Buckling optimization of non-uniform curved grid-stiffened composite structures (NCGCs) with a cutout using conservativeness-relaxed globally convergent method of moving asymptotes

There are renewed interests in grid-stiffened composite structures due to the high structural stability and damage tolerance enabled by multiple intersected stiffeners. The limited design space of repeated straight grid patterns has been remarkably expanded by introducing non-uniform curved grid-stiffened composite structures (NCGCs). In this work, curved stiffener layout optimization for NCGCs with a central cutout is investigated to maximize the critical buckling load under a given weight constraint. The design framework is developed by calling ABAQUS for simulating stiffened models and using numerical sensitivities in order to adopt gradient-based optimization algorithm, where the computational time depends not only on simulation but also the number of design variables. To increase the efficiency, an improvement is proposed based on globally convergent method of moving asymptotes (GCM), as one of the most popularly used structural optimization algorithms, by relaxing the conservativeness (CR-GCM) with an additional relaxation factor and an adaptive limit of the iteration number. Numerical examples show that optimal curved stiffeners around the cutout have the ability to remarkably increase the structural buckling load and the proposed CR-GCM demonstrates the ability of better balancing the computational efficiency and convergence in the optimization process.