• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.198-207
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• 2009

Distribution of cavitation bubbles relative to change of the sound speed and attenuation in the water was estimated using acoustic signal from 20 to 300 kHz in two cases that cavitation bubbles exist and do not exist. To study generation and extinction property of cavitation bubble, bubble distribution was estimated in three cases: change of rotation speed (3000-4000 rpm), surface area of blade ($32-98\;mm^2$) and elapsed time (30-120 sec). As a result, the radii of the generated bubbles ranged from 10 to $60{\mu}m$, and bubble radius of $10-20{\mu}m$ and $20-30{\mu}m$ was accounted for 45 and 25% of the total number of cavitation bubbles, respectively. And generation bubble population correlated closely with the rotating speed of the blades but did not correlate with the surface area of blade. It was observed that 80% of total bubble population disappeared within 2 minutes. Finally, acoustic data of bubble distribution was compared with optical data.

• Journal of the Korea Society of Computer and Information
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• v.15 no.2
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• pp.75-81
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• 2010

Feeling of shooting is one of the most important features of shooting games. Game developers have tried to improve feeling of shooting by using various techniques, such as visual/sound effects, rumble effects, animations, and camera techniques. In this paper, we introduce the results of the empirical analysis of the several techniques in a 2D shooting game. We carried out two experiments in which levels of feeling of shooting were measured in a simple 2D shooting game. The first experiment was configured with 16 combinations of the four techniques (visual, animation, sound, and rumble effects) applied to a shooting object (a cannon), and the second was configured with 16 combinations of the two techniques (visual and sound effects) applied to both or either side of a shooting object and exploding objects (enemy ships). The analysis results of the experiments showed that all of each techniques were statistically significant factors. We could also found that sound effects and rumble effects are more effective than visual effects and animations and that exploding objects are more important that a shooting object.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2
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• pp.66-76
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• 1999

This paper proposes that can take at high speed the information of binocular disparity with moving translational and forward stereo camera to the extent that does not occur the problem of a correspondence point. It shows that in case of stereo vision with translational motion, can take the information of binocular disparity being devoid of error and putting high confidence in, and that in case of stereo vision with forward motion, can take the horizontal component which can not be detected in common stereo vision. Besides, the stereo vision can be done at high speed due to being bright and small a correspondence point comparing not to do, because a correspondence between right and left images is previously limited. But there are problem that a resonable information of binocular disparity can not be taken, if the vicinity of center of image is in accord with the region of occlusion in stereo vision with forward motion.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.353-357
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• 2007

We have been setting up experiments on propagation of shock waves generated by the pulsed laser ablation. One side of a thin metal foil is subjected to laser ablation as a shock wave propagates through the foil. The shock wave, which penetrates through the foil is reflected by an acoustic impedance which causes the metal foil to high-strain rate deform. This short time physics is captured on an ICCD camera. The focus of our research is applying shock wave and deformation of the thin foil from the ablation to accelerating micro-particles to a very high speed.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.109-109
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• 2009

최근 유럽의 완성차 업체에서 조립라인에 적용을 시작하고 있는 레이저 원격 용접기술은 저항 점용접에서의 문제점들을 동시에 해결하고 작업 시간을 획기적으로 감소시켜 생산성을 향상시킬 수 있는 용접공정으로 떠오르고 있다. 레이저 원격 용접기술은 레이저 빔을 용접부의 원거리에서 조사하여 용접하는 기술로서 레이저의 초점거리와 갈바노미터의 고속 이송를 이용한 최첨단 용접공정이다. 높은 생산성을 유지 하기 위하여 정확한 용접 컨트롤이 필요하지만, 레이저 용접의 경우 용접시 안전 문제로 육안으로 관찰하기가 힘들다. 이러한 문제를 해결하기 위하여 모니터링이 필수적이다. 기존의 레이저 모니터링으로는 음향 센서를 이용하여 음향을 측정하는 방법이나 UV 센서, IR 센서 등의 빛을 이용한 방법이 많이 사용되어왔다. 하지만 이 방법들은 간접적인 방법들로 노이즈에 민감하고 또 설치가 까다로운 단점이 있었다. 본 연구에서는 CCD 카메라를 이용하여 시스템의 복잡함을 줄이고 더 정확하고 빠르게 용접 현상을 관찰하기 위하여 동축 모니터링 시스템을 이용하였으며, 이를 통해 Keyhole을 관찰하고 센서를 이용한 용접 변수(레이저 출력, 용접 속도 등)의 변화에 따른 용접 현상을 규명하였다.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.151-162
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• 2020

