Physics-Based Animation

“Procedural methods for animating turbulent fluid are often preferred over simulation, both for speed and for the degree of animator control. We offer an extremely simple approach to efficiently generating turbulent velocity fields based on Perlin noise, with a formula that is exactly incompressible (necessary for the characteristic look of everyday fluids), exactly respects solid boundaries (not allowing fluid to flow through arbitrarily-specified surfaces), and whose amplitude can be modulated in space as desired. In addition, we demonstrate how to combine this with procedural primitives for flow around moving rigid objects, vortices, etc.”

 Curl-Noise for Procedural Fluid Flow

“Liquid and gas interactions often contain bubbles that stay for a
long time without bursting on the surface, making a dry foam structure.
Such long lasting bubbles simulated by the level set method
can suffer from a slow but steady volume error that accumulates
to a visible amount of volume change. We propose to address this
problem by using the volume control method. We trace the volume
change of each connected region, and apply a carefully computed
divergence that compensates undesired volume changes. To
compute the divergence, we construct a mathematical model of the
volume change, choose control strategies that regulate the modeled
volume error, and establish methods to compute the control gains
that provide robust and fast reduction of the volume error, and (if
desired) the control of how the volume changes over time.”

Simulation of Bubbles in Foam with the Volume Control Method

Tim Rowley and Ke-Sen Huang jointly maintain an updated list of upcoming SIGGRAPH papers as they get posted. Apparently there were 108 papers accepted this year, so odds are a healthy chunk of those will be filed under physics-based animation.

SIGGRAPH 2007 papers on the web

So far:

• A Finite Element Method for Animating Large Viscoplastic Flow
• Many-Worlds Browsing for Control of Multibody Dynamics
• Simulation of Bubbles in Foam With The Volume Control Method
• Adaptively Sampled Particle Fluids
• FastLSM: Fast Lattice Shape Matching for Robust Real-Time Deformation
• Volume Conserving Finite Element Simulation of Deformable Models
• Wrinkled Flames and Cellular Patterns
• Curl-Noise for Procedural Fluid Flow
• A Variational Approach to Eulerian Geometry Processing
• A Fast Variational Framework for Accurate Solid-Fluid Coupling
• Continuous Collision Detection for Articulated Models using Taylor Models and Temporal Culling
• TRACK: Toward Directable Thin Shells
• Isosurface Stuffing: Fast Tetrahedral Meshing with Good Dihedral Angles
• Efficient Simulation of Inextensible Cloth

 “We present a fast method for simulating, animating, and rendering lightning using adaptive grids. The “dielectric breakdown model” is an elegant algorithm for electrical pattern formation that we extend to enable animation of lightning. The simulation can be slow, particularly in 3D, because it involves solving a large Poisson problem. Losasso et al. recently proposed an octree data structure for simulating water and smoke, and we show that this discretization can be applied to the problem of lightning simulation as well. However, implementing the incomplete Cholesky conjugate gradient (ICCG) solver for this problem can be daunting, so we provide an extensive discussion of implementation issues. ICCG solvers can usually be accelerated using “Eisenstat’s trick,” but the trick cannot be directly applied to the adaptive case. Fortunately, we show that an “almost incomplete Cholesky” factorization can be computed so that Eisenstat’s trick can still be used. We then present a fast rendering method based on convolution that is competitive with Monte Carlo ray tracing but orders of magnitude faster, and we also show how to further improve the visual results using jittering.”

Fast Animation of Lightning Using an Adaptive Mesh

“We propose a novel approach to fracturing (and denting) brittle materials. To avoid the computational burden imposed by the stringent time step restrictions of explicit methods or with solving nonlinear systems of equations for implicit methods, we treat the material as a fully rigid body in the limit of infinite stiffness. In addition to a triangulated surface mesh and level set volume for collisions, each rigid body is outfitted with a tetrahedral mesh upon which finite element analysis can be carried out to provide a stress map for fracture criteria. We demonstrate that the commonly used stress criteria can lead to arbitrary fracture (especially for stiff materials) and instead propose the notion of a time averaged stress directly into the FEM analysis. When objects fracture, the virtual node algorithm provides new triangle and tetrahedral meshes in a straightforward and robust fashion. Although each new rigid body can be rasterized to obtain a new level set, small shards can be difficult to accurately resolve. Therefore, we propose a novel collision handling technique for treating both rigid bodies and rigid body thin shells represented by only a triangle mesh.”

Fracturing Rigid Materials

“Realistic hair modeling is a fundamental part of creating virtual humans in computer graphics. This paper surveys the state of the art in the major topics of hair modeling: hairstyling, hair simulation, and hair rendering. Because of the difficult, often unsolved problems that arise in alt these areas, a broad diversity of approaches is used, each with strengths that make it appropriate for particular applications. We discuss each of these major topics in turn, presenting the unique challenges facing each area and describing solutions that have been presented over the years to handle these complex issues. Finally, we outline some of the remaining computational challenges in hair modeling.”

A Survey on Hair Modeling: Styling, Simulation, and Rendering

“Back and forth error compensation and correction (BFECC) was recently developed for interface computation using a level set method. We show that BFECC can be applied to reduce dissipation and diffusion encountered in a variety of advection steps, such as velocity, smoke density, and image advections on uniform and adaptive grids and on a triangulated surface. BFECC can be implemented trivially as a small modification of the first-order upwind or semi-Lagrangian integration of advection equations. It provides second-order accuracy in both space and time. When applied to level set evolution, BFECC reduces volume loss significantly. We demonstrate the benefits of this approach on image advection and on the simulation of smoke, bubbles in water, and the highly dynamic interaction between water, a solid, and air. We also apply BFECC to dye advection to visualize vector fields.”

Advections with Significantly Reduced Dissipation and Diffusion

Pong with a Stable Fluids twist… Your paddles shoot bursts of fluid velocity, and the ball reacts to the motion of the fluid. Plus some trippy eye candy.

Plasma Pong

“We present a family of discrete isometric bending models (IBMs) for triangulated surfaces in 3-space. These models are derived from an axiomatic treatment of discrete Laplace operators, using these operators to obtain linear models for discrete mean curvature from which bending energies are assembled. Under the assumption of isometric surface deformations we show that these energies are quadratic in surface positions. The corresponding linear energy gradients and constant energy Hessians constitute an efficient model for computing bending forces and their derivatives, enabling fast time-integration of cloth dynamics with a two- to three-fold net speedup over existing nonlinear methods, and near-interactive rates for Willmore smoothing of large meshes.”

Discrete Quadratic Bending Energies

Admittedly a bit of a stretch as a physics paper, but a primary application of the energies they describe is in accelerating the calculation of bending forces for cloth simulation. (And we’re in a bit of a dry spell as far as new physics papers…)

Keenan Crane, an undergrad at UIUC,  recently implemented a full 3D fluid solver on one of NVIDIA’s latest GPUs, and achieved some pretty stunning speeds.  Could in-game real-time 3D liquid simulations really be just around the corner?

 GPU Fluids