• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.6
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• pp.11-20
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• 2007

In order to make the way to determine the instream flow more practically, we have investigated many case studies and reviewed reports and papers. To validate instream flow level suggested by the case studies, DAWAST and HEC-RAS model were applied to the Gap-stream watershed in Daejeon city. Flow-duration analysis was performed both with the stream flow data gauged in the Indong, Boksu, and Hoeduck stations, and with the stream flow data estimated by the DAWAST model and the specific discharge method. Instream flow was determined among the flow-duration analysis, DAWAST, HEC-RAS model and mass balance approach. It was satisfied with various factors such as target water quality, water depth for eco-system and resorts, water surface width, flow velocity for landscape in dry season. The study suggested that the mean low flow could be replaced into the instream flow for the preliminary study because the instream flow considering ecosystem, landscape, water-friendly environment and water quality was generally close to the mean low flow.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.41 no.4
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• pp.75-86
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• 2004

This paper proposes a method to speed up the document image binarization using a water flow model. The proposed method extracts the region of interest (ROI) around characters from a document image and restricts pouring water onto a 3-dimensional terrain surface of an image only within the ROI. The amount of water to be filed into a local valley is determined automatically depending on its depth and slope. The proposed method accumulates weighted water not only on the locally lowest position but also on its neighbors. Therefore, a valley is filed enough with only one try of pouring water onto the terrain surface of the ROI. Finally, the depth of each pond is adaptively thresholded for robust character segmentation, because the depth of a pond formed at a valley varies widely according to the gray-level difference between characters and backgrounds. In our experiments on real document images, the Proposed method has attained good binarization performance as well as remarkably reduced processing time compared with that of the existing method based on a water flow model.

• Journal of Environmental Science International
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• v.22 no.4
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• pp.407-413
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• 2013

The flow of sewage has been studied for hundreds of years. Reducing drag in pipes can allow sewer to be removed easily and quickly. Drag reduction is not only a macroscale issue. Physical and chemical properties of the nano-scale can affect flow at the macroscopic scale. In this paper the predictability of hydrophobicity at the nano-scale is studied. Molecular dynamics simulations were used to calculate the range of contact angles of water droplets in equilibrium on a pillared graphite surface. It was found that at a pillar height of two graphite layers there was the largest range of contact angles. It is observed that at this height the droplet begins to transition from the Wenzel state to the Cassie-Baxter state. Surfaces with larger pillar heights have much larger contact angles corresponding to a more hydrophobic surface. Silicon dioxide was also simulated in the water droplet. The contaminant slight decreased the contact angle of the water droplet.

• Journal of Wetlands Research
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• v.24 no.3
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• pp.196-203
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• 2022

This paper contributed to the understanding of the effect of the blade relative position on performance of micro gravitational vortex turbine in free water surface. In a constant vortex flow, the rotation, voltage and current of micro vortex water turbine were measured according to the position change of the blade installed at the relative vortex height (y/h_v) ranging from 0 to 0.778 below the free water surface. The flow rate ranged from 0.0063 to 0.00662 m³/s. The results of the experiments showed that relative positions of the blade affected the performance of vortex water turbine because the distributions of incoming flow velocity and turbulence intensity were changed. The highest amount of the energy generated by the vortex water turbine occurred in the relative vortex height ranging from 0.111 to 0.222. The output power at the relative vortex height of 0.111 was about 2.4 times larger than the relative vortex height of 0.588 below the free water surface.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.26-32
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• 2008

Middle Route Project, the largest water conveyance system in China delivers the water of Changjiang River to North China. In order to create canal operation simulation system, mathematical models are established based on the analysis of hydraulics about steady flow, unsteady flow, and check gate. By simulating the canal operation behavior, we improved the check gate control algorithm and predicted the change process of water surface and flow profile which is very valuable to actual canal operation.

