A multilevel framework for optimization of an aircraft wing incorporating postbuckling effects

The optimization of aerospace structures is a very complex problem, owing to the hundreds of design variables a multidisciplinary optimization may contain, so that multilevel optimization is required. This paper presents recent developments to the optimization software VICONOPT MLO, a multilevel optimization interface between the analysis and design software packages VICONOPT and MSC/NASTRAN. The software developed, VICONOPT MLOP (Multilevel Optimization with Postbuckling) incorporates postbuckling behaviour, allowing individual panels to buckle before the design load is reached, while carrying load at a reduced stiffness. By combining two iterative cycles the first of which (known as the analysis cycle) calculates these reduced postbuckling stiffnesses at an individual panel level in order to converge on an appropriate load distribution at a whole structure or system level and the second of which (known as the design cycle) optimizes individual panels based on this load redistribution to converge on an optimized mass for the whole structure. The paper provides a detailed overview of the functionality of the software and a case study is conducted into the optimization of a composite aircraft wing. The results of the case study show substantial mass savings, proving the software’s capabilities when dealing with such problems. The time taken for this multilevel optimization also demonstrates the efficiency of the software