Semi-intrusive stiffener path optimisation for hybrid manufacturing

Abstract The paper presents a new semi-intrusive method to optimise the paths of stiffeners on complex surfaces. One motivation for such approaches is hybrid manufacturing, where a conventionally manufactured shell structure is reinforced by additively manufactured stiffeners. This potential application motivates manufacturing constraints, which are embedded in the new approach. These are, in particular, the requirements that stiffeners should be orthogonal to the geometry they are being printed on, and that parallel stiffeners should have a minimum distance, whilst it shall be allowed for stiffeners to cross. The main challenge when optimising stiffeners on a shell is that connectivity of stiffeners and shell must be maintained, but remeshing of the shell is not desirable. Coupling degrees of freedom via element shape functions however requires full access to the finite element code. In our approach we circumvent both by performing only local mesh modifications. The aforementioned manufacturing constraints are implemented as a layered normal-based parametrisation and an angle-based penalised distance constraint. Everything is implemented in a projection-based setting that allows the stiffeners path to vary along an arbitrarily shaped surface. The applicability of the framework is demonstrated by academic benchmark examples as well as a more challenging industrial-like example.