Optimization of Free Form Surface in Bulge Formed Joint Based on Isogeometric Analysis

The bulge formed joint is a novel free-form surface thin-wall joint structure used in truss structure systems, and its shape characteristics strongly influence the bearing capacity of the structure. The isogeometric analysis method provides a new way to analyze and optimize these free-form surface structures. To enhance the aesthetic appearance, such as the smoothness of the form, and increase the bearing capacity of the structures, an optimal design method for the bulge formed joint based on isogeometric analysis is proposed in this paper. This paper proposes a joint shape evaluation index based on NURBS surface characteristics. It establishes an optimization model for shell surface shape within the isogeometric analysis framework, derives an analytical expression for the sensitivity of design variables, and employs h-refinement to propagate sensitivity across multiple mesh models. The optimization design of joint configuration is realized by combining the moving asymptote method. The optimization results of the T-type and K-type bulge formed joints show that the mechanical properties and morphological smoothness of the free-form surface joint are improved.