<p>Novel design of more efficient, environmentally friendly, quiet, and cost-effective air transportation requires the introduction of 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 ULI (University Leadership Initiative) project funded by NASA (Adaptive Aerostructures for Revolutionary Civil Supersonic Transportation), 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 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. Although SMA actuators are compact, exhibit high energy density, induce high stroke/block forces and operate without producing any noise or debris, their response is highly non-linear, hysteretic and thermomechanically coupled (i.e. latent heat effects accompanying transformation render it highly dependent on ambient conditions as well as the magnitude of any externally applied loads). Furthermore, design objectives such as minimizing power consumption, mass, and cooling time are often competing. To this end, 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 (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/outer radius, and thickness. The objectives are to minimize cooling time, power consumption, and mass while satisfying constraints on required stroke, rigidity to aerodynamic loads, and fatigue life. The exogenous parameters outside of the designer’s control include aerodynamic forces, air temperature, and air velocity. Selected solutions from the optimization study will be further investigated through 3-D Finite Element (FE) simulations in order to verify the operation of the SMA actuators as well as produce more detailed predictions of the developed stress fields, the internal state of the material and the transformation evolution effects during activation-deactivation cycles.</p>

Parametric Optimization of SMA Torsional Actuators for Aircraft Morphing Applications

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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