Finite-state modeling for flutter suppression and gust alleviation

摘要

An efficient tool for aeroservoelastic applications, such as flutter suppression and gust alleviation is reviewed. This consists of a boundary element method for the evaluation of the aerodynamic generalized forces, a modal approach for the structural dynamics, and optimal control theory for feedback control. We present a review of the results obtained in aeroservoelastic modeling for two different configurations: a flexible tail for flutter suppression, and a flexible wing-tail configuration for gust alleviation, both having natural modes of vibration determined by finite elements. Aerodynamic generalized forces (due to Lagrangian variables, control variables, and gust velocity) are approxi-mated on the basis of a finite-state modeling. This methodology is very useful in order to reduce the system in standard state-space form, so that the application of optimal control techniques is straightforward. The use of a linear observer is necessary because the state-space vector includes certain aerodynamic states introduced in the modeling process which are not measurable. A study of the influence of number and position of sensors is presented. For the analysis of vertical gust response and its alleviation, the wing-tail configuration is considered in longitudinal motion with a prescribed center of mass location. The gust distribution is based both on the deterministic "1-cos" model and on the widely-used PSD von Karman model. The responses to both deterministic and stochastic gus in terms of the rms of the acceleration of the center of mas and rootwing and tail-root bending moment are presented with the effects of the application of the alleviation servomechanism.