Modeling, analysis and optimization of cylindrical stiffened panels for reusable launch vehicle structures

The design of reusable launch vehicles is driven by the need for minimum weight structures. Preliminary design of reusable launch vehicles requires many optimizations to select among competing structural concepts. Accurate models and analysis methods are required for such structural optimizations. Model, analysis, and optimization complexities have to be compromised to meet constraints on design cycle time and computational resources.; Stiffened panels used in reusable launch vehicle tanks exhibit complex buckling failure modes. Using detailed finite element models for buckling analysis is too expensive for optimization. Many approximate models and analysis methods have been developed for design of stiffened panels.; This dissertation investigates the use of approximate models and analysis methods implemented in PANDA2 software for preliminary design of stiffened panels. PANDA2 is also used for a trade study to compare weight efficiencies of stiffened panel concepts for a liquid hydrogen tank of a reusable launch vehicle. Optimum weights of stiffened panels are obtained for different materials, constructions and stiffener geometry. The study investigates the influence of modeling and analysis choices in PANDA2 on optimum designs.; Complex structures usually require finite element analysis models to capture the details of their response. Design of complex structures must account for failure modes that are both global and local in nature. Often, different analysis models or computer programs are employed to calculate global and local structural response. Integration of different analysis programs is cumbersome and computationally expensive.; Response surface approximation provides a global polynomial approximation that filters numerical noise present in discretized analysis models. The computational costs are transferred from optimization to development of approximate models. Using this process, the analyst can create structural response models that can be used by designers in optimization. It allows easy integration of analysis models in optimization.; The dissertation investigates use of response surface approximations for integrating structural response obtained from a global analysis in the local optimization of stiffened panels. In addition, response surfaces are used for correcting structural response predictions from a low fidelity model with a few expensive detailed finite element analyses.