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Numerical simulations of blood flow in arterial bifurcation models
Seo, Taewon 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.3
In the study, two different arterial bifurcation model geometries were used in the flow simulation. The model 1 is assumed the internal carotid artery (ICA) and the external carotid artery (ECA) branches of the bifurcation aligned in parallel to each other, while the model 2 is the typical carotid geometry. In the computation the Non-Newtonian behavior of blood was described using Carreau model. Generally, in the comparison between Newtonian and Non-Newtonian results good agreement was observed in the velocity profiles, while some discrepancies were found in the temporal wall shear stress (WSS) distributions as well as pressure profiles due to the shear thinning behavior. The temporal evolution of WSS periodically increases and decreases closely that of the inlet velocity waveform. It was also observed that the reversed flow region in the ICA of model 2 is 2.5 times larger than that of model 1. As a result, the variation of the flow characteristics can be dependent on the geometry as well as the arterial bifurcation geometry plays an important role in the development of atherosclerosis.
Large-Scale Vortical Structures in The Developing Plane Mixing Layer Using LES
Seo, Taewon,Kim, Yeung-Chan,Keum, Kihyun The Korean Society for Aeronautical and Space Scie 2001 International Journal of Aeronautical and Space Sc Vol. No.
Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.
Drug-Eluting Stent Design is a Determinant of Drug Concentration at the Endothelial Cell Surface
Seo, Taewon,Lafont, Antoine,Choi, Sun-Young,Barakat, Abdul I. Springer-Verlag 2016 Annals of biomedical engineering Vol.44 No.2
<P>Although drug-eluting stents (DES) have greatly reduced arterial restenosis, there are persistent concerns about stent thrombosis. DES thrombosis is attributable to retarded vascular re-endothelialization due to both stent-induced flow disturbance and the inhibition by the eluted drug of endothelial cell proliferation and migration. The present computational study aims to determine the effect of DES design on both stent-induced flow disturbance and the concentration of eluted drug at the arterial luminal surface. To this end, we consider three closed-cell stent designs that resemble certain commercial stents as well as three 'idealized' stents that provide insight into the impact of specific characteristics of stent design. To objectively compare the different stents, we introduce the Stent Penalty Index (SPI), a dimensionless quantity whose value increases with both the extent of flow disturbance and luminal drug concentration. Our results show that among the three closed-cell designs studied, wide cell designs lead to lower SPI and are thus expected to have a less adverse effect on vascular re-endothelialization. For the idealized stent designs, a spiral stent provides favorable SPI values, whereas an intertwined ring stent leads to an elevated SPI. The present findings shed light onto the effect of stent design on the concentration of the eluted drug at the arterial luminal surface, an important consideration in the assessment of DES performance.</P>
The Air Flow Model Study within the Electrostatic Precipitator
Seo, Taewon 안동대학교 공업기술연구소 1996 공업기술연구논문집 Vol.3 No.1996
As the industries are rapidly growing, the stringent regulation of clean air is widely spread in the developed countires. In the sense of clean air, the electrostatic precipitator is one of the gas cleaning equipment in the large-scale industries in that the forces separating the particulate from the gas stream are applied directly to the particles. The purposes of this study are to know the flow characteristics and to obtain the uniform velocity distribution within the electrostatic precipitator. The parametric study is conducted to control and manage the flow field in the diverging channel to obtain the satisfying result. The gas flow control devices which are the parameters to be considered to manage the air flow modeling of the electrostatic precipitator are following; ● Guide vane ● Perforated plate ● Grid attached on the perforated plates By the adequate combination of these flow control devices, we can get a uniform velocity distribution within the electrostatic precipitator.
협착 동맥에서의 맥동 혈류 유동에 대한 수치해석적 연구
서태원(Taewon Seo),Bahtiyor Buriev 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.11
In the present computational study, simple stenotic artery models using pulsatile flow condition were investigated. A 1 ㎐ non-reversing sinusoidal velocity for pulsatile flow was imposed at the flow inlet and the corresponding Womersley number based on the vessel radius is 2.75. The simple stenotic geometries have been used that consist of 25%, 50% and 75% semicircular constriction in a cylindrical tube. In this paper, numerical solutions are presented for a first harmonic oscillatory flow using commercial software ADINA 8.4. As stenosis and Reynolds number increase, the maximum wall shear stress(WSS) increases while the minimum WSS decreases. As the stenotic rate increases, the pressure drop at the throat severely decreases to collapse the artery and plaque. It is found that the fluid mechanical disturbances due to the constriction were highly sensitive with rate of stenosis and Reynolds number. When Reynolds number and stenosis increase, the larger recirculation region exists. In this recirculation region the possibility of plaque attachment is increasingly higher. The present results enhance our understanding of the hemodynamics of a stenotic artery.
Robust design of a screw-based crawling robot on a granular surface
ChangKook Seo(서창국),KyungUK Lee,DongHan Son,TaeWon Seo 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
In this paper, a robust design of a screw wheel is presented, based on the Taguchi method to accelerate a screw-based crawling robot. Screw-based crawling robots have been studied before, but their application is limited because of their limited speed. To solve this problem, robust design is applied for the screw wheel geometry driving on granular surfaces, such as desert sand. Each of the four parameters determining the screw wheel geometry and two user conditions were set at three levels, and the Taguchi method was applied through the L_9 (3^4) orthogonal array. The experimentally optimized parameters were as follows: the slope angle was 35°, the height of the blade was 14 mm, the number of spirals was one, and the blade had a semicircular cross-section. In conclusion, the robust design using the Taguchi method is suitable for solving the speed problem of a screw-based crawling robot on a granular surface.
서태원(Taewon Seo),Abdul I. Barakat 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
In this study, we performed computational fluid dynamic simulations to explore how the detailed design of drugeluting stents affects both the flow field in the vicinity of the stent as well as the concentration of the eluted drug at the endothelial cell surface. Simulations were performed on three idealized stent geometries we developed and approximating three commercial stents, Medtronics Aurora stent, Cordis BX Velocity stent, and Boston Scientifics Wallstent. An important contribution of the present study is the introduction of the stent effectiveness index (SEI) which provides a quantitative assessment of stent performance and an objective basis for comparing the performance of different stents. Among the three commercial stents studied, our simulations have revealed that the BX Velocity stent is associated with the lowest in-stent SEI values for the range of flow Reynolds numbers studied (200≤Re≤800). In addition to commercial stent designs, we investigated the SEI in three idealized stents and determined that a spiral stent provides excellent performance (low SEI) under all flow conditions investigated.