• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.855-856
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• 2006

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicate the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The mechanism of deformation was found to be controlled primarily by dynamic recrystallization.

• Proceedings of the Membrane Society of Korea Conference
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• 1999.07a
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• pp.95-96
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• 1999

The ultrafiltration behavior of dilute colloidal solution containing Si particles has been investigated. The experiments in cross flow mode have been performed at different operating condition by using the membrane with 20 kDa cut-off. The flux decline was due to the development of membrane fouling which was a dynamic process of two distinctive stages. For the high trans-membrane pressure, the pore blocking resistance was dominant at the initial period of filtraion and was followed by the cake resistance. And for the low cross flow velocity, the membrane fouling was governed by the cake filtration model at the initial stage of filtration process. Flux jump was observed temporally during the membrane filtration of mixed feed solution.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10b
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• pp.616-618
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• 2003

In this paper particle filter is used as an underlying algorithm to track multiple objects, which are soccer players. Multi-object tracking becomes difficult when two or more players get close to and overlap each other because particles of the filters tend to move to a region of higher posterior probability. To resolve this problem, a blob assignation algorithm which identifies the separated image blobs after occlusion, based on the predicted states according to the dynamic model is suggested. This method performed well on the sequences under general camera work.

• Advances in Energy Research
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• v.4 no.3
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• pp.239-253
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• 2016

Air quality in hospitals has always concerned hospitals' health officials due to its dangerous particles and gases. Because of the importance of air conditioning in the operating room, a system must be embedded in operating rooms to direct the contaminated air outside, and inject fresh filtered air from outside back into the room. In this study, laminar flow air conditioning system is implemented in the operating room by slot linear diffusers and with the help of air curtain. For this, stimulation Computational Fluid Dynamic (CFD) was used due to its efficiency. The aim of the present study was to find a proper solution to overcome the unfavorable factors, namely, contamination, humidity, and also temperature, velocity and pressure inside the room. These factors were implemented with different values and then stimulated through FLUENT software program. Results showed that the aforementioned factors can be overcome using air curtain and slot linear diffusers.

• Korean Journal of Optics and Photonics
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• v.3 no.3
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• pp.167-171
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• 1992

We present the static and dynamic light scattering results of the salt induced restructured colloidal silica aggregates. We also report the results from the transmission electron micrographs which confirms the individual sizes of the particles and the local structure of the ramified aggregates. The fractal dimensions of the restructuring silica aggregates are considerably different with in-situ light scattering measurements. The measured fractal dimensions, $D_{F}$, is 2.21 for the 0.5 wt.% concentration of the salt induced Ludox-AM. The Rayleigh linewidth for 0.1 wt.% concentration of Ludox-AM is discussed.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.260-266
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• 2022

Average aggregate size in particulate suspensions is estimated with scaling theories based on fractal concept and elasticity of colloidal gel. The scaling theories are used to determine structure parameters of the aggregates, i.e., fractal dimension and power-law exponent for aggregate size reduction with shear stress using scaling behavior of elastic modulus and shear yield stress as a function of particle concentration. The structure parameters are utilized to predict aggregate size which varies with shear stress through rheological modeling. Experimentally rheological measurement is conducted for aqueous suspension of zinc oxide particles with average diameter of 110 nm. The predicted aggregate size is about 1135 nm at 1 s^-1 and 739 nm at 1000 s^-1 on the average over the particle concentrations. It has been found that the predicted aggregate size near 0.1 s^-1 agrees with that the measured one by a dynamic light scattering analyzer operated un-sheared.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.825-829
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• 2011

We performed a dynamic characterization of passive flow-rate regulators, which compensate for inlet pressure variation and maintain a constant flow rate for precise liquid control in microfluidic systems. To measure the flow rate for a short time, much less than the period of the dynamic inlet pressure, we use the particle image velocimetry (PIV) method. DI water containing fluorescent beads with a $0.7-{\mu}m$ diameter was supplied to the flow-rate regulators, and two successive images of the particles were taken by a pulse laser and a fluorescent microscope to measure the flow velocity. For a dynamic inlet pressure of frequency 60 Hz, the flow velocity was constant with an average of 0.194 ${\pm}$ 0.014 m/s as the inlet pressure varied between 20 kPa to 50 kPa. The flow-rate regulators provided a constant flow rate of $5.82{\pm}0.29\;{\mu}l/s$ in the frequency range of the inlet pressure from 1 Hz to 60 Hz.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.37-52
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• 2017

