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ELAN - 2024
ELAN - 2024

2024Activity reportProject-TeamELAN

RNSR: 201722615M
  • Research center Inria Centre at Université Grenoble Alpes
  • modELing the Appearance of Nonlinear phenomena
  • In collaboration with:Laboratoire Jean Kuntzmann (LJK)
  • Domain:Applied Mathematics, Computation and Simulation
  • Theme:Numerical schemes and simulations

Keywords

Computer Science and Digital Science

  • A2.5. Software engineering
  • A5.5.4. Animation
  • A6.1.1. Continuous Modeling (PDE, ODE)
  • A6.1.4. Multiscale modeling
  • A6.1.5. Multiphysics modeling
  • A6.2.1. Numerical analysis of PDE and ODE
  • A6.2.5. Numerical Linear Algebra
  • A6.2.6. Optimization
  • A6.2.7. High performance computing
  • A6.2.8. Computational geometry and meshes
  • A6.3.1. Inverse problems
  • A6.5. Mathematical modeling for physical sciences
  • A6.5.1. Solid mechanics
  • A6.5.2. Fluid mechanics
  • A6.5.3. Transport

Other Research Topics and Application Domains

  • B1.1.2. Molecular and cellular biology
  • B3.3.1. Earth and subsoil
  • B5.5. Materials
  • B9.2.2. Cinema, Television
  • B9.5.3. Physics
  • B9.5.5. Mechanics

1 Team members, visitors, external collaborators

Research Scientists

  • Florence Descoubes [Team leader, INRIA, Senior Researcher]
  • Thibaut Metivet [INRIA, Researcher]
  • Victor Romero Gramegna [INRIA, ISFP]

PhD Students

  • Emile Hohnadel [ENS DE LYON, until Aug 2024]
  • Jean Jouve [LJK, from Sep 2024 until Oct 2024]
  • Jean Jouve [ENS RENNES, until Aug 2024]
  • Alice Teixeira Da Silva [INRIA, until Jun 2024]

Technical Staff

  • Octave Crespel [ENSIMAG, Engineer, until Sep 2024]
  • Arun Kumar [INRIA, Engineer, from Sep 2024]

Interns and Apprentices

  • Bastien Brogliato–Martin [UGA, Intern, from May 2024 until Jun 2024]
  • Naomi Bronstein [INRIA, Intern, from Jun 2024 until Jul 2024]

Administrative Assistant

  • Julia Di Toro [INRIA]

2 Overall objectives

Elan is a modelling research team of Inria and Laboratoire Jean Kuntzmann (UMR 5224), with an original positioning across Computer Graphics and Computational Mechanics. The team is focussed on the design of predictive, robust, efficient, and controllable numerical models for capturing the shape and motion of visually rich mechanical phenomena, such as the buckling of an elastic ribbon, the flowing of sand, or the entangling of large fiber assemblies. Target applications encompass the digital entertainment industry (e.g., feature film animation, special effects), as well as virtual prototyping for the mechanical engineering industry (e.g., direct and inverse design of textiles and metamaterials, sport performance optimisation, cosmetology); though very different, these two application fields require predictive and scalable models for capturing complex mechanical phenomena at the macroscopic scale. An orthogonal objective is the improvement of our understanding of natural physical and biological processes involving slender structures and frictional contact, through active collaborations with soft matter physicists. To achieve its goals, the team strives to master as finely as possible the entire modeling pipeline, involving a pluridisciplinary combination of scientific skills across Mechanics and Physics, Applied Mathematics, and Computer Science.

3 Research program

Thanks to an original and transverse positioning across Computer Graphics and Computational Mechanics, complemented by tight connections with physicists, our goal is to tackle some challenging numerical modelling issues related to complex macroscopic phenomena characterised by a nonlinear mechanical behaviour and rich geometrical deformations. One major ambition of the Elan team is to favour interactions between all the relevant communities, with two objectives: 1/ significantly improve our understanding and modelling capabilities of complex mechanical phenomena, in tight connection with physicists, and 2/ better anticipate practical solutions for the wide diversity of exciting applications to come in the near future. We propose in particular to focus on three research axes, detailed below.

3.1 Discrete modelling of slender elastic structures

For the last 15 years, we have investigated new discrete models for solving the Kirchhoff dynamic equations for thin elastic rods  23, 25, 28. All our models share a curvature-based spatial discretisation, allowing them to capture inextensibility of the rod intrinsically, without the need for adding any kinematic constraint. Moreover, elastic forces boil down to linear terms in the dynamic equations, making them well-suited for implicit integration. Interestingly, our discretisation methodology can be interpreted from two different points-of-views. From the finite-elements point-of-view, our strain-based discrete schemes can be seen as discontinuous Galerkin methods of zero and first orders. From the multibody system dynamics point of view, our discrete models can be interpreted as deformable Lagrangian systems in finite dimension, for which a dedicated community has started to grow recently  49. We note that adopting the multibody system dynamics point of view helped us formulate a linear-time integration scheme  24, which had only be investigated in the case of multibody rigid bodies dynamics so far.

High-order spatial discretisation schemes for rods, ribbons and shells

Our goal is to investigate similar high-order modelling strategies for surfaces, in particular for the case of inextensible ribbons and shells. Elastic ribbons have been scarcely studied in the past, but they are nowadays drawing more and more the attention from physicists  38, 47. Their numerical modelling remains an open challenge. In contrast to ribbons, a huge litterature exists for shells, both from a theoretical and numerical viewpoints (see, e.g., 42, 29). However, no real consensus has been obtained so far about a unified nonlinear shell theory able to support large displacements. In  26 we have started building an inextensible shell patch by taking as degrees of freedom the curvatures of its mid-surface, expressed in the local frame. As in the super-helix model, we show that when taking curvatures uniform over the element, each term of the equations of motion may be computed in closed-form; besides, the geometry of the element corresponds to a cylinder patch at each time step. Compared to the 1D (rod) case however, some difficulties arise in the 2D (plate/shell) case, where compatibility conditions are to be treated carefully. In 2 we have proposed a new, curvature-based discretisation for a developable ribbon (i.e., a narrow plate), which we plan to extend for building an inextensible plate model.

Numerical continuation of rod equilibria in the presence of unilateral constraints

In Alejandro Blumentals' PhD thesis  27, we have adopted an optimal control point of view on the static problem of thin elastic rods, and we have shown that direct discretisation methods 1 are particularly well-suited for dealing with scenarios involving both bilateral and unilateral constraints (such as contact). We would like to investigate how our formulations extend to continuation problems, where the goal is to follow a certain branch of equilibria when the rod is subject to some varying constraints (such as one fixed end being applied a constant rotation). To the best of our knowledge, classical continuation methods used for rods  39 are not able to deal with non-persistent or sliding contact.

3.2 Discrete and continuous modelling of frictional contact

Most popular approaches in Computer Graphics and Mechanical Engineering consist in assuming that the objects in contact are locally compliant, allowing them to slightly penetrate each other. This is the principle of penalty-based methods (or molecular dynamics), which consists in adding mutual repulsive forces of the form kf(δ), where δ is the penetration depth detected at current time step  30, 46. Though simple to implement and computationally efficient, the penalty-based method often fails to prevent excessive penetration of the contacting objects, which may prove fatal in the case of thin objects as those may just end up traversing each other. One solution might be to set the stiffness factor k to a large enough value, however this causes the introduction of parasitical high frequencies and calls for very small integration steps  22. Penalty-based approaches are thus generally not satisfying for ensuring robust contact handling.

