• Journal of the Korean Society of Visualization
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• v.19 no.1
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• pp.81-87
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• 2021

Extensional flow of viscoelastic fluids is widely utilized in various industrial processes such as electrospinning, 3D printing and plastic injection molding. Extensional rheological properties, such as apparent viscosity and relaxation time, play an important role in the design and evaluation of the viscoelastic fluid-involved processes. In this work, we propose a lab-built capillary breakup extensional rheometer (CaBER) based on flow image processing to investigate the capillary breakup of polyethylene oxide (PEO) solution and its extensional rheological properties. We found that the apparent extensional viscosity and extensional relaxation time of the PEO solution are independent of the strike time. The proposed CaBER is expected to be applied to characterization of the extensional rheological properties of viscoelastic fluids at low cost with high precision.

• Journal of the Korean Society of Visualization
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• v.17 no.2
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• pp.90-95
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• 2019

In the present work, the effect of flow parameters such as volume flow rate on focal point of fluidic micro lens is investigated numerically. ANSYS Fluent is used for simulations, and the flow parameters and number of simulations are determined using the space filling method of design of experiment (DOE). Having determined the location of interfaces between fluids inside the micro lens which acts as the lens curvature, a ray tracking simulation on each case is performed using COMSOL Multiphysics to determine the focal point for each lens. These data are then used to provide a relation between flow parameters and the focal point of the lens.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.290-296
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• 2008

In this paper development of on-line data visualization program is described and some examples of data postprocessing are shown. The program is written in JAVA language and runs as a JAVA applet on the web browser such as Internet Explorer or Firefox. Remote users can use the program to visualize and analyze their own flow data by accessing the program server through the internet and loading data files in proper formats from their local computers. This paper describes briefly about algorithms for data visualization, structure and available functions of the program, and web sever system. The mechanism of how the JAVA applet can access and process local data files and relevant coding techniques are explained as well. Also explained is what is required for the remote users and client computers to access the program on-line. Some visualization examples performed on a local computer are illustrated by accessing the server remotely.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.290-296
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• 2008

In this paper development of on-line data visualization program is described and some examples of data postprocessing are shown. The program is written in JAVA language and runs as a JAVA applet on the web browser such as Internet Explorer or Firefox. Remote users can use the program to visualize and analyze their own flow data by accessing the program server through the internet and loading data files in proper formats from their local computers. This paper describes briefly about algorithms for data visualization, structure and available functions of the program, and web sever system. The mechanism of how the JAVA applet can access and process local data files and relevant coding techniques are explained as well. Also explained is what is required for the remote users and client computers to access the program on-line. Some visualization examples performed on a local computer are illustrated by accessing the server remotely.

• Journal of Biomedical Engineering Research
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• v.11 no.2
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• pp.233-242
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• 1990

In the current flow visualization studies, the role of non-Newtonian characteristics (such as shearra to dependent viscosity and viscoelasticity ) on flow behavior across the sudden ex- pansion step in a circular pipe as a model for blood flow experiments is investigated over a wide range of Reynolds numbers. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10~35, 000 based on the inlet. diameter. The reattachment longuEs for the viscoelastic fluids in the lami- nar flow regime are found to be much shorter than those for the Newtonian fluid. In addition it decreases significantly with increasing concentration of viscoelastic fluids at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids Is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting In 25 and 28 step-height dis- tances for 500 and 1, 000 lpm ployacrylamide solutions, respectively. This may be due to the fact that the elasticity in pobacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pips flow.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.217-224
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• 2002

It is very important to measure and visualize the changes in the physical properties of fluid flow because this is the foundation of measurement techniques used in aerodynamics, heat transfer, plasma diagnostics, and stress analysis of transparent models. The optical methods are advantageous over probe-based techniques in the optical methods are of high speed, non-contact and are capable of providing full-field results with high spatial resolution. Therefore we propose the electronic speckle pattern interferometry(ESPI) that gives us a solution to overcome those limitations. In this paper the experimental results show qualitative and quantitative visualization of changes in the physical properties of the candle and alcohol lamp with 3D plotting. And we obtained the refractive index, mass density and temperature distribution of fluids. The results clearly show the process of flow phenomena and give the feasibility of quantitative interpretation of gasdynamics.

• 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 computational fluids engineering
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• v.20 no.4
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• pp.28-35
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• 2015

BARAM system that means 'wind' in Korean has been established as a virtual wind tunnel system for aircraft design. Its aim is to provide researchers with easy-to-use, production-level environment for all stages of CFD simulation. To cope with this goal an integrated environment with a set of CFD solvers is developed and coupled with an highly-efficient visualization software. BARAM has three improvements comparing with previous CFD simulation environments. First, it provides a new automatic mesh generation method for structured and unstructured grid. Second, it also provides real-time visualization for massive CFD data set. Third, it includes more high-fidelity CFD solvers than commercial solvers.

• Journal of the Korean Society of Visualization
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• v.5 no.2
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• pp.39-47
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• 2007

This paper describes an experimental study on the droplet formation and the subsequent motion in a microchannel having a cross junction. While one kind of liquid (pure water or water-surfactant mixture) is drawn into a horizontal inlet channel, the other kind (oil) is introduced through two vertical inlet channels. Due to the effect of surface tension on the interface between the two fluids, the droplets of the first fluid are formed near the cross junction. In this study, we have found that the droplet formation is affected even by slight difference in the surface tension. When the surface tension between two fluids is decreased, the droplet size is decreased in order to keep the equilibration between the pressure and the surface tension. In addition, the time interval between each of the droplet formations is decreased and the distance between droplets is also decreased when the surface tension is decreased.