• Transactions of the Korean Society of Mechanical Engineers B
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• 제23권7호
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• pp.937-944
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• 1999

The near-wall flow structures of turbulent boundary layer over riblets having semi-circular grooves were investigated experimentally for the drag decreasing ($s^+=25.2$) and drag increasing ($s^+=40.6$) cases. The field of view used for tho velocity field measurement was $6.75{\times}6.75mm^2$ in physical dimension, containing two grooves. One thousand instantaneous velocity fields over the riblets were extracted for each case of drag increase and decrease. For comparison, five hundreds instantaneous velocity fields over a smooth flat plate were also obtained under the same flow conditions. To see the global flow structure qualitatively, the flow visualization was also performed using the synchronized smoke-wire technique. For the drag decreasing case ($s^+=25.2$), most of the streamwise vortices stay above the riblets, interacting with the riblet tips. The high-speed in-rush flow toward the riblet surface rarely influences the flow inside tho riblet valleys submerged in the viscous sublayer. The riblet tips seem to impede the spanwise movement of the longitudinal vortices and induce secondary vortices. The turbulent kinetic energy in the riblet valley is sufficiently small to compensate the increased wetted area of the riblets. In addition, in the logarithmic region, the turbulent kinetic energy are small or almost equal to that of a smooth flat plato. For the drag increasing case ($s^+=40.6$), however, the streamwise vortices move into the riblet valley freely, interacting directly with the riblet inner surface. The penetration of the high-speed in-rush flow on the riblets increases tho skin-friction. The turbulent kinetic energy is increased in the riblet valleys and even in the outer region compared to that over a flat plate.

• Korean Journal of Materials Research
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• 제24권1호
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• pp.60-65
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• 2014

Fe-based amorphous coatings were fabricated on a soda-lime glass substrate by the vacuum kinetic spray method. The effect of the gas flow rate, which determines particle velocity, on the deposition behavior of the particle and microstructure of the resultant films was investigated. The as-fabricated microstructure of the film was studied by field emission scanning electron microscopy (FE-SEM) and high resolution transmission electron microscopy (HR-TEM). Although the activation energy for transformation from the amorphous phase to crystalline phase was lowered by severe plastic deformation and particle fracturing under a high strain rate, the crystalline phases could not be found in the coating layer. Incompletely fractured and small fragments 100~300 nm in size, which are smaller than initial feedstock material, were found on the coating surface and inside of the coating. Also, some pores and voids occurred between particle-particle interfaces. In the case of brittle Fe-based amorphous alloy, particles fail in fragmentation fracture mode through initiation and propagation of the numerous small cracks rather than shear fracture mode under compressive stress. It could be deduced that amorphous alloy underwent particle fracturing in a vacuum kinetic spray process. Also, it is considered that surface energy caused by the formation of new surfaces and friction energy contributed to the bonding of fragments.

• Journal of the Korean GEO-environmental Society
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• 제14권12호
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• pp.23-30
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• 2013

Bearing capacity of pile is governed by only skin friction in frozen ground condition, while it is generally governed both by skin friction and end bearing capacity in typically unfrozen ground condition. Skin friction force, which arises from the interaction between pile and frozen soils, is defined as adfreeze bond strength, and adfreeze bond strength is one of the most important key parameters for design of pile in frozen soils. Many studies have been carried out in order to analyze adfreeze bond strength characteristics over the last fifty years. However, many studies for adfreeze bond strength have been conducted with limited circumstances, since adfreeze bond strength is sensitively affected by various influence factors such as intrinsic material properties, pile surface roughness, and externally imposed testing conditions. In this study, direct shear test is carried out inside of large-scaled freezing chamber in order to analyze the adfreeze bond strength characteristics with varying freezing temperature and normal stress. Also, the relationship between adfreeze bond strength and shear strength of the frozen soil obtained from previous study was analyzed. The coefficient of adfreeze bond strength was evaluated in order to predict adfreeze bond strength based on shear strength, and coefficients suggested from this and previous studies were compared.

• Journal of the Society of Cosmetic Scientists of Korea
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• 제50권1호
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• pp.11-18
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• 2024

Recently, there have been attempts to claim the hair moisturizing effect for a hair care product, however there has not yet been an official evaluation method because heating temperature for hair has not been established. This study was conducted to establish a quantitative evaluation for hair water content. In order to observe the behavior of water inside hair, heat was applied to hair with various temperatures using thermogravimetric dry residue. As the heating temperature increased, the amount of moisture released from the hair increased. As a result of evaluating hair using a differential scanning calorimeter (DSC), a unique phenomenon in which a rapid endothermic reaction occurs around 75 ℃ was observed. This phenomenon was also observed in different ethnic hair. In hair that damaged the hair cuticle barrier with oxidation and heat, this rapidly rising endothermic reaction temperature occurred at 77 ℃, which was slightly higher, and 73 ℃ was observed when this hair was applied with polar oil, conditioning polymer, or keratin protein. To determine how this reaction affects the hair surface, friction test was performed using an atomic force microscope. When heated above 75 ℃, cuticle friction increased, however when heated above 90 ℃, there was no change in hair cuticle friction. Finally, it was confirmed that around 75 ℃ is the critical temperature at which desorption of water bound to the hair occurs. It is suggested that a heating temperature of 75 ℃ is the optimal temperature for detecting and quantifying the moisture content of hair, and that approximately 10% detected at 75 ℃ can be a standard value for hair moisture content.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• 제15권2호
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• pp.83-94
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• 1979

