• Journal of Mechanical Science and Technology
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• 제19권3호
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• pp.894-904
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• 2005

The flow structure inside the intake head greatly affects the working efficiency of a vacuum cleaner such as suction power and aero-acoustic noise. In this study, the flow inside intake heads of a vacuum cleaner was investigated using qualitative flow visualization and quantitative PIV (Particle Image Velocimetry) techniques. The aerodynamic power, suction efficiency and noise level of the intake heads were also measured. In order to improve the performance of the vacuum cleaner, inner structure of the flow paths of the intake head, such as trench height and shape of connection chamber were modified. The flow structures of modified intake heads were compared with that of the original intake head. The aero-acoustic noise caused by flow separation was reduced and the suction efficiency was also changed due to flow path modification of intake head. In this paper, the variations of flow fields for different intake heads are presented and discussed together with results of aerodynamic power, suction efficiency and noise level.

• 소음진동
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• 제4권4호
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• pp.497-505
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• 1994

This paper presents a design scheme of the active noise absorber that consists of the feedforward and feedback controller. The feedback controller aims to increase damping for the specific acoustic mode. The feedforward controller synthesizes the input signal coherent with the primary noise source in order to attenuate the noise field in the broad frequency range. The feedforward controller is adapted to the variation of acoustic plants using the proposed algorithm which compensates the effect of feedback link. Experimental results demonstrate that the proposed method is effective for the active control of band-limited noise fields in the enclosure.

• Ocean and Polar Research
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• 제31권1호
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• pp.1-9
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• 2009

When evaluating acoustic methods for measuring physical parameters in the ocean, economical and technical considerations are paramount. As an indirect method of estimating ocean dynamics, acoustic tomography has advantages over more conventional approaches. It allows the reconstruction of temperature and flow fields from the acoustic impulse time-of-flight measured along the rays propagating from the source to the receiver. However, many problems require complicated and expensive systems. To use the acoustic tomography method to best effect, developing hardware systems with sources and receivers mounted permanently on the sea bottom is crucial. Akulichev et al. presented some experimental results from shallow zones of the World Ocean that served as a motive for developing a multifunction system with acoustic hardware and software. Here we present technical features and the sea test results of the system.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.536-541
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• 1998

Cylindrical chamber silencers with an extended inlet and outlet are widely used to reduce the propagated noise in ducts in many application fields. In this study, an acoustic analysis is carried out for concentric extended pipes inserted into a simple expansion chambers An algebraic equation is derived by using the eigenfunction expansion and orthogonality principle. Using this analytical method, transmission losses are predicted for several configurations of the concentric extended systems.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 D
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• pp.2625-2627
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• 2001

Recently wavelet transform is used in various fields. Especially it is available in image compression. In this paper we will present wavelet compression of acoustic-based underwater image by simulation.

• 한국공간구조학회논문집
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• 제7권2호
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• pp.105-114
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• 2007

최근 다양한 목적의 대공간 사용이 보편화되고 있다. 이들 공간에 대한 다목적요구로 인해 최근 건립되는 대형 스포츠시설들은 스포츠뿐만 아니라 공연과 같은 다양한 이벤트를 수용하도록 요구받고 있다. 다양한 이벤트 상태의 제공을 위해서 건물의 일부를 부분적으로 개폐하는 방식의 사용이 빈번해지고 있으며 이와 같은 부분적 개폐는 자유음장과 확산음장의음향적 연결을 초래하여 음향설계단계에서 어려움을 초래할 것으로 예상된다. 본 연구에서는 1/10 축소모형을 이용하여 확산음장과 자유음장의 음향적 연결에 따른 음장의 음향특성을 측정 분석하였다. 연구결과, 저중주파수 대역에서의 잔향시간은 개구율이 증가함에 따라 고주파수 대역에서보다 빠른 감쇠를 나타내었다. 또한 EDT는 모든 주파수대역에서 개구율 증가에 선형적으로 비례하여 감쇠하는 것으로 나타났다. 명료도는 개구율이 12.5%에 이르기까지 거의 영향을 받지 않으며 그 이후에는 선형적으로 비례하여 증가하였다. 에너지 감쇠패턴의 분석결과, 이중 및 삼중의 감쇠패턴이 나타나고 있으며, Schroeder 적분에 의한 잔향시간의 산출은 부적절한 것으로 판단된다. 따라서 부분적 개방형 공간의 잔향예측에 있어서 EDT가 보다 적절한 것으로 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1037-1041
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• 2007

With the advent of sound field simulator, many sound fields have been reproduced by obtaining the impulse responses of specific acoustic spaces like famous concert hall, opera house. This sound field reproduction has been done by the linear convolution operation between the sound input signal and the impulse response of certain acoustic space. However, the conventional finite impulse response based linear convolution operation always makes real-time implementation of sound field generator impossible due to the large amount of computational burden. This paper introduces the fast convolution method using perceptual redundancy in the processed signals, input audio signal and room impulse response. Temporal and spectral psycho-acoustic filters considering masking effects are implemented in the proposed convolution structure. It reduces the computational burden of convolution methods for realtime implementation of a sound field generator. The conventional convolutions are compared with the proposed one in views of computational burden and sound quality. In the proposed method, a considerable reduction in the computational burden was realized with acceptable changes in sound quality.

• Ocean Science Journal
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• 제41권2호
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• pp.105-111
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• 2006

In this paper, the lines of investigation on a problem of the development of remote acoustic sensing methods in oceanology are formulated. This paper summarizes the results of investigations into the possibilities for monitoring temperature and flow fields in shallow seas. In the discussed experiments, the instrumentation being constituents of the complex for long-duration remote monitoring of marine medium climatic variability and that of the acoustic tomography of shallow sea dynamic processes is used. The acoustic instruments were located on the POI FEB RAS acousto-hydrophysical polygon (Pacific Oceanological Institute, Far Eastern Branch of the Russian Academy of Sciences) near the Gamov Peninsula. Acoustic receiving and transmitting systems operating with multiplex phase-manipulated signals (of M-codes) at frequency range 250-2500 Hz form the basis for this complex.

• 한국분무공학회지
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• 제10권3호
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• pp.29-37
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• 2005

The spray and acoustic characteristics of a gas/liquid swirl coaxial injector are studied experimentally. The self-pulsation is defined as a pressure and flow rate oscillations by a time-delayed feedback between liquid and gas phase. Self-pulsation has strong influences on atomization and mixing processes and accompanies painful screams. So. the spray and acoustic characteristics are investigated. Spray patterns are observed by shadow photography technique in order to determine the onset of self-pulsation. And self-pulsation boundary with Injection conditions and recess length is get. To measure the frequency of the spray oscillation. oscillation of the laser intensity which passes through spray is analyzed by Fast Fourier Transform. For acoustic tests, a PULSE System was used. Acoustic characteristics of a swirl coaxial injector are investigated according to the injection conditions. such as the pressure drop or the liquid and gas phase. and injector geometries. such as recess length and gap size between the inner and outer injector. Front the experimental results. the increase of recess length leads to the rapid increase of the sound pressure level. And as the pressure drop of the liquid phase increases. the frequency of the self?pulsation shifts to the higher frequency. The frequency of spray oscillations is the same as that of the acoustic fields by self-pulsation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2010년도 춘계학술대회 논문집
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• pp.346-347
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• 2010