Parametric Optimization of SMA Torsional Actuators for Aircraft Morphing Applications

Abstract

Novel design of more efficient, environmentally friendly, quiet, and cost-effective air transportation could be substantially benefited by introducing highly adaptive, multi-functional systems that are able to mimic the operation of biological systems, like birds. Altering the Outer Mold Line (OML) of an aircraft allows for achieving the optimal response under a wide range of operational conditions. In the framework of the “Adaptive Aerostructures for Revolutionary Civil Supersonic Transportation” project funded by NASA, an articulated panel mechanism controlled by Shape Memory Alloy (SMA) actuators is investigated as a means for reducing the perceived loudness of the sonic boom produced by a commercial aircraft when flying at supersonic speeds. A pair of SMA torque tubes is envisioned to induce the required rotation of the panels in order to achieve the desirable OML shapes. However, design objectives such as minimizing power consumption, mass, and cooling time are often competing and the selection of the optimal dimensions is neither elementary nor straightforward. In the research conducted herein, a case study is defined and realized for the optimal design of the SMA torque tubes as part of a larger morphing structure. In the early stages of design, engineers are often faced with the challenge of making decisions with incomplete information. For example, the designer must know the aerodynamic loads to choose the optimal dimensions, but the aerodynamic loads depend on aircraft dimensions. To enable detailed optimization in the early design stages, parametric optimization can be used to solve for the parameterized Pareto frontier. This parameterized Pareto frontier allows a designer to explore how the traditional Pareto frontier might change as exogenous parameters (the values of which are not yet fully known) change. In this work, the design variables under the control of the engineer are the dimensions of the torque tube, i.e. length, inner diameter, and thickness. The objectives are to minimize cooling time and maximize rigidity. The exogenous parameters outside of the designer’s control include the required actuation stroke and aerodynamic forces. Results show the effects of parameters on the objective tradeoffs and demonstrate how an engineer can choose an optimal solution once the parameter values are known.