• Journal of Advanced Marine Engineering and Technology
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• v.28 no.8
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• pp.1258-1269
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• 2004

The fluid dynamic characteristics of a circular arc type sea anchor were calculated by a discrete vortex method. The flow for the surface of the sea anchor was represented by arranging bound vortices at adequate intervals. The simulations were performed by assuming that the separations occur at edges. With time, the drag coefficient was almost constant but the lift coefficient oscillated in a cycle due to von Karman's vortex street. As the camber ratios increase, the drag coefficient and Strouhal number were almost constant but the oscillating amplitude of the lift coefficient increased largely.

• Journal of applied mathematics & informatics
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• v.18 no.1_2
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• pp.393-403
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• 2005

We study the isothermal flow of a dusty viscous incompressible conducting fluid between two types of boundary motions- oscillatory and non-oscillatory, under the influence of gravitational force. Within the frame work of some physically realistic approximations and suitable boundary conditions, closed form solutions were obtained for the velocity profiles and the skin friction of the particulate flow. These results show that for a constant pressure gradient, only the velocity profile of the fluid and the skin friction are unaffected by gravity, while magnetic field is seen to affect both the fluid, particle velocities and the skin friction. Thus, our results are extension of previous results in literature, and graphical demonstration of some these solutions have been presented.

• Proceedings of the KIEE Conference
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• 2002.11d
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• pp.43-45
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• 2002

가스차단기의 성능은 노즐재질, 접점분리 속도 차단기의 치수 그리고 마크시간 등에 좌우되며 이러한 일련의 현상을 고찰하기 위한 유동현상을 모의하기 위해서는 기본적으로 두 접점의 상대운동 및 접점 사이에서 발생하는 아크 플라즈마(arc plasma)에 의한 전도, 대류, 복사현상 뿐만 아니라 아크전류에 의한 로랜츠힘(Lorentz's force), 용삭(ablation)에 의한 화학작용 등과 같은 매우 복잡한 물리적 현상을 고려해야 한다. 본 연구에서는 차단과정 중 대전류 영역에서의 아크특성과 마크에서 방출되는 강한 복사에너지에 의해 발생하는 PTFE 증기에 의한 영향을 고려하기 위해서 상용 CFD 프로그램인 PHOENICS에 아크 모델링과 고온에서의 $SF_6$-PTFE 혼합가스의 물성치 대입을 위한 보조 프로그램을 작성하여 해석을 수행하였다.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.15-23
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• 2004

The present study is aimed to achieve dynamic visualization from the in-house 3-D stereoscopic PIV to represent quantitative flow information such as time-resolved 3-D velocity distribution, vorticity, turbulent intensity or Reynolds stresses and so on. One of the application of the present study is Leading edge extension(LEX) flow appearing on modern delta wing aircraft. The other is mixing flow in stirring tank used in industry field. LEX in a highly swept shape applied to a delta wing features the modern air-fighters. The LEX vortices generated upon the upper surface of the wing at high angle of attack enhance the lift force of the delta wing by way of increased negative suction pressure over the surfaces. The present method resolves also the complicated flow patterns of two type impellers rotating in stirring vessel. Flow quantities such as three velocity vector components, vorticity and other flow information can be easily visualized via the 3D time-resolved post-processing visualization. And it makes the easy understanding of the unsteady flow characteristics of the typical industrial mixers.

