THE EFFECT OF TURBULENCE ON WAVE PROPAGATION IN THE ATMOSPHERE: GENERATION ATTENUATION AND SCATTERING.
Item
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Title
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THE EFFECT OF TURBULENCE ON WAVE PROPAGATION IN THE ATMOSPHERE: GENERATION ATTENUATION AND SCATTERING.
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Identifier
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AAI8023750
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identifier
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8023750
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Creator
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MENDELSOHN, ALFRED.
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Contributor
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Chan Mou Tchen
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Date
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1980
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Language
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English
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Publisher
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City University of New York.
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Subject
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Engineering, Mechanical
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Abstract
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A comprehensive theoretical study of acoustical wave motion in turbulence is presented. The problems of noise generated by turbulence and that of interaction of acoustical waves with turbulence, resulting in either attenuation or scattering of the wave, have been investigated.;From the Lighthill equation for the generation of sound by turbulence, we investigate the spectral structure of sound pressure fluctuations generated by turbulence with strong mean shear. Both the near field noise generated by an infinite turbulent medium and the far field noise generated by a finite volume of turbulence are considered. For frozen turbulence, and a quasi-isotropic turbulent velocity field possessing Kolmogoroff's spectrum F(k) (TURN) k('-5/3), the pressure spectrum is found to be (PI)(k) (TURN) k('-11/3) and (PI)(k) (TURN) k('-8/3) for the near field and far field noise, respectively. The results compare favorably with experiments.;The attenuation by turbulence is investigated for the two extremes of sound wave and incompressible gravity wave. For the sound wave, the turbulence scales responsible for attenuation are in the inertial subrange of the kinetic energy spectrum and give rise to an isotropic spectral dependent eddy diffusivity. For Kolmogoroff spectrum, the sound attenuation coefficient is found to have a frequency dependence of (omega)('2/3) in good agreement with experiments. For the incompressible gravity wave, the turbulence scales responsible for attenuation are in the buoyancy subrange of the spectrum giving rise to an anisotropic spectral dependent eddy diffusivity. For the buoyancy spectrum F(k) (TURN) k('-3) we calculate the minimum vertical scale of gravity wave to have a linear dependence of scale height H, in good agreement with experiments.;The classicial theory of sound scattering by turbulence is extended to include the effects of mean shear. An expression for the scattering cross-section is obtained which explicitly shows the effect of mean shear. Both the spectral dependence and the directional pattern of the scattered sound are affected by the mean shear. To investigate the effects of gravity, a general theory of scattering of acoustic-gravity wave by turbulence is developed. A general expression for the scattering cross-section is calculated which includes the effects of gravity and background stratification. We show that the spectral dependence and the directional pattern of the scattered wave are modified by gravity.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Engineering
