• Water for future
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• v.26 no.4
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• pp.107-115
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• 1993

The results of laboratory experiments on the clear-water local scour of cohesionless bed sediment at three types of the pier shape are presented. Based on the experimental data, the relative equilibrium depth of local scour is related to the pier shape, the geometric standard deviation of the bed material, the velocity ratio and the pier Froude number. The relative local scour depths were smallest ant the round-nosed pier and remarkably reduced at the non-uniform bed sediment, comparing with those at the uniform bed material. The effect of sediment grading on the local scour reduction was discussed and compared with Raudkivi and Ettema's experiments.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.202-211
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• 1995

Heat and hydrogen transfer characteristics have been experimentally investigated for a hydride reaction bed, in which hydride material LaN $i_{4,7}$A $l_{0.3}$ is contained for hydrogen storage. This problem is of particular interest in the design of metal hydride devices such as metal-hydride refrigerators, heat pumps, or metal-hydride storage units. Transient behavior of hydrogen transfer through the hydride materials as well as heat transfer is studied during absorption and desorption processes in detail. The experimental results obtained indicate that the mass flow of the hydrogen is strongly affected by the governing parameters, such as the initial pressure of the reaction bed, absorption or desorption period, and cooling or heating temperature. These mass transfer results are along with the heat transfer rate between hydride materials and heat transfer medium in the reaction bed.d.d.

• Journal of Korean Society of Water and Wastewater
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• v.25 no.3
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• pp.349-357
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• 2011

This study has an objective to estimate effect on water-quality enhancement by removal of contaminated river-bed material using a two-dimensional numerical modeling in the Seonakdong River, the Pyunggang River and the Maekdo River. RMA2 and RMA4 models were used for flow and contaminant transport simulation, respectively. After the analysis of the effects of flow restoration plan for the Seonakdong River system made by Lee et al (2008), simulation have been performed about scenarios which contains operations of the Daejeo Gate, the Noksan Gate, the Makdo Gate (on planning), and the Noksan Pumping Station. Because there is no option for elution from bed sediment in the RMA4 model, a simple technique has been used for initial condition modification for elution. The analyses revealed that the effect on water quality improvement due to dredging of bed sediment seemed to be less than 10 % of the total effect. The most efficient measure for the water quality improvement of the river system was the linked operation of water-gates and pumping station.

• Journal of the Korea Organic Resources Recycling Association
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• v.25 no.3
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• pp.79-89
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• 2017

Changes in pH, EC and water soluble cation and anion of the bed material in the rearing box of earthworms were investigated while sewage sludges or night soil sludge were cumulatively supplied to the 15 grams of initial earthworm population in the rearing box. Initial biochemical properties of sludges such as pH, EC, V.S. and water content were at the edible levels for earthworm. However, as the cumulative amount of sludges supplied to the earthworms were increased, pH of bed material in the rearing box was lowered and EC was increased, which meant that salt contents of bed material in the rearing box had been accumulated. Water soluble cations and anions were also accumulated in the bed material of the rearing box. Accumulation rates of ${NO_3}^-$ were especially prominent. Consequently, feeding rates of earthworm populations were reduced to nearly zero and earthworm populations finally died.

• Journal of Biosystems Engineering
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• v.29 no.2
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• pp.151-158
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• 2004

This research was conducted to study the offensive odor adhesion efficiency of filter bed materials using the experimental column that was designed and constructed in this work. The offensive odor adhesion experiment was conducted using mixture of high physical adhesion efficiency material, and the fixity of deodorization microorganism of selected filter bed material was tested using ammonia exclude microorganism A4-2 and sulfur oxidation microorganism S5-5.2 those were cultured at the Agricultural Chemical Department of Chungnam National University, and deodorization efficiency of selected filter bed material mixture was tested. Followings are summary of these tests results. 1) Amount of elimination of the offensive odor gas ammonia and hydrogen sulfide per unit volume were 0.054 and 0.016 $\ell$/㎤ in rice hull, 0.01 and 0.004 $\ell$/㎤ in rice straw, 0.158 and 0.01 $\ell$/㎤ in coconut, 0.014 and 0.02 $\ell$/㎤ in perlite, 0.004 and 0.003 $\ell$/㎤ in high road ball, and 0.112 and 0.015 $\ell$/㎤ chaff of pine, respectively. 2) Amount of elimination of offensive odor gas of ammonia and hydrogen sulfide per unit vloume were 0.079 and 0.016 $\ell$/㎤ in mixture 1, 0.045 and 0.014 $\ell$/㎤ in mixture 2, 0.123 and 0.017 $\ell$/㎤ in mixture 3, 0.055 and 0.016 $\ell$/㎤ in mixture 4, 0.031 and 0.015 $\ell$/㎤ in mixture 5, and 0.111 and 0.020 $\ell$/㎤ in mixture 6, respectively. 3) The offensive odor elimination microoraganism inoculated to the mixture of chaff of pine (70%) and pert (30%) showed the elimination efficiency of 99.06% and 96.61% against the ammonia and hydrongen sulfide, respectively, during 24 hours period.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.2
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• pp.151-157
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• 2023

