Bilal Mokrani

Synchronized switch damping on inductor and negative capacitance

This article presents a strategy for enhancing the performance of the synchronized switch damping on inductor technique used for the semiactive control of structural vibrations. This enhancement is achieved by adding a negative capacitance to the resonant circuit that dissipates the energy converted by a piezoelectric transducer embedded in the structure. A unidimensional spring-mass system shunted synchronously to a resonant circuit is studied analytically, and the main parameters governing the performances of the system are highlighted. Experimental results obtained with a synthetic negative capacitance demonstrate the enhancement of the performance of synchronized switch damping on inductor and confirm the parametric dependencies identified analytically.

Parallel Piezoelectric Shunt Damping of Rotationally Periodic Structures

This paper considers the RL shunt damping of rotationally periodic structures with an array of regularly spaced piezoelectric patches. The technique is targeted to the damping of a specific mode with nodal diameters. For this particular case, one can take advantage of the shape of the targeted mode to organize the piezoelectric patches as a modal filter (in parallel loops) which reduces the demand on the inductors of the tuned inductive shunt. In the case of a perfectly rotationally periodic structure, it is possible to organize 4 piezoelectric transducers (PZT patches) in two parallel loops of 2 patches each. In this way, the demand on the inductors is reduced by as compared to independent loops, which may allow a fully passive integration of the RL shunt in a turbomachinery application. The method is first illustrated experimentally on a circular plate; it is then applied to a prototype of an industrial bladed drum. The influence of blade mistuning is investigated.

Active Optics of Large Segmented Mirrors: Dynamics and Control

This paper examines the active optics of future large segmented telescopes from the point of view of dynamic simulation and control. The first part of the paper is devoted to the modeling of the mirror. The model has a moderated size and separates the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary or residual response). The second part of the paper is devoted to control. The control strategy considers explicitly the primary response ofthe telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. This approach is very fast and allows extensive parametric studies. The study is illustrated with an example involving 90 segments, 270 inputs, and 654 outputs.

Adaptive Inductor for Vibration Damping in Presence of Uncertainty

This paper considers the RL shunt damping of vibration with a piezoelectric transducer of a structure with a variable natural frequency. The inductive shunt damping is notorious for not being robust when the natural frequency of the electrical circuit does not match the natural frequency of the structure. In the proposed implementation, the shunted piezoelectric transducer is supplemented with a small additional one (with open electrodes) measuring the mechanical extension of the structure at the location of the transducer. The adaptation strategy uses the property that, at resonance, the electric charge in the shunted transducer is in quadrature of phase with the mechanical strain at the location of the transducer (i.e. the voltage in the transducer with open electrodes). A Phase Shift to Voltage Converter, inspired from the Phase Locked Loop technique (PLL), is built to evaluate the phase shift between these two signals and to adapt the (synthetic) inductor L via a voltage controlled resistor, involving a photoresistive optoisolator (photoresistor). The proposed strategy is supported by simulations and experimental results.

Damage Detection in Active Suspension Bridges: An Experimental Investigation

This paper considers a Hilbert marginal spectrum-based approach to health monitoring of active suspension bridge hangers. The paper proposes to takes advantage of the presence of active cables and use them as an excitation mean of the bridge, while they are used for active damping. The Hilbert–Huang transform is used to calculate the Hilbert marginal spectrum and establish a damage index for each hanger of the suspension bridge. The paper aims to investigate the method experimentally, through a series of damage scenarios, on a laboratory suspension bridge mock-up equipped with four active cables; each active cable is made of a displacement actuator collocated with a force sensor. Different locations and levels of damage severity are implemented. For the first time, the investigation demonstrates experimentally the effectiveness of the technique, as well as its limitations, to detect and locate the damage in hangers of a suspension bridge.

A numerical and experimental investigation on passive piezoelectric shunt damping of mistuned blisks

In a previous study, we proposed a method for the damping of rotationally periodic structures, when a specific mode with n nodal diameters is targeted. The proposed method considers 4n lead zirconate titanate patches (or a multiple of) which can be, either, shunted independently on 4n identical resistor–inductor circuits, or mounted in two parallel loops and shunted on only two resistor–inductor circuits. Both configurations offer the same performance; however, the parallel configuration requires only two inductors and it is aimed to reduce the demand on inductors; it works actually like a spatial filter and assumes a perfectly symmetric structure with harmonic mode shapes in the circumferential direction. The study presented in this article is aimed at evaluating the proposed damping technique in the presence of blade mistuning. In the first part, the parallel and the independent configurations are compared numerically on a set of mistuned bladed drums with controlled level of mistuning. In the second part, the parallel and the independent shunts are implemented experimentally on a mistuned bladed drum mock-up. For the considered mock-up, the numerical results show that for moderate levels of mistuning, the parallel shunt performs almost like the independent shunt, while the experimental results confirm this fact.

Electromagnetic and Piezoelectric Transducers

This chapter analyzes the constitutive equations of discrete electromechanical transducers. It begins with the voice coil transducer which can be used as sensor as well as actuator; it is followed by applications to modelling of the proof-mass actuator and the geophone sensor. The single axis gyrostabilizer is briefly discussed next. The second part of the chapter is devoted to the constitutive equations and the modelling of a discrete, single axis piezoelectric transducer. The physical meaning of the electromechanical coupling factor is discussed as well as its measurement. The chapter concludes with a short list of references and a set of problems.

Dynamics, active optics and scale effects in future extremely large telescopes

This paper examines the active optics of future large segmented telescopes from the point of view of dynamic simulation and control. The first part of the paper is devoted to the modelling of the mirror. The model has a moderate size and separates the quasi-static behavior of the mirror (primary response) from the dynamic response (secondary or residual response). The second part of the paper is devoted to control. The control strategy considers explicitly the primary response of the telescope through a singular value controller. The control-structure interaction is addressed with the general robustness theory of multivariable feedback systems, where the secondary response is considered as uncertainty. This approach is very fast and allows extensive parametric studies. The study is illustrated with an example involving 90 segments, 270 inputs, and 654 outputs.