We introduce a method for efficiently animating a wide range of deformable materials. We combine a high resolution surface mesh with a tetrahedral finite element simulator that makes use of frequent re-meshing. This combination allows for fast and detailed simulations of complex elastic and plastic behavior. We significantly expand the range of physical parameters that can be simulated with a single technique, and the results are free from common artifacts such as volume-loss, smoothing, popping, and the absence of thin features like strands and sheets. Our decision to couple a high resolution surface with low-resolution physics leads to efficient simulation and detailed surface features, and our approach to creating the tetrahedral mesh leads to an order-of-magnitude speedup over previous techniques in the time spent re-meshing. We compute masses, collisions, and surface tension forces on the scale
of the fine mesh, which helps avoid visual artifacts due to the differing mesh resolutions. The result is a method that can simulate a large array of different material behaviors with high resolution
features in a short amount of time.
Category: Collisions
Animating developable surfaces using nonconforming elements
We present a new discretization for the physics-based animation of developable surfaces. Constrained to not deform at all in-plane but free to bend out-of-plane, these are an excellent approximation for many materials, including most cloth, paper, and stiffer materials. Unfortunately the conforming (geometrically continuous) discretizations used in graphics break down in this limit. Our nonconforming approach solves this problem, allowing us to simulate surfaces with zero in-plane deformation as a hard constraint. However, it produces discontinuous meshes, so we further couple this with a “ghost” conforming mesh for collision processing and rendering. We also propose a new second order accurate constrained mechanics time integration method that greatly reduces the numerical damping present in the usual first order methods used in graphics, for virtually no extra cost and sometimes significant speed-up.
GDC Physics Tutorial
The slides for Erwin Coumans’ Game Developers Conference Physics Tutorial on parallel SPU physics are available for download and on-line here:
They cover parallelizing a typical collision detection and rigid body dynamics pipeline and provide links for further reading.
Thanks for Erwin for the link.
Phun
Phun is an educational, entertaining and somewhat addictive piece of software for designing and exploring 2D multi-physics simulations in a cartoony fashion.
Fast Collision Detection for Deformable Models using Representative-Triangles
We present a new approach to accelerate collision detection for deformable models. Our formulation applies to all triangulated models and significantly reduces the number of elementary tests between features of the mesh, i.e., vertices, edges and faces. We introduce the notion of Representative-Triangles, standard geometric triangles augmented with mesh feature information and use this representation to achieve better collision query performance. The resulting approach can be combined with bounding volume hierarchies and works well for both inter-object and self-collision detection. We demonstrate the benefit of Representative-Triangles on continuous collision detection for cloth simulation and N-body collision scenarios. We observe up to a one-order of magnitude reduction in feature-pair tests and up to a 5X improvement in query time.
Fast Collision Detection for Deformable Models using Representative-Triangles
An Adaptive Contact Model for the Robust Simulation of Knots
In this paper, we present an adaptive model for dynamically deforming hyper-elastic rods. In contrast to existing approaches, adaptively introduced control points are not governed by geometric subdivision rules. Instead, their states are determined by employing a non-linear energy-minimization approach. Since valid control points are computed instantaneously, post-stabilization schemes are avoided and the stability of the dynamic simulation is improved. Due to inherently complex contact configurations, the simulation of knot tying using rods is a challenging task. In order to address this problem, we combine our adaptive model with a robust and accurate collision handling method for elastic rods. By employing our scheme, complex knot configurations can be simulated in a physically plausible way.
An Adaptive Contact Model for the Robust Simulation of Knots
A Fast and Stable Penalty Method for Rigid Body Simulation
Two methods have been used extensively to model resting contact for rigid body simulation. The first approach, the penalty method, applies virtual springs to surfaces in contact to minimize interpenetration. This method, as typically implemented, results in oscillatory behavior and considerable penetration. The second approach, based on formulating resting contact as a linear complementarity problem, determines the resting contact forces analytically to prevent interpenetration. The analytical method exhibits expected-case polynomial complexity in the number of contact points, and may fail to find a solution in polynomial time when friction is modeled. We present a fast penalty method that minimizes oscillatory behavior and leads to little penetration during resting contact; our method compares favorably to the analytical method with regard to these two measures, while exhibiting much faster performance both asymptotically and empirically.
And Another Thesis
Claude Lacoursiere’s thesis on variational techniques for rigid bodies:
Ghosts and Machines: regularized variational methods for interactive simulations of multibodies with dry frictional contacts
Some Theses…
Frank Losasso’s PhD thesis on fluid simulation, which contains previously unpublished work on coupling together SPH and level set based fluid simulations:
Algorithms for Increasing the Efficiency and Fidelity of Fluid Simulation
Eftychios Sifakis’ PhD thesis on face, muscle, speech, and surgery simulation:
Algorithmic Aspects of the Simulation and Control of Computer Generated Human Anatomy Models
Geoffrey Irving’s PhD thesis on a variety of physics simulation topics:
Methods for the Physically-Based Simulation of Solids and Fluids
Update: While I’m doing the thesis thing, here’s a couple slightly older ones that are probably worth a look.
Adam Bargteil’s PhD thesis on liquid surface tracking.
Surface Tracking and Texturing
Bart Adams PhD thesis on point-based graphics:
Point-Based Modeling, Animation and Rendering of Dynamic Objects
Efficient Bounds for Point-Based Animations
We introduce a new and efficient approach for collision detection in point-based animations, based on the fast computation of tight surface bounds. Our approach is able to tightly bound a high-resolution surface with a cost linear in the number of simulation nodes, which is typically small. We extend concepts about bounds of convex sets to the point-based deformation setting, and we introduce an efficient algorithm for finding extrema of these convex sets. We can compute surface bounds orders of magnitude faster and/or tighter than with previous methods.