M.S. Thesis Presentation by Brian S. Dater

(Dr. Kenneth A. Cunefare, advisor)

"Structural Acoustic Optimization of an Aircraft Fuselage Using the Complex Method"

Abstract

The development, testing, and evaluation of a new optimization program based on M. J. Box's Complex Method of optimization is presented in this thesis. The new program was designed for use in a previously developed, automated design tool for the minimization of interior noise in an aircraft fuselage. The new program's purpose is to either find effective starting points in the design space for another optimization program, CONMIN, thus creating a hybrid optimization program, or to perform the optimization on its own. This style of optimization has not been considered before in structural acoustics, nor has a hybrid algorithm been implemented. Several modifications, which are unique to this research, were made to the original optimization method, and are presented here.

For the purpose of testing the new program, the aircraft fuselage is modeled as an unstiffened vibrating cylinder excited by an exterior, single frequency monopole noise source. Primarily, the program was tested using a problem formulation seeking to minimize interior noise subject to a constraint on the: weight of the cylinder, and upper and lower bounds on the design variables. The new program was evaluated by comparing its repeatability, reliability, computational efficiency, and optimum solution to that of the optimization program CONMIN, running under the same design tool.

It was found that the new optimization program enhanced the ability of the design tool by expanding the search of the design space and providing the ability to perform optimization of complex models, for which the gradients (required by CONMIN) cannot be calculated.