• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.600-605
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• 2012

In this paper, the acoustic performance of a shipboard large-sized room unit is studied. The room unit is a kind of rectangular absorptive chamber with a partition whose surface absorptive material with fabric skin is attached to. The room unit has one inlet and three outlet. At the inlet, a plane damper is installed to control the flow rate. The acoustic performance of a prototype room unit is measured using a HVAC mock-up. It is shown that its insertion loss is comparable with that of a commercially-used room unit but the developed room unit generates flow noise higher than the other one. The major source of flow noise is analyzed by NADS-R, the noise analysis program for room unit. Cone-shaped dampers are proposed to be used as the damper of a room unit to reduce flow noise. It is shown that the cone-shaped damper decrease flow noise remarkably.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.5
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• pp.468-473
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• 2012

In this paper, the acoustic performance of a shipboard large-sized room unit is studied. The room unit is a kind of rectangular absorptive chamber with a partition whose surface absorptive material with fabric skin is attached to. The room unit has one inlet and three outlets. At the inlet, a plane damper is installed to control the flow rate. The acoustic performance of a prototype room unit is measured using a HVAC mock-up. It is shown that its insertion loss is comparable with that of a commercially-used room unit but the developed room unit generates flow noise higher than the other one. The major source of flow noise is analyzed by NADS-R, the noise analysis program for room unit. Cone-shaped dampers are proposed to be used as the damper of a room unit to reduce flow noise. It is shown that the cone-shaped damper decrease flow noise remarkably.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.5
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• pp.44-52
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• 2012

Fuel cell electric vehicles have some noise problems due to its air processing unit which is required to feed the ambient air into the fuel cell stack. Discrete-frequency noises are radiated from a centrifugal blower due to rotor-stator interaction. Their fundamental frequency is the blade passing frequency, which is determined by the number of rotor blades and their rotating speed. To reduce such noises, multi-chamber perforated muffler has been designed. In this paper, in order to improve the transmission loss of a perforated muffler, the relationship between the impedance model of a perforated hole and its noise reduction performance is studied, and the applicability of a short-length perforated muffler to air processing unit of fuel cell system is described using acoustic simulation results and experimental data. The acoustic velocity vector across the neck of a perforated hole is very important design factor to optimize the transmission of an intake muffler. The suggested short-length perforated muffler is effective on discrete-frequency noises while keeping the volume of intake muffler minimized.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.760-765
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• 2013

Eco-friendly material applied to building would be one of the materials which is must developed for global environmental conservation and reduction of carbon dioxide. For development of eco-friendly material, a cellulose sound-absorbing material has been developed with waste paper through adjustment of various mix proportions. The developed cellulose sound-absorbing material has been tested for its acoustic properties such as acoustic absorptivity and dynamic elastic modulus. The absorptivity was evaluated by developing six samples and using impedance tube and reverberation chamber. As a result of the evaluation, 0.64(NRC) was secured in absorptivity and $4.7MN/m^3$ was indicated in dynamic elastic modulus. Also, for practical use of developed sound-absorbing material as inner heartwood in drywall, comparison test of sound reduction index was performed with existing glass wool sound-absorbing material and constructed drywall of gybsum board. The results have shown 55dB(Rw) of sound reduction index in glass-wool wall and 46dB(Rw) in cellulose.

• Journal of the Korean Society of Combustion
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• v.20 no.4
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• pp.10-18
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• 2015

Combustion instability is a major issue in design and maintenance of gas turbine combustors for efficient operation with low emissions. With the thermoacoustic view point the instability is induced by the interaction of the unsteady heat release of the combustion process and the change in the acoustic pressure in the combustion chamber. In an effort to study the combustion dynamics of gas turbine combustors, Morgans et al (2014) have developed OSCILOS (open source combustion instability low order simulator) code and it is currently available online. In this study the code has been utilized to predict the combustion instability of a reported case for lean premixed gas turbine combustion, and then its prediction results have been compared with the corresponding experimental data. It turned out that both the predicted and the experimental combustion instability results agree well. Further the effects of some typical inlet acoustic boundary conditions on the prediction have been investigated briefly. It is believed that the validity and effectiveness of the open source code is reconfirmed through this benchmark test.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.79-84
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• 2009

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within a compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation is associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in a turbocharger system. In this study, a expansion muffler with lids is devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler are investigated which are related to the unsteadiness of turbulence and pressure in the turbocharger system. A transfer matrix method is used to analyze the transmission loss of the muffler. A simple expansion muffler with lids is proposed for the reduction of high frequency component noise. Turbulence simulation is carried out by a standard k - ${\varepsilon}$ model. An optimal design condition of the muffler is obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise is achieved at the optimal design of the muffler as compared with the conventional muffler.

• The Journal of the Acoustical Society of Korea
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• v.15 no.4
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• pp.105-112
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• 1996

A linear acoustic analysis for baffled rocket combustion chambers has been developed. This study provides the comprehensive theoretical background for the baffle as one of the stabilizing devices in a liquid rocket propulsion system. Several specific effects of baffles are presented as mechanisms by which baffles eliminate instability. Included are longitudinalization of transverse waves inside baffle compartments, severe restriction of velocity fluctuations near the injector face, and decreased normal mode frequency of the chamber.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.68-77
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• 2017

High-frequency combustion instability results from a feedback coupling between the unsteady heat release rate and the acoustic waves formed resonantly in the combustion chamber. It can be modeled as thermoacoustic problems with various degrees of the assumptions and simplifications. This paper presents numerical analysis of self-excited combustion instabilities in a variable-length lean-premixed combustor and designs of passive control devices such as baffle and acoustic resonators in a framework of 3-D FEM Helmholtz solver. Nonlinear behaviors such as steep-fronted shock waves and a finite amplitude limit cycle are also investigated with a compressible flow simulation technique.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.724-729
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• 2017

The interaction between the flow of the nozzle and the acoustic motion in the combustion chamber acts as an important factor in suppressing combustion instability where nozzle damping effect can be evaluated by nozzle admittance. In this study, Modified Impedance Tube experiment is implemented to predict the acoustic nozzle damping effect. The experimental admittances are compared to numerical admittances values which are calculated from one-dimensional linearized Euler equation of Crocco's theory. As a result, it was possible to identify qualitatively the tendency between increasing and decreasing parts. Also, Efficient frequency bands of nozzle attenuation can be predicted.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.501-505
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• 2013

It is well known that monolithic glass has specific coincidence dip allowing transmittance of noise around the critical frequency. Laminated glass, made of a polyvinyle butyral(PVB) interlayer sandwiched by two panes of glass sheet, has long served for the advantage in noise attenuation properties as well as the safety purpose. More research on the improvement of sound insulation performance is needed, considering much of the noise is still transmitted through the glass. As a preliminary study, authors have made several test specimens, varied combinations of glass and interlayer film, to optimize the acoustic performance. Experimental investigation was carried out to study the sound transmission loss of test specimens in the reverberation chamber by using sound intensity method. Several new applications, instead of the existing PVB laminated glass, show better results in sound transmission loss and low temperature have a bad influence on the acoustic performance.