This paper presents a novel framework for simulating the stretching and wiggling of liquids. We demonstrate that complex phase-interface dynamics can be effectively simulated by introducing the Eulerian vortex sheet method, which focuses on the vorticity at the interface (rather than the whole domain). We extend this model to provide user control for the production of visual effects. Then, the generated fluid flow creates complex surface details, such as thin and wiggling fluid sheets. To capture such high-frequency features efficiently, this work employs a denser grid for surface tracking in addition to the (coarser) simulation grid. In this context, the paper proposes a filter, called the liquid-biased filter, which is able to downsample the surface in the high-resolution grid into the coarse grid without unrealistic volume loss resulting from aliasing error. The proposed method, which runs on a single PC, realistically reproduces complex fluid scenes.
SIGGRAPH Asia 2009
Ke-Sen’s list of SIGGRAPH Asia 2009 papers is starting to fill out.
Here’s some of the more physics-related ones:
Field3D
Sony has released an open source project that underpins their fluid simulation and volume rendering tools, called Field3D.
SCA 2009 Papers
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
Statistical Simulation of Rigid Bodies
We describe a method for replacing certain stages of rigid body simulation with a statistically-based approximation. We begin by collecting statistical data regarding changes in linear and angular momentum for collisions of a given object. From this data we extract a statistical “signature” for the object, giving a compact representation of the object’s response to collision events. During object simulation, both the collision detection and the collision response calculations are replaced by simpler calculations based on the statistical signature. Using this approach, we are able to achieve significant improvement in the performance of rigid body simulation. The statistical behavior of the simulation is maintained, including achieving valid resting positions. We present results from a variety of simulations that demonstrate the method and its performance improvement. The method is appropriate for rigid body simulation situations requiring significant performance improvement, and allowing for some loss in fidelity
Fluid Simulation with Articulated Bodies
We present an algorithm for creating realistic animations of characters that are swimming through fluids. Our approach combines dynamic simulation with data-driven kinematic motions (motion capture data) to produce realistic animation in a fluid. The interaction of the articulated body with the fluid is performed by incorporating joint constraints with rigid animation and by extending a solid/fluid coupling method to handle articulated chains. Our solver takes as input the current state of the simulation and calculates the angular and linear accelerations of the connected bodies needed to match a particular motion sequence for the articulated body. These accelerations are used to estimate the forces and torques that are then applied to each joint. Based on this approach, we demonstrate simulated swimming results for a variety of different strokes, including crawl, backstroke, breaststroke and butterfly. The ability to have articulated bodies interact with fluids also allows us to generate simulations of simple water creatures that are driven by simple controllers.
Anisotropic Friction for Deformable Surfaces and Solids
This paper presents a method for simulating anisotropic friction for deforming surfaces and solids. Frictional contact is a complex phenomenon that fuels research in mechanical engineering, computational contact mechanics, composite material design and rigid body dynamics, to name just a few. Many real-world materials have anisotropic surface properties. As an example, most textile materials exhibit direction-dependent frictional behavior, but despite its tremendous impact on visual appearance, only simple isotropic models have been considered for cloth and solid simulation so far.
In this work, we propose a simple, application-oriented but physically sound model that extends existing methods to account for anisotropic friction.
The sliding properties of surfaces are encoded in friction tensors, which allows us to model frictional resistance freely along arbitrary directions. We also consider heterogeneous and asymmetric surface roughness and demonstrate the increased simulation quality on a number of two- and three-dimensional examples. Our method is computationally efficient and can easily be integrated into existing systems.
Accurate Tangential Velocities for Solid-Fluid Coupling
We propose a novel method for obtaining more accurate tangential velocities for solid fluid coupling. Our method works for both rigid and deformable objects as well as both volumetric objects and thin shells. The fluid can be either one phase such as smoke or two phase such as water with a free surface. The coupling between the solid and the fluid can either be one-way with kinematic solids or fully two-way coupled. The only previous scheme that was general enough to handle both two-way coupling and thin shells required a mass lumping strategy that did not allow for freely flowing tangential velocities. Similar to that previous work, our method prevents leaking of fluid across a thin shell, however unlike that work our method does not couple the tangential velocities in any fashion, allowing for the proper slip independently on each side of the body. Moreover, since it accurately and directly treats the tangential velocity, it does not rely on grid refinement to obtain a reasonable solution. Therefore, it gives a highly improved result on coarse meshes.
Guiding of Smoke Animations Through Variational Coupling of Simulations at Different Resolutions
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
Fast and Robust Tracking of Fluid Surfaces
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.