303 research outputs found
Mechanical response of a self avoiding membrane: fold collisions and the birth of conical singularities
An elastic membrane that is forced to reside in a container smaller than its
natural size will deform and, upon further volume reduction, eventually
crumple. The crumpled state is characterized by the localization of energy in a
complex network of highly deformed crescent-like regions joined by line ridges.
Previous studies have focused on the onset of the crumpled state by analyzing
the mechanical response and stability of a conical dislocation, while others
have simulated the highly packed regime neglecting the importance of the
connectivity of the membrane. Here we show, through a combination of
experiments, numerical simulations, and analytic approach, that the emergence
of new regions of high stretching is a generic outcome when a self avoiding
membrane is subject to a severe geometrical constraint. We demonstrate that, at
moderate packing fraction, interlayer interactions produce a response
equivalent to the one of a thicker membrane that has the shape of the deformed
one. Evidence is found that friction plays a key role stabilizing the folded
structures.Comment: 10 page
Dynamic Simulations of Elastic Rods for Medical Applications
This study deals with a detailed development of a computational model based on the Cosserat rod theory to describe the motion of elastic filaments such as threads and hair. The need for a simulation software for the act of suturing has motivated this study.
The dynamic equations governing the motion of elastic rods have been solved using a finite difference scheme. The scheme is central difference in space and forward difference in time and is conditionally stable. The simulations are carried out for a cantilever beam for various force and moment inputs at its free end. The results have been validated using known analytical results. The scheme has proven to be fast enough to be used in real-time simulations
Multilayered visuo-haptic hair simulation
Over the last fifteen years, research on hair simulation has made great advances in the domains of modeling, animation and rendering, and is now moving towards more innovative interaction modalities. The combination of visual and haptic interaction within a virtual hairstyling simulation framework represents an important concept evolving in this direction. Our visuo-haptic hair interaction framework consists of two layers which handle the response to the user's interaction at a local level (around the contact area), and at a global level (on the full hairstyle). Two distinct simulation models compute individual and collective hair behavior. Our multilayered approach can be used to efficiently address the specific requirements of haptics and vision. Haptic interaction with both models has been tested with virtual hairstyling tool
A Generative Model of People in Clothing
We present the first image-based generative model of people in clothing for
the full body. We sidestep the commonly used complex graphics rendering
pipeline and the need for high-quality 3D scans of dressed people. Instead, we
learn generative models from a large image database. The main challenge is to
cope with the high variance in human pose, shape and appearance. For this
reason, pure image-based approaches have not been considered so far. We show
that this challenge can be overcome by splitting the generating process in two
parts. First, we learn to generate a semantic segmentation of the body and
clothing. Second, we learn a conditional model on the resulting segments that
creates realistic images. The full model is differentiable and can be
conditioned on pose, shape or color. The result are samples of people in
different clothing items and styles. The proposed model can generate entirely
new people with realistic clothing. In several experiments we present
encouraging results that suggest an entirely data-driven approach to people
generation is possible
An inextensible model for the robotic manipulation of textiles
We introduce a new isometric strain model for the study of the dynamics of cloth garments in a moderate stress environment, such as robotic manipulation in the neighborhood of humans. This model treats textiles as surfaces that are inextensible, admitting only isometric motions. Inextensibility is derived in a continuous setting, prior to any discretization, which gives consistency with respect to remeshing and prevents the problem of locking even with coarse meshes. The simulations of robotic manipulation using the model are compared to the actual manipulation in the real world, finding that the difference between the simulated and the real position of each point in the garment is lower than 1cm in average even when a coarse mesh is used. Aerodynamic contributions to motion are incorporated to the model through the virtual uncoupling of the inertial and gravitational mass of the garment. This approach results in an accurate, when compared to the recorded dynamics of real textiles, description of cloth motion incorporating aerodynamic effects by using only two parameters.Peer ReviewedPostprint (published version
The sedimentation of flexible filaments
The dynamics of a flexible filament sedimenting in a viscous fluid are
explored analytically and numerically. Compared to the well-studied case of
sedimenting rigid rods, the introduction of filament compliance is shown to
cause a significant alteration in the long-time sedimentation orientation and
filament geometry. A model is developed by balancing viscous, elastic, and
gravitational forces in a slender-body theory for zero-Reynolds-number flows,
and the filament dynamics are characterized by a dimensionless
elasto-gravitation number. Filaments of both non-uniform and uniform
cross-sectional thickness are considered. In the weakly flexible regime, a
multiple-scale asymptotic expansion is used to obtain expressions for filament
translations, rotations, and shapes. These are shown to match excellently with
full numerical simulations. Furthermore, we show that trajectories of
sedimenting flexible filaments, unlike their rigid counterparts, are restricted
to a cloud whose envelope is determined by the elasto-gravitation number. In
the highly flexible regime we show that a filament sedimenting along its long
axis is susceptible to a buckling instability. A linear stability analysis
provides a dispersion relation, illustrating clearly the competing effects of
the compressive stress and the restoring elastic force in the buckling process.
The instability travels as a wave along the filament opposite the direction of
gravity as it grows and the predicted growth rates are shown to compare
favorably with numerical simulations. The linear eigenmodes of the governing
equation are also studied, which agree well with the finite-amplitude buckled
shapes arising in simulations
Formulation of a 4-DoF torsion/bending element for the formfinding of elastic gridshells
International audienceThe paper presents a completely novel approach to model elastic gridshells with a 4-DoF element based on recent advances in the field of hair modelling [1]. This element, based on Kirchhoff's beam theory, can account for both bending and torsion behaviours. The reduction from 6 to 4 degrees of freedom is achieved with an appropriate curve framing introduce by R. Bishop [2]. The resulting model is fast and efficient. Its accuracy has been validated on test cases. It opens new outlooks for the design of elastic gridshells
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