• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.454-462
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• 1998

Mechanisms and conditions for rounding of AUC particles were examined during AUC precipitation. Rounding of AUC particle was possible only by external circulation using pump, not by internal circulation using agitator. The rate of AUC rounding $(dn_p/dt)$ was proporational to operation conditions such as magma density $(M_t:g-U/{\iota}l)$, turn over ratio $(T_o)$ and impeller tip velocity of pump (U); $ dn_p/dt{\propto}M_t{\cdot}T_o{\cdot}U^2$. The validity of this relationship was qualitatively confirmed by comparing the expermental results. Two rounding mechanisms were suggested. One is crack formation mechanism and the other etch-pit formation mechanism on the surface of AUC particle. It was found that the crack formation is more dominant at the initial stage and the etch-pit formation at the final stage of the AUC precipitation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.2
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• pp.200-206
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• 2015

In order to verify the lift enhancement of the 2D hydrofoil with trailing edge rotor and check the ability of its practical use, experimental studies were conducted in the caviation tunnel using the test model with NACA0020 section. The three-component forces acting on the model could be measured by exclusively designed sting type multi-component load cell. The trailing edge of the model has been replaced with rotor which could be controlled by DC servo motor installed at the exterior of the tunnel. A typical effect of the trailing edge rotor has been introduced among the systematic experiments on various angular deviation of the model and the rotational velocity of the trailing edge rotor. It is appeared that the circulation control effect could be easily adjusted by selecting the rotational velocity of the trailing edge rotor and the lift force was augmented more than two times. Thus the proposed lifting device could be utilized as a novel high lifting device which has adjustability of lift force.

• Journal of Korea Multimedia Society
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• v.8 no.10
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• pp.1322-1328
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• 2005

The circulation flows passing through the Ekman boundary layer on the rotating disk and transfer the angular momentum into the interior region of the container. Consequently, the circulation enhances the momentum transfer and the interior fluid is divided by a propagating shear front. This investigation focuses on computer vision and image processing technique for analysis of Non-Newtonian Fluids. To visualize marching velocity shear front for the transient flow, a particular shaped particles and light are used. To validate the proposed method, quantitative image are compared with the optical data acquired by a direct measurement of LDV (Laser Doppler Velocimetry).

• Journal of Environmental Science International
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• v.6 no.4
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• pp.323-333
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• 1997

An objective method for the generation of velocity streamfunction is presented for dealing with discretely sampled oceauc data. The method treats a Poisson equation (forced by vorticity) derived from Helmholtz theorem In which streamfunction is obtained by isolating the non-divergent part of the two-dimensional flow field. With a mixed boundary condition and vorticity field estimated from observed field, the method Is Implemented over the Texas-Louisiana show based on the current meter data of the Texas-Louisiana Shelf Circulation and Transport Processes Study (LATEX) measured at 31 moorings for 32 months (April 1992 - November 1994). The resulting streamfunction pattern is quote consistent with observations. The streamfunction field by this method presents an opportunity to initiauze and to verier computer models for local forecasts of enoronmental flow conditions for ell spill, nutrient and plankton transports as well as opportuuty to understand shelf-wlde low-frequency currents.

• Korean Chemical Engineering Research
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• v.47 no.3
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• pp.355-361
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• 2009

Effects of operating variables on solid separation rate in two-interconnected fluidized beds system for selective solid circulation have been investigated. Coarse(212~300 or $425{\sim}600{\mu}m$) and fine($63{\sim}106{\mu}m$) particles were separated using the solid separator and the solid separation rate was ranged from 66 to 987 g/min. The solid separation rate increased as the gas velocity through the solid injection nozzle, solid height, diameter of solid injection nozzle, particle size of coarse particles, aperture of the solid separator, and weight fraction of fines in the solid mixture increased. However, the effect of the fluidization velocity was negligible.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.1
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• pp.1-12
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• 2021

To investigate the effect of freshwater discharge on the seawater circulation in the semi-closed harbor, a 3-D hydrodynamic model was applied to the International Ferry Terminal (IFT). The model run is conducted for 45 days (from May 15 to June 30, 2020), and the reproducibility of the model for time-spatial variability of current velocity and salinity was verified by comparison with model results and observation data. There are two sources of freshwater towards inside of the IFT: Han River and water reservoir located in the eastern part of IFT. In residual current velocity results, the two-layer circulation (the seaward flow near surface and the landward flow near bottom)derived from the horizontal salinity gradient in only considering the discharge from a Han River is more developed than that considering both the Han River and water reservoir. This suggests that the impact of freshwater from the reservoir is greater in the IFT areas than that from a Han River. Additionally, the two-layer circulation is stronger in the IFT located in southern part than Incheon South Port located in northern part. This process is formed by the interaction between tidal current propagating into the port and freshwater discharge from a water reservoir, and flow with a low salinity (near 0 psu) is delivered into the IFT. This low salinity distribution reinforces the horizontal stratification in front of the IFT, and maintains a two-layer circulation. Therefore, local sources of freshwater input are considered to estimate for mass transport process associated with the seawater circulation within the harbor and It is necessary to perform a numerical model according to the real-time freshwater flow rate discharged.

