• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.83-92
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• 2000

Sound intensity method is well known as a visualization technique of sound field or sound propagation in noise control. Sound intensity or energy flux is a vector quantity which describes the amount and the direction of net flow of acoustic energy at a given position. Especially two dimensional sound intensity method is very useful in evaluating periodic characteristics and acoustic propagation mode of noise source. In this paper, we have studied the noise source Identification, acoustic sound field analysis, and characteristics of noise source of rotary compressor and scroll compressor for air conditioner using complex sound intensity method. Also we proposed a now method of time domain analysis which is used in evaluating of position of noise source in rotary and scroll compressor in this paper This paper presents the advantage, simplicity and economical efficiency of this method by analysing the characteristics of noise source with two dimensional complex sound intensity simultaneously.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.37-47
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• 1996

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is related to determination of testing sensitivity, scanning pitch and defect location. This paper investigated the directivity of ultrasonic wave, which scattered from slit defect located in heat-affected zone (HAZ) in butt joint using visualization method. The directivity of shear waves scattered from slit defect were different according to probe direction (far defect, near defect) and probe position (forward movement, maximum echo position, backward movement). The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. In the case of 2 MHz angle probe, the directivity of reflection wave was appeared sharp form because of the relation wave length and defect size.

• Journal of the Korean Society for Advanced Composite Structures
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• v.7 no.1
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• pp.19-24
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• 2016

Most of the soundproof tunnels generate significant discharge noise through their inlets and outlets so that the length of the tunnel has been extended frequently than required to minimize the effect on such discharge noise. Thus, in this paper, we investigate reduction capability of discharge noise from the sound proof tunnel installed with lateral sound-absorbing panels on the partitioned truss members in the longitudinal direction of the tunnel. In conclusion, noise field analysis results shows that the sound proof tunnels with lateral sound-absorbing panels have an effect on discharge noise abatement and thereby tunnel's length reduction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.278-281
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• 2004

Multiple sound sources are controlled to enhance sound power within a zone of interest. The problem of enhancing acoustic variable can be regarded as an optimization problem, which seeks an optimal control input that maximizes the acoustic variable. It should be noted that enhancing sound power of a selected region requires both the magnitude and direction to be controlled. For this reason, two kinds of cost functions that can represent the spatially distributed intensity are defined. Theoretical formulation shows the possibility of sound power control in a zone, and the detailed procedures of the proposed method are validated by numerical simulations.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.39.1-39.1
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• 2012

Nuclear rings in barred galaxies are sites of active star formation (SF). We investigate SF and its feedback effects occurring in barred galaxies, for the first time, using high-resolution grid-based hydrodynamic simulations. The gaseous medium is assumed to be infinitesimally thin, isothermal, and unmagnetized. The SF recipes include a density threshold corresponding to the Jeans condition, a SF efficiency of 1%, and momentum feedback via Type II supernova events together with stellar-wind mass loss. To investigate various environments, we vary the gas sound speed as well as the efficiency of momentum injection in the in-plane direction. We find that when the sound speed is small, the surface density of a ring becomes largely independent of the azimuthal angle, resulting in star-forming regions distributed over the whole length of the ring. When the sound speed is large, on the other hand, the ring achieves the largest density at the contact points between the dust lanes and the ring where SF occurs preferentially, leading to a clear age gradient of star clusters in the azimuthal direction. Since rings shrink with time, a radial age gradient of star clusters naturally develop regardless of sound speed, consistent with observations. SF persists over 200 Myr, with an average rate of ${\sim}1.3M_{\odot}/yr$ similar to observed values. Rings gradually become hostile to SF as they lose gas into stars and turbulent motions dominate.

