• Journal of KSNVE
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• v.9 no.3
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• pp.477-484
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• 1999

This study aims to present proper thickness of resilient mount and pattern of chips for the improvement of impact sound isolation. To achieve this aim, field tests were performed to evaluate the performance of impact sound isolation of pilot samples using waste tire chips against light and heavy-weight impacter, which samples were installed over concrete slabs of an apartment housing. In this study, the experiments were performed by the impact sound level of floors in KS F 2810 "Method for field measurement of floor impact level". As results, a flooring structure using waste tire chips as a resilient mount, with no relation to chip's types, has enhanced performance by 1~2 degree in light impact sound isolation, while it has improvement in heavy impact sound isolation. And fiber-type chips have better performance than granule-type ones when they overlaid concrete slab with 15~20 mm of thickness. For the improvement of impact sound isolation, it is recommended that insulating materials should be applied at joints between floating floors and walls, or floating floors and a doorframes, and also waterproof papers should be used for the effective thickness of resilient mount.ent mount.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.843-846
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• 2004

Cavity tone is generated due to the feedback between flow and acoustic wave. It is recognized that the period is determined by the time required for the flow convection in one direction, the time required for the acoustic propagation in the other direction and the time for phase shift depending on the flows and mode. Most of the phenomena have been investigated by experiments and a simple but fundamental theory. But the cause of the phase shift and the correctness of the theory have not been clearly explained so far. In this paper, the phenomena are calculated numerically to obtain detail information of flow and acoustic wave to explain the mechanism including the phase. High order high resolution scheme of optimized high order compact is used to resolve the small acoustic quantities and large flow quantities at the same time. The data are reduced using cross correlation function in space and time and cross spectral density function which has phase information. Abrupt change in pressure near corner in cavity is observed and is relate to phase variation. The time required for the feedback between the flow and acoustic wave is calculated after the numerical simulation f3r various modes. The periods based on the time calculated using the above method and direct observation from the acoustic waves generated and propagated in the numerical simulation are compared. It is found that no phase shift is required if we examine the time required carefully. Rossiter's formula for the cavity tone used for quick estimation needs to be modified far some modes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.308-311
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• 2004

It is reported that there is a limit in increasing heavy-weight impact noise isolation performance of the load bearing wall system apartments to meet the regulation of the Ministry of Construction and Transportation (MOCT). To increase the heavy-weight impact noise isolation performance, improvement in structural systems such as increasing concrete slab thickness and application of rahmen structure were proposed. In this study floor impact sound levels from toil apartments with two rahmen structure multi-story residential buildings were measured before the construction of the buildings finished. Measurements were made at living room and two bedrooms at each apartment when the finishing processes were finished. The average value of light-weight impact sound level from ten apartments was 56dB (L'$\sub$n,Aw/). The heavy-weight impact sound level was 44dB (L'$\sub$i.Fmax.Aw/) and the impact sound level of the impact ball was 41dB(L'$\sub$i.Fmax.Aw/), As a result floor impact noises at the rahmen structure system were lower than the regulation level.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.203-207
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• 2014

According to the advanced study, Increase of ceiling air space could cause increase of floor impact sound by air-spring effect. So in this research, we studied the increase of floor impact sound caused by ceiling air space in apartment buildings. At first, we evaluated the change of floor impact noise in the condition of with or without ceiling air-space. And then we installed perforated ceiling systems and glass wool at ceiling area. we expected that perforated ceiling systems could prevent air-spring effect in ceiling space. As a result, ceiling air space caused increasement of floor heavy impact noise about 2~4dB. But perforated ceiling & sound-absorbing materials system could give us reduction of heavy floor impact noise about 3dB. So this systems could be a good alternative to obey national regulations, because it can reduce heavy impact noise additional to floating floor systems.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.3
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• pp.213-220
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• 2002

