• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.7
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• pp.679-684
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• 2009

Low frequency exhaust noise of marine diesel engine is one of the most important noise sources in vessels. However, conventional absorptive silencers are ineffective to control exhaust noise because of low absorption in the low frequency range. In the paper, exhaust noise control of marine diesel engine was studied by using the hybrid silencer, which was composed of virtually divided array of concentric hole-cavity resonators and conventional absorptive silencer. A series of tests including field tests were performed to investigate the acoustic performance of the hybrid silencer. Consequently, its high performance of 5${\sim}$10 dB noise reduction in the low frequency range was confirmed and it is expected to be very helpful in reducing the exhaust noise of marine diesel engine.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.186-192
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• 2007

We research into the exhaust system volume what proving the optimum exhaust performance and combustion characteristics. Many automobile manufactures have developed complex exhaust system for environment regulation and noise reduction. This complex exhaust system provides acoustics silencing and low frequency noise for customers demand. Recently, automobile exhaust system have made the Dual muffler concerning to the noise and vibration reduction. Also it bring the engine performance down by decreasing the back pressure and temperature in the exhaust system. The experiments are carried out different volume of exhaust system. In order to establish the optimized conditions design factors which are taking exhaust system volume, it show how the exhaust performance influence on the engine performance in idling.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.3
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• pp.55-62
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• 1993

Autoregressive moving average(ARMA) model which is a time domain parametric modeling method is implemented for modeling and reproducing characteristics of exhaust noise of an automobile in various RPM range. Experiments have been carried out using 9 set of exhaust noise signals measured at 1,000-3,000 RPM range. Characteristics of sampled signals were estimated using ARMA modeling and Akaike's FPE(final prediction error) criterion to define exact model structure and for model validation. The digital filter consisted of the esitmated ARMA(70,1) model parameters was programed to reproduce exhaust noise. The spectral analysis of reproduced noise is very close to original. The results show that our approaching technique for reproducing acoustic characteristics is valid and feasible to apply in the field of noise quality control.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.05a
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• pp.623-627
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• 2001

Suppression of very low-frequency noise from an automobile exhaust system is difficult due mainly to its large wave length. Therefore, the configuration of total exhaust system, i,e., piping and muffler layout, is important at low frequencies. In this paper, an optimal layout technique of exhaust systems has been developed for reducing low-frequency exhaust noise. For this purpose, system insertion loss and virtual attenuation coefficient have been defined by considering the effects of mean flow and temperature gradient in the pipe. The applicability of present method is investigated with an actual automobile exhaust system and an optimized layout of pipes and mufflers is suggested.

• Journal of Advanced Marine Engineering and Technology
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• v.22 no.5
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• pp.635-642
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• 1998

In automobile exhaust system. Internal pressure pulsation and shell vibration greatly affect the surface sound radiation. This noise is emitted from the muffler outer shell due to the pulsation of the exhaust gas pressure. This paper describes an analytical study of these characteristics as influenced by exhaust system structure. An exhaust simulator was used for generating the pressure pulsation. The relationship between shell vibration and radiated noise was used for generating the pressure pulsation. The relationship between shell vibration and radiated noise was identified by finding FRF.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.866-869
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• 2004

Power transformers, air-intakes and stacks in the urban combined power plant are main noisy sources. Because of Inhabitant complaint by abnormal noise transferred from the power plant. the noise was investigated at power plant and uptown area. The result of diagnosis made the acoustic resonance phenomenon by 580Hz's combustion dynamic pressure with the standing wave mode of sound fields in exhaust passageway of gas turbine into main noise source of public complain. The abnormal noise is caused by the resonance exhaust noise transferred through stacks of power plant.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.5
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• pp.374-379
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• 2002

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.54 no.3
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• pp.255-261
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• 2018

High power trends in the diesel engines due to engine downsizing do not provide noise attenuation that can be satisfied with the performance of the existing silencer on account of high frequency increases in the exhaust noise. This study improves the attenuation performance of the exhaust silencer of the diesel engine and suggests silencer structure that performs best attenuation performance, especially at the high frequency range in the exhaust noise. It proposes dual silencer structure with an average attenuation performance of 6.4 dB and a maximum of 10.7 dB in the high frequency range (over 500 Hz), and analyzes its characteristics compared with the existing silencer. The performance analysis is performed according to 'Measurements on silencers in situation-ISO 11820:1996 Acoustics' and describes the results of comparative analysis with the existing silencer.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.1
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• pp.36-42
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• 1998

In this study, active muffler was designed and was manufactured for exhaust noise reduction of commercial vehicle, then experiment of real vehicle was conducted. In a manufactured active muffler, because the flow of exhaust noise in tail pope outlet are become a plane wave, the global reduction if radiation noise from outlet and the placement of error microphone to avoid the exhaust gas of high temperature could be implemented. In control algorithm, reduction of noise of engine driving frequency and harmonic frequency can be archieved using proposed reference signal including a fixed speed state(2,000rpm, 3,000rpm, 4,000rpm) and a run-up speed state(2,000rpm$\rightarrow$4,000rpm) is accomplished with the active muffler installed in vehicle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.883-884
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• 2012

This study deals with design and application of silencer to reduce the exhaust noise, especially at the low frequency range below 200 Hz which is main contribution for the bridge wing noise and the external noise of ships. The designed silencer is composed of side branch resonator, Helmholtz resonator and absorbing material. The resonating frequencies of resonators are set to be the firing order frequencies of the generator engine. Based on the on-board measurement result, it is verified that the designed silencer can effectively reduce the exhaust noise of generator engine.