• Title, Summary, Keyword: Velocity Potential

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Zeta-potential Measurement on Glass Surface by Measuring Electro-osmotic Velocity inside a Micro-channel (마이크로 채널 내부 전기삼투 유속 측정을 통한 유리표면의 Zeta-potential 측정)

  • Han, Su-Dong;Lee, Sang-Joon
    • 한국가시화정보학회:학술대회논문집
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    • pp.80-84
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    • 2005
  • Many important properties in colloidal systems are usually determined by surface charge ($\zeta$-potential) of the contacted solid surface. In this study, $\zeta$-potential of glass $\mu$-channel was evaluated from the electro-osmotic velocity distribution. The electro-osmotic velocity inside a glass $\mu$-channel was measured using a micro-PIV velocity field measurement technique. This evaluation method is more simple and easy to approach, compared with the traditional streaming potential technique. The $\zeta$-potential in the glass $\mu$-channel was measured for two different mole NaCl solutions. The effect of an anion surfactant, sodium dodecyl sulphate (SDS), on the electro-osmotic velocity and $\zeta$-potential in the glass surface was also studied. In the range of $0\∼6$mM, the surfactant SDS was added to NaCl solution in four different mole concentrations. As a result, the addition of SDS increases $\zeta$-potential in the surface of the glass $\mu$-channel. The measured $\zeta$-potential was found to vary from-260 to-70mV. When negatively charged particles were used, the flow direction was opposite compared with that of neutral particles. The $\zeta$-potential has a positive sign for the negative particles.

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Measurement of Zeta-potential of Electro-osmotic Flow Inside a Micro-channel (마이크로 채널 내부 전기삼투 유동의 Zeta-potential 계측)

  • Han Su-Dong;Lee Sang-Joon
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.10
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    • pp.935-941
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    • 2006
  • Many important properties in colloidal systems are usually determined by surface charge $({\zeta}-potential)$ of the contacted solid surface. In this study, ${\zeta}-potential$ of glass ${\mu}-channel$ was evaluated from the electro-osmotic velocity distribution. The electro-osmotic velocity inside a glass f-channel was measured using a micro-PIV velocity field measurement technique. This evaluation method is more simple and easy to approach, compared with the traditional streaming potential technique. The ${\zeta}-potential$ in the glass ${\mu}-channel$ was measured fur two different mole NaCl solutions. The effect of an anion surfactant, sodium dodecyl sulphate (SDS), on the electro-osmotic velocity and f-potential in the glass surface was also studied. In the range of $0{\sim}6mM$, the surfactant SDS was added to NaCl solution in few different mole concentrations. As a result, the addition of SDS increases ${\zeta}-potential$ in the surface of the glass ${\mu}-channel$. The measured $\zeta-potential$ was found to vary from -260 to -70mV. When negatively charged particles were used, the flow direction was opposite compared with that of neutral particles. The ${\zeta}-potential$ has a positive sign for the negative particles.

Collision Avoidance for UAV using Potential Field based on Relative Velocity of Obstacles (장애물의 상대속도를 반영한 포텐셜필드 기반 무인항공기 충돌회피)

  • Ahn, Seung-gyu;Lee, Dongjin
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.26 no.2
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    • pp.47-53
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    • 2018
  • In this paper, we investigate a collision avoidance algorithm for unmanned aerial vehicles using potential field based on the relative velocity of obstacles. The potential field consists of the attraction force and the repulsive force that are generated for the target and the obstacles. And the field can be classified into the attractive potential field generated by the target and the repulsive potential field generated by the obstacle, respectively. In this study, we construct an attractive potential field as a function of the distance between the UAV and the target position. On the other hand, a repulsive potential field is created by a function of distance and the relative velocity of the obstacle with respect to the UAV. The proposed potential field based collision avoidance algorithm is evaluate through simulations.

Analysis of Velocity Potential around Pulsating Bubble near Free or Rigid Surfaces Based on Image Method (이미지 방법을 이용한 자유 및 강체 표면 옆의 맥동하는 버블 주위 속도 포텐셜 해석)

  • Lee, Sangryun;Choi, Gulgi;Kim, Jongchul;Ryu, Seunghwa
    • Journal of Ocean Engineering and Technology
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    • v.32 no.1
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    • pp.28-35
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    • 2018
  • An analytical method for predicting the velocity potential around a pulsating bubble close to a free or rigid wall was established using an image method. Because the velocity potential should satisfy two boundary conditions at the bubble surface and rigid wall, we investigated the velocity in the normal direction at the two boundaries by adding the image bubbles. The potential was analyzed by decomposing the bubble motion as two independent motions, pulsation and translation, and we found that when the number of image bubbles was greater than ten, the two boundary conditions were satisfied for the translation term. By adding many image bubbles after the approximation of the pulsation term, we also confirmed that the boundary condition at the wall was satisfied.

Evaluation of liquefaction potential of soil using the shear wave velocity in Tehran, Iran

  • Rahmanian, Sahar;Rezaie, Fereydoun
    • Geosciences Journal
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    • v.21 no.1
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    • pp.81-92
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    • 2017
  • Shear-wave velocity ($V_S$) offers a means to determine the seismic resistance of soil to liquefaction by a fundamental soil property. Iwasaki's (1982) method is used to measure the liquefaction potential index for both of them. It follows the general format of the Seed-Idriss (1685) simplified procedure based on standard penetration test blow count and shear wave velocity ($V_S$) on the basis of Andrus et al. (2004) using case history data from 43 boreholes in soils ranging from fine sand, silty sand, gravely sand to profiles including silty clay layers and the average soil shear wave velocity ($V_S{^{30}}$) in the south Tehran. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain. The study area is the south-east of Tehran and the route of Tehran Metro Line 7. It is observed that there is not a perfect agreement between the results of the two methods based on five empirical relationships assuming cemented and non-cemented condition for soils. Moreover, the liquefaction potential index (PL) value in the Standard Penetration Test (SPT) method is more than that of the $V_S$ method. Liquefaction potential index (PL) values based on shear wave velocity ($V_S$) using five empirical relationships in two un-cemented and cemented soil show that the used relations are overestimated and most of them have shown non-liquefaction condition for soils in the studied area.

