Effective lightweight design of a rocket interstage ring through mixed-integer optimization

摘要

The full lightweight potential of carbon fiber reinforced plastics in complex structures can onlyrnbe exploited using an adequate combination of material and design. Potential combinations can be found, usingrnan optimization routine integrated into the design process. This paper presents a detailed comparison of thernoptimization results for distinctive rocket interstage design concepts. The complex cylindrical grid structure hasrnto withstand the mission loads while being as light as possible. For the efficient use of the superior materialrnproperties, carbon fiber reinforced plastics are combined with a foam core to form a sandwich configuration.rnTo minimize the total mass, parametric finite element models are used within a constrained, mixed-integerrnoptimization. The structure is modeled using a bottom up strategy. An optimization framework, incorporatingrnthe CAE software Ansys into the multi-purpose optimization package pyOpt, is presented. The augmentedrnlagrangian particle swarm algorithm is used to find the configurations having minimal weight. As manufacturabilityrnis an important design requirement, a winding process is represented by constraints in the parameter set ofrnthe geometry. The stiffnesses of the structure, as well as strength criteria of the laminate are used as inequalityrnconstraints for the optimization. Further on, a lower bound of the first natural eigenfrequency using additionalrnconstraints, is investigated. Finally, the impact of the governing geometry, material parameters and hence theirrninfluences on the optimization problem are carefully reviewed. It is shown that appropriate design – materialrncombinations can significantly reduce the structural mass.