• Composites Research
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• 제17권3호
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• pp.15-22
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• 2004

위성 발사체의 추진 기관에 의한 음향 하중은 이륙 시 작용하는 주요한 동적 하중 중 하나로서, 이에 의한 위성이나 탑재물의 파손이 보고되고 있다. 위성이나 탑재물에 작용하는 음향 하중의 강토를 저감하기 위해서는 노즈 페어링의 구조 설계 시 차음 성능을 고려한 설계가 필요하다. 특히 복합재 구조의 경우 금속재 구조에 비해 비강성이 커서 음향 하중의 차음 측면에서는 불리하다. 본 논문에서는 위성 발사체의 노즈 페어링용 복합재 평판의 차음 특성을 살펴보았다. 노즈 페어링 구조로 사용 가능한 4종의 복합재 구조에 대하여 무한판 이론 및 통계적 에너지 해석법(SEA)을 이용하여 차음 성능을 평가하였다. 해석 결과를 토대로 두 종류의 복합재 평판을 제작하여 이에 대한 차음 성능을 측정하고 예측치와 비교를 수행하였다. 이를 바탕으로 무게 대비 차음 성능이 우수한 노즈 페어링용 복합재 구조를 선정할 수 있었다.

• 한국음향학회지
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• 제33권5호
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• pp.273-281
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• 2014

본 논문은 수온약층이 존재하는 제주도 근처 천해역 환경에서 획득한 수중음향 실험 데이터를 이용하여 장거리 신호 전달에 수온약층이 미치는 영향을 분석한 결과를 제시한다. 제주도 인근 해역에 서 장기간 측정된 한국해양자료센터의 수온 및 염분 관측자료는 계절에 따라 수온약층이 형성되는 것을 보여주며, 수온약층이 형성되는 시기에는 음향 신호가 해저면 방향으로 굴절하며 전파되므로 해저면에서의 반사 손실이 장거리 전파에 매우 큰 영향을 가진다. 본 연구에서는 2013년 5월에 수행한 제주 음향 통신 실험 (JACE13) 데이터를 이용하여, 수온약층이 존재할 때의 해저면 반사 손실을 추정하였다. 추정된 반사 손실은 약 3 dB 미만의 손실 값을 가지는 것으로 나타났으며, 수신기의 수심이 깊을수록 수신 신호 준위가 높게 나타났다. 이는 수온약층이 형성되는 천해역 환경에서는 수온약층 아래의 음향 트랩핑이 장거리 신호 전달의 주요 경로가 될 수 있음을 보여준다.

• 한국소음진동공학회논문집
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• 제24권8호
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• pp.600-605
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• 2014

Two mufflers for a large-size sedan are suggested aiming (1) sporty-sound and (2) quiet-sound as well as both satisfying low back-pressure and low manufacturing cost. Transmission loss prediction considering heat and flow may increase the accuracy and reduce the development cost in muffler design; thus, GT-power prediction considering heat, flow, and acoustics is utilized. By understanding the fundamentals of flow-acoustic theory in small orifice(hole), an effective muffler design concept is proposed. Vehicle tests show the consistence with predictions for sound; also a back-pressure test bench confirms the advantage in pressure drop for both suggested mufflers. Those suggested mufflers also have advantages in manufacturing cost due to simplicity of the design.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.349-354
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• 2007

This paper considers acoustic analysis of silencer within a Dry vacuum pump. Main object is noise reduction of Dry Vacuum Pump using the silencer. First, we measured SPL and Intensity for noise source identification and then, designed for the silencer corresponding with noise character. 4-pole parameter are used for predicting transmission loss which is one of characteristics of silencer when we designed for silencer. Calculated Transmission Loss to change main effective factor and selected to optimal value using Design of Experiment. Finally, noise reduction is estimated to compare existing silencer with optimal silencer.

