Influence and optimization of the electrodes position in a piezoelectric energy harvesting flag

Fluttering piezoelectric plates may harvest energy from a fluid flow by converting the plate's mechanical deformation into electric energy in an output circuit. This work focuses on the influence of the arrangement of the piezoelectric electrodes along the plate's surface on the energy harvesting efficiency of the system, using a combination of experiments and numerical simulations. A weakly non-linear model of a plate in axial flow, equipped with a discrete number of piezoelectric patches is derived and confronted to experimental results. Numerical simulations are then used to optimize the position and dimensions of the piezoelectric electrodes. These optimal configurations can be understood physically in the limit of small and large electromechanical coupling.Comment: To appear in Journal of Sound and Vibratio

Wrinkling hierarchy in constrained thin sheets from suspended graphene to curtains

We show that thin sheets under boundary confinement spontaneously generate a universal self-similar hierarchy of wrinkles. From simple geometry arguments and energy scalings, we develop a formalism based on wrinklons, the transition zone in the merging of two wrinkles, as building-blocks of the global pattern. Contrary to the case of crumple paper where elastic energy is focused, this transition is described as smooth in agreement with a recent numerical work. This formalism is validated from hundreds of nm for graphene sheets to meters for ordinary curtains, which shows the universality of our description. We finally describe the effect of an external tension to the distribution of the wrinkles.Comment: 7 pages, 4 figures, added references, submitted for publicatio

Modelling of an actuated elastic swimmer

International audienceWe study the force production dynamics of undulating elastic plates as a model for fish-like inertial swimmers. Using a beam model coupled with Lighthill's large-amplitude elongated-body theory, we explore different localised actuations at one extremity of the plate (heaving, pitching, and a combination of both) in order to quantify the reactive and resistive contributions to the thrust. The latter has the form of a quadratic drag in large Reynolds number swimmers and has recently been pointed out as a crucial element in the thrust force balance. We validate the output of a weakly nonlinear solution to the fluid– structure model using thrust force measurements from an experiment with flexible plates subjected to the three different actuation types. The model is subsequently used in a self-propelled configuration —with a skin friction model that balances thrust to produce a constant cruising speed— to map the reactive versus resistive thrust production in a parameter space defined by the aspect ratio and the actuation frequency. We show that this balance is modified as the frequency of excitation changes and the response of the elastic plate shifts between different resonant modes, the pure heaving case being the most sensitive to the modal response with drastic changes in the reactive/resistive contribution ratio along the frequency axis. We analyse also the role of the phase lag between the heaving and pitching components in the case of combined actuation, showing in particular a non-trivial effect on the propulsive efficiency

Weakly non-linear model of a piezoelectric plate in an axial flow

International audienceWe present a weakly non-linear model of a piezoelctric flag immersed in an axial flow. Numerical simulations based on Galerkin projections are carried out in order to evaluate the coupling between the flapping piezo-electric flag and a purely resistive circuit intended to simulate the electric energy harvesting circuit. The numerical simulations allow to point out the relevant physical parameters governing the apparition of the flapping instability, power conversion and system’s harvesting efficiency

Spooling and disordered packing of elastic rods in cylindrical cavities

The compaction of elastic rods in rigid cylindrical cavities is experimentally performed. The results show two main packing behaviours: an ordered regime in which the rod spools on the internal surface of the cavity and a disordered phase where the orientation of the coils is randomly distributed. The phase diagram separating these two packing configurations is determined as a function of the aspect ratio of the container and of the intrinsic curvature of the rod. A theoretical stability analysis and an experimental study of the dynamics of the rod at the injection point allow to describe different instability mechanisms that drive the transitions from ordered to disordered packing, leading to the identification of the different disordering scenarios

Locomotion of Ants Walking up Slippery Slopes of Granular Materials

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