627 research outputs found
Swelling-induced bending and pumping in homogeneous thin sheets
We realize steady curved shapes from homogeneous hydrogel flat structures which are in contact with two environments at different chemical conditions. We numerically investigate the behaviour of beam-like and plate-like structures during the transient state, which realize osmotic pumps. Through numerical experiments, we determine the relationship between the difference in the chemical potentials at the top and bottom of a beam and the curvature of the bent beam as well as the Gaussian curvature of a spherical cap morphed from a flat plate. We also propose an approximate modeling of both the beam and the plate, to evaluate explicitly that relationship and show the good agreement between those formulas and the outcomes of the numerical simulations
Actuation performances of anisotropic gels
We investigated the actuation performances of anisotropic gels driven by
mechanical and chemical stimuli, in terms of both deformation processes and
stroke--curves, and distinguished between the fast response of gels before
diffusion starts and the asymptotic response attained at the steady state. We
also showed as the range of forces that an anisotropic hydrogel can exert when
constrained is especially wide;indeed, changing fiber orientation allows to
induce shear as well as transversely isotropic extensions.Comment: 11 pages, 11 figure
Evaluation of the strain-line patterns in a human left ventricle: A simulation study
The aim of this paper is to emphasise the role of the primary strain-line patterns in a human left ventricle (LV) within the complex system that is the heart. In particular, a protocol is proposed for the measurement of the principal strain lines (PSL) in the walls of the LV; this protocol is tested by means of a computational model which resembles a human LV. When the analysis is focused on the epicardial surface, PSL can be used to derive information on the directions of muscle fibres during the entire cardiac cycle, not only the systolic phase. © 2013 Taylor & Francis
Mechanics of bio–hybrid systems
Bio–hybrid system are morphing structures whose shaping can be electrically driven and strongly depends on the geometrical and mechanical characteristics of the system. The estimation of those characteristics which allow for getting target shapes is a great challenge. We present and discuss an approximate model for narrow bio–hybrid strips which works well in plane bending. A generalization towards three–layers bio–hybrid system is presented
Extraction of main levels of a building from a large point cloud
Horizontal levels are references entities, the base of man-made environments. Their creation is the first step for various applications including the BIM (Building Information Modelling). BIM is an emerging methodology, widely used for new constructions, and increasingly applied to existing buildings (scan-to-BIM). The as-built BIM process is still mainly manual or semi-automatic and therefore is highly time-consuming. The automation of the as-built BIM is a challenging topic among the research community. This study is part of an ongoing research into the scan-to-BIM process regarding the extraction of the principal structure of a building. More specifically, here we present a strategy to automatically detect the building levels from a large point cloud obtained with a terrestrial laser scanner survey. The identification of the horizontal planes is the first indispensable step to produce an as-built BIM model. Our algorithm, developed in C++, is based on plane extraction by means of the RANSAC algorithm followed by the minimization of the quadrate sum of points-plane distance. Moreover, this paper will take an in-depth look at the influence of data resolution in the accuracy of plane extraction and at the necessary accuracy for the construction of a BIM model. A laser scanner survey of a three floors building composed by 36 scan stations has produced a point cloud of about 550 million points. The estimated plane parameters at different data resolution are analysed in terms of distance from the full points cloud resolution
Single-tree detection in high-density LiDAR data from UAV-based survey
UAV-based LiDAR survey provides very-high-density point clouds, which involve very rich information about forest detailed structure, allowing for detection of individual trees, as well as demanding high computational load. Single-tree detection is of great interest for forest management and ecology purposes, and the task is relatively well solved for forests made of single or largely dominant species, and trees having a very evident pointed shape in the upper part of the canopy (in particular conifers). Most authors proposed methods based totally or partially on search of local maxima in the canopy, which has poor performance for species that have flat or irregular upper canopy, and for mixed forests, especially where taller trees hide smaller ones. Such considerations apply in particular to Mediterranean hardwood forests. In such context, it is imperative to use the whole volume of the point cloud, however keeping computational load tractable. The authors propose the use of a methodology based on modelling the 3D-shape of the tree, which improves performance w.r.t to maxima-based models. A case study, performed on a hazel grove, is provided to document performance improvement on a relatively simple, but significant, case
