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Search Results: 1 - 10 of 32268 matches for " Antonio DeSimone "
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Motility of a Model Bristle-Bot: a Theoretical Analysis
Giancarlo Cicconofri,Antonio DeSimone
Physics , 2014, DOI: 10.1016/j.ijnonlinmec.2014.12.010
Abstract: Bristle-bots are legged robots that can be easily made out of a toothbrush head and a small vibrating engine. Despite their simple appearance, the mechanism enabling them to propel themselves by exploiting friction with the substrate is far from trivial. Numerical experiments on a model bristle-bot have been able to reproduce such a mechanism revealing, in addition, the ability to switch direction of motion by varying the vibration frequency. This paper provides a detailed account of these phenomena through a fully analytical treatment of the model. The equations of motion are solved through an expansion in terms of a properly chosen small parameter. The convergence of the expansion is rigorously proven. In addition, the analysis delivers formulas for the average velocity of the robot and for the frequency at which the direction switch takes place. A quantitative description of the mechanism for the friction modulation underlying the motility of the bristle-bot is also provided.
A Study of Snake-like Locomotion Through the Analysis of a Flexible Robot Model
Giancarlo Cicconofri,Antonio DeSimone
Physics , 2014,
Abstract: We examine the problem of snake-like locomotion by studying a system consisting of a planar inextensible elastic rod that is able to control its spontaneous curvature. Using a Cosserat model we derive, through variational principles, the equations of motion for two special cases: one in which the system is confined inside a frictionless channel, and one in which it is placed in an anisotropic frictional environment, modeling the dynamical setting of the slithering of snakes on flat surfaces. The presence of constraints in both cases leads to non-standard boundary conditions, that allow us to close the equations of motion reducing them to a differential and an integro-differential equation, respectively, for one end point (the tail) of the active rod. For the snake-like case we also provide analytic solutions for a special class of motions. We highlight the role of the spontaneous curvature in the pushing (and the steering, in the snake-like setting) needed to power locomotion. Comparisons with available experiments confirm that the model is able to capture many of the essential findings in the zoological literature. The complete solvability and the existence of analytic solutions offers a tool that may prove valuable for the design of bio-inspired soft robots.
A robotic crawler exploiting directional frictional interactions: experiments, numerics, and derivation of a reduced model
Giovanni Noselli,Antonio DeSimone
Physics , 2014, DOI: 10.1098/rspa.2014.0333
Abstract: We present experimental and numerical results for a model crawler which is able to extract net positional changes from reciprocal shape changes, i.e. 'breathing-like' 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.
Rigorous derivation of active plate models for thin sheets of nematic elastomers
Virginia Agostiniani,Antonio DeSimone
Mathematics , 2015,
Abstract: In the context of finite elasticity, we propose a plate model describing the bending behavior of a nematic elastomer thin film with splay-bend and twisted distribution of the nematic director along the thickness. The reduced energy functional is derived from a three-dimensional description of the system using rigorous dimension-reduction techniques, based on the theory of $\Gamma$-convergence. The (new) two-dimensional model is a nonlinear plate theory in which deviations from a characteristic target curvature tensor cost elastic energy. Moreover, the stored energy functional cannot be minimized at zero, thus revealing the presence of residual stresses, which are indeed observed experimentally.
Crawling on directional surfaces
Paolo Gidoni,Giovanni Noselli,Antonio DeSimone
Physics , 2014, DOI: 10.1016/j.ijnonlinmec.2014.01.012
Abstract: In this paper we study crawling locomotion based on directional frictional interactions, namely, frictional forces that are sensitive to the sign of the sliding velocity. Surface interactions of this type are common in biology, where they arise from the presence of inclined hairs or scales at the crawler/substrate interface, leading to low resistance when sliding 'along the grain', and high resistance when sliding 'against the grain'. This asymmetry can be exploited for locomotion, in a way analogous to what is done in cross-country skiing (classic style, diagonal stride). We focus on a model system, namely, a continuous one-dimensional crawler and provide a detailed study of the motion resulting from several strategies of shape change. In particular, we provide explicit formulae for the displacements attainable with reciprocal extensions and contractions (breathing), or through the propagation of extension or contraction waves. We believe that our results will prove particularly helpful for the study of biological crawling motility and for the design of bio-mimetic crawling robots.
