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  • 1
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    Algebraically growing waves in ducts with sheared mean flow (1973)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Standing or traveling waves which vary algebraically with the axial distance in uniform ducts with sheared mean velocity profiles are investigated. The results show that such waves are not possible for ducts with uniform cross sections and fully developed mean flows.
    Keywords: PHYSICS, GENERAL
    Type: VPI-E-73-11 , NASA-CR-136503
    Format: application/pdf
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  • 2
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    Nonlinear acoustic propagation in two-dimensional ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The method of multiple scales is used to obtain a second-order uniformly valid expansion for the nonlinear acoustic wave propagation in a two-dimensional duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear effects tend to flatten and broaden the absorption versus frequency curve, in qualitative agreement with the experimental observations. Moreover, the effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material nonlinearity decreases with increasing sound frequency.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 55
    Format: text
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  • 3
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    Sound waves in two-dimensional ducts with sinusoidal walls (1974)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The method of multiple scales is used to analyze the wave propagation in two-dimensional hard-walled ducts with sinusoidal walls. For traveling waves, resonance occurs whenever the wall wavenumber is equal to the difference of the wavenumbers of any two duct acoustic modes. The results show that neither of these resonating modes could occur without strongly generating the other.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 56
    Format: text
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  • 4
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    Non-linear wave propagation in acoustically lined circular ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An analysis is presented of the nonlinear effects of the gas motion as well as of the acoustic lining material on the transmission and attenuation of sound in a circular duct with a uniform cross-section and no mean flow. The acoustic material is characterized by an empirical, nonlinear impedance in which the instantaneous resistance is a nonlinear function of both the frequency and the acoustic velocity. The results show that there exist frequency bandwidths around the resonant frequencies in which the nonlinearity decreases the attenuation rate, and outside which the nonlinearity increases the attenuation rate, in qualitative agreement with experimental observations. Moreover, the effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material nonlinearity decreases with increasing sound frequency.
    Keywords: PHYSICS, GENERAL
    Type: Journal of Sound and Vibration; 36; Sept. 8
    Format: text
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  • 5
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    Effect of transverse velocity and temperature gradients on sound attenuation in two-dimensional ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: An investigation is described of the effect of transverse mean-velocity and temperature gradients on sound attenuation in acoustically treated two-dimensional ducts. The results show that cooling the duct walls leads to channeling the sound toward the walls for both downstream and upstream propagation. The effect of mean-temperature gradients on the attenuation rates of the lowest three modes can be as important as the effect of mean-velocity gradients.
    Keywords: PHYSICS, GENERAL
    Type: Journal of Sound and Vibration; 34; June 22
    Format: text
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  • 6
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    Algebraically growing waves in ducts with sheared mean flow (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Analysis of the behavior of standing and traveling acoustic waves in a smooth duct with a fluid flow having a sheared mean velocity profile, when the waves grow algebraically as they travel along the duct axis. It is shown that standing waves growing algebraically with the axial distance cannot exist in a smooth duct when the duct wall have a finite resistance. The existence of traveling waves subject to the same law of growth is also dismissed under realistic flow conditions.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 55
    Format: text
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  • 7
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    Acoustic propagation in ducts with varying cross sections (1973)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The method of multiple scales is used to derive the equations that describe the spatial and temporal variation of the amplitudes and phases of a wave packet propagating in slowly varying hard-walled or lined ducts. The analysis is carried out for rectangular as well as circular ducts. These equations are statements of the conservation of energy. For large admittance or high-frequency modes, an approximate expression is obtained for the attenuation. This expression shows that all possible acoustic modes are attenuating. The results also show that decreasing the cross sectional area can lead to elimination of some of the acoustic modes.
    Keywords: PHYSICS, GENERAL
    Type: Acoustical Society of America; vol. 54
    Format: text
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  • 8
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    A perturbation analysis of the propagation and instability of waves in ducts with varying cross sections (1974)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: All publications and presented speeches are listed that discuss the various aspects of perturbed wave propagation and noise generation in ducts with varying cross sections.
    Keywords: PHYSICS, GENERAL
    Type: NASA-CR-140401 , VPI-E-74-27
    Format: application/pdf
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  • 9
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    Nonlinear acoustic propagation in rectangular ducts (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The method of multiple scales is used to obtain a second-order uniformly valid expansion for nonlinear acoustic wave propagation in a rectangular duct whose walls are treated with a nonlinear acoustic material. The wave propagation in the duct is characterized by the unsteady nonlinear Euler equations. The results show that nonlinear materials attenuate sound more than linear materials except at high acoustic frequencies. The nonlinear materials produce higher and combination tones which have higher attenuation rates than the fundamentals. Moreover, the attenuation rates of the fundamentals increase with increasing amplitude.
    Keywords: PHYSICS, GENERAL
    Type: Symposium on Finite-amplitude wave effects in fluids; Aug 20, 1973 - Aug 22, 1973; Copenhagen; Denmark
    Format: text
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