Accession Number : ADA309976

Title :   Control of Structural Vibrations by Vorticity Production.

Descriptive Note : Final rept. 1 Jan 94-31 Dec 95,

Corporate Author : BOSTON UNIV MA COLL OF ENGINEERING

Personal Author(s) : Howe, Michael S.

PDF Url : ADA309976

Report Date : FEB 1996

Pagination or Media Count : 161

Abstract : Analytical models are investigated of the damping of sound and structural vibrations by vorticity production in the apertures of bias flow and grazing flow perforated elastic plates. A generalized bending wave equation is formulated for a plate perforated with an homogeneous distribution of small apertures, and is used to predict the attenuation of sound and resonant bending waves. The results depend on the Rayleigh conductivity of an aperture in a thin plate which is determined numerically in the presence of one and two-sided mean grazing flows. The Kutta condition is applied to model the generation of vorticity at the edges of the aperture by an applied time-varying pressure field. The influence of flow nonlinearity in the apertures is investigated by use of a model equation for the aperture flows. Preliminary validation tests are described, and recommendations made for future research.

Descriptors :   *VIBRATION, *ACOUSTIC WAVES, *VORTICES, *ACOUSTIC ATTENUATION, PRESSURE GRADIENTS, MATHEMATICAL MODELS, EQUATIONS OF MOTION, STRUCTURAL PROPERTIES, STRUCTURAL ANALYSIS, DAMPING, FLOW FIELDS, NONLINEAR SYSTEMS, RAYLEIGH SCATTERING, BOUNDARY VALUE PROBLEMS, PERTURBATIONS, MACH NUMBER, UNSTEADY FLOW, FLOW NOISE, ACOUSTIC SCATTERING, INVISCID FLOW, SOUND PRESSURE, APERTURES, REYNOLDS NUMBER, INCOMPRESSIBLE FLOW, RUNGE KUTTA METHOD, ACOUSTIC FIELDS, WAVE EQUATIONS, STEADY FLOW, GRAZING, ACOUSTIC RESONANCE.

Subject Categories : Acoustics
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE