GSSI Gran Sasso Science Institute

L'Aquila, Italy

GSSI Gran Sasso Science Institute

L'Aquila, Italy
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DeSimone A.,International School for Advanced Studies | DeSimone A.,GSSI Gran Sasso Science Institute | Gidoni P.,International School for Advanced Studies | Noselli G.,International School for Advanced Studies
Journal of the Mechanics and Physics of Solids | Year: 2015

In this paper, we speculate on a possible application of Liquid Crystal Elastomers to the field of soft robotics. In particular, we study a concept for limbless locomotion that is amenable to miniaturisation. For this purpose, we formulate and solve the evolution equations for a strip of nematic elastomer, subject to directional frictional interactions with a flat solid substrate, and cyclically actuated by a spatially uniform, time-periodic stimulus (e.g., temperature change). The presence of frictional forces that are sensitive to the direction of sliding transforms reciprocal, 'breathing-like' deformations into directed forward motion. We derive formulas quantifying this motion in the case of distributed friction, by solving a differential inclusion for the displacement field. The simpler case of concentrated frictional interactions at the two ends of the strip is also solved, in order to provide a benchmark to compare the continuously distributed case with a finite-dimensional benchmark. We also provide explicit formulas for the axial force along the crawler body. © 2015 Elsevier Ltd. All rights reserved.


Gidoni P.,International School for Advanced Studies | DeSimone A.,International School for Advanced Studies | DeSimone A.,GSSI Gran Sasso Science Institute
Meccanica | Year: 2016

We formulate and solve the locomotion problem for a bio-inspired crawler consisting of two active elastic segments (i.e., capable of changing their rest lengths), resting on three supports providing directional frictional interactions. The problem consists in finding the motion produced by a given, slow actuation history. By focusing on the tensions in the elastic segments, we show that the evolution laws for the system are entirely analogous to the flow rules of elasto-plasticity. In particular, sliding of the supports and hence motion cannot occur when the tensions are in the interior of certain convex regions (stasis domains), while support sliding (and hence motion) can only take place when the tensions are on the boundary of such regions (slip surfaces). We solve the locomotion problem explicitly in a few interesting examples. In particular, we show that, for a suitable range of the friction parameters, specific choices of the actuation strategy can lead to net displacements also in the direction of higher friction. © 2016 Springer Science+Business Media Dordrecht


Colombo M.,Normal School of Pisa | Crippa G.,University of Basel | Spirito S.,GSSI Gran Sasso Science Institute
Networks and Heterogeneous Media | Year: 2016

The aim of this short note is twofold. First, we give a sketch of the proof of a recent result proved by the authors in the paper [7] concerning existence and uniqueness of renormalized solutions of continuity equations with unbounded damping coefficient. Second, we show how the ideas in [7] can be used to provide an alternative proof of the result in [6, 9, 12], where the usual requirement of boundedness of the divergence of the vector field has been relaxed to various settings of exponentially integrable functions. © American Institute of Mathematical Sciences.


Montino A.,GSSI Gran Sasso Science Institute | DeSimone A.,GSSI Gran Sasso Science Institute | DeSimone A.,International School for Advanced Studies
European Physical Journal E | Year: 2015

Abstract.: One of the simplest model swimmers at low Reynolds number is the three-sphere swimmer by Najafi and Golestanian. It consists of three spheres connected by two rods which change their lengths periodically in non-reciprocal fashion. Here we investigate a variant of this model in which one rod is periodically actuated while the other is replaced by an elastic spring. We show that the competition between the elastic restoring force and the hydrodynamic drag produces a delay in the response of the passive elastic arm with respect to the active one. This leads to non-reciprocal shape changes and self-propulsion. After formulating the equations of motion, we study their solutions qualitatively and numerically. The leading-order term of the solution is computed analytically. We then address questions of optimization with respect to both actuation frequency and swimmer’s geometry. Our results can provide valuable conceptual guidance in the engineering of robotic microswimmers. Graphical abstract: [Figure not available: see fulltext.] © 2015, The Author(s).


Noselli G.,International School for Advanced Studies | DeSimone A.,International School for Advanced Studies | DeSimone A.,GSSI Gran Sasso Science Institute
Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014

We present experimental and numerical results for a model crawler which is able to extract net positional changes fromreciprocal shape changes, i.e. 'breathinglike' deformations, thanks to directional, frictional interactions with a textured solid substrate, mediated by flexible inclined feet. We also present a simple reduced model that captures the essential features of the kinematics and energetics of the gait, and compare its predictions with the results from experiments and from numerical simulations. © 2014 The Author(s) Published by the Royal Society. All rights reserved.


Crippa G.,University of Basel | Spirito S.,GSSI Gran Sasso Science Institute
Communications in Mathematical Physics | Year: 2015

In this paper we prove that solutions of the 2D Euler equations in vorticity formulation obtained via vanishing viscosity approximation are renormalized. © 2015 Springer Science+Business Media New York.

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