Fluid

Description

fluid and fluid3D are a 2D and 3D fluid simulator, respectively, implemented in C++ and Open Inventor. They solve the Navier-Stokes equations for fluid-like flow (pic). For the fluid solver, I began with Jos Stam's 2D 60-line solver based on the fast fourier transform (FFT) (ref), which has period boundaries. To this I added various visualization and interaction abilities, such as texture advection, plus improved fluid solver techniques such as vorticity confinement and monotonic cubic interpolation (ref).

For the 3D version I modified the solver to use Gauss-Seidel relaxtion to solve for the pressure term, instead of the FFT, again using source code provided by Jos Stam (ref). Of course, I also extended his solver to 3D. I added a texture based volume renderer (using transparent, grid-aligned texture-mapped quads), I also added Andrew Selle's vortex-particle method (ref) for adding fine turbulent flow features for explosions. Implementing this method took about a day. Finding and fixing the bugs, and running dozens of simulations to fine tune parameters took weeks, or months.

For photorealistic results I used my ray tracer to render the density as smoke or fog (using isotropic scattering). You can see my results below.

2D simulation

Density advection with vortex confinement	Texture coordinate advection, with grid texture (left) and a photograph of me (right).
Color coded visualization of the velocity.	Added particled advection and mouse interaction. You can use the mouse to add a velocity force, to stir things up.

3D simulation

3D simulation using vortex particles running on a 180x260x180 grid. See movie below for an animation.

I implemented blackbody emission in my ray tracer, and incorporated several constants defined in "Physically Based Modeling and Animation of Fire" by Nguyen at al., including bouyancy, smoke density, etc. Left to right: Smoke simulation with new constants, flame (5000K), flame (50000K), flame together with smoke (flame is scaled by a constant, a hack).

Christmas tree-shaped green fog. The fog is initialized as a cone and perturbed with 12000 vortex particles (Selle et al.), then scaled by a Perlin noise volumetric heightfield (hyper texture) during rendering. The ground is a fractally displaced 2D heightfield.

Movies

Getting the smoke to behave in a particular way is a difficult. Here is a compilation movie of 56 smoke test-run simulations in my effort to reproduce the vortex particle method paper results. Click image to download. Size: 5.6 MB. Length: 4:47 s.

This movie shows a smoke simulation on a 180x260x180 grid, using the method described in the Siggraph 2005 paper titled A Vortex Particle Method for Smoke, Water, and Explosions. This effort was meant to reproduce one of their results, a rising smoke plume. The simulation required about 4 minutes per frame. Rendering was done with my ray tracer using photon mapping to simulation indirect illumination for a full global illumination solution. Download: avi gif

Future work

Acknowledgements

Source Code

• fluidSim.tar.gz (910k)

  Contains both fluid simulator code and compatible version of Pane to render the generated volumetric data.

References