This paper presents an acoustic inversion method for estimating the bubble size distribution. The estimation error of the attenuation coefficient represented by a Fredholm integral equation of the first kind is defined as an objective function, and an optimal solution is found by applying the Levenberg-Marquardt (LM) method. In order to validate the effectiveness of the inversion method, numerical simulations using two types of bubble distribution are performed. In addition, a series of experiments are carried out in a water tank (1.0 m × 0.54 m × 0.6 m), using bubbles generated by three different generators. Images of the distributed bubbles are obtained by a high-speed camera, and the insertion losses of the bubble layer are measured using a source and a hydrophone. The image is post-processed to glance a distribution characteristics of each bubble generator. Finally, the size distribution of bubbles is estimated by applying the inversion method to the measured insertion loss. From the inversion results, it was observed that the number of bubbles increases exponentially as the bubble size decreases, and then increases again after the local peak at 70 ㎛ - 120 ㎛.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.4
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• pp.181-190
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• 2014

The underwater acoustic lens system is one of the systems getting high-resolution images on the seafloor by the beam forming method using acoustic lens. The beam forming using acoustic lenses reduces complexity and driving power. When receiving an incoming beam with the acoustic lens array, beam pattern analysis and arrangement problem of the array sensor must be addressed. Introducing SIR (Signal to Interference Ratio), the relationship among sensor interval, beam pattern and image quality would be analyzed. Generally if the sensor interval getting wider, the less effect of the side lobes makes SIR high. If the amplitude of a side lobe is high, SIR is generally getting low. The type of the apodization function changes the width, shape and amplitude of both main lobe and side lobes. Thus an appropriate apodization function can improve SIR. In this paper, SIR is stable at the sensor interval of 13mm with 0-10dB, which is not high relatively. By applying the Chebyshev function, the SIR becomes 80dB over the sensor interval of 37 mm or higher. The Hann and triangular functions demonstrate better SIR when the sensor interval becomes narrower.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.233-242
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• 2023

In this paper, the effect of mass injection on the control of tip vortex cavitation was studied experimentally. A mass injection system for a 3D hydrofoil was designed to control the location of injection as well as the injection rate. A series of cavitation tests were carried out in a cavitation tunnel for different injection locations and rates. The cavitation behaviour was observed using a high-speed camera and the corresponding noise was measured using a hydrophone installed in the observation window. The results showed that the tip vortex cavitation was suppressed under certain conditions and the noise was reduced in some frequency bands. It was also found that there is a location where the effect of mass injection could be maximized and hence the noise reduction.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.243-249
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• 2023

The occurrence of cavitation on the propeller is directly linked to the naval ship's survivability, and it is necessary to design a propeller shape that delays the cavitation inception. However, the propeller cavitation can occur under various operating conditions, thus it is important to identify whether the propeller cavitation exists during operation as well as in the design phase. To this end, it is necessary to use noise or vibration signals on board to monitor the cavitation inception. In this study, a hydrophone and an accelerometer were installed on the ship hull right above the propeller to compare the performance of analyzing cavitation inception between acoustic and vibration signals. Also, a high speed camera was used to visually observe the occurrence of cavitation through an observation window. The measured results showed that the spectral shapes between acoustic and vibration signals were different, but the level increases at each frequency band and the overall level of the frequency band from 1 kHz to 10 kHz showed a similar tendency. The Detection of Envelope Modulation On Noise (DEMON) analysis also showed similar results for both acoustic and vibration signals, confirming that both hydrophones and accelerometers can be utilized in the analysis of cavitation inception.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.626-629
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• 2007

Vibration originated from the fuel pump is transmitted to the fuel pump module and fuel tank. Fuel tank transmits it to chassis of vehicle. Also, noise perturbed through fuel and fuel tank is radiated out. Dynamic characteristics of fuel tank are composed of tank structure and containing fuel quantity. Therefore, this study is focused at fuel tank with various quantity. As a result, characteristics of vibration for various fuel quantity in a tank are identified as the more mass of fuel is, the less the 1st resonance frequency decrease. Also, between acoustic camera and mode shape of modal analysis are used for searching the positions of radiated noise and are found to be in accordance with each other.