• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.2
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• pp.159-170
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• 2023

In the present study, the dynamic behavior characteristics of an amphibious assault vehicle during water entry were analyzed using STAR-CCM+, a commercial computational fluid dynamics(CFD) code. All computations were performed using an overset mesh system and a RANS based flow-solver coupled with dynamic fluid-body interaction(DFBI) solver for simulating three degrees of freedom motion. For numerical validation of the solver, a water entry simulation of inclined circular cylinder was conducted and it was compared between an existing experiment data and CFD results. The pitch angle variation and the trajectory of the circular cylinder during water entry shows good agreement with previous experimental and numerical studies. For the water entry simulations of the amphibious assault vehicle, the analysis of dynamic behaviors of the amphibious assault vehicle with different slope angles, submerged depths and initial velocities were conducted. It is confirmed that the steep slope angle increases the submerged volume of the amphibious assault vehicle, so the buoyancy acting on the vehicle is increased and the moved distance for the re-flotation is decreased. It is also revealed that the submerged volume is increased, bow-up phenomenon occur earlier.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.291-298
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• 2004

The observations of rapid motion of bubbles under water for approximately 50 ms or less in high-magnetic fields of 10 T have been carried out successfully for the first time. The observation system constructed is composed of a high-speed video camera, a telescope, a cryostat with a split-type superconducting magnet, a light source, a mirror and a transparent sample cell. Using this system, the influence of magnetic field on the path and shape of single bubbles of O$_2$ (paramagnetism) and N$_2$ (diamagnetism) has been examined carefully. Experimental values describing the path are in good agreement with theoretical values calculated on the basis of the magneto-Archimedes effect, despite the effect of magnetism on the bubble. However, no effect of magnetism on the shape of the bubble is observed. In addition, the influence of magnetic field on drag coefficient of the bubble is discussed.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1240-1247
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• 2003

Water jet nozzle for LCD has been used as a wet cleaning process in many industries. It is necessary for the nozzle to consider cleaning effect and flux. In this paper, we applied the bubble dynamic theory(Rayleight-Plesset equation) to improve the cleaning efficiency. Generally, Rayleigh-Plesset equations for cavitation bubbles are used in analyzing computer simulation for caviting flows. Burst of bubbles causes potential energies and we can use these energies to remove organic and inorganic compounds on the LCD. Therefore, it is necessary to analyze the bubble generations and axiomatic design by computational fluid dynamics(CFD). By comparing the weight matrix of neural networks to the design matrix of axiomatic design, we propose methods to verify designs objectively. The optimal solution could be deduced by the regression analysis using the design parameters.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.11 no.1
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• pp.71-83
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• 2007

The double diffusive convection of cold water in the vicinity of its density maximum in a rectangular partitioned enclosure of aspect ratio 5 with isothermal side walls and insulated top and bottom is studied numerically. A thin partition is attached to the hot wall. The species diffusivity of the fluid is assumed to vary linearly with concentration. The governing equations are solved by finite difference scheme. The effects of position and height of the partition, variable species diffusivity and enclosure width are analyzed for various hot wall temperatures. It has been found that adding partition on the hot wall reduces the heat transfer. The density inversion of the water has a great influence on the natural convection. When increasing species diffusivity parameter heat and mass transfer rate is decreased.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.4
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• pp.425-432
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• 2010

From the results of tracer test for the existing clearwell in Y water treatment plant, $T_{10}$ and T10/T were calculated as 150 min and 0.24, respectively. Therefore it required the modification schemes for improving hydraulic efficiency, surrogated by $T_{10}$ and $T_{10}$/T, and disinfection performance. In this study, using transient CFD(Computational Fluid Dynamics) simulation technique, tracer tests on dynamic condition for the suggested schemes were simulated. From the results of simulation, it was revealed that 8~6 baffles are necessary to guarantee the disinfection ability in the existing clearwell. Also, installing orifice baffle in the vicinity of inlet could increase plug flow fraction within clearwell.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.101-107
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• 1998