Development of a Current-Type Electromagnetic Flowmeter to Obtain the Liquid Mean Velocity in Two-Phase Slug Flow (슬러그류 액상속도 측정용 전류형식 전자기유량계 개발)

  • Kang, Deok-Hong;Ahn, Yeh-Chan;Kim, Jong-Rok;Oh, Byung-Do;Kim, Moo-Hwan
    • Proceedings of the KSME Conference
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    • pp.1951-1956
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    • 2004
  • The transient nature and complex flow geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et $al.^{(1)}$). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. To do this, the velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for the simulated slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are required for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

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Numerical Signal Prediction and Calibration Using the Theory of a Current-Type Electromagnetic Flowmeter for Two-Phase Slug Flow (슬러그 2상유동에서 전류형식 전자기유량계 수치적 신호예측 및 보정)

  • Ahn Yeh-Chan;Oh Byung Do;Kim Jong-Rok;Kim Moo Hwan;Kang Deok-Hong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.29 no.6
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    • pp.671-686
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    • 2005
  • The transient nature and complex geometries of two-phase gas-liquid flows cause fundamental difficulties when measuring flow velocity using an electromagnetic flowmeter. Recently, a current-sensing flowmeter was introduced to obtain measurements with high temporal resolution (Ahn et al.). In this study, current-sensing flowmeter theory was applied to measure the fast velocity transients in slug flows. The velocity fields of axisymmetric gas-liquid slug flow in a vertical pipe were obtained using Volume-of-Fluid (VOF) method, and the virtual potential distributions for the electrodes of finite size were also computed using the finite volume method for simulating slug flow. The output signal prediction for slug flow was carried out from the velocity and virtual potential (or weight function) fields. The flowmeter was numerically calibrated to obtain the cross-sectional liquid mean velocity at an electrode plane from the predicted output signal. Two calibration parameters are proposed for this procedure: a flow pattern coefficient and a localization parameter. The flow pattern coefficient was defined by the ratio of the liquid resistance between the electrodes for two-phase flow with respect to that for single-phase flow, and the localization parameter was introduced to avoid errors in the flowmeter readings caused by liquid acceleration or deceleration around the electrodes. These parameters were also calculated from the computed velocity and virtual potential fields. The results can be used to obtain the liquid mean velocity from the slug flow signal measured by a current-sensing flowmeter.

Reliability Improvement of In-Place Concreter Strength Prediction by Ultrasonic Pulse Velocity Method (초음파 속도법에 의한 현장 콘크리트 강도추정의 신뢰성 향상)

  • 원종필;박성기
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.43 no.4
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    • pp.97-105
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    • 2001
  • The ultrasonic pulse velocity test has a strong potential to be developed into a very useful and relatively inexpensive in-place test for assuring the quality of concrete placed in structure. The main problem in realizing this potential is that the relationship between compressive strength ad ultrasonic pulse velocity is uncertain and concrete is an inherently variable material. The objective of this study is to improve the reliability of in-place concrete strength predictions by ultrasonic pulse velocity method. Experimental cement content, s/a rate, and curing condition of concrete. Accuracy of the prediction expressed in empirical formula are examined by multiple regression analysis and linear regression analysis and practical equation for estimation the concrete strength are proposed. Multiple regression model uses water-cement ratio cement content s/a rate, and pulse velocity as dependent variables and the compressive strength as an independent variable. Also linear regression model is used to only pulse velocity as dependent variables. Comparing the results of the analysis the proposed equation expressed highest reliability than other previous proposed equations.

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Design and Simulation of Very Low Head Axial Hydraulic Turbine with Variation of Swirl Velocity Criterion

  • Muis, Abdul;Sutikno, Priyono
    • International Journal of Fluid Machinery and Systems
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    • v.7 no.2
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    • pp.68-79
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    • 2014
  • The type of turbine developed is based on the very low head of water potential source for the electric power production. The area of research is focused for the axial water turbine that can be applied at the simple site open channel with has a very low cost and environmental impact compared to the conventional hydro installation. High efficiency of axial turbine which applied to the very low potential head will made this type of turbine can be used at wider potential site. Existing irrigation weir and river area will be the perfect site for this turbine. This paper will compare the effects of the variation of swirl velocity criterion during the design of the blade of guide vane and rotor of the turbine. Effects of the swirl velocity criterion is wider known as a vortex conditions (free vortex, force vortex and swirl velocity constant), and the free vortex is the very popular condition that applied by most of turbine designer, therefore will be interesting to do a comparison against other criterion. ANSYS Fluent will be used for simulation and to determine the predictive performance obtained by each of design criteria.

Wave Friction Factor far Rough Turbulent Flow (전난류에서의 파마찰계수)

  • 유동훈
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.5 no.2
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    • pp.51-57
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    • 1993
  • It is often assumed that the wave velocity at the bottom given by potential wave theory il the same as the wave velocity at the top of the turbulent boundary layer. This assumption is found to be the major cause of the error detected by recent elaborate theories and numerical models for the description of velocity profile near the sea bottom. A relationship is suggested between the potential velocity and the real boundary velocity. Based on this relation, the existing theories of Jonsson (1967) and Fredsoe (1984) are refined for the estimation of wave friction factor, and the computation results of the modified theories are favourably compared with the published laboratory results.

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