It is more than half a century since anchovy boat seine has been introduced in Korean fishery to catch anchovies, but the study on it was began in 1970's by the authors. In 1971, the authors carried out an experiment about the net formation of the traditional gear in tow by using model net, and in 1978, about the patti net gear, commercially used in Japan. Now, the authors investigated the new model net, model 79, expecting to be suitable for commercial fishery in Korea, with the strong point of those two gears kept and the weak point of them corrected. The experimental gear was constructed attached the long net pendants to the fore end of extension wing by shortening its length in two-third of the traditional gear. Inside wing was improved so as to show high opening in tow. Rubber bobbins and hanging rings are used to prevent the heavy friction of bosom ground rope against the sea bed. The gear was used to catch anchovies in the commercial fishing ground in the south-eastern coastal waters of Korea, from May to October in 1979. From the experiment, the following results are found. 1. In opening height, the experimented gear was 30 percent greater than the traditional one. 2. It took 3 to 5 minutes for the bosom ground rope to sink from the surface to the sea bed, while 10 to 15 minutes for the traditional gear to do. 3. Ground rope never scooped mud, even in the muddy sea bed. 4. The gear showed better catchability than the traditional gear.

• Applied Chemistry for Engineering
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• 제7권6호
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• pp.1027-1033
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• 1996

Under the Irradiation of the radiofrequency wave, the dipole materials vibrate as microwavic phase change. This causes friction between adjacent molecules and enables an unique charateristics of interior heating of the materials. When dipole gases are adsorbed inside of a solid radiofrequency wave absorber, the gases can be decomposed easily by the microwave energy. The decomposition of sour gases was successfully tested in this manner to develop a sour gas removal process from the combustion flue gas. The standard gas bearing NO and $SO_2$ was passed through and microwave was applied on the calcined char bed as the wave absorber and the gas adsorbent. It was found that more then 95% of NO and 70 % of $SO_2$ was decomposed to the environmentally clean elements during the passage through the 20 gram char bed under the microwave impingement. The surface area and the porosity of char increased because the oxygen radicals produced from decomposed gas attacked carbon in the char capillaries and formed $CO_2$. For a lower concentration of sour gas, general cases in the commercial combustion processes, almost complete decomposion is believed possible and this method is surely expected to be useful for the prevention of air pollutions.

• Journal of the Korean GEO-environmental Society
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• 제9권5호
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• pp.71-81
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• 2008

Active earth pressure formula, which can consider the effects of ground surface inclination, inclination of inside retaining wall face, wall friction, line load, uniform load, soil cohesion and adhesion, was derived based on the force equilibrium principle. In order to verify the accuracy of this proposed formula, the calculated active earth pressures by the proposed formula were compared with those of graphical solutions. Also, the active earth pressures determined by the proposed formula were compared with those by Coulomb's, Rankine's and Mazindrani's solution under specific conditions. The results matched quite well not only with the graphical solutions but also with those by three other methods. Also, the trend of active earth pressures by the proposed formula were corresponded with results of experimental study by Fang, et al. It can be concluded that this generalized formula not only can overcome the limitations of Rankine's, Coulomb's and Mazindrani's active earth pressure formula but also can consider the external loading conditions.

• Journal of the Korean Geosynthetics Society
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• 제20권4호
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• pp.85-93
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• 2021

The seventy percentage of Korean Peninsular is covered by the mountainous area, and the depth of west sea and south sea is relatively shallow. Therefore, a large scale land reclamation from the sea has been implemented for the construction of industrial complex, residental area, and port and airport facilities. The common problem of reclaimed land is consisted of soft ground, and hence it has low load bearing capacity as well as excessive settlement upon loading on the ground surface. The hollow concrete block has been used to reinforce the loose and soft foundation soil where the medium-high apartment or one-story industrial building is being planned to be built. Recently the earthquakes with the magnitude of 4.0~5.0 have been occurred in the west coastal and southeast coastal areas. Lee (2019) reported the advantages of hollow concrete block reinforced shallow foundation through the static laboratory bearing capacity tests. In this study, the dynamic behavior of hollow concrete block reinforced sandy ground with filling the crushed stone in the hollow space has been investigated by the means of shaking table test with the size of shaking table 1000 mm × 1000 mm. Three types of seismic wave, that is, Ofunato, Hachinohe, Artificial, and two different accelerations (0.154 g, 0.22 g) were applied in the shaking table tests. The horizontal displacement of structure which is situated right above the hollow concrete block reinforced ground was measured by using the LVDT. The relative density of soil ground are varied with 45%, 65%, and 85%, respectively, to investigate the effectiveness of reinforcement by hollow block and measured the magnitude of lateral movement, and compared with the limit value of 0.015h (Building Earthquake Code, 2019). Based on the results of shaking table test for hollow concrete block reinforced sandy ground, honeycell type hollow block gives a large interlocking force due to the filling of crushed stone in the hollow space as well as a great interface friction force by the confining pressure and punching resistance along the inside and outside of hollow concrete block. All these factors are contributed to reduce the great amount of horizontal displacement during the shaking table test. Finally, hollow concrete block reinforced sandy ground for shallow foundation is provided an outstanding reinforced method for medium-high building irrespective of seismic wave and moderate accelerations.