• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.914-920
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• 2002

Nonlinear flow-induced vibration characteristics of a generic missile wing (or control surface) are investigated in this study. The wing model has freeplay structural nonlinearity at its pitch axis. Nonlinear aerodynamic flows with unsteady shock waves are considered in the transonic flow region. To practically consider the effects of freeplay structural nonlinearity, the fictitious mass method (FMM) is applied to structural vibration analysis based on a finite element method (FEM). A computational fluid dynamics (CFD) technique is used for computing the nonlinear unsteady aerodynamics of all-movable wings. The aerodynamic analysis is based on the efficient transonic small-disturbance aerodynamic equations of motion using the potential-flow theory. To solve the nonlinear aeroelastic governing equations including the freeplay effect, a modal-based computational structural dynamic (CSD) analysis technique based on fictitious mass method (FMM) is used in time-domain. In addition, CSD and unsteady CFD techniques are simultaneously coupled to give accurate computational results. Various aeroelastic computations have been performed for a generic missile wing model. Linear and nonlinear aeroelastic computations have been conducted and the characteristics of flow-induced vibration are introduced.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.634-642
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• 2011

A numerical analysis of steady/unsteady flow applying cavitation model and moving mesh method was carried out in order to analyze flow and response characteristics inside the pilot valve which controls the flight actuator system. The flow of the valve was assessed according to operation temperature and time. This research has found that valve characteristics became stable at above a specific temperature and the cavitation affected valve's performance. Internal pressure and response characteristics of the valve were analyzed and flow characteristics of steady and developed unsteady flow were confirmed to be matched each other.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.27-31
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• 2009

An experimental study on the unsteady effect of the extinction limit was performed in ethene jet diffusion flames. To impose the unsteadiness on jet flames, the amplitude and frequency of a co-flow velocity was varied, and the two inert gases, $N_2$ and $CO_2$, were used to dilute the oxidizer for extinguishing concentration. The experimental results shows that large amplitude of velocity induces a low extinguishing concentration, which implies that flow variation affects the blow out mechanism. Also, the flow oscillation effects under high frequency attenuates the flame extinction. These results means that flow unsteadiness extends the extinction limit and finally minimum extinction concentration by inert gases. When the Stoke's 2nd Problem is introduced to explain the flow unsteadiness on extinction concentration, the solution predicts the effect of amplitude and frequency of velocity well, and hence it is concluded the effect of low frequency velocity excitation was attributed only to flow effect.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.352-357
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• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcaiton) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• Journal of computational fluids engineering
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• v.15 no.3
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• pp.54-59
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• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcation) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1750-1756
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• 2001

Three-dimensional and unsteady flow analysis is a practical target of high performance computation. As recently advances of computers, a numerical prediction by the large eddy simulation (LES) are introduced and evaluated for various engineering problems. Its advanced methods for the complex turbulent flows are discussed by several examples applied for aerodynamic designs, analysis of fluid flow mechanisms and their interaction to complex phenomena. These results of time-dependent and three-dimensional phenomena are visualized by interactive graphics and animations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1512-1521
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• 1991

본 연구에서는 유속과 압력등이 시간과 위치의 함수로 표현되는 비정상 유체 가 흐를 때 그 유동 특성이 파이프계에 미치는 영향을 고찰하기 위해 비정상 유동을 포함한 파이프계의 운동방정식을 유도하고 유동 변수가 파이프계의 안정성에 미치는 영향을 연구하였다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.6 no.2
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• pp.63-73
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• 2002

The influence of unsteady boundary layer magnetohydrodynamic flow with thermal relaxation of perfectly conducting fluid, past a semi-infinite plate, is considered. The governing non linear partial differential equations are solved using the method of successive approximations. This method is used to obtain the solution for the unsteady boundary layer magnetohydrodynamic flow in the special form when the free stream velocity exponentially depends on time. The effects of Alfven velocity $\alpha$ on the velocity is discussed, and illustrated graphically for the problem.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1447-1451
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• 2004

The laminar impinging jet thermal fields were investigated with or without magnetic fields. The transient phenomenon from steady to unsteady flow was founded at specific Reynolds number ranges. In unsteady flow region, the magnetic fields make flow stable. So the characteristics of heat transfer at impingement wall are changed

• The Pure and Applied Mathematics
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• v.13 no.1 s.31
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• pp.1-10
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• 2006

The unsteady Hartmann flow of an electrically conducting, viscous, incompressible fluid bounded by two parallel non-conducting porous plates is studied with heat transfer. An external uniform magnetic field and a uniform suction and injection are applied perpendicular to the plates while the fluid motion is subjected to a constant pressure gradient. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are included in the energy equation. The effect of the magnetic field and the uniform suction and injection on both the velocity and temperature distributions is examined.