
Accession Number : ADA020106
Title : Submarine Radiated Noise FarField Beam Patterns for Discrete Frequencies from NearField Measurements.
Descriptive Note : Master's thesis,
Corporate Author : NAVAL POSTGRADUATE SCHOOL MONTEREY CALIF
Personal Author(s) : Crawford,Frederick Roberts
Report Date : DEC 1975
Pagination or Media Count : 47
Abstract : A theoretical model was developed which can predict discrete frequency farfield radiation patterns of submerged submarines from nearfield measurements. The model developed uses the Helmholtz integral equation and the assumptions of the DRL method of nearfield measurements. The DRL working formula is further modified by using a plane surface of integration and restricting the farfield points of interest to a horizontal plane containing the source. These assumptions and restrictions lead to a mathematical solution of the Helmholtz equation which is in the form of a Fourier transform. Nearfield measurements on a horn speaker in an anechoic chamber were taken and the farfield beam pattern predicted by the model developed, using a simple computer program containing a Fourier transform routine. Computed beam patterns were in satisfactory agreement with measured farfield beam patterns, errors being concentrated in the outer side lobes from the acoustic axis. Problems which would be encountered in applying this model to at sea acoustic measurements are discussed.
Descriptors : *Submarines, *Acoustic fields, *Underwater sound, Antisubmarine warfare, Far field, Near field, Hydrophones, Fourier transformation, Mathematical models, Computer programs
Subject Categories : Undersea and Antisubmarine Warfare
Acoustic Detection and Detectors
Acoustics
Distribution Statement : APPROVED FOR PUBLIC RELEASE