• 제목/요약/키워드: Velocity Potential

검색결과 832건 처리시간 0.028초

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

  • 한수동;이상준
    • 한국가시화정보학회:학술대회논문집
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    • 한국가시화정보학회 2005년도 추계학술대회 논문집
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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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마이크로 채널 내부 전기삼투 유동의 Zeta-potential 계측 (Measurement of Zeta-potential of Electro-osmotic Flow Inside a Micro-channel)

  • 한수동;이상준
    • 대한기계학회논문집B
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    • 제30권10호
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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.

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

  • 안승규;이동진
    • 한국항공운항학회지
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    • 제26권2호
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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.

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

  • 이상륜;최걸기;김종철;유승화
    • 한국해양공학회지
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    • 제32권1호
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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.

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

  • 강덕홍;안예찬;김종록;오병도;김무환
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 춘계학술대회
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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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슬러그 2상유동에서 전류형식 전자기유량계 수치적 신호예측 및 보정 (Numerical Signal Prediction and Calibration Using the Theory of a Current-Type Electromagnetic Flowmeter for Two-Phase Slug Flow)

  • 안예찬;오병도;김종록;김무환;강덕홍
    • 대한기계학회논문집B
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    • 제29권6호
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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.

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

  • 원종필;박성기
    • 한국농공학회지
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    • 제43권4호
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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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바닥 조파장치가 설치된 수로에서 규칙파의 유속장에 관한 해석해 개발 (Development of Analytical Solutions on Velocities of Regular Waves Generated by Bottom Wave Makers in a Flume)

  • 정재상;이창훈
    • 한국해안·해양공학회논문집
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    • 제34권3호
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    • pp.58-71
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    • 2022
  • 본 연구에서는 바닥 조파장치가 설치된 수로에서 재현된 규칙파의 2차원 유속장에 대한 해석해를 유도하였다. 바닥 조파장치로 삼각형 및 사각형 형상이 적용되었다. 선형파 이론과 움직이는 바닥에 대한 경계조건, 동역학적 및 운동학적 자유수면 경계조건을 이용하여 속도포텐셜을 유도하였으며, 이로부터 각 방향 성분의 유속에 대한 해석해를 구하였다. 적분식 형태로 유도된 속도포텐셜 및 유속에 대한 해석해를 수치해석으로 계산하였다. 유도된 해석해는 바닥 조파장치가 설치된 조파수로에서 규칙파의 유속 특성에 대해 물리적으로 타당한 결과를 보였다.

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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    • 제7권2호
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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.

전난류에서의 파마찰계수 (Wave Friction Factor far Rough Turbulent Flow)

  • 유동훈
    • 한국해안해양공학회지
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    • 제5권2호
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    • pp.51-57
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    • 1993
  • 포텐셜 이론으로 구해지는 해저면 유속은 일반적으로 난류경계층에서의 파유속과 같다고 가정한다. 해저면 가까이에서 파운동에 의한 유속분포를 해석하기 위한 최근의 이론과 수치모형에서 발견되는 실험결과와의 오차는 주로 이 가정의 문제점으로부터 연유하는 것으로 사료된다. 경계층 최상점에서의 유속에 대한 이론치와 실유속치와의 관계식을 본고에서 제의하였다. 이 관계식을 이용하여 Jonsson(1967)과 Fredsoe(1984)가 각각 개발한 기존 이론식을 수정하였으며, 수정된 이론을 이용하여 파마찰계수를 산정한 결과, 발표된 실험치들과 비교하여 상당한 향상을 얻을 수 있었다.

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