• Wind and Structures
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• v.20 no.1
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• pp.95-115
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• 2015

Wind effects on roofs are usually considered by equivalent static wind loads based on the equivalence of displacement or internal force for structural design. However, for large-span spatial structures that are prone to dynamic instability under strong winds, such equivalent static wind loads may be inapplicable. The dynamic stability of spatial structures under unsteady wind forces is therefore studied in this paper. A new concept and its corresponding method for dynamic instability-aimed equivalent static wind loads are proposed for structural engineers. The method is applied in the dynamic stability design of an actual double-layer cylindrical reticulated shell under wind actions. An experimental-numerical method is adopted to study the dynamic stability of the shell and the dynamic instability originating from critical wind velocity. The dynamic instability-aimed equivalent static wind loads of the shell are obtained.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.339-346
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• 2001

The impulsive spin-up flow in a shallow rectangular container is analyzed numerically by quasi 3-D unsteady laminar flow. In the non-inertia coordinates, the flow is generated by the virtual forces as Coriolis force, etc.. After the boundary layers grow up near sidewalls, primary vortexes separate from the sidewalls. As the Reynolds number increases, the subsidiary vortexes take place in the boundary layer. The rigid body rotation is started from the inner region and propagated to the outer region, finally all the fluid reaches the rigid body rotation. According to the Reynolds number and the aspect ratio, the development of vortex pattern is symmetric or asymmetric.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1825-1829
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• 2004

A numerical simulation was performed of flow behind a squareback car with a rear spoiler. Influence of the rear spoiler on drag force has been studied. A lattice Boltzmann method was utilized to portray the unsteady aerodynamics of wake flows. The pressure distributions were employed to examine the vortex formation mode against the rear spoiler. It was found that the separation flow at roof end and c-pillar makes three dimensional vortex structures and the rear spoiler increases pressure on the rear glass surface.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.127-134
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• 2017

Vortex Induced Vibration (VIV) is a typical flow-structure interference phenomenon which causes an unsteady flow pattern due to vortex shedding at or near the structure's natural frequency leading to resonant vibrations. VIV may cause premature fatigue failure of marine risers and pipelines. A test model was carried out to investigate the role of a stationary fairing by varying the caudal horn angle to suppress riser VIV taking into account the effect of wake interference. The test results show significant reduction of VIV for risers disposed in tandem and side-by-side. In general, fairing with a caudal horn of $45^{\circ}$ and $60^{\circ}$ are efficient in quelling VIV in risers. The results also reveal fairing can reduce the drag load of risers arranged side-by-side. For the tandem configuration, a fairing can reduce the drag load of an upstream riser, but will enlarge the drag force of the downstream riser.

• 유체기계공업학회:학술대회논문집
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• 2003.12a
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• pp.231-237
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• 2003

A numerical study has been conducted to investigate the effect of an inlet flow pulsation on mixing of two solutions with different concentrations in a micro conduit. We treat an unsteady, incompressible and two-dimensional flow through a micro conduit by adopting the momentum equations with the electrostatic force due to streaming current and the concentration equation. The feasibility of the inlet flow pulsation to enhance the mixing process inside the micro conduit is carefully examined by varying the inlet pulsation frequency. When a low-frequency pulsation is induced at the inlet, the interface between two solutions with different concentrations becomes wavy, which results in mixing enhancement. As the pulsation frequency increases, the waviness of the interface becomes meager, and the concentration gradients at the interface approach the value for the non-pulsating steady flow.

• International Journal of Fluid Machinery and Systems
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• v.9 no.4
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• pp.382-393
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• 2016

Flow over a bluff body is an attractive research field in thermal engineering. In the present study, laminar flow over a confined heated square cylinder using CuO-Water nanofluid is considered. Unsteady two-dimensional Navier-Stokes and energy equations are solved numerically using finite volume method (FVM). Recent correlations for the thermal conductivity and viscosity of nanofluids, which are function of nanoparticle volume fraction, temperature and nanoparticle diameter, have been employed. The results of numerical solution are obtained for Richardson number, nanoparticle volume fractions and nanoparticle diameters ranges of 0-1, 1-5% and 30-100 nm respectively for a fixed Reynolds number of Re = 150. At a given volume concentration, the investigations reveal that the decreasing in size of nanoparticles produces an increase in heat transfer rates from the square cylinder and a decrease in amplitude of the lift coefficient. Also, the increment of Nusselt number is more pronounced at higher concentrations and higher Richardson numbers.