View Full Version : Intuitive fluid control?

07 July 2008, 09:54 PM
Hey, .. So I have a bit of a convoluted question regarding fluids, maybe there is an easier way to do what I'm trying to figure out, ... I need to use fluids because I have the "look" there.. Its more about deriving the motion.

I am trying to do a stylistic fire (more motion, not visual/color/etc), so rather than your normal flame that rises fast, flickers and wisps... Is there any suggestion on how to further the control a bit tighter, such as making it twist or spiral as it rises? I've tried using volume axis and vortex fields but they're a bit overbearing and start to take away from the overall fluid simulation from voxel to voxel.

Is there a way, other than having to use collisions (I've tried tubes with deformers, extruded tubes with hair curves, etc..) to get the flames to bend, wiggle and twist which seem to get me something closer but again, this takes away from the sim aspect and now confines it to this extremely tubular looking hose which won't work either. Think in terms of say, using particles and a flow field to drive the velocity perhaps, of the container?

So to break down simpler, is there a way to clearly manipulate the behavior and overall movement of the fluid/fire/flame without compromising the integrity of the flame too much?

07 July 2008, 08:08 AM
Once I used animated drag fields with to do something similar, not precisely on fire, but i think it may worth a try.

07 July 2008, 05:40 AM
Under the Shading Tab, I would animate the Input Bias attribute of Incandescence and Opacity...there are several attributes in the Texturing tab as well which may help...

07 July 2008, 10:21 PM
mmm.. not quite exactly what I mean... I've resorted more to using particle motion to drive the velocity of the fluid which seems to work out well. Wish there was a more intuitive approach but this seems to reda with what I am trying to do I guess.

Would be nice to have some kind of influences on the fluids to try and really do abnormal behaviors. I know this kind of defeats the purpose of physically correct smoke/fire, but say you wanted the smoke to bend and twist around itself as it rose from buoyancy? Not quite as easy to simulate (that I've figured out at least). Using curve and surface flows with particles seems to help drive that, but its not great...

07 July 2008, 11:59 PM
Yeah its really differcult trying to get little eddies and unique swirls within the fluid. I would probably go with using turbulence fields on particles and setFluidAttrs on position to emit density and temp, though Ive never tried it before. Maybe you could use lifespan to control temp emssion so it stops emitting temp. Ive never been successful at using just fluids alone.

07 July 2008, 12:07 AM
Yeah thats pretty much exactly what I am doing right now. It is working pretty well, but.. Could be WAAAAY more intuitive. I'm considering trying to wrap it into some kind of MEL tool for fluid usage. We'll see.. There is a lot of possibilities, just kinda redundant to be using particle dynamics to drive fluid dynamics (if that sounds right?) :)

I actually am pretty proficient with fluids. I understand them very well and use them quite frequently, but in the sense where you want fluids to do "un-fluid" behaviors, yet still have that fluid sim going... it can get odd.. If that makes any lick of sense :)

07 July 2008, 12:21 AM
Theres a tool on Highend called voxelMaster, I dont know if you are aware of it but it does the particle to fluid emission thingy although Im guessing this method isnt that hard for you to set up. Can you let us know what kind of problems you are running into or where it is lacking? What I mean is, is this method worth pursuing and does it have potential here?

07 July 2008, 12:35 AM
It all depends on really what you're trying to do (haha, could that be anymore open ended?)o.. I think in terms of using particles over fields to drive velocity, it is a lot more "predictable" because you can physically see where the particles are, how fast they're moving and exactly what they're doing. When you start modifying the behavior of fluids with dynamic fields (which, if not careful, will blow your fluids apart) you not only lose the integrity of the fluid sim but its hard to understand exactly what you're going to get out of it. Particles playback much faster, fluids don't so this is where you can begin to see the waiting game happening.

I am going to check out Voxel Master right now, see what exactly it can do for me or speed up. Setting up the expressions isn't difficult, but tweaking values becomes redundant unless you setup custom attributes on a locator or elsewhere to change/keyframe them on the fly.

Something I wish you could do, that you currently cannot (unless you use particles which isn't what I am looking for) is fluid emission via a texture from an object.

07 July 2008, 12:47 AM
Hey Seth just an idea on particle control is obviously a curve flow object, with voxelMaster you may be able to setup several particle objects in one fluid....not sure. Also just had an idea for fluid emission from file color......colorAtPoint here using -su -sv? I dont know just throwing some ideas out there. Anyway gtg to lunch let us know how you go :)

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