• International Journal of Railway
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• v.4 no.1
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• pp.19-27
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• 2011

Many studies for improving the railway vehicle's performance and comfort such as speed, weight and noise are currently in progress. Improving the structural characteristics of the vehicle for greater noise insulation is considered important for reducing disturbance due to noise, but measuring transmission loss entails large costs. This study explores an alternative method for estimating and measuring the railway vehicle's transmission loss that involves on applying the numerical analysis coupled with scaled reverberation chamber measurement. The transmission loss measurement using scaled reverberation chamber was performed after the compensation value was found through 1mm thickness(1t) specimen. For numerical analysis, a commercially available acoustics solver VA ONE was used. The proposed method is found to lead to transmission loss measurement comparable to the measurements based on large-scale reverberation chamber. Thus, it can be argued that a reliable method has been developed for measuring railway vehicle's transmission loss.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.1067-1071
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• 2004

In this paper, the characteristic of the regenerative pump is reviewed by the measurement and the analysis. The dominant noise sources are harmonic components of the rotating impeller frequency. The acoustic characteristics and the noise source position at the dump are identified. In order to reduce the high-level peak noise, the interior flow of the pump chamber is analyzed by CFD (Computational Fluid Dynamics). Acoustic pressure is calculated with Ffowscs Williams and Hawkings equation. As the result of the analysis new design of the pump chamber is recommended. The recommended pump is compared with original pump by evaluating the RMS value of a interior static pressure and the sound pressure level. The new pump chamber recommended by analysis results is proved by a process of the measurement. The overall SPL of a recommended pump is reduced about 3 dBA.

• Journal of Environmental Impact Assessment
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• v.20 no.6
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• pp.787-795
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• 2011

Noise barrier is generally used with welding of joint rail for railway noise reduction in our country. But the noise barrier for high speed railway has weak point in low frequencies about 315Hz band. In this study, For developing of Interference-type Noise Reduction Device(INRD), acoustic analysis were performed using commercial software. For verifying the improvement in the noise reduction, noise measurement before and after installing of INRD were performed in Anechoic Chamber. From these acoustic analysis and noise measurement, it was known that developed INRD has a good noise reduction performance and can be used efficiently with conventional noise barrier.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.790-795
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• 2004

The characteristics of refrigerator noise recorded in anechoic chamber was investigated in condition of a the real living room and a kitchen. To predict the noise propagation in an apartment unit, room acoustic simulation software was used. It was found that the noise level in the real living room was $4\sim8dB$ higher than in the anechoic chamber. When a noise barrier and absorption materials were used on the rear wall and floor, the noise level reduced up to $3\sim4dB$. In addition, when the subjective evaluation of auralized refrigerator noise was undertaken using headphone, it was revealed that 21dB (A) is the allowable sound pressure level of 95% satisfaction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1376-1378
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• 2006

Numerical and experimental study were carried out to characterize sound fields of low frequency in a scaled reverberation chamber for measurement of sound insulation of panels. By using BEM, lower modes of the chamber are identified and then predicted the effect of diffusers in order to destruct lower modes. Compared results with measurements show reasonable agreements, especially at the first end second modes. Based on numerical prediction, the diffuser are installed in order to improve sound fields to be more diffuse than ever. It is found that the diffuser put in nodal line of the chamber destruct evidently the first mode. Consequently, the measuring error at the low frequency can be relatively reduced compare to the case of without diffuser.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.383-386
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• 2003

This paper deals with transmission loss of 3-dimensional rectangular plenum lined chamber. There are three kinds of rectangular plenum lined chamber: throughflow type, flow-reversal type, and end-in/side-out type. The combination of above three types of rectangular plenum lined chamber is used for the commercial HVAC system and automobile exhaust system. However, the ambiguity and complexity of sound absorbing material property and 3-dimensional property have impeded research. In this paper, the transmission loss of three kinds of rectangular plenum lined chamber is derived and calculated. The effect of increase of sound absorbing material is also considered. Analytical solution is calculated by using the locally-reacting property of sound absorbing material.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.2
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• pp.28-33
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• 2008

In a scanning electron microscope (SEM), outside acoustic noise causes image noise that distorts observations of the specimen being examined. A SEM that is less sensitive to acoustic noise is highly desirable. This paper investigates the image noise problem by addressing the mode shapes of the base plate and the transmission path of the acoustic noise and vibration. By arranging the position of the rib, a new SEM base plate was developed that had twisting as the 1st and 2nd modes. In those two twisting modes, vibration nodes existed near the center of the base plate where the specimen chamber is placed. Less vibration was transmitted to the chamber and to the specimen by the twisting modes compared to bending ones, which are the 2nd and 3rd modes for a rectangular plain base plate. An SEM with the developed base plate installed exhibited a significant reduction of image noise when exposed to acoustic noises below 250 Hz.

• Journal of the Korea Safety Management & Science
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• v.22 no.2
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• pp.15-21
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• 2020

Industrial facilities need design to predict and reduce noise from design to prevent and reduce noise. The purpose of this study is to predict worker's environment and evaluate safety by analyzing noise inside underground blower room and air compressor room with fluid machinery in waste facility. This waste incineration facility was analyzed based on the ground floor, ground floor blower chamber, and air compressor chamber. The results of SPL(Sound Pressure Level) analysis at 1.5m away, which are frequently used to measure the SPL as a noise source, are as follows. SPL of basement level: 46.80[dB], SPL of ground layer: 48.57[dB]. As a result, it was expected that the noise level would be considerably lower than the 8 hours 50[dB] noise exposure per day.

• The Journal of the Acoustical Society of Korea
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• v.8 no.1
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• pp.59-66
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• 1989

This study aims to provide the basic data useful in assessing indoor-noise and designing sound devices in office buildings of HVAC system. The measurements of HVAC noise were carried out in office room and mechanical room. The performance of absorptive chamber and side branch was also estimated in the office buildings which have HVAC noise problems. The results of experiments show that the NR value of indoor HVAC noise is rather higher than that of ISO recommendations at the frequencies below 500Hz. In addition, the results indicated that the absorptive chamber attenuates noise over broad band frequencies and side branch reduces noise at the special resonant frequency.

• The KSFM Journal of Fluid Machinery
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• v.9 no.6 s.39
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• pp.54-62
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• 2006

An experiment about performance characteristics is conducted on a double chamber vane-type rotor. Three different rotors, which have 6, 8 and 9 vanes, are applied to the driver and various lift holes at the rear plate are used to increase the effective vane height. The inner diameter of a double chamber cylinder is ${\phi}27mm$, and the length of the cylinder is 65 mm. The maximum offset length between the rotor outer surface and the cylinder inner surface is 4.5 mm. In this study, specific output torques and powers are measured, and also noise and vibration are measured at the real operating situation. The operating torque on the double chamber is increased to 17% compared to the operating torque obtained at the single chamber which has the same size. The experimental results of noise and vibration show that the operating sound and vibration are directly related to the operating power generated by the double chamber rotor.