• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.373-380
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• 2001

In this study, a single Taylor bubble and a train of Taylor bubbles rising in a vertical tube were simulated numerically. A finite difference method was used to solve the mass and momentum equations for the liquid-gas region. The liquid-gas interface was captured by a level set function which is defined a signed distance from the interface. For a train of Taylor bubbles repeated periodically in space, the periodic conditions were imposed at the boundaries normal to the gravitational direction and the pressure boundary conditions were iteratively determined so that the computed flow rate should be equal to a given flow rate. Based on the numerical simulation, the calculated shape and rise velocity of a Taylor bubble were found to be in good agreement with the experimental data reported in the literature.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.34S no.3
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• pp.46-54
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• 1997

In this paper, we psropose the feedback linearization technique for a nonlinear system using genetic algorithms (GAs) and fuzzy logic system. The proposed control scheme approximates the nonlinear term of a nonlinear system using the fuzzy logic system and computes the control input for cancelling the nonlinear term. Then in the fuzzy logic system, the number and shape of membership function of the premise aprt will be tuned to minimize the control error boundary using GAs. And the parameters of the consequence of fuzzy rule will be tuned by the adaptive laws based on lyapunov stability theory in order to guarantee the closed loop stability of control system. The evolution of fuzzy logic system is processed during the on-line adaptive control. The effectiveness of proposed method will be demonstrated by computer simulation of simple nonlinear sytem.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.584-591
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• 2002

The objective of the present study is to develop a model to predict heat and gas flow movement by fire in a tunnel. The model includes component models such as turbulence model, combustion model, fire model, jet fan model, etc. It has been validated using the data from Memorial Tunnel Fire Ventilation Test Program. The predictions are in good quantitative agreement with the experimental data in the far-field region of the tunnel. It should be further investigated to develop models for radiation between surfaces, for composite boundary conditions for conduction and convection, and for vigorous turbulent mixing in a tunnel especially for a large size of fire.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.167-173
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• 2003

For the measurement of mass flow rate at a wide range of operation conditions, it is required that the critical nozzle gas different diameters, since the mass flow rate through the critical nozzle depends on the nozzle supply conditions and the nozzle throat diameter. In the present study, both computational and experimental investigations are performed to explore the variable critical nozzle. Computational work using the 2-dimensional, axisymmetric, compressible Navier-Stokes equations are carried out to simulate the gas flow through variable critical nozzle. In experimnet, a cylinder with several different diameters is inserted into the critical nozzle to vary the nozzle throat diameter. Computational results are compared with the experimented ones. The computed results are in close agreement with experiment. It is found that the displacement and momentum thickness of variable critical nozzle are given as a function of Reynolds numbers. The discharge coefficient of the variable critical nozzle is predicted using an empirical equation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.5
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• pp.1011-1018
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• 1992

A series of experiment has been performed on the spray characteristics in a cylindrical confined space with the injection pressure taken as a parameter. By using a single-hole patternator and the Malvern particle sizer, the spray mass flux, drop size and volume concentration distributions along the radial and axial directions were obtained ; the line-of- sight data by Malvern particle sizer have been converted to the ring-of-sight data by using the tomographical transformation techniqe. The experimental results show that, due to the restriction on the ambient gas entrainment by the wall boundary, the effective spray angle is increasing. The spray drops were measured to be smaller in the confined space because of a large number of floating small drops by recirculation of the gas phase and the breakup of large drops by the wall collision. Also the details on the flow behavior of the confined spray are discussed.

• Journal of Korea Water Resources Association
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• v.38 no.7 s.156
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• pp.537-544
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• 2005

For the proper management of high pressurized gas storage caverns, analysis of groundwater flow field and inflow quantity according to the groundwater head, gas storage pressure and water curtain head should be performed. The finite element method has been widely used for the groundwater flow analysis surrounding underground storage cavern because it can reflect the exact shape of cavern. But the various simulations according to the change of design factors such as the width of water curtain, shape of cavern etc. are not easy when elements were set up. To overcome these limitations, two dimensional groundwater flow model is established based on the boundary element method which compute the unknown variable by using only the boundary shape and condition. For the exact computation of drainage rate into cavern, the model test is performed by using the exact solution and pre-developed finite element model. The test result shows that the model could be used as an alternative to finite element model when various flow simulations are needed to determine the optimizing cavern shape and arrangement of water curtain holes and so forth.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.04a
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• pp.20-20
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• 2000

초음속 과소팽창 제트는 베럴충격파(Barrel shock), 팽창파(Expansion fan), 반사충격파(Reflected shocks), 마하디스크(Mach disc), 그리고 제트경계면(Exhaust-gas Jet boundary)로 이루어지는 여러 충격파 셀(Shock ceil)의 유동 형태를 나타난다. 이러한 초음속 과소팽창 제트가 수직 평판에 충돌하면 초음속 자유 제트와는 다른 변형된 유동장이 형성된다.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1475_1476
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• 2009

본 논문에서는 스트리머 방전에 대한 연구의 일환으로 전자사태의 발생과정 및 절연파괴현상을 2차원 유한요소법을 이용하여 해석하였다. 평행 평판 전극을 모델로 도입하고 전자밀도에 대한 경계조건을 변화시켜 각각 시뮬레이션을 통하여 신뢰성 있는 결과를 도출하였다.

• Tribology and Lubricants
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• v.7 no.2
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• pp.51-60
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• 1991

For the accurate run-out of a light rotor shaft the sliding bearings supplied with externally pressurized air are effectively applied, and it is important to predict the static and dynamic characteristics of rotor-bearing system. In this study direct numerical method is applied to solve the perturbed Reynolds' equation. To solve it the perturbed dimensionless mass flow rate is used as the boundary condition under the inherently-compensated restrictor. The dynamic characteristics of a rotor supported in the externally pressurized air bearings are analyzed, and as a result the orbit of the journal center is calculated. The theoretical results are investigated and discussed.

• 한국가스학회:학술대회논문집
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• 2005.10a
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• pp.157-162
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• 2005