• Steel and Composite Structures
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• v.18 no.6
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• pp.1451-1464
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• 2015

Recently, in recognition of their outstanding structural performance, the use of Concrete Filled Steel Tube (CFT) columns has been increased. New shape welded built-up square tube was developed by the authors for broader usability using thin steel plates which were bent to be L-shaped (Channel) and each unit members were welded to form square steel tube as an cost-efficient use of expensive steel. In addition, since the rib placed at the center of the tube width acts as an anchor; higher load capacity of buckling is achievable. In order to apply the new shape built-up square columns, the structural behavior and stress distribution with parameter width of thickness (b/t), with and without rib were predicted. The New shape welded built-up square tube effectively delayed the local buckling of the steel tube, which led to a greater strength and ductility than regular HSS.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.1-8
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• 2014

Two-dimensional laminar numerical analyses were carried out for investigating the thermo-hydraulic characteristics of wavy channels with different shape parameters ($0.5{\leq}{\in}{\leq}1.5$, $0.1{\leq}{\gamma}{\leq}0.4$). PAO (polyalphaolefin), which is used for electronics cooling, is considered as the working fluid. In addition, constant properties, periodically developed flow, and uniform channel wall temperature conditions are assumed. Streamline and temperature fields, isothermal Fanning friction factors, and Colburn factors are presented for different Reynolds numbers in the laminar region ($1{\leq}Re{\leq}1000$). The results show that heat transfer is enhanced when the channel corrugation ratio (${\gamma}$) is large and channel spacing ratio (${\in}$) is small in the low Reynolds number region (Re < 50) and when ${\in}$ and ${\gamma}$ are large in the high Reynolds number region ($Re{\geq}50$).

• Mass Spectrometry Letters
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• v.7 no.1
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• pp.21-25
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• 2016

Dual-channel nano-electrospray has recently become an ionization technique of great promise especially in biological mass spectrometry. This unique approach takes advantage of the mixing processes that occurs during electrospray. Understanding in more detail the fundamental principles influencing spray formation further study of the origins of the mixing processes: (1) in a Taylor cone region, (2) in charged droplets or (3) in both environments. The dual-channel emitters were made from borosilicate theta-shape glass tubes (O.D. 1.2 mm) and had a tip diameters of less than 4 μm. Electrical contact was achived by deposition of a thin film of an appropriate metal onto the surface of the emitter. The experimental investigation of the Taylor cone formation in a dual-channel electrospray emitter has been carried out by injection of polystyrene beads (diameter 3 μm) at very low concentrations into one of the channels of the non-tapered theta-glass tubes. High-speed camera experiments were set up to visualize the mixing processes in Taylor cone regions for dual-channel emitters. Mass spectra from dual nano-electrospray are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.1861-1866
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• 1999

ISDN provides mB+1D channel to users. An AO/D1 scheme means D-channel can be used for a permanent low speed connection. When user needs more bandwidth for high speed transfer, the AO/D1 scheme automatically provide greater capacity in the shape of ISDN B-channels. In this paper, we analyze the performance of the AO/D1 scheme with multiple ON-OFF sources in ISDN. We consider multiple ON-OFF sources connected through mB+1D ISDN link. Without the AO/D1 scheme, the required bandwidth will be the sum of peak bandwidth of all sources. With the implementation of the AO/D1 scheme, the required bandwidth is reduced to what is really needed.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.3
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• pp.217-223
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• 2016

In this paper, the movement of a liquid metal droplet in a channel by continuous electrowetting effect is analyzed. The channel is fabricated using two glass substrates and silicone rubber as spacers, and a mercury droplet and dilute sulfuric acid are added into the channel. The droplet is moved according to voltage applied at both ends of the channel through an electrolyte. According to the shape of the droplet and the applied voltage, the velocity of the droplet is changed. The velocity is proportional to the applied voltage and inversely proportional to the length of the droplet, both theoretically and experimentally. Contact angle hysteresis and a meniscus change were also found in the moving state. This implies the existence of a threshold in movement by Laplace pressure difference. The experiment indicated that the sliding angle was inversely proportional to the width of the droplet but that the voltage threshold was proportional to the width.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.851-857
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• 2010