Temperature-driven volume transition in hydrogels: phase--coexistence and interface localization
We study volume transition phenomenon in hydrogels within the framework of
Flory-Rehner thermodynamic modelling; we show that starting from different
models for the Flory parameter different conclusions can be achieved, in terms
of admissible coexisting equilibria of the system. In particular, with explicit
reference to a one-dimensional problem we establish the ranges of both
temperature and traction which allow for the coexistence of a swollen and a
shrunk phase. Through consideration of an augmented Flory-Rehner free-energy,
which also accounts for the gradient of volume changes, we determine the
position of the interface between the coexisting phases, and capture the
connection profile between them
Morphing of Geometric Composites via Residual Swelling
Understanding and controlling the shape of thin, soft objects has been the
focus of significant research efforts among physicists, biologists, and
engineers in the last decade. These studies aim to utilize advanced materials
in novel, adaptive ways such as fabricating smart actuators or mimicking living
tissues. Here, we present the controlled growth--like morphing of 2D sheets
into 3D shapes by preparing geometric composite structures that deform by
residual swelling. The morphing of these geometric composites is dictated by
both swelling and geometry, with diffusion controlling the swelling-induced
actuation, and geometric confinement dictating the structure's deformed shape.
Building on a simple mechanical analog, we present an analytical model that
quantitatively describes how the Gaussian and mean curvatures of a thin disk
are affected by the interplay among geometry, mechanics, and swelling. This
model is in excellent agreement with our experiments and numerics. We show that
the dynamics of residual swelling is dictated by a competition between two
characteristic diffusive length scales governed by geometry. Our results
provide the first 2D analog of Timoshenko's classical formula for the thermal
bending of bimetallic beams - our generalization explains how the Gaussian
curvature of a 2D geometric composite is affected by geometry and elasticity.
The understanding conferred by these results suggests that the controlled
shaping of geometric composites may provide a simple complement to traditional
manufacturing techniques
Geometry and Mechanics of Thin Growing Bilayers
We investigate how thin sheets of arbitrary shapes morph under the isotropic
in-plane expansion of their top surface, which may represent several stimuli
such as nonuniform heating, local swelling and differential growth. Inspired by
geometry, an analytical model is presented that rationalizes how the shape of
the disk influences morphing, from the initial spherical bending to the final
isometric limit. We introduce a new measure of slenderness that
describes a sheet in terms of both thickness and plate shape. We find that the
mean curvature of the isometric state is three fourth's the natural curvature,
which we verify by numerics and experiments. We finally investigate the
emergence of a preferred direction of bending in the isometric state, guided by
numerical analyses. The scalability of our model suggests that it is suitable
to describe the morphing of sheets spanning several orders of magnitude.Comment: 5 pages, 4 figure
Torque-induced reorientation in active fibre-reinforced materials
We introduce a continuum model for a fibre reinforced material in which the
reference orientation of the fibre may evolve with time, under the influence of
external stimuli. The model is formulated in the framework of large strain
hyperelasticity and the kinematics of the continuum is described by both a
position vector and by a remodelling tensor which, in the present context, is
an orthogonal tensor representing the fibre reorientation process. By imposing
suitable thermodynamical restrictions on the constitutive equation, we obtain
an evolution equation of the remodelling tensor governed by the Eshelby torque,
whose stationary solutions are studied in absence of any external source terms.
It is shown that the fibres reorient themselves in a configuration that
minimises the elastic energy and get aligned along a direction that may or may
not be of principal strain. The explicit analysis of the Hessian of the strain
energy density allows us to discriminate among the stationary solutions, which
ones are stable. Examples are given for passive reorientation processes driven
by applied strains or external boundary tractions. % Applications of the
proposed theory to biological tissues, nematic or magneto-electro active
elastomers are foreseen.Comment: 23 pages, 4 figure
- …