• Proceedings of the KSLP Conference
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• 1998.11a
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• pp.201-207
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• 1998

현악기의 대표격 악기라고 할 수 있는 바이올린이나 기타는 소리(음원)를 만들어 내는 역할을 하는 줄(현)과 공명통이 합쳐져 있는 모양을 하고 있다. 활로 바이올린 줄은 긁거나 기타줄을 손으로 튕겨서 소리를 만들어 내면, 이 소리는 공명통을 울려서 크고 아름다운 소리가 발생되는 것이다. 사람의 목소리도 이러한 현악기와 비슷한 구조를 가지고 있어서, 두 개의 줄모양을 하고 있는 성대에서 성대음(glottal sound)을 만들어 내며 이 성대음이 성도(성도, vocal tract)를 통과하면서 여과(filtration) 되고 성도의 모양에 따른 특성에 따라 공명(resonance) 현상을 일으켜서 입술이나 콧구멍 바깥으로 방출되어 말소리(speech sound)를 만들어내는 것이다. (중략)

• Journal of the Korean Society for Railway
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• v.13 no.5
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• pp.476-480
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• 2010

In the corrugated steel panels used for railway vehicles, sound insulation performance is significantly deteriorated by local resonance effect. In this study, as a countermeasure, polyurethane foam is filled in the corrugated steel panel and glass wool layer is inserted in the layered floor panel, and then improvement effect of the sound insulation performance is experimentally estimated. Based on ASTM E2249-02, intensity transmission loss is measured and estimated on the corrugated panel and floor structure. The aim of the study is to identify how the foam filling and inserting glass wool layer improve the sound insulation performance of the train body structure in aspect of the weight increment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.1061-1066
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• 2016

Corrugation of a corrugated panel dramatically increases the bending stiffness per weight. However, corrugated panels show lower sound insulation performance than that of the flat plate having the same weight. Especially, in a particular frequency region, the sound transmission loss significantly decreases. Main reason of the problem is known as the local resonance. A number of local resonance modes occur above a certain frequency band and modal density rapidly increases. In this study, we investigate the relation of the sound transmission loss and the modal density. Finally, we propose a design methodology in terms of the modal density to improve the sound insulation performance of the corrugated panels without weight increase.

• Proceedings of the Korean Fiber Society Conference
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• 1998.04a
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• pp.244-248
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• 1998

The sound absorption materials are generally classified by three types, such as porous, resonator, panel. All of these types are based on theory of energy transform from sound energy to thermal energy. At first, the sound energy transform from the porous type uses to friction and viscose resistance. Secondly, resonator type uses to resonance frequency, absorption coefficient reach the highest.(omitted)

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2185-2190
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• 2008

In a high speed train, multi-layered panels for floor, side wall and roof are important sound insulating part. As these multi-layered panels require high bending strength vs. weight, corrugated steels or aluminium honeycomb panel are generally used. However, with some inevitable factors, these panels show lower sound insulation performance than that of the plate with the same weight. Transmission loss(TL) often severely decreases in a particular frequency range because of the decrease of the critical frequency, occurrence of local resonance modes and cavity resonance modes, which are not shown in a plate. In this study, frequency range and cause of the TL drop are investigated on the corrugated and honeycomb panels.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.796-799
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• 2005

In 2005, a regulation on the heavy-weight impact sound was released, which restricted concrete slab thickness of standard floor to 210mm. To reduce heavy-weight impact sound, damping materials and structural reinforcement system have been proposed. In this study, the effect of compressive strength on the heavy-weight impact vibration and sound were investigated. FEM analysis was conducted for the 34PY apartment with different concrete strength (210, 350, 420kg/cm$^2$). In addition, apartment floors with different concrete strength were constructed and the floor impact vibration and sound were measured. Results of FEM analysis and measurement show that the resonance frequency of concrete slab was increased by the increment of concrete strength. However, floor impact sound pressure level did not decrease because the nor impact vibration and sound pressure level in 63Hz band increased.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.130-140
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• 2016

Floating floor is most commonly used at apartment houses in Korea for thermal insulation and reducing impact noise. But it in proven that the floating floor is not effective for reducing the floor impact noise in low frequency range. In most cases, impact sound pressure level under 63 Hz frequency band were actually increased by the resonance of resilient material, lightweight concrete and the finishing mortar installed on it. In this paper, an integrated floor system consist of 70 mm light weight concrete and 40 mm finishing mortar successively installed on the concrete slab was suggested to avoid the resonance. Integrated floor system increases total flexural stiffness and mass per unit area. The natural frequencies of first and second vibration mode were increased and acceleration response and floor impact sound level was decreased in all measurement range.

• The Journal of the Acoustical Society of Korea
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• v.19 no.4
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• pp.69-76
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• 2000

In this research, with the FEM we analyzed the variation of the sound pressure and thermal distribution of a Class IV Flextensional transducer in relation to its material properties and structures. Based on the results, we determined optimal structure of a Class IV Flextensional transducer that had maximum sound pressure, minimum thermal distribution, and 1 kHz resonance frequency. The sound pressure by the optimal structure is higher than that of the basic structure by two times, and the thermal distribution is much lower. Results of the present work can be utilized to design Class IV Flextensional transducers of various resonance frequency, maximum sound pressure, and minimum thermal distribution.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.98-103
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• 2003

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a HRSG. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At this tube bank, dominant frequencies of vibration in this system were 43.5, 67.5㎐. The 3$\^$rd/ acoustic natural frequency calculated was 68.5㎐. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}$20%, acoustic resonance could occur. In this system, in order to prevent acoustic resonance, acoustic baffle was installed in the tube bank before operating. But acoustic resonance occurred. So, we evaluate the effect of acoustic mode due to baffle extension length. After investigating, we did revise acoustic baffle to eliminate acoustic resonance effectively.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.305-313
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• 2017

In this paper, sound absorption of thin elastic plates installed in a rigid duct is discussed using an analytic method. The number of plates can be one or two, and each plate might have micro-perforation. Vibration of the plates and sound pressure fields inside the duct and air cavity are expressed in terms of an infinite series of modal functions. Under the plane wave assumption, a low frequency approximation is derived by including the first few plate modes. It is found that the sound absorption coefficient of the plates without micro-perforation shows sharp peaks at resonance frequencies, and due to the interaction between the plates and air cavity, the resonance frequencies move as the cavity depth changes. For the case of micro-perforated plates, it is found that the sound absorption is mainly affected by the perforation ratio. When the perforation ratio is order of few percent, the sound absorption is almost independent of plate vibration.