• Journal of Advanced Marine Engineering and Technology
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• v.11 no.1
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• pp.63-71
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• 1987

The measuring of acoustic intensity has been investigated by many researchers and practicians during the last several decades. But due to the lack of measurement accuracy, they have had no practical use. In recent years, the two microphone acoustic intensity method has been developed by the advancement of FFT analysis technique and the digital data processing equipment. This new method of using two microphones gives informations on the noise source survey and the acoustic power of sound radiation source without the anechoic room. In this paper, theoretical formulae for the two microphone acoustic intensity method and the sound transmission loss are checked. The obtained results for the acoustical enclosure of gas heat pump were compared with the classical field incidence mass law. The surface vibration modes for a panel of enclosure were also estimated.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.251-257
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• 1998

Active mufflers have been mainly applied in the large industrial engine due to considerable expense for implementation, but a necessity of development has been increased by the tightened regulation of exhaust noise and the request of high power. In this study, the active muffler prototype for installing in an automobile is designed and constructed. The active muffler is designed so that the primary noise and the control sound are propagated as a plane wave in the outlet. Therefore, the error microphone could be placed outside the high temperature centers of the tail pipe, and the noise radiating to the outside could be reduced in the whole areas around the outlet. For evaluating the control performance of the prototype, the control experiments of band-pass filtered random signal and the modulation of sinusoidal signal which are generated from the primary noise speaker as practical exhaust sound level are implemented. And to investigate the radiation pattern from the outlet of tail pipe and the noise reduction level of points placed adjacent to the outlet, the sound level of adjacent points of thirty is measured.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.713-722
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• 2022

In this paper, the flow performance and aero-acoustic noise generated by the target centrifugal fan system were investigated numerically and experimentally. Also, the numerical method for Computational Aero-Acoustics were evaluated by comparing each method. To analyze the performance of the centrifugal fan experimentally, the acoustic power level was measured in the semi-anechoic chamber using microphones, and the active frequency range for the noise performance was identified and that frequency range was applied for Computational Aero-Acoustics (CAA) techniques as sampling frequency. Then, Navier-Stokes equation and the Ffowcs Williams&Hawking equations were used to analyze the flow and sound power numerically, respectively, and a virtual acoustic radiation plane was designed and used for the implementation of the sound field. The accuracy and numerical characteristics of the numerical methods were validated by comparing simulated acoustic power levels with acoustic power levels measured.

• The Journal of the Acoustical Society of Korea
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• v.24 no.8
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• pp.431-440
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• 2005

The precise measurement of ultrasonic power is important to the qualify assurance and the safety of medical ultrasonic equipments In the Present work, a brier theory was introduced to determine the ultrasonic Power from the time valving balance-indication due to the radiation force acting on an absorbing target and/or other causes such as buoyancy during the repetition of on/off behavior of ultrasonic irradiation. The developed automated system measuring the ultrasonic power was described in detail with the precise mechanical alignment tool , the electric signal generation network, the control and measurement network and the appropriate procedure. The ultrasonic power measured by the developed system was compared to the reference data calibrated by the other national metrology institute at 1 MHz, 5 MHz, 10 MHz, and 15 MHz over the range 10 mW to 10 W. Their relative differences are within $5\%$.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.10
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• pp.1006-1013
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• 2008

In this study, it is outlined that heavy weight floor impact noise induced by the vibration of slab can be reduced using multi tuned mass damper(MTMD) effectively. Substructure synthesis is utilized to develope analytical model of the slab coupled with MTMD and acoustic power is introduced to evaluate the performance of noise control for simplicity. Numerical analysis is carried out to investigate the effect of the properties of MTMD on the vibration and noise control of the simply supported slab. Numerical analysis shows that mass ratio of MTMD is critical on the vibration and noise control of the slab and it is also essential to reduce the vibration in higher modes of slab in the light of its great effect on the radiation of sound.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.659-664
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• 2008

In this study, it is outlined that heavy weight floor impact noise induced by the vibration of slab can be reduced by multi tuned mass damper(MTMD) effectively. Substructure synthesis is utilized to develope analytical model of slab coupled with MTMD and acoustic power is introduced to evaluate the performance of noise control for simplicity. Numerical analysis is carried out to investigate the effect of the properties of MTMD on the vibration and noise control. Numerical analysis shows that mass ratio of MTMD is critical on the vibration and noise control of the slab and it is essential to reduce the vibration in higher modes of slab because it has a great effect on the radiation of sound.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.11
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• pp.1837-1843
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• 1997

This study experimentally demonstrates the use of active muffler attached to the automotive exhaust system to reduce exhaust noise. For improving the signal to noise ratio in the process of estimation of secondary path transfer functions, the on-line algorithm that conventional inverse modeling is combined with adaptive line enhancer is used as the control algorithm. Active muffler is designed that the primary noise and the control sound are propagated as a plane wave in the outlet. Therefore, the error microphone could be placed out of the tail pipe center of a high temperature and the radiation noise to the outside could be reduced in the whole area around the outlet. The control experiment for reducing exhaust noise with active muffler is implemented during run-up at no load. From the experimental results presented, compared with the conventional off-line method, the proposed on-line method is capable to acquire a reduction of exhaust noise above 5 dB in overall sound power level.

• Steel and Composite Structures
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• v.28 no.5
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• pp.629-639
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• 2018

In this paper, the vibroacoustic responses of baffled laminated composite sandwich flat panel structure under the influence of harmonic excitation are studied numerically using a novel higher-order coupled finite-boundary element model. A numerical scheme for the vibrating plate has been developed in the frame work of the higher-order mid-plane kinematics and the eigen frequencies are obtained by employing suitable finite element steps. The acoustic responses are then computed by solving the Helmholtz wave equation using boundary element method coupled with the structural finite elements. The proposed scheme has been implemented via an own MATLAB base code to compute the desired responses. The validity of the present model is established from the conformance of the current natural frequencies and the radiated sound power with the available benchmark solutions. The model is further utilized to scrutinize the influence of core-to-face thickness ratio, modular ratio, lamination scheme and the support condition on the sound radiation characteristics of the vibrating sandwich flats panel. It can be concluded that the present scheme is not only accurate but also efficient and simple in providing solutions of the coupled vibroacoustic response of laminated composite sandwich plates.

• 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.