• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.196-196
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• 2016

Landslide dam failure presents as a severe natural disaster due to its adverse impact to people and property. If the landslide dams failed, the discharge of a huge volume of both water and sediment could result in a catastrophic flood in the downstream area. In most of previous studies, breaching process used to be considered as a constructed dam, rather than as a landslide dam. Their erosion rate was assumed to relate to discharge by a sediment transport equation. However, during surface erosion of landslide dam, the sediment transportation regime is greatly dependent on the slope surface and the sediment concentration in the flow. This study aims to accurately simulate the outflow hydrograph caused by landslide dam by overtopping through a 2D surface flow erosion/deposition model. The lateral erosion velocity in this model was presented as a function of the shear stress on the side wall. The simulated results were then compared and it was coherent with the results obtained from the experiments.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.155-162
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• 2012

When RC (Reinforced Concrete) structures are exposed to sea water, steel corrosion can occur and this leads a degradation of structural performance. Referring the electro-deposition system with sea water from the 1st step research, durability and structural performance are evaluated in coated steel and RC members containing it in the 2nd research. In the durability performance test, Half Cell Potential test is performed and the coated steel is evaluated to have the high resistance to corrosion, which shows only 35% of corrosion velocity in normal (bare) steel. In the structural performance test, tensile strength, adhesive strength, and flexural/shear in RC member are performed. For the electro-deposit coated steel, increasing ratios of 3.2% and 8.8% are evaluated in the test of tensile strength and adhesive strength, respectively. For the structural test in RC member, there is no big difference between RC members with coated and non-coated steel in ultimate load and failure pattern It is evaluated that the chemical compound with $CaCO_3$ and $Mg(OH)_2$ from electro-deposition causes slightly increased structural performance. The electro-deposit coated steel can be more widely applied after performance verification from several tests like fatigue, resistance to impact, and long term-submerging test.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.34-34
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• 2012

Heavy storms rainfall has caused many landslides and slope failures especially in the mountainous area of the world. Landslides and slope failures are common geologic hazards and posed serious threats and globally cause billions in monetary losses and thousands of casualies each year so that studies on slope stability and its failure mechanism under rainfall are being increasing attention of these days. Rainfall-induced slope failures are generally caused by the rise in ground water level, and increase in pore water pressures and seepage forces during periods of intense rainfall. The effective stress in the soil will be decreased due to the increased pore pressure, which thus reduces the soil shear strength, eventually resulting in slope failure. During the rainfall, a wetting front goes downward into the slope, resulting in a gradual increase of the water content and a decrease of the negative pore-water pressure. This negative pore-water pressure is referred to as matric suction when referenced to the pore air pressure that contributes to the stability of unsaturated soil slopes. Therefore, the importance is the study of saturated unsaturated soil behaviors in evaluation of slope stability under heavy rainfall condition. In an actual field, a series of failures may occur in a slope due to a rainfall event. So, this study attempts to develop a numerical model to investigate this failure mechanism. A two-dimensional seepage flow model coupled with a one-dimensional surface flow and erosion/deposition model is used for seepage analysis. It is necessary to identify either there is surface runoff produced or not in a soil slope during a rainfall event, while analyzing the seepage and stability of such slopes. Runoff produced by rainfall may result erosion/deposition process on the surface of the slope. The depth of runoff has vital role in the seepage process within the soil domain so that surface flow and erosion/deposition model computes the surface water head of the runoff produced by the rainfall, and erosion/deposition on the surface of the model slope. Pore water pressure and moisture content data obtained by the seepage flow model are then used to analyze the stability of the slope. Spencer method of slope stability analysis is incorporated into dynamic programming to locate the critical slip surface of a general slope.

