• Title/Summary/Keyword: velocity gradient

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The Influence of K-ratio and Seepage Velocity on Piping Occurrence (Piping현상 발생에 미치는 투수계수비와 침투유속의 영향에 대한 연구)

  • Huh, Kyung-Han;Chang, Ock-Sung
    • Journal of the Korean Society of Hazard Mitigation
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    • v.8 no.2
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    • pp.129-138
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    • 2008
  • In case of judging the stability of dike or dam structures which need hydraulic interception, the first thing to do is to examine whether a piping phenomenon occurred or not. Generally, dike or dam structures are constructed while layer compacting is executed, so permeability is likely to be anisotropic- different from each other in hydraulic conductivity in the horizontal direction [$k_x$] and hydraulic conductivity in the vertical direction[$k_y$]. This study looked into exit hydraulic gradient and Seepage velocity by conducting an Seepage analysis subsequent to various hydraulic conductivity ratios[k-ratio = ky / kx] and examined the influence on piping by comparing & examining critical Seepage Velocity based on critical hydraulic gradient in theoretical equation and critical Seepage Velocity in empirical equation. As the research result, it was found that hydraulic conductivity ratio operates as a very important factor in case the stability against piping occurrence is considered with the concept of critical hydraulic gradient, but relatively the hydraulic conductivity ratio is very low in its importance in relation to the concept of critical Seepage Velocity.

An Experimental Analysis for the Stability Investigation of Slope on Saemangeum Lake Dykes (새만금 방수제 축조사면의 안정성 검토를 위한 실험적 분석)

  • Jang, Dong-Gi;Kim, Ki-Nyun;Kim, Dong-Hwan;Seo, Kwan-Seok;Son, Moon-Joon
    • Proceedings of the Korean Geotechical Society Conference
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    • 2010.09a
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    • pp.687-697
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    • 2010
  • This study was designed to carry out studies on critical seepage velocity and critical hydraulic gradient using a piping test targeting SM and ML which are widely distributed ahead of and behind the depth of E.L(-)10m in Saemangeum area in order to examine stability of embankment built on the ground vulnerable to piping. The effects of relative densities on critical hydraulic gradient and critical velocity were also compared and analyzed using empirical formula and theoretical formula, and relative densities were set up as respectively 9%, 25%, 50%, and 75% for this experiment. As a result, for critical hydraulic gradient, most of specimens detected piping at lower values than the empirical formula of Terzaghi(1922). It is, therefore, considered that the empirical formula devised by Kalin(1977) or Hayashi(1978) is more reasonable to be conservative. It was also found that critical velocity decreased as relative density increased, and critical velocity predicted was mostly lower than the theoretical formula.

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A Study of Micro Induction-type EHD Pump with Temperature Gradient (온도차를 이용한 유도형 마이크로 EHD 펌프에 관한 연구)

  • Youn, Yong-Kyu;Kim, Yung-Kwon
    • Proceedings of the KIEE Conference
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    • 1993.07b
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    • pp.1069-1071
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    • 1993
  • This paper presents the characteristics of micro induction EHD(Electro Hydro Dynamic) pump in which the fluid has a temperature gradient to the transverse direction of a traveling wave. The effects of the channel depth, the wave length and wave form of the treveling wave has been investigated in micro pump. The effect of temperature gradient also has been investigated. The fluid velocity becomes large as the wave length becomes small and the temperature gradient becomes high. The channel depth has little influence on the fluid velocity. The EHD pump driven by the square wave has the larger fluid velocity than that driven by the sinusoidal wave.

