• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.851-856
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• 2012

Automotive turbochargers have become common in gasoline engines as well as diesel engines. They are excellent devices to effectively increase fuel efficiency and power of the engines, but they unfortunately cause several noise problems. The noises are classified into mechanical noises induced from movement of a rotating shaft and aerodynamic noises by air flow in turbochargers. The mechanical noises are whine and howling noises, and the aerodynamic noises are BPF (blade-passing frequency), pulsation, surge, some special frequency noises. These noises are bothering passengers because their levels are higher or their frequencies are clearly separated from engine or vehicle noises. The noise investigated in this paper is a BPF noise induced by compressor wheels, whose frequency is the multiplication of the number of compressor wheel blades and its rotational speed. The noise is strongly dependent upon the geometry of wheels and the number of blades. This study tried to apply a groove close to the inlet side of compressor wheels in order to reduce the BPF noise. The groove has successfully reduced the noise of narrow band frequency of a turbocharger. It shows that the groove could reduce the wide band frequency noise, the compressor BPF noise with a best shape of the groove.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.10 s.115
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• pp.1005-1013
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• 2006

A survey and auditory experiment on multiple residential noises such as floor impact, airborne, bathroom, drainage and traffic noises were conducted to develop a combined rating system and to establish criteria for multiple residential noises. Subjective reactions such as annoyance, activity disturbance, sleep disturbance, and satisfaction to overall noise environment and each residential noise were recorded. The effect of individual noise perception on the evaluation of the overall noise environment was also investigated. The survey results showed that satisfaction for floor impact noise most greatly affects the overall satisfaction for overall noise environment and annoyance most greatly affects the satisfaction for individual noise sources. Auditory experiments were undertaken to determine the percent satisfaction for individual noise levels. Result of auditory experiment showed that the noise level corresponding to 40 % satisfaction is 49 dB $(L_{i,Fmax,AW})$ for floor impact and is about 40 dB(A) for airborne, drainage and traffic noise. From the results of the survey and the auditory experiments, an equation for predicting the overall satisfaction for multiple noises was developed and a classification of multiple residential noises was proposed.

• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.134-138
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• 2005

The crosstalk noise of thick holographic photopolymer is studied. Three different experiments, (1) reading area dependency (2) post-exposure effect (3) effect of later recorded holograms on earlier recorded holograms, have been accomplished and a tendency of crosstalk noises has been found for each case. The larger reading area, the higher crosstalk noises fur the later recorded holograms. Before the post-exposure the crosstalk noises are higher in the earlier recorded holograms, but after the post-exposure the crosstalk noises we higher in the later recorded holograms. The crosstalk noises of the earlier recorded holograms become higher as more holograms are recorded by multiplexing. To explain the tendency of crosstalk noises of these experiments, we suggest a model considering the anisotropic shrinkage of the photopolymer According to the model. the shrinkage is more dominant at the center of the recorded region than the edge of that. After the post-exposure, however, the amount of shrinkage becomes the same far the whole recorded region. The results of all three experiments are well explained by this model.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.1
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• pp.28-34
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• 2017

The vehicle stabilizer link is one of the suspension components that reduces the bumping and rolling during vehicle driving. However, this stabilizer link could be a source of the abnormal noises when its free gaps have higher than normal values. Therefore, the current study aims at investigating the quantitative relationships between the abnormal noises and free gaps of the vehicle stabilizer links, as well as the length of time that the vehicle stabilizer links could be used without generating abnormal noises. In this study, the abnormal noises were measured based on the magnitude of the stabilizer link vibration, while the free gaps were quantified through the force-displacement curves of the stabilizer links. Harsh durability tests were also conducted in order to quantify the operating cycles of the stabilizer links before generating the abnormal noises, along with the concomitant measurements of the free gaps. The current results showed that the abnormal noises of the stabilizer links were detected when its free gaps were larger than 0.12 mm. However, the free gaps of the stabilizer links, which are bigger than 0.1 mm, produced the abnormal noises at 1.5 million cycles under harsh durability test conditions. A parametric study in the future that would reflect the different shapes and sizes of the stabilizer links for diverse vehicles could determine more generalized relationships between the abnormal noises and free gaps of the vehicle stabilizer links.

