Category: Uncategorized

The list of papers from the 2009 Symposium on Computer Animation have been up for a while at Ke-Sen Huang’s page.

Here’s the subset that fall most directly under physics-based animation:

• A Point-based Method for Animating Elastoplastic Solids
• Statistical Simulation of Rigid Bodies
• Anisotropic Friction for Deformable Surfaces and Solids
• Energy Stability and Fracture for Frame Rate Rigid Body Simulations
• Real-Time Deformation and Fracture in a Game Environment
• Guiding of Smoke Animations Through Variational Coupling of Simulations at Different Resolution
• Accurate Tangential Velocities For Solid Fluid Coupling
• Fast and Robust Tracking of Fluid Surfaces
• A Point-based Method for Animating Incompressible Flow

We propose a novel approach to guiding of Eulerian-based smoke animations through coupling of simulations at different grid resolutions. Specifically we present a variational formulation that allows smoke animations to adopt the low-frequency features from a lower resolution simulation (or non-physical synthesis), while simultaneously developing higher frequencies. The overall motivation for this work is to address the fact that art-direction of smoke animations is notoriously tedious. Particularly a change in grid resolution can result in dramatic changes in the behavior of smoke animations, and existing methods for guiding either significantly lack high frequency detail or may result in undesired features developing over time. Provided that the bulk movement can be represented satisfactorily at low resolution, our technique effectively allows artists to prototype simulations at low resolution (where computations are fast) and subsequently add extra details without altering the overall “look and feel”. Our implementation is based on a customized multi-grid solver with memory-efficient data structures.

Guiding of Smoke Animations Through Variational Coupling of Simulations at Different Resolutions

Surface tracking is an important problem with applications in many research fields. Among the most famous examples in computer graphics is the simulation and rendering of liquids with free surfaces. A surface that is advected by a general velocity field constantly changes its topology. This is the main reason why moving surfaces are typically defined implicitly as the zero set of a scalar field rather than by an explicit representation such as a mesh for instance.
In this paper we present a method for tracking fluid surfaces using triangle meshes. This is done in two steps. First, the vertices are advected by the velocity field of the fluid. Second, self-penetrations are fixed using marching cubes triangle templates. The technique is efficient in terms of computation and memory consumption, it is simple to implement and allows for direct control of volume and feature preservation.

Fast and Robust Tracking of Fluid Surfaces

We present a practical approach to isotropic tetrahedral meshing of 3D domains bounded by piecewise smooth surfaces. Building upon recent theoretical and practical advances, our algorithm interleaves Delaunay refinement and mesh optimization to generate quality meshes that satisfy a set of user-defined criteria. This interleaving is shown to be more conservative in number of Steiner point insertions than refinement alone, and to produce higher quality meshes than optimization alone. A careful treatment of boundaries and their features is presented, offering a versatile framework for designing smoothly graded tetrahedral meshes.

Interleaving Delaunay Refinement and Optimization for Practical Isotropic Tetrahedron Mesh Generation

We develop a method for reliable simulation of elastica in complex contact scenarios. Our focus is on firmly establishing three parameter-independent guarantees: that simulations of well-posed problems (a) have no interpenetrations, (b) obey causality, momentum- and energy-conservation laws, and (c) complete in finite time. We achieve these guarantees through a novel synthesis of asynchronous variational integrators, kinetic data structures, and a discretization of the contact barrier potential by an infinite sum of nested quadratic potentials. In a series of two- and three-dimensional examples, we illustrate that this method more easily handles challenging problems involving complex contact geometries, sharp features, and sliding during extremely tight contact.

Asynchronous Contact Mechanics

This paper introduces a data-driven representation and modeling technique for simulating non-linear heterogeneous soft tissue. It simplifies the construction of convincing deformable models by avoiding complex selection and tuning of physical material parameters, yet retaining the richness of non-linear heterogeneous behavior. We acquire a set of example deformations of a real object, and represent each of them as a spatially varying stress-strain relationship in a finite-element model. We then model the material by non-linear interpolation of these stress-strain relationships in strain-space. Our method relies on a simple-to-build capture system and an efficient run-time simulation algorithm based on incremental loading, making it suitable for interactive computer graphics applications. We present the results of our approach for several nonlinear materials and biological soft tissue, with accurate agreement of our model to the measured data.

Capture and Modeling of Non-Linear Heterogeneous Soft Tissue

It’s that time of year again… Here’s the link to Ke-Sen’s more complete list.

Physics-related papers:

• Energy-Preserving Integrators for Fluid Animation
• Interactive Simulation of Surgical Needle Insertion and Steering
• Modular Bases for Fluid Dynamics
• Numerical Coarsening of Inhomogeneous Elastic Materials
• Capture and Modeling of Non-Linear Heterogeneous Soft Tissue
• Interleaving Delaunay Refinement and Optimization for Practical Isotropic Tetrahedron Mesh Generation
• Physically Guided Liquid Surface Modeling from Videos
• Deforming Meshes that Split and Merge
• Predictive-Corrective Incompressible SPH
• Preserving Topology and Elasticity for Embedded Deformable Models
• Deformable Object Animation Using Reduced Optimal Control
• Enrichment Textures for Detailed Cutting of Shells
• Directable, High-Resolution Simulation of Fire on the GPU
• Asynchronous Contact Mechanics
• Detail-Preserving Continuum Simulation of Straight Hair

We present a method for simulating highly detailed cutting and fracturing of thin shells using low-resolution simulation meshes. Instead of refining or remeshing the underlying simulation domain to resolve complex cut paths, we adapt the extended finite element method (XFEM) and enrich our approximation by custom designed basis functions, while keeping the simulation mesh unchanged. The enrichment functions are stored in enrichment textures, which allows for fracture and cutting discontinuities at a resolution much finer than the underlying mesh, similar to image textures for increased visual resolution. Furthermore, we propose harmonic enrichment functions to handle multiple, intersecting, arbitrarily shaped, progressive cuts per element in a simple and unified framework. Our underlying shell simulation is based on discontinuous Galerkin (DG) FEM, which relaxes the restrictive requirement of C1 continuous basis functions and thus allows for simpler, C0 continuous XFEM enrichment functions.

Enrichment Textures for Detailed Cutting of Shells

We present a novel, incompressible fluid simulation method based on the Lagrangian Smoothed Particle Hydrodynamics (SPH) model. In our method, incompressibility is enforced by using a prediction-correction scheme to determine the particle pressures. For this, the information about density fluctuations is actively propagated through the fluid and pressure values are updated until the targeted density is satisfied. With this approach, we avoid the computational expenses of solving a pressure Poisson equation, while still being able to use large time steps in the simulation. The achieved results show that our predictive-corrective incompressible SPH (PCISPH) method clearly outperforms the commonly used weakly compressible SPH (WCSPH) model by more than an order of magnitude while the computations are in good agreement with the WCSPH results.

Predictive-Corrective Incompressible SPH

We present a new approach to fluid simulation that balances the speed of model reduction with the flexibility of grid-based methods. We construct a set of composable reduced models, or tiles, which capture spatially localized fluid behavior. We then precompute coupling terms so that these models can be rearranged at runtime. To enforce consistency between tiles, we introduce constraint reduction. This technique modifies a reduced model so that a given set of linear constraints can be fulfilled. Because dynamics and constraints can be solved entirely in the reduced space, our method is extremely fast and scales to large domains.

Modular Bases for Fluid Dynamics