• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.400-405
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• 2020

To analyze the flow distribution formed by multiple acoustic sources, the distribution of acoustic streaming speed caused by an ultrasonic transducer composed of two identical piezoelectric vibrators was examined for various angles between the sound sources. In order to measure the distribution of the speed along the acoustic axis of the transducer, a simple measurement method using a droplet indicator having density similar to that of water is suggested. The simulation results calculated by a numerical method and experimental results showed a similar tendency, and the change of flow speed distribution with the intersection angle between acoustic beams radiated from two acoustic sources was analyzed.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.262-267
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• 2004

Ultrasonic machining has been known as one of the conventional machining methods in the glass fabrication processes. In ultrasonic machining, typically, glass is removed by the impulse energy of the abrasive generated by the ultrasonic power. However, when the machining feature decrease under hundreds of micrometers, as conventional ultrasonic machining uses only the impulse energy of the abrasive, the speed of ultrasonic machining decreases significantly and the surface roughness becomes deteriorated. To overcome this size effect, the chemicals which can erode glasses, such as HF, XF, etc, are added to the slurry. The chemical-assisted ultrasonic machining method, so called, is another alternating effective way for micro machining of glasses. In previous work, we used the hydrofluoric acid (HF) as an additive chemical. But, as the HF solution is too poisonous to be used as a ultrasonic process additive, it is needed to be substituted by other safe chemicals. As results of the machinability comparison of several chemicals, the GST-500F was selected to replace the HF. The GST-500F (pH $4.0{\pm}1.0$) is non-volatile, odorless. During experimental works, it was shown that the machining rate increases 1.5 times faster than the conventional ultrasonic machining. The machining load also decreases. However, the enlargement of the hole diameter and significant tool wear are still the problems to be solved.

• Journal of Mechanical Science and Technology
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• v.18 no.9
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• pp.1630-1639
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• 2004

The present paper investigated the correlation between the acoustic pressure variations and the augmentation of heat transfer in the ultrasonic induced acoustic fields. The augmentation ratios of heat transfer coefficient were experimentally measured and were compared with the profile of the pressure distribution in the acoustic fields predicted by numerical analysis. For numerical analysis, a coupled finite element-boundary element method (coupled FE-BEM) was applied. The results of the present study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The augmentation trend of heat transfer is similar with the profile of the acoustic pressure distribution. In other words, as the acoustic pressure increases, the higher augmentation ratio of heat transfer is obtained. Numerical and experimental studies clearly show that the acoustic pressure variations are closely related to the augmentation of heat transfer in the acoustic fields.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.2058-2065
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• 2004

A light collecting probe named Multi-color Integrated Cassegrain Receiving Optics (MICRO) is applied to spark-ignited spherical spray flames to obtain the flame propagation speed in freely falling droplet suspension produced by an ultrasonic atomizer. Two MICRO probes are used to monitor time-series signals of OH chemiluminescence from two different locations in the flame. By detecting the arrival time difference of the propagating flame front, the flame propagation speed is calculated with a two-point delay-time method. In addition, time-series images of OH chemiluminescence are simultaneously obtained by a high-speed digital CCD camera to ensure the validity of the two-point delay-time method by the MICRO system. Furthermore, the relationship between the spray properties measured by phase Doppler anemometer (PDA) and the flame propagation speed are discussed with three different experimental conditions by changing the fuel injection rate. It was confirmed that the two-point delay-time method with two MICRO probes is useful and convenient to obtain the flame propagation speed and that the flame propagation speed depends on the spray properties.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.4
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• pp.45-51
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• 2015

An experimental study was performed for the analysis of frequency-equivalence ratio correlation in the methane-air premixed flame influenced by ultrasonic standing wave. The propagating flame was caught by high-speed Schlieren photography, and the variation of flame-behavior including the flame structure was investigated in detail employing a post-processing analysis of the high-speed images. It was found that a structural variation and propagation-velocity augmentation of the methane-air premixed flame by the intervention of ultrasonic standing wave were more caused off around the stoichiometry. Also, a dependency of the flame behaviors on the driving frequency and equivalence ratio of the reactants was confirmed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.8
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• pp.1971-1979
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• 1993

In this paper, a new method to estimate stress status in metal nondestructively by using nonlinear dependency of sound speed on stress is proposed. For the purpose, equivalent nonlinear elastic constants up to fourth-order are introduced and a new characteristic parameter given as a function of these constants is presented. And a concrete system to measure the characteristic parameter is constructed by electromagnetic pumping wave and ultrasonic probing wave system. Some experimental results for Al alloy showed that the estimation of stress status in metal is possible by the proposed method.

• Journal of the Korean Wood Science and Technology
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• v.36 no.1
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• pp.61-68
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• 2008

The effect of rupture on the speed of ultrasonic wave was investigated with the PUNDIT and the effective detecting method of defects, moving transmitter and receiver. The speed of ultrasonic wave according to the course of rupture was not affected by transmitter and receiver and in the course of parallel rupture, but only in the course of vertical rupture. When rupture was not located on the ultrasonic wave progressing course, rupture was not detected. However, if rupture was formed perpendicularly to the ultrasonic wave progressing course but located on the ultrasonic wave progressing direction, rupture can be detected. Also, the rupture can be detected, when one transmitter and receiver was placed at top and the other at bottom. After detecting rupture in a part, rupture was determined accurately, placing and moving two transmitters and receivers at width.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.6
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• pp.291-296
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• 2015

The tire damage classification method is researched on the periodicity detection of ramdomness ultrasonic signals to occur at the driving vehicle tire. Setting method of adaptive threshold is proposed in order to valid pulse detection by tire damage in ultrasonic noise on the road and used low pass filter for decrease signal ramdomness as preprocessing. Time interval of detected pulse is setted the density function depend on the vehicle's speed and the method of tire damage detection is proposed that measuring the first peak's time of time density function.The result of time density function in case of one damage material, the first peak's time is measured within the error limit of tire's rotation period, 169.8ms and 97.9ms and 81.8ms, about the speed of 50km/h and 80km/h and 100km/h. In case of more than one damage material, the sum of each peak's time is measured within the error limit of tire's rotation period about the speed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.627-630
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• 2004

Transducer for linear ultrasonic motor with symmetric and anil anti-symmetric modes was studied. The transducer was composed of two Langevin-type vibrators that cross at right angles with each other at tip. In order to excite two vibration modes, two Langevin-type vibrators must have 90-degree phase difference with each other. As a result, tip of transducers moves in elliptical motion. Elliptical trajectoric of transducer was analyzed by employing the finite element method. From these results, the ultrasonic motor was fabricated and was measured for characteristics. In this paper compared an ANSYS analysis with an experiment results. The no-road maximum speed was 113.1[cm/s].

• Journal of radiological science and technology
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• v.41 no.1
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• pp.53-60
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• 2018

The purpose of this study was investigating the effect of 3D printing technology that changes the speed of sound (SOS) and the broadband ultrasound attenuation (BUA) by controlling the density of the media phantom. We used 3D printers which called additive manufacturing (AM) by using material with polylactic acid (PLA). The inside of the medium phantom was filled crossly with 100%, 90%, 80%, 70%, 60%, and 50% of the material. The ultrasonic instrument measured the SOS and the BUA using a 0.55 MHz ultrasound output in opposing mode with a pair of transducers. As a result, the density of the medium phantoms with the SOS showed very high correlation (r = 0.944), but the SOS showed very low correlation (r = 0.500). It is expecting that the manufacturing and measurement method of the medium phantom using 3D printing technology will be used as basic data for ultrasonic bone mineral density.