• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.39-45
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• 2005

The aim of this research is to predict the thickness and loading noise of the round-tip shaped Hartzell propeller currently used in the general aviation aircraft. Before implementing the noise analysis, the pressure distribution on the propeller was obtained by using the free wake panel method and unsteady Bernoulli's equation. The noise signal at observer position can be obtained by using the FW-H equation. The noise prediction results for the propeller indicates that the thickness noise has s symmetric directivity pattern with respect to the tip path plane, while the noise due to loading shows higher noise directivity toward downstream than the upstream direction from the rotor plane. The loading noise is dominant rather than the thickness noise in normal operating condition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.353-358
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• 2013

Present paper deals with turbulence-airfoil interaction noise and mainly investigates the effects of airfoil thickness on the broadband noise spectrum. The acoustic power radiation from an airfoil is predicted using high-order time-domain method, which is based on the computational aeroacoustic technique solving the linear Euler equations. The homogeneous and isotropic turbulence is generated by utilizing the synthetic turbulence modeling based on random particle method. The airfoils taken into consideration are a flat-plate and a NACA0012 airfoil aligned with uniform mean flow. The effects of airfoil thickness on the radiated inflow turbulence noise are investigated by comparing acoustic power spectrum predicted for each airfoil. The comparison of acoustic power spectrum reveals that the airfoil thickness significantly contributes the high frequency noise reduction.

• Journal of Radiation Industry
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• v.11 no.3
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• pp.151-155
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• 2017

MDCT is used to determine how the noise changes as the slice thickness changes. Noise according to thickness of 1.5, 3.0, 5.0 and 10.0 mm was analyzed using the Siemens (Somatom Definition Flash, Germany) equipment and calibration conditions such as tube voltage and tube current using the calibration QC phantom. 1.5, 3.0, 5.0 and 10.0 mm, respectively. The mean HU was 1.5 mm (7.7 HU), 3.0 mm (4.9 HU) and was reduced by 59.5% from 1.5 mm. 5.0 mm (3.9 HU) and 97.6% compared to 1.5 mm, 10.0 mm (3.1 HU) and 148% less than 1.5 mm. It was found that as slice thickness increased, noise decreased, while slice thickness decreased. In conclusion, setting the appropriate slice thickness for each site may be useful for obtaining appropriate noise and image quality.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.04a
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• pp.403-407
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• 2009

It is reported that the heavy weight floor impact noise of a slab system is very sensitive to the location of microphone and impact load. In addition, it is known that the aspect raio, thickness and boundary condition of a slab also have great effect on the noise induced by impact load. However, the effect has been mainly evaluated by experimental test and numerical analysis is nearly performed to verify the effect quantitatively. In this study, the effect of the aspect ratio, thickness and boundary condition on the heavy weight floor impact noise is examined through numerical analysis for simple rectangular slab system. The results show that the thickness and boundary condition have a strong correlation with the noise of the slab, on the contrary, the aspect ratio has little relation with the noise.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.520-525
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• 2003

Supersonic jet issuing from a nozzle invariably cause high-frequency noises. These consist of three principal components ; the turbulent mixing noise, the broadband shock-associated noise, and the screech tone. In present study, it was experimentally investigated to the effect of nozzle lip thickness on the characteristics of supersonic jet noise. The convergent-divergent nozzle of a design Mach number 2.0 was used in experiment. With three different nozzle-lip thicknesses, the jet pressure ratio was varied in the range between 2.0 and 12.0. Acoustic measurements were conducted by microphones in an anechoic room, and the major structures of the supersonic jets were visualized by a Schlieren optical system to investigate the effect of nozzle lip thickness. The measured results show that the characteristics of supersonic jet noise, such as overall sound pressure level (OASPL) and screech frequency, strongly depend upon the thickness of nozzle-lip.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1463-1466
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• 2007

Visco-elastic damping material for reducing heavy-weight floor impact noise and vibration in reinforced concrete structures was tested according to its thickness in the damping layer. The effect of damping material was compared with 20, 15, 10 and 5mm thickness. The wave propagation characteristics was measured for suggestion of an efficient method to reduce the floor impact noise. The method was proposed using the flexural wave propagation characteristics. The result showed that reduction of the thickness of damping layer made a slight difference; the natural frequency moved to higher frequency and the amplitude increased at low frequencies with 5mm thickness of damping material.