In the same vein, the friction law between solid objects, or within a yield-stress fluid (used to model foam, sand, or cement, which, unlike water, cannot flow beyond a certain threshold), is commonly modeled using a regularised friction law (sometimes even with simple viscous forces), for the sake of simplicity and numerical tractability (see e.g., 48, 41). Such a model cannot capture the threshold effect that characterises friction between contacting solids or within a yield-stress fluid. The nonsmooth transition between sticking and sliding is however responsible for significant visual features, such as the complex patterns resting on the outer surface of hair, the stable formation of sand piles, or typical stick-slip instabilities occurring during motion.

The search for a realistic, robust and stable frictional contact method encouraged us to depart from those, and instead to focus on rigid contact models coupled to the exact nonsmooth Coulomb law for friction (and respectively, to the exact nonsmooth Drucker-Prager law in the case of a fluid), which better integrate the effects of frictional contact at the macroscopic scale. This motivation was the sense of the hiring of F. Bertails-Descoubes in 2007 in the Inria/LJK Bipop team, specialised in nonsmooth mechanics and related convex optimisation methods. In the line of F. Bertails-Descoubes's work performed in the Bipop team, the Elan team keeps on including some active research on the finding of robust frictional contact algorithms specialised for slender deformable structures.

Optimised algorithms for large nodal systems in frictional contact

In the fibre assembly case, the resulting mass matrix M is block-diagonal, so that the Delassus operator can be computed in an efficient way by leveraging sparse-block computations  32. This justifies solving the reduced discrete frictional contact problem where primary unknowns are forces, as usually advocated in nonsmooth mechanics  44. For cloth however, where primal variables (nodal velocities of the cloth mesh) are all interconnected via elasticity through implicit forces, the method developed above is computationally inefficient. Indeed, the matrix M (only block-sparse, but not block-diagonal) is costly to invert for large systems and its inverse is dense. Recently, we have leveraged the fact that generalised velocities of the system are 3D velocities, which simplifies the discrete contact problem when contacts occur at the nodes. Combined with a multiresolution strategy, we have devised an algorithm able to capture exact Coulomb friction constraints at contact, while retaining computational efficiency  45. This work also supports cloth self-contact and cloth multilayering. How to enrich the interaction model with, e.g., cohesion, remains an open question. The experimental validation of our frictional contact model is also one of our goals in the medium run.

Continuum modelling of granular and fibrous media

Though we have recently made progress on the continuum formulation and solving of granular materials in Gilles Daviet's PhD thesis  35, 33, 31, we are still far from a continuum description of a macroscopic dry fibrous medium such as hair. One key ingredient that we have not been considering in our previous models is the influence of air inside divided materials. Typically, air plays a considerable role in hair motion. To advance in that direction, we have started to look at a diphasic fluid representation of granular matter, where a Newtonian fluid and the solid phase are fully coupled, while the nonsmooth Drucker-Prager rheology for the solid phase is enforced implicitly  34. This first approach could be a starting point for modelling immersed granulars in a liquid, or ash clouds, for instance.

A long path then remains to be achieved, if one wants to take into account long fibres instead of isotropic grains in the solid phase. How to couple the fibre elasticity with our current formulation remains a challenging problem.

3.3 Inverse design of slender elastic structures [ERC Gem ]

With the considerable advance of automatic image-based capture in Computer Vision and Computer Graphics these latest years, it becomes now affordable to acquire quickly and precisely the full 3D geometry of many mechanical objects featuring intricate shapes. Yet, while more and more geometrical data get collected and shared among the communities, there is currently very little study about how to infer the underlying mechanical properties of the captured objects merely from their geometrical configurations.

An important challenge consists in developing a non-invasive method for inferring the mechanical properties of complex objects from a minimal set of geometrical poses, in order to predict their dynamics. In contrast to classical inverse reconstruction methods, our claim is that 1/ the mere geometrical shape of physical objects reveals a lot about their underlying mechanical properties and 2/ this property can be fully leveraged for a wide range of objects featuring rich geometrical configurations, such as slender structures subject to contact and friction (e.g., folded cloth or twined filaments).

In addition to significant advances in fast image-based measurement of diverse mechanical materials stemming from physics, biology, or manufacturing, this research is expected in the long run to ease considerably the design of physically realistic virtual worlds, as well as to boost the creation of dynamic human doubles.

To achieve this goal, we shall develop an original inverse modelling strategy based upon the following research topics:

Design of well-suited discrete models for slender structures

We believe that the quality of the upstream, reference physics-based model is essential to the effective connection between geometry and mechanics. Typically, such a model should properly account for the nonlinearities due to large displacements of the structures, as well as to the nonsmooth effects typical of contact and friction.

It should also be parametrised and discretised in such a way that inversion gets simplified mathematically, possibly avoiding the huge cost of large and nonconvex optimisation. In that sense, unlike concurrent methods which impose inverse methods to be compatible with a generic physics-based model, we instead advocate the design of specific physics-based models which are tailored for the inversion process.

More precisely, from our experience on fibre modelling, we believe that reduced Lagrangian models, based on a minimal set of coordinates and physical parameters (as opposed to maximal coordinates models such as mass-springs), are particularly well-suited for inversion and physical interpretation of geometrical data  37, 36. Furthermore, choosing a high-order coordinate system (e.g., curvatures instead of angles) allows for a precise handling of curved boundaries and contact geometry, as well as the simplification of constitutive laws (which are transformed into a linear equation in the case of rods). We are currently investigating high-order discretisation schemes for elastic ribbons and developable shells 26, 2.

Static inversion of physical objects from geometrical poses

We believe that pure static inversion may by itself reveal many insights regarding a range of parameters such as the undeformed configuration of the object, some material parameters or contact forces.

The typical settings that we consider is composed of, on the one hand, a reference mechanical model of the object of interest, and on the other hand a single or a series of complete geometrical poses corresponding each to a static equilibrium. The core challenge consists in analyzing theoretically and practically the amount of information that can be gained from one or several geometrical poses, and to understand how the fundamental under-determinacy of the inverse problem can be reduced, for each unknown quantity (parameter or force) at play. Both the equilibrium condition and the stability criterion of the equilibrium are leveraged towards this goal. On the theoretical side, we have recently shown that a given 3D curve always matches the centerline of an isotropic suspended Kirchhoff rod at equilibrium under gravity, and that the natural configuration of the rod is unique once material parameters (mass, Young modulus) are fixed 1. On the practical side, we have recently devised a robust algorithm to find a valid natural configuration for a discrete shell to match a given surface under gravity and frictional contact forces 4. Unlike rods however, shells can have multiple inverse (natural) configurations. Choosing among the multiple solutions based on some selection criteria is an open challenge. Another open issue, in all cases, is the theoretical characterisation of material parameters allowing the equilibrium to be stable.

Dynamic inversion of physical objects from geometrical poses

To refine the solution subspaces searched for in the static case and estimate dynamic parameters (e.g., some damping coefficients), a dynamic inversion process accounting for the motion of the object of interest is necessary.

