View Full Version : stepping effect in fluid

12 December 2010, 06:09 PM

I've been simulating a dynamic fluid and at low resolutions it looks ok. But when I playback at higher grid resolutions I start to see the stepping effect in the image. The fluid is being emitted and pushed in x by an air field (the fluid has no buoyancy).

I've tried increasing the output from the emitter, thinking there were too few voxels, but this didin't work.

Any ideas?



12 December 2010, 06:44 PM
If the change in voxels from the base resolution to a high resolution is too much, your simulation will look very different. Every parameter will affect the simulation differently because now your grid has more voxels.

Try baby steps, go increasing and changing your simulation to match your new resolution.

12 December 2010, 06:44 PM
increase the sub samples in your dynamics tab of your fluid. Also check in your fluid emitter tab and uncheck jitter. Should help.

if this is for a rocket or jet exhaust type of effect you may consider using a static fluid and driving a high frequency high velocity through it using the fluid textures. Ive done a lot of these type effects and ive found that jet exhaust that has fluid type movement always appears slow or totally fake.

play your uncached fluid to a state where it is the right shape set initial state then make velocity and density constants. Texture and animate the y origin (or whichever axis) Obviously the smoke trail part would need to be dynamic

good luck

12 December 2010, 08:00 PM
Thanks for the responses guys, helped me understand fluids a little better.

Mandark, if I do this (set initial state then change grids to static) I don't see the texture update in the viewport, but it does change when I test the render between two frames. If I do this do I still need to cache out the time line or is the texture independent of the simulation, so I can just render?

thanks again,


12 December 2010, 09:30 PM
Fluid nCache:
evaluate every: 0.5 frames
save every: 2 evaluations

due to what the reaction will proceed a little faster and stepping effect is almost gone.

Hope it help.

12 December 2010, 10:13 PM
the static fluid approach is like this.

generate your fluid like you would normally until you have the desired shape. Set initial state and change the velocity grid and the density grid to static. Then your done you dont need to cache anymore frames. The texture thing can be exhaustive depending on your video card, but my suggestion would be to go to Highend3d and download the "fluidtextureizer" mel. This is an awesome little script that helps visualize what the procedural textures are actually doing in your fluid. then it is just a matter of playing with the texture translate keyframes and maybe some texture time to get the look you want.

When i do this i usually have multiple fluids that have low opacity and i give each a different texture with subtely different animation, this helps to make everything look random and natural but is light weight to render.

Good luck.

after looking at your response, textures can be independent of cache as long as the interpolation is set to fixed. Grid method requires you to cache the fluid with your grid enabled to get best results of textures following your fluids movements

this effect wont work for your thrust hitting anything but a simple group pivot to your thrust nozzle can make vectorable thrust work well. you could also play with scaleing teh container(s) to get a believable ignition etc.

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12 December 2010, 10:13 PM
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