Basic criteria to design and produce multistable shells

A shell can have multiple stable equilibria either if its initial curvature is sufficiently high or if a suitably strong pre-stress is applied. Under the hypotheses of a thin and shallow shell, we derive closed form results for the critical values of curvatures and pre-stresses leading to bistability and tristability. These analytical expressions allow to easily provide guidelines to build shells with different stability propertie

Chaotic and regular dynamics of a morphing shell with a vanishing-stiffness mode

Thin elastic shells are almost inextensible but easy to bend. In the presence of prestresses, geometric frustrations can produce complex elastic energetic landscapes, which have been tailored for the design of morphing structures with multiple stable equilibria or neutrally stable manifolds. We show that the co-existence of stiff and floppy modes leads to unexploited dynamical features. We build a neutrally stable cylindrical shell that under dynamical excitation alternates a chaotic behavior with a surprisingly regular regimes with a continuous precession of the curvature axis at a constant speed. We explain the experimental findings with a minimal model, showing how the intriguing dynamics is due to the subtle coupling between the prestress, geometrical nonlinearity, material anisotropy and inertial effects. Our results shed a new light on morphing structures dynamics and can be exploited in engineering applications such as energy harvesting

Depth calibration of fibre-optic distributed vibration sensing measurements

Depth calibration for conventional vertical seismic profile (VSP) tools is relatively straightforward. For fibre-optic distributed vibration sensing (DVS) measurements, however, depth calibration is more problematic and has been identified as a particular drawback. In this paper we describe four different methods for calibrating the depth of DVS recording channels. The end-of-fibre and freeze methods can be applied to both permanent and temporary fibre installations whereas the downhole source method is primarily applicable to permanent installations. Methods based on the raw backscatter measurements are more likely to be accurate because they do not involve any effects from the processing stages required to extract the phase. The freeze and downhole source methods both suffer from problems associated with picking an amplitude peak that has been smoothed by the gauge length. If a permanently installed fibre must be depth calibrated at a variety of depths, the downhole source appears to be the most promising method. The error associated with the hammering technique is significantly larger than the other techniques and thus we do not recommend its use

Optimal Real-Time Navigation System Application to a Hybrid Electrical Vehicle

International audienc

Optimal Real-Time Navigation System Application to a Hybrid Electrical Vehicle

International audienc

Video of the precession of the shell curvature axis, view 1 from Multi-parameter actuation of a neutrally stable shell: a flexible gear-less motor

Precession of the shell maximal curvature axis induced by the multiparameter piezoelectric actuatio

Real time energy management algorithm for hybrid electric vehicle

International audienc

Energy optimal real-time navigation system: Application to a hybrid electrical vehicle

International audienc