CFD/CSD-based IOROM Construction for mAEWing1 initial design

Abstract

This working paper summarizes the construction of the Input to Output Reduced Order Model (IOROM) for mAEWing1. The linear time invariant (LTI) IOROM is based on a fixed trimmed flight condition and is represented as a state space system with the traditional four matrix quadruple: [A, B; C, D]. These IOROMs are entirely software-based models that start with a detailed Computational Fluid Dynamic / Computational Structural Dynamic (CFD/CSD)-based model built in the CMSoft, Inc. AERO software suite. The nonlinear full order AERO model (NFOM) is millions of degrees of freedom and is unsuitable for open loop dynamic analysis and control system design. From this model, a linear time invariant reduced order aeroelastic model (ROM) is built describing the modal structural dynamics coupled with the unsteady aerodynamic forces. This model is represented in an inertial frame since that is the frame for the finite element model (FEM). This ROM is sent to the STI ASETool software where the structural rigid body states are cast into the traditional body-fixed frame, and the input and output effect is added with user defined descriptions of actuation and sensor nodes resulting in the IOROM.

The IOROM is a linear model of significantly reduced order that is in the ideal form for dynamic analysis and control system design. It includes all rigid body states, structural modal states, and unsteady aerodynamic states. The 12 rigid body states include the translational and rotational displacements and velocities and are represented in their traditional body-fixed frame of reference, making this model in an ideal form for complete control system design that includes primary flight control and flutter suppression. Stability and control derivatives can be directly extracted from the IOROM for direct comparison to experimental test data or other analytical models. These models are also used for novel system analysis using phasor diagrams where rigid body and flexible dynamic coupling can be clearly characterized. Approximate linear parameter varying models can also be created from the IOROMs that are dependent on a variable trim velocity. These models can be used for traditional flutter analysis (e.g., V-G diagrams, etc.) and LPV control design.