• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.5
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• pp.612-619
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• 2003

This work experimentally studies the fundamental mechanisms by which the ultrasonic vibration enhances convection and pool boiling heat transfer. A thin platinum wire is used as both a heat source and a temperature sensor. A high speed video imaging system is employed to observe the behavior of cavitation and thermal bubbles. It is found that when the liquid temperature is below its boiling point, cavitation takes place due to ultrasonic vibration while cavitation disappears when the liquid reaches the boiling point. Moreover, when the gas dissolved in liquid is removed by pre-degassing, the cavitation arises only locally. Depending on the liquid temperature, heat transfer rates in convection, subcooled boiling and saturated boiling regimes are examined. In convection heat transfer regime, fully agitated cavitation is the most efficient heat transfer enhancement mechanism. Subcooled boiling is most enhanced when tile local cavitation is induced after degassing. In saturated boiling regime, acoustic pressure is shown to be a dominant heat transfer enhancement mechanism.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.119.1-119.1
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• 2012

It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations roughly satisfies the order of ~0.01. In addition, we extended this study for the plasma sheet boundary layer (PSBL) region. We can discuss the maximum disturbances of the Alfven via mode conversion becomes differently saturated through each region.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2002.10a
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• pp.265-268
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• 2002

The ground water regime analysis method, numerical analysis method, water budget method, and baseflow analysis method have been used for estimating ground water recharged quantity. This study, adapting water budget concept of unsaturated zone, and saturated zone of the DAWAST model, proposed a new method to estimate ground water recharged quantity.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.669-685
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• 2015

A three-dimensional elastoplastic constitutive model, also known as a UH model (Yao et al. 2009), was developed to describe the stress-strain relationship for normally consolidated and over-consolidated soils. In this paper, an acoustic tensor and discriminator of bifurcation for the UH model are derived for the strain localization of saturated clays under undrained and fully and partially drained conditions. Analytical analysis is performed to illustrate the points of bifurcation for the UH model with different three-dimensional stress paths. Numerical analyses of cubic specimens for the bifurcation of saturated clays under undrained and fully and partially drained conditions are conducted using ABAQUS with the UH model. Analytical and numerical analyses show the similar bifurcation behaviour of overconsolidated clays in three-dimensional stress states and various drainage conditions. The results of analytical and numerical analyses show that (1) the occurrence of bifurcation is dependent on the stress path and drainage condition; and (2) bifurcation can appear in either a strain-hardening or strain-softening regime.

• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.39.2-39.2
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• 2010

Field line resonances (FLRs) observed in the magnetosphere often have the amplitude of a few nT, which indicates that dB/B roughly satisfies ~0.01. It is well known that the FLRs are excited by compressional waves via mode conversion, but there has been no apparent criterion on the maximum amplitude in the regime of linear approximations. Such limited range of amplitude should be understood by including nonlinear saturation of FLRs, which has not been examined until now. In this study, using a three-dimensional magnetohydrodynamic (MHD) simulation code, we examine the evolution of nonlinear field line resonances (FLRs) in the cold plasmas. The MHD code used in this study allows a full nonlinear description and enables us to study the maximum amplitude of FLRs. When the disturbance is sufficiently small, it is shown that linear properties of MHD wave coupling are well reproduced. In order to examine a nonlinear excitation of FLRs, it is shown how these FLRs become saturated as the initial magnitude of disturbances is assumed to increase. Our results suggest that the maximum amplitude of FLRs become saturated at the level of the same order of dB/B as in observations. In addition, we discuss the role of both linear terms and nonlinear terms in the MHD wave equations.

• Nuclear Engineering and Technology
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• v.50 no.3
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• pp.432-438
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• 2018

The occurrence of saturation in the CR-39 detector reduces and limits its detection dynamic range; nevertheless, this range could be extended using spectroscopic techniques and by measuring the net bulk rate of the saturated CR-39 detector surface. CR-39 detectors were irradiated by 1.5 MeV high alpha-particle fluence varying from $0.06{\times}10^8$ to $7.36{\times}10^8\;alphas/cm^2$ from Am-241 source; thereafter, they were etched in a 6.25N NaOH solution at a temperature of $70^{\circ}C$ for different durations. Net bulk etch rate measurement of the 1.5 MeV alpha-irradiated CR-39 detector surface revealed that rate increases with increasing etching time and reaches its maximum value at the end of the alpha-particle range. It is also correlated with the alpha-particle fluence. The measurements of UV-Visible (UV-Vis) absorbance at 500 and 600 nm reveal that the absorbance is linearly correlated with the fluence of alpha particles at the etching times of 2 and 4 hour. For extended etching times of 6, 10, and 14.5 hour, the absorbance is saturated for fluence values of $4.05{\times}10^8$, $5.30{\times}10^8$, and $7.36{\times}10^8\;alphas/cm^2$. These new methods pave the way to extend the dynamic range of polymer-based solid state nuclear track detectors (SSNTDs) in measurement of high fluence of heavy ions as well as in radiation dosimetry.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.146-151
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• 2002

