• 대한기계학회논문집B
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• 제39권8호
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• pp.677-682
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• 2015

격자 볼츠만 기법(Lattice Boltzmann method)을 사용하여 에멀전의 유변학적 특성을 파악하기 위한 시뮬레이션을 수행하였다. 간단한 전단 유동하에서 온도와 전단속도, 계면장력에 변화를 주어 에멀전(decane-in-water)의 상대점도를 계산하고 이를 분석하였다. 에멀전의 상대점도는 온도가 증가함에 따라 감소하였고, 전단속도가 증가함에 따라 감소하는 전단박하(Shear thinning) 현상을 보여주었다. 이는 크로스 모델(Cross model)을 통해 검증하였고 일치하는 경향을 보여주었다. 계면에 존재하는 계면활성제(Surfactant)를 통해 제어되는 계면장력이 증가할수록 상대점도는 감소하는 경향을 보여주었다. 이것은 큰 계면장력에서는 기름방울의 변형이 억제되고 점도가 상대적으로 높은 기름방울의 표면적이 감소하면서 나타난다고 해석할 수 있다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.224-227
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• 2010

In the present study, the characteristics of blood flow inside a carotid artery numerically investigated with shear rate specific blood viscosity. To simulate the blood flow with a patient-specific arterial geometry, the geometry of a carotid artery was constructed from 2D rain MRA data. The measured data of blood flow velocity at the common carotid artery were used as boundary conditions of the simulation. For the blood rheology data to be used in the simulation, the patient specific blood viscosity over the whole ranges of shear rate was obtained using $BioVisco^{TM}$. From the numerical results of the blood flow in the carotid artery, the increase of blood viscosity and the decrease of wall shear stress could be found in the carotid bifurcated region, more specifically at the post-plaque dilated region. These characteristics of blood viscosity and wall shear stress can be used more precisely and efficiently to predict the region vulnerable to plaque growht or thrombosis on top of the plaque.

• International Journal of Vascular Biomedical Engineering
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• 제1권1호
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• pp.24-31
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• 2003

As endothelial cells are subject to flow shear stress, it is important to determine the detailed velocity distribution in microvessels in the study of mechanical interactions between blood and endothelium. This paper describes a velocity field of the arteriole in the rat mesentery using an intravital microscope and high-speed digital video system obtained by a highly accurate PIV technique. Red blood cells (RBCs) velocity distributions with spatial resolutions of $0.8{\times}0.8{\mu}m$ were obtained even near the wall in the center plane of the arteriole. By making ensemble-averaged time-series of velocity distributions, velocity profiles over different cross-sections were calculated for comparison. The shear rate at the vascular wall also evaluated on the basis of the ensemble-averaged profiles. It was shown that the velocity profiles were blunt in the center region of the vessel cross-section while they were steep in the near wall region. The wall shear rates were significantly small, compared with those estimated from the Poiseuille profiles.

• 대한기계학회논문집B
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• 제21권5호
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• pp.628-636
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• 1997

Flow visualization technique incorporating photochromic dye is used to study the flow characteristics of the gravity driven laminar wavy film. The film thickness and wave speed are successfully measured by flow visualization. As the inclination angle increases, the waves have higher peaks and lower substrate thickness. The measured cross stream velocity at the free surface is up to 10% of stream wise velocity, which shows enhanced mixing in the lump of the film. The measured stream wise velocity profiles are close to parabolic profile near the substrate and the peak but show significant velocity defect near the rear side of the wave. The measured wall shear rate distributions show good agreement with the previous workers' numerical results.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제21권4호
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• pp.245-275
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• 2017

The present investigation deals, Dufour and heat source effects on radiative MHD slip flow of a viscous fluid in a parallel porous plate channel in presence of chemical reaction. The non-linear coupled partial differential equations are solved by using two term perturbation technique subject to physically appropriate boundary conditions. The numerical values of the fluid velocity, temperature and concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. By increasing the slip parameter at the cold wall the velocity increases whereas the effect is totally reversed in the case of shear stress at the cold wall. It is observed that the effect of Dufour and heat source parameters decreases the velocity and temperature profiles.

