• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1015-1020
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• 2004

The road traffic noise becomes aggravated due to the rapid increase of vehicles. It has a great effect on the dwelling environment. Therefore we investigate the characteristics and sources of the road traffic noise through grasping the status of the road traffic noise. This paper is concerned with the description of the various factors affecting the generation and propagation of outdoor traffic noise. It is particularly concerned with the mathematical interpretation of these processes and the resulting development of prediction techniques which are now broadly used for both the environment impact assessment of road traffic noise and the planning and design of roads and adjoining land use.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.557-563
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• 1997

In order to satisfy the regulations concerned with the noise emission of fork-lift trucks and thereby increase export to the western countries, a noise reduction technique should be developed in the early design stage. In this paper, several noise sources are identified using the sound suppression method and sound intensity measurement, and their contributions to the sound levels at the operator's ears and at the distance of 7m from the vehicle are studied. For each of the major noise producting components, noise abatement alternative are suggested and their effects are analyzed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.946-950
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• 2006

This paper proposed the ways for reduction of the prominent peak of the tone noise in air conditioning units. In order to find out the sources of the tone noise, the resonant frequencies and modes of the fans were investigated. Also, the effects of the ambient temperatures and material properties of the fans on the tone noise were studied. From the experiments, it was shown that the tone noise was greatly influenced by the torsional resonance of the fan and motor system and commutation frequency. In other words, the torsional resonance of the fan and motor system has not to be close to the commutation frequency (torque ripple frequency) which creates a rate of change in the angular acceleration in order to reduce the tone noise in air conditioning units.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.208-213
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• 2003

The purpose of this study is to review the use of a new standard impactor, the impact ball, in evaluating heavy-weight impact noises in reinforced concrete structures. A survey revealed that children running and jumping are the major heavy-weight impact sources in multi-story residential buildings. The noise from the impact ball was measured and psychoacoustically assessed. The relationship between the noise levels and the subjective responses was also investigated. Results showed that the noise from the impact ball is similar to the noise of children running and jumping. It was also found that the noise level of the impact ball is slightly higher than the noise level of a bang machine, although the impact ball has a lower impact force.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.21-32
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• 2004

The non-cavitating noise of underwater propeller is considered numerically in this study. The main purpose is to analyze non-cavitating noise from underwater propellers in various operating conditions with different configurations. Noise is predicted by using time-domain acoustic analogy, boundary element method, and computational hydro-acoustics. The flow field is analyzed with potential-based panel method, and then time-dependant pressure data are used as the input for Focus Williams-Hawkings formulation to predict far field acoustics. Furthermore, boundary element method and computational hydro-acoustics are also considered to investigate duct propeller and ducted multi-stage propeller to consider the reflection and diffraction of sound waves. With this methodology, noise intensity and directivity of each noise sources could be well analyzed.

• Journal of the Korean Society of Safety
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• v.26 no.4
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• pp.20-26
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• 2011

This paper is to investigate noise source for reciprocating type air compressors. The reciprocating type air compressors are widely used in the small and medium sized enterprise and many employees are affected and irritated by their noise during working. The investigation and analysis of the noise source were made according to the ISO 1680/1 and MIL-STD 7410-1 and noise evaluation of each part of compressors was made. Noise emitted from the intake and exhaust valve and the air receiver tank were dominant compared with those from other parts of compressor. Noise from the motor and the revolution of crank mechanism was negligible relatively with the noise sources as mentioned above.

• Journal of the Korean Society of Safety
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• v.26 no.5
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• pp.23-26
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• 2011

The aim of this paper is to evaluate noise characteristics of an electric power driven hammer. These investigation and analysis were made according to the ISO 1680/1 and MIL-STD 7410-1 and lead-wrapping experiment method that was used to identify the principal noise sources and analyze its noise. Hammer generates loud noise and it irritates and affects many people. Repeated exposures to loud noise can lead people to permanent hearing loss. Based on the contribution analysis, we confirm that the striker part is a major noise source and it has directional noise radiation pattern, which is left and right.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.866-869
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• 2004

Power transformers, air-intakes and stacks in the urban combined power plant are main noisy sources. Because of Inhabitant complaint by abnormal noise transferred from the power plant. the noise was investigated at power plant and uptown area. The result of diagnosis made the acoustic resonance phenomenon by 580Hz's combustion dynamic pressure with the standing wave mode of sound fields in exhaust passageway of gas turbine into main noise source of public complain. The abnormal noise is caused by the resonance exhaust noise transferred through stacks of power plant.

• Journal of IKEEE
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• v.18 no.4
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• pp.625-629
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• 2014

This study derives the asymptotic phase noise formula of the oscillators perturbed by the colored noises. Based on the derived formula, this study presents a sub-1V series-tuned differential Colpitts VCO. The ADS simulation result on the phase noise shows that the presented VCO exhibits about 3dBc/Hz lower phase noise at the 1MHz offset frequency from the oscillation frequency of 4.8GHz than the existing series-tuned differential Colpitts VCO with the inductor current sources.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.433-437
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• 2015

We show the results of a time series analysis of the long-term light curves of four blazars. 3C 279, 3C 345, 3C 446, and BL Lacertae. We used densely sampled light curves spanning 32 years at three frequency bands (4.8, 8, 14.5 GHz), provided by the University of Michigan Radio Astronomy Observatory monitoring program. The spectral indices of our sources are mostly flat or inverted (-0.5 < ${\alpha}$ < 0), which is consistent with optically thick emission. Strong variability was seen in all light curves on various time scales. From the analyses of time lags between the light curves from different frequency bands and the evolution of the spectral indices with time, we find that we can distinguish high-peaking flares and low-peaking flares according to the Valtaoja et al. classification. The periodograms (temporal power spectra) of the light curves are in good agreement with random-walk power-law noise without any indication of (quasi-)periodic variability. We note that random-walk noise light curves can originate from multiple shocks in jets. The fact that all our sources are in agreement with being random-walk noise emitters at radio wavelengths suggests that such behavior is a general property of blazars. We are going to generalize our approach by applying our methodology to a much larger blazar sample in the near future.