• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.83.2-83.2
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• 2017

We report observations of light bridge (LB) jets taken with the New Solar Telescope. Jets as dark, fine threads occurred lined along both edges of a LB of a sunspot, which is a bright and elongated structure that divides a sunspot's umbra into two or more parts. This LB jets are observed for about three hours with $H{\alpha}$ filtergraph at ${\pm}0.4{\AA}$, ${\pm}0.8{\AA}$ from the line center, TiO filtergraph, and near infra-red imaging spectropolarimeter (NIRIS). High resolution $H{\alpha}$ data revealed that subsequent ejection of LB jets were associated with subsequent brightening along the edge of the LB. Also, this subsequent brightening was spatially correlated with both photospheric flow and magnetic field change detected from the TiO and NIRIS data, respectively. Preliminary results of LB jet observation and discussions on its formation mechanism will be presented.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.205-213
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• 2005

The drop ejection process from a micro nozzle is investigated by numerically solving the conservation equations for mass and momentum. The liquid-gas interface is tracked by a level set method which is extended for two-fluid flows with irregular solid boundaries. Based on the numerical results, the liquid jet breaking and droplet formation behavior is found to depend strongly on the pulse type of forcing pressure and the contact angle at the gas-liquid-solid interline. The negative pressure forcing can be used to control the formation of satellite droplets. Also, various nozzle shapes are tested to investigate their effect on droplet formation.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.26-34
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• 2013

An analytic approach to determine the optimal conditions for maximizing altitude of a sounding rocket is suggested. The behavior of the one-dimensional momentum equation including thrust, gravitational force and aerodynamic drag force is investigated. For the case where an analytic solution exists, a characteristic equation for determining optimal condition for maximizing altitude at the burn-out state and that for maximizing altitude at the stationary state are developed and verified with numerical experiments.

• International Journal of Vascular Biomedical Engineering
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• v.4 no.2
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• pp.13-18
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• 2006

Direct injection of a fibrinolytic agent to the intra-arterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. Computational fluid dynamic methods were used in order to predict clot lysis for different jet velocities and nozzle arrangements. Firstly, thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about 20% increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. Secondly, thrombolysis was modeled based on the enzyme transport and the fluid flow equations, and quasi steady numerical analysis was performed. Clot lysis efficiency was also increased as injection velocity increased.

• International Journal of Fluid Machinery and Systems
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• v.6 no.4
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• pp.213-221
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• 2013

The characteristics of the thrust for ship propulsion equipment directly driven by air compressed by pressure fluctuation in a blower piping system are investigated. The exhaust valve is positioned upon the air ejection hole in the discharge pipe in order to induce the large-scale pressure fluctuation, and the effects of the valve on the pressure in the pipes and the thrust for the propulsive nozzle are examined. The pressure in the pipes decreases immediately after the valve is opened, and it increases just before the valve is closed. The thrust for the propulsive nozzle monotonically increases with increasing number of revolutions and depth. The interfacial wave in the nozzle appears in the frequency of approximately 4Hz, and it is important for the increase of the thrust to synchronize the opening-closing cycle for the exhaust valve with the generation frequency of the interfacial wave. The finite difference lattice Boltzmann method is helpful to investigate the characteristics of the flow in the nozzle.

• The KSFM Journal of Fluid Machinery
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• v.17 no.5
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• pp.43-53
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• 2014

This paper presents a the study on air curtain system of top and bottom bi-directional jet air discharge for blocking the spread of smoke in case of tunnel fire. The five kinds different air curtains of A, B, C, D, and E of models for various performance tested after manufactured. A results of the various performance test obtained the best efficiency from E model air curtain. And optimize the injection angle of the air curtain nozzle through the three-dimensional computational fluid dynamics (CFD) analysis and analyzed the effects of external pressure of tunnel. and also single factor design have been applied. At present, our attention is focused on the velocity distribution(flow width and flow position) of 1.5m on the ground in tunnel. Also, analyzed the influence of draft in the tunnel. Detailed effects of discharge angle of air curtain and velocity at nozzle exit are discussed.

