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  • 1
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    Correlation of the effects of grazing flow on the impedance of Helmholtz resonators (1982)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-18
    Beschreibung: Measurements of the acoustic impedance of a two-dimensional Helmholtz resonator, i.e., a cavity coupled to the environment through a high-aspect ratio slot are presented as a function of the velocity of a steady flow above the orifice of the resonator. The structure of the unsteady flow above the orifice is outlined from hot-wire measurements. A simplified model of it is proposed and analyzed, leading to a successful correlation of both the resistance and the reactance of the resonator.
    Schlagwort(e): ACOUSTICS
    Materialart: Acoustical Society of America; vol. 72
    Format: text
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  • 2
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    The velocity perturbations above the orifice of an acoustically excited cavity in grazing flow (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Detailed measurements of the time-dependent velocities induced inside and outside the opening of an acoustically excited, two-dimensional Helmholtz resonator imbedded in a grazing flow are presented. The remarkably clear structure of the perturbation field which evokes a pulsating source and a coherently pulsating vortex-image pair is described.
    Schlagwort(e): ACOUSTICS
    Materialart: Journal of Fluid Mechanics (ISSN 0022-1120); 128; March 19
    Format: text
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  • 3
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    The velocity field near the orifice of a Helmholtz resonator in grazing flow (1981)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: Measurement of the time-dependent velocities induced inside and outside the opening of acoustically excited, two-dimensional Helmholtz resonator imbedded in a grazing flow are presented. The remarkably clear structure of the perturbation field which evokes a pulsating source and a coherently pulsating vortex-image pair is described. The simple phenomenological "lid-model" which correlates the variation in the components of the acoustic impedance with the velocity of the grazing flow is discussed and extended.
    Schlagwort(e): ACOUSTICS
    Materialart: NASA-CR-168548 , UCLA-ENG-81-101
    Format: application/pdf
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  • 4
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    Comparing the relationships between noise level and annoyance in different surveys - A railway noise vs. aircraft and road traffic comparison (1982)
    In:  Other Sources
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    Publikationsdatum: 2019-06-28
    Beschreibung: Annoyance expressed in a railway noise survey is compared with that from two road traffic and three aircraft surveys in order to determine whether responses to various types of environmental noise are source-specific. Railway noise is found to be less annoying than other noises at any given high noise level. Railway noise annoyance rises less rapidly with increasing noise level. At high levels, this gap in reactions averages about 10 dB; it ranges from 4 dB to more than 20 dB. The methods used for comparing the surveys are examined. It is found that methodological uncertainties lead to imprecise comparisons and that different annoyance scales yield different estimates of intersurvey differences.
    Schlagwort(e): ACOUSTICS
    Materialart: Journal of Sound and Vibration; 81; Mar. 8
    Format: text
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  • 5
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    Effect of flow on the acoustic performance of extended reaction lined ducts (1983)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: A model is developed for the effects of uniform and boundary-layer mean flow on the attenuation and propagation of harmonically excited sound waves in an extended reaction lined cylindrical duct. A duct geometry consisting of an annular outer region of bulk material surrounding an inner cylinder of air is utilized. A numerical solution is obtained for the coupled wave equations governing the motion of the sound in both the inner and annular regions. It is found that the numerically predicted attenuation and propagations constants are in excellent agreement with measured values using Kevlar as the liner material for plane-wave mode (O,O) excitation over a wide range of mean flows and sound frequency. The boundary-layer effects are determined to be unimportant, at least for plane-wave sound. In addition, numerical studies indicate small differences between the use of either the radial velocity or the radial displacement boundary conditions.
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA PAPER 83-0778 , American Institute of Aeronautics and Astronautics, Aeroacoustics Conference; Apr 11, 1983 - Apr 13, 1983; Atlanta, GA
    Format: text
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  • 6
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    Analytical and experimental investigation of the propagation and attenuation of sound in extended reaction lined ducts (1981)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Results are presented of an analytical and experimental study of the attenuation and propagation of harmonically excited sound waves in an extended reaction lined cylindrical duct. The duct geometry considered consisted of an annular outer region of bulk material surrounding an inner cylinder of air. The coupled wave equations governing the motion of the sound in both the inner and annular regions were solved numerically. The numerically predicted attenuation and propagation constants were in excellent agreement with measured values using Kevlar as the liner material for plane-wave mode (0,0) excitation over the frequency from 100 to 7,000 Hz. Although the numerical model was verified using Kevlar, it can be used with any fibrous constructed bulk liner. The results of this study demonstrate that a good start has been made on the numerical modelling of the acoustic performance of extended reaction liners.
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA PAPER 81-2014 , Aeroacoustics Conference; Oct 05, 1981 - Oct 07, 1981; Palo Alto, CA
    Format: text
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  • 7
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    Acoustic behavior of fibrous bulk materials (1980)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: A semiempirical model of the acoustic behavior of fibrously constructed bulk materials of Hersh and Walker (1979) is generalized to take into account the filtration or removal of particles by fibrous mats and heat conduction between the material fibers and the surrounding fluid. Equations governing the propagation and attenuation of sound waves in a fibrous material are derived on the basis of a solution of the Navier Stokes equation for momentum conservation and a one-dimensional model of heat transfer between the sound field and the fibers. A comparison of the two propagation constants and material impedance specified by the model and experimental measurements for Kevlar 29 indicates the accuracy of the model over a wide range of sound frequencies, material porosities and specimen thickness. It is also found that heat transfer effects are relatively unimportant, while the attenuation constants and material characteristic impedance are a function of fiber orientation relative to sound field propagation direction.
    Schlagwort(e): ACOUSTICS
    Materialart: AIAA PAPER 80-0986 , Aeroacoustics Conference; Jun 04, 1980 - Jun 06, 1980; Hartford, CT
    Format: text
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