Mohamed Ichchou

Wave Motion Optimization in Periodically Distributed Shunted Piezocomposite Beam Structures

This article proposes a new, simple, and efficient strategy, allowing one to optimize the diffusion operator between a passive beam coupled to a like beam equipped with a periodically distributed network of shunted piezoelectric patch actuators. A multimodal wave dispersion model is used to compute the diffusion operator and analyze the stability properties of the combined system. Based on this mathematical tool, specific optimization procedures are introduced to allow maximization or minimization of the wave transmissibility between the passive and the active distributed beam. A specific example is used to demonstrate the capability of the shunted piezoelectric system to induce total reflection through the total absorption of incoming propagating flexural waves while guaranteeing the stability, robustness, and realizability of such a system.

Structural energy flow optimization through adaptive shunted piezoelectric metacomposites

In this article, a numerical approach for modeling and optimizing two-dimensional smart metacomposites is presented. The proposed methodology is based on the Floquet–Bloch theorem in the context of elastodynamics including distributed shunted piezoelectric patches. The dedicated numerical technique is able to cope with the multimodal wave dispersion behavior over the whole first Brillouin zone for periodically distributed two-dimensional shunted piezomechanical systems. Some indicators allowing the optimization of the shunt impedance for specific performance objectives are presented and applied for illustration purposes on the design of an adaptive metacomposite with specific functionalities. In order to validate the strategy, the designed metacomposite is integrated in a support structure, and a full three-dimensional model is derived to illustrate the efficiency of the approach.

Reliability assessment of complex mechatronic systems using a modified nonparametric belief propagation algorithm

Various parametric skewed distributions are widely used to model the time-to-failure (TTF) in the reliability analysis of mechatronic systems, where many items are unobservable due to the high cost of testing. Estimating the parameters of those distributions becomes a challenge. Previous research has failed to consider this problem due to the difficulty of dependency modeling. Recently the methodology of Bayesian networks (BNs) has greatly contributed to the reliability analysis of complex systems. In this paper, the problem of system reliability assessment (SRA) is formulated as a BN considering the parameter uncertainty. As the quantitative specification of BN, a normal distribution representing the stochastic nature of TTF distribution is learned to capture the interactions between the basic items and their output items. The approximation inference of our continuous BN model is performed by a modified version of nonparametric belief propagation (NBP) which can avoid using a junction tree that is inefficient for the mechatronic case because of the large treewidth. After reasoning, we obtain the marginal posterior density of each TTF model parameter. Other information from diverse sources and expert priors can be easily incorporated in this SRA model to achieve more accurate results. Simulation in simple and complex cases of mechatronic systems demonstrates that the posterior of the parameter network fits the data well and the uncertainty passes effectively through our BN based SRA model by using the modified NBP.

A wave-based design of semi-active piezoelectric composites for broadband vibration control

This paper deals with the design of periodic piezoelectric structures for broadband vibration control. By shunting identical negative capacitances to the periodically distributed piezoelectric patches, a wide and continuous band gap is created so as to cover the frequency range of interest. This way the modal density of the structure is reduced and the modal shapes are localized at the boundaries. A large proportion of the energy can then be removed or dissipated by a small number of dampers or energy harvesters integrated within the negative capacitance circuits. A design process is proposed to achieve the wide band gap. The overall amount of piezoelectric materials is constrained in order to keep mass of structures low. The wave electromechanical coupling factor is proposed and used as a criterion. This allows to reach the largest width of the band gap by using a stable value of negative capacitance. The control of multiple high-order modes of a cantilever beam is considered as an example. The vibration reduction performance of the designed piezoelectric structures is presented and the influences of band gap resonance, resistor and the boundary condition are discussed. The proposed approach is fully based on wave characteristics and it does not rely on any modal information. It is therefore promising for applications at mid- and high frequencies where the access to the exact modal information is difficult.

Experimental characterization of a bi-dimensional array of negative capacitance piezo-patches for vibroacoustic control

This study presents an experimental investigation of the application of a periodic array of shunted piezoelectric patches with negative capacitance for the broadband control of waves propagating on a flexible plate. A 15 × 5 array of piezoelectric patches is bonded onto the top surface of a freely supported rectangular plate. The patch array is intended to serve as an active interface between two regions of the plate, where one region has an input disturbance force and the other does not. Each patch is shunted through a single circuit, reproducing a resistance in series with a negative capacitance. The magnitude of the reactive part of the negative shunting impedance is tuned close to the intrinsic capacitance of the piezoelectric patch. The real part is adjusted for either light damping so as to induce a reactive (reflective) response, or with heavy damping to induce greater absorption. The experimental responses of the system equipped with this active interface display a strong attenuation or reflection of vibrations, depending on the shunt resistance, over a large frequency range, including the mid-frequency regime. In an effort to control vibroacoustic phenomena, this study represents the first attempt to implement an integrated smart metacomposite active interface on a plate structure.