• 오토저널
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• 제12권5호
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• pp.85-96
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• 1990

The object of this study is to develop the computer program to predict the transmission loss of a perforated tube muffler with mean flow, and to investigate the influence of porosity and mean flow on the performance of the muffler. The numerical model is made by dividing the muffler into small segments and estimating the transfer matrices for each segment. The computer program is developed for the calculation of the transmission loss of a through-or cross-flow perforated muffler. The experiment is performed for the measurement of the transmission loss and/or the pressure drop for various porosity and flow velocity. From the comparison between computation and experiment, is known that the numerical model agrees well with the experimental result. The effect of porosity and flow velocity on the acoustic performance and the flow resistance of a muffler is presented.

• 한국소음진동공학회논문집
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• 제17권10호
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• pp.950-957
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• 2007

This paper considers acoustic characteristics of silencer within a dry vacuum pump. The main objective is to reduce noise in dry vacuum pump using the new designed silencer. First, SPL and sound intensity are measured for noise source identification and the new model silencer is designed corresponding to noise characteristics. 4-pole parameters are used to predict the transmission loss which is one of the interest characteristics of the new silencer. The calculated transmission loss is then used to change main effective factor and optimal value is selected by using design of experiment. By conducting an experiment, it is proved that the new designed silencer has reduced noise level by 6 dB(A) more than the original one.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.935-946
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• 2014

This paper investigates the noise transmission performance of industrial mufflers widely used in ships based on the CAE modeling and simulation. Since the industrial mufflers have very complicated internal structures, the conventional Transfer Matrix Method (TMM) is of limited use. The CAE modeling and simulation is therefore required to incorporate commercial softwares: CATIA for geometry modeling, MSC/PATRAN for FE meshing and LMS/SYSNOISE for analysis. Main sources of difficulties in this study are led by complicated arrangement of reactive elements, perforated walls and absorption materials. The reactive elements and absorbent materials are modeled by applying boundary conditions given by impedance. The perforated walls are modeled by applying the transfer impedance on the duplicated node mesh. The CAE approach presented in this paper is verified by comparing with the theoretical solution of a concentric-tube resonator and is applied for industrial mufflers.

• 한국자동차공학회논문집
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• 제20권5호
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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.

• 한국소음진동공학회논문집
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• 제20권12호
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• pp.1210-1215
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• 2010

Unit cabin means room, which is installed in the high value-added vessel such as drill ship, offshore platform and FPSO, after pre-assembled. In order to develop the noise control design for a unit cabin, a variety of acoustic tests such as sound absorption, transmission and radiation measurements were carried out by using the deckhouse mock-up. From the tests, it was found out that the sound transmission loss between cabin and corridor was 13 dB below than FPSO standard and the combined noise level of the unit cabin was dominated by the radiated noise from wall panel in low frequency range. Based on the test results, design guidelines for the noise control of the unit cabin were fully established, such as the improvement of sound transmission loss between the cabin and corridor, and radiated cabin noise reduction.

• 한국전자통신학회논문지
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• 제12권6호
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• pp.997-1002
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• 2017

무선전파를 사용하는 지상통신과는 달리 1500[m/s] 속도의 음향채널이 사용되는 수중통신은 수중온도, 염도를 비롯한 통신환경에 민감할 뿐 아니라 3D 공간의 영향을 받는다. 3D 수중통신은 통신공간의 복잡성과 더불어 음파의 전파손실, 해저환경에서 발생되는 음향잡음 등에 민감하다. 본 연구에서는 이와 같은 3D 수중통신환경의 특성을 고려하여 3D 수중통신환경에서 운용되는 MANET을 대상으로 전송성능을 측정 분석하고 이를 토대로 수중 MANET 운용조건을 제시한다. 본 연구는 NS-2를 기반으로 구축한 수중통신 시뮬레이터를 사용하여 수행하며, 성능파라미터로는 처리율, 전송지연, 패킷손실율 및 소비에너지를 사용한다.