This study presents the design and implementation of a spatial H 1 controller for the active vibration control of a smart beam. The smart beam was modeled by assumed-modes method that results in a model including large number of resonant modes. The order of the model was reduced by direct model truncation and the model correction technique was applied to compensate the effect of the contribution of the out of range modes to the dynamics of the system. Additionally, spatial identification of the beam was performed, by comparing the analytical and experimental system models, in order to determine the modal damping ratios of the smart beam. Then, the spatial H 1 controller was designed and implemented to suppress the first two flexural vibrations of the smart beam.
This work presents the theoretical and experimental studies conducted in Aerospace Engineering Department of Middle East Technical University on smart structures with particular attention given to the structural modelling characteristics and active suppression of in-vacuo vibrations. The smart structures considered in these analyses are finite and flat aluminium cantilever beam-like (called as smart beam) and plate-like (called as smart fin) structures with surface bonded lead-zirconate-titanate patches. Finite element models of smart beam and smart fin are obtained. Then the experimental studies regarding open loop behaviour of the structures are performed by using strain gauges and laser displacement sensor to determine the system models. Further studies are carried out to obtain H ∞ and msynthesis controllers which are intended to be used in the suppression of free and forced vibrations of the smart structures. It is observed that satisfactory attenuation levels are achieved and robust performance of the systems in the presence of uncertainties is ensured. In that respect a comparative study involving H ∞ and sliding mode controls is also conducted. Recently, the studies involving aerodynamic loading are also gathering pace.
Summary The ability of helicopters to hover and land vertically has spurred an interesting field of research on the development of autonomous flight for these rotatory wing aircrafts. Linear control theory with gain scheduling, which is based on linearizing the system at the equilibrium points, dominated the helicopter autopilot design. Unlike the linear cascaded autopilot structure used in the existing literature, this paper uses state‐dependent linear like structure, including rate‐limited actuator dynamics, with cascaded autopilot topology. This approach allows nonlinear control laws to be implemented throughout the entire flight envelope, providing satisfactory robustness and stability over the various parameter uncertainties and time delays. The cascaded autopilot topology with nonlinear dynamical equations contains a new sliding sector control (SSC) mechanism which is derived for multi‐input nonlinear dynamical systems. The proposed SSC structure for multi‐input nonlinear systems is used in the inner loop of the cascaded autopilot system where the fastest dynamics are required to be controlled for rapid changes in the helicopter dynamical characteristics which enables one to stabilize the helicopter over a wide range of flight conditions. The proposed cascaded autopilot topology with the new SSC mechanism is tested in simulations to assess its robustness and stability properties. To establish its feasibility, the proposed control method is replaced with a suboptimal control method, namely state‐dependent differential Riccati equation (SDDRE) method, for the inner loop and the results of the proposed control architecture are compared with those of SDDRE method.
Theoretical and experimental results of the dynamic response of a flexible structure augmented with shape memory wires are presented. A nonlinear model of the stress-strain behavior of shape memory alloy wires that includes the behavior of the material within the pseudoelastic hysteresis loop is used to produce simulations of the dynamic response of the augmented system. A frequency domain model is posed for the shape memory elements; analytical results are presented and compared with experimental results of the flexible structure with shape memory wire damping elements. The results demonstrate the effectiveness of shape memory wires for producing passive damping in lightly damped structures. (Author) Page 1 Downloaded by CORNELL UNIVERSITY on July 30, 2015 | http://arc.aiaa.org | AbstractTheoretical and experimental results of the dynamic response of a flexible structure augmented with shape memory wires are presented. A non-linear model of the stress-strain behaviour of shape memory alloy wires that includes the behaviour of the material within the pseudoelastic hysteresis loop is used to produce simulations of the dynamic response of the augmented system. A frequency domain model is posed for the shape memory elements and analytical results are presented and compared with experimental results of the flexible structure with shape memory wire damping elements. The results demonstrate the effectiveness of shape memory wires for producing passive damping in lightly damped structures.
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