• Journal of the Korean Society of Visualization
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• v.6 no.2
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• pp.28-32
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• 2008

Contrary to the flow rate in fully filled pipe flows, the flow rate in partially filled pipe flows is significantly influenced by the variation of water level, channel slop, and so on. The major difference in these two flows results from the existence of a free surface. To make it clear, in the present study, a similarity of the velocity profile in a partially filled circular pipe has been investigated according to the water level. A particle image velocimetry (PIV) technique was applied to measure the three-dimensional velocity profiles. As a result, there is found a similarity of the velocity profile near the central region. However, near the side wall, the similarity is broken due to the interaction between the wall and the free surface.

• Water Engineering Research
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• v.6 no.2
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• pp.49-61
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• 2005

This paper presents the numerical study to examine characteristics of fluid flow and solute transport in a rough fracture subject to effective normal stresses. The aperture distribution is generated by using the self-affine fractal model. In order to represent a nonlinear relationship between the supported normal stress and the fracture aperture, we combine a simple mechanical model with the local flow model. The solute transport is simulated using the random walk particle following algorithm. Results of numerical simulations show that the flow is significantly affected by the geometry of aperture distribution varying with the effective normal stress level while it is slightly affected by the fractal dimension that determines the degree of the fracture surface roughness. However, solute transport is influenced by the effective normal stress as well as the fracture surface roughness.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.732-737
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• 2000

The purpose of this study is to compare the SMD(Sauter mean diameter) with different vibrant plates. Each vibrant plates have different surface roughness. Also liquid film thickness are measured for explanation how to concern atomization. Ultrasonic waves is used for vibration. Immersion liquid method is used for the measure of SMD and also liquid film thickness is measured using of point needle method. Distilled water and gasoline fuel are used to liquids. Supplied liquid flow rates are $18{\sim}296cc/min$. Centerline average roughness of vibrant plates are 0.5, 2.0, 4.7, $9.5\;{\mu}m$ and diameter of vibrant plate is 60mm. In result, good atomization of liquid is obtained in widen flow rates. The mean droplet size is increased in orders of 4.7, 2.0. 9.5, $0.5\;{\mu}m$ surface roughness. Distilled water has a big mean droplet size than gasoline fuel in low flow rate. Above the 78cc/min flow rates, distilled water has a small mean droplet size than gasoline fuel. Liquid films changes are measured with ultrasonic power. Also, cavitation effect on sprays is observed.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1434-1436
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• 2005

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.1
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• pp.69-78
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• 2015

The objective of this study was to investigate characteristics of irrigation return flow from paddy block in a reservoir irrigated district during growing seasons. The irrigation return flow was divided into three parts, quick return flow from irrigation canal (RFI), quick return flow from drainage canal (RFD), and delayed return flow (DRF). The RFI was calculated from water level and stage-discharge relationships at the ends of the irrigation canals. The DRF was estimated using measured infiltration amount from paddy fields of the irrigated district. A combined monitoring and modeling method was used to estimate the RFD by subtracting surface runoff from surface drainage. The paddy block irrigated from the Idong reservoir was selected to study the irrigation return flow components. The results showed that daily agricultural water supply (AWS), the RFI, and the RFD were $27.4mm\;day^{-1}$, $4.9mm\;day^{-1}$, and $19.8mm\;day^{-1}$, respectively in May, which were greater than other months (p<0.05). The return flow ratio of the RFI and the RFD were the greatest in July (34.6%) and May (72.3%), respectively. The daily AWS was closely correlated with the RFD (correlation coefficients of 0.76~0.86) in except for July with, while correlation coefficient with the RFI were 0.56 and 0.42 in June and July, respectively (p<0.01). The total irrigation return flow was 1,965 mm in 2011, and 1,588 mm in 2012, resulting in total return flow ratio of 84.6% and 79.1%, respectively. This results indicate that substantial amounts of agricultural water were returned to streams as irrigation return flow. Thus, irrigation return flow should be fully considered into the agricultural water resources planning in Korea.