• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.187-192
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• 2006

Helicopter noise has been considered as one of major design factors like a performance and safety since the public acceptance, comfortability and stealth aspects were important for customers. According to the airworthiness regulation, the noise levels in throe different flight conditions shall comply with the specific limits. Main and tail rotors noise is most dominant in far field due to the low and mid range frequency characteristics. It is an air-born noise so That the accurate aerodynamic data is necessary for the accurate noise prediction. In KARI, low noise main and tail rotors as well as analysis codes have been developed since 2000. The approach for low noise main rotor is a kind of tip modifications, so called twin vortices tip to reduce the BVI noise. Analysis results show the 9.3dB reduction in terms of pseudo EPNL. The uneven spacing concept is applied for low noise tail rotor. Three or four decibel noise reduction is achieved by new optimized uneven spacing. Rotor noise and aerodynamic prediction codes have been improved also.

• Journal of Environmental Health Sciences
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• v.34 no.4
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• pp.311-315
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• 2008

This study was performed to investigate propagation characteristics and effects of road traffic noise generated from vehicles. Noise levels of expressway and general road were measured at four points in a straight line based on distance from the road, and analyzed. The average noise level of expressway was 78.9 dBA at 5 m, 76.4 dBA at 10 m, 72.0 dBA at 20 m, 69.0 dBA at 30 m. That of general road was lower about $3.1{\sim}3.5\;dBA$ than that of expressway. There was no significant difference in distance attenuation between expressway noise and general road noise. The farer the distance from source is, the more the attenuation is. The influence range of noise is assessed by noise environmental standards or road noise limits. Noise levels of the time zone were measured at a boundary line of apartment to grasp noise variation by time. The time zone of lowest noises was $3{\sim}4$ a.m. and that of highest noise was $8{\sim}10$ a.m. Data recorded on tapes were analyzed to understand the characteristics of frequency because these characteristics are important factors to plan the noise reduction measures, namely path measures.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.876-878
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• 2008

The standards of acceptable limit and compensation is one of the most important things in environmental noise and vibration disputes resolution. In this paper, review on the present acceptable limit level and compensation standard in National Environmental Dispute Resolution Commission is introduced. Discordance of standards between in the regulation law and in the dispute resolution commission and it's improvement are discussed. Abnormal reasoning for compensation standards is pointed out from a author's private view.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.37-45
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• 2003

The diesel engines was invented a little more than one hundred years ago and has ever since been developed for better fuel economy, increased power and smaller size. Thanks to its fuel economy, the diesel engine is today the dominating prime mover in many applications, such as smaller power plants, commercial ships, trains, trucks, buses and all kinds of mobile construction machinery. As engine for passenger cars, the diesel engine is steadily increasing its share of the market. However, its versatility and, consequently, large prevalence have led to environmental demands to its exhaust emissions, noise and vibration. This paper deals with the noise aspects of diesel engine designs of the so-called low speed two-stroke type installed in most large ships.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.535-540
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• 2005

In environmental impact assessment, noise impact assessment usually consists of three stages surveying the existing noise levels by measurements, predicting noise levels induced by construction works and predicting noise levels after the completion of project. When predicting noise level in urban area, this method does not consider acoustic phenomena like multi reflection, diffraction and absorption due to complex topographic configuration of building and terrains. For the purpose, a noise mapping tool is utilized to produce a series of noise maps, which are those for the present, for the works of construction and for the future. For accurate noise mapping, acoustical and topographic information is essential. Standard sound power levels and directivities of various construction equipments are required and scheduling of construction processes and locations of the equipments should be provided. In the case of exceeding legal limit, mitigation measures are applied to satisfy the legal limits and subsequent noise map is obtained and checked.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.11 s.104
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• pp.1311-1317
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• 2005

