Passing particles through geometry holes

# 1 07-10-2005 , 07:42 PM

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I have a grate that I want smoke to filter through. Right now I have the fluidShape resolution:size ratio at 6:1. It works, but bogging down on my system. If I make the res. much lower, it seems the particles become too big to pass through the grate holes (geometry is already as big as container will allow). Is there a way to make the particles smaller at low fluid resolution?

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# 2 10-10-2005 , 11:28 AM

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Decrease your gravity to zero and increase your bouyancy. Also check the viscosity of the fluid. Make sure it's set to zero. The fluid should come through even with a low res fuid container. Are you using a volume emitter? You should. One last thing I can think of; turn off all turbulence and discipation and dispersion..

One more thing. Maybe the fluid IS coming through but you have your opacity ramp set wrong. Let the sim run for a while then play around with the opacity ramp. The fluid might be coming through but it is so thin that it just isn't visible. Adjusting the opacity ramp could make it visible again. You might want to turn up the density scale. I think it's default is .5 . Try turning it up to 1 or higher.

One more thing. You could turn the heat up on your fluid emitter(s) then turn the bouyancy for the temperature up also. Let us know how it turns out.

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# 3 11-10-2005 , 02:06 PM

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I agree with some of what Velusion is saying

temperature is only used if you have some sort heat(or cold) source, so it depends on what you're doing... Just what kind of effect are you doing? Smoke, fire..??

Your system will get bogged down, there's no way around it, even on a workstation it will bog down, thats the price of having good looking fluids and you have to be willing to make that sacrifice sometimes. There is such a thing though as going too high of a resolution, and for smoke you don't need high resolutions...

You don't need to touch your density scale, but you do need to fool around with your opacity ramp and raise the boyancy of your density, but leave the gravity at its default 9.8....also put a damp of .005 on it, its always good to sort of dampen things to "keep it real"

The opacity ramp... From left to right is 0 to 1 outside to inside and how many points you add depends on what you're doing. Transparency and Opacity go hand in hand for this particular effect.

you need some sort of dissipation on the density, for this I recommend about .15... you need a little bit of turbulence to throw and mix around, .03 would be good for this, any more than .1 and it will throw your fluids around too much....

Now depending on what you're doing, you will set the resolution accordingly, don't forget that you can use the normal scale tool also, you just have to raise or lower your resolution as needed, but you can also use extend fluids, that also depends on the situation.

Just what effect are you doing with fluids? Smoke? Fire? Dry Ice? .....

Neil
www.delta3d.com
https://twitter.com/frescalus

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# 4 11-10-2005 , 03:29 PM

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The point is that Fluids are very complex. Nothing I wrote is incorrect nor is it absolute. They are things you can try. Be careful when people tell you "this is what you MUST do".

Another thought: You can add fields to the sim to do things like create newton fields, turbulence, vortex and a few other things. these are a little tricky to figure out but they work very well.

Here's a like to an explosion test I did that used a mild vortex field.

test explosion 500kb quicktime file

Last edited by Velusion; 11-10-2005 at 03:34 PM.

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# 5 11-10-2005 , 03:40 PM

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maybe we should see what kind of fluid effect he's doing first, it would give us a better idea what he's doing when we go to aid him

Neil
www.delta3d.com
https://twitter.com/frescalus

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# 6 13-10-2005 , 05:18 PM

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Thanks guys. I was making a sort of dry ice smoke. I had a -9.8 gravity and a volume field blowing it up and out of my container grate holes. Velusion, I'm pretty sure I had all the settings you mentioned tuned correctly. But until I made the voxel size smaller than the holes, the particles didn't escape. Also, at low resolution, the fluid would show through the walls of my container. My concept of fluid collisions is that the voxel size also determines the geometry bounding box resolution. Am I confused? I also struggled with particle lifespans. It seems fluidEmitter particles don't have this, only dissapate. Is that right?

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# 7 13-10-2005 , 07:33 PM

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Fluid life span kind of doesn't exist. What I mean is that the fluid is always there but depending on how you set your opacity graph, it can have so little density that you can't see it. Even if you make a simple whisp of smoke that vanishes because of turbulence, it's really still there but it becomes so dissipated that you just don't see it. Did you know that the fluid container is actually COMPLETELY full of fluid all the time? It is.. You're right. Dissipation does kind of control the "life span" in a way but there are other factors.

Collision problems happen with my fluid sims if the tesselate isn't set high enough. When you create a collision between the fluid and an object, a geo connection is made and shows up in the attribute editor. If you click on it, you will see where you can adjust the tesselate. I always have penetration problems with very thick fluids. I'm not sure why. Maybe voxel resolution does have something to do with it. Thanks for the idea.

Post a clip when you get it all figured out!

Last edited by Velusion; 13-10-2005 at 07:39 PM.

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# 8 13-10-2005 , 08:06 PM

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you shouldn't really need a very high tesallation value(I use 1000) for collision objects in fluids. One of the problems with collision is that the emitter is a volume emitter and not omni, omni technically doesn't have a problem with collisions because the fluids flow freely, but a volume emitter for some reason does because there isn't a wide enough space for the fluid to flow freely(even if you resize the volume emitter, there's still a problem) and it won't matter how high you set the tessalation.

As for your penetration problem Vel, if you're using volume render its just a matter of setting your opacity graph with transparency, but if you're using surface render then modifying the surface tolerance(doesn't really do much of anything) and threshold would help reduce that, though its touchy and hard to work with, so its a damned if you do and damned if you don't situation. The fluid resolution may help some, but you again get expensive with higher resolutions and really the cost vs effect isn't worth it.

Neil
www.delta3d.com
https://twitter.com/frescalus

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Passing particles through geometry holes

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