A simple, effective design for enclosing portable generators to reduce the radiated
noise is an idea that seems to be desired by the consumers in this market. This
investigation is to determine the feasibility of producing such an enclosure for a generator.
Several engineering aspects are incorporated in the design of the enclosure. The
first, and probably the most paramount, are the acoustical effects of the enclosure itself.
The investigation follows the theories for insertion loss of a close fitting enclosure.
The
thesis examines the system behavior of a close fitting enclosure that most acoustic text
books ignore and how the material stiffness, density and source-to-enclosure distance
affect the insertion loss and effectiveness of the enclosure. Measured and theoretical
sound pressure level around the generator before and after the application of the enclosure
are presented using standards described by ISO standard 1344.
The second important consideration for the enclosure design involves the heat
transfer characteristics. The requirements of cooling air to the generator are discussed.
Also presented are some acoustic design considerations to prevent any “direct line of
sight” to any of the necessary openings which will help in the overall insertion loss.
The use of an optimal engineering design technique is presented, demonstrating its
strengths and weakness in this application. The optimization method used for the study is
the Hooke and Jeeves, or pattern search method. This method solved for the optimum
material properties in approximately 30 iterations depending on the initial starting points
and the desired weighting parameters
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