Control systems for active flutter suppression (AFS) of a two-dimensional airfoil are designed by means of two methods in which the frequency shaping is taken into consideration. The one is the frequency-shaped weighting LQG (FWLQG). In the method, the performance variables are considered in the frequency domain in order that the controlled system may be robust. The another is the mixed sensitivity reduction problem in
H∞ control theory (
H∞-mix). Aeroelastic systems, in general, change their internal parameters with free stream velocity. When the system becomes unstable, flutter occurs. To be robust for the parameter perturbation, AFS control systems are designed so that the sensitivity may be low in the low frequency region. As a result, FWLQG and
H∞-mix compensators can increase the flutter velocity more than LQG ones. In particular, a
H∞-mix compensator of two-output case in which the vertical displacement of the airfoil and its acceleration are considered can increase the flutter velocity by 43.2 percent. Comparing both methods,
H∞-mix is superior to FWLQG because the former can shape the frequency response more closely.
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