Modeling and Nonlinear Structural Analysis of a Large-Scale Launch Vehicle

Advanced modeling and analysis capabilities of a state-of-the-art general purpose finite element code, developed for nonlinear structural analysis of launch vehicles, are described. In particular, the application of these capabilities to nonlinear analyses of the new Space Shuttle superlightweight external liquid-oxygen tank are presented that can be used as a guide for conducting similar analyses on future launch vehicles. A typical prelaunch loading condition with combined thermal and mechanical loads is considered, and applications of the advanced modeling and analysis capabilities to linear bifurcation buckling and nonlinear static analyses are presented. The results for this problem illustrate a localized short-wavelength bending response, and that a high-fidelity model is required to represent accurately the behavior. A mesh refinement strategy is presented that is based on the linear bifuraction buckling analyses and does not require respecification of the shell wall properties and loads. Specifically, mesh refinement is simplified by using user-written subroutines to describe the spatial distribution of complex shell wall properties and loading conditions. In addition, a procedure for assessing the sensitivity to initial shell wall geometric imperfections is presented. For the prelaunch load condition considered, the deformations from a nonlinear analysis using these capabilities are found to be similar in shape to the linear bifurcation buckling mode shape and insensitive to initial geometric imperfections. Recommended solution procedures for large-scale nonlinear analysis include using an arc-length projection method, and a combination of modified and true Newton refactoring schemes to balance computational efficiency and robustness, with careful monitoring of the stability of the obtained solutions.