Characteristics of flow rate control has been studied for a cavitating venturi adopted in a liquid rocket propellant feed system. Numerical simulation has been peformed to give about $10\%$ discrepancy of mass flow rate to the experimental data for cavitating flow regime. Mass flow rate is confirmed to be saturated for pressure difference higher than $3\times10^5$pa when the upstream pressure is fixed to $22.8\times10^5$pa and the downstream pressure is varied. The evaporation amount depends substantially to non-condensable gas concentration. However the mass flow rate characteristic is relatively insensitive to the mass fraction of non-condensable gas. So it is reduced by only $2\%$ when the non- condensable gas concentration is increased from 1.5PPM to 150PPM. From the previous comparison the expansions of the non-condensable gas and the evaporation of liquid are verified to have same effect to pressure recovery.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2464-2476
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• 2021

Direct-contact heat transfer of a single saturated droplet upon colliding with a heated wall in the regime of film boiling was experimentally investigated using high-resolution infrared thermometry technique. This technique provides transient local wall heat flux distributions during the entire collision period. In addition, various physical parameters relevant to the mechanistic modelling of these phenomena can be measured. The obtained results show that when single droplets dynamically collide with a heated surface during film boiling above the Leidenfrost point temperature, typically determined by droplet collision dynamics without considering thermal interactions, small spots of high heat flux due to localized wetting during the collision appear as increasing We_n. A systematic comparison revealed that existing theoretical models do not consider these observed physical phenomena and have lacks in accurately predicting the amount of direct-contact heat transfer. The necessity of developing an improved model to account for the effects of local wetting during the direct-contact heat transfer process is emphasized.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.432-438
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• 2005

CMP characteristics such as material removal rate and edge effect were measured and investigated in accordance with pad grooving effect, groove width, depth and pitch. GSQ (Groove Stiffness Quotient) and GFQ (Groove Flow Quotient) were proposed to estimate pad grooving characteristics. GSQ is defined as groove depth(D) divided by pad thickness(T) and GFQ is defined as groove width(W) divided by groove pitch(P). As GFQ value increased, material removal rate increased some point but gradually saturated. It seems that material removal rate is not affected by each parameter respectively but by interaction of these parameters such as groove dimensions. In addition, an increase in GFQ and GSQ causes edge effect to be improved. Because, pad stiffness decreases as GSQ and GFQ increase. In conclusion, groove influences relative pad stiffness although original mechanical properties of pad are unchanged by grooving. Also, it affects the flow of slurry that has an effect on the lubrication regime and polishing results. The change of groove dimensions has influence on pad stiffness and slurry flow, so that polishing results such as removal rate and edge effect become changed.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.32.3-33
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• 2021

We present H I gas kinematics and star formation activities of NGC 6822, a dwarf galaxy located in the Local Volume at a distance of ~ 490 kpc. We perform profile decomposition of the line-of-sight velocity profiles of the high-resolution (42.4" × 12" spatial; 1.6 km/s spectral) H I data cube taken with the Australia Telescope Compact Array (ATCA). For this, we use a new tool, the so-called BAYGAUD (BAYesian GAUssian Decompositor) which is based on Bayesian Markov Chain Monte Carlo (MCMC) techniques, allowing us to decompose a line-of-sight velocity profile into an optimal number of Gaussian components in a quantitative manner. We classify the decomposed H I gas components of NGC 6822 into bulk-narrow, bulk-broad, and non_bulk with respect to their velocity and velocity dispersion. We correlate their gas surface densities with the surface star formation rates derived using both GALEX far-ultraviolet and WISE 22 micron data to examine the impact of gas turbulence caused by stellar feedback on the Kennicutt-Schmidt (K-S) law. The bulk-narrow component that resides within r25 is likely to follow the linear extension of the Kennicutt-Schmidt (K-S) law for molecular hydrogen (H2) at the low gas surface density regime where H I is not saturated.