• Journal of Korea Water Resources Association
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• v.38 no.2
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• pp.133-142
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• 2005

The settling concentration of fine suspended solid particles(alumina(Al$_2$O$_3$) and quartz(SiO$_2$)) is investigated with the physico-chemical effects(initial concentration, pH and NaCl). Laboratory tests have confirmed the significant influence of increasing initial concentration and salinity which can lead to flocculation due to the intermolecular attraction. Furthermore, the influence of the pH value on the concentration-time corves of alumina has been on firmed. Besides a numerical model to predict the behaviour of cohesive deposit under still water is analyzed by solving the unsteady one-dimensional diffusion-advection equation with a explicit, implicit, Crank-Nicolson and finite difference scheme. The model predicts the existence of an equilibrium concentration. Application of the model with implicit centered difference to data from settling experiments shows a similar distribution.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1053-1060
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• 2011

This study is performed to determine the drug concentration profiles of drug-eluting stents (DES) for an ideal circular ring stent and intertwined stent models for various Reynolds numbers (Re = 200, 400, and 800). The Navier.Stokes equations coupled with the advection-diffusion equation are solved numerically in order to determine how the flow patterns and drug deposition are affected in the in-stent and post-stent regions where flow separation and recirculation occur. The presence of DES within the arterial segment affects the local drug distribution in the flow field. As a result, the drug concentration for the intertwined stent is higher over the in-stent region in comparison with the ideal stents. For a given stent geometry, the local drug concentration in the in-stent region decreases with Reynolds number, while for a given Reynolds number, the local drug concentration is relatively insensitive to the stent geometry. The results show that drug concentration along the arterial wall is significantly higher within the in-stent and post-stent regions for the intertwined stent geometry than for the ideal stent geometries.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.2
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• pp.20-30
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• 1999

To improve water quality particularly for sea bathers along the Fylde coastal zone near Blackpool, North West England, waste water from a sewage outfall is studied using a mathematical model. The explicit second order accurate central scheme and the third order accurate QUICKEST scheme are used to represent the diffusion terms and the advection terms of the advective-diffusion equation, respectively. Hydrodynamic model is run for a coarse and fine grid, of 1km and 200m, respectively, obtaining good agreement with measured data. Water quality model is then used to predict faecal coliform levels in the region for four different scenarios, including discharges from: - (i) Fleetwood outfall, (ii)River Ribble for summer condition, (iii)River Ribble for winter condition, and (iv)combined sewer overflows for the Blackpool and Fleetwood communities. Main findings from the simulations are:- (i) Fleetwood outfall has a negligible impact on the beaches with respect to pathogen levels; (ii) Discharge from River Ribble for both summer and winter conditions is predicted in the range of coliform levels 10 -500 counts/100ml along the beach at Lytham St. Annes; and (iii) The CSO effluent discharges are predicted not to advect out into offshore by stronger tidal currents.

• Journal of Korea Water Resources Association
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• v.39 no.2 s.163
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• pp.99-108
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• 2006

To describe the behavior of suspended-sediment particles in turbulent open-channel flows, the advection-diffusion equation or its simplified form has been used. Though this equation was derived upon several assumptions, only a few studies tried to evaluate the limit of the assumptions. The reason is that it is very difficult to measure turbulence in open-channel flows and to discriminate the velocities of water and sediment particles. The present study aims to measure the velocity profiles of water and sediment particles in open-channel flows by using PTV (Particle Tracking Velocimetry), a kind of PIV (Particle Image Velocimetry). The measured results showed that sediment particles moved slower than water tracers did in the outer region. In the present study, the amount of velocity-lag reached about $5\%$ of the mom flow velocity and the position of the maximum velocity-lag was $g/h\approx0.05\;(g^{+}=30\~50)$ The main cause of the velocity-lag of sediment particles seems that the sediment particles have larger density than water has. On the other hand, in the viscous sublayer, sediment particle has a larger velocity than water tracers. The reason of the inversion of velocity-lag may be due to the no-sleep condition of water at the solid boundaries.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.6B
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• pp.731-741
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• 2008

Previous studies on the numerical simulation at the tidal reach of Han River tend to restrict downstream boundary as Jeon-ryu station due to difficulties in gaining cross section data and tidal elevation values at Yu-do. But, in this study, geometries beyond the confluence of Gok-reung stream and Im-jin River are constructed based on the numerical sea map; tidal elevation at the downstream boundary, Yu-do is estimated by harmonic analysis of In-cheon tide gage station so that hydrodynamic and diffusion behavior have been analyzed. The domain ranging from Shin-gok submerged weir to Yu-do is selected (which is 36.8 km in length). RMA-2 and RAM4 developed by Il Won Seo (2008) are applied to simulate flow and diffusion behavior, respectively. Numerical results of flow characteristic are compared with the measured data at Jeon-ryu station. Simulation is carried out from June 23 to 25 in 2006 on the ground that hydrologic data is satisfactory and tidal difference is huge during that period. The result shows that reverse flow occurs 5 times according to the tidal elevation at Yu-do and the maximum reverse flow is observed up to Jang-hang IC, which is 32.9 km in length. Also analysis is focused on the process of generation and disappearance of reverse flow, the distribution of water surface elevation and velocity along the maximum velocity line, and the transport of nonconservative pollutant. Pollutant injected from Gul-po stream spreads widely across the river; however, the size of BOD cloud entering from Gok-reung stream is relatively small because water depth at the mid and left side becomes deeper and maximum velocity occurs along the right bank so that transverse mixing is completed quickly. Finally, mixing characteristic of horizontal salinity distribution is obtained by estimating the salinity input with analytical solution of 1D advection-dispersion equation.