In this study, the prediction and control of the acoustic radiation from a Bristol H25A refrigeration compressor are investigated. For the acoustic prediction, a modal decomposition approach is used. To this end, a boundary element model of the shell is created, and it is used to compute the modal radiation efficiency curves of the shell. These radiation efficiencies are then used in conjunction with the experimentally measured spring forces to obtain the acoustic power radiated by the compressor. Of twenty-three structural modes included in the analysis, it is found that eight have high radiation efficiency and six contribute significantly to the total radiated power. The analytically predicted overall radiated sound power of 82.2 dBA agrees very well with the 82 dBA experimentally measured.
For the noise control of the compressor, three approaches are investigated to reduce the forces transmitted to the shell and thus the radiation. (a) The spring mounts are moved to various locations on the shell, (b) dynamic vibration absorbers (DVAs) are added to the mounts, and (c) low modulus materials are inserted between the mounts and the springs to create an impedance mismatch. For all three approaches, efficient analytical methods to compute the radiated acoustic power upon the system modifications are developed. The most promising approach is the insertion of the low modulus materials, which yields a reduction of 6.4 dBA on the total radiated acoustic power. The addition of DVAs and the relocation of the mounts yield a reduction of 5.5 dBA and 1.7 dBA in the total radiated acoustic power, respectively. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/44610 |
| Date | 05 September 2009 |
| Creators | Rankle, Hugo Elias Camargo |
| Contributors | Mechanical Engineering |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 112 leaves, BTD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 34221183, LD5655.V855_1995.R365.pdf |
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