• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.9 s.114
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• pp.971-981
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• 2006

This paper presents the design and characterization of a novel fiber optical coupler for intensity modulated fiber optical microphone. Theoretical equations for the optical power coupling are presented in detail including optical path analysis and misalignment. Various optical couplers are simulated and manufactured. A multi-mode to multi-mode coupler is characterized by static and dynamic movements of mirror on a well designed experimental stage.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1704-1709
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• 2000

This paper proposes a spherical probe allowing acoustic intensity measurements in three dimensions to be made, which creates a diffracted field that is well-defined, thanks to analytic solution of diffraction phenomena. Six microphones are distributed on the surface of the sphere along three rectangular axes. Its measurement technique is not based on finite difference approximation, as is the case for the ID probe but on the analytic solution of diffraction phenomena. In fact, the success of sound source identification depends on the inverse models used to estimate inverse diffraction phenomena, which has non-linear properties. In this paper, we introduce the concept of nonlinear inverse diffraction modeling using a neural network and the idea of 3 dimensional sound source identification with several tests.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.216-221
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• 2000

This paper deals with the Gain Control in the processing of the underwater acoustic image obtained from side scan sonar(SSS) system. At first, this paper describes the principles of SSS that is a surveying equipment for the underground of the rivers or dams as well as sea floor. Then this paper analyzes the cause and effects of the time varying intensity from the view point of transmission loss and beam pattern. At last, the time varying gain filter that is adopted by the towfish is introduced.

• Journal of Ocean Engineering and Technology
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• v.10 no.4
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• pp.51-57
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• 1996

A standard method for the evalution of the fracture toughness of the high polymer materials has not been fully developed in comparison with that for metallic materials, and has not yet established. In this paper, fracture toughness tests using polycarbonate specimens were carried out. The fracture thughness tests using polycabonate specimens were carried out. The fracture toughness of commercial polycarbonate were dependent on the specimen thickness. The specimen thickness is necessary above 8mm to obtain the valid $K_{IC}$. A cumulative counts were slightly dependent on specimen thickness.

• Ocean and Polar Research
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• v.25 no.4
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• pp.437-446
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• 2003

Field measurements of directional waves were carried out during the summer of 2002 at two coastal sites in water of finite depth. A couple of general purpose instruments were used employing acoustic Doppler technology. The aim of the study was to investigate the spatial behavior of the directional movement of waves as they come ashore. In total,74 tests were carried out during which sea states of low to moderate intensity were recorded. A great number of these runs displayed bimodal characteristics of the spreading function at high frequencies. It was found that in general, the frequency-integrated directional width tends to broaden as the water shoals and when refraction effects are negligible. This is attributed to wave-wave interactions that become pronounced in shallow water. The same directional width showed, also, a tendency to increase with increasing peak frequency of the sea state spectrum. The behavior of the kurtosis of the spreading function was also examined. It was found that for higher frequencies this index tends to increase in wave spectra above a certain sea severity threshold.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.547-552
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• 2001

An intensity-based optical fiber vibration sensor is applied to detect and evaluate damages and fiber failure of composites. The optical fiber vibration sensor is constructed by placing two cleaved fiber end, one of which is cantilevered in a hollow glass tube. The movement of the cantilevered section lags behind the rest of the sensor in response to an applied vibration and the amount of light coupled between the two fibers is thereby modulated. Vibration characteristics of the optical fiber vibration sensor are investigated. Surface mounted optical fiber vibration sensor is used in tensile and indentation test. Experimental results show that the optical fiber sensor can detect damages and fiber failure of composites correctly.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.324-329
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• 2003

An air-conditioner has various noise sources such as cooling fan noise, pumping noise, flow noise and impact noise. Among these, impact noise is the most unpleasant source. This is because the noise is produced in indoor unit of air-conditioner. To control the noise source effectively, first we must identify the noise sources. When we identify impact noise source, the measurement have to be carried out simultaneously. So we use beamforming method that requires less measurement points than intensity method and acoustic holography. The objective of this paper is to estimate the location of impact source. This objective can be achieved by using minimum variance cepstrum that is able to detect impulse embedded in noise. In this study, modified beamforming method based on cepstrum domain is proposed. Then this method applied to air-conditioner noise sources which produce impact noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.543-548
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• 2002

Nowadays since the customers of HDD's are interested in their noise levels in addition to their primary performances such as their average access time, capacity, HDD manufacturers make efforts on reducing the noise. The works to reduce noise are usually based on the measurable physical quantities such as SPL or acoustic intensity level. However, since the HDD noise is Judged by human beings, the basis of noise reduction should be human sensations. In this paper, the noise levels of various HDD's are evaluated by the human jury test to find a relationship between the physical quantities used for noise control and the human sensations of noise. Discrepancies are found in the judgments by the human beings and by the physical quantities. The loudness level, a psychoacoustic variable, is used to solve the discrepancy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.950-957
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• 2007

This paper considers acoustic characteristics of silencer within a dry vacuum pump. The main objective is to reduce noise in dry vacuum pump using the new designed silencer. First, SPL and sound intensity are measured for noise source identification and the new model silencer is designed corresponding to noise characteristics. 4-pole parameters are used to predict the transmission loss which is one of the interest characteristics of the new silencer. The calculated transmission loss is then used to change main effective factor and optimal value is selected by using design of experiment. By conducting an experiment, it is proved that the new designed silencer has reduced noise level by 6 dB(A) more than the original one.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.7 no.1
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• pp.56-60
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• 1996

The vocal efficiency(VE) can be calculated as the ratio of acoustic power to aerodynamic power. It relates to the vocal intensity, air Sow rate and subglottic pressure. In this study, we treated 20 cases of vocal polyps and 10 cases of vocal nodules by way of laryngo-microsurgery or laser laryngo-microsurgery. The VE was measured preoperatively and postoperatively in all cases. The results showed that there was a significant improvement of VE postoperatively than that of preoperative measurement(p＜0.01) in vocal Polyp group. However, there was no significant difference(p＞0.05) in vocal nodule group. Through comparing the results, we obtained the conclusion : The laryngo-microsurgery is the reliable method of management for the vocal polyps, but f3r the vocal nodules, the laryngo-microsurgery should be selected after other more conservative approaches fail to produce the desired results.