• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1145-1151
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• 2007

In this paper, vibration sources of an electric forklift are identified and the forklift vibrations are reduced by structural modification. For vibration identification, vibration signals are measured by an accelerometer when the forklift is moving. These signals are presented in a waterfall plot in order to find the dependency of frequency components on the forklift speed. It is found that main vibration source is tire pattern excitation. From some experiments and finite element analyses, it is also found that resonances occur because the natural frequencies of the forklift exist in usual driving speed range. To shift the natural frequencies outside the driving speed range, the connection parts between main body and loader are modified to increase stiffness. It is verified that considerable amount of vibration are reduced by the structural modification.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1044-1049
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• 2001

Classical deconvolution methods for source identification following linear filtering can only be used if the transfer function of the system is known. For many practical situations, however, this information is not accessible and/or is time varying. The problem addressed here is that of reconstruction of the original input from only the measured signal. This is known as 'blind deconvolution'. By using Higher Order Statistics (HOS), the restoration of the input signal is established through the maximisation of higher order moments (cumulants) with respect to the characteristics of the signals concerned. This restoration is achieved by constructing an inverse filter considering the choice of the initial inverse filter type. As a practical application, an experimental verification is carried out for the restoration of our impacting signal arising in the response of a cantilever beam with an end stop when randomly excited.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.2
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• pp.108-116
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• 2014

With the increasing the importance of emotional quality of vehicle, the sound quality of systems with electric motor components has become increasingly important. Electric motors are used for windows, seats, sun roof, mirrors, steering columns, windshield wiper and climate control blowers, etc. In this paper, a study was conducted to identify sound quality factors that contribute to customer's satisfaction and preference of the window lift system. Jury test for subjective evaluation was carried out and sound quality index was developed. Averaged sound pressure level and sharpness were significant factors when glass moves down. Also, maximum loudness at stop section and averaged loudness were significant factor when glass moves up. Next, noise source identification was carried out using beam forming method during glass transferred section and impulsive noise at stop section. Several improvement methods were applied using the source identification result. And finally, the degree of sound quality improvement was judged using sound quality index.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.91-97
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• 1996

We have all heard sounds that did not sound "right" while riding in an automobile. Objectionable sounds are difficult to find and understand because the sound field is complex and dynamic in the near field of an automobile. Many different noise sources and transmission paths must be understood before an engineering change can be recommended. This paper reviews the fundamental characterization of sound and chscusses the Sound Intensity measurement technique. Sound intensity measurements locate sources and sinks of acoustic energy. Used with narrowband analysis equipment, acoustic noise sources can be identified. Sound intensity measurements are made -in-situ and do not require specmi anechoic facilities. The measurement results in a vector representation of the near field sound field and can discriminate between multiple sound sources.d sources.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.855-860
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• 2001

In this study, the improvement work to reduce the steering wheel vibration of a forklift truck is performed. The forklift truck newly developed possesses a trans-axle type power train to achieve a compact and low-price design. The forklift truck is directly subjected to a high-level engine vibration through hard mounted trans-axle housing. The engine vibration shakes the whole system of the forklift truck, and then a high level local vibration of steering wheel could not be avoided. As the results, the vibration source and path mechanisms are experimentally identified and then an improvement design is proposed to minimize the steering wheel vibration.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.839-845
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• 2003

This paper introduces multichannel blind source separation (BSS) and multichannel blind deconvolution (MBD) based on higher order statistics of signals from convolutive mixtures. In particular, we are concerned with the case that the number of inputs is the same as the number of outputs. Simulations for two input two output cases are carried out and their performances are assessed. One of the major applications of those sequential algorithms (BSS and MBD) is demonstrated through the fault signal detection from only a single measurement of rotating machine, which offers a certain degree of practicability in the engineering field such as machine health monitoring or condition monitoring.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.2
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• pp.129-136
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• 2011

The aim of this paper is to present the method of identifying the impact location on the plate. This basic research has the future purpose to achieve the human-interaction technology based on the signal processing, piezoelectric materials, and wave propagation. The present work concerning the location identification of a single impact on the plate simulated the waveform numerically generated by impact force and applied the SWFOM(sliced Wigner higher fourth order moment) to the waveform to get the arrival time differences due to impact force between three sensors attached to the plate. The simulated signal is useful to get the information for time interval for the only direct wave. This information is used the source localization by using experimental work. The measured signal is also used for source localization of a single impact based on the higher order time frequency as a novel work.

• 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.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.106-113
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• 2008

The starter motor noise is usually well identified by the customers since it is operated while the engine is quiet, and leaves distinct impressions of the vehicle. In this study the design of experiments(DOE) was applied to the identification of the noise sources of direct drive starter motor since this process usually requires lengthy analysis and elaborate experiments. In the first stage of the test, five controllable factors(alignment and dynamic unbalance of armature, tightening torques of T/bolt and center bracket bolt, and alignment of the center bracket-yoke-rear bracket), excluding static unbalance, are sorted out of all possible factors. Test results showed that the dynamic unbalance and misalignment of armature are the major factors. However, the error level of the first test was relatively high, indicating that there might be some missing major factors. In the second stage test the results showed that both static and dynamic unbalances are the dominant factors contributing to more than 80% of the overall noise, while the misalignment contributes around 12%. Error of the second test was about 4% that could be considered satisfactory. The noise level of the optimal product was predicted to be reduced by 19dBA, and verification test showed the average noise reduction of 16.8dBA with the standard deviation of 3.2dBA, and proved the usefulness of the whole DOE process.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.348-353
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• 2012

This paper presents the HRTF based experimental approach to figure out why the human auditory perception on the interior noise source including the directional tonal components does not well match with the dominant features extracted from recorded acoustic signals in terms of psycho-acoustics. Since the general objective evaluation models for tonalness among various sound attributes are a function of width, frequency, excessive level of tonal components respectively, the directional tonal components cannot be properly evaluated without considering the effects of head-related transfer function on the binaural auditory perception. Thus, the directivity of source is additionally considered to prevent the erroneous conclusions from the same sound source in the process of source identification. The signal synthesis technique is used to solve a little difficulty in measuring all of desired acoustic signals for jury evaluation. The sound attributes of synthetic acoustics signals are analyzed to roughly predict the results of jury evaluation in advance by using sound quality factors such as loudness, sharpness, roughness, fluctuation strength and tonality. The jury evaluation is carefully conducted based on the recommended guideline suggested by N. Ottoet al. Each sound is respectively evaluated by selecting a value between -2 and 2 in intervals of 0.2 point. Through above procedure, based on the results of jury evaluation, it is confirmed that serious problems can be caused in the process of analyzing the dominant sound attributes in terms of psycho-acoustics according to the type of a microphone and a playback system.