In this study, an experiment was performed to obtain the optimum design of a passive micromixer for effective mixing by using a microsized device and rectangular obstacles; a low Reynolds number was maintained in the microchannel. The experiment was carried out by varying the number, size, and location of the rectangular obstacles. Further, the Y-channel's shape was optimized for maximizing the mixture ratio, which has limit qualification that an allowed value of pressure drop. The increase in the efficiency of mixing was observed to be greater than that in the case of circular obstacles by approximately 2.5%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.853-858
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• 2003

The suitable estimation of the filter width in the dynamic eddy viscosity model were investigated in high Reynolds number channel flow. In this study, the improvement on matters by optimizing the test filter shape was attempted through the numerical experiment. The way that select optimum test filter width is recommended. Some test filters, one is based on a discrete representation of the top-hat filter and another are based on a high-order filtering operation, are evaluated in simulations of the turbulent channel flow at Reynolds number 1020, based on friction velocity and channel half width. It appears that the estimation of test filter width practically can decrease the dissipative nature of dynamic eddy viscosity model with explicit test filter. It shows that the value of the filter width ratio used in the dynamic procedure must match the properties of the test filter actually used in the calculation.

• Structural Engineering and Mechanics
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• v.74 no.3
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• pp.445-455
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• 2020

Shear lag phenomenon has long been taken into consideration in various structural codes; however, the AISC provisions have not proposed any specific equation to calculate the shear lag ratio in some cases such as fillet-welded connections of front-to-front double channel sections. Moreover, those equations and formulas proposed by structural codes are based on the studies that were conducted on riveted and bolted connections, and can be applied to single channel sections whilst using them for fillet-welded double channels would be extremely conservative due to the symmetrical shape and the fact that bending moments will not develop in the gusset plate, resulting in less stress concentration. Numerical models are used in the present study to focus on parametric investigation of the shear lag effect on fillet-welded tension connection of double channel section to a gusset plate. The connection length, the eccentricity of axial load, the free length and the thickness of gusset plate are considered as the key factors in this study. The results are then compared to the estimates driven from the AISC-LRFD provisions and alternative equations are proposed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.383-390
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• 2008

Flow pattern of cavitation around a plano-convex foil, whose shape is similar to the inducer impeller of the turbo-pumps in the liquid fuel rocket engine, was observed by using a cryogenic cavitation tunnel of blowdown type for visualization. Working fluids were liquid nitrogen and hot water. The parameter range to be varied was between 20 and 60mm for channel width, 20 and 60mm for foil chord, -1.8 and 13.2 for cavitation number, 3.7 and 19.5m/sec for averaged inlet velocity, $8.5{\times}10^4$ and $1.5{\times}10^6$ for Reynolds number, -8 and $8^{\circ}$ for angle of attack, respectively. Especially at positive angle of attack, namely, convex surface being downstream, the whole cavity or a part of the cavity on the foil surface departs periodically. Periodic cavitation occurs only in case of smaller cavitation size than twice foil chord. Cavitation thickness and length in 20mm wide channel are larger than those in 60mm due to the wall confinement effect. Therefore, periodic cavitation in 60mm wide channel easily occurs than that in 20mm. These results suggest that the periodic cavitation is controlled by not only the hydrodynamic effect of vortex shedding but also the channel wall confinement effect.

• Journal of the Korean Geographical Society
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• v.32 no.4
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• pp.421-434
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• 1997

Flume experiments are conducted to describe channel adjustments at stream confluences and to examine some factors to which changes in channel characteristics are subject. There are different factors controlling channel size and shape; shereas the fomer is primarily controlled by water discharge alone, the latter including channel slope is influenced by sediment load as well as water discharge. The morphometric adjustments of confluent tributaries can be consequently classified into three types based upon changes in sediment concentration which are associated with the relative increasing rates of water discharge and sediment load at these sites. Flow is accelerated at stream confluences due to the convergence of confluent flows, causing an sharp increase in velocity. It restrains an increase in channel capacity, and furthers a decrease in channel slope, of a receiving stream. As a result, effects of slight increases in sediment concentration hardly appear on changes in channel characterisitics at stream confluences.