Collaborative optimization and 6σ design for composite pressure hull of underwater vehicle based on lamination parameters

Considering material designability and the effect of uncontrollability in processing structural performances of composite material, an optimization method for composite pressure hull of underwater vehicle is proposed, which balances the structural weight and reliability. A two-level optimization is conducted first. The first level is layout optimization minimizing the structural weight when the material performance parameters are certain. Fiber volume fraction and laminate plate thickness are set as design variables. Neural network approximation model is utilized. In the second level of optimization (layup optimization) the lamination parameters are introduced. Based on the results of the two-level optimization a collaborative optimization combined with 6σ design theory is implemented, where the σ level is recognized as an evaluation index and the requirements of structure and material are both met. Optimization results show that the σ level of critical buckling pressure and failure index are above 6 as well as the reliability reaches 100%, meanwhile the weight decreases by 15.3%. Collaborative optimization based on lamination parameters and 6σ design can optimize the composite pressure hull effectively with high reliability and solve the problem of low efficiency and non-convergence of direct optimization with design variables.