• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.581-587
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• 2014

Intake silencers of high performance and with less pressure drop are developed for a household oxygen generator. First, the acoustic power of the target oxygen generator are experimentally evaluated according to ISO code. Then, the transmission loss of and the flow characteristics inside the existing intake silencer are predicted and analyzed. On a basis of these results, two intake silencers are proposed, which are designed to induce the swirling flow inside the intake silencer and thus to reduce the flow loss. The predicted TL and the pressure drop for these two new silencers are compared to the existing one, which shows that the proposed ones have higher TLs as well as less pressure drop. The reason for these improvements are explained by investigating the flow characteristics of the new silencers in detail.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.11
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• pp.846-853
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• 2014

High performance intake silencer with low pressure drop are developed for a household oxygen generator. First, the acoustic power of the target oxygen generator are experimentally evaluated according to ISO code. Then, the transmission loss of and the flow characteristics inside the existing intake silencer are predicted and analyzed. On a basis of these results, two intake silencers are proposed, which are designed to induce the swirling flow inside the intake silencer and thus to reduce the flow loss. The predicted TL and the pressure drop for these two new silencers are compared to the existing one, which shows that the proposed ones have higher TL as well as low pressure drop. The reason for these improvements are explained by investigating the flow characteristics of the new silencers in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.676-681
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• 2001

We usually divide the noise of exhaust system into pulsation noise and flow noise. Pulsation noise is the shock wave to occur when the burning gas of low pressure emits and include harmonic having basic frequency as the exhaust cycle of engine. Flow noise is the noise that is produced when gas flow emits into the atmosphere through the pipe and has the character of frequency like pink noise which has the high level of high frequency component. A muffler is divided into reflective type and absorptive type. We usually use the muffler compounding the property of them. In this study, it is the case of transfer matrix method that a muffler is compounded to analyze the elements of each section according to sound wave's proceed direction. But we use simple model. So, we use finite element method that takes short time to analyze. Acoustic analysis gives us transfer matrix to use FEA of SYSNOISE and we use STAR-CD for fluid analysis. We made database that is based on analytical results about the muffler of expansion type, extended type, offset type, reverse type, and perforated type and developed the muffler design system to perform work efficiently.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.1
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• pp.49-54
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• 2019

Since the underwater communication environment, which is used mainly in acoustic channel, is different from terestrial communication, it needs to analyze the appropriate transmission performance in underwater environment to implement the communication services. Appropriate traffic process method for a communication service is required through transmission performance of object traffic for the communication service. In this paper, transmission performance of video traffic on underwater MANET(Mobile Ad-hoc Network) is analyzed and video traffic configuration scheme on underwater MANET with results of performance analysis is suggested, This study is done with computer simulation based on NS(Network Simulator)-3. throughput, transmission delay, packet loss rate is used for transmission performance.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.12
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• pp.32-40
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• 2015

Code division multiple access (CDMA) is one of the promising medium access control scheme for underwater acoustic sensor networks due to its beneficial features such as robustness against frequency-selective fading and high frequency-reuse efficiency. In this paper, we design a closed-loop power control scheme for the underwater CDMA, to adapt time-varying acoustic channel. In the proposed scheme, sink node sends to sensor nodes the associated path loss which is acquired by uplink-channel analysis based on received packets from the sensor nodes. Then, sensor nodes adjust their transmission power in an adaptive manner to time-varying underwater acoustic channel, according to the informations sent by the sink node.

• Korean Journal of Audiology
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• v.24 no.4
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• pp.174-179
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• 2020

Background and Objectives: The integration of auditory-visual speech information improves speech perception; however, if the auditory system input is disrupted due to hearing loss, auditory and visual inputs cannot be fully integrated. Additionally, temporal coincidence of auditory and visual input is a significantly important factor in integrating the input of these two senses. Time delayed acoustic pathway caused by the signal passing through digital signal processing. Therefore, this study aimed to investigate the effects of hearing loss and hearing aid digital delay circuit on sound-induced flash illusion. Subjects and Methods: A total of 13 adults with normal hearing, 13 with mild to moderate hearing loss, and 13 with moderate to severe hearing loss were enrolled in this study. Subsequently, the sound-induced flash illusion test was conducted, and the results were analyzed. Results: The results showed that hearing aid digital delay and hearing loss had no detrimental effect on sound-induced flash illusion. Conclusions: Transmission velocity and neural transduction rate of the auditory inputs decreased in patients with hearing loss. Hence, the integrating auditory and visual sensory cannot be combined completely. Although the transmission rate of the auditory sense input was approximately normal when the hearing aid was prescribed. Thus, it can be concluded that the processing delay in the hearing aid circuit is insufficient to disrupt the integration of auditory and visual information.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.10B
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• pp.1200-1209
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• 2011

In this paper, we propose a novel energy efficient MAC protocol which is based on orthogonal frequency division multiple access (OFDMA) and exploits the physical characteristic that propagation loss of acoustic wave depends on the distance. In the proposed scheme, sensor nodes are grouped according to the distance to sink node. Then, each group uses a different frequency band. The proposed scheme not only enables all sensor nodes to maintain the signal-to-noise ratio above a certain required level (Accepted Minimum SNR, AMS), but also reduces overall transmission power consumption. In addition, the dynamic sub-channel allocation is employed in order to improve data transmission rate. Simulations show that proposed MAC protocol has better performance in a delay-tolerant underwater acoustic sensor networks.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.245-246
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• 2006

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.371-374
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• 2001

내연기관의 흡기 소음을 줄이기 위한 효과적인 소음 제어 요소로서 다공형 직조관(porous woven hose)이 널리 사용된다. 직조관이 사용된 흡기계의 음향 특성을 예측하기 위해서는 직조관의 임피던스(acoustic wall impedance)에 대한 정보를 알아야 한다. 그러나, 높은 저항(resistance), 두께, 곡률, 비균질성 등의 특수한 음향학적/구조적 특성 때문에 직조관의 임 피던스를 정확하게 측정하는 것은 쉽지 않다. 본 연구에서는 소음기의 전달손실(transmission loss)을 측정하는데 널리 사용되는 간단한 측정장치를 이용하여 직조관의 임피던스를 측정하였다. 측정된 임피던스에 대해 직조상태를 나타내는 인자와 주파수를 독립 변수로 사용하여 curve-fitting을 수행하여, 직조상태가 다른 직조관의 임피던스를 예측하였다. 이렇게 예측된 임피던스로부터 실제 사용되는 범위 내에서 임의의 길이를 가지는, 직조상태가 다른 직조관의 전달 손실을 예측하였고, 측정된 전달손실과 비교하여, 잘 일치하는 것을 확인하였다. 본 연구에서 제시한 방법은 직조관의 음향 특성을 파악하고, 직조관이 사용된 자동차 흡기계의 음향성능을 예측하는데 유용하게 사용될 수 있다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.5
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• pp.497-503
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• 2016

In this study, we formulate an acoustical topology optimization problem to optimally design a partition layout inside the expansion chamber of a muffler. The lower-limit insertion loss value at a target frequency is constrained, and the partition volume is selected as an object function. In this study, we calculate the insertion loss outside the duct, while to determine the noise-attenuation performance, we use the insertion loss value calculated inside the duct or transmission loss value obtained in a previous study. We employ the finite-element model for acoustical analysis, and we determine the transmission of an incident acoustic wave through each finite element using the functions of design variables that change continuously between "0" and "1." The rigid body elements, which totally reflect incident waves, build up partitions. Finally, we compare optimal topologies that depend on the target frequency and the allowed lower-limit value of insertion loss.