In contrast to the static case where we can afford to rely on exact geometrical poses, our analysis in the dynamic case will have to take into account the imperfect quality of input data with possible missing parts or outliers. One interesting challenge will be to combine our high-order discretised physics-based model together with the acquisition process in order to refine both the parameter estimation and the geometrical acquisition. Our pluridisciplinary work 6 gives encouraging results regarding the ability to recover material parameters and friction coefficient from merely visual observations of elastic bodies in motion.

Experimental validation with respect to real data

The goal will be to confront the theories developed above to real experiments. Compared to the statics, the dynamic case will be particularly involving as it will be highly dependent on the quality of input data as well as the accuracy of the motion predicted by our physics-based simulators. Such experiments will not only serve to refine our direct and inverse models, but will also be leveraged to improve the 3D geometrical acquisition of moving objects. Besides, once validation will be performed, we shall work on the setting up of new non-invasive measurement protocols to acquire physical parameters of slender structures from a minimal amount of geometrical configurations. Our recent publication on validation benchmarks 7 represents a first important milestone towards this research direction.

4 Application domains

4.1 Mechanical Engineering

Many physicists and mathematicians have strived for centuries to understand the principles governing those complex mechanical phenomena, providing a number of continuous models for slender structures, granular matter, and frictional contact. In the XXth century, industrial applications such as process automatization and new ways of transportation have boosted the fields of Mechanical Engineering and Computer-Aided Design, where material strength, reliability of mechanisms, and safety, standed for the main priorities. Instead, large displacements of structures, buckling, tearing, or entanglement, and even dynamics, were long considered as undesirable behaviors, thus restraining the search for corresponding numerical models.

Only recently, the engineering industry has shown some new and growing interest into the modeling of dynamic phenomena prone to large displacements, contact and friction. For instance, the cosmetology industry is more and more interested in understanding the nonlinear deformation of hair and skin, with the help of simulation. Likewise, auto and aircraft manufacturers are facing new challenges involving buckling or entanglement of thin structures such as carbon or optical fibers; they clearly lack predictive, robust and efficient numerical tools for simulating and optimizing their new manufacturing process, which share many common features with the large-scale simulation scenarii traditionally studied in Computer Graphics applications.

4.2 Computer Graphics

In contrast, Computer Graphics, which has emerged in the 60's with the advent of modern computers, was from the very beginning eager to capture such peculiar phenomena, with the sole aim to produce spectacular images and create astonishing stories. At the origin, Computer Graphics thus drastically departed from other scientific fields. Everyday-life phenomena such as cloth buckling, paper tearing, or hair fluttering in the wind, mostly ignored by other scientists at that time, became actual topics of interest, involving a large set of new research directions to be explored, both in terms of modelling and simulation. Nowadays, although the image production still remains the core activity of the Computer Graphics community, more and more research studies are directed through the virtual and real prototyping of mechanical systems, notably driven by a myriad of new applications in the virtual try on industry (e.g., hairstyling and garment fitting). Furthermore, the advent of additive fabrication is currently boosting research in the free design of new mechanisms or systems for various applications, from architecture design and fabrication of metamaterials to the creation of new locomotion modes in robotics. Some obvious common interests and approaches are thus emerging between Computer Graphics and Mechanical Engineering, yet the two communities remain desperately compartmentalized.

4.3 Soft Matter Physics

From the physics-based viewpoint, since a few decades a new generation of physicists became interested again in the understanding of such visually fascinating phenomena, and started investigating the tight links between geometry and elasticity 2. Common objects such as folded or torn paper, twined plants, coiled honey threads, or human hair have thus regained some popularity among the community in Nonlinear Physics 3. In consequence, phenomena of interest have become remarkably close to those of Computer Graphics, since scientists in both places share the common goal to model complex and integrated mechanical phenomena at the macroscopic scale. Of course, the goals and employed methodologies differ substantially from one community to the other, but showcase some evident complementarity: while computer scientists are eager to learn and understand new physical models, physicists get more and more interested in the numerical tools, in which they perceive not only a means to confirm predictions afterwards, but also a support for testing new hypothesis and exploring scenarios that would be too cumbersome or even impossible to investigate experimentally. Besides, numerical exploration starts becoming a valuable tool for getting insights into the search for analytic solutions, thus fully participating to the modeling stage and physical understanding. However, physicists may be limited to a blind usage of numerical black boxes, which may furthermore not be dedicated to their specific needs. According to us, promoting a science of modeling in numerical physics would thus be a promising and rich avenue for the two research fields. Unfortunately, very scarce cooperation currently exists between the two communities, and large networks of collaboration still need to be set up.

5 Social and environmental responsibility

5.1 Footprint of research activities

The Elan team is environment-sensitive. Since its creation in 2017, 100% of its research staff moves daily from home to the lab using soft transportation means (biking, public transportation). Intercontinental missions are limited while train is the preferred mode of transportation in Europe.

5.2 Impact of research results

A large part of the research conducted in the team is of fundamental level. Direct applications lie in numerical arts, cloth design, sports, and environmental studies, all of these being of limited negative impact for the environment. Collaborations with industry leading specially harmful activities to the environment are avoided.

6 Highlights of the year

6.1 International conference

Thibaut Metivet has organized, in collaboration with Philippe Peyla (LIPhy, UGA), Aurélie Dupont (LIPhy, CNRS) and Carine DOUARCHE (FAST, Univ. Paris-Saclay), the international conference “Collective motion of animals and robots”. Hosted at the IESC (Institut d'Etudes Scientifiques de Cargèse, Corsica), from 27th to 31st, May 2024, this conference focussed on the collective behaviour within groups of agents, whether they be animals, robots or algorithmic variables. Covering a broad range of topics, from active matter, to insect biology, crowd dynamics or decentralised robotics, the event attracted a very international and pluridisciplinary audience, highlighting strong thematic convergences in these usually very distinct communities. The hybrid programme, featuring lectures, plenary sessions, short presentations and posters, fostered constructive and meaningful interactions among all the participants, from the young to expert researchers.

6.2 Keynote

Florence Bertails-Descoubes was a keynote speaker at the 2024 Colloque National en Calcul des Structures (CSMA 2024).

6.3 Defenses

Jean Jouve defended his PhD thesis on november 21st in front of a multidiciplinary jury composed by researchers from Computer Graphics, Physics and Mechanics 17. He was awarded the PhD degree for his work in the numerical modelling of feathers, which was presented and published in Siggraph 2024 11. The corresponding developed software is now part of our team's software toolbox 7.1.8.