• Korea-Australia Rheology Journal
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• 제21권3호
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• pp.175-183
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• 2009

This article describes the numerical investigation of blood flow in the stenosed artery bifurcation with acceleration of the human body. Using the commercial software FLUENT, three-dimensional analyses were performed for six simulation cases with different body accelerations and bifurcation angles. The blood flow was considered to be pulsation flow, and the blood was considered to be a non-Newtonian fluid based on the Carreau viscosity model. In order to consider periodic body acceleration, a modified, time-dependent, gravitational-force term was used in the momentum equation. As a result, flow variables, such as flow rate and wall shear stress, increase with body acceleration and decrease with bifurcation angle. High values of body acceleration generate back flow during the diastolic period, which increases flow fluctuation and the oscillatory shear index at the stenosis.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.78-91
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• 2024

Double steel plate concrete composite shear wall (SCSW) has been widely utilized in nuclear power plants and high-rise structures, and its shear connectors have a substantial impact on the seismic performance of SCSW. Therefore, in this study, the mechanical properties of SCSW with angle stiffening ribs as shear connections were parametrically examined for the reactor containment structure of nuclear power plants. The axial compression ratio of the SCSW, the spacing of the angle stiffening rib arrangement and the thickness of the angle stiffening rib steel plate were selected as the study parameters. Four finite element models were constructed by using the finite element program named ABAQUS to verify the experimental results of our team, and 13 finite element models were established to investigate the selected three parameters. Thus, the shear capacity, deformation capacity, ductility and energy dissipation capacity of SCSW were determined. The research results show that: compared with studs, using stiffened ribs as shear connectors can significantly enhance the mechanical properties of SCSW; When the axial compression ratio is 0.3-0.4, the seismic performance of SCSW can be maximized; with the lowering of stiffener gap, the shear bearing capacity is greatly enhanced, and when the gap is lowered to a specific distance, the shear bearing capacity has no major affect; in addition, increasing the thickness of stiffeners can significantly increase the shear capacity, ductility and energy dissipation capacity of SCSW. With the rise in the thickness of angle stiffening ribs, the improvement rate of each mechanical property index slows down. Finally, the shear bearing capacity calculation formula of SCSW with angle stiffening ribs as shear connectors is derived. The average error between the theoretical calculation formula and the finite element calculation results is 8% demonstrating that the theoretical formula is reliable. This study can provide reference for the design of SCSW.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.19-20
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• 2015

Building exterior wall's energy loss is very high rate comparing to all part of a buildings. And it account for upper 40% of cooling and heating load. So many studies conducted improving insulation performance of building's exterior, appeared about sandwich insulation wall which could be gaining merit of traditional insulation method those are exterior insulation and interior insulation. In this study, we inform structural performance of sandwich insulation wall for RC wall. For this, first, we define each wall's role and design sandwich insulation wall. At last, analyze structural performance of sandwich insulation wall. This study can contribute to apply it safely where side wall which toilet, stair area, etc.

• Advances in Computational Design
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• 제5권2호
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• pp.111-125
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• 2020

The flow behavior of polymer melts within a slit die is an important consideration when designing a die geometry. The quality of the extruded polymer product can be determined through an evaluation of the flow homogeneity, wall shear rate and pressure drop across the central height of the die. However, mathematical formulations cannot fully determine the behavior of the flow due to the complex nature of fluid dynamics and the nonlinear physical properties of the polymer melts. This paper examines two slit die geometries in terms of outlet velocity uniformity, shear rate uniformity at the walls and pressure drop by using the licensed computational fluid dynamics package, Ansys POLYFLOW, based on the finite element method. The Carreau-Yasuda viscosity model was used for the rheological properties of the polypropylene. Comparative analysis of the simulation results will conclude that the modified die design performs better in all three aspects providing uniform exit velocity, uniform wall shear rates, and lower pressure drop.

• 대한기계학회논문집B
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• 제25권6호
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• pp.751-757
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• 2001

An experimental study of impinging jet-flow structure has been carried out for a fully developed single circular jet impingement cooling on a flat plate, and the effect of the wall thickness at nozzle exit edge is investigated. Impinging jet flow structures have been measured by Laser-Doppler Velocimeter to interpret the heat transfer results presented previously by Yoon et al.(sup)(10) The peaks of heat transfer rate are observed near the nozzle edge owing to the radial acceleration of jet flow when the nozzle locates close to the impingement plate. The growth of the velocity fluctuations in the wall jet flow is induced by the vortices which originate in the jet shear layer, and consequently the radial distribution of local Nusselt numbers has a secondary peak at the certain radial position. As a wall of circular pipe nozzle becomes thicker for small nozzle-to-target distance, the entrainment can be inhibited, consequently, the acceleration of wall jet flow is reduced and the heat transfer rate decreases.