Author: Harry J. AuvermannPublisher:
ISBN:
Category : Backscattering
Languages : en
Pages : 19
Book Description
Shadow Zone Boundary Limitation of the Effective Acoustical Turbulence Scattering Volume Using the Turbule Ensemble Model
Author: Harry J. AuvermannPublisher:
ISBN:
Category : Backscattering
Languages : en
Pages : 19
Book Description
Shadow Zone Boundary Limitation of the Effective Acoustical Turbulence Scattering Volume Using the Turbule Ensemble Model
Author: Harry J. AuvermannPublisher:
ISBN:
Category : Backscattering
Languages : en
Pages : 19
Book Description
Acoustic Scattering Into Shadow Zones from Atmospheric Turbulence
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
When acoustic scattering estimates are desired from atmospheric regions containing fully developed isotropic homogeneous turbulence, scattering formulas based upon statistical representations of the turbulence well represent the experimental results. However, there is a class of battlefield scenarios where these provisos of fully developed, isotropic and homogeneous sometimes do not apply. The example of this class that is most familiar is that of source and detector near the ground. At ground level, the wind velocity is zero, while at altitude it is not. Thus a gradient of wind velocity exists. There exists often a temperature gradient caused by heating or cooling of the air by contact with the ground. These gradients are recognized in propagation codes by modeling the atmosphere as stratified with each stratum bounded by planes parallel to the assumed flat ground. The anisotropy of the atmosphere near the ground recognized in propagation codes carries over into the generation of turbulence. The above discussion leads to the conclusion that anisotropy in turbulence is to be expected in scenarios played out near the ground, scenarios common to Army operations. The understanding that high sound levels in shadow zones (those regions in an acoustical field in which no sound can reach if the field is determined by ray theory) is caused by scattering from turbulence is very important. This importance arises from the possibility that shadow zone sensors may be used to achieve passive non-line-of-sight detection of enemy assets. This paper unites the above considerations by calculating the shadow zone signal level for a representative battlefield scenario using a structural model of turbulence.
Turbule Ensemble Model of Atmospheric Turbulence: Progress in Its Development and Use in Acoustical-Scattering Investigations
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
The objective of one portion of the Army Research Laboratory program on acoustic propagation on the battlefield is to develop an advanced method of accounting for the effects of anisotropic inhomogeneous turbulence. The approach chosen was to extend the idea of eddies under the assumption that the turbulence field is made up of a multiplicity of isolated eddies of different sizes. This method of describing turbulence is called the Turbule Ensemble Model (TEM). A turbule is defined to be a localized inhomogeneity of any type. The primary types are temperature and velocity inhomogeneities; the term turbule is an extension of the idea of an eddy, which is normally associated with a velocity disturbance. In the TEM, then, the turbulent region is populated with a collection of turbules of different sizes and types with the locations of the turbules chosen according to some rule. Since the program began in 1992, a number of publications have been generated that have dealt with the details of creating and using the TEM concept. This report contains information on these reports including author, title, where copies may be obtained, date, and a brief description.
Acoustic Propagation Through Turbulence
Author: David Hattis MarlinPublisher:
ISBN:
Category : Atmospheric turbulence
Languages : en
Pages : 336
Book Description
Tenative Method for Calculation of the Sound Field about a Source Over Ground Considering Diffraction and Scattering Into Shadow Zones
Author: David C. Pridmore-BrownPublisher:
ISBN:
Category : Diffraction
Languages : en
Pages : 33
Book Description
A semiempirical method is given for the calculation of the sound field about a source over ground considering the effects of vertical temperature and wind gradients as well as scattering of sound by turbulence into shadow zones. The diffracted field in a wind-created shadow zone is analyzed theoretically in the two-dimensional case and is shown to be similar to the results obtained for a temperature created shadow field as givenin NACA TN 3494. The frequency and wind-velocity dependence of the scattered field into the shadow zone is estimated from Lighthill's theory, and on the basis of these two field contributions a semiempirical formula is constructed for the total field which contains two adjustable parameters. From this expression a set of charts has been prepared showing equal sound-pressure contours at 10 feet above ground for various source heights, wind velocities, and frequencies.
Aeroacoustics of Flight Vehicles
Author: Harvey H. HubbardPublisher:
ISBN:
Category : Aerodynamic noise
Languages : en
Pages : 620
Book Description
Sound Propagation Through Anisotropic, Inhomogeneous and Intermittent Turbulence
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 10
Book Description
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.
Sound Propagation in the Sea
Author: Robert J. UrickPublisher:
ISBN:
Category : Sound
Languages : en
Pages : 268
Book Description
Numerical Computations of Turbulence Amplification in Shock Wave Interactions
Author: Thomas A. ZangPublisher:
ISBN:
Category : Shock waves
Languages : en
Pages : 40
Book Description