• Journal of radiological science and technology
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• v.44 no.4
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• pp.327-333
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• 2021

Magnetic resonance imaging(MRI) uses strong magnetic field to image the cross-section of human body and has excellent image quality with no risk of radiation exposure. Because of above-mentioned advantages, MRI has been widely used in clinical fields. However, the noise generated in MRI degrades the quality of medical images and has a negative effect on quick and accurate diagnosis. In particular, examining a object with a detailed structure such as brain, image quality degradation becomes a problem for diagnosis. Therefore, in this study, we acquired T2 weighted 3D data of multiple sclerosis disease using BrainWeb simulation program, and used quantitative evaluation factors to find appropriate slice thickness among 1, 3, 5, and 7 mm. Coefficient of variation and contrast to noise ratio were calculated to evaluate the noise level, and root mean square error and peak signal to noise ratio were used to evaluate the similarity with the reference image. As a result, the noise level decreased as the slice thickness increased, while the similarity decreased after 5 mm. In conclusion, as the slice thickness increases, the noise is reduced and the image quality is improved. However, since the edge signal is lost due to overlapped signal, it is considered that selecting appropriate slice thickness is necessary.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.11
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• pp.1222-1230
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• 2009

A theoretical model was developed to compute the effect of a bubble layer in reducing the radiation noise generated by a force applied on an infinite flat plate considering the noise of multi-bubbles. Using the model, the effectiveness of a bubble layer in reducing the structure-borne noise of the plate was evaluated to consider various parameters such as the source noise levels, the thickness of bubble layers, the volume fractions and the frequency characteristics of bubbly fluids. Considering the noise of multi-bubbles, the actual reduction effect of radiation noise using a bubble layer was expected in cases of high source levels, high volume fractions of bubbles and large thickness of the bubble layer above the resonance frequency of the bubble layer. Accordingly, it is recommended that the thickness of a bubble layer, the source noise level and the characteristics of bubbly fluids should be optimized cautiously to maximize noise reduction effects.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1347-1354
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• 1994

This paper deals with the experimental research, including measurement and analysis and field survey, on the causes of occurring noise defective gear boxes in hoist production plant in order to reduce the fraction of their occurrence. In this reserch following investigations are performed : measurement and gear-boxes, examination of each machining process of production, measurement and analysis of dimensional accuracy of each part, comparative vibration test with exchanging inaccurate parts. From these investigations, it is found that the machining accuracy of pinion gear tooth thickness is the most sensitive factor of noise problem. By maintaining the tooth thickness error within 0.05 mm tolerance in the gear cutting process, the fraction of noise defective gear-boxes are greatly reduced to less than 2%, where the usual rate of it has been 20-50%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.849-854
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• 2001

A study on performance of the sound absorbing noise barrier is presented. Noise barrier of sound absorbing type is composed of the front panel, sound absorbing material, and back panel. For allowing sound path, front panel is usually perforated. The performance of the noise barrier is governed by the opening ratio of the perforated panel, sound absorption coefficient of the sound absorbing material. In this study, the effects of the opening ratio, diameter of the hole, thickness of the sound absorbing material are investigated. It is found that the thickness of the sound absorbing material must be at least 50 mm to ensure the required minimum NRC value 0.70, and the opening ratio is greater than 0.2. It is shown that the thickness of the back panel is crucial in providing required STL (Sound Transmission Loss) value. The performance of the developed noise barrier is measured, where its sound absorbing coefficient and sound transmission loss satisfy the criteria.