• 한국해양학회지
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• v.26 no.4
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• pp.332-339
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• 1991

The sedimentation pattern in Namhaepo Bay, a macrotidal coastal embayment of western Korea, was investigated by means of analysing high-resolution seismic profiles, sediment samples, and tidal currents. Recent sediments up to 20 m which overlie the irregular surface of the acoustic basement. The sediments consist mainly of sandy silt and silt; the mean grain size of these sediments ranges from 4 to 5.5 phi, showing a shoreward-fining distribution pattern. This distribution pattern agrees are largely reversed during ebb, with a maximum velocity of 39 cm/sec. The calculated shear velocity of the tidal currents at sea bed ranges from 0.5 to 3.3 cm/sec during flood and from 0.7 to 2.5 cm/sec during ebb. The mean values of these velocities exceed the critical shear velocity for the silt particles. The data suggest that the tidal currents play an important role in the transportation and deposition of sediments in the bay and the surface topography of the sea floor is largely deter-mined by tidal sedimentation.

• Asian-Australasian Journal of Animal Sciences
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• v.28 no.7
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• pp.976-986
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• 2015

The present study was conducted to determine the effects of lipid sources with different fatty acids profile on meat fatty acids profile and beef quality traits of Nellore. A total of 45 Nellore animals with an average initial body weight of $419{\pm}11kg$ (at $15{\pm}2mo$) were distributed in a completely randomized design consisting of 5 treatments and 9 replicates. The roughage feed was maize silage (600 g/kg on a dry matter [DM] basis) plus concentrate (400 g/kg on a DM basis). The dietary treatments were as follows: without fat (WF), palm oil (PO), linseed oil (LO), protected fat (PF), and soybean grains (SG). No effects of lipid sources were observed (p>0.05) on beef color, pH, water-holding capacity, and sarcomere length. Beef from cattle fed PO had greater shear-force values (p<0.05) compared to beef from cattle fed WF. Deposition of main unsaturated fatty acids (oleic, linoleic, and linolenic) was greater in treatments WF, SG, and LO, respectively, while the values of conjugated linoleic acid (CLA) were greater when animals were fed LO. The inclusion of LO in the diet enhances the concentration of CLA in longissimus muscle and subcutaneous fat besides improving the atherogenicity index and elongase activity. As such, LO can be used with the aim to improve the quality of beef from confined Nellore cattle. Conversely, the use of PO is not recommended since it may increase the concentration of undesirable unsaturated fatty acids in muscle and subcutaneous fat, shear-force and the atherogenicity index.

• Membrane Journal
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• v.25 no.3
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• pp.268-275
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• 2015

Effects of aeration intensity on local fouling were investigated in submerged membrane modules. Higher liquid velocities were observed at the section with the lower fiber packing density. The liquid velocity is increased with increasing the gas-liquid injection factor. The high shear stress coincided with the high liquid velocity. The shear stress increases with the increasing of gas-liquid injection factor and the liquid velocity improves with the increasing of gas-liquid injection factor. Irreversible fouling resistance ($R_{ir}$) of the fiber position is significant in a local region of high suction pressure near the suction point of the fiber (position 1). The ratio of $R_{ir}/R_m$ and $R_{ir}/R_r$ of position 1 was highest compared to the position 2 and 3. Irreversible fouling resistances results confirmed the preferential deposition of foulants near the suction part of the fiber where the local suction pressure is the highest and correspondingly, more particles are accumulated to the membrane surface. The effects of local fouling along the fiber length are significant factors to optimize the design of submerged modules.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.1
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• pp.45-52
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• 2020

Even though sewers have been conventionally designed to prevent from sediment deposition using a specified minimum velocity or shear stress at a particular depth of flow or with a particular frequency of occurrence, it was appreciated that these methods do not consider the characteristics and concentration of the sediment and the specific hydraulic conditions of the sewer with sediment. In this study, a densimetric Froude number formula was suggested considering particle diameter and volumetric concentration of the sediment as well as flow depth and flowrate, based on several domestic field inspections, which was compared with other formulas proposed by previous investigators. When the sediment concentration was not considered, the calibration coefficient of 0.125-1.5 to the densimetric Froude numbers of this study was needed to obtain the similar ones with previous investigators'. For the densimetric Froude number formula obtained with consideration of sediment concentration, the exponent value of term C_v was almost the same as that of previous results and that of d₅₀/R_h was similar for F_r < 2.2.