7 New software, platforms, open data

7.1 New software

7.1.1 Feel++

  • Keywords:
    High order finite elements, Discontinuous Galerkin, High-Performance Computing
  • Functional Description:
    Feel++ is a high-performance C++ library for the resolution of general variational formulations, including continuous and discontinuous Galerkin methods, finite element or spectral element methods, reduced basis formulations, etc. It features a high-level domain specific embedded language (DSEL) for Galerkin methods, space dimension-agnostic computation kernels and seamless and automatic parallelism. It also includes applicative toolboxes to solve physics problems in fluid mechanics, solid mechanics, thermal conduction, and the corresponding multi-physics coupling.
  • Release Contributions:
    - Support of distance-based contact forces between immersed bodies - BVH implementation for contact pruning - Various improvements in expression support
  • URL:
    https://­docs.­feelpp.­org/­home/­index.­html
  • Contact:
    Thibaut Metivet
  • Partners:
    Université de Strasbourg, UGA, Inria

7.1.2 Sand6

  • Keywords:
    Granular matter, Frictional contact, Drücker-Prager rheology
  • Scientific Description:
    sand6 is a software to simulate the dynamics of granular matter using a continuum approach accounting for non-smooth flow rules. It is based on the nonsmooth Material Point Method described in [DBD16a] and is currently maintained and developed in the team for various aspects related to the modeling of frictional contact in continuous systems.
  • Functional Description:
    Simulation of granular matter as a continuum media
  • Release Contributions:
    This software contains a C++ implementation of the algorithms described in the 2016 ACM SIGGRAPH paper entitled "A Semi-Implicit Material Point Method for the Continuum Simulation of Granular Materials" by Gilles Daviet and Florence Bertails-Descoubes. It is currently maintained and further developed by Thibaut Métivet. It was notably updated and physically validated in the context of transient granular collapses in the paper [Rousseau G, Métivet T, Rousseau H, Daviet G, Bertails-Descoubes F. Revisiting the role of friction coefficients in granular collapses: confrontation of 3-D non-smooth simulations with experiments. Journal of Fluid Mechanics. 2023 Nov,975:A14.].
  • URL:
    https://­gitlab.­inria.­fr/­elan-public-code/­sand6
  • Publications:
    hal-01310189, hal-03845323, hal-04884362, hal-04884407
  • Contact:
    Thibaut Metivet
  • Participants:
    Thibaut Metivet, Florence Bertails Descoubes, Gilles Daviet

7.1.3 MERCI

  • Name:
    Energy Minimisation of Curvature-based numerical models for Inextensible Ribbons
  • Keywords:
    Thin elastic rod, Thin elastic ribbon, Physical simulation
  • Scientific Description:

    MERCI is a C++/lua software for computing the statics of thin elastic ribbons discretised with curvature-based elements. It is based on the super-ribbon model described in [Charrondière et al. 2020, Charrondière et al. 2024], and relies on the free [IPOPT](https://coin-or.github.io/Ipopt/) optimisation software (coinor project) for the static solver. The ribbon can be clamped at one or both ends, and even closed. Contact is treated by contraints with planes. Once the setup is defined, the equilibrium of the ribbon under the specified boundary conditions, external forces, and constraints, is computed. MERCI can be used as a C++ library, or via its lua interface.

    Reference code of the PhD thesis:

    Raphaël Charrondière, "Modélisation numérique de rubans par éléments en courbures", 2021, Université Grenoble Alpes, https://hal.inria.fr/tel-03545017v2

    and of the following papers:

    R. Charrondière, F. Bertails-Descoubes, S. Neukirch, V. Romero, "Numerical modeling of inextensible elastic ribbons with curvature-based elements", Computer Methods in Applied Mechanics and Engineering 364, June 2020, p. 1–32, [doi:10.1016/j.cma.2020.112922], [hal-02515877].

    R. Charrondière, S. Neukirch, F. Bertails-Descoubes, "MERCI: Mixed curvature-based elements for computing equilibria of thin elastic ribbons", to appear in 2024.

  • Functional Description:

    MERCI is a C++/lua software for computing the statics of thin elastic ribbons discretised with curvature-based elements. It is based on the super-ribbon model described in [Charrondière et al. 2020, Charrondière et al. 2024], and relies on the free [IPOPT](https://coin-or.github.io/Ipopt/) optimisation software (coinor project) for the static solver. The ribbon can be clamped at one or both ends, and even closed. Contact is treated by contraints with planes. Once the setup is defined, the equilibrium of the ribbon under the specified boundary conditions, external forces, and constraints, is computed. MERCI can be used as a C++ library, or via its lua interface.

    Reference code of the PhD thesis:

    Raphaël Charrondière, "Modélisation numérique de rubans par éléments en courbures", 2021, Université Grenoble Alpes, https://hal.inria.fr/tel-03545017v2

    and of the following papers:

    R. Charrondière, F. Bertails-Descoubes, S. Neukirch, V. Romero, "Numerical modeling of inextensible elastic ribbons with curvature-based elements", Computer Methods in Applied Mechanics and Engineering 364, June 2020, p. 1–32, [doi:10.1016/j.cma.2020.112922], [hal-02515877].

    R. Charrondière, S. Neukirch, F. Bertails-Descoubes, "MERCI: Mixed curvature-based elements for computing equilibria of thin elastic ribbons", Transactions on Graphics, 2024.

  • URL:
    https://­gitlab.­inria.­fr/­elan-public-code/­merci
  • Publications:
    hal-02515877, hal-04583083, hal-04601301, tel-03545017
  • Contact:
    Florence Bertails Descoubes
  • Partners:
    Sorbonne Université, UGA

7.1.4 ElanFab

  • Keywords:
    Experimental mechanics, Experimental design, Thin elastic ribbon, Thin elastic rod, Thin elastic shell, Frictional contact
  • Functional Description:

    Experimental platform of the ELAN team.

    The aim of this platform is to experimentally explore the mechanics and geometry of highly deformable elastic objects of low dimensions (rods, fibers, plates, shells).

    The platform allow us to fabricate with controlled materials and geometries elastic objects. By means of state of the art manufacturing techniques we are able to make curved elastic objects, with a controlled target geometry. For the moment we use elastomeric materials to remain in the elastic regime, however we are interested in exploring new materials to include viscous and plastic effects.

    Our platform has a modular mechanical testing device that allow load and tensile testing in multiple configurations for a wide range of force magnitudes, from 1e-3 to 100 Newtons. In this setup we have tested highly compliant, as well as, very stiff materials, for example we study the tensile response of feathers and elastic knotted rods.

    The platform is constantly undergoing new improvements to allow us to obtain geometrical information by means of a combination of image analysis and computer vision techniques. Multiple views are obtained by using multiple cameras and mirrors or by using one single camera that moves in a highly controlled manner. Furthermore we are implementing the use of a semi fast camera to study dynamic phenomena of complex elastic objects assemblies. We are also implementing structured light into our setup to improve the accuracy of our measurements.

  • Contact:
    Victor Romero Gramegna

7.1.5 so-bogus

  • Keywords:
    Frictional contact, Constraint solving
  • Scientific Description:
    The so-bogus library, based on the bogus library, implements several methods (analytical solver, Gauss-Seidel solver, root-finding solver, etc.) for solving Signorini-Coulomb problems in 2D and 3D. It serves as the reference code for the paper "A Hybrid Iterative Solver for Robustly Capturing Coulomb Friction in Hair Dynamics", Daviet et al. 2011, ACM Transactions on Graphics (SIGGRAPH Asia 2011).
  • Functional Description:

    A fast and robust solver for capturing frictional contact between many Lagrangian systems with exact Coulomb friction. Reference code for the paper "A Hybrid Iterative Solver for Robustly Capturing Coulomb Friction in Hair Dynamics", Daviet et al. 2011, ACM Transactions on Graphics (SIGGRAPH Asia 2011).

