Hi everyone :-)
It's probably my first post here, so I hope I'm writting on the right forum.

I'm making a waterfall creation animation, and cannot really figure out some stuff concerning FLIP fluids.
Thing is, as long as I don't modify my terrain object (which is a RBD collision object in this case), particles behave as expected (meaning, I can create, say a river, with no problems). But as soon as I animate terrain deformations (made by boolean operations, and some remeshing), they start to fly in all directions. I suppose it has something to do with collision settings in DOP network, but at this point, I feel I've tried everything I could, with no results.
I'm pretty sure there's something I don't know about, and something I'm doing wrong, as I'm just starting to play with FLIP fluids…

Any ideas, any help? :-)

This is a known bug in Houdini, it needs to be fixed. When you animated the collision object, unwanted velocity is introduced into the system. none of the standard velocity controls can remove that. You can drop down a drag force node, which does reduce the unwanted velocity, but it won't remove it entirely.

Oh, thanks for the info. For anyone interested, I believe I might have found a way around this. It is to convert the animated and deformed geometry to VDB,and then back to polygons. I have no idea why, but it works for me.
EDIT: No, not really. The problem still exists. I believe the particles behaviour is a little bit better, but it as well might be my wishful thinking…

You can use the volume source to plug a collision sdf right into the flip solver so you don't need the static solver, and then you don't introduce new velocity if you don't want to.

mkps, thanks, but it's not really helping. I suppose it's because you plugged the volume to velocity input in flip solver, particles start to behave unnatural (as in the picture below). They don't fall as they would in real waterfall, they stick to the ground.

Ok guys, I figured out a way around this bug (sort of). I don't see it as a solution to the problem, but if you'd like to make an animation similar to mine, it works (at least for me it does).

Thing is, the solver works great when importing static objects, or active objects, which are not deforming. RBD Packed Object node imports (or creates) an object at a given frame (by default, animation starting frame). So I figured I'd try to import one new object every frame, each of which would be another state of my deforming (animated) object from SOP. This way I could fake importing deforming object, using advantages of importing static one. Easiest way to do it was to use $F variable in creation frame field of the RBD Packed Object node. Only problem caused by that was that after say, 10 frames, you end up with 10 collision objects in the sim. So I createed referenced copies of the original RBD PO node, each for one frame of animation, and put them all into switch node (order of inputs doesn't matter). Switch node input select field is also driven by $F variable. This way… The animation finally works as expected!

Above described “solution” is not really very convinient to use. So I created a node network, neat, and clear, with relatively easy way to set number of needed frames. But… It doesn't work :-) See the attached file, if you can get it working, please let me know what have I missed this time creating it. Also, hope this workaround can help someone ;-)