• 한국가시화정보학회:학술대회논문집
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• 2005.12a
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.10 s.253
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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.

• 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.

• 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.

• Proceedings of the KSME Conference
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• 2004.04a
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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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.

• 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.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.34 no.3
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• pp.58-71
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• 2022

Analytical solutions for two-dimensional velocities of regular waves generated by bottom wave makers in a flume were derived in this study. Triangular and rectangular bottom wave makers were adopted. The velocity potential was derived based on the linear wave theory with the bottom moving boundary condition, kinematic and dynamic free surface boundary conditions. Then, analytical solutions of two-dimensional particle velocities were derived from the velocity potential. The velocity potential and two-dimensional particle velocities which were derived as complex integral equations were numerically calculated. The solutions showed physically valid results as velocities of regular waves generated by bottom wave makers in a flume.

• 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.

• 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.