• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1196-1204
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• 2001

The rivulet is a narrow stream of liquid flowing down a solid surface. When the rivulet\`s flow rate exceeds a certain limit, it tends to meander exhibiting the instability of its interface. This analysis performs a perturbation analysis of this meandering rivulet assuming an inviscid flow possessing contact angle hysteresis at the contact line. The analysis reveals that the contact angle hysteresis as well as the velocity difference across the inter-face, strongly induces the instability of the liquid interface. Moreover, when the rivulet veto-city is low, it is predicted that the axisymmetric disturbance amplifies more rapidly than the anti-axisymmetric disturbance, which explains the emergence of the droplet flow at the low velocity regime.

• Ecology and Resilient Infrastructure
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• v.4 no.1
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• pp.24-33
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• 2017

This study investigates the flow characteristics and bed changes with discharge using a two-dimensional numerical model, Nays2DH. The water depth at the outer part of curved channel is formed deeper from the narrow part after passing through the curved part. The point bar is developed in the wide section and water depth is shallow in the inside of the curved section. The flow is concentrated in the outer pater of the meandering section, which leads to the deep water. In the downstream section where the straight line formed, the flow is concentrated at the center of the bed. Alternating deep water and shallow places are generated due to the continuous formation of meandering. These characteristics are formed by the influence of strong two-stream flow in meandering stream. The dimensionless tractive force is also large in the region where the flow velocity is concentrated. However, in the narrow and sharp meandering river reaches, the pattern of bed changes and the spatial distribution patterns of flow velocity and dimensionless tractive force are inconsistent in the narrow and sharp meandered reaches due to the strong secondary flow.

• KCID journal
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• v.21 no.1
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• pp.118-126
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• 2014

In this study, the use of the spur of riverbank technique is being investigated. The spur of the riverbank typically reduces the velocity of flow and protects the embankments by increasing friction along the water and the banks. This also has an effect in the rise of water level upstream. It is also used for the rectification of riverside line and restoration of the waterway through sedimentation near the spur of the riverbank. In this study, physical-scaled experiments are conducted to investigate the process of creating a mild meandering channel using the spur of the riverbank with varying water flows and sedimentation functions. The hydraulics observations are taken with respect to the varying heights and length of the riverbank's spurs and the distance between each spur for the formation of the mild meandering channel. It is observed that for 1.06 times of the meander length, it requires 2 times of the interval with each spur of river width. Similarly, 1.25L times of the meander length, it requires 0.5 times of the interval with each spur of river width. The sand accumulation is induced by the spur of riverbank when the spur of riverbank's heights are more than 40% of water depth and the length of the spur of riverbank needs under than 20% of river width for avoid exaggerated sand accumulation in the center of channel.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.799-802
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• 2008

General behaviors based on hydraulic characteristics of natural streams and channels have been recently analyzed and developed via various numerical models. However in the states of natural hydraulics, an experimental research must be performed simultaneously with the mathematical analysis due to effects of hydraulic properties such as meander, sediment, and so on. In this study based on 2-D advection-dispersion equation, flow and tracer experiments were performed in the S-curved meandering laboratory channel with a rectangular cross-section. The channel was equipped with instrument carriages which was equipped with an auto-traversing system to be used with velocity measuring sensors throughout the depth and breadth of the flow field. To measure concentration distribution of the salt solution was adjusted to that of the flume water by adding methanol and a red dye (KMnO4) was added to aid the visualization of the tracer cloud, the tracer was instantaneously injected into the flow as a full-depth vertical line source by the instantaneous injector and the initial concentration of the tracer was 100,000 mg/l. The secondary current as well as the primary flow pattern was analyzed to investigate the flow distribution in the meandering channels. The velocity distribution of the primary flow for all cases skewed toward the inner bank at the first bend, and was almost symmetric at the crossovers, and then shifted toward the inner bank again at the next alternating bend. Thus, one can clearly notice that the maximum velocity occurs taking the shortest course along the channel, irrespective of the flow conditions. The result of the tracer tests shows that pollutant clouds are spreading following the maximum velocity lines in each cases with various mixing patterns like superposition, separation, and stagnation of pollutant clouds. Flow characteristics in each cases performed in this study can be compared with tracer dispersion characteristics with using evaluation of longitudinal and transverse dispersion coefficients(LDC, TDC). As expected, LDC and TDC in meandering parts have been evaluated with increasing distribution and straight parts have effected to evaluate minimum of LDC and TDC due to symmetric flow patterns and attenuations of secondary flow.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.858-867
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• 2018

