• ETRI Journal
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• v.44 no.1
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• pp.125-134
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• 2022

Visible light communication (VLC) systems incorporate ambient lighting and wireless data transmission, and the experienced channel in indoor VLC is a major topic that should be examined for reliable communication. In this study, it is realized that multiple transmitters in classical alignment are the forceful factors for channel characteristics. In the frequency band, fluctuations with sudden drops are observed, where the fluctuation shape is related to the source layout and receiver location. These varying frequency-selective channels need solutions, especially for mobile users, because sustained channel estimation and equalization are necessary as the receiver changes its location. It is proven that using light-emitting diodes (LEDs) with highly directional beams as sources or using a detector with a narrow field of view (FOV) in the receiver may help partially alleviate the problem; the frequency selectivity of the channel reduces in some regions of the room. For flat fading channel characteristics all over the room, LEDs should be aligned in hexagonal cellular structure, and detector FOV should be arranged according to the cell dimension outcomes.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1571-1575
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• 2006

Channel form discharge which determines shape and character of a channel is named as dominant discharge. Assuming that fixed discharge flows in the fluvial plain for a long time, it is channel form discharge of a certain channel if it changes the fluvial plain into shape of the channel. Channel form discharge can be demonstrated by concept of bankfull or effective discharge. 1.01, 1.58, 2, 2.33 and 5 year flood discharge were used in order to determine channel form discharge. Each frequency discharge was determined by 80 year flood discharge by a research result conducted by Kim and Won. 1.01 year frequency discharge was selected as the most similar discharge to bankfull discharge. 1.58 year frequency discharge habitually used in Korea exceeded bankfull discharge.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1107-1111
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• 2006

Channel form discharge which determines shape and character of a channel is named as dominant discharge. Assuming that fixed discharge flows in the fluvial plain for a long time, it is channel form discharge of a certain channel if it changes the fluvial plain into shape of the channel. Channel form discharge can be demonstrated by concept of bankfull or effective discharge. 1.01, 1.58, 2, 2.33 and 5 year flood discharge were used in order to determine channel form discharge. Each frequency discharge was determined by 80 year flood discharge by a research result conducted by Kim and Won. 1.01 year frequency discharge was selected as the most similar discharge to bankfull discharge. 1.58 year frequency discharge habitually used in Korea exceeded bankfull discharge.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1191-1197
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• 1994

The purpose of this study is to examine morphometric characteristics in a channel bend reach. The new shape factor is suggested that channel deformation rate of cross section (${\Delta}A_s$) showed the variation of concentrated location of force due to the current and the variation of erosional section in alluvial channel. In the downstream direction the meaning of decreasing "${\Delta}A_s$" is the stability of channel bed. This study was analyzed morphological characteristics of cross section-width of channel ($W_s$), width to the thalweg ($W_{th}$), maximum depth ($D_{th}$)-on the Guem River, and typical cross sections in channel bend were proposed. The channel migration rate (M) for the study river was represented that the zones of curvature ratio (R/W) with 2~4 were larger 12% than other zones.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.9
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• pp.1351-1359
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• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.

• Journal of the Korean Society of Marine Environment & Safety
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• v.8 no.1
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• pp.101-108
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• 2002

This experimental study was performed to investigate internal flow and unsteady flow characteristics using a model for actual shape of a Plate heat exchanger and visualization of flow through the particle image velocimetry. Seven Reynolds numbers were selected by calculation with the height of grooved channel and sectional mean velocity of inlet flow in the experiment, and instantaneous velocity distributions and flow characteristics were experimently investigated. The triangular grooved channel had a compound flow consisting of the flow in lower channel and the groove flow receiving shear stress by the channel flow in the experiment. The sheared mixing layer, in the boundary between the triangular groove and the channel. affected main flow to raise turbulent in the channel.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2791-2796
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• 2007

In their long journey through the cardiovascular circuit, erythrocytes are coerced to shape transform and assume different shapes on account of varying flow conditions in different blood vessels. The present work was aimed to visualize these erythrocyte shape transformations by an invitro microcirculatory model, and assess multi-shape erythrocyte deformability. The model uses an in-house fabricated, inexpensive disposable micro flow channel to mimic certain invivo conditions and a fast frame video microscopic system for imaging the shape changes in erythrocytes. Results show the multi-shape transformation of erythrocyte christened as discoidal shape, the asymmetrically deformed 'hat' and 'bullet-like' shapes, and the axially deformed 'slipper' and 'spindle-like' shapes. Specific erythrocyte showed the shape transition and transformation while passing through the observed window. The obtained erythrocyte shapes very analyzed for deformability index using image processing techniques that varied significantly (p <0.001) for different shapes as compared with the resting shape.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2008.04a
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• pp.495-498
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• 2008

In this paper applicable range of U-Channel Bridge (UCB) that has recently been introduced as a new bridge type was studied. For structural analysis models used with the frame and plate elements was proposed, and verification of the models were performed. Using these structural models structural analysis of models with span length of 20m-45m and inner width of 5m-13m were performed. As a result for U-shape sections were applicable in the range of 20m span and 35m span, slab was applicable in the range of 5m inner width and 12m inner width. To increase applicable range of UCB H-shape sections and slab with rib were proposed. As a result UCB were applicable in the range of 20m span and 45m span, in the range of 5m inner width and 13m inner width.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.1
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• pp.69-76
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• 2011

PEMFC (polymer electrolyte membrane fuel cell) is device that generates electricity from hydrogen. It is one of the subjects related to renewable energy and various research has been conducted on the PEMFC. PEMFC has low operating temperature and high efficiency among fuel cells, and is given attention as means for automobile and domestic use. Analysis of flow field pattern in supplying hydrogen and oxygen is part of the research to increase PEMFC efficiency. In this study, separation plate currently used in PEMFC is transformed to wave shape and mass transfer characteristics in the channel is examined through numerical and experimental analysis. Wave shape separation plate yielded 18% increase of efficiency compared to separation plate used in normal channel. And improvements in mass transfer characteristics were verified.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.7
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• pp.8-13
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• 2019

As increasing demand for precise machining in advanced disciplines, especially in semi-conductor, aeronautical and automotive industries, the magnetic abrasive deburring(MAD) which is able to eliminate micro-sized burr on complex surface in less time has drawn the attention in the last decades. However, the performance of MAD is subject to shape and size of a tool. Therefore, this study aim to identify deburring behavior of MAD in U-type flow channel by measuring the length rate of burr removal in radial distance of the cylindrical tool under four process factors. In order to evaluate the deburring effect of MAD on the surface, finishing regions are divided based on center of the circular cutting tool. As a results, it was defined that the amount of burr removal in a downward direction moving toward flow channel from the top surface was higher than upward direction. This is because the magnetic abrasives were detached from magnetic lines of force due to geometrical shape.