• Journal of Digital Convergence
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• v.19 no.7
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• pp.217-226
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• 2021

The use of personal mobility(PM) is increasing because of preading shared mobility, but, it causes risk of accidents and fear to pedestrians because of lack of sound. The purpose of this study is to find out the effects of the alert sound in PM and driving direction on risk perception of pedestrians, awareness on PM driver, and allowance for driving on each road. The 8 videos were produced from a pedestrian perspective, depending on the alert sound type(silent, vess, bell, voice) and direction of driving(front, back). After watching each video, participants completed surveys. There was a non-effect on the driving direction. Regardless of the alert sound type, all of the sounds reduced the risk perception. Also, the awareness of PM drivers and allowance for driving on each road were positive. This study found that PM needed an alert sound for pedestrian safety. We expect the results of the study to help improve awareness of PM and make policies and regulations.

• Journal of Korean Physical Therapy Science
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• v.1 no.1
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• pp.175-185
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• 1994

The purpose of this study was to evaluate and compare the biceps muscles activity at the different angle and direction of the base of support on sitting position in hemiplegic patients. The biceps muscles activity was measured at the $0^{\circ},\;10^{\circ}$ of posterior tilt, $10^{\circ}$ of anterior tilt, $10^{\circ}$ of affected side tilt and $10^{\circ}$ of sound side tilt of the base of support by EMG biofeedback (MYOMED 432. ENLAF NONIUS CO.) In this study, 24 out-patients were evaluated who were treated at Yonsei University Medical College Rhabilitation Hospital. This study was carried out from December 5. 1993 to March 30. 1994. In order to determine the statistical significance of result, the ANOVA, and t-test were applied at the 0.05 level of significance. The results were as follows : 1. The biceps muscles activity of the sound side was no significantly difference at the different angle and direction of the base of support on sitting position(p>0.05). 2. The biceps muscles activity of the affected side was significantly increased at the 100 of sound side tilt and $10^{\circ}$ of posterior tilt of the base of support on sitting position(p<0.05). 3. There was no significantly difference in the change of the biceps muscles activity of the affected side between the affected group and the intact group of propriocetive sense(p>0.05). 4. The change of the biceps muscles activity of the affected side was significantly higer in the group of G 2 spasticity compared to that of G 1, G 1+ spasticity(p<0.05). These results showed that the biceps muscles activity of affected side was significantly increased when the base of support was tilted toward the sounde side and posterior direction on sitting position. In order to prevent the increment of biceps muscle activity, the patients must avoid to sit toward sound side and posterior tilt.

• IEMEK Journal of Embedded Systems and Applications
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• v.13 no.1
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• pp.33-43
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• 2018

In this paper, we describe an sound tracking mobile robot suitable for areas where GPS is not available. Sound sensors are attached to four sides of the robot in order to locate the person in a danger, and the robot is supposed to move to the yelling person. The traveling distance of the mobile robot is calculated by the encoder attached to the wheel of the mobile robot. The moving direction of the mobile robot is measured by a gyro sensor on the robot. When the person in danger pushes a button of the mobile robot, the mobile robot transmits the trajectory data to a designated server.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.92-96
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• 2007

Microphone array beamforming method has been recognized as an important aeroacoustic research field and become a standard technique in localizing sound sources. This method also used in flight acoustic measurement, and especially, it is very useful when measure sounds inside the wind tunnel. In measuring sound which is inside the wind tunnel by traditional beamforming method, there are some errors caused by airstream. The speed and the propagation path of the sound changes as it travel through the airstream. This makes the error which the position of sound is changed a little bit to the down stream direction. In this paper, validation test has made about the correction equation for this wind effects of previous researches. And beamforming including shear layer correction was performed about a sound source in the anechoic open-jet windtunnel.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1995.11a
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• pp.202-204
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• 1995

An acoustic sensor using PVDF film is proposed in this paper. And its properties, such as sensitivity level, identification of sound source frequencies. and directivity, were experimented. Sensitivity level measured at the distance of 1[m] was limited in the range of ${\pm}$10dB. Adjacent three frequencies were also tested to identify the frequency of sound sources. In the range of audible frequencies, it could distinguish the frequencies of a complex sound. In addition, it was found that the sensor outputs were maximum in the coincided direction with a source, when directivity was experimented with three sound sources and FFT. The proposed PVDF film sensor has good characteristics of directivity and identifying ability as an acoustic sensor.