• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.483-488
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• 2008

The exhaust system, including a muffler, is one of the major sources to generate the radiated noise of construction equipment. In general, the muffler is applied to construction equipment in order to reduce the exhaust noise. Sometimes, however, the higher exhaust noise can be experienced due to the flow effect inside a muffler. So, it is required to consider the flow effect to reduce the exhaust noise level of construction equipment. In this paper, various tests were performed to calculate the flow noise effect inside a muffler. Through a series of tests with respect to a variety of design parameters, a new design program for low noise muffler was developed and applied to reduce the exhaust noise of the construction equipments. These results make it possible to understand the dynamic characteristics of the flow noise and to design the low noise muffler for the construction equipments.

• Proceedings of the KSR Conference
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• 1999.11a
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• pp.487-494
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• 1999

The object of this study is to reduce the subway noise by the low noise wheel. The vibro-acoustic reduction was predicted from the FRF difference between low noise wheel and solid wheel by experimental modal analysis. The low noise wheel and solid wheel were compared in viewpoint of car interior/exterior noise. The effect of low noise wheel on the noise of subway train of 6 vehicles was obtained. But, the application of low noise wheel must be reviewed in some aspect.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.326-329
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• 2002

Engine noise is one of the major causes of the interior noise, and so has been studied in various ways in recent days. Recently Intake noise has been extensively studied to reduce the engine noise. Conventional method to reduce the noise is adding several resonators to the induction system. However this causes a reduction of engine output power and an increase of fuel consumption. In this study, the prototype of Active Intake Noise Control System is developed by using the Filtered-x LMS algorithm to reduce the Intake noise during acceleration. Intake noise is more excessively increased when the engine is rapidly accelerated. So, Normalized LMS algorithm is applied to improve the control performance under the rapid acceleration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.862-867
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• 2000

The auxiliary engine exhaust noise in ships are directly transmitted to bridge wing with the only distance attenuation. It is not so practical that no special treatment can be applied between exhaust pipe and bridge wing in order to reduce the transmission of the exhaust noise. In general, a silencer is fitted to reduce the exhaust noise and also noise of bridge wing. The silencer should be properly designed under the consideration of the frequency component of the exhaust noise and the required insertion loss. In this paper, the frequency component of exhaust noise of various engines are compared and a design and a design and installation of silencer to reduce low frequency is introduced.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1998.06a
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• pp.745-749
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• 1998

Mathematical morphology (MM) has been introduced as a powerful tool for studying the geometrical properties of images, MM is a good approach to digital image processing , which is based on the shape feature. The MM operators such as dilation, erosion, closing and opening have been applied successfully to image noise reduction. The MM filters can easily filter the noise when the noise factors are known. However it is very difficult to reduce the noise when images are ambiguous, because the boundary between the noise and object is vague. In this paper, we propose a new method to reduce noise from ambiguous images by using Fuzzy Mathematical Morphology (FMM) operators. Performance evaluation via simulations show that the FMM filters efficiently reduce the image noise. Furthermore, the FMM filters show a good performance compared with the conventional filters.

• Journal of Biosystems Engineering
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• v.20 no.2
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• pp.127-132
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• 1995

In the first part of this paper, an analysis of the cab noise of a selected agricultural tractor was presented. In this study, using the results of the previous analysis, two passive noise control measures of the sound insulation and absorption were conducted to reduce the noise level inside the cab. These measures of noise control reduced the total noise level by 6.2㏈(A) at the operator position inside the cab. In order to further reduce the cab noise, particularly, of lower frequencies than 630Hz, stiffness and damping of the floor panel should be enforced. It was also suggested that a proper suspension for the cab mounting is necessary to reduce the level of structure-born noises.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.2
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• pp.324-330
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• 2013

The dispersion of acoustic noise during the turn-on and turn-off switching of HEV(hybrid electric vehicle) relay was experimentally analyzed to identify the reason for the dispersion of noise level. An effective method was proposed to reduce the dispersion of noise level. First, a method to wrap the side of moving core with a tape was adopted to reduce the transverse vibration. It enabled the moving core to make a consistent motion and reduce the dispersion of noise level from switching operation of relay. Second, the dispersion of noise level from vibration transmission of parts such as the outer frame and yoke caulking part of relay were tested to find out main sources. From this result, it was identified that the yoke caulking part made inconsistent transient vibration and noise dispersion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.367-370
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• 2005

This paper investigated the sound characteristics in an apartment complex. The field measurement was conducted in order to examine the acoustical characteristics of the apartment complex in situ. As a result, it shows that there are around 3 sec. reverberation time and the additional sound reinforcements at the area of high height due to the surrounded buildings. Thus, 1:50 Scale model measurement and Raynoise computer simulation were carried out with insertion of the parapet and the canopy on the balcony. In case of a single building, the parapet was effective to reduce noise level at low floor levels, and the canopy was effective to reduce noise level at high floor levels. But it also shows that both the parapet and the canopy were not effective to reduce noise level at middle floor levels. In case of an apartment complex, the canopy was less effective to reduce noise level at each floor in comparison with case of the single building.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.633-638
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• 2002

The vacuum cleaner that has no dust bag generates very high level annoying noise. The dominant noise source is the 2$\^$nd/ BPF tone of the rotating impeller. In order to reduce the noise, we identify the acoustic characteristics and reduce the noise of the vacuum cleaner and centrifugal fan. The resonance phenomenon is observed in blade passages and we found out that the resonance frequency is very close to the 2$\^$nd/ BPF. In order to reduce this high-level peak noise, new impeller is designed in this paper. The trailing edge of new impeller is inclined and this makes the flow interactions between the rotating impeller and the stationary diffuser vane occurs with some phase shift. The performance of new impeller is similar to the old one but the overall SPL is reduced about 3.6dBA. The SPL of BPF is reduced about 6dBA and 2$\^$nd/ BPF is reduced about 20dBA. The vacuum cleaner, which uses newly developed centrifugal fan, generate more comfortable noise than the old model and the strong tonal sound was dramatically reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.764-769
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• 2004

The DC Motor in a vehicle may cause noise and vibration because of high speed revolution, which can make a driver feel uncomfortable. There have been various studies attempting to solve these problems, focusing mostly on the causes of and ways to reduce noise and vibration. It is suggested that the noise in a DC Motor may be primarily due to interaction between a brush and a commutator. Brush noise, the most common noise in a DC Motor, results from a brush bounced from the surface of the commutator, fluctuation of the friction between the brush and the commutator, and the impact on the brush when passing over slots of the commutator. Based on the noise test, one of the most important design parameters was shown to be the roundness of the commutator. As the DC motor is used, the roundness of the commutator gets bigger with subsequent increase of the level of brush noise and vibration. There must be a threshold in order to prevent the brush noise from getting worse. Using the method of CAE is more efficient than the real test for purposes of looking for various design parameters to maintain the roundness of the commutator. In this study, the design process to reduce the brush noise is presented with the use of a computer model. The design parameters to reduce the brush noise and vibration are proposed by using FEM. The design parameters are used to reduce the noise and vibration of a DC motor and it is verified with the test results on a fan DC motor in a vehicle. This method may be applicable to various DC motors.