• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.138-148
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• 1998

The aim of the work described in this paper is to develop a complex underground acoustic system which detects and localizes the origin of an underground hammering sound using an array of hydrophones located about loom underground. Three different methods for the sound localization will be presented, a time-delay method, a power-attenuation method and a hybrid method. In the time-delay method, the cross correlation of the signals received from the way of sensors is used to calculate the time delays between those signals. In the power-attenuation method, the powers of the received signals provide a measure of the distances of the source from the sensors. A new hybrid method has been developed for estimating the origin of the underground acoustic source by coupling both methods. The Nelder-Meade simplex search algorithm is then used to numerically estimate the position of the source in those methods. For each method the sound localization is carried out in three dimensions underground. The distance between the true and estimated origins of the source is in some cases less than 6m for a search area of radius 250m.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.10a
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• pp.227-236
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• 1997

Construction equipment noise has caused much annoyance for a number of dwellers in nearby construction field and has become a very serious issue in our living environment. Therefore, in our country, a practical solution and a better method of reducing construction equipment noise are highly required in construction field. Practical solutions for the construction equipment noise, however, are very difficult because the poorness of basic data and insufficiency of the existing research. Especially, in order to establishment of sound insulation plan about pilings work noise that has highly sound pressure level and impactive, a real situation of sound characteristics about pilings work noise in foundation work demands close investigation. In this point, this study attempts to surveys the characteristics of attenuation and propagation of construction equipment noise in pilings work using SIP(soilcement injected precast pile) method. And this study intends to get the basic data for establishment of a standard about construction noise.

• Journal of KSNVE
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• v.9 no.2
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• pp.302-309
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• 1999

In this paper, a circular lined-duct is modeled by using an axisymmetric foam finite element, which is based on elastic porous material theory of Biot. For various thicknesses of three kinds of lining materials, finite element predictions are compared with measurement results and Morse's analytical results. While the analytical model has larger error as the lining becomes thicker, results of the present model have a good agreement with experimental results for all the thicknesses considered here. It has also been found that constraining the axial motion on the circumferential surface of the lining enhances sound attenuation at low freqneucies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.554-558
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• 2004

In this paper, we introduce noise prediction program of HVAC system to assist low-noisy design of ship's cabin. The developed program calculates sound power levels at HVAC components considering primary and secondary noise generated by fan and duct element, duct element noise attenuation, and duct break-in noise based on the authentic empirical method suggested by NEBB and acoustic power balancing method. Sound pressure level at cabin with or without ceiling system is evaluated by the diffuse-field theory considering diffuser and duct break-out sound powers. Moreover, the program provides intuitive pre- and post-processors using modem GUI functions to help efficient modeling and evaluation of cabin and HVAC component noise. To validate the accuracy and convenience of the program, noise prediction for a HVAC system is demonstrated.

• Journal of the Society of Disaster Information
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• v.12 no.3
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• pp.235-241
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• 2016

Recently our country was entering a high-tech society with social and economic development. However, the individual's ability to respond to disasters is lowered by the increase in complexity society. Accurate situation assessment and disaster response by a margin of personal information that can identify when a disaster has been difficult. Until now, by leveraging Standard speaker was the emergency alert broadcast. However, it was difficult to have regular speakers reverberation, a distinct attenuation of sound by listening to the sound, etc. due to the reflection of sound. By using a directional speaker that is characteristic of the sound attenuation of sound is straight to solve this problem and obtain feedback on measures that can effectively provide the oocytes to a valid information on a disaster situation and the evacuation.

• The Journal of the Acoustical Society of Korea
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• v.13 no.5
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• pp.5-14
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• 1994

In this study, the ground impedance is measured using the standing wave method in a free field on the grass, the soil, and the ground covered with asphalt and cement. And the excess attenuation of sound is investigated. Results are obtained in the frequency range between 300Hz and 1000Hz. There are very good agreements between the results of the measured ground impedance and the prediction of Delanyand Bazley. The ground impedance is increased in order the grass, the soil, the asphalt and the cement road, decreased with frequency for each the ground. The excess attenuation of sound is mainly determined by the ground impedance. The experimental results of the excess attenuation over the different types and the microphone heights are compared with the theoretical values.

• Journal of KSNVE
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• v.7 no.3
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• pp.401-409
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• 1997

This study observed the meterological influence on the excess attenuation with various flow resistivities. The flow resistivity is simulated up to 30, 000 cgs rayls. There is no significant differences among results from spherical wave analysis for excess attenuation, from plane wave analysis, and from locally reacting analysis. This is validated only when the flow resistivity is more than 100 cgs rayls. For the determination of effective flow resistivity of ground by measuring the excess attenuation experimentally, it is highly recommended that the distance between source and receiver is about 2.5m, and that the height of them is 0.3-0.4 m in case that they have the same height. Under this proposed conditions, the flow resistivity of 6-month-passed asphalt ground is estimated to 5, 000 cgs rayls by comparing the measured excess attenuation with the calculated.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2E
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• pp.76-82
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• 1994

The characteristics of bottom sediment may be able to vary within a few meters of depth in shallow water. Since bottom attenuation coefficient as well as sound velocity in the bottom layer is determined by the composition and characteristics of sediment itself, it is reasonable to assume that the bottom attenuation coefficient is accordingly variable with depth. In this study, we use a parabolic equation scheme to examine the effects of depth-varying compressional wave attenuation on acoustic wave propagation in the low frequency ranging from 100 to 805 Hz. The sea floor under consideration is sandy bottom where the water and the sediment depths are 40 meters and 10 meters, respectively. Depending on the assumption that attenuation coefficient is constant or depth-varying, the propagation loss difference is as large as 10dB within 15 km. The predicted propagation loss is very much comparable to the measured one when we employ a depth-varying attenuation coefficient.

• Progress in Medical Physics
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• v.18 no.3
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• pp.172-178
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• 2007

An ultrasonic bone densitometer has been developed by measuring speed of sound signal transmitted and received on the skin, not through the horizontal axis but through the vertical one in tissue. The SOS(speed of sound) method measuring the time difference between the ultrasound signals reflected from the both sides of surface of bone could produce more precise result compared with the BUA(broadband ultrasound attenuation) method measuring the frequency difference. Middle finger is selected to be the best measurement position in order to increase the accuracy, after due consideration that the thickness of flesh at the down part of thumb shows too much variation although the ratio of the receiving signal is higher than the other fingers. The measured value by using SOS method shows almost the same result as compared with the conventional DEXA method.

• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.3
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• pp.217-224
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• 2007

The present work addresses an experimental study on sound attenuation characteristics of silencer by live firing test. When a gun fires, there exists excessive noise which propagates as a form of blast wave. As muzzle energy of the weapon systems increases, the level of impulsive noise also increases. It is well known that the impulsive noise from a gun gives a serious damage to human bodies and structures. The adverse effects of impulsive sound also cause both social and military problems. So it is very important to study the characteristics of the impulsive sound attenuation. The live firing test is performed to evaluate the effect of four different silencers. The test result is compared with the case of bare muzzle which is not installed the silencer. The frequency characteristics are also analyzed to investigate the diminution of sound pressure level. The results of this study will be helpful to the designing silencer for large caliber weapon systems.