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Wave propagation and vibration of FG pipes conveying hot fluid

  • Zhang, Yi-Wen;She, Gui-Lin
    • Steel and Composite Structures
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    • v.42 no.3
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    • pp.397-405
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    • 2022
  • The existing researches on the dynamics of the fluid-conveying pipes only focus on stability and vibration problems, and there is no literature report on the wave propagation of the fluid-conveying pipes. Therefore, the purpose of this paper is to explore the propagation characteristics of longitudinal and flexural waves in the fluid-conveying pipes. First, it is assumed that the material properties of the fluid-conveying pipes vary based on a power function of the thickness. In addition, it is assumed that the material properties of both the fluid and the pipes are closely depended on temperature. Using the Euler-Bernoulli beam equation and based on the linear theory, the motion equations considering the thermal-mechanical-fluid coupling is derived. Then, the exact expressions of phase velocity and group velocity of longitudinal waves and bending waves in the fluid-conveying pipes are obtained by using the eigenvalue method. In addition, we also studied the free vibration frequency characteristics of the fluid-conveying pipes. In the numerical analysis, we successively studied the influence of temperature, functional gradient index and liquid velocity on the wave propagation and vibration problems. It is found that the temperature and functional gradient exponent decrease the phase and group velocities, on the contrary, the liquid flow velocity increases the phase and group velocities. However, for vibration problems, temperature, functional gradient exponent parameter, and fluid velocity all reduce the natural frequency.

Reduction of Skin Friction Force for Turbulent Boundary Layer (난류 경계층의 표면 마찰력 감소화)

  • Kim, Si-Young
    • Journal of Fisheries and Marine Sciences Education
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    • v.5 no.2
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    • pp.128-137
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    • 1993
  • This paper presents a new concept to reduce turbulent frictional drag by injecting micro-bubble into buffer layer of turbulent boundary layer on flat plate. The buffer layer of boundary was specified by minus velocity gradient of law of the wall. When the buffer layer region of turbulent boundary layer is filled with micro-bubble of air and viscous of the region is kept low, the velocity profile in the region should be changed substantially. Then the Reynolds stress in the buffer layer region becomes less, which guide to higher velocity gradient there. It results in reduction of velocity gradient at the viscous sublayer, which gives the reduction of shear stress at the wall.

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An Experimental Study on the Effect of Fuel Dilution on the Propagation Velocity of Triple Flames in a Diverging Channel (연료희석이단면확대채널에형성된삼지화염의전파속도에미치는영향에관한실험적연구)

  • Seo, Jeong-Il;Shin, Hyun-Dong;Kim, Nam-Il
    • 한국연소학회:학술대회논문집
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    • 2007.05a
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    • pp.13-18
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    • 2007
  • When triple flames propagated in a diverging channel, the effects of fuel dilution on the lift-off characteristics of triple flames were investigated. A multi-slot burner was used to stabilize the lift-off flame especially at weak fuel concentration gradients. It was reported that there is a maximum propagation velocity at a critical concentration gradient in an open jet regardless of fuel dilution. The enhancement of a diffusion flame affected to increase the propagation velocity around critical concentration gradients. However, the influence of a confined channel on the structure of triple flames according to fuel dilution needs to be investigated compared with an open jet case. This study aimed to examine the effect of a confined channel on the structure and the propagation velocity of the triple flames according to fuel dilution. Lift-off height and propagation velocity of triple flames were investigated by employing three kinds of fuel compositions diluted by nitrogen (0%, 25%, 50% $N_2$), Fuel dilution reduced the propagation velocity of triple flame in a confined channel mainly due to the decrease of flame temperature in premixed branch. Despite the difference in fuel dilution, the propagation velocity has a maximum value at a specific fuel concentration gradient even though the critical concentration gradient increases with fuel dilution. And the critical concentration gradient in a confined channel is larger than that in an open jet due to enhancement of convective diffusion.

