A generic topological framework for physical simulation

This paper presents the use of a topological model to simulate a soft body deformation based on a Mass-Spring System. We provide a generic framework which can integrate any kind of geometrical meshes (hexahedral or tetrahedral elements), using several numerical integration schemes (Euler semi-implicit or implicit). This framework naturally allows topological changes in the simulated object during the animation. Our model is based on the 3D Linear Cell Complex topological model (itself based on a 3D combinatorial map), adding the extra information required for simulation purposes. Moreover, we present some adaptations performed on this data structure to fit our simulation requirements, and to allow efficient cutting or piercing in a 3D object

Implicit Tensor-Mass solver on the GPU

International audienceThe realist and interactive simulation of deformable objects has become a challenge in Computer Graphics. For this, the Tensor-Mass model is a good candidate: it enables local solving of mechanical equations, making it easier to control deformations from collisions or tool interaction. In this paper, a GPU implementation is presented for the implicit integration scheme. Results show a notable speedup, especially for complex scenes

Resolution of Non-Linear Problems In Realistic-Lung-Inflating Simulation with Finite Element Method.

International audienceHadrontherapy treatment needs accurate tumour targeting, which is difficult for lung cancer due to breathing motions. We propose to quantify lung deformation and displacement by a simulation technique based on the geometrical and mechanical properties of organs. Thereby, we model lung behaviour by a 3D dynamic deformable model derived from continuous mechanics, computed with finite elements method (FEM)

Simulation of Lung Behaviour with Finite Elements : Influence of Bio-Mechanical Parameters

International audienceMotivated by medical needs, we propose to simulate lung deformation and motion during respiration to track tumours. This paper presents a model of lung behaviour based on a continuous media mechanics model and solved with a finite element method. The result is a simulation of a normal breathing, matching with patient customised data. Moreover, we carried out numerical experiments to evaluate our algorithms and to measure the influence and the relevance of mechanical parameters

Lung Mesh Generation to Simulate Breathing Motion with a Finite Element Method

International audienceNumerical modelling of lung behaviour during the respiration cycle is a difficult challenge due to its complex geometry and surrounding environment constraints. This paper presents an approach to simulate a patient's lung motion during inhaling and exhaling based on a continuous media mechanics model and solved with a finite element method. One of the key problems is an adequate lung mesh generation, which is specifically developed in this paper

Towards Accurate Tumour Tracking in Lungs

International audienceMotivated by radiotherapy and hadrontherapy improvement, we consider in a first step the potential of simple elastic mechanical modelling of the lung. We propose to simulate his deformation and motion during respiration towards tracking tumours. We present two approaches, based on finite-elements method and mass-spring system. For this, we suggest a personalised model based on the measurement of patient's physical and geometrical data

Segmentation d'images IRM du cerveau pour la construction d'un modèle anatomique destiné à la simulation bio-mécanique