Integrating dielectric materials into LTCC is a convenient method to increase the integration density in electronic circuits. To enable co-firing of the high-k and low-k dielectric LTCC materials in a multi-material hetero-laminate, the shrinkage characteristics of both materials should be similar. Moreover, thermal expansion mismatch between materials during co-firing should be minimized. The alternating stacking of an LTCC with silica filler and that with calcium-zirconate filler was observed to examine the use of the same glass in different LTCCs to minimize the difference in shrinkage and thermal expansion coefficient. For the LTCC of silica filler with a low dielectric constant and that of calcium zirconate filler with a high dielectric constant, the amount of shrinkage was examined through a thermomechanical analysis, and the predicted appropriate fraction of each filler was applied to green sheets by tape casting. The green sheets of different fillers were alternatingly laminated to the thickness of 500 ㎛. As a result of examining the junction, it was observed through SEM that a complete bonding was achieved by constrained sintering in the structure of 'calcium zirconate 50 vol%-silica 30 vol%-calcium zirconate 50 vol%'.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.17-17
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• 2011

As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. However, most of them can treat movable bed only and cannot be applied to the bed deformation process of sediment on rocks. If the friction angle between the sediment and the bed surface is assumed to be the same as the friction angle between the sediment and the sediment, sediment transport rate must be smaller without sediment deposition layer on the rocks. As a result, the reproduced bed geometry is affected very well. In this study, non-equilibrium transport process of non-cohesive sediment on rigid bed is introduced into the horizontal two dimensional bed deformation model and the model is applied to the erosion process of replenished sediment on rock in the Nakagawa, Japan. Here, the Japanese largest scale sediment augmentation has been performed in the Nakagawa. The results show that the amounts of the eroded sediment and the remained sediment reproduced by the developed numerical model are $56300m^3$ and $26800m^3$, respectively. On the other hand, the amounts of the eroded sediment and the remained sediment measured in the field after the floods are $56600m^3$ and $26500m^3$, respectively. The difference between the model and field data is very small. Furthermore, the bed geometry of the replenished sediment after the floods reproduced by the developed model has a good agreement with the measured bed geometry after the floods. These results indicate that the developed model is able to simulate the erosion process of replenished sediment on rocks very well. Furthermore, the erosion speed of the replenished sediment during the decreasing process of the water discharge is faster than that during the increasing process of the water discharge. The replenished sediment is eroded well, when the top of the replenished sediment is covered by the water. In general, water surface level is kept to be high during the decreasing process of the discharge during floods, because water surface level at the downstream end is high. Hence, it is considered that the high water surface level during the decreasing process of the water discharge affects on the fast erosion of the replenished sediment.

• Journal of Environmental Science International
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• v.20 no.5
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• pp.555-564
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• 2011

This study examines the potential restoration of abandoned channels of the Mangyeong River in South Korea. To analyze the morphological changes and equilibrium conditions, a flow duration analysis was performed to obtain the discharge of 255 m3/s with a recurrence interval of 1.5 year. It is a gravel-bed stream with a median bed diameter of 36 mm. The reach-averaged results using HEC-RAS showed that the top width is 244 m, the mean flow depth is 1.11 m, the width/depth ratio is very high at 277, the channel velocity is 1.18 m/s, and the Froude number is also high at 0.42. The hydraulic parameters vary in the vicinity of the three sills which control the bed elevation. The total sediment load is 6,500 tons per day and the equivalent sediment concentration is 240 mg/l. The Engelund-Hansen method was closer to the field measurements than any other method. The bed material coarser than 33 mm will not move. The methods of Julien-Wargadalam and Lacey gave an equilibrium channel width of 83 m and 77 m respectively, which demonstrates that the Mangyeong River is currently very wide and shallow. The planform geometry for the Mangyeong River is definitely straight with a sinuosity as low as 1.03. The thalweg and mean bed elevation profiles were analyzed using field measurements in 1976, 1993 and 2009. The measured profiles indicated that the channel has degraded about 2 m since 1976. The coarse gravel material and large width-depth ratio increase the stability of the bed material in this reach.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.149-157
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• 2010

The purpose of this study is to analyse characteristics of roughness coefficient based on bed-material size of the gravel-bed rivers using field data obtained from nine domestic rivers. Roughness coefficient is calculated using Manning's equation. Roughness coefficient decreases with increasing discharge, but above a certain discharge, it tends to be constant. Similarly, roughness coefficient shows reverse relationship with relative smoothness (R/D). The regression equation adopting theoretically derived value of 2.03 as log coefficient indicates close similarity with the previous equation proposed by Limerinos (1970). Roughness coefficient values converged above certain discharges lie in the range from 0.024 to 0.045. From them, empirical equations based only on bed-material size are derived and compared with those suggested by the previous studies.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.651-655
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• 2000

The objective of present work is to investigate experimentally the characteristics of heat transfer. A fluidized bed combustion has advantages of pollution control, fuel flexibility and excellent heat transfer. The present study investigates fundamental phenomena of bed-to-surface heat transfer in high temperature fluidized beds to improve design of immersed tube surface. The tested operating variables are bed temperature, supeficial velocity, mean size of bed material, and the rake angle of fin. Generally, heat transfer rates between the fluidized bed and immersed finned-tube are much higher than those of a smooth tube. A life time of finned-tube is generally longer than that of smooth tube.