About me

Since November 2021, I am a post-doc in Chris Wojtan's group at IST Austria.

Before that, I received in 2017 my engineering degree in computer science and applied maths from Grenoble INP - Ensimag with highest honors. Then, I prepared and obtained my PhD in 2021 at Inria Grenoble-Rhône Alpes / LJK in the Elan team under the supervision of Florence Bertails-Descoubes and Mélina Skouras (funded by the ERC project GEM).

Publications

Below is a manually actualized list of my publications. The full list can be found here.

Validation

Physical validation of simulators in Computer Graphics: A new framework dedicated to slender elastic structures and frictional contact
(website, paper, accompanying video, supplemental , recipe manual for the tests )
Victor Romero, Mickaël Ly, Abdullah-Haroon Rasheed, Raphaël Charrondière, Arnaud Lazarus, Sébastien Neukirch, Florence Bertails-Descoubes - ACM Transactions on Graphics 2021 (SIGGRAPH)
Abstract:
We introduce a selected set of protocols inspired from the Soft Matter Physics community in order to validate Computer Graphics simulators of slender elastic structures possibly subject to dry frictional contact. Although these simulators were primarily intended for feature film animation and visual effects, they are more and more used as virtual design tools for predicting the shape and deformation of real objects; hence the need for a careful, quantitative validation. Our tests, experimentally verified, are designed to evaluate carefully the predictability of these simulators on various aspects, such as bending elasticity, bend-twist coupling, and frictional contact. We have passed a number of popular codes of Computer Graphics through our benchmarks by defining a rigorous, consistent, and as fair as possible methodology. Our results show that while some popular simulators for plates/shells and frictional contact fail even on the simplest scenarios, more recent ones, as well as well-known codes for rods, generally perform well and sometimes even better than some reference commercial tools of Mechanical Engineering. To make our validation protocols easily applicable to any simulator, we provide an extensive description of our methodology, and we shall distribute all the necessary model data to be compared against.


ProjectiveFriction

Projective Dynamics with Dry Frictional Contact
(website, paper, accompanying video, code )
Mickaël Ly, Jean Jouve, Laurence Boissieux, Florence Bertails-Descoubes - ACM Transactions on Graphics 2020 (SIGGRAPH)
Abstract:
Projective dynamics was introduced a few years ago as a fast method to yield an approximate yet stable solution to the dynamics of nodal systems subject to stiff internal forces. Previous attempts to include contact forces in that framework considered adding a quadratic penalty energy to the global system, which however broke the simple, constant matrix, structure of the global linear equation, while failing to treat contact in an implicit manner. In this paper we propose a simple yet effective method to integrate in a unified and semi-implicit way contact as well as dry frictional forces into the nested architecture of Projective dynamics. Assuming that contacts apply to nodes only, the key is to split the global matrix into a diagonal and a positive matrix, and use this splitting in the local step so as to make a good prediction of frictional contact forces at next iteration. Each frictional contact force is refined independently in the local step, while the original efficient structure of the global step is left unchanged. We apply our algorithm to cloth simulation and show that contact and dry friction can be captured at a reasonable precision within a few iterations only, hence one order of magnitude faster compared to global implicit contact solvers of the literature.


Inversion

Inverse Elastic Shell Design with Contact and Friction
(website, paper, accompanying video, press release)
Mickaël Ly, Romain Casati, Florence Bertails-Descoubes, Mélina Skouras, Laurence Boissieux - ACM Transactions on Graphics 2018 (SIGGRAPH Asia)
Abstract:
We propose an inverse strategy for modeling thin elastic shells physically, just from the observation of their geometry. Our algorithm takes as input an arbitrary target mesh, and interprets this configuration automatically as a stable equilibrium of a shell simulator under gravity and frictional contact constraints with a given external object. Unknowns are the natural shape of the shell (i.e., its shape without external forces) and the frictional contact forces at play, while the material properties (mass density, stiffness, friction coefficients) can be freely chosen by the user. Such an inverse problem formulates as an ill-posed nonlinear system subject to conical constraints. To select and compute a plausible solution, our inverse solver proceeds in two steps. In a first step, contacts are reduced to frictionless bilateral constraints and a natural shape is retrieved using the adjoint method. The second step uses this result as an initial guess and adjusts each bilateral force so that it projects onto the admissible Coulomb friction cone, while preserving global equilibrium. To better guide minimization towards the target, these two steps are applied iteratively using a degressive regularization of the shell energy. We validate our approach on simulated examples with reference material parameters, and show that our method still converges well for material parameters lying within a reasonable range around the reference, and even in the case of arbitrary meshes that are not issued from a simulation. We finally demonstrate practical inversion results on complex shell geometries freely modeled by an artist or automatically captured from real objects, such as posed garments or soft accessories.


Teaching