Comment obtenir des données anatomiques pendant une neurochirurgie ? a été ce qui a guidé le travail développé dans le cadre de cette thèse. Les IRM sont actuellement utilisées en amont de l'opération pour fournir cette information, que ce soit pour le diagnostique ou pour définir le plan de traitement. De même, ces images pre-opératoires peuvent aussi être utilisées pendant l'opération, pour pallier la difficulté et le coût des images per-opératoires. Pour les rendre utilisables en salle d'opération, un recalage doit être effectué avec la position du patient. Cependant, le cerveau subit des déformations pendant la chirurgie, phénomène appelé Brain Shift, ce qui altère la qualité du recalage. Pour corriger cela, d'autres données per-opératoires peuvent être acquises, comme la localisation de la surface corticale, ou encore des images US localisées en 3D. Ce nouveau recalage permet de compenser ce problème, mais en partie seulement. Ainsi, des modèles mécaniques ont été développés, entre autres pour apporter des solutions à l'amélioration de ce recalage. Ils permettent ainsi d'estimer les déformations du cerveau. De nombreuses méthodes existent pour implémenter ces modèles, selon différentes lois de comportement et différents paramètres physiologiques. Dans tous les cas, cela requiert un modèle anatomique patient-spécifique. Actuellement, ce modèle est obtenu par contourage manuel, ou quelquefois semi-manuel. Le but de ce travail de thèse est donc de proposer une méthode automatique pour obtenir un modèle du cerveau adapté sur l'anatomie du patient, et utilisable pour une simulation mécanique. La méthode implémentée se base sur les modèles déformables pour segmenter les structures anatomiques les plus pertinentes dans une modélisation bio-mécanique. En effet, les membranes internes du cerveau sont intégrées: falx cerebri and tentorium cerebelli. Et bien qu'il ait été démontré que ces structures jouent un rôle primordial, peu d'études les prennent en compte. Par ailleurs, la segmentation résultante de notre travail est validée par comparaison avec des données disponibles en ligne. De plus, nous construisons un modèle 3D, dont les déformations seront simulées en utilisant une méthode de résolution par Éléments Finis. Ainsi, nous vérifions par des expériences l'importance des membranes, ainsi que celle des paramètres physiologiques.The general problem that motivates the work developed in this thesis is: how to obtain anatomical information during a neurosurgery?. Magnetic Resonance (MR) images are usually acquired before the surgery to provide anatomical information for diagnosis and planning. Also, the same images are commonly used during the surgery, because to acquire MRI images in the operating room is complex and expensive. To make these images useful inside the operating room, a registration between them and the patient's position has to be processed. The problem is that the brain suffers deformations during the surgery, in a process called brain shift, degrading the quality of registration. To correct this, intra-operative information may be used, for example, the position of the brain surface or US images localized in 3D. The new registration will compensate this problem, but only to a certain extent. Mechanical models of the brain have been developed as a solution to improve this registration. They allow to estimate brain deformation under certain boundary conditions. In the literature, there are a variety of methods for implementing these models, different equation laws used for continuum mechanic, and different reported mechanical properties of the tissues. However, a patient specific anatomical model is always required. Currently, most mechanical models obtain the associated anatomical model by manual or semi-manual segmentation. The aim of this thesis is to propose and implement an automatic method to obtain a model of the brain fitted to the patient's anatomy and suitable for mechanical modeling. The implemented method uses deformable model techniques to segment the most relevant anatomical structures for mechanical modeling. Indeed, the internal membranes of the brain are included: falx cerebri and tentorium cerebelli. Even though the importance of these structures is stated in the literature, only a few of publications include them in the model. The segmentation obtained by our method is assessed using the most used online databases. In addition, a 3D model is constructed to validate the usability of the anatomical model in a Finite Element Method (FEM). And the importance of the internal membranes and the variation of the mechanical parameters is studied.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

The multiscale hybrid mixed method in general polygonal meshes

This work extends the general form of the Multiscale Hybrid-Mixed (MHM) method for the second-order Laplace (Darcy) equation to general non-conforming polygonal meshes. The main properties of the MHM method, i.e., stability, optimal convergence, and local conservation, are proven independently of the geometry of the elements used for the first level mesh. More precisely, it is proven that piecewise polynomials of degree k and k+1, k 0, for the Lagrange multipliers (flux), along with continuous piecewise polynomial interpolations of degree k+1 posed on second-level sub-meshes are stable if the latter is fine enough with respect to the mesh for the Lagrange multiplier. We provide an explicit sufficient condition for this restriction. Also, we prove that the error converges with order k +1 and k +2 in the broken H1 and L2 norms, respectively, under usual regularity assumptions, and that such estimates also hold for non-convex; or even non-simply connected elements. Numerical results confirm the theoretical findings and illustrate the gain that the use of multiscale functions provides

Les "pôles secondaires" dans la réorganisation des mobilités : maturité et durabilité des espaces périurbains ?

International audienceCette recherche faisait l'hypothèse que les mobilités des habitants des zones périurbains se recomposaient à partir de polarités nouvelles ou plus anciennes, de tailles différentes, dans un espace où cohabitent diverses formes de développement urbain.Ces recompositions seraient par ailleurs, renforcées par une diversification des sociétés locales, une inflexion des comportements de mobilité, et une montée en compétence des acteurs locaux. In fine, il s'agissait dans cette recherche, d'interroger les préjugés pesant sur ces espaces dits "périurbains"