View Full Version : Simulation change with auto resize fluid

04 April 2010, 10:26 AM
Has anyone noticed a big change in their fluid simulation when going from standard fluid to auto-resize? More specifically Im emitting fluids from particles and when I change to auto resize, I have to change all my settings on the fluid to try and achieve the same effect, primarily in the contents details section.

Any ideas?

04 April 2010, 01:34 PM
noticed that too when I spent 5 mins seeing what goodies 2011 has...
im sure Duncan will tell all, but im sure it has to do with the velocities being different because the rest of the fluid size isnt there...

ie. normally at start you had a 20 x 20 x 20 fluid, but now it starts at something like 2 x 2 x 2 and builds up...

or maybe were just not turning something on to compensate?

04 April 2010, 01:55 PM

Are you emitting using the old add method, or the new replace? I find the replace to be much easier to tweak. It seems more predictable, at least to me.

04 April 2010, 08:33 PM
Guys, Its more to do with the emission/dissapation settings than with velocity. My fluid when on auto size doesnt actually change the size at all because of the way I am emitting particles and yet it will change sim when I swap methods.

@ KidderD okay I will give that a go as it seems more to do with this.

04 April 2010, 08:48 PM
Same here guys!
I have been experiencing way too different behaviour here. My old explosion scene file aren`t looking same in maya 2011. I didnt change anything though just set the auto resize option ON & it produces more crappy result.
In few cases the auto resize fails to catch up with my fluid progression & it chops from the top.
Not sure why it happened may be I`ll play with the thresold value but I do have feeling that there is a hughe difference in Maya 2011 fluid solver with compare to the old one.
I`ll figure & will let u know If I happen to find a way to match the sims with the old maya version.

04 April 2010, 12:11 AM
Vik, keep in mind the auto size is based on density values only so if your temperature takes off ahead of your density, the container willnot auto size to fit it in. I had the same problem.

04 April 2010, 02:06 AM
In few cases the auto resize fails to catch up with my fluid progression & it chops from the top.

A workaround that was proposed for this situation, is to create a new emitter, scale and animate as needed for it to cause the autosize prior to your sim. So, in a sense animating your resize. I can't fully recall this part, but I think I recall that this emitter should only emit speed into the sim, no Dens, temp, fuel. Just tried, it, and yeah, if you emit just speed, it does resize.

04 April 2010, 07:56 AM
thanxs Guys!
thats very helpful, I have being lazy to read the docs.., thats a very quick & fast solution here.
but do any of you experience a difference in Solver behaviour?
I`ll try to switch my emission method to replace instead of Add & see how close I get to my old sim.

04 April 2010, 02:56 PM
The Maya Help (docs) has suggestions when working with auto-resized fluids.

There are two topics in the Fluid Effects > Modifying fluids section called "Controlling auto-resized boundaries" and "Auto-resizing fast moving and high resolution fluids".

These may help.

04 April 2010, 12:40 AM
I've noticed auto resize default settings sometimes let the fluid get too close to the edges and you have to make sure that density is your main driving factor... meaning temp isn't bleeding out as density doesn't auto resize. I don't use auto resize 100% of the time yet.

A great tip I found is making sure to close off some borders and tell auto resizer to not size those. That helps with ground and possibly -Z.

04 April 2010, 12:45 AM
Another observation and probably old hat for some of you guys is deciding whether to have bounded fluid or not especially with fire. I've noticed that when its not bounded the velocites tend to suck inward and upward creating an undesirable vacuum. Whereas when they are bounded there is more of just the upward force based on bouyency which is much nicer I feel.

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04 April 2010, 12:45 AM
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