Feasibility of implementing near-field acoustic holography at large scale

Abstract

This paper presents the results of a numerical investigation into the technical feasibility of implementing near-field acoustic holography (NAH) at large scale. Results are presented using both numerically generated hologram plane pressures for ka<4.0, as well as measured hologram plane pressures for a small scale ribbed cylindrical model (ka<20). The focus of the investigation is to determine whether or not large scale implementation of NAH is feasible given the magnitude of background noise levels and sensor placement inaccuracies likely to be encountered. Background noise for various lake and ocean environments are considered. The effect of both random and systematic axial, circumferential and radial sensor placement errors is assessed and compared. The majority of the results are presented as wave number comparisons of contaminated and uncontaminated surface pressure reconstructions. In general, the effects of data contamination are evident in these comparisons as high wave number noise. It is shown for these simulations that the success of implementing NAH at large scale relies largely on the selection of a low-pass wave number filter with a cutoff frequency suitable for removing these contaminating factors while preserving the cylinder’s actual wave number response. [Work supported by ONR.]