Accession Number : ADA323832

Title :   Feasibility of Implementing Near-Field Acoustic Holography at Large Scale.

Descriptive Note : Research and development rept. 1 Jun-27 Nov 96,

Corporate Author : NAVAL SURFACE WARFARE CENTER CARDEROCK DIV BETHESDA MD SHIP HYDROMECHANICS D EPT

Personal Author(s) : Carroll, Gerard P.

PDF Url : ADA323832

Report Date : MAR 1997

Pagination or Media Count : 47

Abstract : This report presents the results of a numerical investigation into the technical feasibility of implementing near-field acoustic holography (NAH) at large scale using the Intermediate Scale Measurement System (ISMS) . Results are presented using two data sets, one corresponding to numerically generated hologram plane pressures for the Whitefish model and the other to actual experimental data for the Naval Research Laboratory (NRL) C-50 model. The numerically generated hologram plane pressures are valid in the range ka < 4.0 while the C-50 data is valid up to ka < 20. The focus of the investigation is to determine whether or A not large scale implementation of NAH is feasible given the magnitude of background noise levels and sensor placement inaccuracies likely to be encountered. Measured ambient noise levels for the ISMS range are used in this investigation. The effect of both random and systematic axial, circumferential and radial sensor placement errors are assessed and compared. The majority of the results are presented as wavenumber comparisons of contaminated and uncontaminated surface pressure reconstructions. In general, the results are very favorable regarding the feasibility of implementing NAH at ISMS. It is shown that both background noise and sensor placement error result in high wavenumber noise and that the success of implementing NAH at large scale relies largely on the selection of low-pass wavenumber filters suitable for removing these contaminating factors while preserving the cylinder's actual wavenumber response.

Descriptors :   *ACOUSTIC FIELDS, *ACOUSTIC HOLOGRAPHY, *HELMHOLTZ EQUATIONS, DATA BASES, MATHEMATICAL MODELS, COMPUTERIZED SIMULATION, FEASIBILITY STUDIES, ACOUSTIC MEASUREMENT, ACOUSTIC FILTERS, ACOUSTIC DATA, SOUND PRESSURE, NEAR FIELD, BACKGROUND NOISE, LOW PASS FILTERS, HOLOGRAMS.

Subject Categories : Holography
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE