A symbolic LFT approach for robust flutter analysis of high-order models

The paper proposes an alternative methodology to build Linear Fractional Transformation (LFT) models of uncertain aeroelastic systems described by Fluid-Structure Interaction (FSI) solvers with the aim of studying flutter with the μ analysis technique from robust control. Two main issues can be identified for the fulfillment of this task. On the one hand, there is the difficult reconciliation between sources of physical uncertainty (well distinguishable in the original high-order system) and the abstracted uncertainties (defined in the reduced-order size representation used for the robust analyses). On the other hand, the large size of the resulting LFT model can prevent the application of robust analysis techniques. The solution proposed here consists of a symbolic LFT algorithm applied at FSI solver level, which guarantees the connection between the physical uncertainties and the parameters captured by the LFT. It also alleviates the final size of the LFT by exploiting the modal-oriented approach taken in introducing the uncertainties. Application of the framework using an unconventional aircraft layout as case study is finally discussed.