Analytical modeling equations are proposed for the conventional and modified three-section branch-line couplers. The analytical equations are explicit and capable of determining the characteristic impedance of each branch line for the coupler at desired coupling level as well as the suitability of broadband S-parameters analysis. In addition, a bandwidth extension and miniaturization of three-section branch-line coupler using slow-wave and meandering line structures were designed. The modified coupler, which is able to operate within frequencies from 1.5 to 3.32 GHz has been fabricated, tested and compared. A bandwidth extension of 600 MHz and 53% reduced size of the modified coupler have been achieved compared to a conventional coupler. The modified coupler has roughly insertion loss and coupling of -4 dB and -3.2 dB, while the isolation and return loss, respectively less than -14 dB with fractional bandwidth of 77 %, as well as phase imbalances less than $2^{\circ}$ over the operating bandwidth. Overall, the derived analytical model, simulation and measurement results demonstrated a good agreement.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.979-991
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• 2004

In this study, RMA2 and RMA4, the 2-D depth-averaged models, were employed to simulate the two-dimensional mixing characteristics of the pollutants in the natural streams. The velocity and depth were first calculated using RMA2, 2-D hydrodynamic model, and then the resulting flow field was inputted to RMA4, 2-D water quality model, to compute the concentration field. RMA models were verified using the velocity and concentration data measured in S-curved meandering channel. The results showed that the RMA2 model simulated well the phenomenon that the maximum velocity line is located at the Inner bank of meandering channel, and the RMA4 model was well adapted to reproduce the general mixing behavior and the separation of tracer clouds. Comparing model simulations with measured data in the field experiments, RMA2 model simulated well general flow field and tendency that the maximum velocity line skewed toward the outer bank which were found in field experiments. The simulations of RMA4 model showed that the center of the tracer cloud tends to follow the path in which the maximum velocity occurs. In this study, the dispersion coefficients are fine-tuned based on the measured coefficients calculated using field concentration data, and the results show reasonable agreement with predictive equations.

• Journal of the Korean Geotechnical Society
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• v.25 no.9
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• pp.101-106
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• 2009

In this study we analyzed the seepage characteristics of meandering section of rivers commonly seen in domestic terrain. The seepage analysis is designed to be more realistic by considering a tangent and meandering section of levee. The levee was idealized to reflect the relevant characteristics by considering the curved angle of 90 degrees and 130 degrees in the spatial frequencies, water elevation conditions, and hydraulic conductivities. Seepage analysis becomes more detailed and precise with the seepage curve shape which is interpreted to indicate the flow of three-dimensional numerical analysis program using VisualFEA. As a result of the analysis, it is shown that the water level in the straight levee was constant, regardless of hydraulic conductivities, and the total head in the meandering section was increased by the overlapping of seepage. Consequently, it is found that the total head was increased more significantly in the case of 90 degrees curved levees than 130 degrees, and the total head showed similar characteristics In the straight levee.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.62-65
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• 2017

In this paper, three DC Block designs are presented which efficiently meet the need of modern-day compactsize wireless communication systems. As one of the important parts of a complete system design, the proposed microstrip-based DC block with coupled transmission lines efficiently attenuates unwanted frequencies that cause damage to the system. The compact-sized DC block structures are created by incorporating an extended coupled-line section with a radial stub, an enveloped coupled-line section, and using alternate up-down meandering techniques. The structures are analyzed for the L-Band using a high-resistive silicon substrate. At a resonating frequency of 1.575 GHz, the designed DC Block structures have a return loss better than -10 dB, an insertion loss of around -1 dB, and also possess wide pass-band characteristics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.469-479
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• 2006

In order to investigate characteristics of the primary flow and the secondary currents in meandering channels, the laboratory experiments were conducted in S-curved channels with angle of bend, $150^{\circ}$, and sinuosity of 1.52. The experimental conditions was decided varying average depth and velocity. Under these experimental conditions, spatial variations of the secondary currents in multiple bends were observed. The experimental results revealed that the distribution of primary flow in straight section is symmetric without respect to the experimental condition and the maximum velocity line of the primary flow occurs along the shortest path in experimental channel, supporting the result of previous works. The secondary currents in second bend became more developed than those in first bend. Particularly, the outer bank cell developed distinctively and the secondary current intensity was low at the straight section and high at the bends, periodically. Also, the secondary current intensity at the bends was as twice to three times as that at the straight section, and has its maximum value at the second bend. The turbulent flow characteristics of meandering channel was investigated with turbulent intensity of the primary flow and Reynolds shear stress. It was observed that the turbulent intensity is increasing when the velocity deviation of the primary flow is large whereas Reynolds shear stress increases when both the velocity deviation of the primary flow and the secondary current are large.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.139-144
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• 2000

This paper presents development of meander monitoring system base reliable detection at conveyer belt used for materials transport line of steel company. Conventional detection method is losed the confidence, because of the place with bad surroundings of measurement so much that materials production line are completely exposed to dust, moisture and vibration. For the solution of this problem, we developed infrared meander detection system using the infrared sensor array and one chip microprocessor which is available for bad surroundings and inexpensive. The reliability of the system was estimated by experiment.