• Korean Chemical Engineering Research
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• v.58 no.4
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• pp.665-674
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• 2020

Low-frequency pressure fluctuations in an external-loop airlift reactor were investigated. Low-frequency pressure fluctuations could be measured by shooting videos about liquid levels in the four piezometric tubes which were installed at the lower and upper parts of the riser and downcomer using a cellular phone. The periodic characteristics of pressure fluctuations were proved by the calculation of their auto-correlation function and cross-correlation function. Even if the riser superficial gas velocity was constant, the riser and downcomer gas holdups as well as wall pressures were periodically changed due to the inertia of circulating liquid. In general, the intensity of pressure fluctuations increased with an increase in the gas velocity. When the unaerated liquid height was 0.04 m, the maximum period of pressure fluctuations was found at the specific gas velocity (0.14 ms^-1). It was because the maximum inertia of circulating liquid resulted from a reduction in the increasing rate of the liquid circulation velocity and a decrease in the volume of the effectively circulating liquid with an increase in the gas velocity.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.864-870
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• 2001

Flame propagation along vortex tube was experimentally investigated. The vortex tube was generated by the ejection of propane from a nozzle through a single stroke motion of a speaker and the ignition was induced from a single pulse laser. Non-reactive flow fields were visualized using shadow technique. From these images, vortex ring size and translational velocity were measured in order to determine the ignition time and position. Flame structure and flame speed were measured using high speed CCD camera. Flame speed was accelerated during the initial stage of flame kernel growth, and reached near constant value during steady propagation period. Near the completion of propagation, flame speed was decelerated and then extinguished. Flame speed along the non-premixed vortex tube was found to be linearly proportional to circulation, which was similar to that of the flame propagation along premixed vortex ring. Ignition position minimally affects the propagation characteristics. These imply that flame is propagating along the maximum speed locus expected to be along stoichiometric contour and also support the existence of tribrachial flames.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.109-113
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• 2009

Several tidal current power plants are being planned and constructed in Korea utilizing the strong tidal currents along the west and south coasts. A tidal current reaches 9.7 m on the west coast; there are few potential regions for tidal current power generation. The construction of a dam to store water can prevent the circulation of water, causing a great environmental impact on the coast and estuary. The tidal barrage could produce a large amount of power, but it should be carefully considered. The purpose of developing renewable energies is to minimize the environmental impact and to maximize the utilization of clean energy. To produce a great quantity of power, tidal current farms require the placement of numerous units in the ocean. The power generation is very dependent on the size of the rotor and the incoming flow velocity. Also, the interactions between devices contribute greatly to the production of power. The efficiency of a power farm is estimated to determine the production rate. This paper introduces 3 D interaction problems between rotating rotors, considering the axial, transverse, and diagonal distances between horizontal axis tidal current devices.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.1 no.2
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• pp.119-124
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• 1997

Cloud streets were successfully simulated by numerical model (RAMS) including an isolated mountain near the coast, large sensible heat flux from the sea surface, uniform stratification and wind velocity with low Froude number (0.25) in the inflow boundary. The well developed cloud streets between a pair of convective rolls are simulated at a level of 1 km over the sea. The following five results were obtained: 1) For the formation of the pair of convective rolls, both strong static instability and a topographically induced mechanical disturbance are strongly required at the same time. 2) Strong sensible heat flux from the sea surface is the main energy source of the pair of convective rolls, and the buoyancy caused by condensation in the cloud is negligibly small. 3) The pair of convective rolls is a complex of two sub-rolls. One is the outer roll, which has a large radius, but weak circulation, and the other is the inner roll, which has a small radius, but strong circulation. The outer roll gathers a large amount of moisture by convergence in the lower marine boundary, and the inner roll transfers the convergent moisture to the upper boundary layer by strong upward motion between them. 4) The pair of inner rolls form the line-shaped cloud streets, and keep them narrow along the center-line of the domain. 5) Both by non-hydrostatic and by hydrostatic assumptions, cloud streets can be simulated. In our case, non-hydrostatic processes enhanced somewhat the formation of cloud streets. The horizontal size of the topography does not seem to be restricted to within the small scale where non-hydrostatic effects are important.