• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.241-250
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• 2000

In this study, condensation heat transfer tests were conducted in flat aluminum multi-channel tubes using R-22. Two internal geometries were tested ; one with smooth inner surface and the other with micro-fins. Data are presented for the followin~ range of variables ; vapor quality($0.1{\sim}0.9$), mass flux($200{\sim}600kg/m^2s$) and heat flux($5{\sim}15kW/m^2$). The micro-fin tube showed higher heat transfer coefficients compared with those of the smooth tube. The difference increased as the vapor quality increased. Surface tension force acting on the micro-fin surface at the high vapor quality is believed to be responsible. Different from the trends of the smooth tube, where the heat transfer coefficient increased as the mass flux increased, the heat transfer coefficient of the micro-fin tube was independent of the mass flux at high vapor quality, which implies that the surface tension effect on the fin overwhelms the vapor shear effect at the high vapor quality. Present data(except those at low mass flux and high quality) were well correlated by equivalent Reynolds number, Existing correlations overpredicted the present data at high mass flux.

• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1203-1212
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• 2004

The purpose of this study is to predict and understand the hydrodynamic forces and their nonlinear behaviors of fluid motion around the submerged plate oscillating near a free surface. To achieve this objective, we have developed a composite grid method for the solution of a radiation problem. The domain is divided into two different grids; one is a moving grid system and the other is a fixed grid system. The moving grid is employed for the body fitted coordinate system and moves with the body. This numerical method is applied to calculation of radiation forces generated by the submerged plate oscillating near a free surface. In order to investigate the characteristics of the radiation forces, the forced heaving tests have been performed with several amplitudes and different submergences near a free surface. These experimental results are compared with the numerical ones obtained by the present method and a linear potential theory. As a result, we can confirm the accuracy of the present method. Finally, the effect of nonlinear and viscous damping has been evaluated on the hydrodynamic forces acting on the submerged plate.

• Geomechanics and Engineering
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• v.18 no.3
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• pp.247-258
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• 2019

Soil strength and failure surface geometry directly influence magnitudes of passive earth thrust acting on geotechnical retaining structures. Accordingly, it is expected that as long as the shape of the failure surface geometry and strength parameters of the backfill are known, magnitudes of computed passive earth thrusts should be highly accurate. Building on this premise, this study adopts conventional method of slices for calculating passive earth thrust and combines it with equations for estimating failure surface geometries based on in-situ stress state and density. Accuracy of the proposed method is checked using the results obtained from small-scale physical retaining wall model tests. In these model tests, backfill was prepared using either air pluviation or compaction and different backfill relative densities were used in each test. When the calculated passive earth thrust magnitudes were compared with the measured values, it was noticed that the results were highly compatible for the tests with pluviated backfills. On the other hand, calculated thrust magnitudes significantly underestimated the measured thrust magnitudes for those tests with compacted backfills. Based on this observation, a new approach for the calculation of passive earth pressures is developed. The proposed approach calculates the magnitude and considers the influence of locked-in stresses that are the by-products of the backfill preparation method in the computation of lateral earth forces. Finally, recommendations are given for any geotechnical application involving the compaction of granular bodies that are equally applicable to physical modelling studies and field construction problems.

• Journal of the Korean Institute of Landscape Architecture
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• v.32 no.1
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• pp.69-79
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• 2004

This Paper examines theoretical terrains and design strategies of landscape urbanism which is an emerging hybrid field at the intersection of architecture, landscape architecture, and urbanism. Landscape urbanism offers alternative approaches for theory, education, and practice in contemporary landscape architecture. It views the emergent urban complex sites-post-industrial sites, landfill, brownfield, urban void, etc., not as a weakness, but as a strength. Landscape urbanism poses an understanding of landscape as an element of urban infrastructure. In this sense, the landscape is seen in the context of contemporary urban development and public works. As a complex amalgam, landscape urbanism is more than a design style it is an ethos, an attitude, a way of thinking and acting. We can chart the main characteristics of landscape urbanism such as horizontality and surface, infrastructure, process, technique, and ecology. Multilayered examples of landscape urbanism can be seen in several experimental practices such as worts of Rem Koolhaas, MVRDV, Adriaan Geuze/West 8, James Comer, etc. It is possible to summarize the productive strategies for landscape urbanism as follows : thickening, folding, new materials, nonprogrammed use, impermanence, and movement.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.41-49
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• 1994