Modifying effects of the rectangular forward step for suppressing the unsteady pressure fluctuation during interaction between the upstream vortical flow and the edge are studied numerically. The vertical flow is modeled by a point vortex, and the unsteady pressure coefficient is obtained from the velocity and the potential fields. To investigate the effects of the edge shape the rectangular forward step is chamfered wish various angles. Calculation shows that the pressure peaks become decreased by increasing the vortex height as well as the chamfering angle. The pressure amplitudes are very sensitive to the change of the initial vertex height and its strength. From this study we can find out that the chamfered edge has two effects; the one is that it suppresses the pressure amplitude generated from the edge, and the other is that it decreases the time variation of unsteady pressure fluctuation. These modifying concepts can be applied to attenuate the self-sustained oscillation mechanism at the open cavity flow.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.3
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• pp.228-235
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• 2002

Two kinds of experimental modal analyses have been performed on a radial tire for passenger car under fixed axle. One is the modal analysis to obtain three-dimensional modes of tire using accelerometers and the other is the one to identify cavity resonance frequency using a pressure sensor. From the first analysis, we have obtained three-dimensional natural modes and their decomposed 3-D modes in each direction, which make it possible to grasp the features of the modes that cannot be identified in the conventional 2-D modes and to classify the vibrationall modes into symmetric, non-symmetric, and antisymmetric modes in a simple way by using the experimental results. From the second experimental analysis, the cavity resonance frequency is found. Coomparing the results of the two analyses, we have Identified the three-dimensional mode of the cavity resonance. We also haute shown that natural frequencies of structural vibration depends on inflation Pressure while the cavity resonance does not.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.1 s.106
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• pp.19-26
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• 2006

The test blasts were carried out by detonating some single blastholes at two upper sites of the underground storage cavern for the crude oil. One was performed at the entrance site of the construction tunnel and the other at the middle area of the underground storage cavern. Based on the blast-induced nitration measured by the test blasts, we suggested the propagation equations of blasting vibration that were capable of estimating the peak particle velocity. In addition, in order to assess the stability of the adjacent ground storage tank, we did the frequency analysis and the response spectrum analysis with the particle velocity-time history and the particle acceleration-time history that were measured by the test blast carried out on the entrance site of the construction tunnel. In result, it was predicted that the displacement on the highest part of the tank shell was less than the allowable displacement.

• Journal of KSNVE
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• v.2 no.1
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• pp.21-31
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• 1992

In the previous paper, we report a practical floor impact sound level prediction method for a heavyweight impact source(Tire), soft impact source such as children jumping and running. According to these results, the calculated value and the measured value correspond comparatively well, regardless of differences in the floor structures. And the floor impact sound for a heavyweight impact source, soft source was strongly influenced by structural factors such as floor slab stiffness and peripheral support conditions. But the floor impact sound for a light impact source (Tapping machine), hard impact source was influenced by resilient layers, composed of multi-layer in floor structures. Thus, In this paper, 4 actual floor structures, all with differing resilient layers, were calculated using impedance method. When these calculation values were compared with the measured values, approximately all the values fell with one rank of the sound insulation grade, reference curve(L curve) by the JIS standard. So, a sample of measured values and calculated values from floor structures is presented to show the accuracy and appropriateness of the impedance method in domestic.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.505-513
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• 2017

Cavitation is a phenomenon caused by vapour cavities that is produced in rapid pressure changes. When the cavitation happened, the sound pressure level of a underwater radiated noise is increased rapidly. As a result, it can increase the probability of the identification or classification of a our warship's acoustic signature by an enemy ship. However, there is a problem that it is hard to precisely detect the occurrence of a cavitation noise. Therefore, this paper presents recent improvements in terms of the cavitation noise measurement by using continuous wavelet transform and DEMON(Detection of Envelope Modulation on Noise) signal processing. Then, we present that the suggested scheme is more suitable for detecting the cavitation than existing algorithms.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.479-484
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• 2005

The test blasts were carried out by detonating some single blastholes at two upper sites of the underground storage cavern the crude oil. One was performed at the entrance site of the construction tunnel and the other at the middle part of the underground storage cavern. Based on the blast-induced vibration measured by the test blasts, we suggested the propagation equations of blasting vibration that were capable of estimating the peak particle velocity. In addition, in order to assess the stability of the nearest ground storage tank, we did the frequency analysis and the response spectrum analysis with the particle velocity-time history and the particle acceleration-time history that were measured by the test blast carried out on the entrance site of the construction tunnel. In result, it was predicted that the displacement on the highest part of the tank shell was less than the allowable displacement.