• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.10-16
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• 2019

Considering the role of viscosity in the hemorheology, the characteristics of non-Newtonian fluid are important in the pulsatile blood flows. Stenosis, with an abnormal narrowing of the vessel, contributes to block blood flows to downstream tissue and lead to plaque rupture. Therefore, systematic analysis of blood flow around stenosed vessels is crucial. In this study, non-Newtonian behaviors of blood analog fluids around the micro-stenosis with 60 % severity in diameter of $500{\mu}m$ was examined by using CFX under the pulsatile flow conditions with the period of 10 s. Viscosity information of two non-Newtonian fluids were obtained by fitting the value of normal blood and highly viscous blood. As the Newtonian fluid, the water at room temperature was used. During the pulsatile phase, wall shear stress (WSS) is highly oscillated. In addition, high viscous solution gives rise to increases the variation in the WSS around the micro-stenosis. Highly oscillating WSS enhance increasing tendency of plaque instability or rupture and damage of the tissue layer. These results, related to the influence on the damage to the endothelium or stenotic lesion, may help clinicians understand relevant mechanisms.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.214-220
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• 2010

This article described that a high Reynolds number version of a turbulence model was modified by using drag reduction to analyze the turbulent flows of non-Newtonian fluid with visco-elastic viscosity and it was applied hemodynamics which was representative of visco-elastic fluid. The turbulence characteristics of visco-elastic fluid was expanded viscous sublayer region and buffer layer region by drag reduction phenomenon and also Newtonian turbulence models does not predict because viscosity was related with shear rate of fluid flow. Hence numerical simulation using a modified turbulence model was conducted under the same conditions that were applied to obtain the experiment results and previous turbulence models and then the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.6
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• pp.773-778
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• 1997

The present study investigates the effect of the shear rate-dependent thermal conductivity of non-newtonian fluids on the heat transfer enhancement in a 2:1 rectangular duct flow. An axially-constant heat flux and a peripherally-constant temperature boundary conditions(H1) was adopted for a top-wall-heated configuration. The present numerical results of Nusselt numbers for SRDC(Separan) show heat transfer enhancement over those of SRIC. The Nusselt numbers increased linearly as Reynolds numbers increased. The heat transfer enhancement is due to an increased thermal conductivity near the wall, which is attributed to the shear rate-dependence.

• Journal of The Korean Astronomical Society
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• v.46 no.2
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• pp.93-96
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• 2013

Modified Newtonian Dynamics (MOND) is a possible solution for the missing mass problem in galactic dynamics; its predictions are in good agreement with observations in the limit of weak accelerations. However, MOND does not derive from a physical mechanism and does not make predictions on the transitional regime from Newtonian to modified dynamics; rather, empirical transition functions have to be constructed from the boundary conditions and comparisons with observations. I compare the formalism of classical MOND to the scaling law derived from a toy model of gravity based on virtual massive gravitons (the "graviton picture") which I proposed recently. I conclude that MOND naturally derives from the "graviton picture" at least for the case of non-relativistic, highly symmetric dynamical systems. This suggests that-to first order-the "graviton picture" indeed provides a valid candidate for the physical mechanism behind MOND and gravity on galactic scales in general.

• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.613-622
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• 2001

Interaction of blood flow and leaflet behavior in a bileaflet mechanical heart valve was investigated using computational analysis. Blood flows of a Newtonian fluid and a non-Newtonian fluid with Carreau model were modeled as pulsatile, laminar, and incompressible. A finite volume computational fluid dynamics code and a finite element structure dynamics code were used concurrently to solve the flow and structure equations, respectively, where the two equations were strongly coupled. Physiologic ventricular and aortic pressure waveforms were used as flow boundary conditions. Flow fields, leaflet behaviors, and shear stresses with time were obtained for Newtonian and non-Newtonian fluid cases. At the fully opened phase three jets through the leaflets were found and large vortices were present in the sinus area. At the very final stage of the closing phase, the angular velocity of the leaflet was enormously large. Large shear stress was found on leaflet tips and in the orifice region between two leaflets at the final stage of closing phase. This method using fluid-structure interaction turned out to be a useful tool to analyze the different designs of existing and future bileaflet valves.

• Journal of the Korean Society of Visualization
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• v.14 no.1
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• pp.33-39
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• 2016

Radio-cephalic arteriovenous fistula(RC-AVF) is the most recommended operation of achieving access for hemodialysis. However, it has high rates of early failure depending on the many haemodynamic conditions. To increase RC-AVF patency rate, many researches were performed by in-vitro experiment via artificial vessel and blood analogue fluid, and there were conflicting opinions about whether the non-Newtonian properties of blood have an influence on the flow in large arteries. To investigate the influence of viscoelasticity of blood within the RC-AVF, we fabricated three dimensional artificial RC-AVF and two kinds of blood analogue fluid. The velocity field of two fluids within the vessel were measured by micro-particle velocimetry(m-PIV) and compared with each other. The velocity profiles of both fluids for systolic phase were matched well while those for diastolic phase did not correspond. Therefore, it is desired to use non-newtonian fluid for in-vitro experiment of RC-AVF.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.1
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• pp.114-122
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• 1996

Pipeline transport of dredged soils has been widely used for reclamation. In this case the fluid mixed with soils, so called slurries, has very much different characteristics from pure fluids. As the slurry fluid has a peculiar mode in the viscosity, a proper equation of friction factor has to be used which is pertinent to the characteristics of slurry flow for the estimation of pipeline transport of dredged soils. The slurry fluid has the characteristics of Newtonian fluid or non-Newtonian fluid largely depending on the size of particles. In the present study, new forms of pipe friction factor equations have been suggested for both conditions, and using these forms explicit equations have been developed for the computation of relevant pipe diameter and discharge as well as pumping power.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.690-695
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• 1999

An experimental study for mesophase pitch prepared from coal tar pitch has been carried out to clarify the rheological behaviors in the molten state. The apparent viscosity, shear stress, shear rate, Qunoline insoluble(QI), and softening point(SP) change were investigated especially. The conditions to increase mesophase content during polymerization were heat treatment time of 5 hrs, catalyst concentration of 3% and reaction temperature of $420^{\circ}C$. Apparent viscosity change with increase in temperature of pitches was different according to the heat treatment conditions and apparent viscosity increased with increasing heat treatment temperature, heat treatment time, contents of mesophase, on the contrary, fluidity is decreased. Rheological behavior of molten mesophase pitches at about $270^{\circ}C$ showed Newtonian behavior below $375^{\circ}C$ and non-Newtonian behavior above $270^{\circ}C$, the flow behavior was analyzed with Casson model.