Models for Aeroservoelastic Analysis with Smart Structures

Abstract

Modal-based mathematical models for the analysis of control-augmented aeroelastic systems are expanded to facilitate the use of distributed strain actuators. Smart actuators are constructed of structural elements, such as piezoelectric patches, that change their shape due to electric inputs. When embedded in the structure, the deforming smart elements introduce structural strains that change the shape of the structure and, consequently, the aerodynamic load distribution. The voltage‐strain relations, the overdetermined nature of the elastic actuator‐ structure equilibrium, the relatively large number of involved interface coordinates, and the high importance of local strains that typically limit the actuator performance require substantial modifications in the modeling process compared to that with common control-surface actuators. Fictitious masses are used in a way that causes the inclusion of important actuator strain information in the modal data with a minimal increase in the number of structural states. A control mode is defined by the static deformations due to a unit static voltage command. Huge dummy masses may be used to generate the control modes as part of a standard normal-modes analysis. State-space aeroservoelastic equations are constructed by the use of the minimum-state rational aerodynamic approximation approach. Two options are given for the introduction of control forces: a direct application of the forces, and an indirect application through the control mode. A numerical application for an unmanned aerial vehicle with a piezoelectric-driven control surface demonstrates the two options and shows that the control-mode option has some numerical advantages.