• Proceedings of the Korean Society of Rheology Conference
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• 2001.09a
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• pp.158.4-158
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• 2001

• Interaction and multiscale mechanics
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• v.6 no.2
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• pp.157-172
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• 2013

This paper presented an investigation of macromolecular suspension in a grooved channel by using the dissipative particle dynamics (DPD) with finitely extensible non-linear elastic (FENE) bead spring chains model. Before studying the movement and evolution of macromolecules, the DPD method was first validated by modeling the simple fluid flow in the grooved channel. For both simple fluid flow and macromolecular suspension, the flow fields were analyzed in detail. It is found that the structure of the grooved channel with sudden contraction and expansion strongly affects the velocity distribution. As the width of the channel reduces, the horizontal velocity increases simultaneously. Vortices can also be found at the top and bottom corners behind the contraction section. For macromolecular suspension, the macromolecular chains influence velocity and density distribution rather than the temperature and pressure. Macromolecules tend to drag simple fluid particles, reducing the velocity with density and velocity fluctuations. Particle trajectories and evolution of macromolecular conformation were investigated. The structure of the grooved channel with sudden contraction and expansion significantly influence the evolution of macromolecular conformation, while macromolecules display adaptivity to adjust their own conformation and angle to suit the structure so as to pass the channel smoothly.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.468-474
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• 2011

The flow field around baffle located sudden expansion and contraction channel was measured by PIV method and the effect according to height change of baffle built in the flow field was evaluated. The inlet flow velocity and the baffle height influence mutually to the size and flow pattern of the recycle flow of the back of the baffle and the size of the area of the water power jump passing the upper part of the baffle. In case of Reynolds number $Re=4{\times}10^3$, the critical value of baffle height is estimated around h/H=1.6 and there was a decreasing tendency as the inlet flow velocity was increased.

• Korea-Australia Rheology Journal
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• v.21 no.1
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• pp.59-69
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• 2009

The prediction of pressure drop for a droplet flow in a confined micro channel is presented using FE-FTM (Finite Element - Front Tracking Method). A single droplet is passing through 5:1:5 contraction - straight narrow channel - expansion flow domain. The pressure drop is investigated especially when the droplet flows in the straight narrow channel. We explore the effects of droplet size, capillary number (Ca), viscosity ratio ($\chi$) between droplet and medium, and fluid elasticity represented by the Oldroyd-B constitutive model on the excess pressure drop (${\Delta}p^+$) against single phase flow. The tightly fitted droplets in the narrow channel are mainly considered in the range of $0.001{\leq}Ca{\leq}1$ and $0.01{\leq}{\chi}{\leq}100$. In Newtonian droplet/Newtonian medium, two characteristic features are observed. First, an approximate relation ${\Delta}p^+{\sim}{\chi}$ observed for ${\chi}{\geq}1$. The excess pressure drop necessary for droplet flow is roughly proportional to $\chi$. Second, ${\Delta}p^+$ seems inversely proportional to Ca, which is represented as ${\Delta}p^+{\sim}Ca^m$ with negative m irrespective of $\chi$. In addition, we observe that the film thickness (${\delta}_f$) between droplet interface and channel wall decreases with decreasing Ca, showing ${\delta}_f{\sim}Ca^n$ Can with positive n independent of $\chi$. Consequently, the excess pressure drop (${\Delta}p^+$) is strongly dependent on the film thickness (${\delta}_f$). The droplets larger than the channel width show enhancement of ${\Delta}p^+$, whereas the smaller droplets show no significant change in ${\Delta}p^+$. Also, the droplet deformation in the narrow channel is affected by the flow history of the contraction flow at the entrance region, but rather surprisingly ${\Delta}p^+$ is not affected by this flow history. Instead, ${\Delta}p^+$ is more dependent on ${\delta}_f$ irrespective of the droplet shape. As for the effect of fluid elasticity, an increase in ${\delta}_f$ induced by the normal stress difference in viscoelastic medium results in a drastic reduction of ${\Delta}p^+$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.591-597
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• 2013

Because most existing non-Newtonian models are not suitable for application to the lattice Boltzmann method, theoretical and numerical studies in this regard remain challenging. In this study, the hydrokinetic (HK) model was modified and applied to a 3D sudden contraction-expansion channel flow, and the characteristics of the HK model flow were evaluated to generate non-trivial predictions in three-dimensional strong shear flows. The HK model is very efficient for application to the lattice Boltzmann method because it utilizes the shear rate and relaxation time. However, the simulation would be unstable in a high shear flow field because the local relaxation time sharply decreases with an increase in the shear rate in a strong shear flow field. In the HK model, it may become necessary to truncate the relaxation time and non-dimensional parameter to obtain stable numerical results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.468-478
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• 2020

