Optimization Framework for Dynamic Analysis and Design of Active Twist Rotors

This paper presents the development of an optimization framework for the aeroelastic analysis and design of active twist rotors. The active twist is generated by piezoelectric material in the form of AFC (Active Fiber Composite) or an MFC (Macro Fiber Composite) embedded in the blade cross section. Proper tailoring of the blade properties can lead to the maximization of the active twist authority under operating conditions. Thus, using mathematical optimization, the cross-sectional layout is designed for an active composite rotor blade to maximize the dynamic active twist while satisfying a series of constraints on blade cross section parameters, stiffness and strength. The optimization framework developed includes IXGEN as the cross-section and mesh generator, UM/VABS for active cross-sectional analysis, and RCAS for aeroelastic analysis of the active twist rotor blade. All these components along with stress/strain analysis are integrated in ModelCenter for parametric and optimization studies. The optimization problem is solved using a surrogate-based approach in which the "true" objective function and constraints are replaced with computationally efficient functional relationships. Since approximation errors can lead to sub-optimal solutions, the Efficient Global Optimization algorithm, which accounts for uncertainty in surrogate predictions, is employed. Results show that the optimum design corresponding to maximum dynamic twist is different from the optimum design corresponding to maximum static twist. The optimum blade design based on maximizing 4/rev actuation authority in hover shows superior performance in forward flight conditions for a range of actuation frequencies.