• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.346-351
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• 2002

Noise of the VVVF inverter and DC/DC converter, which are the most dominant noise sources of maglev train at low speed, is studied, The coils inside inverter and converter are excited by electro-magnetic forces, which results in core vibration and generations of the noise. It is found that the spectra of the noise show many harmonics, where there exist several different fundamental frequencies. Some noise reducing techniques are known for the transformer noise such as changing stiffness and using different core materials, which make less electrostatic responses, and consequently less noise. In this study, it is shown that the most effective and feasible noise reducing method is to increase the switching frequencies of the inverter and converter, where peaks in higher frequency are significantly reduced.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1049-1053
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• 2007

Cogged belts get unpleasant noise when the speed is up and down. This paper investigates optimum condition for reducing a belt noise that is caused by a belt shape and properties of the material. Order tracking is used analyze belt noise. First step, the pitch length exerts an important influence on the order noise. Second step, material of belt is also important for reducing noise level. The experimental results showed the modified form and material of belts to reduce the noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.636-642
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• 2000

A method for reducing the contact noise of the Progressive Multi-Leaf Spring was investigated. It was found that the contact noise between the main and the help springs is the main source of the noise through our experiments. The conclusions from our experiments were compared with those from our numerical analysis by use of ABAQUS. The main parameters for the unexpected noise in the leaf spring were investigated through structural analysis to make describing noise generation. The contact process between the two leaves is examined by numerical calculations by ABAQUS. The noise produced by the leaf spring could be dramatically reduced by changing the shape of help spring so as to remove a translational jump of the contact point between the main and the help springs. Even with the help spring of the new proposed shape the stiffness of the whole spring did not change much.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1067-1070
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• 2003

The effects of traffic noise are a serious concern in many urban communities throughout the world. Environmental noise at high intensities directly affects human health by causing hearing loss and indirectly affects human welfare by interfering with sleep, thought, and conversation. In general, portland cement concrete(PCC) pavement is known to create more noise than asphaltic surfaces though it has the advantage of durability and superior surface. However, the results of preliminary laboratory test showed exposed aggregate concrete(EAC) have an effect on reducing traffic noise. Based on the laboratory test, pilot construction of exposed aggregate concrete was performed and series of in-situ measurements were conducted for noise analysis which included the pass-by noise measurement and the close-proximity method. Conclusively, It is expected that tire/pavement noise which is represented much noise levels at higher frequencies would be significantly reduced on special textures of pavement as like exposed aggregate concrete.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.170-175
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• 2005

In this study, experimental and theoretical methods were applied to understand brake squeal noise VVVF rolling stock on tracks. Trailer cars needed to payed a particular attention, because they were the major source of brake noise. VVVF rolling stocks for lines no 1 of the subway system in Seoul were used for experimental analyses. In order to study brake squeal noise, a dynamometer test at the S&T Brake, Co., which was a manufacturer of brake pads had performed. For measuring vibration and noise, vibration tests of brake parts (brake lining, brake lining head, back plates, etc.) at the SNUT were executed. Also, vibration tests of disc assembly and lining block at the heavy maintenance shop of the Gunja depot were performed. The modal analyses by using an ANSYS which was one of the CAE commercial program were simulated to know the relationship to the mechanism of brake noise. On the based of the tests and the simulations it was found that specific frequencies of the brake parts affected squeal noise, and improvements for reducing squeal noise were proposed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.3 s.120
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• pp.226-234
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• 2007

This study aims to evaluate noise emission from water supply and drain installations in apartment bathroom. These noise were one of the most annoying noise sources in apartment houses. Especially, drain plumbing system have used bellow bathroom ceiling, it was very discomfort to hear the noise in bellow apartment. Noise of closets and faucets were measured which were main noise source, then these noise were evaluate and analyzed the emitting characteristics varying the supplying water pressure. As increasing the water pressure, also total noise level of the water supplying stool noise and faucet noise were increased. Especially the water closet showed remarkably the increasing noise level in middle and high frequency bandwidth, while the noise level of faucets increased in $50\;Hz{\sim}250\;Hz$ of low frequency bandwidth. Vortex closet were favorable to syphon closet, and lever faucet were favorable to conventional lavatory faucet on reducing the noise. Above these results could be used in basic data establishing KS (Korean Standard) for evaluation and rating procedure and measures reducing these noise.

• International Journal of Highway Engineering
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• v.18 no.5
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• pp.31-37
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• 2016

PURPOSES : The purpose of this study is to evaluate the effect of the quiet pavement on reducing a barrier height by using a prediction tool called SoundPLAN. METHODS : Firstly, the prediction was carried out to evaluate the difference in the maximum noise level at a building facade between the normal and the quiet pavements without a barrier. After calculating the noise reduction effect by the quiet pavement, a comparable barrier height to obtain the same noise reduction effect with it was predicted according to designable factors including road-building distance(10 m, 20 m, 40 m) and road-barrier distance(5 m, 10 m, 20 m, 30 m). RESULTS : The result showed that within the considered designable factors, the maximum barrier height was 37 m, 52 m, and 55 m to have the same noise reduction effect by the quiet pavement reducing 1 dBA, 3 dBA, and 5 dBA, respectively. It was evaluated that the barrier height increased with the increase of the road-building and road-barrier distances. To simulate the real situation in urban areas and to evaluate the combined effect of the normal/quiet pavement and barrier, the barrier height was fixed as 6 m. It was predicted that the noise level would reduce to as low as 0.2 dBA by the combination of normal pavement and barrier. On the other hand, the combination of the quiet pavement and barrier reduced 1.2 dBA, 3.2 dBA, and 5.2 dBA, respectively, for quiet pavement reducing 1 dBA, 3 dBA, and 5 dBA. CONCLUSIONS : A guideline needs to be suggested to select appropriate noise abatement schemes by considering factors such as the roadbuilding and road-barrier distances.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.96-102
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• 1997

Eigenvalue analysis of vibration mode and an analysis by frequency response among the methods of predicting gear noise are related with transmitting sound of vibration. In this study we intended to reduce the vibration noise of differential gear by reducing torque fluctuation of drive pinion shaft which causes vibration noise of differential gear in rear wheel drive vehicles. For this we developed multi-degree of freedom analysis model in which mass moment of inertia and torsional spring combined and we examined the influence of torsional vibration of driveline elements by performing forced vibration analysis of engine excitation torque. We studied the methods for reducing torsional vibration of driveline according to the design factor of propeller shaft and examined the effects reducing vibration in differential gear by applying flexible coupling.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.9
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• pp.791-796
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• 2010

Installing noise barriers is the most common method for reducing the highway traffic noise to the road side residential area. After the report about edge potential concept of a noise barrier, various types of noise reducing devices(NRDs) called "noise reducers" have been suggested for getting more shielding effect on the top of highway noise barriers. But, it has been doubtful about effect of the NRDs in field because there was no appropriate and unified method to estimate the acoustic performance by using field measurement of the NRDs in Korea. In this study, the authors have considered to setup a practical method to test and estimate the acoustic performance of NRDs. For eliminating the noise reduction effect of the NRDs height itself, the source and measuring points are adjusted as highly as the NRDs height. For the frequency weighting in the estimation of the NRDs effect, the highway noise spectra were measured at asphalt and concrete road side and then averaged for a unit spectral parameter.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.702-703
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• 2014