An MDO exercise using response surface methodology: optimal shape and composite structure of a wing for optimal range

Official URL: http://risc01.sabanciuniv.edu/record=b1558943 (Table of Contents)

Engineering problems of multidisciplinary nature are challenging where design optimization requires effective communication of the disciplines. This communication is typically referred as multidisciplinary design optimization (MDO) framework. One of the strategies in such a framework is to use of approximations within and among the disciplines to facilitate the navigation of information through a discipline A by an expert in discipline B. Response surface methodology (RSM) for instance is an effective way to bridge the information and expertise between the disciplines within the framework to complete an MDO problem. This thesis makes a demonstration of RSM in an aircraft composite wing design example. Approximation by RSM aims to generate a prediction tool for optimal structural weight which is required to optimize wing exterior planform for maximum performance, here set as the range of the aircraft. Three planform/shape parameters are chosen: wing span, tip and chord length. For each planform there exists an optimal structure to be found by finite element based structural optimization. The structural optimization level for a given planform makes also use of a different kind of approximation associated with the laminated composite materials. Laminates are treated as homogenized through the thickness and equivalent laminate mechanical properties are implemented. In other words, homogenized laminates approach allows using single continuous thickness variables for each assigned laminate domain replacing the ply-by-ply description of the laminated structure within the structural analyses. Comparison of the homogenized laminate approach and ply-by-ply analyses for a reference wing design is also provided and concluded that former can be incorporated into the design optimization cycles. The MDO framework for the present example is as follows: Wing planforms are described by full factorial DOE. For each configuration/planform: a) LAMDES was used to calculate aerodynamic forces., b) weight optimization of the wing structure subject to displacement and stress constraints was accomplished using MSC Nastran SOL 200 module. Statistical software JMP 7 was then used to construct an RS weight equation. Genetic Algorithm tool of MATLAB was applied for the range optimization.