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An Effects of $CO_2$ Addition on Flame Structure in a Non-premixed Counterflow Flame (비예혼합 대향류 화염에서 $CO_2$ 첨가가 화염 구조에 미치는 영향 연구)

  • Lee, Kee-Man
    • Transactions of the Korean Society of Automotive Engineers
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    • v.15 no.3
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    • pp.166-173
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    • 2007
  • A numerical study was conducted to have the effect of $CO_2$ addition to fuel on the chemical reaction mechanism with the change of the initial concentration of $CO_2$ and the axial velocity gradient. From this study, it was found that there were two serious effects of $CO_2$ addition on a non-premixed flame ; a diluent effect by the reactive species reduction and chemical effect of the breakdown of $CO_2$ by the third-body collision and thermal dissociation. Especially, the chemical effect was serious at the lower velocity gradient of the axial flow. It was certain that the mole fraction profile of $CO_2$ was deflected and CO was increased with the initial concentration of $CO_2$. It was also ascertained that the breakdown of $CO_2$ would cause the increasing of CO mole fraction at the reaction region. It was also found that the addition of $CO_2$ did not alter the basic skeleton of $H_2-O_2$ reaction mechanism, but contributed to the formation and destruction of hydrocarbon products such as HCO. The conversion of CO was also suppressed and $CO_2$ played a role of a dilution in the reaction zone at the higher axial velocity gradient.

An Efficient Method to Obtain Wind Speed Gradient with Low PRF Radar

  • 이종길
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.8 no.1
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    • pp.28-33
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    • 2004
  • The measurement of wind speed gradient is very important for the detection of hazardous wind shear conditions since they are characterized by the abrupt shift of wind velocity and direction. These weather conditions usually imply high wind speed which requires a high PRF radar for the measurement. However, the measurement of a large absolute wind velocity is not necessary to obtain wind speed gradient. In this paper, a method was proposed to obtain wind speed gradient with a simple low PRF radar which may be very useful for the purpose of practical applications.

A New Control Volume Finite Element Method for Three Dimensional Analysis of Polymer Flow (고분자 유동의 3차원 해석을 위한 새로운 검사 체적 유한 요소법)

  • 이석원;윤재륜
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.05a
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    • pp.461-464
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    • 2003
  • A new control volume finite element method is proposed for three dimensional analysis of polymer flow. Tetrahedral finite element is employed and co-located interpolation procedure for pressure and velocity is implemented. Inclusion of pressure gradient term in the velocity shape functions prevents the checkerboard pressure field from being developed. Vectorial nature of pressure gradient is considered in the velocity shape function so that velocity profile in the limit of very small Reynolds number becomes physically meaningful. The proposed method was verified through three dimensional simulation of pipe flow problem for Newtonian and power-law fluid. Calculated pressure and velocity field showed an excellent agreement with analytic solutions for pressure and velocity. Driven-cavity problem, which is reported to yield checkerboard pressure filed when conventional finite element method is applied, could be solved without yielding checkerboard pressure field when the proposed control volume finite element method was applied. The proposed method could be successfully applied to the three dimensional mold filling problem.

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An Experimental Study of Vortex Formation of a Circular Cylinder with Serrated Fins (Serrated Fin Tube 후류에 대한 유동가시화 적용 및 근접후류 특성에 관한 연구)

  • Boo Jung-Sook;Kim Kyung-Chun;Ryu Byong-Nam
    • 한국가시화정보학회:학술대회논문집
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    • 2002.11a
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    • pp.27-30
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    • 2002
  • An experimental study is performed to investigate the characteristics of near wake behind a circular cylinder with serrated fins using the constant temperature anemometer and through flow visualization. Previous report(Boo at al., 2001) shows that there are three different modes in vortex shedding behavior. This paper is focused on the identification of the physical reasons why the difference is occured in vortex shedding. The through flow velocity crossing fins decreases as increasing fin height and decreasing fin pitch mainly due to the flow resistence. Vortex shedding is affected strongly by velocity distribution around fin tube, especially by the velocity gradient. The velocity distribution at X/d=0.0 has lower gradient with increasing freestream velocity and fin height and decreasing fin pitch. Those differences in velocity gradients generate different vortex shedding mechanism.

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