Keywords: composites, structures, optimization, multimodal, genetic algorithm, species conservation.

The optimal design of hybrid composite laminate structures including material selection and optimal topology of the structure is a multimodal optimization problem [1]. Using a defined material topology it is possible to optimise the composite structure relatively to the ply angle and thickness of each laminate or other variables related to the strength or load capacity of the structure. In this way there is an optimal solution associated with each predefined material topology. The additional problem of finding optimal material selection and topology of the structure changes the objective of the global structural optimization of composites searching multiple optima each one representing a different design proposal.

There are practical reasons justifying the benefits of locating multiple optima in structural optimization. Firstly, the search of multiple optima increases the possibility of finding the global optimum. Secondly, in the design context, the identification of a set of several solutions with high quality will provide an insight of the space design suggesting alternative and innovative solutions for the designer.

Aiming to solve the optimal design of a hybrid composite structure as a multimodal optimization problem a new approach based on a hierarchical genetic algorithm with an age structure is proposed in this work [1,2,3]. The approach addresses the optimal stacking sequence and material topology as a multimodal optimization problem. More similar concepts used in parallel genetic algorithms are a hierarchical relationship among sub-populations together with an evolutionary philosophy based on the species conservation concept. In the proposed approach individuals corresponding to the same material selection and topology of the hybrid composite structure belong to the same species.

The cooperation between elitist evolutionary strategies based on fitness used at the sub-population level and the species conservation concept is implemented [1,2,3]. Using appropriate selection criteria for migration flows and adopting an age structure in the deletion process of individuals, equilibrium between elitism and the need for species conservation is reached. Results show that the procedure for species control is effectively able to allow multiple optimal solutions and guarantees the sub-population diversity. In the design context, the identification of a high quality set of solutions will provide an insight of the space design suggesting alternative and innovative solutions for robust design optimization of composite structures.

1

C.A. Conceição António, "A hierarchical genetic algorithm with age structure for multimodal optimal design of hybrid composites", Structural and Multidisciplinary Optimization, 31, 280-294, 2006. doi:10.1007/s00158-005-0570-9

2

C.A. Conceição António, "A study on synergy of multiple crossover operators in a hierarchical genetic algorithm applied to structural optimization", Structural and Multidisciplinary Optimization, 38 (2), 117-135, 2009. doi:10.1007/s00158-008-0268-x

3

C. Conceição António, "Self-adaptation procedures in genetic algorithms applied to the optimal design of composite structures", International Journal of Mechanical Materials and Design, Springer, 2009. doi:10.1007/s10999-009-9102-x

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