System Identification for Coupled Fluid-Structure: Aerodynamics is Aeroelasticity Minus Structure

A new method that identifies coupled fluid-structure systems with a reduced set of state variables is presented. Assuming that the structural model is known a priori, from either an analysis or a test and using linear transformations between structural and aeroelastic states, it is possible to deduce aerodynamic information from sampled time histories of the aeroelastic system. More specifically, given a finite set of structural modes, the method extracts a generalized aerodynamic force matrix corresponding to these mode shapes. Once the aerodynamic forces are known, an aeroelastic reduced-order model can be constructed in discrete-time state-space format by coupling the structural model and the aerodynamic system. It is demonstrated that the resulting reduced-order models are accurate, robust, and suitable for aeroelastic analysis at constant Mach, varying density conditions.