GPU Gems 3 is out, and it contains a chapter on real-time 3D simulation & rendering of fluids (smoke and liquids) on the GPU, and is available as a free sample chapter online. You may have seen some of these results before on Keenan Crane’s website.
Month: August 2007
Animating Corrosion and Erosion
In this paper, we present a simple method for animating natural phenomena such as erosion, sedimentation, and acidic corrosion. We discretize the appropriate physical or chemical equations using finite differences, and we use the results to modify the shape of a solid body. We remove mass from an object by treating its surface as a level set and advecting it inward, and we deposit the chemical and physical byproducts into simulated fluid. Similarly, our technique deposits sediment onto a surface by advecting the level set outward. Our idea can be used for off-line high quality animations as well as interactive applications such as games, and we demonstrate both in this paper.
Velocity-Based Shock Propagation for Multibody Dynamics Animation
Multibody dynamics are used in interactive and real-time applications, ranging from computer games to virtual prototyping, and engineering. All these areas strive towards faster and larger scale simulations. Particularly challenging are large-scale simulations with highly organized and structured stacking. We present a stable, robust, and versatile method for multibody dynamics simulation. Novel contributions include a new, explicit, fixed time-stepping scheme for velocity-based complementarity formulations using shock propagation with a simple reliable implementation strategy for an iterative complementarity problem solver specifically optimized for multibody dynamics.
Velocity-Based Shock Propagation for Multibody Dynamics Animation
Impulse-Based Dynamic Simulation in Linear Time
This paper describes an impulse-based dynamic simulation method for articulated bodies which has a linear time complexity. Existing linear-time methods are either based on a reduced-coordinate formulation or on Lagrange multipliers. The impulse-based simulation has advantages over these well-known methods. Unlike reduced-coordinate methods, it handles nonholonomic constraints like velocity-dependent ones and is very easy to implement. In contrast to Lagrange multiplier methods the impulse-based approach has no drift problem and an additional stabilisation is not necessary. The presented method computes a simulation step in O(n) time for acyclic multi-body systems containing equality constraints. Closed kinematic chains can be handled by dividing the model into different acyclic parts. Each of these parts is solved independently from each other. The dependencies between the single parts are solved by an iterative method. In the same way inequality constraints can be integrated in the simulation process in order to handle collisions and permanent contacts with dynamic and static friction.
Fast Fluid Simulation using Residual Distribution Schemes
We present a fast method for physically-based animation of fluids on adaptive, unstructured meshes. Our algorithm is capable of correctly handling large-scale fluid forces, as well as their interaction with elastic objects. Our adaptive mesh representation can resolve boundary conditions accurately while maintaining a high level of
efficiency.
Solving General Shallow Wave Equations on Surfaces
We propose a new framework for solving General Shallow Wave Equations (GSWE) in order to efficiently simulate
water flows on solid surfaces under shallow wave assumptions. Within this framework, we develop implicit
schemes for solving the external forces applied to water, including gravity and surface tension. We also present a
two-way coupling method to model interactions between fluid and floating rigid objects. Water flows in this system
can be simulated not only on planar surfaces by using regular grids, but also on curved surfaces directly without
surface parametrization. The experiments show that our system is fast, stable, physically sound, and straightforward
to implement on both CPUs and GPUs. It is capable of simulating a variety of water effects including:
shallow waves, water drops, rivulets, capillary events and fluid/floating rigid body coupling. Because the system
is fast, we can also achieve real-time water drop control and shape design.
Stable Advection-Reaction-Diffusion Systems
Turing first theorized that many biological patterns arise through the processes of reaction and diffusion. Subsequently, reaction-diffusion systems have been studied in many fields, including computer graphics. We first show that for visual simulation purposes, reaction-diffusion equations can be made unconditionally stable using a variety of straightforward methods. Second, we propose an anisotropy embedding that significantly expands the space of possible patterns that can be generated. Third, we show that by adding an advection term, the simulation can be coupled to a fluid simulation to produce visually appealing flows. Fourth, we couple fast marching methods to our anisotropy embedding to create a painting interface to the simulation. Unconditional stability to maintained throughout, and our system runs at interactive rates. Finally, we show that on the Cell processor, it is possible to implement reaction-diffusion on top of an existing fluid solver with no significant performance impact.
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.
Many Worlds Browsing for Control of Multibody Dynamics
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.
We introduce Many-Worlds Browsing, a method which circumvents these limits by exploiting the speed of multibody simulators to compute numerous example simulations in parallel (offline and online), and allow the user to browse and modify them interactively. We demonstrate intuitive interfaces through which the user can select among the examples and interactively adjust those parts of the scene that don’t match his requirements. We show that using a combination of our techniques, unusual and interesting results can be generated for moderately sized scenes with under an hour of user time. Scalability is demonstrated by sampling much larger scenes using modest offline computations.
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