• Title/Summary/Keyword: acoustic energy

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The Effect of Turbulent Premixed Flame on the Wave Scattering (난류예혼합화염이 음파의 산란에 미치는 영향에 관한 연구)

  • Cho, Ju-Hyeong;Baek, Seung-Wook
    • Journal of the Korean Society of Combustion
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    • v.12 no.1
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    • pp.1-10
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    • 2007
  • Analytical investigation of acoustic wave scattering from turbulent premixed flames was conducted to evaluate the acoustic energy amplification/damping. Such acoustic energy change is attributed to the acoustic velocity jump due to flame's heat release. Small perturbation method up to second order and stochastic analysis were utilized to formulate net acoustic energy and the energy transfer from coherent to incoherent energy. Randomly wrinkled flame surface is responsible for the energy transfer from coherent to incoherent field. Nondimensional parameters that govern net acoustic energy were determined: rms height and correlation length of flame front, incident wave frequency, incidence angle, and temperature ratio. The dependence of net acoustic energy upon these parameters is illustrated by numerical simulations in case of Gaussian statistics of flame front. Total net energy was amplified and the major factors that affect such energy amplification are incidence angle and temperature ratio. Coherent (incoherent) energy is damped (amplified) with rms height and correlation length of flame front.

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A method of Shaped Sound Focusing Using Multiple Monopole Sources: Hollow Cylinder shape (다수의 단극 음원들을 이용한 속이 빈 실린더 형상의 응향 위치 에너지 집적공간 형성방법)

  • Park, Jin-Young;Kim, Yang-Hann
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11a
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    • pp.537-540
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    • 2005
  • Shaped Sound Focusing is defined as the generation of acoustically bright zone with a certain shape in space using multiple sources. The acoustically bright zone is a spatially focused region with relatively high acoustic potential energy level. In view of the energy transfer, acoustic focusing using multiple sources is essential because acoustic energy is very small to use other type of energy. It can be done by taking optimization techniques which can be acoustic brigtness control and acoustic contrast control. But it has not been frequently concerned about several cases, so the case of hollow cylinder shaped sound focusing is adapted and there wi11 be arguments about available control variables and spatially controllable region in this case.

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The Acoustic Emission Energy Analysis of Subambient Pressure Tri-Pad Slider

  • Pan Galina;Hwang Pyung;Xuan Wu
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2004.11a
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    • pp.139-142
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    • 2004
  • The object of the present work is the acoustic emission energy analysis of subambient pressure tri-pad slider. Head/disk interaction during start/stop and constant speed were detected by using acoustic emission (AE) test system The frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction Natural frequency analysis was performed using Ansys program. Acoustic emission energy was calculated for the slider modes.

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Robust Energy Efficiency Power Allocation for Uplink OFDM-Based Cognitive Radio Networks

  • Zuo, Jiakuo;Dao, Van Phuong;Bao, Yongqiang;Fang, Shiliang;Zhao, Li;Zou, Cairong
    • ETRI Journal
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    • v.36 no.3
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    • pp.506-509
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    • 2014
  • This paper studies the energy efficiency power allocation for cognitive radio networks based on uplink orthogonal frequency-division multiplexing. The power allocation problem is intended to minimize the maximum energy efficiency measured by "Joule per bit" metric, under total power constraint and robust aggregate mutual interference power constraint. However, the above problem is non-convex. To make it solvable, an equivalent convex optimization problem is derived that can be solved by general fractional programming. Then, a robust energy efficiency power allocation scheme is presented. Simulation results corroborate the effectiveness of the proposed methods.

Damage progression study in fibre reinforced concrete using acoustic emission technique

  • Banjara, Nawal Kishor;Sasmal, Saptarshi;Srinivas, V.
    • Smart Structures and Systems
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    • v.23 no.2
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    • pp.173-184
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    • 2019
  • The main objective of this study is to evaluate the true fracture energy and monitor the damage progression in steel fibre reinforced concrete (SFRC) specimens using acoustic emission (AE) features. Four point bending test is carried out using pre-notched plain and fibre reinforced (0.5% and 1% volume fraction) - concrete under monotonic loading. AE sensors are affixed at different locations of the specimens and AE parameters such as rise time, AE energy, hits, counts, amplitude and duration etc. are obtained. Using the captured and processed AE event data, fracture process zone is identified and the true fracture energy is evaluated. The AE data is also employed for tracing the damage progression in plain and fibre reinforced concrete, using both parametric- and signal- based techniques. Hilbert - Huang transform (HHT) is used in signal based processing for evaluating instantaneous frequency of the acoustic events. It is found that the appropriately processed and carefully analyzed acoustic data is capable of providing vital information on progression of damage on different types of concrete.