    The so-bogus software is currently maintained and further developed by Thibaut Métivet and Florence Bertails-Descoubes.

  • URL:
    https://­gitlab.­inria.­fr/­elan-public-code/­so-bogus
  • Publication:
    hal-00647497
  • Contact:
    Thibaut Metivet
  • Participants:
    Florence Descoubes, Thibaut Metivet, Gilles Daviet

7.1.6 meche2D

  • Name:
    meche2D
  • Keywords:
    Physical simulation, Thin elastic rod, Frictional contact
  • Scientific Description:
    Meche2D is a library for coupling 2D elastic fibers with frictional contact. It relies on the supercircle code for fibers, and on so-bogus for frictional contact.
  • Functional Description:
    Meche2D is a library for coupling 2D elastic fibers with frictional contact. It relies on the supercircle code for fibers, and on so-bogus for frictional contact. New since 2020-2023: fibers can be clamped or unclamped, and contact detection is exact between two circular arcs.
  • Publications:
    hal-03996830, hal-03962464, hal-04225083, hal-04388542, hal-03962464, hal-04265998
  • Contact:
    Florence Bertails Descoubes
  • Participants:
    Florence Bertails Descoubes, Emile Hohnadel, Thibaut Metivet

7.1.7 meche3D

  • Name:
    meche3D
  • Keywords:
    Physical simulation, Frictional contact, Thin elastic rod
  • Functional Description:
    Meche3D is a library for coupling 3D elastic fibers with frictional contact. It relies on the supercircle code for fibers, and on so-bogus for frictional contact. New since 2024: contact detection is exact between two helical arcs, thanks to the inclusion of the module curly-splits designed by the team.
  • News of the Year:
    News in 2024: contact detection is exact between two helical arcs, thanks to the inclusion of the module curly-splits designed by the team.
  • Publication:
    hal-04364565
  • Contact:
    Florence Descoubes
  • Participants:
    Florence Descoubes, Emile Hohnadel, Octave Crespel, Thibaut Metivet

7.1.8 feather-shell

  • Name:
    Arcsim implementation for Feathers
  • Keywords:
    3D animation, Physical simulation, Cloth dynamics, Structural Biology
  • Functional Description:
    Feathers are complex structured fiber base objects, thus their mechanical response is complex and difficult to simulate given their strong anisotropy. Feather-Shell is an implementation of ArcSim that permits the homogenized simulation of feathers as a mebranes.
  • URL:
    https://­gitlab.­inria.­fr/­elan-public-code/­feather-shell
  • Publications:
    hal-04633434, hal-04610994, hal-04083228
  • Contact:
    Victor Romero Gramegna
  • Participants:
    Jean Jouve, Victor Romero Gramegna, Florence Descoubes

7.1.9 curly-splits

7.1.10 grenouille

  • Name:
    grenouille
  • Keywords:
    3D visualisation, Thin elastic rod
  • Scientific Description:
    3D Visualisation and manipulation of slender geometries made of piecewise helical arcs
  • Functional Description:
    3D Visualisation and manipulation of slender geometries made of piecewise helical arcs
  • Contact:
    Octave Crespel
  • Participant:
    Octave Crespel

8 New results

8.1 High-order contact detection between fibres

Participants: Octave Crespel, Émile Hohnadel, Thibaut Métivet, Florence Bertails-Descoubes.

In this work we analyse the contact forces yielded by fibre models coupled to a segment-based contact detection algorithm. We note the occurrence of spurious jumps which, to the best of our knowledge, were never reported before. We demonstrate that these artifacts are actually directly linked to the low-order contact detection being used between the fibre and the obstacles, and that they worsen as curvature at contact increases. Low-order detection, based on segment proxys, is classically used due to its simplicity of treatment, even for fibre models possessing a higher-order geometry like super-helices. We show that spurious artifacts occur whatever the fibre model and contact response solver used, as soon as a segment-segment detection scheme is employed. To remove such numerical artifacts in the force profile, which can accumulate to yield large force errors, we introduce an efficient high-order detection algorithm, relying on an efficient adaptive pruning strategy.

This work has been published in the ACM Transactions on Graphics journal (ACM SIGGRAPH 2024) 10, and presented at the corresponding ACM SIGGRAPH 2024 conference. It was also presented to the French Nonlinear Physics community at the national RNL 2024 conference 19.

8.2 Numerical modeling of a feather's vane, a highly anisotropic membrane

Participants: Jean Jouve, Victor Romero, Florence Bertails-Descoubes.

In the context of Jean Jouve's doctoral thesis, in collaboration with Rahul Narain (Indian Institute of Technology Delhi, India) and Theodore Kim (Yale University, United States), we have developed a macroscopic shell simulator capable of dealing with highly anisotropic materials, such as feathers.

Feathers have a multi-scale structure with very interesting properties. From a central stiff rod (the rachis) hundreds of small fibers (barbs) come out to form a membrane-like structure, which is held together by yet another set of smaller fibers (barbules). This intricate structure drives the elastic response of the membrane and gives feathers the capability of reversible rupture. Our interest is to produce a simulator capable of realistically portray the deformation of a feather. This simulation is challenging because the membrane has two main directions with elastic coefficients differing by 4 orders of magnitude. We have compared and validated our results with experimental data. We have published and presented our findings in a conference paper at the ACM SIGGRAPH 2024 conference 11 .

8.3 Mixed elements for a curvature-based ribbon model

Participants: Florence Bertails-Descoubes.

In collaboration with Sébastien Neukirch (Institut D'Alembert, Sorbonne Université) and our former Ph.D. student Raphaël Charrondière, we have improved our initial curvature-based numerical model for thin elastic ribbons 2 by developing a mixed strategy, where each ribbon element is treated independently, and glued to each other only at the final solving stage through well-chosen bilateral constraints.

Thanks to this mixed variational strategy, which yields a banded Hessian, our algorithm recovers the linear complexity of low-order models while preserving the quadratic convergence of curvature-based models. As a result, our approach is scalable to a large number of elements, and suitable for various boundary conditions and unilateral contact constraints, making it possible to handle challenging scenarios such as confined buckling experiments or Möbius bands with contact. Additionally, our numerical model can incorporate various ribbon energies, including the recent 20 model for quasi-developable ribbons recently introduced in Physics, which allows to transition smoothly between a rectangular Kirchhoff rod and a (developable) Sadowsky ribbon. Our numerical scheme is carefully validated against demanding experiments of the Physics literature, which demonstrates its accuracy, efficiency, robustness, and versatility.

This work has been published in the ACM Transactions on Graphics journal (ACM SIGGRAPH 2024) 9, and presented at the corresponding ACM SIGGRAPH 2024 conference. It was also presented to the French Mechanical Engineering community at the national CSMA 2024 conference 9.

8.4 Nonsmooth simulations of 3D Drucker-Prager granular flows and validation against experimental column collapses

Participants: Thibaut Métivet, Florence Bertails-Descoubes.

