• Ocean Science Journal
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• v.40 no.4
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• pp.191-200
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• 2005

In this study an analytical tide model of uniform width with three sub-regions is presented. The three-subregions model takes into account step-like variations in depths in the direction of the channel as a way to examine the $M_2$ tide of the East China Sea (ECS) as well as the Yellow Sea (YS). A modified Proudman radiation condition has been applied at the northern open head, while the sea surface elevation is specified at the southern open boundary. It is seen that, due to the presence of an abrupt change in depth, co-amplitude lines of the $M_2$ tide are splitted to the east and west near the end of the ECS shelf region. Variations in depths, bottom friction and the open head boundary conditions all contribute to the determination of formation of amphidromes as well as overall patterns of $M_2$ tidal distribution. It is seen that increasing water depth and bottom friction in the ECS shelf results in the westward shift of the southern amphidrome. There is however no hint at all of the well-known degenerated tidal pattern being formed. It is inferred that a lateral variation of water depth has to be somehow incorporated to represent the tidal patterns in ECS in a realistic manner. Regarding the radiation factor introduced by Fang et al. (1991), use of a value larger than one, possibly with a phase shift, appears to be a proper way of incorporating the reflected waves from the northern Yellow Sea (NYS).

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.51-60
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• 2020

Estimation of passive earth pressure is an important factor in anchor block, temporary retaining wall and support block of raker that resist lateral earth pressure. In practice, due to ease of use, it is common to estimate the earth pressure using the theory of Coulomb and Rankine, which assumes the failure plane as a straight line. However, the passive failure plane generated by friction between the wall surface and the soil forms a complex failure plane: a curve near the wall and a flat plane near the ground surface. In addition, the limit displacement where passive earth pressure is generated is larger compared to where the active earth pressure is generated. Thus, it is essential to calculate the passive earth pressure that occurs at the allowable displacement range in order to apply the passive earth pressure to the design for structural stability reasons. This study analyzed the mobilized passive earth pressured to various displacement ranges within the passive limit displacement range using the semi-empirical method considering the complex failure plane.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.110-110
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• 2011

The nanomechanical properties of fully lithiated and unlithiated silicon nanowire deposited on silicon substrate have been studied with atomic force microscopy. Silicon nanowires were synthesized using the vapor-liquid-solid process on stainless steel substrates using Au catalyst. Fully lithiated silicon nanowires were obtained by using the electrochemical method, followed by drop-casting on the silicon substrate. The roughness, derived from a line profile of the surface measured in contact mode atomic force microscopy, has a smaller value for lithiated silicon nanowire and a higher value for unlithiated silicon nanowire. Force spectroscopy was utilitzed to study the influence of lithiation on the tip-surface adhesion force. Lithiated silicon nanowire revealed a smaller value than that of the Si nanowire substrate by a factor of two, while the adhesion force of the silicon nanowire is similar to that of the silicon substrate. The Young's modulus obtained from the force-distance curve, also shows that the unlithiated silicon nanowire has a relatively higher value than lithiated silicon nanowire due to the elastically soft amorphous structures. The frictional forces acting on the tip sliding on the surface of lithiated and unlithiated silicon nanowire were obtained within the range of 0.5-4.0 Hz and 0.01-200 nN for velocity and load dependency, respectively. We explain the trend of adhesion and modulus in light of the materials properties of silicon and lithiated silicon. The results suggest a useful method for chemical identification of the lithiated region during the charging and discharging process.

