• Title/Summary/Keyword: velocity fields

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Effect of the Pulsatile Flow on the Morphological Changes of the Endothelial Cells in Blood Vessel (맥동유동이 혈관내 내피세포의 형태변화에 미치는 영향)

  • Suh, Sang-Ho;Yoo, Sang-Sin;Cho, Min-Tae;Park, Chan-Young;Chang, Jun-Keun
    • 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.

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Control of Flow around an Airfoil Using Piezo-ceramic Actuators (압전세라믹 액추에이터를 이용한 익형 후류 제어)

  • Choi, Jin;Jeon, Woo-Pyung;Choi, Hae-Cheon
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.491-496
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    • 2000
  • The objective of this study is to increase lift and decrease drag of an airfoil by delaying flow separation with piezo-ceramic actuators. The airfoil used is NACA 0012 and the chord length is 30cm. An experiment is performed at the freestream velocity of 15m/s at which the Reynolds number is $3{\times}10^5$. Seven rectangular actuators are attached to the airfoil surface and move up and down based on the electric signal. At the attack angle of $16^{\circ}$, the separation point is delayed downstream due to momentum addition induced by the movement of the actuators. Drag and lift are measured using an in-house 2-dimensional load cell and the surface pressures are also measured. Lift is increased by 10%, drag is reduced by 50%, and the efficiency is increased to 170%. The flow fields with and without control are visualized using the smoke-wire and tuft techniques.

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Buoyant Convection in a Cylinder with Azimuthally-varying Sidewall Temperature (방위각방향 온도변화를 가지는 실린더 내의 부력 유동)

  • Chung, K.H.;Hyun, J.M.;Song, T.H.
    • Proceedings of the KSME Conference
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    • 2000.04b
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    • pp.45-50
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    • 2000
  • A numerical investigation is made of three-dimensional buoyant convection of a Boussinesq-fluid in a vertical cylinder. The top and bottom endwalls are thermally insulated. Flow is driven by the substantial azimuthal variations in thermal boundary conditions. Comprehensive numerical solutions to the Navier-Stokes equations are obtained. The representative Rayleigh number is large, thus, the overall flow pattern is of boundary layer-type. Three-dimensional (low characteristics are described. Specially, the global flow and the heat transfer features are delineated when the severity of azimuthal variation of sidewall temperature n, is intensified. Temperature and velocity fields on the meridional planes and the planes of constant height are presented. The global flow weakens as n becomes large. The pattern of the local Nusselt number on the surface of cylinder is similar regardless of n. The convective gain in heat transfer activities is reduced as n increases.

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Application of Holographic Interferometry and 2-D PIV for HSC Convective Flow Diagnostics (Hele-Shaw Cell 내부의 열유동 해석을 위한 홀로그래픽 간섭계와 2차원 PIV의 적용)

  • Kim, Seok;Lee, Sang-Joon
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.682-687
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    • 2003
  • The variations of temperature and velocity fields in a Hele-Shaw convection cell (HSC) were investigated using a holographic interferometry and 2-D PIV system with varying Rayleigh number. To measure quasisteady changes of temperature field, two different measurement methods of holographic interferometry; double-exposure method and real-time method, were employed. In the double-exposure method, unwanted waves can be eliminated effectively using digital image processing technique and the reconstruction images are clear, but transient flow structure cannot be reconstructed clearly. On the other hand, transient convective flow can be reconstructed well using the real-time method. However, the fringe patterns reconstructed by the real-time method contain more noises, compared with the double-exposure method. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow structure at high Rayleigh numbers. The periodic flow pattern at high Rayleigh numbers obtained by the real-time holographic interferometer method is in a good agreement with the PIV results.

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Large Eddy Simulation of Flow and Heat Transfer in a Rotating Ribbed Channel (요철이 설치된 회전하는 채널 내부의 유동 및 열전달의 큰에디모사)

  • Ahn, Joon;Choi, Hae-Cheon;Lee, Joon-Sik
    • Proceedings of the KSME Conference
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    • 2003.11a
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    • pp.193-198
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    • 2003
  • A gas turbine blade has an internal cooling passage equipped with ribs, which can be modeled as a ribbed channel. We have studied a flow inside a ribbed channel using large eddy simulaton (LES) with a dynamic subgrid-scale model. The simulation results are compared with the experimental ones. The turbulence intensity and local heat transfer near the rib have not been well captured by the conventional Reynolds averaged Navier-Stokes simulation (RANS). However, these variables obtained by the present LES agree well with those from experiments. From the instantaneous velocity and temperature fields, we explain the mechanisms responsible for the local peaks in the heat transfer distribution along the channel wall. We have also investigated the effect of rotation on the flow and heat transfer in the ribbed channel.