• Tribology and Lubricants
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• v.38 no.6
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• pp.235-240
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• 2022

Atomically-thin 2D nanomaterials can be easily deformed and have surface corrugations which can influence the frictional characteristics of the 2D nanomaterials. Chemical vapor deposition (CVD) graphene can be grown in a wafer scale, which is suitable as a large-area surface coating film. The CVD growth involves cooling process to room temperature, and the thermal expansion coefficients mismatch between graphene and the metallic substrate induces a compressive strain in graphene, resulting in the surface corrugations such as wrinkles and atomic ripples. Such corrugations can induce the friction anisotropy of graphene, and therefore, accurate imaging of the surface corrugation is significant for better understanding about the friction anisotropy of CVD graphene. In this work, the combinatorial analysis using friction force microscopy (FFM) and transverse shear microscopy (TSM) was implemented to unveil the friction anisotropy of CVD bi-layer graphene. The periodic friction anisotropy of the wrinkles was measured following a sinusoidal curve depending on the angles between the wrinkles and the scanning tip, and the two domains were observed to have the different friction signals due to the different directions of the atomic ripples, which was confirmed by the high-resolution FFM and TSM imaging. In addition, we revealed that the atomic ripples can be easily suppressed by ironing the surface during AFM scans with an appropriate normal force. This work demonstrates that the friction anisotropy of CVD bilayer graphene is well-correlated with the corrugated structures and the local friction anisotropy induced by the atomic ripples can be controllably removed by simple AFM scans.

• Journal of the Korean Professional Engineers Association
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• v.21 no.1
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• pp.5-12
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• 1988

The purpose of this paper is to investigate on the optimum coating thickness layer of TiC-Al$_2$O$_3$ coated cemented carbide tool. Chemical Vapor Deposition (CVD) of a thick film of TiC-A1$_2$O$_3$ on a cemented carbide produces an intermediate layer, $1.5mutextrm{m}$, 4.5${\mu}{\textrm}{m}$, 7.5${\mu}{\textrm}{m}$ 10.5${\mu}{\textrm}{m}$, 4 kind of TiC between the substrate and the $1.5mutextrm{m}$ constant thick A1$_2$O$_3$ coating. Experiments were carried out with the test relationship between coating thickness and shear angle, surface roughness, cutting force, microphotograph of crater wear, flank wear, tool life. From the experimental results, it was found that the optimum coating thickness of TiC-A1$_2$O$_3$ is 6${\mu}{\textrm}{m}$. Although the coating thickness layer 9${\mu}{\textrm}{m}$. 12${\mu}{\textrm}{m}$ have a much loger tool wear than an 3${\mu}{\textrm}{m}$, 6${\mu}{\textrm}{m}$ coating tool in cutting condition feed 0.05mm/rev, and the condition of feed 0.2mm/rev, 0.3mm/rev has upon in the shot time phenomenon of chipping.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.2
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• pp.51-60
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• 2003

An experimental research program is being undertaken to develop a regeneratively-cooled experimental thrust chamber of liquid rocket engine using liquefied natural gas and liquid oxygen as propellants. Prior to firing test using a regenerative cooling with liquefied natural gas in this program, several firing tests were conducted with water as a coolant. Experimental thrust chambers with a thrust of about 10tf were developed and their firing test facility was built up. Injector used in the thrust chamber was of shear-coaxial type appropriate for propellants of gas and liquid phase and cooling channels are of milled rectangular configuration. Periodical variation of the soot deposition and discoloration was observed through an eyes' inspection on the inner wall of a combustion chamber and a nozzle after each firing test, and an intuitive concept of the periodical variation of mixture ratio near the inner wall of a combustion chamber and a nozzle at once was brought about and analyzed quantitatively. Thermal heat flux to the coolant was calculated and modified with the periodical variation model of mixture ratio, and the increment of coolant temperature at cooling channels was compared with measured one.