• The KSFM Journal of Fluid Machinery
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• v.9 no.1 s.34
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• pp.25-31
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• 2006

The present study investigates the effects of bleed flow on heat/mass transfer and pressure drop in a rotating channel with transverse rib turbulators. The hydraulic diameter $(D_h)$ of the square channel is 40.0mm. The bleed holes are located between the rib turbulators on leading surface and the hole diameter (d) is 4.5 mm. The square rib turbulators are installed on both leading and trailing surfaces. The rib-to-rib pitch is 10.0 times of the rib height(e) and the rib height-to-hydraulic diameter ratio $(e/D_h)$ is 0.055. The tests were conducted at various rotation numbers (0, 0.2, 0.4), while the Reynolds number and the rate of bleed flow to main flow (BR) were fixed at 10,000 and $10\%$, respectively. The results suggest that the heat/mass transfer characteristics in the internal cooling passage are influenced by rib turbulators, bleed flow and the Coriolis force induced by rotation. For the rotating ribbed passage with bleed flow, the heat/mass transfer on the leading surface is hardly affected by bleed flow, but that on the trailing surface decreases due to the diminution of main flow. The results also show that the friction factor decreases with the bleed flow.

• Geotechnical Engineering
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• v.9 no.2
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• pp.41-54
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• 1993

This paper presents the two and three -dimensional stability analysis of nonhom- ogeneous, c-o soil slopes. Potential failure surface is assumed as a logspiral curve refracted in boundaries of layers. In 3-D analysis, rotational soil mass is assumed with a cylindroid central part terminated with plane ends. Seismic force is considered by sesmic intensity. The program developed in this study is compared with the program PCSTABLS. The ratio of three-dimensional minimum factor of safety to two-dimensional case is examined and factor of safety changes are showed for the ratio of cylindroid length to slope height and numbers of slice. On such bases the following conclusions may by made : (1) The program developed in this program is less conservative than the program PCSTABLS. (2) The value of F2 of this study shows the larger differences than that of PCSTABLS with increasing friction angle (3) Factors of safety computed for 3-D geometry differ considerablely from ordinary 2-D factors of safety. Since Fb/F2 exceeds unity, three -dimensional effects tend to increase the factor of safety. (4) As the ratio of three - dimensional failure width of slope height, b/H increase, the value of Fb/Ff decreases and approaches 1.0 when bye is 14. (5) In calculating the factor of safety using the developed program the number of slices is suitable with the ranges of 30-40

• The KSFM Journal of Fluid Machinery
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• v.10 no.2 s.41
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• pp.32-40
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• 2007

The present study investigated local pressure drop in a rotating smooth square duct with turning region. The duct has a hydraulic diameter $(D_h)$ of 26.7mm and a divider wall of 6.0mm or $0.225D_h$. The distance between the tip of the divider and the outer wall of the duct is $1.0D_h$. The Reynolds number (Re) based on the hydraulic diameter is kept constant at 10,000, and the rotation number (Ro) is varied from 0.0 to 0.20. The pressure coefficient distribution $(C_p)$, the friction factor (f) and the thermal performance $({\eta})$ are presented on the leading, the trailing and the outer surfaces. It is found that the curvature of the $180^{\circ}-turn$ produces Dean vortices that cause the high pressure drop in the turning region. The duct rotation results in the pressure coefficient discrepancy between the leading and trailing surfaces. That is, the high pressure values appear on the trailing surface in the first-pass and on the leading and side surfaces in the second-pass. As the rotation number increases, the pressure discrepancy enlarges. In the fuming region, a pair of the Dean vortices in the stationary case transform into one large asymmetric vortex cell, and then the pressure drop characteristics also change.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.6
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• pp.389-395
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• 2009

A specially designed flat plate was mounted vertically over the axial line in the wind tunnel of the Pusan National University. Strain balances were mounted in the trailing part of the plate to measure the skin friction drag over removable insertions of $0.55{\times}0.25m^2$ size. A set of the insertions was designed and manufactured: 3 mm thick polished metal surface and three compliant surfaces. The compliant surfaces were manufactured of a silicone rubber Silastic$^{(R)}$ S2 (Dow Corning company). To modify the viscoelastic properties of the rubber, its composition was varied: 90% rubber + 10% catalyst (standard), 92.5% + 7.5% (weak), 85% + 15% (strong). Modulus of elasticity and the loss factor were measured accurately for these materials in the frequency range from 40 Hz to 3 kHz. The aging of the materials (variation of their properties) for the period of one year was documented as well. Along with the drag measurement using the strain balance, velocity and pressure were measured for different coating. The strong compliant coating achieved 5% drag reduction within a velocity range $20{\sim}40$ m/s while standard and weak coatings increased drag reduction.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1057-1062
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• 2009

