Waveguide Sound Propagation in a Turbulent Atmosphere Above Randomly Rough Ground PDF Download
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Author: Vladimir Ostashev
Publisher:
ISBN:
Category : Acoustical engineering
Languages : en
Pages : 20
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Author: Vladimir Ostashev
Publisher:
ISBN:
Category : Acoustical engineering
Languages : en
Pages : 20
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Book Description
Author: Vladimir E. Ostashev
Publisher:
ISBN:
Category : Atmosphere
Languages : en
Pages : 15
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Book Description
Most previous research on sound propagation in the turbulent atmosphere has focused on nearly horizontal propagation. Sound propagation over vertical and slanted paths is fundamentally different from horizontal propagation in that the variances and length scales of the turbulence depend on the height above the ground. In this paper, propagation over vertical and slanted paths is studied using approaches and methods developed for wave propagation through inhomogeneous, random media. Statistical characteristics of sound signals such as the extinction coefficient of the mean sound field, the strength parameter, the transverse mutual coherence function, the coherence radius, and the correlation functions and variances of the phase and log-amplitude fluctuations are calculated for arbitrary spectra of temperature and wind velocity fluctuations, and then specialized to the von Kármán model for the turbulence spectra. The extinction coefficient and coherence radius are analyzed numerically for various meteorological conditions of the atmospheric boundary layer. The results obtained are compared with those for near-horizontal sound propagation. The theory has applications to localization of elevated sound sources with ground-based microphone arrays, and the detection of ground-based sources with elevated arrays.
Author:
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Category :
Languages : en
Pages : 17
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In complex environments the modelling of outdoor sound propagation implies to take into account the mixed influence of ground characteristics (topography, obstacles, impedance, etc.) and atmospheric conditions (refraction and turbulence). During the last decade significant progress has been made in the modelling of sound propagation over distances ranging from hundreds meters to kilometres, and the agreement between calculated and measured fields has been greatly improved. New developments appear in the parabolic-equation method. In this paper we present a method which evaluates the propagation of an acoustic wave above uneven terrains including realistic meteorological parameters. In our approach the effects of the topography are modelled using appropriate rotated co-ordinates systems in order to treat the non-flat ground as a succession of flat domains. We also examine the influence of scale resolution on numerical simulation of long range sound propagation through the turbulent atmosphere. Currently, we generate the turbulence using a Random Fourier Modes technique, such that the turbulent fluctuation at any point in the medium (either scalar or vectorial in nature) is calculated from the sum of a chosen number of modes. Our model of outdoors sound propagation is validated both with classical numerical benchmark cases and recent outdoor experiments.
Author:
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ISBN:
Category : Aeronautics
Languages : en
Pages : 704
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Author:
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ISBN:
Category :
Languages : en
Pages : 198
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Propagation of sound waves close to the ground is a complex problem involving many interesting mechanisms. In addition to geometrical spreading and molecular absorption, which are reasonably well understood, the three main mechanisms which influence the acoustic field are reflection with phase change due to the finite impedence of the ground, refraction by wind and temperature gradients, and scattering by atmospheric turbulence. Outdoor sound propagation in a turbulent medium is not a well understood process and has only recently begun to receive serious attention. This report is the first of a series of reports on sound propagation through a turbulent atmosphere. It documents the experimental configuration and describes data analysis. The data analysis includes plots of the real and imaginary parts of the acoustic pressure as a function of time (scatter plots), probability of observing a particular amplitude, and the more familiar structure functions. A preliminary analysis of data suggests reasonable agreement in structure functions at frequencies of 500 Hz and above. At lower frequencies, phase and log amplitude structure functions are both larger than predicted from theory. A tentative explanation for this difference is under development and will be presented in the third of the three volume series. The second volume will be devoted to refractive effects. Keywords: Computer programs; Outdoor sound.
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Category :
Languages : en
Pages : 0
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The foundations of the modern theory of sound propagation and scattering in a homogeneous and isotropic atmospheric turbulence are developed: The sound scattering cross-section for von Karman spectra of temperature and wind velocity fluctuations is calculated; the rigouros theory of line of sight sound propagation in an atmosphere with Kolmogorov, Gaussian and von Karman spectra of temperature and wind velocity fluctuations is developed; a new theoretical formulation of the interference of the direct wave from source to receiver and that reflected from the ground in a turbulent atmosphere is presented; the sound scattering cross section in an atmosphere with arbitrary profiles of temperature and wind velocity is calculated; some predictions of the modern theory are verified experimentally; correct wideangle parabolic equations for sound waves in a turbulent atmosphere are derived and used for numerical simulations of sound propagation. The modern theory has already been adopted by scientists for calculations of sound propagation in turbulent media and as a basis for development of new acoustic remote sensing techniques of the atmosphere and ocean in several countries and organizations including the U.S. Army Research Laboratory.
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Category :
Languages : en
Pages : 0
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Three-dimensional models of anisotropic and inhomogeneous spectra of temperature and wind velocity fluctuations in unstable atmospheric boundary layers have been developed, modified or extended. Furthermore, theories of sound propagation through anisotropic, inhomogeneous, and intermittent atmospheric turbulence have been developed. These theories allow consideration of different geometries of sound propagation: line-of-sight sound propagation, interference of the direct and ground reflected waves, sound scattering into a refractive shadow zone, and waveguide sound propagation. Using the spectra developed or adopted from the literature, it was shown that anisotropy, inhomogeneity, and intermittency of atmospheric turbulence can significantly affect the statistical moments of a sound field for these geometries. Some of the theoretical results obtained have been verified experimentally. Two related tasks have also been accomplished. First, a new scheme of source localization in the atmosphere by means of acoustic tomography was proposed. The scheme accounts for sound refraction in the atmosphere and allows retrieval of vertical profiles of temperature and wind velocity. Secondly, it was shown that, in many cases, the effects of sound refraction on acoustic remote sensing of wind velocity and the structure parameters of temperature and velocity fluctuations are significant. Algorithms were developed to account for these effects in acoustic remote sensing of the atmosphere.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722750305
Category :
Languages : en
Pages : 56
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Theoretical, computational, and experimental techniques were developed for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that: (1) is not idealizable as being perfectly flat, or (2) that is not idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence. Berthelot, Yves H. and Pierce, Allan D. and Kearns, James A. and Zhou, Ji-Xun Unspecified Center...
Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 338
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Author:
Publisher:
ISBN:
Category : Physics
Languages : en
Pages : 812
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