Numerical Strategies for Stroke Optimization of Axisymmetric Microswimmers
Fran?ois Alouges,Antonio DeSimone,Luca Heltai
Mathematics , 2009,
Abstract: We propose a computational method to solve optimal swimming problems, based on the boundary integral formulation of the hydrodynamic interaction between swimmer and surrounding fluid and direct constrained minimization of the energy consumed by the swimmer. We apply our method to axisymmetric model examples. We consider a classical model swimmer (the three-sphere swimmer of Golestanian et al.) as well as a novel axisymmetric swimmer inspired by the observation of biological micro-organisms.
The role of membrane viscosity in the dynamics of fluid membranes
Marino Arroyo,Antonio DeSimone,Luca Heltai
Mathematics , 2010,
Abstract: Fluid membranes made out of lipid bilayers are the fundamental separation structure in eukaryotic cells. Many physiological processes rely on dramatic shape and topological changes (e.g. fusion, fission) of fluid membrane systems. Fluidity is key to the versatility and constant reorganization of lipid bilayers. Here, we study the role of the membrane intrinsic viscosity, arising from the friction of the lipid molecules as they rearrange to accommodate shape changes, in the dynamics of morphological changes of fluid vesicles. In particular, we analyze the competition between the membrane viscosity and the viscosity of the bulk fluid surrounding the vesicle as the dominant dissipative mechanism. We consider the relaxation dynamics of fluid vesicles put in an out-of-equilibrium state, but conclusions can be drawn regarding the kinetics or power consumption in regulated shape changes in the cell. On the basis of numerical calculations, we find that the dynamics arising from the membrane viscosity are qualitatively different from the dynamics arising from the bulk viscosity. When these two dissipation mechanisms are put in competition, we find that for small vesicles the membrane dissipation dominates, with a relaxation time that scales as the size of the vesicle to the power 2. For large vesicles, the bulk dissipation dominates, and the exponent in the relaxation time vs. size relation is 3.
One-dimensional swimmers in viscous fluids: dynamics, controllability, and existence of optimal controls
Gianni Dal Maso,Antonio DeSimone,Marco Morandotti
Mathematics , 2013,
Abstract: In this paper we study a mathematical model of one-dimensional swimmers performing a planar motion while fully immersed in a viscous fluid. The swimmers are assumed to be of small size, and all inertial effects are neglected. Hydrodynamic interactions are treated in a simplified way, using the local drag approximation of resistive force theory. We prove existence and uniqueness of the solution of the equations of motion driven by shape changes of the swimmer. Moreover, we prove a controllability result showing that given any pair of initial and final states, there exists a history of shape changes such that the resulting motion takes the swimmer from the initial to the final state. We give a constructive proof, based on the composition of elementary maneuvers (straightening and its inverse, rotation, translation), each of which represents the solution of an interesting motion planning problem. Finally, we prove the existence of solutions for the optimal control problem of finding, among the histories of shape changes taking the swimmer from an initial to a final state, the one of minimal energetic cost.
A stable and adaptive semi-Lagrangian potential model for unsteady and nonlinear ship-wave interactions
Andrea Mola,Luca Heltai,Antonio DeSimone
Mathematics , 2012, DOI: 10.1016/j.enganabound.2012.09.005
Abstract: We present an innovative numerical discretization of the equations of inviscid potential flow for the simulation of three dimensional unsteady and nonlinear water waves generated by a ship hull advancing in water. The equations of motion are written in a semi-Lagrangian framework, and the resulting integro-differential equations are discretized in space via an adaptive iso-parametric collocation Boundary Element Method, and in time via adaptive implicit Backward Differentiation Formulas (BDF) with variable step and variable order. When the velocity of the advancing ship hull is non-negligible, the semi-Lagrangian formulation (also known as Arbitrary Lagrangian Eulerian formulation, or ALE) of the free surface equations contains dominant transport terms which are stabilized with a Streamwise Upwind Petrov-Galerkin (SUPG) method. The SUPG stabilization allows automatic and robust adaptation of the spatial discretization with unstructured quadrilateral grids. Preliminary results are presented where we compare our numerical model with experimental results on the case of a Wigley hull advancing in calm water with fixed sink and trim.
Folding Energetics in Thin-Film Diaphragms
Gustavo Gioia,Antonio DeSimone,Michael Ortiz,Alberto M. Cuitino
Physics , 2000,
Abstract: We perform experiments on thin-film diaphragms to show that the folding patterns of anisotropically compressed diaphragms are strikingly different from those of isotropically compressed ones. We then use a simple von Karman model to relate the overall features of these folding patterns to the underlying energetics. We show that the differences between the isotropic and anisotropic cases can be traced back to fundamental changes in the energy structure of the diaphragms. Finally, we point out that the energy structure of thin-film diaphragms is similar to that of many other systems in physics and engineering, into which our study may provide interesting insights.
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