• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.407-412
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• 2013

In dry wall, noise is passed through gypsum board and stud. Noise makes gypsum board vibration. Then, the vibration passes through stud and gypsum board as resonation. And radiation as noise from surface of gypsum board into adjacent room. At this moment, according to thickness, placement and cross-section of stud, noise transmission ratio changes. Thicker stud has better sound insulation performance. Studs are apart from each other, has better sound insulation performance. But, single stud structure has restriction of thickness and arrange of studs. In this article, Sound insulation performance varies depending on the shape of the studs were studied.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.972-975
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• 2004

In order to reduce the noise of BLDC motor, a systematic optimization procedure for rotor structure is presented. The noise index is defined as the sum of volume velocity of FE-model that are calculated at the dominant frequencies during dehydration process, which is based on the principle of radiation simple volume source. Then, the five design variables are selected to represent the shape and layout or rotor structure. This discrete design optimization problem for minimizing the noise index is solved by 3-level orthogonal array based effect analysis. Finally, the response surface method (RSM) combined optimization approach is employed for more refining the approximate optimum.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.6-12
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• 2010

The source of wayside noise for the train are the aerodynamic noise, wheel/rail noise, and power unit noise. The major source of railway noise is the wheel/rail noise caused by the interaction between the wheels and rails. The Structure borne noise is mainly a low frequency problem. The train noise and vibration nearby the elevated railway make one specific issue. The microphone array method is used to search sound radiation characteristics of elevated structure to predict the noise propagation from an elevated railway. In this paper, the train noise and structure borne noise by train are measured. From the results, we investigated the effect on the sound absorption tunnel for elevated railway.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.193-198
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• 2004

In order to keep the market competitiveness, it is desirable for automotive manufacturer to meet the customer's various aspects of requirements. The overall NVH (Noise, Vibration, and Harshness) performance has been an important measure when evaluating overall vehicle performance, product quality, and enhancing customers' loyalty to the product. The noise and vibration, while the engine is idling, has been brought particular attention to the drivers and passengers, because they encounter the operation conditions quite frequently without other masking noise sources: wind noise, road noise, and even powertrain radiated noise at higher speed driving. The specific noise, defined as 'CHIT' noise, has been identified as a potential customer issue, from the Pickup Truck with newly developed V8 powertrain. This paper describes the definition of the noise, identifying the potential sources, and noise radiation mechanisms, based on series of powertrain and vehicle test and verification processes. Then, based on the root-cause identified, the design change has been proposed and validated with several vehicles in order to have a complete satisfaction of the customer.

• The Journal of the Acoustical Society of Korea
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• v.14 no.5
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• pp.11-19
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• 1995

The Interaction between tire and road is responsible for the excited vibration of the tire, and It is also important for the sound radiation. In this paper. measurement of tire structural vibration noise from a chassis dynamometer using Spatial Transformation of Sound Field(STSF) technique is studied. STSF involving a scan that uses an array of transducers over a planar surface close to the source is under investigation. From cross spectra measurement during the scan, a principal component representing the sound field is extracted. Any power descriptor of the near field can then be investigated by means of near-field acoustic holography, while the distant field can be determined by application of Helmholtz integral equation. The results of the measurement were used to obtain the radiation sound pattern from the center line of the tire, and to locate the radiation sound generating regions in the vicinity of the tire.

• The Journal of the Acoustical Society of Korea
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• v.16 no.6
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• pp.12-18
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• 1997

Beamforming method has a limited spatial resolution because of finite aperture size, so that the estimated source distributions are smoothed within the resolution. Especially for low frequency noise such as mechanical noise, this limitation often diminishes the direct use of beamforming method. In this study, the relation between smoothed beamforming and radiation power distribution of plate has been addressed. By adjustment of aperture size of array, the smoothed beamforming power shows radiation power distribution of plate. Numerical simulations are carried for simply supported plate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.62-67
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• 1995

A method for determining impulsive responses and acoustic radiation for submerged shells of finite length has been presented. The method is a modal-based method, and uses a surface variational principle to obtain data in the frequency domain. The fast Fourier transform technique is used to convert the data to the time domain. The surface pressure responses of a cylindrical shell with endcaps wer compared with those of an infinite shell. It was shown that the surface pressures coincide exactly before any significant reflections from the endcaps occur. Traces of different types of waves were identified from the dispersion relations of the infinite shell. The contributions of flexural and longitudinal waves and these due to the direct radiation from the driving force to the fluid pressure were demonstrated using near-field plots. The exchange of energy between the shell and fluid was examined for shells with and without bulkheads. It was shown that a significant amount of the energy which enters the fluid returns to the shell and most of the energy is dissipated in the shell. It was also shown that the shell with bulkheads radiate significantly more energy into the far-field than the empty shell.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.1032-1037
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• 2003

Although the holes on the shell case are very important fer the acoustic performance, it is difficult to solve the problem because the case includes thin bodies. Hence, in the past, only the method of trial and error, which depends on the engineer's intuition and experience, was available fur the design of holes. Many researchers have tried to solve the thin-body acoustic problems, since the conventional boundary element method (BEM ) using the Helmholtz integral equation fails to yield a reliable solution fer the numerical modelling of radiation anti scattering of sound from thin bodies. In the area of the analysis of thin-body acoustic problem, three approaches are generally used; the multi-domain BEM, the indirect variational BEM, and the normal derivative integral equation And there has been just a f9w study reported on the design optimization for the acoustic radiation problems by using only the conventional BEM. For the thin-body acoustics, however, no further study in the optimization fields has been reported. In this research, the normal derivative integral equation is adopted as an analysis formulation in the thin-body acoustics, and then used fur the optimization. The analytical approaches for the design of holes are proposed by using a topology optimization technique and a genetic algorithm. The proposed approaches are implemented and validated using numerical examples.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.4
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• pp.1024-1030
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• 2015

Safety and security system have been internationally enhanced in a field of shipping logistics. Accordingly, techniques for safety and security have been studied steadily. The need of portable radiation detection device is increasing by the search of the container is enhanced. In this paper, we propose a study to improve the life of the system and the realization of portable radiation detection device based on Cortex-A9. Configuration of a portable radiation detection device is configured largely to an analog board and the digital platform and the sensor module. The power used in each stage of the analog board is varied. Uses a switching regulator to use various power supply thereby to generate an error result and cause the switching noise. It is proposed to reduce the power consumption reducing technique for the study.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.1482-1489
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• 2007

In this paper, characteristics of infrasound and low-frequency noise emission from large modern wind turbines are experimentally investigated. The sound measurement procedures of IEC 61400-11 and ISO 7196 are utilized to field test and evaluation of noise emission from each of 1.5 MW and 660 kW wind turbines using the stall regulation and the pitch control for the power regulation, respectively. It was found that the G-weighted SPLs of low-frequency noise including infrasound shows positive correlation with the wind speeds, irrespective of methods of power regulation. This highlights the potential complaint of local community against the infrasound and low-frequency noise of wind turbines. The comparison of measured data with the existing hearing thresholds and criteria curves shows that it is highly probable that the low-frequency noise from the 1.5 MW and 660 kW wind turbines in the frequency range over 30 Hz leads to the psychological complaint of ordinary adults, and that the infrasound in the frequency range from 5 Hz to 8 Hz causes the complaint by rattling the house fitting such as doors and windows.