• 한국가시화정보학회:학술대회논문집
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• 2004.11a
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• pp.76-79
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• 2004

Dynamic oscillation motion of a pendant drop has been Investigated experimentally when acoustic wave is applied. This problem is of particular interest in the understanding of transport phenomena, accompanied by liquid drop. In this experiment, pendant drop was made to oscillate by inducing the acoustic wave and the subsequent drop motion was recorded by a high-speed camera. The results obtained indicate that liquid drop hanging on the flat surface has resonant frequencies on each shape oscillation modes. It is also found that exists the swing mode of oscillation on the pendant drop.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.4
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• pp.295-303
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• 2001

Condensation of vapor on solid inherently accompanies generation of liquid drops on the solid surface. However, these drops prevent the solid surface from directly contacting the saturated vapor, thus causing thermal resistance. This work investigates a novel mechanism for enhancing the condensation process, in which the condensed drops are rapidly removed from a solid surface by imposing vibration on them. In the experiments, a water drop pendant from a solid surface is vibrated at a fixed frequency while increasing the vibration amplitude. Upon repeating the experiments using various frequencies, it is revealed that there exist resonant frequencies at which the minimum vibration amplitudes inducing a fall-off of the pendant drops are remarkably less than those at neighboring frequencies. These frequencies are supposed to correspond to the resonant frequencies for different modes of drop shape oscillations. They are compared with the resonant frequencies predicted by relatively simple analyses, and the factors causing discrepancy between then are discussed.

• Journal of the Korean Ceramic Society
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• v.33 no.12
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• pp.1325-1330
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• 1996

A new numerical method for determining the surface tension of a liquid drop by experimental measurement of the contour of the sessile drop is explained. in the present method a very simple and short computer program enables the calculation of surface tension in a few seconds even by a low speed personal computer. It need not the use of any other numerical tables or complex techniques. X and Z-corrdinates at one point on the contour of a sessile drop and the tangential angle at that point are all the data needed when the density of the drop is known. The results were compared with the values derived by a conventional method. This method can be used for the confirmation of measuring accuracy. Also the same concepts can be applied for the pendant drop method by changing only the sign of Z-coordinate from "+" to "-"ot; to "-"ot;-"quot.

• Korea-Australia Rheology Journal
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• v.18 no.2
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• pp.41-49
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• 2006

A modified Volume-of-Fluid (VOF) numerical method is used to predict the dynamics of a liquid drop of a low viscosity dilute polymer solution, forming in air from a circular nozzle. Viscoelastic effects are rep-resented using an Oldroyd-B model. Predicted drop shapes are compared with experimental observations. The main features, including the timing of the shape evolution and the 'bead-on-a-string' effect, are well reproduced by the simulations. The results confirm published conclusions of the third author, that the deformation is effectively Newtonian until near the time of Newtonian pinch-off and that the elastic stress becomes large in the pinch region due to the higher extensional flow there.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.6 s.249
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• pp.523-530
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• 2006

One of the fascinating prospects is the possibility of new hydrodynamics technology on micro-scale system since oscillations of micro-droplets are of practical and scientific importance. It has been widely conceived that the lowest oscillation mode of a pendant droplet is the longitudinal vibration, i.e. periodic elongation and contraction along the longitudinal direction. Nonlinear and forced oscillations of supported viscous droplet were focused in the present study. The droplet has a free contact line with solid plate and inviscid fluid. Natural frequencies of a pendant droplet have been investigated experimentally by imposing the acoustic wave while the frequency is being increased at a fixed amplitude. It is found that a pendant droplet shows the resonant behaviors at each mode similar to the theoretical analysis. The rotation of the droplet about the longitudinal axis is the oscillation mode of the lowest resonance frequency. This rotational mode can be invoked by periodic acoustic forcing and is analogous to the pendulum rotation. It is also found that the natural frequency of a pendant droplet is independent of the drop density and surface tension but inversely proportional to the square root of the droplet size.

• Journal of Fashion Business
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• v.15 no.6
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• pp.23-39
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• 2011

Scythian Earrings in the Black Sea region had completely degenerated, stifled by motifs and shapes of Greek origin, retaining its representational realism and its full emotional vitality. The purpose of this study is to review and research the symbolic meaning and classifying the types of the Scythian Earrings style through the tombs bequests. The Scythian Earrings were divided into the styles according to the shape, Earring with Ends Shaped like animal's Heads, Boat-Shaped Earrings, Bird-Shaped Pendants earrings, Earrings with a Disc and a Pendant, Earrings Shaped like the Figures, Earring with the drop Pendant, Spiral Earrings. Earrings based on the boat shape enjoyed a long popularity among the Scythians. As that form became elaborated and combined with the disk-pendent, it reflected native rather than Asian or Hellenic tastes. Although Scythian earrings were produced based on the shapes of Greece earrings, they recreated these as Scythian unique style. In particular, the animal motive and the decoration have various changes. The exquisite earrings attest to the elegant taste and splendid wealth of the upper classes.

• Journal of Welding and Joining
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• v.27 no.1
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• pp.59-64
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• 2009

In order to determine the One-Drop One-Pulse(ODOP) condition of the pulsed gas metal arc(GMA) welding, the drop detaching phenomenon during the peak time is investigated using the force-displacement model. The drop detaching criterion is established based on the displacement of the pendant drop, and the forces exerted on the drop are calculated using the Modified Force Balance Model(MFBM). The effects of wire melting on the drop size and force are included in the force-displacement model. While the peak current has most significant effects on the drop detaching time, the initial drop mass prior to the peak time also influences drop transfer. The calculated results show good agreements with the experimental data, which implies that the ODOP condition can be predicted using the force-displacement method.

• Journal of Welding and Joining
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• v.20 no.4
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• pp.491-497
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• 2002

Dynamic behavior of the molten drop during the peak period in the pulsed-GMAW is simulated in this work using the VOF(volume of the fluid) algerian. The dynamic characteristics of molten drop such as minimum radius, average velocity and displacement of mass center were computed as well as the internal pressure and velocity. The minimum and maximum peak durations for detaching a drop were calculated.. The result of Analysis reveals that peak current and volume of pendant drop are important factors which affecting drop detachment. A simplified model of constant acceleration is proposed to describe the behavior of molten drop during peak current, and its results agree with the experimental results.

• Journal of Welding and Joining
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• v.19 no.4
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• pp.399-405
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• 2001

A dynamic force balance model is proposed in this work as an extension of the previous static force balance model to predict metal transfer in arc welding. Dynamics of a pendant drop is modeled as the second order system, which consists of the mass, spring and damper. The spring constant of a spherical drop at equilibrium is derived in the closed-form equation, and the inertia force caused by drop vibration is included in the drop detaching condition. While the inertia force is small in the low current range, it becomes larger than the gravitational force with current increase. The inertia force reaches half of the electromagnetic force at transition current, and has considerable effects on drop detachment. The proposed dynamic force balance model predicts the detaching drop size more accurately than the static force balance model.

• Journal of Welding and Joining
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• v.19 no.6
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• pp.643-651
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• 2001

A new waveform control technique has been developed for suppressing the spatter generation in the repelled transfer mode of high current $CO_2$ welding. Based on the spatters in repelled transfer, a waveform concept of concept was established in a way to drop the welding current to lower level right before the pendant weld drop detatchment so that the explosion force associating with drop detatchment was decreased. There were several variables to be controlled such as the moment of current drop, the base current and the time of retention at the base current. Either at lower base current or at longer retention time, the more instantaneous shot circuits were int개duced and thus the spatter generation rates were increased. With optimizing the control variables, the amount of spatter generated was decreased by about 30%.