Bifrost Forum
Welcome to the Bifrost Forum. This is the place for artists using Bifrost to ask and answer questions, browse popular topics, and share knowledge about creating effects procedurally using Bifrost. You can also visit the Bifrost Community on AREA to download an array of ready-to-use graphs, read Bifrost news and updates, and find the latest tutorials.
Showing results for 
Show  only  | Search instead for 
Did you mean: 

Aero sim with negative radial influence giving weird results

Message 1 of 5
600 Views, 4 Replies

Aero sim with negative radial influence giving weird results



I wanted to draw the smoke from a ring of source geo to the centre and decided to use a radial influence with a negative magnitude, and it has given me some strange results.


Here's the scene with just a default basic aero graph with the density scaled up, an added radial influence at (0,0,0) and no other changes:


You can see that it stops before hitting the middle and then twitches about for a bit. Here's the graph:

Annotation 2019-12-16 1253312.png


You can see that even with a completely clean test scene and no drag on the influencer with again just the default basic_aero_graph we still get weird results:
As you can see it gets pulled around randomly instead of always getting pulled to  (0,0,0). The scene file is attached as "".


When I give it a drag of 99 so we just see the effects of the radial influence and also pipe it into a default particle graph, we get the behaviour I expect to happen in the particles and some even weirder behaviour with the smoke:



If you set the magnitude to positive it seems to work just fine. I checked the part in the solver that calculates the radial force, and it seems both correct and pretty straight forward. Is this to do with the other forces in play like buoyancy? Any help will be appreciated!


Files are here:

And I'm using Maya 2020 with Bifrost version




Message 2 of 5
in reply to: Anonymous

Have you tried an attract_repulse influence? Maybe thats working as expected.


Looking weird though...

Message 3 of 5
in reply to: Anonymous


I have not checked your scene yet, but i guess the problem is related to density / compressibility of the air.

If you move everything from around to the center this will create a force that tries to compensate for this.

Message 4 of 5
in reply to: Anonymous


The problem is the density / compressibility of the air mentioned by @mspeer .

In order to get around this issue, you can use the modulate_influence node to exclude any voxels with a fog density of 0 (to avoid moving air where there is no smoke). 


Radial_Influence_V01.gif  Radial_Influence_V02.gif


There are multiple ways to dissipate the smoke before they collide in the center.


Option 1) dissipate_influence

Option 2) kill_influence

Option 3) modifier_influence 


Here is an example using a combination of kill_influence and mask_influence.




I hope this helps.

Aslan Jafari
Sr QA Analyst
Message 5 of 5
in reply to: Aslan.Jafari

Perfect, thank you so much!

Can't find what you're looking for? Ask the community or share your knowledge.

Post to forums