Design Optimization of Mechanism-Free Ornithopters Based on a Coupled State-Space Model

Abstract A so-called solid-state (i.e., mechanism-free) ornithopter can be achieved by utilizing induced-strain actuators such as piezoelectric material-based devices — specifically piezocomposite devices. Such ornithopters with induced-strain actuated wings eliminate the need for electromagnetic motors and conventional power transmission mechanisms, potentially saving weight and energy consumption, improving reliability and flexibility, and reducing overall mechanical complexity. Given the complexity of such system, featuring a high number of design variables and nonlinearities, achieving an optimized configuration is crucial. In their previous research, the authors developed a novel model to account for dynamic two-way coupling and nonlinearities using a state space representation for mechanism-free ornithopters. The model considered (1) two-way fluid-structure interaction, (2) body-wing coupling, and (3) wing bend-twist coupling. Based on the state space representation of the ornithopter, the current paper focuses on a design optimization framework utilizing a multi-objective genetic algorithm. The design variables considered include ornithopter body inertia, piezocomposite device positions and orientations, excitation voltage, frequency, etc. The optimization algorithm is initially validated for convergence using established test functions. Subsequently, the optimization procedure is carried out for multiple case studies with a variation of fitness metrics that represent the aerodynamic and structural performance of the ornithopter. The selected objective functions encompass structural metrics such as wing weight and compliance, as well as aerodynamic metrics such as lift and thrust force amplitudes.