FLIP Collision Problem?

[Atom]

Hi All,

I have a simple FLIP setup of a flip tank created with the shelf tools and an impulse force. I also have collision geometry in the form of a tube. I want the fluid to rise up and remain inside the tube. I have set the object as a Rigid Collision object. I have tried Volume Based and Non-Volume based collision but nothing seems to work.

I have read that there are really two collision volumes in a FLIP sim and I can see the second one if I turn on the visualization guide inside the FLIP object. In my screenshot it is gold and wrong (with interfering cross bars). I realize this gold based collision object does not have enough resolution and thus us causing the problem, however, I can not find any parameters in my current node network that allows me to adjust the resolution of this secret second collision object. (why are there two again..?)

 

How do I set the resolution of this second collision object that is displayed by the Visualization system?

 

Thanks

ap_suck_fluid_through_tube.hipnc

Edited June 1, 2016 by Atom

[Skybar]

Don't turn off "Use Volume Based Collision Detection". Turn on Collision Guide for your Static Object, and there you see the problem with the actual collision volume. Not sure what you mean by secret second collision object - but the volume of the Static Object will get copied into the FLIPs collision field, and you can control it under the Volume tab on the Static Object.

[Atom]

I am working on a MacMINI today, which is not officially supported. Initially when I turned on the Collision Guide Houdini 15.5 would crash. So I left Collision Guide off and blindly set the Uniform Division to something very high, like 256 in my file. I have never really needed Uniform Division that high so I thought it was enough for a simple tube. I tried enabling the Collision Guide again to view the geometry and Houdini did not crash this time. I was able to see the problem with the collision geometry but even setting the Uniform Division as high as 512 I still see holes in my simple tube collision geometry.

 

I read an OdForum post from 2013-2014 that mentioned you could use Bullet for FLIP collisions. How would I enable that? Does this feature still exist in H15.5?

Inside the FLIP solver I see Velocity Type of Rigid, Point and Volume. Is this how I select what type of collision method is evaluated on the Static Object?

edit

.

.

.

Nah, after reading the help card, that aint it.

Edited June 1, 2016 by Atom

[rbowden]

If I am understanding this right, you are saying that the collisions don't look right on the torus object and the fluid isn't staying inside the tube like it should? If that is the case, check out the attached modified file. I have turned your torus object into a vdb and used the volume sample in the static object in dops to point to that vdb. With geometry like this, I have noticed in the past it is easier to get a cleaner SDF this way and you don't have to push your divisions through the roof on the static object to get it to work.

Turn off the collision guide in your static object and display the geometry if you want playback in the viewport to happen quicker. I left it on in the file so you could see the clean collision geo.

On a side note, this is some weird shaped geo you have going on here...

ap_suck_fluid_through_tube_RB.hipnc

[Atom]

Thanks Ryan, for demonstrating how to setup a Proxy Volume. I have never used that feature before. I think I prefer this method over using the Collision generation of the Static Object.

It is weird, I was just playing around with the impulse force and looking at it from above. It looked a lot like an organic tunnel and I thought if I could just take one still geo frame I could use it as an organic tunnel for a spaceship to fly through. Then I got draw into understanding how to make the collision object work better.

[Guest tar]

Using the 'Deforming Object' shelf tool automagically sets up a vdb Proxy Volume on the Static Object. Just turn off 'Use Deforming Geometry' if it's statik.

[Atom]

Cool, I'll have to try out that tool, I must admit I have not even come close to using all the tools yet.

I went ahead and installed the fill holes SOP Solver from the thin sheets fluid example file I found here on OdForce and it helped out a lot. It is essentially an additional particle separation system that runs inside an Attribute VOP connected to the post-solve of the FLIP solver. It helps smooth out the outer surface of fluid by keeping particle equal distance from one another.

Now I'm starting to see a better pathway for my ship to fly through, as well as some alternate routes for the enemy.

ap_suck_fluid_through_tube_thin_sheet.hipnc

Edited June 2, 2016 by Atom