The wave interaction problem with a vertical slotted breakwater, consisting of impermeable upper, lower parts and a permeable middle part, has been studied theoretically. An analytical model was presented for the estimation of reflection and transmission of monochromatic waves by a slotted breakwater. The far-field solution of the wave scattering involving nonlinear porous boundary condition was obtained using eigenfunction expansion method. The empirical formula for drag coefficient in the near-field, representing energy dissipation across the slotted barrier, was determined by curve fitting of the numerical solutions of 2-D channel flow using CFD code StarCCM+. The theoretical model was validated with laboratory experiments for various configurations of a slotted barrier. It showed that the developed analytical model can correctly predict the energy dissipation caused by turbulent eddies due to sudden contraction and expansion of a slotted barrier. The present paper provides a synergetic approach of the analytical and numerical modelling with minimum CPU time, for better estimation of the hydrodynamic performance of slotted breakwater.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.1
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• pp.1-9
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• 2003

The examinations of the operating mechanism of an oscillating capillary tube heat pipe (OCHP) using the visualization method revealed that the working fluid in the OCHP oscillated to the axial direction by the contraction and expansion of vapor plugs. The contraction and expansion were due to the formation and extinction of bubbles in the evaporating and condensing part, respectively The actual physical mechanism, whereby the heat which was transferred in such an OCHP was complex and not well understood. In this study, a theoretical model of the OCHP was developed to model the oscillating motion of working fluid in the OCHP. The differential equations of two-phase flow were applied and simultaneous non-linear partial differential equations were solved. From the analysis of the numerical results, it was found that the oscillating motion Of working fluid in the OCHP was affected by the operation and design conditions such as the heat flux, the charging ratio of working fluid and the hydraulic diameter of flow channel. The simulation results showed that the proposed model and solution could be used for estimating the operating mechanism in the OCHP.

• Economic and Environmental Geology
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• v.42 no.5
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• pp.509-512
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• 2009

Powder diffraction patterns of the zeolite mesolite ($Na_{5.33}Ca_{5.33}Al_{16}Si_{24}O_{80}{\cdot}21.33H_2O$), with a natrolite framework topology were measured as a function of pressure up to 5.0 GPa using a diamond-anvil cell and a $200{\mu}m$-focused monochromatic synchrotron X-ray. Under the hydrostatic conditions mediated by pore-penetrating alcohol and water mixture, the elastic behavior of mesolite is characterized by continuous volume expansion between ca. 0.5 and 1.5 GPa, which results from expansion in the ab-plane and contraction along the c-axis. Subsequent to this anomalous behavior, changes in the powder diffraction patterns suggest possible reentrant order-disorder transition. The ordered layers of sodium- and calcium-containing channels in a 1:2 ratio along the b-axis attribute to the $3b_{natrolite}$ cell below 1.5 GPa. When the volume expansion is completed above 1.5 GPa, such characteristic ordering reflections disappear and the $b_{natrolite}$ cell persists with marginal volume contraction up to ca. 2.5 GPa. Further increase in pressure leads to progressive volume contraction and appears to generate another set of superlattice reflections in the $3c_{natrolite}$ cell. This suggests that mesolite in the pressure-induced hydration state experiences order-disorder-order transition involving the motions of sodium and calcium cations either through cross-channel diffusion or within the respective channels.

• The Korean Journal of Physiology
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• v.27 no.1
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• pp.51-55
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• 1993

The effects of a calcium channel blocker and an activator on the release of atrial natriuretic peptide (ANP) were investigated in rats. They were volume expanded (VE) up to 5% of the body weight over 30min by being infused with iso-oncotic saline. Following VE, plasma ANP concentration markedly increased in association with increases in the right atrial pressure. Addition of either nifedipine ($0.4{\mu}m/min$) or Bay K 8644 ($0.4{\mu}m/min$) in the infusate potentiated the VE-induced release, although neither of them affected the right atrial pressure. The nifedipine added group showed a lower mean arterial pressure than the Bay K added group throughout the infusion period. VE decreased plasma renin concentration, the magnitude of which was attenuated by nifedipine but not by Bay K. It may be hypothesized that a decrease in cytoplasmic calcium is primary stimulus far the ANP release, and an increase plays o role in secondary liberation of the ANP accumulated in the interstitium into the lumen of the atria through myocardial contraction. further studies will be needed to confirm the hypothesis.

• Journal of the Korean Society of Combustion
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• v.8 no.3
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• pp.15-23
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• 2003

Partial quenching structure of turbulent diffusion flames in a turbulent mixing layer is investigated by the method of flame hole dynamics in order to develop a prediction model for turbulent flame lift off. The essence of flame hole dynamics is derivation of the random walk mapping, from the flame-edge theory, which governs expansion or contraction of flame holes initially created by local quenching events. The numerical simulation for flame hole dynamics is carried out in two stages. First, a direct numerical simulation is performed for constant-density fuel-air channel mixing layer to obtain the turbulent flow and mixing fields, from which a time series of two dimensional scalar dissipation rate array is extracted at a fixed virtual flame surface horizontally extending from the end of split plate to the downstream. Then, the Lagrangian simulation of the flame hole random walk mapping projected to the scalar dissipation rate array yields temporally evolving turbulent extinction process and its statistics on partial quenching characteristics. The statistical results exhibit that the chance of partial quenching is strongly influenced by the crossover scalar dissipation rate while almost unaffected by the iteration number of the mapping that can be regarded as a flame-edge speed.