• Computers and Concrete
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• v.13 no.3
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• pp.309-323
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• 2014

Based on the compositions and structures of cement-based materials, the geometrical models of the tortuosity of transport paths in hardened cement pastes, mortar and concrete, which are associated with the capillary porosity, cement hydration degree, mixture particle shape, aggregate volume fraction and water-cement ratio, are established by using a geometric approach. Numerical simulations are carried out to investigate the effects of material parameters such as water-cement ratio, volume fraction of the mixtures, shape and size of aggregates and cement hydration degree, on the tortuosity of transport paths in hardened cement pastes, mortar and concrete. Results indicate that the transport tortuosity in cement-based materials decreases with the increasing of water-cement ratio, and increases with the cement hydration degree, the volume fraction of cement and aggregate, the shape factor and diameter of aggregates, and the material parameters related to cement pastes, such as the water-cement ratio, cement hydration degree and cement volume fraction, are the primary factors that influence the transport tortuosity of cement-based materials.

• Journal of Korea Water Resources Association
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• v.34 no.6
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• pp.687-699
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• 2001

A 2-dimensional numerical sediment transport model has been developed by using erosion rates observed by SEDFLUME. The model un boundary-fitted coordinate can reduce inaccuracy of sediment model with accurate erosion data. Suspended transport and bed load transport are included in the model together. The model results gave good agreement with particle size distributions in 1-d channel and was more accurate than that of HIDAS of 1-dimensional model. The model applied to an enlarging channel to check model performance in 2-dimensional domain. Bed coarsening reduced erosion and deposition.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1583-1594
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• 1992

A numerical calculation on the flame structure and soot particle distribution in a coannular laminar diffusion flame was performed. Flame analysis model utilized basically flame sheet concepts, Shvab-Zel'dovich assumption, and one step overall irreversible reaction. It was also considered the variation of thermodynamics and transport properties, and the stagnation enthalpy was used for solving temperature field. Radiation was taken into account, since it has been found to be important in determining the flame temperature in sooty flames. For soot particle analysis, we adopted the coagulation, suface condensation, and the oxidation model in addition to tesner's two-step formation model. Equations for primary soot particle excluding the agglomeration process were solved. Based on the results, the regions of soot generation, growth, and oxidation in the flame have been observed and radiation strongly influenced flame temperature and soot distribution.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.321-327
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• 2010

A simplified analytical modeling for micro-sized single metal particle combustion in air was conducted in the present study. The metal particle combustion consists of two distinct reaction regimes, ignition and quasi-steady burning, and the thermo-fluidic phenomena in each stage are formulated by virtue of the conservation and transport equations. Reliability of the model is shown by rigorous validation of the method with emphasis laid on the characterizing the commanding parameters. Effects of Initial particle size, initial oxide film thickness, convection, ambient pressure and temperature are examined and addressed with validation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.10a
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• pp.160-163
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• 2001

In order to develop a nodule conveying system through a flexible pipe out of the deep-seabed manganese nodule miner, an experimental study of the solid-water slurry flow in vertical pipe is performed as the first stage of total experiments. Hydraulic characteristics of the pipe slurry flow such as slip velocity, transport concentration and pressure gradient are investigated for the size of particle, load ratio, and flow rate of water. The higher the load ratio is, the larger the transport concentration and pressure gradient become. The bigger the size of particles is, the larger the pressure gradient becomes. The effectiveness of the flow rate to hydraulic performance is also investigated. This results are to be used for designing crusher and pump, and operating the conveying device.

• Journal of the Korean GEO-environmental Society
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• v.7 no.5
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• pp.79-87
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• 2006

This paper presents the numerical model developed to simulate the solute transport in rough and smooth single fractures. The roughness of these fractures is represented by using the fractal surface method. In this study, the 3D transport model, which is based on the random walk technique, is used to simulate the dispersion process of a solute which is represented by numerical particles. As the simulation results, it can be observed that the dispersion of solute in the fracture is significantly affected by the fracture roughness and particle size.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.211-216
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• 1997

The tungsten disulfide (WS$_2$) solid lubricant was synthesized by two different reaction processes, and the chemical and physical characteristics of synthesized WS$_2$ powder were analyzed in terms of the average particle size, morphology, crystalline phase. The solid WO$_3$ powder with the average size of 0.2 $\mu$m was reacted with CS$_2$ gas flowed with N$_2$ or 96% N$_2$ + 4% H$_2$ forming gas for 36 h and 24 h at 900$\circ$C respectively. In the case of vapour phase transport method, the 3.5 wt% iodine was added as a vapour transport reagent into the composition of tungsten and sulfur powders maintaining a constant molar ratio of W : S = 1 : 2.2. The mixture was then heat treated at 850$\circ$C for 2 weeks in vacuum The reaction product obtained showed the average size of 12 $\mu$m and the hexagonal plate shape of typical solid lubricant with 2H-WS$_2$ crystalline phase.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.6
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• pp.305-311
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• 2004

Charge transport phenomena of polyaniline-DBSA/High Impact Polystyrene (PAM-DBSA/HIPS) blends have been studied through an examination of electrical conduction. HIPS used host polymer in the blends and PANI-DBSA obey a space charge limited conduction mechanism and a ohmic conduction mechanism respectively. However, PANI-DBSA/HIPS blends do not obey any classical conduction mechanism. Analysis of conduction mechanism revealed that the charging current of PANI-DBSA/HIPS blends increased with the increase of PANI-DBSA content. This result migrlt be explained by the reduction in the distance between PANI-DBSA particles enabling the charge carriers to migrate from a chain to a neighboring chain via hopping or micro tunneling. It was also found that the charging current of PANI-DBSA/HIPS blends decreased as the temperature was elevated, which is of typical phenomena in metals. It is speculated that the charge transport in PANI-DBSA particle was somewhat constrained due to strong phonon scattering.

• Proceedings of the Korea Water Resources Association Conference
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• 2002.05b
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• pp.1027-1033
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• 2002

The solute transport in a two-dimensional heterogeneous porous medium is numerically studied by using a random walk particle tracking (RWPT) method. Lognormally isotropic hydraulic conductivity fields are generated by using the turning band methods with mean zero and four different values of standard deviation. The numerical transport experiments are carried out to investigate the large time and spatial effects of the variable pore velocity field on solute plumes. The behavior of the solute plume through numerical simulations is presented in terms of longitudinal and transverse spatial moments: displacement of center-of-mass, plume spread variance and skewness coefficient. It was observed that the dispersive behavior of the solute plume is strongly affected by the degree of heterogeneity in the flow domain.

• Proceedings of the Korean Environmental Sciences Society Conference
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• 2006.11a
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• pp.249-251
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• 2006