In collaboration with Gauthier Rousseau (TU Wien, formerly post-doc in the team), Hugo Rousseau (INRAE) and Gilles Daviet (NVIDIA, formerly Ph.D. student in the team), we have performed thorough comparisons between the predictions of our numerical solver Sand6 for granular flows 7.1.2, and collapse experiments conducted in a narrow channel (in collaboration with EPFL). We have shown that our nonsmooth simulator, which relies on a constant friction coefficient corresponding to the yield angle of a granular heap, is able to reproduce with high fidelity various experimental granular collapses over inclined erodible beds. Our results, obtained for two different granular materials and for various bed inclinations, suggest that a simple constant friction rheology choice remains reasonable for capturing a large variety of unsteady granular flows at low inertial number. Using the versatility of our numerical approach, we have further analysed the possible biases pertaining to laboratory-scale experiments, and shown that, in the case of granular collapses, accurate predictions could be performed as long as care was taken in measuring yield angle of the granular material appropriately. Our numerical simulations demonstrate the specific nature of transient granular flows, which are mainly driven by successive layered avalanches, and we have explored the role of metastability and hysteresis in the onset of flow and inner dissipation within the material. This study has been published in the Journal of Fluid Mechanics 8 along with all the research data at doi.org/10.5281/zenodo.7288829. It has been presented at several international conferences 12, 15, 16.

8.5 Hydrodynamic model for fish locomotion

Participants: Thibaut Métivet.

In collaboration with Bruno Ventéjou (co-supervised post-doc at LIPhy, UGA), Philippe Peyla (LIPhy, UGA) and Aurélie Dupont (LIPhy, CNRS), we study the respective roles of hydrodynamic and social interactions within schools of fish, in the context of the FISHSIF ANR project. As a first step toward the simulation of large assemblies of swimming fish, we have developed a simplified hydrodynamic model of a swimmer, able to account for individual fish swimming and stigmergy, in particular regarding the generation of vortices wakes, without the need to introduce deformation of the body of the fish. We have performed detailed hydrodynamic scaling analyses of the velocity of a moving immersed body, and shown that the motion of swimmers obeys a universal scaling law expressed in terms of only two dimensionless quantities describing the relative importance of inertia, viscosity and swimming forces. Using extensive numerical simulations, we have shown excellent agreement between our theoretical scaling laws and the swimming behaviour of our model fish. The validity of our scaling laws notably extend across a wide range of hydrodynamic regimes (from the Stokes to the turbulent regime), and demonstrates the ubiquitous decrease in swimming efficiency as the velocity increases. We have further compared our results to experimental data collected among many aquatic species, with very different body shapes, deformations, and swimming velocities. The overall collapse of swimmers' data onto our single master curve supports the robustness and genericity of our analysis and model. The corresponding publication is available as a preprint 18 and is currently under review.

9 Bilateral contracts and grants with industry

9.1 Bilateral contracts with industry

  • Participants: Florence Bertails-Descoubes, Emile Hohnadel.

    In March 2024, the ELAN team has started a 2-year research collaboration with L'Oréal Recherche (Paris) on the fundamental understanding of the mechanical properties of hair.

10 Partnerships and cooperations

10.1 European initiatives

10.1.1 H2020 projects

THREAD

THREAD project on cordis.europa.eu

  • Title:
    Joint Training on Numerical Modelling of Highly Flexible Structures for Industrial Applications
  • Duration:
    From October 1, 2019 to March 31, 2024
  • Partners:
    • UNIVERSITE DE LIEGE (ULIEGE), Belgium
    • ECOLE NATIONALE SUPERIEURE D'ARTS ET METIERS (ENSAM), France
    • FRIEDRICH-ALEXANDER-UNIVERSITAET ERLANGEN-NUERNBERG (FAU), Germany
    • MARTIN-LUTHER-UNIVERSITAT HALLE-WITTENBERG (MLU), Germany
    • FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV (Fraunhofer), Germany
    • SVEUCILISTE U RIJECI, GRADEVINSKI FAKULTET U RIJECI (UNIVERSITY OF RIJEKA, FACULTY OF CIVIL ENGINEERING UNIRIFCE), Croatia
    • C3M DOO, CENTER ZA RACUNALNISTVO VMEHANIKI KONTINUUMA - MODELIRANJE IN TRZENJE (C3M DOO), Slovenia
    • UNIVERSITAET INNSBRUCK (UIBK), Austria
    • CENTRALESUPELEC, France
    • NORGES TEKNISK-NATURVITENSKAPELIGE UNIVERSITET NTNU (NTNU), Norway
    • UNIVERZA V LJUBLJANI (UL), Slovenia
    • UNIVERSIDAD DE SEVILLA, Spain
  • Inria contact:
    Florence DESCOUBES
  • Coordinator:
  • Summary:

    Virtual prototyping is a cornerstone in modern product development cycles: It accelerates the design process, reduces costs and improves product performance and quality. Highly flexible slender structures like yarns, cables, hoses or ropes are essential parts of high-performance engineering systems. The complex response of such structures in real operational conditions is far beyond the capabilities of current virtual prototyping tools.

    There is a pressing need for a new generation of young scientists capable of solving fundamental problems related to slender structures and transferring results to applications. THREAD addresses the mechanical modelling, mathematical formulations and numerical methods for highly flexible slender structures. It brings mechanical engineers and mathematicians together around major challenges in industrial applications and open-source simulation software development. It establishes an innovative modelling chain starting from detailed 3D modelling and experimental work to build validated 1D nonlinear rod models, which are then brought to a system-level simulation thanks to the outstanding numerical properties of the developed algorithms. This holistic approach combines advanced concepts in experimental and theoretical structural mechanics, non-smooth dynamics, computational geometry, discretisation methods and geometric numerical integration and will enable the next generation of virtual prototyping.

    The ESRs will receive comprehensive local and network-wide training covering state-of-the-art research topics as well as valuable transferable skills. They will benefit from close cooperation with twelve industrial partner organisations implementing a comprehensive programme of research secondments and contributing their experience. As a main objective of THREAD, interdisciplinary and inter-sectoral training boosts the career development of young researchers and supports them to solve future challenges.

10.2 National initiatives

FISHSIF ANR Project

Participants: Thibaut Métivet.

  • Title:
    FISHSIF: Fish In Silico with Hydrodynamics and Social Forces
  • Duration:
    01/10/2021 - 31/12/2025
  • Summary:
    The FISHSIF project has received a four-year funding from the ANR (Agence Nationale pour la Recherche). The goal of this project is to introduce dynamical cognition models within full hydrodynamic simulations in order to understand the role played by social or flow interactions in the organisation and behaviour of schools of fish. The project will be led in a collaboration between the ELAN team, the Laboratoire Interdisciplinaire de Physique (LIPhy, UGA/CNRS) and the Laboratoire de Psychologie et NeuroCognition (LPNC, UGA/CNRS).
  • Partners:
    • Elan Inria project-team
    • Laboratoire Interdisciplinaire de Physique (LIPhy), Université Grenoble-Alpes (UGA)
    • Laboratoire de Psychologie et NeuroCognition (LPNC), Université Grenoble-Alpes (UGA)
National collaborations
  • Collaboration with Philippe Peyla, Aurélie Dupont (LIPhy, UGA/CNRS) and Christian Graff (LPNC, UGA/CNRS) within the FISHSIF project.
  • Collaboration with Baptiste Darbois-Texier (FAST, Univ. Paris Saclay/CNRS).
  • Long-term collaboration with Arnaud Lazarus and Sébastien Neukirch (Institut Jean le Rond d'Alembert, Sorbonne Université).
  • Long-term collaboration with Christophe Prud'homme and Vincent Chabannes (Université de Strasbourg and Centre de modélisation et de simulation de Strasbourg).
  • Collaboration with Olivier Pouliquen and Joël Marthelot (IUSTI, Aix-Marseille University).
Regional collaborations
  • Collaboration with Mélina Skouras (Inria/LJK - Anima team).
  • Collaboration with Stefanie Wuhrer and Jean-Sébastien Franco (Inria/LJK - Morphéo team).

