• Journal of the Korean Wood Science and Technology
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• 제46권4호
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• pp.362-367
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• 2018

This study estimates the sound absorption capability of rice straw particle mats by two methods: the transfer function method and the reverberation room method. In the reverberation method, the central frequency was set to the one-third octave band in the 100-5000 Hz range; in the transfer function method, the frequency range was 500-6400 Hz. Both methods yielded similar noise reduction coefficients of the rice straw mats. The noise reduction coefficient was approximately 0.8, indicating a high sound-absorption property of the mats. Therefore, rice straw matting is a suitable candidate material for sound-barrier walls against highway noise.

• Journal of the Korean Wood Science and Technology
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• 제38권6호
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• pp.463-469
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• 2010

속성수의 이용가능성을 파악하기 위하여 일본산 속성수 중의 하나인 찬친모도키(Choerospondias)의 물리적 성질, 역학적 성질 그리고 흡음특성을 조사하여 주거재료로서의 적용가능성을 검토하였다. 찬친모도키재는 평균 연륜폭이 약 8 mm 정도로 생장이 빨랐으며 기건비중은 약 0.55이었다. 찬친모도키재는 다른 건축자재에 비하여 흡음성능이 열등하지 않았고 비교적 우수한 강도적 성질을 나타내어 구조재나 마감재 등에의 이용이 가능할 것으로 사료되었다.

• Physical Therapy Rehabilitation Science
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• 제11권3호
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• pp.321-328
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• 2022

Objective: The purpose of this study was to investigate the effect of neck stabilization exercise combined with vibroacoustic sound on patients with chronic neck pain and tension-type headache. Design: Two group pre test - post test design. Methods: 36 patients participated. Headache impact test-6(HIT-6), numerical rating scale(NRS) and muscle characteristics were measured at pre-post test. Participants divided into vibroacoustic sound group(VSG, n=18), control group(CG, n=18). VSG performed neck stabilization exercise and vibroacoustic sound stimulation. CG performed neck stabilization exercise. Both groups participated 3 times a week for a total of 4 weeks. Results: NRS showed a significant difference before and after intervention in both groups (p<0.05). HIT-6 showed a significant difference before and after intervention in the VSG group (p<0.05). Muscle tone showed a significant difference before and after intervention in the experimental group (p<0.05). There was no significant difference in muscle stiffness and muscle elasticity before and after the intervention in both groups (p>0.05). Conclusions: Based on the results of the study, it is thought that sonic vibroacoustic sound can be established as an effective treatment tool through a study applied to various diseases and symptoms.

• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.272-285
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• 2004

The losses at off-design points from a compressor cascade occur due to the deviation from a design incidence angle at the inlet of the cascade. The self-noise from the blade cascade at off-design points comes from a separated boundary layer and vortex sheddings. If the incidence angle to the cascade increases, stalling in blades may occur and the noise level increases significantly. This study applied Large-Eddy Simulations (LES) using deductive and deductive dynamic SGS models to low Mach-number, turbulent flow with each incidence angle to the cascade ranging from -40$^{\circ}$ to +20$^{\circ}$ and compared numerical predictions with measured data. It was observed that the oscillating separation bubbles attached to the suction surface do not modify wake flows dynamically for cases of negative incidence angles. However, an incidence angle greater than 8$^{\circ}$ caused a separated vortex near the leading edge to be shed downstream and created stalling. The computed performance parameters such as drag coefficient and total pressure loss coefficient showed good agreement with experimental results. Noise from the cascade of the compressor is summarized as sound generated by a structure interacting with unsteady, turbulent flows. The hybrid method using acoustic analogy was observed to closely predict the measured overall sound powers and directivity patterns at design and off-design points of blade cascade.

• 한국소음진동공학회논문집
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• 제17권8호
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• pp.673-682
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• 2007

Recently the trend of automobile industry is that IQS evaluation index against a sensitivity quality is increasing. To reduce rattle noise due to speaker sound at low frequencies, it is required the advanced technology analysis process of body structure. This paper optimized the design parameters of package tray panel according to the theoretical background about robust design and suggested the design guideline for resonance avoidance and the reduction of vibrational sensitivity considering the excitation frequency of woofer speaker. And this paper described the design process of a door module panel through the sensitivity analysis in case of the door speaker excitation. Finally, the analysis of the quality deviation using mother car is suggested to guarantee the stable characteristics of vehicle vibration in the early stage of vehicle development. These improvements can lead to shortening the time needed to develop better vehicles.

