reduction.

• Journal of Powder Materials
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• v.27 no.5
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• pp.381-387
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• 2020

In this work, TiO₂ 3D nanostructures (TF30) were prepared via a facile wet chemical process using ammonium hexafluorotitanate. The synthesized 3D TiO₂ nanostructures exhibited well-defined crystalline and hierarchical structures assembled from TiO₂ nanorods with different thicknesses and diameters, which comprised numerous small beads. Moreover, the maximum specific surface area of TiO₂ 3D nanostructures was observed to be 191 ㎡g^-1, with concentration of F ions on the surface being 2 at%. The TiO₂ 3D nanostructures were tested as photocatalysts under UV irradiation using Rhodamine B solution in order to determine their photocatalytic performance. The TiO₂ 3D nanostructures showed a higher photocatalytic activity than that of the other TiO₂ samples, which was likely associated with the combined effects of a high crystallinity, unique features of the hierarchical structure, a high specific surface area, and the advantage of adsorbing F ions.

• Geomechanics and Engineering
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• v.16 no.4
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• pp.341-353
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• 2018

A reinforced concrete pedestrian tunnel is constructed under a four-track surface railway. Heavy rainfall and soil exposure to drying lead to soil with different water content throughout the year. A railway is an open utility that is subject to rainfall without control on the quantity of the water on it and when there is a tunnel under a railway, the water content of the soil around the tunnel is very influential. This research shows the effects of change of water content in the soil around a pedestrian tunnel under a four-track surface railway. The pedestrian tunnel and the soil block around the tunnel are modeled in 3D by the FEM and are studied under the vibrations induced by the moving trains on the four-track surface railway for different soil water contents and the effects of the soil water content on the dynamic behavior of the tunnel and the surrounding soil are demonstrated.

• Journal of Physiology & Pathology in Korean Medicine
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• v.18 no.3
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• pp.729-733
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• 2004

Jaeum-Dan was reported new anti-aging effect formula previously. We investigated the physiological effects on human skin with Jaeum-Dan essence (JED). We made a skin application product as essence form contained oriental herbs, and measured various physiological effects such as skin moisture contents, red blood cell flow rates, skin surface temperature, corneocyte exfoliation and skin intensity when volunteers(female, n=40) used the application product for 4 weeks. The results were as follows: The skin moisture contents were not only increased in human face skin through using the product, but also red blood cell flow :rates in face skin were increased. After using the essence, the face skin temperature rose and corneocyte exfoliation was decreased. Furthermore the upper dermis intensity of skin in female face was subsequently increased 4 weeks later. The results indicate that the application product containing JED was improved the physiological effects of human facial skin..

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.418-422
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• 2005

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire has been investigated. Test pieces were fabricated using die series with different mean and final reduction ratio. Surface residual stresses in the axial direction were measured by X-ray diffraction, Broker's 2-dimensional GADDS system. Results were compared with stress profiles which were calculated by 3D and 2D finite element simulation, Hibbitt's ABAQUS 6.4 program in Finite Element Analysis. By means of FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.

• Transactions of Materials Processing
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• v.15 no.2 s.83
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• pp.153-157
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• 2006

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire have been investigated. Test pieces were fabricated using die series with different mean and final reduction ratios. Surface residual stresses in the axial direction were measured by X-ray diffraction, Bruker's 2-dimensional GADDS system. The results were compared with stress profiles that were calculated by 3D and 2D finite element simulations, ABAQUS 6.4 program in finite element analysis(FEA). By means of the FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.