A three-dimensional multi-phase flow is simulated around a smooth tire. This simulation is conducted by solving Navier-Stokes equation with a k-$\varepsilon$ turbulent model. The numerical calculations are carried out by modeling a multi-phase free surface flow mixed with air and water at the inlet. The numerical solutions show an intuitively resonable behavior of water around a moving tire. The calculated pressure around the tire surface along the moving direction is presented. The moving velocities of the tire are chosen to be 30, 40, 60, and 70 km/h. The numerically simulated pressures around the tire are compared with existing experimental data. The comparison shows a new possible tool of analyzing a hydroplaning phenomenon for an automobile tire by means of a computational fluid dynamics.

• Journal of Korean Society of Water and Wastewater
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• v.24 no.5
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• pp.519-525
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• 2010

From the results of tracer test for the existing chlorine contactor in Y water treatment plant, $T_{10}$ and $T_{10}$/T were calculated as 130 min and 0.16, respectively. Therefore it required the modification schemes for improving hydraulic efficiency, surrogated by T10 and $T_{10}$/T, and disinfection performance. In this study, in order to reduce dead zone within contactor, the installation of porous baffles in the near of each corner was suggested and verified using transient CFD(Computational Fluid Dynamics) simulation technique and tracer tests on dynamic condition. From the results of simulation and tracer tests, it was revealed that porous baffles installed have been effective to reduce dead zone within contactor, and increase plug flow fraction.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2390-2395
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• 2008

The water droplet motion in an air flow microchannel with pores through which water emerges is studied numerically by solving the equations governing the conservation of mass and momentum. The gas-liquid interface is tracked by a level set method which is based on a sharp-interface representation for accurately imposing the matching conditions at the interface and is modified to implement the contact angle conditions on the wall and pores. The numerical results show that the droplet growth and detachment pattern depend significantly on the contact angle and inlet air velocity. Also, the dynamic interaction between the droplets growing on multiple pores is investigated. The pore arrangement subject to droplet merging is found to be not effective for water removal.

• Journal of Navigation and Port Research
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• v.28 no.2
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• pp.141-148
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• 2004

The observations of rapid motion of bubbles under water for approximately 50ms or less in high . magnetic fields of 10 T have been carried out successfully for the first time. The observation system constructed is composed of a high-speed video camera, a telescope, a cryostat with a split-type superconducting magnet, a light source, a mirror and a transparent sample cell. Using this system, the influence of magnetic field on the path and shape of single bubbles of $O_2$(paramagnetism) and $N_2$ (diamagnetism) has been examined carefully. Experimental values describing the path are in good agreement with theoretical values calculated on the basis of the magneto-Archimedes effect, despite the effect of magnetism on the bubble. However, no effect of magnetism on the shape of the bubble is observed In addition, the influence of magnetic field on drag coefficient of the bubble is discussed.

• Journal of Korean Society on Water Environment
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• v.37 no.3
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• pp.168-174
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• 2021

Mixing is a very important unit in water treatment process. A mechanical stirring method is generally used for mixing, but recently, the use of pressurized water mixing method (pump diffusion flash mixer) has gained interest because it is more advantageous in terms of mixing time, noise, energy consumption, and maintenance. The following conclusions were obtained from the study of pressurized water mixing method by Computational Fluid Dynamics. Firstly, the mixing degree in the pipe increased as the density of water increased. Secondly, even if the relative velocity between flow rate in the pipe and the pressurized water was constant, the mixing degree decreased as the flow velocity in the pipe increased. Thirdly, the stronger the injection energy the higher the mixing degree. It was also found that the mixing degree was greatly affected by the injection velocity as compared to the injection flow amount. Finally, the required energy to achieve 95% mixing degree at the distance of 10 times diameter in big pipes of 500 mm to 3000 mm was 0.3 to 4.5 kJ. The result of this study could be used in the process design of injection with water purification chemicals, such as, ozone, chlorine, and coagulant.