대부분의 홍수 예측모형은 도달시간 산정에 있어 지표면 흐름을 중력흐름으로 가정한다. 그러나 Woo & Brater(1961)의 실험결과 지표면 흐름의 마찰계수는 바닥정사의 함수인 것으로 나타나며 수심이 매우 얕은 흐름의 경우 조고뿐만 아니라 바닥경사에 의한 영향이 매우 큰 것으로 나타났다. 새로운 무차원수 Y는 바닥경사, 수심, 조고 및 표면장력 등을 고려하는 인자로서 중력흐름과 표면장력흐름의 각 흐름특성을 반영하기 위한 새로운 도달시간 산정식을 개발하였다. 새로운 무차원수 Y는 표면장력과 관계된 후르드수 및 웨버수의 조합으로 조고뿐만 아니라 바닥경사, 수심의 함수로 나타난다. 지표면 흐름의 마찰계수 산정시 비례상수 ${\alpha}$를 새로운 무차원수 Y의 함수로 취하여 Butler(1977)의 실험자료를 분석하였다. 중력흐름의 경우 조고만의 함수로 나타나지만 표면장력흐름은 조고뿐만 아니라 바닥경사의 영향이 매우 중요한 것으로 나타났다. 중력흐름만을 고려하여 도달시간 산정시 관측치보다 작게 산정되는 반면 표면장력흐름으로 고려하여 도달시간 산정시 관측치와 근접하게 산정되었다. 따라서 지표면 유출 흐름은 중력과 함계 표면장력의 영향이 크게 작용하는 것으로 판단된다. 분석결과와 같이 표면장력흐름 특성을 고려한 도달시간 산정식을 모형에 적용할 경우 유출모형을 통한 유출량산정의 정확도 향상에 기여할 것으로 판단된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.598-598
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• 2013

The short lifetime of Proton Exchange Membrane Fuel Cell (PEMFC) is the one of the main problems to be solved for commercializing. Especially, the weak adhesion between metal nanoparticles and supports deteriorate the performances of nanocatalysts, therefore, it is considered to be a major failure mechanism. Using force-distance spectroscopy of atomic force microscopy (AFM), we characterized the adhesion between Pt nanoparticles and carbon supports that is crucially related to the durability for membrane fuel cell (MFC) electrode. In our study, force distance curves measured with Pt coated AFM cantilever, mimicking the behavior of corresponding nanoparticles on carbon supports, leads to the adhesion between metal nanoparticles and carbon supports. We found that theadhesion between Pt and HNO3-treated carbon is enhanced by a factor of 4, compared to Pt and bare carbon support, that is consistent with the macroscopic durability test of PEMFC. The higher adhesion between Pt and HNO3-treated carbon can be explained in light of the stronger chemical interaction by C/O functional groups.

• Transactions of Materials Processing
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• v.14 no.9 s.81
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• pp.772-778
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• 2005

This paper is concerned with the analysis of material flow characteristics of combined tube extrusion using pipe. The analysis in this paper concentrated on the evaluation of the design parameters for deformation patterns of tube forming, load characteristics, extruded length, and die pressure. The design factors such as punch nose radius, die corner radius, friction factor, and punch face angle are involved in the simulation. The combined tube extrusion is analyzed by using a commercial finite element code. This simulation makes use of pipe material and punch geometry on the basis of punch geometry recommended by International Cold Forging Group. Deformation patterns and its characteristics in combined forward and backward tube extrusion process were analyzed for forming loads with primary parameters, which are various punch nose radius relative to backward tube thickness. The results from the simulation show the flow modes of pipe workpiece and the die pressure at the contact surface between pipe workpiece and punch. The specific backward tube thickness and punch nose radius have an effect on extruded length in combined extrusion. The combined one step forward and backward extrusion is compared with the two step extrusion fer forming load and die pressure.