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Effects of Asymmetric Tip Clearance on Centrifugal Compressor Flow (비대칭 팁간극이 원심압축기의 유동에 미치는 영향)

  • Yoon, Yong-Sang;Song, Seung-Jin
    • 유체기계공업학회:학술대회논문집
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    • 2005.12a
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    • pp.533-541
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    • 2005
  • Compared to axial compressors, an analytical model capable of analyzing the flow in centrifugal compressor lacks because of the difficulty in governing equations for radial duct. Therefore, this paper presents a new model to predict flow field in a centrifugal compressor with a sinusoidal asymmetric tip clearance. To predict the 2 dimensional flow in the inlet and exit of the centrifugal compressor, the two flow fields are connected with compressor characteristic based on Moore-Greitzer model. Contrary to axial compressors, the nonuniformity of impeller exit pressure in centrifugal compressor decreases as flow coefficient decreases. In addition, that is sensitive to the slope of pressure rise by eccentricity. The maximum velocity exists right before the maximum tip clearance.

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Numerical Analysis of Shallow Water Equation with Fully Implicit Method (음해법을 이용한 천수방정식의 수치해석)

  • Kang, Ju Whan;Park, Sang Hyun;Lee, Kil Seong
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.13 no.3
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    • pp.119-127
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    • 1993
  • Recently, ADI scheme has been a most common tool for solving shallow water equation numerically. But ADI models of tidal flow is likely to cause so called ADI effect in such a region of the Yellow Sea which shows complex topography and has submarine canyons especially. To overcome this, a finite difference algorithm is developed which adopts fully implicit method and preconditioned conjugate gradient squared method. Applying the algorithm including simulation of intertidal zone to Sae-Man-Keum. velocity fields and flooding/drying phenomena are simulated well in spite of complex topography.

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Development of Hybrid Micro/Nano PIV system (하이브리드 마이크로/나노 PIV 시스템 개발)

  • Min, Young-Uk;Lee, Dong-Yeop;Kim, Kyung-Chun
    • Journal of the Korean Society of Visualization
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    • v.8 no.4
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    • pp.31-37
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    • 2010
  • In this study, a novel hybrid micro/nano PIV system combining defocusing and TIRFM technique has been developed for the multiscale flow measurement. With the developed system, both far and near field velocity fields have been measured simultaneously in a 2D straight microchannel and the particle trajectories were extracted by the nearest tracking algorithm. The shear rate values taken from experimental results have been estimated by comparing with the analytical solution of 2D Poiseuille flow and it is confirmed that the result shows good agreement with the theoretical value.

Trajectory Planning of Articulated Robots with Minimum-Time Criterion (최소시간을 고려한 다관절 로봇의 궤적계획)

  • Choi, J.S.;Yang, S.M.;Kang, H.Y.
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.6
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    • pp.122-127
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    • 1996
  • The achievement of the optimal condition for the task of an industrial articulated robot used in many fields is an important problem to improve productivity. In this paper, a minimum-time trajectory for an articulated robot along the specified path is studied and simulated with a proper example. A general dynamic model of manipulator is represented as a function of path distance. Using this model, the velocity is produced as fast as possible at each point along the path. This minimum-time trajectory planning module together with the existing collision-free path planning modules is utilized to design the optimal path planning of robot in cases where obstacles present.

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An Experimental Study Using Plasticine for the Hot Extrusion Processes of Regular Square Sections throuth Square Dies (플라스티신을 이용한 정사각형재의 열간 평금형 압출공정에 관한 실험적 연구)

  • 변삼수;한철호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1995.04b
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    • pp.187-191
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    • 1995
  • An experimental study to analyze thd hot extrusion processes of regular square section through square dies is carried out by using plasticine as a model material at room temperature. The experimental setup for the extrusion of squared section from round billets through square dies is designed and manufactured. In order to visullize the plastic flow in the extrusion process the technique of gridding on the planes of the sysmmetries and a stacking the desks with different colors are employed. Velocity fields on the symmetry planes are obtained by using grid distortion.

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