Category: Uncategorized

Optimizing Cubature for Efficient Integration of Subspace Deformations

We propose an efficient scheme for evaluating nonlinear subspace forces (and Jacobians) associated with subspace deformations. The core problem we address is efficient integration of the subspace force density over the 3D spatial domain. Similar to Gaussian quadrature schemes that efficiently integrate functions that lie in particular polynomial subspaces, we propose cubature schemes (multi-dimensional quadrature) optimized for efficient integration of force densities associated with particular subspace deformations, particular materials, and particular geometric domains. We support generic subspace deformation kinematics, and nonlinear hyperelastic materials. For an r-dimensional deformation subspace with O(r) cubature points, our method is able to evaluate subspace forces at O(r^2) cost. We also describe composite cubature rules for runtime error estimation. Results are provided for various subspace deformation models, several hyperelastic materials (St.Venant-Kirchhoff, Mooney-Rivlin, Arruda-Boyce), and multimodal (graphics, haptics, sound) applications. We show dramatically better efficiency than traditional Monte Carlo integration.

Optimizing Cubature for Efficient Integration of Subspace Deformations

Thesis: Controlling Multibody Dynamics via Browsing and Time Reversal

Christopher Twigg’s thesis from CMU:

“Animation techniques for controlling passive simulation are commonly based on an optimization paradigm: the user provides goals a priori, and sophisticated numerical methods minimize a cost function that represents these goals. Unfortunately, for multibody systems with discontinuous contact events these optimization problems can be highly nontrivial to solve, and many-hour offline optimizations, unintuitive parameters, and convergence failures can frustrate end-users and limit usage. On the other hand, users are quite adaptable, and systems which provide interactive feedback via an intuitive interface can leverage the user’s own abilities to quickly produce interesting animations. However, the online computation necessary for interactivity limits scene complexity in practice. This thesis presents two methods for controlling the rigid body simulations.

The first is Many-Worlds Browsing, a method which exploits the speed of multibody simulators to compute numerous simulations in parallel (offline and online), and allow the user to browse and modify them interactively. By bolting responsive, powerful, intuitive interfaces onto relatively simple sampling techniques we get a method that enables animators to produce compelling results with a minimum of effort. The second method is time-reversed simulation: we provide only the final resting configuration of the system and run the simulator backwards in time. During the development of this method we encountered a number of surprisingly counter-intuitive results, which can be elucidated using a combination of numerical simulation and thought experiments.”

Controlling Multibody Dynamics via Browsing and Time Reversal

Fool Me Twice: Exploring and Exploiting Error Tolerance in Physics-Based Animation

The error tolerance of human perception offers a range of opportunities to trade numerical accuracy for performance in physics-based simulation. However, most previous approaches either focus exclusively on understanding the tolerance of the human visual system or burden the application developer with case-specific implementations. In this paper, based on a detailed set of perceptual metrics, we propose a methodology to identify the maximum error tolerance of physics simulation. Then, we apply this methodology in the evaluation of two techniques. The first is the hardware optimization technique of precision reduction which reduces the size of floating point units (FPUs), allowing more of them to occupy the same silicon area. The increased number of FPUs can significantly improve the performance of future physics accelerators. A key benefit of our approach is that it is transparent to the application developer. The
second is the software optimization of choosing the largest timestep for simulation.

Fool Me Twice: Exploring and Exploiting Error Tolerance in Physics-Based Animation

SIGGRAPH 2008 papers list

The 2008 edition of the annual unofficial list of SIGGRAPH papers is up.

It’s looking like a big year for physics – just over 14% so far…

SCA 2008 Papers List

The list of papers accepted to the 2008 Symposium on Computer Animation is up here.

The physics-oriented subset of those papers:

Real-Time Breaking Waves for Shallow Water Simulations

We present a new method for enhancing shallow water
simulations by the effect of overturning waves. While full
3D fluid simulations can capture the process of wave breaking,
this is beyond the capabilities of a pure height field
model. 3D simulations, however, are still too expensive for
real-time applications, especially when large bodies of water
need to be simulated. The extension we propose overcomes
this problem and makes it possible to simulate scenes
such as waves near a beach, and surf riding characters in
real-time. In a first step, steep wave fronts in the height field
are detected and marked by line segments. These segments
then spawn sheets of fluid represented by connected particles.
When the sheets impinge on the water surface, they
are absorbed and result in the creation of particles representing
drops and foam. To enable interesting applications,
we furthermore present a two-way coupling of rigid bodies
with the fluid simulation. The capabilities and efficiency of
the method will be demonstrated with several scenes, which
run in real-time on today’s commodity hardware.

Real-Time Breaking Waves for Shallow Water Simulations

SIGGRAPH Sketches

With SIGGRAPH kicking off next week, thought I’d iterate a (probably incomplete) list of primarily physics-oriented sketches.

Is This For Real?
Implementing Wave Particles for Real-Time Water Waves With Object Interaction

Let’s Get Physical
Modal Locomotion: Controlling Passive Elastic Dynamics
Contact Trees: Adaptive Contact Sampling for Robust Dynamics
Blobtacular: Surfacing Particle Systems in “Pirates of the Caribbean 3”
Dynamic Execution Tracing of Physical Simulations

Bend and Stretch
Simulating Coordinated Movement With Tendons

Oh, Rats!
Chop It Up!: Animation-Driven Modeling, Simulation, and Shading in the Kitchen
Virtual Tailoring for “Ratatouille”: Clothing the Fattest Man in the World

Drat, More Rats!
Acting With Contact: Interactive Cartoon Collision & Response
An Effects Recipe for Rolling a Dough, Cracking an Egg, and Pouring a Sauce
Simulating Whitewater Rapids in “Ratatouille”
Extracting and Parametrizing Temporally Coherent Surfaces From Particles

Go With The Flow
Simulation, Simulation, Simulation
300’s Liquid Battlefield: Fluid Simulation Spartan Style

Highlights from SCA

Real-Time Simulation of Thin Shells

This paper proposes a real-time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real-time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. [GHDS03]. For real-time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique [CK05] which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real-time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism.

Real-Time Simulation of Thin Shells

*Updated* SIGGRAPH papers list

The official list of SIGGRAPH was posted today… Thought I would re-post the physics sub-list for good measure.

Official list

Unofficial SIGGRAPH 2007 papers on the web

Physics papers: