• Proceedings of the KSME Conference
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• 2000.04b
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• pp.531-534
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• 2000

The objective of this investigation is to find effects of the pulsatile flow on the morphological changes of the endothelial cell(E.C.) in blood vessel. The shear flow experiment system is used to get the morphological changes of the E.C. The shapes of E.C. are simulated by the cosine curves and computer simulation is used to calculate the pressure and shear stress fields on the E.C. The inlet boundary condition is given from the measured velocity data of femoral artery. The endothelial cells reduce their heights in the flow field so as to reduce the pressure and wall shear stress on the surface. As the exposed time increases, the shear stress and pressure on the E.C. are reduced under the pulsatile flow. The shear stresses on the cell surface show the minimum values during the deceleration phase.

• The KSFM Journal of Fluid Machinery
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• v.14 no.6
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• pp.45-53
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• 2011

Multiphase lattice Boltzmann method (LBM) has been used to simulate the nucleate pool boiling directly. For the phase change model, the thermal model and the Stefan boundary condition were introduced to the isothermal LBM. The phase change model was validated by the bubble growth in a superheated liquid under no gravity. The bubble growth on and departure from a superheated wall has been simulated successfully. The preliminary results showed that the detail process of nucleate pool boiling was in good agreement with the experimental results.

• KSTLE International Journal
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• v.7 no.1
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• pp.22-26
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• 2006

A simple finite element analysis is performed to simulate the thermal characteristics of a micro sensor package with thin film heater embedded in the glass wall of a micro-channel. In this paper, Electric characteristics of ITO sputtered heater were presented in this study, which can be used as a map of heater design in the range of available system temperature. The effects of thermo-physical properties of materials, geometrical structure and boundary condition on the thermal performance are also investigated. Finally, the design of micro-flow induced thermal sensor that is capable of measuring fluid flow with a lower flow detection limit of approximately 24pL/s is presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.1010-1015
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• 2002

Over the last few decades, noise has played a major role in the development of aircraft engines. The dominant noise is generated by the wake interactions of fan and downstream stator. Engine inlet and exhaust ducts are being fitted with liner materials that aid in damping fan related noise. In this paper, the radiation of duct internal noise from duct open ends with liners is studies via numerical methods. The linearized Euler's equations in generalized curvilinear coordinates are solved by the DRP scheme. The far field sound pressure levels are computed by the Kirchhoff integration method. Through comparison of sound directivity from bell-mouth duct with and without liners, it is shown that radiation from engine inlet is affected by liner effects or a soft wall boundary condition.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.4
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• pp.1-8
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• 1996

The sound quality of the car audio system is affected by the serveral factors such as the dimensions of the room, the boundary condition of the wall, the location of the speakers, etc. Among these factors, the location of the car speakers has been focused to find the best location of the car speakers assuming that the flat response is better. To verify the suggestion, the subjective test is adopted using 10 people. The developed method is utilizd to evaluate the function of the audio system with fixed speaker position.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.56-64
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• 2000

A friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was carefully designed to control the effect of the piston secondary motion and the temperature of cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner, was measured under the condition of flooded oil supply. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(midstroke and dead centers). The modes could be identified on the Stribeck diagram of the friction coefficients and the dimensionless number of ㎼/p, where the friction coefficients are evaluated at near the midstroke and dead centers.

• Journal of Ocean Engineering and Technology
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• v.29 no.6
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• pp.427-435
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• 2015

This paper provides the numerical results of a simulation of the flow around a propeller working beneath the free surface. A finite volume method is used to solve the unsteady Reynolds averaged Navier-Stokes (URANS) equations, where the wave-making problem is solved using a volume-of-fluid (VOF) method. The numerical analysis focuses on the propeller wake structure affected by the free surface, where we consider another free surface boundary condition that treats the free surface as a rigid wall surface. The propeller wake under the effect of these two free surface conditions shows a reduction in the magnitude of the longitudinal and vertical flow velocities, and its vortical structures strongly interact with the free surface. The thrust and torque coefficient under the free surface effect decrease about 3.7% and 3.1%, respectively. Finally, the present numerical results show a reasonable agreement with the available experimental data.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.1013-1018
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• 2010

This paper presents a numerical evaluation of the launch dynamics and thermo-fluid phenomena for gas generator launch eject system. The existing gas dynamic model for launching eject body used ideal gas and adiabatic assumption with empirical energy loss model. In present study, a turbulent Navier-Stokes solver with CHIMERA mesh is employed to predict the detail unsteady thermo-fluid dynamics for the launched body. The calculation results show that proper grid number is necessary for good agreement with experimental data. The important effects for accurate prediction are a gap distance and thermal boundary condition on the wall. The computational results show good agreement with experiment data.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.3
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• pp.179-186
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• 1993

The characteristics of pressure-drop oscillations(PDO) in boiling channel are studied experimentally. The effects of initial and boundary conditions on PDO are investigated in terms of oscillation period and amplitude. The period and amplitude of PDO are increased with the increase in the compressible volume in surge tank and heat input. However the amplitude of PDO is decreased with fluid temperature under low subcooling condition. Higher initial insurge flowrate resulted in almost invariant oscillation period but lower amplitude. At higher heat input the oscillation of heater wall temperature is significant, whose period is the same as that of pressure-drop instability.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.337-342
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• 2013

이번 연구에서는 de Laval nozzle를 이용하여 다양한 유체해석 모델과 프로그램을 비교하여 그 성능을 파악하였다. de Laval nozzle은 eigenvalue에 의해 eigenvector값이 '-'와 '+'값을 동시에 갖는 물리현상을 내포하고 있으며, 압력조건에 따라 내부에서 Normal shock이 발생하게 된다. 이러한 non-linearity를 현재 우리가 주로 사용하고 있는 상용프로그램(cfx, fluent)과 EDISON, 직접 코딩한 프로그램(Matlab이용)이 얼마나 잘 표현하는지 알아보았다. 그 결과 Van Leer Vector Splitting을 이용할 경우 물리현상을 제일 잘 표현 하였다. 또한 난류 유동(Turbulence flow)을 고려하게 될 경우, Mesh가 Boundary layer를 표현할 정도로 정밀하지 못하다면 제대로 된 해석 결과를 얻을 수 없었으며, Wall 근처에서 Non-slip condition에 의해 Vortex가 형성되고, 이 Vortex가 Back flow를 유도하여 해가 수렴하는데 방해를 하게 됨을 알 수 있었다. 이를 방지하기 위해서는 유동이 잘 표현될 수 있도록 적절한 Computational environment를 형성해 주는 것이 매우 중요하다.