The Effect of Acoustic Energy on the Collection Efficiency of the Electrostatic Precipitator (음파에너지가 전기 집진기의 집진 효율에 미치는 영향)

  • 정상현;홍원석;김용진;심성훈
    • Journal of Energy Engineering
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    • v.12 no.3
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    • pp.207-215
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    • 2003
  • An experimental study on the characteristics of collection efficiency for electrostatic precipitator under the action of acoustic energy in the gas stream was performed. In the experiment, the acoustic energy which has 2 kHz and 141 dB was applied to electrostatic precipitator inlet, and the test parameters were used in terms of the magnitude of gas velocity. From the results of experiment, the collection efficiency of ESP was increased due to acoustic energy, and this effect was much clearer at high velocity. This means that the acoustic energy can play an important role in the enlargement of specific collection area of the electrostatic precipitator.

An Analysis of Acoustic Features Caused by Articulatory Changes for Korean Distant-Talking Speech

  • Kim Sunhee;Park Soyoung;Yoo Chang D.
    • The Journal of the Acoustical Society of Korea
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    • v.24 no.2E
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    • pp.71-76
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    • 2005
  • Compared to normal speech, distant-talking speech is characterized by the acoustic effect due to interfering sound and echoes as well as articulatory changes resulting from the speaker's effort to be more intelligible. In this paper, the acoustic features for distant-talking speech due to the articulatory changes will be analyzed and compared with those of the Lombard effect. In order to examine the effect of different distances and articulatory changes, speech recognition experiments were conducted for normal speech as well as distant-talking speech at different distances using HTK. The speech data used in this study consist of 4500 distant-talking utterances and 4500 normal utterances of 90 speakers (56 males and 34 females). Acoustic features selected for the analysis were duration, formants (F1 and F2), fundamental frequency, total energy and energy distribution. The results show that the acoustic-phonetic features for distant-talking speech correspond mostly to those of Lombard speech, in that the main resulting acoustic changes between normal and distant-talking speech are the increase in vowel duration, the shift in first and second formant, the increase in fundamental frequency, the increase in total energy and the shift in energy from low frequency band to middle or high bands.

Radiation Power Control by Means of Absorptive Material Arrangement in an Enclosure (흡음재 배치를 통한 닫힌 공간에서의 소음원 방사 파워 제어)

  • 조성호;김양한
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2004.05a
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    • pp.688-691
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    • 2004
  • We have studied the possibility of global noise reduction by the sound power control through selection of distribution and impedance of absorptive materials. It is necessary to investigate the relation between the global sound energy in the field and the total sound power radiated by sources. In the previous work (1,2), the authors presented a useful design method to change boundary condition that can be useful to reduce noise in acoustically small enclosures. The possibility of total acoustic potential energy reduction by acoustic source power control is examined in an acoustically small cavity. Using acoustic energy balance equation, the relation between global noise control performance and absorptive material's arrangement/impedance is deduced. Numerical simulation is performed to interpret its physical meaning in terms of absorbent's distribution and impedance.

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Room Acoustic Properties of Coupled Rooms Connected by an Aperture in the Steady State Condition (정상상태조건에서의 개구부로 연결된 커플룸의 음향 특성)

  • Na, Hae Joong;Lim, Byoung-Duk
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.26 no.3
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    • pp.315-322
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    • 2016
  • Room acoustic properties of coupled rooms connected by an aperture has been analyzed using statistical acoustic model based on the diffused sound field assumption, which has limitation in dealing with the parameters such an room geometries and non uniform absorptivity of the boundary surfaces. In order to overcome these difficulties the acoustic diffusion model has been introduced, by which distribution of the acoustic energy density can be analyzed for various shapes and wall absorptivity. In this study acoustic properties of coupled rooms connected by an aperture(e.g. door) is analyzed using acoustic diffusion equation, which is solved numerically. The mean energy densities of two rooms obtained by the diffusion model are compared with those from the statistical model. The results show good agreement for various coupling aperture sizes and absorption coefficients. For a limiting case when the partition wall is substituted by an aperture and the two rooms eventually forms a single room, results of coupled room analysis using diffusion model show good agreement with those of a single room.

Note on the Two-Microphone Methods for the Measurement of Acoustic Impedance (음향 임피던스 측정을 위한 이중 마이크로폰 기법에 대한 고찰)

  • SEO, SEONGHYEON
    • Transactions of the Korean hydrogen and new energy society
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    • v.29 no.2
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    • pp.163-169
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    • 2018
  • The present article discusses about the measurement techniques of acoustic impedance that becomes one of the important acoustic characteristics of various boundaries found inside of propulsion systems. Acoustic characteristics including acoustic impedance and reflection coefficient can be often assessed and estimated by use of the two-microphone method. Theoretical expressions of acoustic impedance and reflection coefficient measured in an impedance tube are presented for both cases with mean flow and without flow, and the practical application of the method through calibration is also provided. The acoustic impedance and the reflection coefficient are related with axial locations of microphones, thermodynamic characteristics of gas inside, and the transfer function between the pressure wave measurements at multiple locations.