MERITS AND LIMITATIONS OF OPTIMALITY CRITERIA METHOD FOR STRUCTURAL OPTIMIZATION

The merits and limitations of the Optimality Criteria (OC) method for the minimum weight design of structures subjected to multiple load con ditions under stress, displacement and frequency constraints were inve stigated by examining several numerical examples. The examples were so lved utilizing the OC design code that was developed for this purpose at the NASA Lewis Research Center. This OC code incorporates OC method s available in the literature with generalizations for stress constrai nts, fully utilized design concepts, and hybrid methods that combine b oth techniques. It includes multiple choices for Lagrange multiplier a nd design variable update methods, design strategies for several const raint types, variable linking, displacement and integrated force metho d analysers, and analytical and numerical sensitivities. On the basis of the examples solved, the optimality criteria for general applicatio n were found to be satisfactory for problems with few active constrain ts or with small numbers of design variables. However, the OC method w ithout stress constraints converged to optimum even for large structur al systems. For problems with large numbers of behaviour constraints a nd design variables, the method appears to follow a subset of active c onstraints that can result in a heavier design. The computational effi ciency of OC methods appears to be similar to some mathematical progra mming techniques.