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This paper presents the initial development of an optimization framework for designing active twist helicopter rotor blade cross sections with embedded anisotropic piezocomposite actuators. Optimum design of active twist blades is a complex task, since it involves a rich design space with tightly coupled design variables, e.g., the simple orientation of the actuators aects the blade natural frequencies. Therefore, it becomes advantageous to apply the principle of mathematical optimization to the design task. In the proposed framework, the blade cross-sectional internal layout is designed to maximize the static twist actuation while satisfying a series of blade requirements. These requirements are associated with locations of the center of gravity and elastic axis, blade mass per unit span, fundamental rotating blade frequencies, and the blade strength based on local threedimensional stress and strain fields under worst loading conditions. An active composite cross-sectional analysis and a geometrically exact one-dimensional beam analysis, along with other related analysis routines, are combined with a gradient-based optimizer within MATLAB. The developed optimization framework is exemplified by using the NASA/Army/MIT Active Twist Rotor blade and its baseline design. |
