Aircraft Multidisciplinary Design Optimization Using Design of Experiments Theory and Response Surface Modeling Methods

Design engineers often employ numerical optimization techniques to assist in the evaluation and comparison of new aircraft conngurations. While the use of numerical optimization methods is largely successful, the presence of numerical noise in realistic engineering optimization problems often inhibits the use of many gradient-based optimization techniques. Numerical noise causes inaccurate gradient calculations which in turn slows or prevents convergence during optimization. The problems created by numerical noise are particularly acute in aircraft design applications where a single aerodynamic or structural analysis of a realistic aircraft connguration may require tens of CPU hours on a supercomputer. The computational expense of the analyses coupled with the convergence diiculties created by numerical noise are signiicant obstacles to performing aircraft multidisciplinary design optimization. To address these issues, a procedure has been developed to create two types of noise-free mathematical models for use in aircraft optimization studies. These two methods use elements of statistical analysis and the overall procedure for using the methods is made compu-tationally aaordable by the application of parallel computing techniques. The rst modeling method, which has been the primary focus of this work, employs classical statistical techniques in response surface modeling and least squares surface tting to yield polynomial approximation models. The second method, in which only a preliminary investigation has been performed, uses Bayesian statistics and an adaptation of ii the Kriging process in Geostatistics to create exponential function-based interpolating models. The particular application of this research involves modeling the subsonic and supersonic aerodynamic performance of high-speed civil transport (HSCT) aircraft conngurations. The aerodynamic models created using the two methods outlined above are employed in HSCT optimization studies so that the detrimental eeects of numerical noise are reduced or eliminated during optimization. Results from sample HSCT optimization studies involving ve and ten variables are presented here to demonstrate the utility of the two modeling methods. iii Acknowledgments I was fortunate to have a unique educational experience in that I participated in a research project where a group of graduate students and faculty members met weekly to discuss the progress and diiculties of their respective portions of the project. This environment fostered much interaction both among the students, and between each student and the various faculty members. This experience has done much to further my academic and professional growth. My advisor and committee chairman, Dr. Bernard Grossman, was a constant source of advice and encouragement throughout my graduate studies. He …