• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.97-103
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• 2016

The sensitivity of interior noise that the passengers perceive is comparatively high in the train, and structure-borne and air-borne types of noises come into the train. In this paper, to analyze contributions of these noise sources operational transfer path analysis(OTPA) is used. OTPA has some advantages of executing the contribution rates of several sources simultaneously, and in this work, 29 points are measured while running. Transfer functions between reference measurement points and response measurement points are calculated by the singular value decomposition(SVD) and Principal component analysis(PCA) method, and the frequency characteristics of the noise source are successfully derived. Also the interior noise is predicted and compared with measurement data to show the reliability.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.667-671
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• 2012

Low frequency noises (up to about 200 Hz) mainly occur due to particular modes, resulting in booming noises, and in general the solutions may be found based on mode controls where conventional methods such as FEM can be used. However, at higher frequencies between 0.3~ 1 kHz, as the number of modes rapidly increase, radiation characteristics from structures, performances of damping sheets and sound packages may be more crucial rather than particular modes, and consequently the conventional FEM may be less practical in dealing with this kinds of structure-borne problems. In this context, so-called 'mid-frequency simulation model' based on FE-SEA hybrid method is studied and validated. Energy Transmission loss (i.e. air borne noise) is also studied. A dash panel component is chosen for this study, which is an important path that transfers both structure-borne and air borne energies into the cavity. Design modifications including structural modifications, attachment of damping sheets and application of different sound packages are taken into account and the corresponding noise characteristics are experimentally identified. It is found that the dash member behaves as a noise path. The damping sheet or sound packages have similar influences on both sound radiation and transmission loss. The comparison between experiments and simulations shows that this model could be used to predict the tendency of noise improvement.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.4
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• pp.335-343
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• 2012

As a matter of fact, it has been not allowed to modify the shape of a vehicle body skeleton since the technical definition for the structure was fixed and the corresponding molds were developed. By the way, if it is available to apply an alternative to reinforce the skeleton without changing its mold, it must be much flexible to improve the performance qualities relevant to not only NVH(noise, vibration and harshness) but also crash and durability. Recently, a solution of so-called composite body becomes available for the need. We present a design method to insert the composite body inside a vehicle body skeleton in order to improve a structure-borne noise at the idle condition. The algorithms, topology optimization and design sensitivity analysis, are applied to mainly search the sensitive structural sections in the body skeleton and to extract the target stiffness of the sections. Inserting the composite bodies into the sensitive portions, it is predicted to achieve the countermeasures which can compromize the design availability in terms of the idle noise and weight. According to the validation result with test vehicles, the concerned noise transfer function is reduced and the idle booming noise is resultantly improved.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.904-907
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• 2002

Optical disk drive device is improved in rotating speed for faster data reading. In the case of CD-ROM, rotating speed is over 10000 rpm in the practical use. As a result of high rotating speed, unexpected effects as like increasing disk fluctuation and acoustic noise are raised by the air friction on the rotating disk and the eccentricity of rotating parts. The overall acoustic noise of running CD-ROM could be classified into two different characterized noise. The first is the structural-borne noise which is generated from vibrating solid body. By the reason, the signal of structural borne noise has very similar to the signal of surface vibrating one. It has dense noise energy at specific frequency region. The other is the air-borne noise which is generated from turbulence or vortex caused by friction between disk and air. The signal of air-borne noise has no dominant peak point at acoustic pressure-frequency domain. The noise energy is widely distributed while comparatively high and large frequency region. The structural-borne noise could be reduced by reducing vibration of structure and in addition it's target reducing frequency is narrow. However the air-borne noise reduction is effectively needed of enclosing method for the noise source located near the disk surface because it is difficult to define target frequency point. In this study, the acoustic noise at driving CD-ROM is classified by the sides of it's character and tried to reduce the overall acoustic noise.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.628-635
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• 2014

The procedure to estimate the sources of noise and vibrations in a typical drum-type washing machine was presented. The sources should be identified to predict the radiated noise with computational model of structure. Source identification techniques based on singular decomposition were implemented using the measured signals of accelerometers and microphones. The finite element analysis and indirect boundary element analysis were implemented to predict the structural vibrations and the acoustic pressures at the field points. The predicted results by only structural sources were compared with those by both structural and acoustical sources. It was verified that not only the structural-borne source but also air-borne source should be considered to predict the radiated noise with better accuracy. The contribution analysis with respect to the transfer path was also preformed.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.258-264
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• 2007

Floating floors, which are mainly used for reducing interior noise levels of railway vehicle, are known to be superior to single structure in respect to sound transmission loss and vibration reduction performances. The stiffness of isolator is one of the important design variables in floating floors. From modal tests, modal properties of underframe, top floor and isolators are derived. They are used as input parameters for predicting structure-borne noise using AUTOSEA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.365-370
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• 2011

Structure-bone noise is an important aspect to consider during the design and development of a vehicle. Reduction of structure-bone noise of the compartment in a vehicle is an important task in automotive engineering. Many methods which analyze transfer path of noise have been used for structure-bone noise. The existing method to measure of frequency response function of transfer path has been tested by removing a source. This Paper presents an experimental analysis about Transfer Path Analysis of the vehicle interior noise according to Excitation or not. To identify these points of difference, experiment were conducted through an experimental test using simulation vehicle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.863-868
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• 2008

This paper investigates the abnormal noise of polygon mirror scanner motor due to the mechanical contact. In the high speed polygon mirror scanner motor the vibration of polygon mirror scanner motor is one of the main sources of abnormal noise, because structure-borne noise due to the vibration is bigger than aerodynamic noise, especially when the rotating part contacts the stationary parts. This research determines the main harmonics of structure-borne noise by using sound quality evaluation. It also develops an experimental set-up to measure the mechanical contact and vibration of polygon mirror scanner motor simultaneously. This paper also show that mechanical contact between rotating shaft and stationary sleeve is one of the dominant vibration sources of structure-borne noise which cause the abnormal noise of the high speed polygon mirror scanner motor by using the developed experimental set-up.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.596-599
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• 2008

Traditionally, tire made a role of function, which is supporting vehicle load, making brake, transferring traction, etc. But tire is a part of vehicle design, nowadays. In accordance with this market trend, customers need a wide tread design tire (i.e. low series tire). Generally low Series Tire means stiffer than general tire. That brings out increasing road noise. (Especially tire cavity resonance noise) Tire noise is divided in structure home noise and air borne noise. Tire cavity resonance noise (structure home noise) come from vibration between tire and vehicle. In the study, we investigated that tire cavity resonance noise is affected by stiffness of tread and sidewall.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.122-133
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• 1998

This paper presents the static analysis, the modal analysis and the forced vibration analysis on engine structures to find out the structure-borne noise sources by finite element method. The deformation of engine structures under the maximum combu- stion gas force was calculated through the static analysis, and the resonance possibilities were predicted by the modal analysis which ascertains mode shapes and the corresponding frequencies of engine global and its major noise sources in engine surfaces were investigated with the forced vibration analysis by means of finding the transfer mobilities on engine surfaces due to the piston impact and the velocity levels due to the combustion in consideration of oil film stiffness and damping coefficients. Finally, the direction of engine structure-borne noise reduction can be estabilished by the above-mentioned analysis procedure and the reduction effect of cost on proto-type engine build-up is expected.