Fountain mess

[virtualvision]

Hi All
Trying to get my head around Phoenix liquid and wondering if someone can help me tweak this.
The attached fountain is particles but I seem to be getting random sprays of water coming out of the jet stream.
I realise it must be gravity pulling some water down but it looks ugly. Any way to fix this?

The material is just white at this stage to demonstrate the problem.

I am also having trouble getting a velocity pass from the water. Is this possible? (Rendering with Vray)

http://www.youtube.com/watch?v=LPKlPt03cmc

[Ivaylo Katev]

hi,
can't determine the reason from the movie, would you attach the scene?
about the velocity - you have to export it, by default the simulation does not export the velocity.

[virtualvision]

Hi Ivaylo
I have emailed the file to phoenix@chaosgroup.com
I could not seem to attach it for some reason.

Thanks
Wayne

[Ivaylo Katev]

well, i saw the scene. there are two things that i think can be the problem: first you have zero for approach steps of the liquid simulation, set it to be 1. zero does not produce adequate simulation and the parameter can be zero only for some special purposes. the second thing is that you actually use the particles to force the fountains trajectory, and the particles produce liquid that becomes more and more along their path. i would recommend to produce the water directly at the place where now you create the particles and with the appropriate velocity (the discharge controls it) it will follow the same path as the particles.

regards,
ivo

[Ivaylo Katev]

and one more thing - will be much faster if you rotate the grid on 45 degrees, to avoid the huge size that is needed now.

[virtualvision]

Thanks Ivaylo
Had a play and it's getting close to what I am after.
So you should not use particle emitters using liquids?

[Ivaylo Katev]

i know that the particle emmiters are wide spread practice when simulating smokes and explosions, because the simulation is unpredictable and the particles are used as work around to achieve strongly determined route of the smoke, however for you target i would not use particles. the liquid jet will produce the needed rainbow-like trajectory, you have not to worry about it. and one more thing - the default mode for the particle sources is "inject", i suppose this produces the weird behavior, for liquids "brush" would be more suitable in my oppinion.

[virtualvision]

Starting to make sense. Alot of new concepts here for me sorry.
I have tried to get the velocity pass (for post motion blur) without any luck.
Sorry if it's in the help file but I can't find it. Could you outline the process for this please.

Also - Any reason why the simulation throws a wobbly when you reduce the grid size and the emmitter size?
I am trying to get a narrow jet of water and it works fine until you get to the smaller sizes.

[Ivaylo Katev]

did you export the velocity channel?
what you understand under "small grid size" is this small cell size (this means big amount of cells) or small count of cells (this means big cell size).
for narrow jet you need small cell size i.e. big amount of cells

[virtualvision]

The solution was:
-Don't use particles for liquid sims
-For small sources lower the gravity (there is a more accurate method but this is easy and it works)
-Velocity does not render out animation, only a single frame. The workaround from Ivaylo is below.

create a phoenix texture that exports the velocity. select the texture in some dummy material and shade a dummy object with it.
This will update the velocity channel before each frame and the renderelement should work. The reason of the bug is the lack of update of the velocity channel before rendering