.

11 Dissemination

11.1 Promoting scientific activities

11.1.1 Scientific events: organisation

Collective motion of animals and robots
  • Title:
    “Collective motion of animals and robots” international conference
  • Participants:
    Thibaut Métivet , Philippe Peyla (LIPhy, UGA), Aurélie Dupont (LIPhy, CNRS), Carine DOUARCHE (FAST, Univ. Paris-Saclay)
  • Description:
    The international conference “Collective motion of animals and robots” has been organized at IESC (Cargèse, Corsica) from 27th to 31st, May 2024. This conference proposed an hybrid scientific programme, with lectures, plenary sessions, short presentations and posters. It gathered a wide range of scientists from different communities (in particular physics, mathematics, computer science and biology) working on collective motion, within living organisms, statistical systems or decentralized algorithmics. The conference attracted a very international and pluridisciplinary audience, highlighting strong thematic convergences in these usually very distinct communities.

11.1.2 Scientific events: selection

Member of the conference program committees

Florence Bertails-Descoubes was member of the ACM Siggraph Technical Technical Paper Program Committee in 2024.

Thibaut Metivet was an organizer and member of the Scientific Committee of the “Collective motion of animals and robots” international conference.

Reviewer

Thibaut Métivet, Victor Romero and Florence Bertails-Descoubes were reviewers for ACM Siggraph and ACM Siggraph Asia in 2024.

11.1.3 Journal

Member of the editorial boards

Since 2020, Florence Descoubes has been an Associate Editor for ACM Transactions on Graphics, the premier journal for Computer Graphics.

Reviewer - reviewing activities
  • Siggraph (ACM, accepted papers published in ACM Transactions on Graphics)
  • Siggraph Asia (ACM, accepted papers published in ACM Transactions on Graphics)

11.1.4 Invited talks

Florence Bertails-Descoubes was a keynote speaker at the 2024 Colloque National en Calcul des Structures (CSMA 2024).

11.2 Teaching - Supervision - Juries

11.2.1 Teaching

Licence
  • Victor Romero : Electromagnétisme et optique pour la chimie, PHY405, 33h, DLST, Université Grenoble Alpes, Grenoble.
Master
  • Thibaut Métivet , Florence Bertails-Descoubes and Mélina Skouras : Mécanique Numérique, 36h, Ensimag 3A/MSIAM, Grenoble INP/UGA.

11.2.2 Supervision

Post-doctoral researchers
  • Bruno Ventéjou: 01/05/2022-, supervised by Thibaut Métivet and Philippe Peyla (LIPhy, UGA)
PhDs
  • Emile Hohnadel : 01/09/2021-, supervised by Florence Bertails-Descoubes and Thibaut Métivet
  • Alice Teixeira Da Silva : 01/02/2021-30/06/2024, supervised by Thibaut Métivet , Florence Bertails-Descoubes , and Mélina Skouras (Anima, Inria GRE)
Engineers
  • Octave Crespel : 01/09/2023-30/09/2024, supervised by Florence Bertails-Descoubes and Thibaut Métivet
Internships
  • Bastien Brogliato-Martin: 06/05/2024-14/06/2024, supervised by Florence Bertails-Descoubes and Thibaut Métivet
  • Stéphane Gaydier: 18/03/2024-13/09/2024, internship mentoring by Thibaut Métivet

11.2.3 Juries

  • Florence Bertails-Descoubes was a member of the Ph.D committees of Chloé Paliard (Computer Graphics), as a reviewer, June 27 2024, at Télécom Paris Tech, of Donald Zeka (Mechanics), as an examiner, October 14 2024, at Université Paris-Saclay, and of Quentin Le Lidec (Robotics), as a reviewer, December 17 2024, at Inria Paris.
  • Florence Bertails-Descoubes was a member of the Maître de Conférence Concours n° 562 (section 60) at Sorbonne Université in 2024.
  • Florence Bertails-Descoubes was a member of the Inria Grenoble ISFP admission committee in 2024.

11.3 Popularization

11.3.1 Productions (articles, videos, podcasts, serious games, ...)

Mediation paper

Participants: Florence Bertails-Descoubes.

Following the ACM Siggraph Asia 2023 Test of time award for the success of a former paper of the team on frictional contact in fibres 32, Florence Descoubes has participated, together with Bernard Brogliato and Gilles Daviet, to a mediation paper published on the national Inria website. The paper notably traces back the history of nonsmooth mechanics, from the pioneering work of Jean-Jacques Moreau in Montpellier in the 80's to many extensions made by the Bipop team at Inria Grenoble, in particular towards the numerical modelling of fibrous materials, and finally to its original application in special effects for movies (The Hobbit, Avatar 2, etc.).

