XM Magdalena 3D print, GGeorgy (3D)
LC #42 Pipers Alley

View Full Version : Water gushing

03-30-2011, 03:12 PM
Hi, I want to try high-velocity water gushing out of a mouth like the one in the reference (instead of fire), I increase the number of velocity in the particular direction but it seems quite fake and less convincing. Can anybody give me advice to kick start this? Thank you


03-30-2011, 06:51 PM
If you have very large velocities coming out of the mouth, you may have to increase the number of substeps at the top level DOP Network node. I don't set the min and max substeps on solvers unless I have something specific I need to sort out. Most always set the substeps at the top level DOP Network node so all the solvers march to the same beat.

Sometimes increasing just to 2 substeps is all that it takes to get a better source emission of fluid and the velocity should be more accurate.

If you can post a file, that would be great.

03-31-2011, 01:47 AM
hey thanks for the advice. I will try to put up a file asap.

04-04-2011, 04:40 AM
here is the test file

04-04-2011, 04:41 AM
a very, very simple test file

04-04-2011, 03:26 PM
Lots of things to cover.

Don't use Gravity as a force to push your fluid in a particular direction. Best to keep gravity at defaults going down in Y using 0, -9.81, 0. You can apply additional global forces to any simulation object but not for emission velocity.

You have two fluid sources in your network: Pump and Source emitters. Btw these are both Source Apply DOPs that have their Relationship set differently with the Fluid Solver. Just need one. I removed the Source Apply DOP that was set to Pump.

All you need to do to get initial velocity on your source is to add a "v" velocity point attribute to your emitter geometry using a Point SOP. I changed the source geometry to a polygonal sphere from a primitive sphere. Per point velocity attributes are added to the sphere in the correct orientation. In your case this was the X axis. This allows you to parent this emitter to your character's mouth and as the head animates, your emitter will as well and the initial velocity will follow along as it is pegged to the emitter geometry parented to your head and is transformed correctly. I set this up in your scene parenting the sphere to an animated null.

One of the main keys to any successful fluid simulation is what I call noisy emitters. Not only is the source volume made noisy, the source velocity has some additional noise added to it. You can add noise in the Apply Source DOP which I did. I built you a nice point velocity VOP SOP to add initial velocity to your sphere with animated noise and flare. Just copy-paste whenever. Turn it in to an asset if you wish.
Another thing I like to do is to shape the emitter to match the emission shape look I am after. A sphere rarely gives me the emission shape I like. Shaped tubes or rounded boxes work better for me as fluid emitters.

See the attached hip file. I added notes to the emitter object's SOPs and the DOP network for what I changed. Not much really. It's all in the initial velocity of your emitters. That was your only real emission.

watergush_jw_v001.hipnc.zip (http://forums.cgsociety.org/attachment.php?attachmentid=160857&stc=1)

Oh and here's a tip. Always us the Technical Desktop. In the preferences set this up as your default desktop. It just helps you see the entire landscape of Houdini better what with the persistent Tree View and the Details View always ready below the viewport in a stow bar.

04-04-2011, 03:35 PM
I check out your hip file and it was awesome. I shall dive in deeper to check things out. Thank you.

04-06-2011, 03:10 AM
oh, there is this part where you added a point velocity attribute to source, may i know where is it? I cant seems to find it.

04-06-2011, 09:15 AM
I also have another question, is that when i wanted to scale the container (if I am not wrong, under the autoDOPnetwork > fluid node > size) it will somehow affects the entire simulation. Is there anyway to fix this? Thank you

04-06-2011, 08:13 PM
oh, there is this part where you added a point velocity attribute to source, may i know where is it? I cant seems to find it.

If you dive in to the emitter SOPs, you can enable the display of velocity attributes. Just hit the "d" key in the viewport and turn on the velocity display in the Custom area. Now you should be able to see the velocity attributes on your tube geometry.

As for seeing the velocity attributes in your simulation, go to the fluid Fluid Object DOP and in the Guides > Visualization tab, turn on the display of the Velocity tails.

04-10-2011, 05:51 AM
yes, found it. Thank you.

04-10-2011, 06:00 AM
Hi, here is the re-did file. I like the head of the water blast and I also added motion blur for testing fast action flow. Thank you.

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