A reduced order system ID approach to the modelling of nonlinear structural behavior in aeroelasticity

A method is proposed for identifying a set of reduced order, nonlinear equations which describe the structural behavior of aeroelastic configurations. The strain energy of the system is written as a (polynomial) function of the structures' modal amplitudes. The unknown coefficients of these polynomials are then computed using the strain energy data calculated from a steady state, high-order, nonlinear finite element model. The resulting strain energy expression can then be used to develop the modal equations of motion. From these equations, zero and nonzero angle of attack flutter and limit cycle oscillation data are computed for a 45∘ delta wing aeroelastic model. The results computed using the reduced order model compare well with those from a high-fidelity aeroelastic model and to experiment. A two to three order of magnitude reduction in the number of structural equations and a two order of magnitude reduction in total computational time is accomplished using the current reduced order method.