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 Noodle!01-06-2011, 12:35 PMTitle might be a misnomer, but my smoke and explosions always seem to just stop "acting" and just dissipate in place, which looks very odd. Buoyancy and fields doesn't seem to do much. I've uploaded a video, which obviously is not something complete, but illustrates what I mean considering this happens all the time. http://www.youtube.com/watch?v=GM7GHn4ruYU near the middle it just stops and dissipates, looking very unnatural. How do I avoid this? How can I keep it simulating like it should?
Phlok
01-06-2011, 12:42 PM
No constant source of emission?

Noodle!
01-06-2011, 12:46 PM
Yes, the emission turns off, but shouldn't the fluid that is already there keep simulating properly?

dizzyone
01-06-2011, 01:45 PM
I've had similar problems when importing older fluids I made into a scene, I believe the problems just went away when I switched to the 64 bit version of maya 2011.

However, it could just be your setup, as the problems I had were slightly more severe. It could have something to do with the way you set up your fuel or temperature, if you're even using those.

Noodle!
01-06-2011, 02:45 PM
I'm using the 64 bit version of Maya 2011 (at university). I'll fiddle with temperatures and see if that solves it, though I've had the same with just pure density emission.

Phlok
01-06-2011, 03:04 PM
Due to the calculus behind Computational Fluid Dynamics (CFD), the fluids tend to dissipate over time. The more turbulence (no matter what kind of turbulence- just whatever's pushing your fluid around) you use, the stronger is this effect. If you need the fluid to stay, you might lower your simulation rate scale, another thing you might try is giving the fluid a bit of diffusion.

Also you can do a lot with your transparency and the opacity graph...this can control the density/ opacity relationship of your voxels.

Duncan
01-06-2011, 05:54 PM
Yes, it looks like there is a lot of dissipation due to high turbulence in the flow. As well the opacity looks like the graph may be thresholded so that low density is fully transparent. This makes it look like the density dissappears, instead of dissipating into thin wisps. However with the default fluid solver density can also vanish( with open boundaries ) when the flow is fast and turbulent. Increasing substeps can improve this, as the fluid can then better handle fast motion. Turning on high detail solve may also help. Forward advection may also help, as it preserves the total density (the default advection only preserves total density when all boundaries are closed).

Duncan

Noodle!
01-07-2011, 08:54 AM
Thanks for these very informative replies, guys! High detail solving is on, but I'll increase substeps and see to perhaps animating the opacity bias.

pixelranger
01-07-2011, 09:25 AM
Could it be due to the fluid having opacity texture? Try putting '=time/3' in the texture origin Y attribute, which will make the texture coordinates drift upwards.

Noodle!
01-07-2011, 03:15 PM
Here I am again. I've sort of got the dissipation problem under control, but as it is now my explosion is way too "blobby".

http://img837.imageshack.us/img837/3736/skitr.jpg

As you can see it lacks detail, especially around the edges. I've fiddled around with most settings but can't seem to figure out how to get it. Is it turbulence to break it up? Adding several turbulence emitters seem to just completely break it. I've got one volume axis field at the bottom, should I add more just to break it up? It's driving me mad, haha.

Thanks again guys.

quirkalfeeg
01-07-2011, 03:38 PM
Sounds like you might have over cranked the input bias on the opacity? Duncan also mentioned this above...have you got it a long way off the mid default? Just an idea...

pixelranger
01-07-2011, 06:09 PM
Maybe you can add some turbulence in the fluidShape node (tweak frequency) or have a volume axis field with turbulence that covers the whole container?

psilo
01-07-2011, 10:00 PM
Depending on your fluid transform scale , could be due to the fluid drop off of the parameter,.Do you have any dissipation on your density?

Noodle!
01-08-2011, 11:55 AM
Sounds like you might have over cranked the input bias on the opacity? Duncan also mentioned this above...have you got it a long way off the mid default? Just an idea...
The input buias for opacity is animated from 0.6 to about -0.4, I've changed it around but it doesn't seem to affect the blobbyness.

Depending on your fluid transform scale , could be due to the fluid drop off of the parameter,.Do you have any dissipation on your density?

Right now there's no dissipation, but with dissipation at 0.6 the results were much the same.

I'm going to try adding some turbulence with some axis fields, to see if that helps. Thanks guys!

Noodle!
01-08-2011, 12:50 PM
I feel like I'm lacking some extremely fundamental knowledge.

start of explosion:
http://img207.imageshack.us/img207/9098/ski2y.jpg

I'm changing frequency ratio, ratio, depth max, amplitude as well as adjusting input bias, transparency, density of the fluid. I'm at a complete loss.

Noodle!
01-09-2011, 12:48 PM
http://img513.imageshack.us/img513/5854/trashn.jpg
http://dl.dropbox.com/u/7770783/explosion.mb

Even at a resolution of 160 I get this weird effect where each voxel shows up, besides it being too smooth.
On the off chance anyone would want it, I uploaded the maya file (maya 2011). I just can't figure out what I'm doing wrong.

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