• Nuclear Engineering and Technology
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• v.24 no.3
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• pp.274-284
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• 1992

A 1/15-scale CREARE experiment, which simulates the thermal-hydraulic behavior in the reactor pressure vessel of a PWR during a hypothetical Loss Of Coolant Accident, has been analyzed using CATHARE code for the associated model assessment to represent the phenomenon. The key parameters examined in the CREARE experiment were known as ECC water injection rate. ECC water subcooling, system pressure, and steam flow rate coming out from the core bottom. The present CATHARE simulation, however, has been mainly focused on qualitative analysis of a countercurrent flow in the downcomer. The discrepancy of the simulation results with the experimental data is considered arising primarily from an inadequate numerical representation as well as an interfacial friction model. Accordingly it is suggested from the sensitivity studies that either multidimensional approach or further examination of momentum equations at a junction near a volume element in CATHARE be necessary in order to represent the phenomenon more realistically.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.31 no.2 s.51
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• pp.135-140
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• 2005

A solid state emulsion haying high velocity gradient shows two important transition ranges in the plot of storage modulus(G') as a function of shear strain, when the state is changed from solid to liquid. However, a solid state emulsion having low velocity gradient shows only one apparent transition range when the change from solid to liquid state takes place. The result implies the importance of the surface properties in the solid state emulsion. The addition of water phase in the solid state emulsion reduces the modulus in the modulus in the surface transition range by increasing interfacial friction and weakening the matrix. The addition of pigments increases the modulus in the modulus in the surface transition range by reinforcing the matrix, when there is no wafer phase in the solid state emulsion. When the solid state emulsion has water phase, however, the addition of pigments decreases the modulus in the modulus in the surface transition range.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.7
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• pp.777-782
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• 2011

Micro features on the surface are well-known to have significant effects on optical or mechanical properties such as the optical interference, reflectance at the surface, contact angle, interfacial friction, etc. These surface micro features are increasingly employed to enhance the functionality of the applications in various application areas such as optical components for LCD or solar panel. Diverse surface features have been proposed and some of them are showing excellent efficiency or functionality, especially in optical applications. Most applications employing the micro features need manufacturing process for mass production and the injection molding and roll-to-roll forming, which are typical processes for mass production adopting polymeric materials, may be also preferred for micro patterned plastic product. Since the functionality or efficiency of the surface structures generally depends on the shape and the size of the structure itself or the array of the structures on the surface, it would be very important to replicate the features very precisely as being designed during the molding the micro pattern applications. In this paper, a series of research activities is introduced for roll-to-roll forming of micro patterned film including filling of patterns with UV curable resin, demolding of surface structures from the roll tool, control of surface energy and cure shrinkage of resin and dispose time and intensity of the UV light for curing of UV curable resin.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.9 no.1
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• pp.9-23
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• 1997

A numerical study of a two-layer, stratified flow is investigated, using the implicit finite difference method in one dimension. The results of computational method have been tested and, in case of lock exchange flow, compared with the results of experimental data. The results of model experiments with various interfacial, bottom friction coefficients along with various time weighting factor of numerical scheme and dissipative interface are shown and discussed. Two-layer model experiment has been also carried out to investigate the generation and propagation characteristics of internal tidal wave over the steep bottom topography under stratified condition. The internal wave seems to well radiate through the downstream boundary under the experiments adopting radiation conditions both at two layers and only at upper layer, confirming the applicability of radiational boundary condition in stratified flows. It is also shown that the internal wave through the downstream boundary propagates more actively with increasing thickness of lower layer in the downstream. This implies that the potential tidal energy in the interface will depend upon the thickness of lower layer for the constant thickness of upper layer.

• Elastomers and Composites
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• v.39 no.1
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• pp.12-22
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• 2004

The plasma surface modification of natural rubber vulcanizate was carried out using chlorodifluoromethane in a radio-frequency (13.56 MHz) electrodeless bell type plasma reactor. The modification was qualitatively assessed by Fourier transform infrared spectroscopy. The frictional force of the plasma-treated surface was found to decrease with the time of plasma treatment. An increase in the surface polarity, as evidenced by the decrease in contact angle of a sessile drop of water and ethylene glycol on the natural rubber vulcanizate surface, was noted with the plasma modification. In the case of similar plasma treatment of glass surface, only a reduction in the polarity was observed. The use of geometric and harmonic mean methods was found to be useful to evaluate the London dispersive and specific components of surface free energy. Irrespective of the method used for evaluation, an increasing trend in the surface free energy was noted with increasing plasma treatment time. However, the harmonic mean method yielded comparatively higher values of surface free energy than the geometric mean method. The plasma surface modification was found to vary the frictional coefficient by influencing the interfacial, hysteresis and viscous components of friction in opposing dual manners.

• Composites Research
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• v.34 no.3
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• pp.192-198
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• 2021

Due to enormous market growing of electric vehicles without combustion engine, reducing unwanted BSR (buzz, squeak, and rattle) noise is highly demanded for vehicle quality and performance. Particularly, innerbelt weatherstrips which not only block wind noise, rain, and dust from outside, but also reduce noise and vibration of door glass and vehicle are required to exhibit high damping properties for improved BSR performance of the vehicle. Thermoplastic elastomers (TPEs), which can be recycled and have lighter weight than thermoset elastomers, are receiving much attention for weatherstrip material, but TPEs exhibit low material damping and compression set causing frictional noise and vibration between the door glass and the weatherstrip. In this study, high damping EPDM (ethylene-propylene-diene monomer)/PP (polypropylene) thermoplastic vulcanizates (TPV) were investigated by varying EPDM/PP ratio and ENB (ethylidene norbornene) fraction in EPDM. Viscoelastic properties of TPV materials were characterized by assuming that the material damping is directly related to the viscoelasticity. The optimum material damping factor (tanδ peak 0.611) was achieved with low PP ratio (14 wt%) and high ENB fraction (8.9 wt%), which was increased by 140% compared to the reference (tanδ 0.254). The improved damping is believed due to high fraction of flexible EPDM chains and higher interfacial slippage area of EPDM particles generated by increasing ENB fraction in EPDM. The stick-slip test was conducted to characterize frictional noise and vibration of the TPV weatherstrip. With improved TPV material damping, the acceleration peak of frictional vibration decreased by about 57.9%. This finding can not only improve BSR performance of electric vehicles by designing material damping of weatherstrips but also contribute to various structural applications such as urban air mobility or aircrafts, which require lightweight and high damping properties.