Showing papers by "Manuel Collet published in 2015"

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

Abstract: 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...

Collective dynamics of periodic nonlinear oscillators under simultaneous parametric and external excitations

Abstract: The collective dynamics of a periodic structure of coupled Duffing–Van Der Pol oscillators is investigated under simultaneous external and parametric excitations. An analytico-computational model based on a perturbation technique, combined with standing wave decomposition and the asymptotic numerical method is developed for a finite number of coupled oscillators. The frequency responses and the basins of attraction are analyzed for the case of small arrays, demonstrating the importance of the multi-mode solutions and the robustness of their attractors. This model can be exploited to design periodic structure-based smart systems with high performance, by taking advantage of the multi-modes induced by the collective dynamics.

Damping Enhancement of Composite Panels by Inclusion of Shunted Piezoelectric Patches: A Wave-Based Modelling Approach

Abstract: The waves propagating within complex smart structures are hereby computed by employing a wave and finite element method. The structures can be of arbitrary layering and of complex geometric characteristics as long as they exhibit two-dimensional periodicity. The piezoelectric coupling phenomena are considered within the finite element formulation. The mass, stiffness and piezoelectric stiffness matrices of the modelled segment can be extracted using a conventional finite element code. The post-processing of these matrices involves the formulation of an eigenproblem whose solutions provide the phase velocities for each wave propagating within the structure and for any chosen direction of propagation. The model is then modified in order to account for a shunted piezoelectric patch connected to the composite structure. The impact of the energy dissipation induced by the shunted circuit on the total damping loss factor of the composite panel is then computed. The influence of the additional mass and stiffness provided by the attached piezoelectric devices on the wave propagation characteristics of the structure is also investigated.

Effect of fretting wear damage in RF connectors subjected to vibration: DC contact resistance and phase-noise response

Abstract: In many applications, RF connectors are subjected to severe environmental vibration. Vibration induces micro-displacements, leading to fretting wear damage in the contact. The purpose of this study is to investigate the effect of fretting wear on the microwave signal and more precisely on the additive phase noise [1, 2]. A dedicated vibration test was developed, combining DC and microwave measurement. It consisted of a shaker, a vector network analyzer, a phase-noise analyzer using a cross-correlation technique, and a system for measuring electrical contact resistance. Degradation of phase noise by fretting wear was demonstrated. Two contributions were identified: relative fretting displacement amplitude, by fluctuating the total transmission distance, induced phase noise at the specific fretting frequency proportional to the fretting displacement; also, by inducing oxide debris in the interface, gross slip fretting wear damage decayed DC electrical contact resistance and microwave signal transmission. The study established quantitative correlations between the evolution of DC, transmission loss and phase-noise parameters.

Periodically distributed piezoelectric patches optimization for waves attenuation and vibrations damping

Abstract: The deformation of a structure can be understood as a superposition of waves which are induced by the excitation and reflected by the boundaries. According to this regard, attenuations of waves can lead to a strong reduction of the structural response and prevent energy to be propagated. In this work we consider periodically distributed piezoelectric patches onto the host structure so that by designing shunted electric circuits the properties of the waves can be modified. The success of the idea is also directly related to the extent of electromechanical coupling. In terms of structural modes, the coupling factor can be estimated by the open-circuit (OC) and short-circuit (SC) natural frequencies. However, in terms of waves, few criteria are available. In this work, a wave-based criterion is proposed to evaluate the coupling factor of the piezoelectric composite. To do this, enhanced Wave and Finite Element Method (WFEM) is employed to obtain the dispersion relations and the shapes of the waves. Then, the factor can be calculated in three different but equivalent formulas. An example is given thereafter, where a piezoelectric waveguide with semi-active circuits is used to control the energy flow from a source to the far-field. We show that the coupling factor is frequency dependent and it is strongly related to the geometric parameters; therefore, it significantly changes the optimal performance of the piezoelectric waveguide and it capacity to dampen vibrations.

Control strategies for a distributed active acoustic skin

Abstract: New miniaturization and integration capabilities made available from the emerging MEMS technology allow for the design of artificial linings involving distribution of a large number of elementary cells, that may be composed of loudspeakers and microphones. These smart materials pose the challenge of developing new control strategies to engineer target acoustical impedances, in order to control acoustic fields. This paper investigates the acoustical capabilities of such a distributed active acoustic skin by comparing two control strategies. The first approach is based on local control, where each loudspeaker is current-driven, using a current-pressure transfer function which is designed according to a target acoustic impedance. In the second approach, a distributed control system is implemented such that acoustic waves cannot propagate in a certain direction. Numerical results demonstrate how a well-controlled active skin can substantially modify sound transmission along a waveguide. In this study, each strategy is characterized in terms of efficiency, frequency bandwidth, and robustness. Finally, design parameters for a future prototype are proposed.

Outils Numériques pour la Simulation de Propagation d'Ondes dans les Structures Périodiques Amorties

Abstract: Periodic structures exhibit very specific properties in terms of wave propagation. In this paper, some numerical tools for dispersion analysis of periodic structures are presented. The classical Floquet-Bloch approach is first presented, as a reference. This technique uses proper boundary conditions on the unit cell, it is quite simple to implement but dealing with damping is not easy for 2D or 3D cases. Secondly, the "Shifted-Cell Operator" technique is described. It consists in a reformulation of the PDE problem by "shifting" in terms of wave number the space derivatives appearing in the mechanical behavior operator inside the cell, while imposing continuity boundary conditions on the borders of the domain. Damping effects can be introduced in the system. This strategy make it possible to solve the problem with an arbitrary frequency dependency of the physical properties of the cell. This method is presented as well as an application case about a damped periodic structure. Mots clefs : Structure Périodique, Dispersion, Amortissement. 22ème Congrès Français de Mécanique Lyon, 24 au 28 Août 2015