Ricerc@Sapienza

Feedback control techniques for vibrations suppression are widely investigated in the technical literature. However, the most powerful method in this context, the optimal control theory, despites its generality and flexibility related to the user defined cost function, meets serious engineering limitations. This is due to the lack of a feedback law, because of the intrinsic formulation of the Pontryagin optimality criterion. This paper proposes a novel method of control that, still maintaining the structure of the optimal control technique, provides a feedback control.

Vertical landing is becoming popular in the last fifteen years, a technology known under the acronym VTVL, Vertical Takeoff and Vertical Landing [1,2]. The interest in such landing technology is dictated by possible cost reductions [3,4], that impose spaceship’s recycling. The rockets are not generally de- signed to perform landing operations, rather their design is aimed at takeoff operations, guaranteeing a very high forward acceleration to gain the velocity needed to escape the gravitational force.

The response of single and two-degree-of-freedom mechanical systems with elements exhibiting a hysteretic restoring force is studied under harmonic imposed motion to characterize the nonlinear dynamic properties of the system. The hysteretic behavior of the element is described by the Bouc-Wen model, which is simple but able to represent different hysteretic behaviors. Since for a given restoring force the nonlinear response is affected by the oscillation amplitude, frequency-response curves for various excitation levels are constructed.

We propose a framework for designing observers for noisy nonlinear systems
with global convergence properties and performing robustness and noise sensitivity. Our state
observer is the result of the combination of a state norm estimator with a bank of Kalman-type
lters, parametrized by the state norm estimator. The state estimate is sequentially processed
through the bank of lters. In general, existing nonlinear state observers are responsible for
estimation errors which are sensitive to model uncertainties and measurement noise, depending