• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.858-861
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• 2006

In this paper, a study on the noise reduction in a mobile fuel cell system is presented. Among various fuel cell systems around 20W capacities designed for mobile electronic devices, the active direct methanol fuel cell (DMFC) systems have been recently developed. In such systems, the primary noise source is the air pump which provides sufficient air flow ($5{\sim}6$ liter/min) for electrochemical reaction with methanol fuel while the noise contributions from other auxiliary parts are relatively small. Especially, the discrete noise tones generated by the air pump are dominant and those frequency peaks related to the rotor harmonics are needed to be suppressed by a silencer. Therefore. the Herschel/Quinke (HQ) tubes, which use the out-of-phase cancellation of acoustic waves propagating through direct and indirect pathways, are applied to the inlet of the air pump. Performance of noise reduction with HQ silencer is analytically estimated by calculating the transmission. The length and number of thin HQ tubes are optimized to decrease the radiated noise. As a result, the sound pressure level could be successfully reduced by about 10 dB after applying three serially connected HQ tubes.

• 수산해양기술연구
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• 제54권1호
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• pp.73-80
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• 2018

Intermittent duty of emergency generator has problems emitting large quantities of PM and NOx in exhaust gas. The aim of this study is to propose DPF system which can be applied to medium-large emergency generators. The system is composed of soot dust collector, silencer and filter trap, which is designed to reduce PM emissions at the emergency generator start-up. The pneumatic system controls a flow direction of exhaust gas to pass through the soot collector and filter trap until the engine reaches complete combustion condition. An experiment is performed to measure PM content and concentration to analyze the performance and characteristics of the proposed system.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1970-1974
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• 2010

This paper is how to improve contaminated air by the pollutant from vehicles through ventilators and entrance at the underground station. We are looking for the environment management to take care of customers. There is two ventilation systems. One is natural ventilation system, the other is forced ventilation system. Usually, subway ventilators were installed low on the sidewalk. There are lots of craps on the ventilators, so these things interrupt influx of outside air. But the gas from the vehicles comes into the station through entrance. There is lots of noise while ventilations run. So we install the supply air vents away from the road for the customers. If it's difficult, we cover around the ventilator with clear plastic plates more than 2M heights. We also install silencer on the ventilators. We install the air curtains on the entrances to prevent dust from outside. Seoul Metropolitan has a plan to make 60M deep underground road. To improve underground road air quality, ventilators should be installed that consider the above information.

• 소음진동
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• 제3권3호
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• pp.271-278
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• 1993

Acoustic characteristics of silencer system are affected by various geometric parameters such as cross sectional geometry, size of chamber, and location of inlet-outlet port. It is impossible to obtain exact solutions of the equations of acoustic wave propagation except few simple cases. So, we resort to numerical techniques to analyze performance of acoustic system. In this work, finite element formulation has been obtained to predict transmission loss of an arbitrary 3-dimensional muffler in the presence of mean flow of low mach number. The effect of the degree of the ellipticity of expansion chambers on the transmission loss has been studied using the resulting finite element equation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.383-386
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• 2003

This paper deals with transmission loss of 3-dimensional rectangular plenum lined chamber. There are three kinds of rectangular plenum lined chamber: throughflow type, flow-reversal type, and end-in/side-out type. The combination of above three types of rectangular plenum lined chamber is used for the commercial HVAC system and automobile exhaust system. However, the ambiguity and complexity of sound absorbing material property and 3-dimensional property have impeded research. In this paper, the transmission loss of three kinds of rectangular plenum lined chamber is derived and calculated. The effect of increase of sound absorbing material is also considered. Analytical solution is calculated by using the locally-reacting property of sound absorbing material.

• 한국안전학회지
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• 제26권1호
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• pp.8-14
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• 2011

Noise and vibration are likely to disturb the sensory system of human body leading to psychological stress and thereby property damage. In this research, a cut out switch(COS) with a built-in acoustic absorber along with a COS fuse broken was developed to reduce percussion noise. This new system is based on a design approach that combines existing absorber systems: expansion type, resonator type, and acoustic absorber type silencer The noise performance of the new system was simulated using the $SYSNOISE^{TM}$ software under optimized parameters: the diameter of perforated plate 2 mm, the plate thickness 3 mm, the width of expansion room 25 mm, the impinging vortex room 14 mm, and the noise absorbtion room 10 mm. The results showed that it reduced noise by approximately 41.1 dB compared to the current systems available in the market. Furthermore, it showed reduced noise by approximately 12 dB more than a product with an acoustic absorber of the Fault Tamer(USA).

• 오토저널
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• 제14권6호
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• pp.48-59
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• 1992

This study is on the performance of the perforated tube muffler when it operates as an exhaust silencer with through-flow, steady or pulsating. Theoretical estimation of the insertion loss was made by means of transfer matrix and by using the impedance equation for the perforated tube obtained for the case of low-speed steady through-flow. Experiment was performed for the measurement of the insertion loss at two flow conditions. The one is a steady flow from the exhaust pipe of an idling diesel engine. The effect of the through-flow velocity and steadiness on the muffler performance was obtained. By comparing the theoretical prediction with the experimental result, the validity of the impedance equation in the theoretical model was discussed. It has been found that steadiness as well as magnitude of the through-flow has a significant effect on the performance of the perforated tube muffler. Especially, the self-noise due to the pulsating flow in the engine exhaust system must be taken into account for the prediction of the muffler performance.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.625-628
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• 2005

Silencers are extensively used for reducing noise in an exhaust system of internal combustion Engine and fluid machineries. The prediction and measurement of the transmission loss as the acoustic performance of silencers are important in early design stage. In the measurement of transmission loss, the semi-anechoic terminations are general used for reducing unwanted effects by reflecting wave. However it is very hard to remove reflecting wave perfectly. So the research about the error made by reflecting wave is important. The analysis about errors made by reflections and modification techniques are proposed. For an application example, the diesel particulate filter (DPF) is chosen. The transmission loss of DPF is measured with and without considerations of reflecting wave.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.27-33
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• 2001

Linear harmonic analysis is a convenient and generally accurate method to use for the acoustic analysis of intake and exhaust silencers for IC engines. The major uncertainty in this form of modelling is the characterisation of the source, which is inherently nonlinear and time-variant. Experimental methods are generally used to determine the source characteristics, and in particular the indirect method is most suitable for an IC-engine source. With reference to an idealised linear time-variant source, it is found that the characteristics of a time-variant source as determined by the indirect method have no physical relevance. The direct method of experimental measurement appears to have some advantage over the indirect method, although in practice it is difficult to apply to an IC engine source. Again, an idealised linear time-variant source can be used to indicate that the characteristics of a time-variant source as determined by the direct method also have no physical relevance. Strangely, these meaningless measured source properties can nevertheless be used to accurately predict the radiated noise from an IC engine and silencer system.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.904-910
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• 2007

In this study an experimental research has been conducted to reduce NOx and smoke emission from diesel engine exhaust gas simultaneously by application of corona discharge type electrostatic precipitator(ESP). The ESP was installed between exhaust gas silencer and outlet terminal of exhaust gas system. The operating conditions as input parameters taken in this experiment were corona power input, gas velocity and equivalence ratio of gas. It was found that the corona discharge type ESP has notable effect on reducing smoke in exhaust gas but appeared to bring slight effect on reducing NOx.