12 Scientific production

12.1 Major publications

12.2 Publications of the year

International journals

International peer-reviewed conferences

National peer-reviewed Conferences

Conferences without proceedings

Doctoral dissertations and habilitation theses

Reports & preprints

Other scientific publications

12.3 Cited publications

  • 20 articleB.Basile Audoly and S.Sébastien Neukirch. A one-dimensional model for elastic ribbons: A little stretching makes a big difference.Journal of the Mechanics and Physics of Solids1532021, 104457DOIback to text
  • 21 articleB.B. Audoly and S.S. Neukirch. Fragmentation of Rods by Cascading Cracks: Why Spaghetti Does Not Break in Half.Physical Review Letters9592005, 095505back to text
  • 22 inproceedingsD.D. Baraff. Analytical methods for dynamic simulation of non-penetrating rigid bodies.Computer Graphics Proceedings (Proc. ACM SIGGRAPH'89 )New York, NY, USAACM1989, 223--232back to text
  • 23 inproceedingsF.F. Bertails, B.B. Audoly, M.-P.M.-P. Cani, B.B. Querleux, F.F. Leroy and J.-L.J.-L. Lévêque. Modélisation de coiffures naturelles à partir des propriétés physiques du cheveu.Journées Francophones d'Informatique Graphique (AFIG)AFIG / EG-FranceStrasbourg, Francenov 2005back to text
  • 24 articleF.F. Bertails. Linear Time Super-Helices.Computer Graphics Forum (Proc. Eurographics'09)282apr 2009, URL: http://www-ljk.imag.fr/Publications/Basilic/com.lmc.publi.PUBLI_Article@1203901df78_1d3cdaa/back to text
  • 25 articleF.F. Bertails-Descoubes. Super-Clothoids.Computer Graphics Forum (Proc. Eurographics'12)312pt22012, 509--518URL: http://www.inrialpes.fr/bipop/people/bertails/Papiers/superClothoids.htmlDOIback to text
  • 26 inproceedingsA.Alejandro Blumentals, F.Florence Bertails-Descoubes and R.Romain Casati. Dynamics of a developable shell with uniform curvatures.The 4th Joint International Conference on Multibody System DynamicsMontréal, CanadaMay 2016HALback to textback to text
  • 27 phdthesisA.Alejandro Blumentals. Numerical modelling of thin elastic solids in contact.Université de Grenoble AlpesJuly 2017back to text
  • 28 articleR.R. Casati and F.F. Bertails-Descoubes. Super Space Clothoids.ACM Transactions on Graphics (Proc. ACM SIGGRAPH'13)324July 2013, 48:1--48:12URL: http://doi.acm.org/10.1145/2461912.2461962DOIback to text
  • 29 bookD.Dominique Chapelle and K.K.J. Bathe. The Finite Element Analysis of Shells - Fundamentals - Second Edition.Computational Fluid and Solid MechanicsSpringer2011, 410HALDOIback to text
  • 30 inproceedingsP.P. Cundall. A computer model for simulating progressive large scale movements of blocky rock systems. In Proceedings of the Symposium of the International Society of Rock Mechanics.Proceedings of the Symposium of the International Society of Rock Mechanics11971, 132--150back to text
  • 31 articleG.Gilles Daviet and F.Florence Bertails-Descoubes. A semi-implicit material point method for the continuum simulation of granular materials.ACM Transactions on Graphics354July 2016, 13HALDOIback to text
  • 32 articleG.G. Daviet, F.F. Bertails-Descoubes and L.L. Boissieux. A hybrid iterative solver for robustly capturing Coulomb friction in hair dynamics.ACM Transactions on Graphics (Proc. ACM SIGGRAPH Asia'11)3062011, 139:1--139:12URL: http://www.inrialpes.fr/bipop/people/bertails/Papiers/hybridIterativeSolverHairDynamicsSiggraphAsia2011.htmlback to textback to text
  • 33 articleG.Gilles Daviet and F.Florence Bertails-Descoubes. Nonsmooth simulation of dense granular flows with pressure-dependent yield stress.Journal of Non-Newtonian Fluid Mechanics234April 2016, 15-35HALDOIback to text
  • 34 unpublishedG.Gilles Daviet and F.Florence Bertails-Descoubes. Simulation of Drucker--Prager granular flows inside Newtonian fluids.February 2017, working paper or preprintHALback to text
  • 35 phdthesisG.G. Daviet. Modèles et algorithmes pour la simulation du contact frottant dans les matériaux complexes : application aux milieux fibreux et granulaires.Grenoble Alpes UniversitésDecember 2016back to text
  • 36 articleA.A. Derouet-Jourdan, F.F. Bertails-Descoubes, G.G. Daviet and J.J. Thollot. Inverse Dynamic Hair Modeling with Frictional Contact.ACM Trans. Graph.326November 2013, 159:1--159:10URL: http://doi.acm.org/10.1145/2508363.2508398DOIback to text
  • 37 articleA.A. Derouet-Jourdan, F.F. Bertails-Descoubes and J.J. Thollot. Stable Inverse Dynamic Curves.ACM Transactions on Graphics (Proc. ACM SIGGRAPH Asia'10 )296December 2010, 137:1--137:10URL: http://doi.acm.org/10.1145/1882261.1866159DOIback to text
  • 38 articleM. A.Marcelo A. Dias and B.Basile Audoly. ``Wunderlich, Meet Kirchhoff'': A General and Unified Description of Elastic Ribbons and Thin Rods.Journal of Elasticity1191Apr 2015, 49--66URL: https://doi.org/10.1007/s10659-014-9487-0DOIback to text
  • 39 manualE. J.E. J. Doedel, R. C.R. C. Pfaffenroth, A. R.A. R. Chambodut, T. F.T. F. Fairgrieve, Y. A.Y. A. Kuznetsov, B. E.B. E. Oldeman, B.B. Sandstede and X.X. Wang. AUTO 2000: Continuation and Bifurcation Software for Ordinary Differential Equations (with HomCont).March 2006back to text
  • 40 miscESPCI. Rencontre en l'honneur de Yves Pomeau, octobre 2016.https://www.sfpnet.fr/rencontre-celebrant-la-medaille-boltzmann-d-yves-pomeauESPCI2016, URL: https://www.sfpnet.fr/rencontre-celebrant-la-medaille-boltzmann-d-yves-pomeauback to text
  • 41 articleI.I.A. Frigaard and C.C. Nouar. On the usage of viscosity regularisation methods for visco-plastic fluid flow computation.Journal of Non-Newtonian Fluid Mechanics1271April 2005, 1--26DOIback to text
  • 42 bookA. L.A. L. Gol'Denveizer. Theory of Elastic Thin Shells.Pergamon Press1961back to text
  • 43 articleR. E.Raymond E. Goldstein, P. B.Patrick B. Warren and R. C.Robin C. Ball. Shape of a Ponytail and the Statistical Physics of Hair Fiber Bundles.Phys. Rev. Lett.1087Feb 2012, 078101URL: https://link.aps.org/doi/10.1103/PhysRevLett.108.078101DOIback to text
  • 44 articleM.M. Jean. The Non Smooth Contact Dynamics Method.Computer Methods in Applied Mechanics and Engineering177Special issue on computational modeling of contact and friction, J.A.C. Martins and A. Klarbring, editors1999, 235-257back to text
  • 45 articleJ.Jie Li, G.Gilles Daviet, R.Rahul Narain, F.Florence Bertails-Descoubes, M.Matthew Overby, G.George Brown and L.Laurence Boissieux. An Implicit Frictional Contact Solver for Adaptive Cloth Simulation.ACM Transactions on Graphics374August 2018, 1-15HALDOIback to text
  • 46 inproceedingsM.M. Moore and J.J. Wilhelms. Collision detection and response for computer animation.Computer Graphics Proceedings (Proc. ACM SIGGRAPH'88 )1988, 289--298back to text
  • 47 articleD.D. Moulton, P.P. Grandgeorge and S.S. Neukirch. Stable elastic knots with no self-contact.Journal of the Mechanics and Physics of Solids1162018, 33--53URL: http://www.sciencedirect.com/science/article/pii/S0022509617310104DOIback to text
  • 48 articleJ.J. Spillmann and M.M. Teschner. An Adaptive Contact Model for the Robust Simulation of Knots.Computer Graphics Forum272Proc. Eurographics'082008back to text
  • 49 articleH.H. Sugiyama, J.J. Gertsmayr and A.A. Mikkola. Flexible Multibody Dynamics — Essential for Accurate Modeling in Multibody System Dynamics.Journal of Computational Nonlinear Dynamics91Novembler 2013back to text
  1. 1Within this optimal control framework, our previous curvature-based methods can actually be interpreted as a special case of direct single shooting methods.
  2. 2In France this new trend was particularly stimulated by the work of Yves Pomeau, who convinced many young scientists to study the nonlinear physics of common objects such as paper, plants, or hair  40.
  3. 3It is however amusing to observe that research in these areas is quite successful in obtaining the IG Nobel prize  21, 43, thus still being considered as an exotic research topic by physicists.