• Nuclear Engineering and Technology
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• v.31 no.2
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• pp.192-201
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• 1999

This paper proposes an improved signal processing strategy for accurate feedwater flowrate estimation in nuclear power plants. It is generally known that ∼2% thermal power errors occur due to fouling Phenomena in feedwater flowmeters. In the strategy Proposed, the noises included in feedwater flowrate signal are classified into rapidly varying noises and gradually varying noises according to the characteristics in a frequency domain. The estimation precision is enhanced by introducing a low pass filter with the wavelet analysis against rapidly varying noises, and an autoassociative neural network which takes charge of the correction of only gradually varying noises. The modified multivariate stratification sampling using the concept of time stratification and MAXIMIN criteria is developed to overcome the shortcoming of a general random sampling. In addition the multi-stage robust training method is developed to increase the quality and reliability of training signals. Some validations using the simulated data from a micro-simulator were carried out. In the validation tests, the proposed methodology removed both rapidly varying noises and gradually varying noises respectively in each de-noising step, and 5.54% root mean square errors of initial noisy signals were decreased to 0.674% after de-noising. These results indicate that it is possible to estimate the reactor thermal power more elaborately by adopting this strategy.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.132-135
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• 2000

In this paper, we propose to exploit a multi-code CDMA scheme for power line communication (PLC) systems, and its performance on non-Gaussian impulse and harmonic noises is presented. The proposed multi-code CDMA scheme utilizes convolutional coding and block interleaving to combat with the non-Gaussian noises, and simulation results indicate effective alleviation of these noises, and thus significant bit error rate improvement by the proposed scheme even under strict restriction of frequency band allowed in PLC systems.

• 전기의세계
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• v.22 no.4
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• pp.17-24
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• 1973

In the view point of practical engineering the identification problem may be considered as a problem to determine the optimal model in the sense of minimizing a given criterion function using the input-output records of the plant. In the system identification the statistical approach has been known to be very effective when the topological structure of the system and the statistical characteristics of the observation noises are known a priori. But in the practical situation there are many cases when the inforhation about the observation noises or the system noises are not available a priori. Here, the authors propose a new identification method which can be used effectively even in the cases when the variances of observation noises are unknown a priori. In the method, the identification of unknown parameters of a linear diserete system is achieved by minimizing the improved quadratic criterion function which is composed of the term of square equation errors and the term to eliminate the affection of observation noises. The method also gives the estimate of noise variance. Numerical computations for several examples show that the proposed procedure gives satisfactory results even when the short time observation data are provided.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.666-669
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• 2005

Social noise survey and auditory experiment on residential noises such as floor impact, air-borne, bathroom, drainage and traffic noises were conducted to classily a noise insulation Performance in apartment building. The survey results showed that annoyance among subjective responses to residential noises was most greatly affecting to satisfaction with noises. In the survey, boundary limit between satisfaction and dissatisfaction was also determined. Auditory experiments was also undertaken to determine noise insulation performance according to the percent of satisfaction for individual noise source. Result of auditory experiment showed that the noise insulation performance for floor impact, airborne, drainage and traffic noise corresponding to 40 % satisfaction is 49 dB (L$_{i,Fmax,AW}$), 48 dB (R'w), N-41, and N-40, respectively. Finally, classes of noise insulation performance in apartment building were proposed according to satisfaction with noises

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.8 s.101
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• pp.904-910
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• 2005

A 7-point verbal noise annoyance scale for residential noises was developed in this study. An auditory experiment using major residential noises such as air-borne, bathroom drainage, and traffic noises was conducted to develop a noise annoyance scale for rating residential noises and allowable limit of them. The modifiers used in the scales were selected according to the method proposed by ICBEN(international commission on the biological effect of noise) Team 6. Results showed that the intensity of the selected words in the 7-point noise annoyance scale was highly correlated with noise levels. and that the intensity difference between each pair of successive levels in the 7-point annoyance scale was almost identical. The allowable limit of residential noise was also investigated in the auditory experiment and that of airborne, drainage and traffic noises were 42.3 dB(A), 41.0 dB(A) and 42.7 dB(A), respectively.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.3
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• pp.395-403
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• 2014

This paper presents a new approach to improve the signal to noise ratio (SNR) for local seismic disaster preventing system in densely populated area. The seismic data measured in the local site includes various sensing noises (offset or measurement noise) and man-made/natural noises (road and rail traffic noise, rotating or hammering machinery noise, human activity noise such as walking and running, wind/atmospheric pressure-generated noise, etc.). These additive noises are different in time and frequency characters. The proposed method uses 3-stages processing to reduce these different additive noises. In the first stage, misalignment offset noise are diminished by time average processing, and then the second and third stages, coherent/incoherent noises such as man-made/natural noises are suppressed by array stacking. In addition, we derived the theoretical equation of the SNR gain improved by the proposed method. To evaluate the performance of the proposed method, computer simulations were performed with real seismic data and test equipment generated data as the input.