An Intestinal Surgery Simulator: Real-Time Collision Processing and Visualization

International audienceThis research work is aimed towards the development of a VR-based trainer for colon cancer removal. It enables the surgeons to interactively view and manipulate the concerned virtual organs as during a real surgery. First, we present a method for animating the small intestine and the mesentery (the tissue that connects it to the main vessels) in real-time, thus enabling user-interaction through virtual surgical tools during the simulation. We present a stochastic approach for fast collision detection in highly deformable, self-colliding objects. A simple and efficient response to collisions is also introduced in order to reduce the overall animation complexity. Secondly, we describe a new method based on generalized cylinders for fast rendering of the intestine. An efficient curvature detection method, along with an adaptive sampling algorithm is presented. This approach, while providing improved tessellation without the classical self-intersection problem, also allows for high-performance rendering, thanks to the new 3D skinning feature available in recent GPUs. The rendering algorithm is also designed to ensure a guaranteed frame rate. Finally, we present the quantitative results of the simulations and describe the qualitative feedback obtained from the surgeons

Variational and linearly implicit integrators, with applications

We show that symplectic and linearly implicit integrators proposed by Zhang & Skeel (1997, Cheap implicit symplectic integrators. Appl. Numer. Math., 25, 297–302) are variational linearizations of Newmark methods. When used in conjunction with penalty methods (i.e., methods that replace constraints by stiff potentials), these integrators permit coarse time-stepping of holonomically constrained mechanical systems and bypass the resolution of nonlinear systems. Although penalty methods are widely employed, an explicit link to Lagrange multiplier approaches appears to be lacking; such a link is now provided (in the context of two-scale flow convergence (Tao, M., Owhadi, H. & Marsden, J. E. (2010) Nonintrusive and structure-preserving multiscale integration of stiff ODEs, SDEs and Hamiltonian systems with hidden slow dynamics via flow averaging. Multiscale Model. Simul., 8, 1269–1324). The variational formulation also allows efficient simulations of mechanical systems on Lie groups

Simulação interativa de tecidos e roupas: técnicas para o desenvolvimento de um simulador

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Ciências da Computação, Florianópolis, 2014.Há o interesse na simulação de roupas em qualquer aplicação onde há a presença de humanos virtuais. Contudo, simular o comportamento de tecidos no corpo de uma pessoa é uma tarefa complexa. Além disso, existe a constante necessidade de se obter resultados mais rápidos que viabilizem a simulação de indumentárias cada vez mais detalhadas. Este trabalho aborda técnicas relativas a diferentes etapas e aspectos do processo de simulação. Propõe-se uma otimização para um método para gerar efeitos de rasgo e corte. Ainda, introduz-se um algoritmo para a geração de linhas de costura em malhas de triângulos. As técnicas aqui descritas são utilizadas na implementação de um simulador cujo propósito é agilizar o desenvolvimento de sistemas para projeto e confecção de roupas.Abstract : There is interest in the simulation of clothes in any application where there is the presence of virtual humans. However, simulate the behavior of fabric on the body of a person is a complex task. In addition, there is a constant need to get faster results that allow the simulation of increasingly detailed garment. This work discusses techniques for different stages and aspects of the simulation process. We propose an optimization for a method used to generate effects of tearing and cutting. Also, we introduce an algorithm to generate seam lines for triangle meshes. The techniques described herein are used in the implementation of a simulator whose purpose is to facilitate the development of systems for designing and making clothes

Efficient numerical methods for the simulation of particulate and liquid-solid flows

In this work a set of efficient numerical methods for the simulation of particulate flows and virtual prototyping applications are proposed. These methods are implemented as modular components in the FEATFLOW software package which is used as the fluid flow solver. In direct particulate flow simulations the calculation of the hydrodynamic forces acting on the particles is of central importance. For this task acceleration techniques are proposed based on hierarchical spatial partitioning. For arbitrary shaped particles the usage of distance maps to rapidly process the needed geometric information is employed and analyzed. In case of collisions between the particles it is shown how these same structures can be used to efficiently handle the collision broad phase and narrow phase. The computation of collision forces in the proposed particulate flow solving scheme can be handled by several collision models. The used models are based on a constrained-based formulation which leads to a linear complementarity problem (LCP). Another approach is added into the particulate flow solver that is based on the discrete element method (DEM). This approach is suited very well to an Implementation on graphic processing units (GPU) as the particles can be handled independently and thus excellent use of the massive parallel computing capabilities of the GPU can be made. In order to extend the DEM to handle non-spherical particles or rigid bodies, an inner sphere representation of such shapes is used. Furthermore, a mesh adaptation technique to increase the numerical efficiency of the CFD-simulations is shown which is based on Laplacian smoothing with special weights. The proposed techniques are validated in various benchmark configurations or comparisons to experimental data

Dynamiksimulation in der Computergraphik

Die interaktive physikalisch-basierte Simulation von Starrkörpern und deformierbaren Festkörpern ist ein wichtiges und aktuelles Forschungsgebiet in der Computergraphik und ein essentieller Bestandteil in vielen Anwendungen, wie z.B. Virtual Prototyping, Computerspiele oder Trainingssimulatoren. In dieser Arbeit werden interaktive Simulationsmethoden für Mehrkörpersysteme, Textilien und inkompressible deformierbare Volumenkörper vorgestellt

Constraints methods for flexible models

Simulating flexible models can create aesthetic motion for computer animation. Animators can control these motions through the use of constraints on the physical behavior of the models. This paper shows how to use mathematical constraint methods based on physics and on optimization theory to create controlled, realistic animation of physically-based flexible models. Two types of constraints are presented in this paper: reaction constraints (RCs) and augrmented Lagrangian constraints (ALCs). RCs allow the fast computation of collisions of flexible models with polygonal models. In addition, RCs allow flexible models to be pushed and pulled under the control of an animator. ALCs create animation effects such as volume-preserving squashing and the molding of taffy-like substances. ALCs are compatible with RCs. In this paper, we describe how to apply these constraint methods to a flexible model that uses finite elements

Constraints methods for flexible models

Simulating flexible models can create aesthetic motion for computer animation. Animators can control these motions through the use of constraints on the physical behavior of the models. This paper shows how to use mathematical constraint methods based on physics and on optimization theory to create controlled, realistic animation of physically-based flexible models. Two types of constraints are presented in this paper: reaction constraints (RCs) and augrmented Lagrangian constraints (ALCs). RCs allow the fast computation of collisions of flexible models with polygonal models. In addition, RCs allow flexible models to be pushed and pulled under the control of an animator. ALCs create animation effects such as volume-preserving squashing and the molding of taffy-like substances. ALCs are compatible with RCs. In this paper, we describe how to apply these constraint methods to a flexible model that uses finite elements