• 한국음향학회:학술대회논문집
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• 한국음향학회 2004년도 추계학술발표대회논문집 제23권 2호
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• pp.221-224
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• 2004

A theoretical model has been studied to describe the sound radiation analysis for structure vibration noise of vehicle tires under the action of random moving line forces. When a tire is analyzed, it had been modeled as curved beams with distributed springs and dash pots that represent the radial , tangential stiffness and damping of tire, respectively. The reaction due to fluid loading on the vibratory response of the curved beam is taken into account. The curved beam is assumed to occupy the plane y=0 and to be axially infinite. The curved beam material and elastic foundation are assumed to be lossless Bernoulli-Euler beam theory including a tension force, damping coefficient and stiffness of foundation will be employed. The expression for sound power is integrated numerically and the results examined as a function of Mach number, wave-number ratio and stiffness factor. The experimental investigation for structure vibration noise of vehicle tire under the action of random moving line forces has been made. Based on the Spatial Transformation of Sound Field techniques, the sound power and sound radiation are measured. Results strongly suggest that operation condition in the tire material properties and design factors of the tire govern the sound power and sound radiation characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.81-84
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• 2007

In this paper, fiber optic sound and vibration monitoring sensor which is latticed shape structure based on Sagnac interferometer is fabricated and tested in laboratory conditions. To detect external vibrations surface mounted fibers on the latticed steel wire fence with a dimension of 170cm by 180cm is used. To detect external sound frequency the tightened fiber optic itself wire netting fence with a dimension of 50cm by 50cm is used. Experiments for the detection of the excited vibration and sound signals were performed. A small vibrator induced external vibration signal and it is applied to the latticed structure in the range of 100Hz to several kHz. External sound signal applied to the fiber optic sensor net using non-directional sound speaker. The detected optical signals were compared and analyzed to the detected both accelerometer and microphone signals in the time and frequency domain. Based on the experimental results, distributed fiber optic sensor using Sagnac interferometer detected effectively external vibration and sound signal and had a good performance. This system can be expanded to the monitoring of a significant system and to the structural health monitoring system.

• 소음진동
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• 제5권2호
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• pp.169-181
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• 1995

A theoretical model has been studied to describe the sound radiation analysis for structural vibration noise control of tire under the action of random moving line forces. When a tire is analyzed, it has been modeled as a curved beam with distributed springs and dash-pots which represent the radial, tangential stiffness and damping of tire, respectively. The reaction due to fluid loading on the vibratory response of the curved beam is taken into account. The curved beam is assumed to occupy the plane y = 0 and to be axially infinite. The material of curved beam and elastic foundation are assumed to be lossless, and governed by the law of Bernoulli-Euler beam theory. The expression for sound power is integrated numerically and its results examined as a function of Mach number(M), wavenumber ratio(.gamma.) and stiffness factor(.PSI.). The experimental investigation for structural vibration noise of tire under the action of random moving line forces has been made. Based on the STSF(Spatial Transformation of Sound Field) techniques, the sound power and sound radiation are measured. The experimental results show that operating condition, material properties and design factors of the tire have a great effect on the sound power and sound radiation characteristics.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.427-430
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• 2005

The quality of various noises generated in the refrigerator is one of the important factors in deciding quality of the product. The main focus of sound control design has been shifted from reduction of sound level to improvement of sound duality for customer's preference. Up to date the purpose of noise control is the minimization of noise level. However despite of gradual decrease of noise level, occasionally the perceptional quality of noise has not been improved. In this paper, the relation between subjective and objective evaluation of sound quality has established and sound quality index is developed using ANN for evaluation of refrigerator's noise of both the starting noise and the stable running noise of compressor. To verify the usefulness of the index, the results in this paper have been compared with those surveyed by Consumer Union in USA.

• 대한기계학회논문집A
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• 제35권5호
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• pp.567-574
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• 2011

알미늄 압출재는 고속열차의 경량화를 위하여 기존의 주름강판을 대체하여 널리 사용된다. 알미늄 압출재는 고속열차 적층재 가운데 가장 큰 차음 기여도를 보이나, 동일한 중량의 평판과 비교할 때, 국부공진 주파수 대역에서 투과손실이 크게 떨어진다. 이 연구에서는 차세대 400km/h급 고속철도 차량용 알미늄 압출재를 대상으로 차음 문제를 검토하고, 차음성능의 향상 방안을 제시한다. 코어 구조를 변경시켜 국부공진 대역을 높이고, 우레탄 폼을 코어에 충진시킬 때의 차음성능 향상효과를 실험적으로 확인한다. 최종적으로 제시된 방법이 바닥 적층재의 총 투과손실을 어느 정도 개선시키는가를 평가한다.