Optimal design of geodesically stiffened composite cylindrical shells

Abstract

An optimization system based on the finite element code CSM Testbed and the optimization program ADS is described. The optimization system can be used to obtain minimum-weight designs of composite stiffened structures. Ply thicknesses, ply orientations, and stiffener heights can be used as design variables. Buckling, displacement, and material failure constraints can be imposed on the design. The system is used to conduct a design study of geodesically stiffened shells. For comparison purposes, optimal designs of unstiffened shells and shells stiffened by rings and stringers are also obtained. Trends in the design of geodesically stiffened shells are identified. An approach to include local stress concentrations during the design optimization process is then presented. The method is based on a global/local analysis technique. It employs spline interpolation functions to determine displacements and rotations from a global model which are used as "boundary conditions" for the local model. The organization of the strategy in the context of an optimization process is described. The method is validated with an example.