Phase and gain control policies for robust active vibration control of flexible structures

The interest of this paper is to develop a general and systematic robust control methodology for active vibration control of flexible structures. For this purpose, first phase and gain control policies are proposed to impose qualitative frequency-dependent requirements on the controller to consider a complete set of control objectives. Then the proposed control methodology is developed by employing phase and gain control policies in the dynamic output feedback H??control: according to the set of control objectives, phase and gain control policies incorporate necessary weighting functions and determine them in a rational and systematic way; on the other hand, with the appropriate weighting functions efficient H??control algorithms can automatically realize phase and gain control policies and generate a satisfactory H??controller. The proposed control methodology can be used for both SISO and MIMO systems with collocated or non-collocated sensors and actuators. In this paper, it is validated on a non-collocated piezoelectric cantilever beam. Both numerical simulations and experimental results demonstrate the effectiveness of the proposed control methodology.

Dynamic Damping Properties of Thermoplastic Elastomers Based on EVA and Recycled Ground Tire Rubber

Recycling waste tires being important for both economical and environmental reasons, ground tire rubber can be blended with other polymers, modifying their properties. In order to characterize and explain these modifications, an experimental study was carried out concerning the improvement in the dynamic damping properties when adding recycled ground tire rubber (GTR) fillers to an elastomeric matrix (ethylene vinyl acetate, EVA).To evaluate the influence of both the GTR and the porosity in a GTR/ EVA composite, three samples have been elaborated by injection:the EVA matrix alone, a GTR/EVA composite, and a GTR/EVA porous composite. Dynamic measurements of the samples were performed using dynamic mechanical thermal analysis. The Young’s modulus and loss factor of these materials are estimated using the frequency—temperature equivalence introduced by Williams—Landel—Ferry expanding the measurement of the dynamic properties over a wider range of frequencies. This method showed that in low-frequency bandwidth, the loss factor has been improved by the addition of GTR to the EVA matrix. The α-relaxation study showed lower activation energy for both the GTR-filled composites leading to the conclusion that the mobility of the polymer chains has been improved by addition of GTR. The impact behavior study carried out using a weight drop test experiment also concluded to better impact energy absorption for the GTR-filled composites at the expense of a larger maximum displacement.

Impact of the irregular microgeometry of polyurethane foam on the macroscopic acoustic behavior predicted by a unit-cell model

This paper deals with the prediction of the macroscopic sound absorption behavior of highly porous polyurethane foams using two unit-cell microstructure-based models recently developed by Doutres, Atalla, and Dong [J. Appl. Phys. 110, 064901 (2011); J. Appl. Phys. 113, 054901 (2013)]. In these models, the porous material is idealized as a packing of a tetrakaidecahedra unit-cell representative of the disordered network that constitutes the porous frame. The non-acoustic parameters involved in the classical Johnson-Champoux-Allard model (i.e., porosity, airflow resistivity, tortuosity, etc.) are derived from characteristic properties of the unit-cell and semi-empirical relationships. A global sensitivity analysis is performed on these two models in order to investigate how the variability associated with the measured unit-cell characteristics affects the models outputs. This allows identification of the possible limitations of a unit-cell micro-macro approach due to microstructure irregularity. The sensitivity analysis mainly shows that for moderately and highly reticulated polyurethane foams, the strut length parameter is the key parameter since it greatly impacts three important non-acoustic parameters and causes large uncertainty on the sound absorption coefficient even if its measurement variability is moderate. For foams with a slight inhomogeneity and anisotropy, a micro-macro model associated to cell size measurements should be preferred.

Novel Approach of Self-Sensing Actuation for Active Vibration Control

In a self-sensing actuator, the same piezoelectric element functions as both a sensor and an actuator. Due to their advantages of reducing the number of needed piezoelectric elements and true collocation of sensors and actuators, self-sensing actuators have attracted the attention of many researchers and many studies have been reported. Since the actuator signal and the sensor signal are mixed together in a self-sensing actuator, usually a bridge circuit is used to separate the two signals. It has been found that the two signals cannot be separate ideally, because the bridge is difficult to balance and the actuator signal is much larger than the sensor signal. In this study, the influence of the local strain on the output signal of a piezoelectric sensor is investigated numerically and experimentally. In order to delete the influence of local strain on performance of the self-sensing actuator, a new method using neural network is proposed to identify the strain of global vibration. The identified signal is used as feedback signal for an adaptive control system and the effectiveness in suppressing the beam vibration is verified in the experiment.

A finite-element study of a piezoelectric/poroelastic sound package concept

This paper presents a complete finite-element description of a hybrid passive/active sound package concept for acoustic insulation. The sandwich created includes a poroelastic core and piezoelectric patches to ensure high panel performance over the medium/high and low frequencies, respectively. All layers are modelled thanks to a Comsol environment. The piezoelectric/elastic and poroelastic/elastic coupling are fully considered. The study highlights the reliability of the model by comparing results with those obtained from the Ansys finite-element software and with analytical developments. The chosen shape functions and mesh convergence rate for each layer are discussed in terms of dynamic behaviour. Several layer configurations are then tested, with the aim of designing the panel and its hybrid functionality in an optimal manner. The differences in frequency responses are discussed from a physical perspective. Lastly, an initial experimental test shows the concept to be promising.