Gas turbines operating in dusty or sandy environment polluted with micron-sized solid particles are highly prone to blade surface erosion damage in compressor stages and molten sand attack in the hot-sections of turbine stages. Commercial/Military fixed-wing aircraft engines and helicopter engines often have to operate over sandy terrains in the middle eastern countries or in volcanic zones; on the other hand gas turbines in marine applications are subjected to salt spray, while the coal-burning industrial power generation turbines are subjected to fly-ash. The presence of solid particles in the working fluid medium has an adverse effect on the durability of these engines as well as performance. Typical turbine blade damages include blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicate (CMAS) attack, oxidation, plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. The focus of this research work is to simulate particle-surface kinetic interaction on typical turbomachinery material targets using non-linear dynamic impact analysis. The objective of this research is to understand the interfacial kinetic behaviors that can provide insights into the physics of particle interactions and to enable leap ahead technologies in material choices and to develop sand-phobic thermal barrier coatings for turbine blades. This paper outlines the research efforts at the U.S Army Research Laboratory to come up with novel turbine blade multifunctional protective coatings that are sand-phobic, sand impact wear resistant, as well as have very low thermal conductivity for improved performance of future gas turbine engines. The research scope includes development of protective coatings for both nickel-based super alloys and ceramic matrix composites.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.531-539
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• 2015

Properties of normal-strength mortar containing coarsely-crushed coal bottom ash considering standard particle size distribution of fine aggregate were investigated. Mortar containing raw bottom ash was applied as a reference. By crushing the bottom ash with a particle size larger than fine binder but smaller than fine aggregates, i.e., coarse-crushing, water absorption and specific gravity of the particles could be controlled as similar levels to those of natural fine aggregates. Workability and strength of the mortar were not changed and even increased when the coarsely-crushed bottom ash was added considering standard particle size distribution in Standard Specification for Concrete, while those were decreased when raw bottom ash was added without any treatment. When a replacement ratio of coarsely-crushed bottom ash was less than 30 vol.%, there were no significant decrease in dynamic modulus of elasticity and dry shrinkage of the mortar.

• Journal of The Korean Astronomical Society
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• v.35 no.4
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• pp.159-174
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• 2002

Cosmological hydrodynamic simulations of large scale structure in the universe have shown that accretion shocks and merger shocks form due to flow motions associated with the gravitational collapse of nonlinear structures. Estimated speed and curvature radius of these shocks could be as large as a few 1000 km/s and several Mpc, respectively. According to the diffusive shock acceleration theory, populations of cosmic-ray particles can be injected and accelerated to very high energy by astrophysical shocks in tenuous plasmas. In order to explore the cosmic ray acceleration at the cosmic shocks, we have performed nonlinear numerical simulations of cosmic ray (CR) modified shocks with the newly developed CRASH (Cosmic Ray Amr SHock) numerical code. We adopted the Bohm diffusion model for CRs, based on the hypothesis that strong Alfven waves are self-generated by streaming CRs. The shock formation simulation includes a plasma-physics-based 'injection' model that transfers a small proportion of the thermal proton flux through the shock into low energy CRs for acceleration there. We found that, for strong accretion shocks, CRs can absorb most of shock kinetic energy and the accretion shock speed is reduced up to $20\%$, compared to pure gas dynamic shocks. For merger shocks with small Mach numbers, however, the energy transfer to CRs is only about $10-20\%$ with an associated CR particle fraction of $10^{-3}$. Nonlinear feedback due to the CR pressure is insignificant in the latter shocks. Although detailed results depend on models for the particle diffusion and injection, these calculations show that cosmic shocks in large scale structure could provide acceleration sites of extragalactic cosmic rays of the highest energy.