Lucian Iorga

H ∞ Control with μ-analysis of a Piezoelectric Actuated Plate

This paper presents the development of a multimodal H∞controller for piezoelectric actuated plates designed to simultaneously suppress vibrational components of the first two modes. The controller is developed for a reduced structural model. The closed-loop control scheme is subject to both uncertainties due to control and observation spillover in the unmodeled residual modes and to parametric errors in the structural model. The closed-loop stability and performance robustness is analyzed using μ-analysis, and numerical investigations indicate that the controller tolerates uncertainties of significant size.

Neuro‐fuzzy synthesis of flight control electrohydraulic servo

Presents a switching type neuro‐fuzzy control synthesis. The control algorithm supposes as a component part a neurocontrol designed to optimize a performance index. Whenever the neurocontrol saturates or a certain performance parameter of the system decreases, the scheme of control switches to a feasible and reliable fuzzy logic control. Describes the procedure of return to the optimizing neurocontrol which is essential. This methodology of control synthesis ensures antisaturating, antichattering and robustness properties of the controlling system, as illustrated by numerical simulation in the case of a primary flight controls electrohydraulic servo actuator

Finite element dynamic analysis of soft tissues using state-space model.

A finite element (FE) model is employed to investigate the dynamic response of soft tissues under external excitations, particularly corresponding to the case of harmonic motion imaging. A solid 3D mixed ‘u–p’ element S8P0 is implemented to capture the near-incompressibility inherent in soft tissues. Two important aspects in structural modelling of these tissues are studied; these are the influence of viscous damping on the dynamic response and, following FE-modelling, a developed state-space formulation that valuates the efficiency of several order reduction methods. It is illustrated that the order of the mathematical model can be significantly reduced, while preserving the accuracy of the observed system dynamics. Thus, the reduced-order state-space representation of soft tissues for general dynamic analysis significantly reduces the computational cost and provides a unitary framework for the ‘forward’ simulation and ‘inverse’ estimation of soft tissues. Moreover, the results suggest that damping in soft-tissue is significant, effectively cancelling the contribution of all but the first few vibration modes.

Pseudo-Active Control of Helicopter Blade Vibration Using Piezoelectric Actuators

In this paper we develop a closed-loop algorithm for vibration control of helicopter blades incorporating Piezoelectric Fiber Composite actuators for Active Twist Control. A reduced-state sequential feedback controller is designed based on the linear piezoelectric constitutive equations. We use a simple aeroelastic model that includes 4 bending and 4 torsional degrees of freedom for an initial estimation of the eectiveness of the controller in reducing the vibrational components of the loads transmitted to the hub. The influence of the nonlinear material piezoelectric properties of the actuators is studied by taking into account terms quadratic in the electric field in the piezo constitutive equations. The control method is a velocity feedback scheme incorporating a switching mechanism based on a conditioning function inspired by the force balance logic used in sequential semi-active control syntheses for vibration control. A genetic algorithm is employed to select the optimal control gains. Significant reductions of the magnitudes of the periodic components of the root shear force can be achieved in the desired range of frequencies. Accounting for the system nonlinearities implicitly through the optimization process is observed to improve the control system performance.

Refined Analysis of the Piezoelectric Pseudo-Active Control for Helicopter Blades Vibration

In this paper we extend the analysis of a closed-loop control law for vibration reduction in helicopter blades using piezoelectric fiber composites that provide both bending and torsional actuation capabilities. A simple aeroelastic model incorporating lead-lag, flapping and torsional degrees of freedom is chosen to evaluate a reduced-state sequential velocity feedback control law. The gain switching logic destined to reduce the transmitted force is complemented by a floating-point genetic algorithm optimization procedure that ensures that optimal values of the control gains are chosen. The control law is shown to be able to generate significant reductions in the harmonics of interest of the blade loads, but inclusion of the higher frequencies in the control synthesis introduces high frequency components in the control inputs.