In environmental Impact assessment, noise impact assessment usually consists of three stages-surveying the existing noise levels by measurements, predicting noise levels induced by construction works and predicting noise levels after the completion of a project. The distance-attenuation relation of a point source, which has been used to predict the noise level due to its simplicity does not consider complex acoustic phenomena like multi-reflection, -diffraction and -absorption due to complex topographic configuration of buildings and terrains. For the consideration of such physical complexities. a noise mapping tool is adopted to produce a series of noise maps, which are those for the present, tot the works of construction and for the future. For accurate noise mapping, acoustical and topographic Information is used. Standard sound power levels and directivities of various construction equipments are need and scheduling of construction processes and locations of the equipments should be provided. In the case of exceeding legal limit, mitigation measures are applied to satisfy the legal limits and subsequent noise map is obtained and checked.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.659-666
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• 2009

As the density and height of the buildings nearby subway lines get higher, the unprecedented residents' appeals for noise are on the rise. Furthermore, in accordance with the revision of enforcement regulations on the Noise and Vibration Control Act, the night time noise standards have been reinforced by 5dB effective on January 1st 2010 and the appropriate measures shall be taken accordingly. For the settlement of the public grievances against noise and vibration generated on tracks in at-grade and elevated section, the installation of continuously-welded-rail, rail lubrication system, improved fastening system and higher noise barrier is currently executed. Nevertheless, the noise and vibration levels in some areas are still exceeding the limits required in the regulation. Among the measures, an installation of higher noise barrier or noise tunnel seems to be the most effective way; however, it has limitations owing to the structural stability of existing elevated structures. The paper in consideration of the local conditions and foreign practices discusses the installation of fairing system under the train body as an noise insulation panel in order to reduce the rolling noise and under-carriage noise. Based on the result of this study, a performance verification test during actual train operation is in progress for further study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.917-917
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• 2003

The auditory experiments based on the subjective annoyance responses were undertaken for the establishment of the adverb modifiers of the heavy-weight impact noises. The standard heavy weight impact noise, impact ball noise and adult walking noise were recorded by dummy head at a newly-built apartment and were presented to the subjects by headphones. The levels of the three impact noises were varied from 30 to 60㏈(A) and the subjects matched one of the adverb modifiers to each level of the noise sources. As a result, seven scale modifiers were established and the intervals between the modifiers were found as equal. In addition, it was found that the lower annoyance noise limits for the heavyweight impact, impact ball and walking were 40-45㏈ (L$\sub$I, Fmax. AW), which is 6㏈ lower than in the previous study. The background noise level was as low as 21㏈(A) in the test booth, therefore, the testing conditions need to be concerned for evaluation of floor impact noise.

• Structural Engineering and Mechanics
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• v.44 no.5
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• pp.585-600
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• 2012

This paper presents a Modified Tikhonov Regularization (MTR) method in model updating for damage identification with model errors and measurement noise influences consideration. The identification equation based on sensitivity approach from the dynamic responses is ill-conditioned and is usually solved with regularization method. When the structural system contains model errors and measurement noise, the identified results from Tikhonov Regularization (TR) method often diverge after several iterations. In the MTR method, new side conditions with limits on the identification of physical parameters allow for the presence of model errors and ensure the physical meanings of the identified parameters. Chebyshev polynomial is applied to approximate the acceleration response for moderation of measurement noise. The identified physical parameter can converge to a relative correct direction. A three-dimensional unsymmetrical frame structure with different scenarios is studied to illustrate the proposed method. Results revealed show that the proposed method has superior performance than TR Method when there are both model errors and measurement noise in the structure system.

• Journal of the Korean Institute of Navigation
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• v.16 no.3
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• pp.65-76
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• 1992

An algorithm to determine the optimum nominal value of geometrical and material parameters in divice modelling is proposed. The algorithm uses the yield and variance prediction formula and Monte-Carlo analysis. The performance specification of the noise figure must also be satisfied. In this paper, the total number of considered devices is 1000, and each parameter of geometrical and material parameters is generated randomly within the limits of ${\pm}3%$ of nominal value, and the distribution of 1000 geometrical and material parameters is gaussing distribution.