Admissible large perturbations in structural redesign

Abstract

A new algorithm for structural redesign by perturbation is developed. It allows for large changes between baseline and objective structures and can satisfy both modal and static displacement objectives. It is faster and more accurate than previously developed perturbation resizing methods because it advances incrementally to the objective structure using large admissible perturbations. The computer code developed is used as postprocessor to general or special purpose finite element codes, to improve upon the design of structures with unacceptable modal and/or static displacement response. Depending on the relation between the number of redesign goals, allowable structural changes, and admissibility constraints, the desired redesign may be feasible-either locally optimal or unique-or may not exist. In the latter case, a minimum-error inadmissible design is produced. Several numerical examples are used to study the effects of definition and relaxation of the redesign admissible domain and demonstrate the accuracy of the new redesign algorithm. An offshore tower with repeated eigenvalues and 192 degrees of freedom is also redesigned subject to frequency, static displacement goals, and admissibility constraints. © 1991 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.