• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2844-2851
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• 2011

The purpose of this study is to set up an acoustic prediction technique and to perform the IL test of scale down noise reducing device for the development of the noise reducing device as the development of 400km/h class high speed train. First of all, the IL prediction of noise reducing device was performed with the 2D BEM method. And the noise test of scale down noise reducing device in anechoic chamber was performed for the verification of acoustic prediction technique and IL performance evaluation. As the results, the acoustic prediction technique for the development of noise reducing device was verified because the averaged IL difference between prediction and test is in 2dB(A). And the measured IL value of noise reducing device is less than 2dB(A), and additional IL with polyester absorption material is increased about 0.5dB(A).

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.344-352
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• 1993

The purpose of this study is to investigate the possibility of the non-destructive quality evaluation for food by the acoustic non-linear parameter B/A which is a measure of the non-linearity of the state equation of the medium in terms of pressure and density. The B/A of water, corn oil O/W(oil in water) emulsion and milk were measured by using a sound velocity measuring system. The B/A value of water was measured for ascertaining reliability of our experimental system. Corn oil W/W emulsion was prepared as a model of milk . It was proved that the B/A value of O/W emulsion was related to the oil concentration by a law of mixture. We applied this result to milk and obtained satisfactory results for predicting the milk fat concentration.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.289-294
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• 2003

The object of this study is to investigate the effect of compounded welding by using acoustic emission (AE) signals fur weld heat affected zone (HAZ) in tensile testing. This study was carried out a SM 490A high tension steel for electronic shielded metal are welding (SMAW), $\textrm{CO}_2$ gas arc welding and TIG welding. And correspondingly, the root openings are 3, 4 and 2.8mm. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. These history plots give us useful and powerful information to analyze the results of material evaluation testing.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.11 no.6
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• pp.75-81
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• 2012

Dissimilar material friction welding such as STD11 and SCM440, we are considering of such things as strength and tenacity of welding interface, which consist of friction welding rotation frequency, friction heating pressure, upset forging-pressure, friction heating time, and upset forging-pressure time. From the study, obtaining the interrelationship between welding condition and quality(toughness, tenacity), we can set the best range of welding condition. while performing acoustic emission examination for the nondestructive evaluation, we can deduce the interrelationship among total acoustic emission counts, friction welding variable, and quality during friction welding, which can solve the manufacturing difficulty and enhance the economic value.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.1
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• pp.24-33
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• 2004

Recently, ship acoustics takes more important role in acoustic stealth and classification of underwater targets. In this paper, a theoretical concept is proposed for M＆S-based test and evaluation of ship acoustics. The concept is based on two different approaches: on Top-Down method which emphasizes the survivability of the ship and on Bottom-Up method which considers acoustic characteristics of the ship-equipments. In order to improve the effectiveness of M＆S-based T＆E for ship acoustics, it is recommended in this paper to compromise the two approaches as adequate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.226-230
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• 2007

In case of domestic performance hall, it is real situation that the demand of multipurpose hall that accommodative a lecture, gathering activity, drama and concert than a professional performance hall such as opera house, is on increasing. Accordingly, since such multipurpose hall, in view of its characteristics, is emphasizing the clearness of sound, also it requiring the repletion or abundance of sound simultaneously, it could be said that the sufficient examination and plan with regard to the architectural acoustics design is indispensable. However, since most of multipurpose hall has ever been designed and constructed without any consideration on an acoustic factor, many problem points are generating. Standing on such viewpoint, this Research has measured the physical acoustic characteristics about the small-scaled multipurpose hall recently built without any acoustic consideration, and through the above, tried to grasp the acoustic defect and controversial point thereof. It is deemed that such study result could be utilized as an important material for improvement the acoustic performance of the multipurpose hall.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.101-106
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• 2011

In the present paper, the phenomena of abnormal noise and vibration due to acoustic resonance of CFBC(Circulating Fluidized Bed Combustion) boiler was presented. The acoustic resonance which occurred in the gas path of CFBC boiler system was caused by coincidence of vortex shedding frequency of tube bank and acoustic natural frequency of duct and hopper. And, the phenomena of beating arose from the interference of two closed resonant waves at 66.4Hz and 70.8Hz. There are two control methods for acoustic resonance in this system. The first method is to change the vortex shedding frequency from the structural alterations on the tube bank. And the second method is to change the acoustic natural frequency of the gas path with the installation of anti-noise baffles. The second one which is relatively easy to apply, was adapted in this study. As a result, the noise and vibration level have been decreased by 41dB and 94% at 66.4Hz, respectively. And the improvement of noise and vibration at 70.8Hz was identified by sensory evaluation.

• Applied Microscopy
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• v.50
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• pp.25.1-25.11
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• 2020

Scanning acoustic microscopy (SAM) or Acoustic Micro Imaging (AMI) is a powerful, non-destructive technique that can detect hidden defects in elastic and biological samples as well as non-transparent hard materials. By monitoring the internal features of a sample in three-dimensional integration, this technique can efficiently find physical defects such as cracks, voids, and delamination with high sensitivity. In recent years, advanced techniques such as ultrasound impedance microscopy, ultrasound speed microscopy, and scanning acoustic gigahertz microscopy have been developed for applications in industries and in the medical field to provide additional information on the internal stress, viscoelastic, and anisotropic, or nonlinear properties. X-ray, magnetic resonance, and infrared techniques are the other competitive and widely used methods. However, they have their own advantages and limitations owing to their inherent properties such as different light sources and sensors. This paper provides an overview of the principle of SAM and presents a few results to demonstrate the applications of modern acoustic imaging technology. A variety of inspection modes, such as vertical, horizontal, and diagonal cross-sections have been presented by employing the focus pathway and image reconstruction algorithm. Images have been reconstructed from the reflected echoes resulting from the change in the acoustic impedance at the interface of the material layers or defects. The results described in this paper indicate that the novel acoustic technology can expand the scope of SAM as a versatile diagnostic tool requiring less time and having a high efficiency.

• International Journal of Automotive Technology
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• v.6 no.4
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• pp.367-374
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• 2005

This paper proposes a sound quality index to evaluate the vehicle interior noise. The index was developed using a correlation analysis of an objective measurement and a subjective evaluation data. First, the objective set of measurements was obtained at two specified driving conditions. One is from a wide-open test condition and the other is from a constant-speed test condition. At the same time, subjective evaluation was carried out using a score of ten scale where 17 test engineers participated in the experiment. The correlation analysis between the psycho-acoustic parameters derived from the objective measurement and the subjective evaluation was performed. The most critical factors at both test conditions were determined, and the corresponding equations for the sound quality were obtained from the multiple factor regression method. Finally, a comparative work between previous index and present index was performed to validate the effectiveness of the proposed index.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.12-19
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• 2000

In this paper, not only the development of optimizing of friction welding with more reliability and more applicability but also development of in-process real-time weld quality(such as strength and toughness) evaluation technique by acoustic emission for friction welding of the engine exhaustive valve(SUH3-SUH35 dissimilar steels of 12.3mm, 16mm, 20mm and 24mm in diameters) were performed, comparing with the other FRW matches of materials such as SUH3 to SUH31, SUH3 to STS303 and SUH3 to STS304. As an important result, the techniques for dissimilar friction welding optimization of engine heat resisting steels SUH3 and SUH35( 12.3mm, 16mm, 20mm, 24mm) and its real-time weld quality evaluation by AE were developed, considering on both diameter and carbon equivalent effects.