The leak-before-break(LBB) design on the large structures such as ship's hull, tank structure, pressure vessels etc. is one of the most inportant subjects for the evaluation and the assurance of safety. In these structures, various loads are acting. In some structural members, therefore, out-of-plane stress due to bending often may become with in-plane stress due to stretching. In the present report, the characteristics of fatigue life and peneration behaviour from a surface cracked plate under combined tension and bending have been studied experimentally and analytically by using eccentricity. Estimation of fatigue crack growth was done with the Newman-Raju formula before penetration, and with the stress intensity factor after penetration proposed by the author. Calculated aspect ratio showed the good agreement with the experimental result. It was also found that particular crack growth behaviour and crack shape after penetration can be satisfactorily evaluated using the K solution proposed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1812-1817
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• 2008

A cooling system for microelectronics is becoming more important as its surface heat density is projected to reach that of the sun surface. The existing technologies using natural and forced convection are limited to solve the problems. Recently, an electrohydrodynamic driven flow is studied as one of the means to cope with this problems. A new method, utilizing a needle-centered nozzle electrode, has been proposed and investigated. The I-V characteristics of the nozzle electrode for deionized water and silicone oil were significantly different from that of without liquid, which might be due to the liquid drop covered on the nozzle tip by the EHD force acting near the needle tip. Results showed that the liquid pumping rate and flow efficiency of the nozzle electrode were very high, especially for the silicone oil. Theoretical analysis also showed the effectiveness of the needle electrode centered in the ceramic nozzle, which, however, can be a means as a liquid pump.

• Biomolecules & Therapeutics
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• v.12 no.2
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• pp.57-61
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• 2004

In the present study, we investigated whether lipopolysaccharide induce mucin release and erythro-mycin affect basal and adenosine triphosphate-induced (stimulated mucin release, from airway goblet cells. Confluent primary hamster tracheal surface epithelial cells were metabolically radiolabeled and chased for 30 min or 24 hr in the presence of varying concentrations of lipopolysaccharide or erythromycin to assess the effects on $^3H$-mucin release. The results were as follows : 1) Lipopolysaccharide failed to induce mucin release, 2) Erythromycin showed no effect on both basal and stimulated mucin release during 30 min of 24 hr treatment period. We conclude that lipopolysaccharide and erythromycin can not affect mucin release by direct acting on airway mucin-secreting cells.

• Bulletin of the Society of Naval Architects of Korea
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• v.22 no.2
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• pp.27-34
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• 1985

In this paper, the second order time mean forces acting on the circular cylinder floating on the free surface of a finite water depth are calculated. Under the assumption that fluid is idea and the wave the linear gravity wave, the velocity potential is calculated by the source distribution method, and the second order time mean lateral and vertical drifting forces are calculated by the direct integration of fluid pressures over the immersed body surface. The comparison of the lateral drifting forces with Rhee's results by momentum theorem shows good agreements. And it is shown that the second order time sinkage forces of a floating circular cylinder cross zero for all water depths.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.478-485
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• 2001

A dynamic load simulator(DLS) which can reproduce on-ground the aerodynamic hinge moment of control surface is an essential rig for the performance and stability test of aircraft actuation system. By setting up load actuator as counter acting with the control surface driving actuator and designing an appropriate force control system for load actuator, DLS can be mechanized. Obtaining an accurate mathematical model for the DLS is the first step to successfully design an aerodynamic load replicati on system. Two theoretical models are presented and tested for their validities with the experimental results, which turns out to be not successful. An alternative way of using system identification approaches in investigated to develop a good nominal model for DLS dynamics, and suitable uncertainty bounds for this nominal model are proposed with the consideration of experimental results.

• Journal of Industrial Technology
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• v.5
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• pp.51-57
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• 1985

The object of this study is in the development of the computer program to predict the performance of rotor in hovering by getting the aerodynamic load acting on blade. For this work the vortex theory was chosen among the aerodynamic theories, blade was replaced by planar vortex panels, and prescribed wake for the wake geometry was selected and then represented by vortex lattices. To get the aerodynamic load on blade, flow was assumed to be incompressible, irrotational and steady, and the surface boundary condition of inviscid flow was used as boundary condition. Then the relationships between this load and flight condition and blade geometry were examined.