Nonlinear Model Order Reduction of a Strut-Braced Ultra-High Aspect Ratio Wing for Gust Load Analysis

This work presents efforts towards accelerating gust load analysis of ultra-high aspect ratio strut-braced wing systems via model order reduction. Reduced Order Models (ROMs) are constructed using the eigenspectrum of the linear aeroelastic system, projecting a Taylor series expansion of the Full Order Model (FOM) onto a reduced basis of eigenvectors. Nonlinearities are retained using source-transformation automatic differentiation to form nonlinear ROM derivative codes. Nonlinear ROMs are formed for a pitch-plunge aerofoil with cubic structural nonlinearity coupled with compressible indicial aerodynamics. Seven modes of the 14 state FOM are required to capture the exact FOM dynamics due to gust-excitation. ROMs are formed also for a strut-braced wing system. The linear dynamics in response to gust excitation of the 986-state strut-braced wing FOM are accurately represented using a basis of 30 modes. The linear ROM performs gust analysis 50 times faster than the linear FOM. The nonlinear ROM has stability issues, where certain modes cause the dynamics to explode. Further investigation of the strut-braced ROM system is required.