Near field acoustic and vibration studies with a cantilever beam

Klein, Ken (1995) Near field acoustic and vibration studies with a cantilever beam. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (14MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

Several acoustic investigations were conducted with the near field radiated from a vibrating cantilever beam. -- The objective of the first investigation was to experimentally determine the spatial distribution of acoustic intensity close to the beam. Difficulties that occur with acoustic intensity measurements made this a non trivial task and led to the development of an experimental procedure for mapping the spatial distribution of acoustic intensity in the near field. The mapping procedure combined the physics of a closed surface with approximations from an analysis with Taylor's series. The method was successfully tested on the field radiated by the beam. It was then shown that the reliability of the spatial distribution of intensity that resulted from this method could be statistically evaluated from the measured data alone without making assumptions about the nature of the acoustic field. -- A second experimental investigation demonstrated the practicality of constructing acoustic intensity with transfer functions. The expression for acoustic intensity, normally formulated in terms of acoustic pressures, was expressed in terms of transfer functions between pressures and the force exciting the cantilever beam. -- In the third and last investigation, the source of the acoustic field, the cantilever beam, was modelled with Euler-Bernoulli theory. Elements of modal analysis were used to obtain the modal parameters of the beam and a value for Young's Modulus for the material of the beam. This vibration model was then used in an integral approximation for the acoustic field close to the beam. The acoustic near field was calculated and compared with experimental measurements. The results were used to examine the distribution of phase in the near field as it pertained to the measurement of acoustic intensity.

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