• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.04a
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• pp.257-262
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• 1996

The first purpose of this study investigates the influence of stiffening on the acoustic response of stiffened plates, which are often employed in steel structures. And the radiation efficiency is measured by average mean square velocity and sound intensity of stiffened plates. The second, it determines influence of mass, damp and stiffeness due to the partial adhesive visco-elastic material to reduce radiated sound power.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.1
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• pp.101-107
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• 2018

In this study, the analysis of radiation noise and chattering noise of vehicle seat recliner was conducted through testing and analysis. First, operating noise was measured by seat back frame and recliner, and chattering noise was confirmed. Next, the transient dynamic analysis was performed, and the result was mapped to the acoustic analysis. Finally, the test and analysis were compared and analyzed. The results are as follow. First, it was found that the peaks appeared in common in the range of 620~650Hz, 1,240~1,290 Hz, and 1,840~1,940 Hz. It was judged that the dynamic characteristics of the recliner system overlapped with the rotation component of the motor to cause amplification of noise and vibration. Next, as a result of imaging the radiation noise analysis, it was judged that the noise radiated in the forward and backward direction has a greater influence than the direction of the rotation axis when the ear position of the person is taken as a reference.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.388-394
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• 2023

When the vibration of the thin panel by exciting single point is used to radiate sound, the inherent vibration characteristic of the plate itself causes influence on the radiated sound. A conventional panel speaker system usually uses the single or double point excitations for generating the sound through the panel itself. The radiated sound can be easily distorted due to the modal characteristics of the plate so it is difficult to expect sufficient sound power or high radiation efficiency. In this paper, to achieve an immersive sound field, the multiple speaker zones on a thin panel are created with the limited number of actuators. The designated vibration field which can generates directional sound is realized by employing the vibro-acoustic inverse rendering methods. Actuators are arranged from the positions which have the advantage of implementing with multi-modal excitations. The location and number of actuators are compared with the location and number of controllable speaker zones by conducting numerical simulations.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.10
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• pp.770-779
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• 2014

In this study, a numerical estimation method for 3D underwater radiated noise pattern using hull vibration and total acoustic power of the vibrating structure in the far-field is proposed. The underwater radiated noise pattern is known to be predicted using the vibration signals and radiation efficiency of each surface patch. But it is very difficult to know radiation efficiency of each surface patch which is one of important factors to calculate the 3D underwater radiated noise pattern. Instead of using radiation efficiency of each patch, the underwater radiated noise level is modified with the total acoustic power of the vibrating structure. The suggested estimation method for underwater radiated noise pattern is discussed with numerical model.

• The Journal of the Acoustical Society of Korea
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• v.13 no.2
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• pp.13-22
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• 1994

A theoretical model is studied to describe the sound radiation by the surface vibration of in-service tires. The tire is modeled as a circular ring model. The effects of normalized frequency and structrual loss factor are included. Through numerical integration of the sound pressure, the radiated sound power is calculated as a fuction of normalized frequency and structural loss factor. The basic sound radiation mechanism is shown to be the damped progressive wave field on the structure in the vicinity of the applied force. The results indicate that the potential sound reduction might be obtained if values of normalized frequency and structural loss factor are investigated.

• The Journal of the Acoustical Society of Korea
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• v.43 no.2
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• pp.162-167
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• 2024

Low frequency noise emitted by wind turbines is one of the most noise complaints. In this study, the reliability of the models was examined by comparing the measured sound pressure levels with the predicted levels based on Denish model and commercial programs of the SounPLAN and the ENPro based on ISO 9613. As a result of applying it to representative 3 MW wind turbines, on lnad, the measured and the predicted values differed within a maximum of 5 dB in the frequency range of 12.5 Hz to 80 Hz. It may be due to the change in the acoustic power levels because the wind turbines have been in operation for more than 7 years. However, considering that the Boundary Element Method (BEM) predicted value, which is known to be the most accurate in the low frequency band, the predicted values are well matched within 2.5 dB, the models of this study are expected to be used as deviation within 3 dB.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.12
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• pp.992-998
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• 2014

Acoustic radiation efficiency is one of the important factors in the prediction of underwater radiated noise of ships. A ship has much equipment to operate successful mission in a ship. Most of equipment is running simultaneously as multi-excitation and becomes the source of underwater radiated noise. In many cases of multi-excitation, phase difference between multi-excitation is not considered. Because vibration response under multi-excitation is the vector sum of each single excitation, acoustic radiation efficiency based on surface velocity field can be affected by phase of excitation. In this study, acoustic radiation efficiency of a plate on air and a stiffened cylindrical model in water under multi-excitation with phase difference is investigated.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.688-691
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• 2004

We have studied the possibility of global noise reduction by the sound power control through selection of distribution and impedance of absorptive materials. It is necessary to investigate the relation between the global sound energy in the field and the total sound power radiated by sources. In the previous work (1,2), the authors presented a useful design method to change boundary condition that can be useful to reduce noise in acoustically small enclosures. The possibility of total acoustic potential energy reduction by acoustic source power control is examined in an acoustically small cavity. Using acoustic energy balance equation, the relation between global noise control performance and absorptive material's arrangement/impedance is deduced. Numerical simulation is performed to interpret its physical meaning in terms of absorbent's distribution and impedance.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.5
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• pp.430-436
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• 2011

The purpose of this study is to analyze the vibration and sound generation characteristics of the sandwich panel. Two thick panels were assumed to be separated by a compliant viscoelastic core. The transverse vibration induced by an external impact was analyzed using the Rayleigh-Ritz method. For applying arbitrary boundary condition of the panels, the edges were assumed to be supported by the translational and rotational springs. The beam functions were used as the trial functions. The effect of the boundary condition and viscoelastic core on the resulting vibration characteristics was investigated. The radiated sound power was analyzed using the proposed numerical model and the Rayleigh integral. The dynamic properties of the core and the mass-stiffness-mass resonance frequency had significant influence on the impact sound.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.521-526
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• 2004

This paper introduces works performed for reducing high frequency noise of a reciprocating compressor. Noise in a high frequency range strongly affects sound quality as well as increases total noise level of the compressor. In order to reduce the noise, two different works were carried out. the first work was to measure the vibration Power transferred through suspension spring and discharge pipe; and the second one was to obtain operational deflection shape from cross-power spectrum measured on shell. Based on the information, Adequate structural modification of the transfer path and shell resulted in noise reduction in a high frequency range.