• Journal of Aerospace System Engineering
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• v.12 no.6
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• pp.1-8
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• 2018

ACF, which is used for the transparent electrode film is manufactured by the thermocompression method with conductive particles. However, the method has disadvantages since there are many wasted materials and the process is complex. To overcome the demerits of the conventional method, EHD printing technology with conductive particles ink is proposed. The line thickness of patterning is influenced by the characteristics of the inks and the printing conditions. Therefore, it is salient to find the most conducive conditions for the micro patterning. In this paper, the ink with conductive particles was manufactured, and the patterning results were obtained by varying the nozzle thickness and the flow rate. The electrical conductivity according to the ejection of the particles ink is obtained.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.79-85
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• 2006

In this study, to increase the mixing between flue gas and reducing agent, new shapes of $NH_3$ ejection nozzles are designed and experimentally and numerically tested. The nozzles have six holes perpendicular to the ambient flue gas flow and the tilting angle between direction of ambient flow and the hole axis is varied. To evaluate the mixing efficiency of the proposed nozzles, numerical and experimental tests are applied to several flow conditions comparing with single hole nozzle, which is commonly used in conventional SCR process. From the results the nozzle with tilted multi-holes has the large region of high turbulent intensity compared with conventional single hole nozzle. This is originated from the high vorticity near the upstream of the jet flow issuing from the hole. The high turbulent intensity and vorticity magnitude lead to enhanced mixing between flue gas and reducing agent. Hence, the most suitable moral ratio between NOx and reducing agent for the catalytic reaction can be obtained on behalf of the intensified scalar mixing within shorter physical mixing length.

• Journal of Biomedical Engineering Research
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• v.26 no.3
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• pp.157-161
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• 2005

Direct injection of a fibrinolytic agent to the intraarterial thrombosis may increase the effectiveness of thrombolysis by enhancing the permeation of thrombolytic agents into the blood clot. Permeation of fibrinolytic agents into a clot is influenced by the surface pressure, which is determined by the injection velocity of fibrinolytic agents. In order to calculate the pressure distribution on the clot surface for different jet velocities (1, 3, 5 m/sec) and nozzle arrangements (1, 9, 17 nozzles), computational fluid dynamic methods were used. Thrombolysis of a clot was mathematically modeled based on the pressure and lysis front velocity relationship. Direct injection of a thrombolytic agent increased the speed of thrombolysis significantly and the effectiveness was increased as the ejecting velocity increased. The nine nozzles model showed about $20\%$ increase of the lysed volume, and the one and seventeen nozzles models did not show significant differences. The wall shear stress decreased as the number of nozzles increased, and the wall shear stress in most vessel wall was lower than 25 Pa. The results implied that thrombolysis could be accelerated by direct injection of a drug with the moderate velocity without damaging the blood vessel wall.

• Journal of the Korean Society of Visualization
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• v.20 no.2
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• pp.45-54
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• 2022

We analyzed the low wall-shear stress area in the intracranial aneurysm that occurred at an anterior communicating artery with a special emphasis on vortical structures close to the wall. We reconstructed the aneurysm model from patient CTA data. We assumed blood as an incompressible Newtonian fluid and treated the blood vessel as a solid wall. The pulsatile boundary condition was applied at the inlet of the anterior cerebral artery. From the instantaneous flow field, we computed the histogram of the wall-shear stress over the aneurysm wall and found the low wall-shear stress event (< 0.4 Pa). This extreme event was due to the low wall-shear stress area that occurred at the daughter sac. We found that the merging of two vortices induced the low wall-shear stress area; one arises from the morphological characteristics of the daughter sac, and the other is formed by a jet flow into the aneurysm sac. The latter approaches the daughter sac, which ultimately leads to the strong ejection event near the daughter sac.