smooth out scalloping? how do?!

[kleer001]

I have a large smooth object with tiny pits in it that small slow particulate is rolling over. And I'm getting these ugly lines, scallops are tasty but not good to look at. This seems to be where the RBD volume is stepped. I already have the uniform divisions at 150 and that's taking several minutes to create (ugh, too long). How can I get smooth yet detailed collisions in this context?

 

My volume collions on the flipsolver is a

velocity scale of 1

velocity type = Point

Surface Extrapolation = 0.25

Volume Fraction Method = Tetrahedral (looking at the manual this should be "Voxel Face Area")

 

I'm also turning up Volume Motion Smoothing from the default 0.3 to 0.6.

 

Can I use a VDB with FLIP? I think I saw that somewhere.

 

Any other ideas? Halp.

[bandini]

Yeah, you can use VDB with flip, but that is probably not what is causing the problem. To use VDB collisions, use it in the velocity update input (source volume dop set to collision). Make sure to invert the density channel and make sure vdb volumes are named correctly (collision and collisionvel). Check your collision representation in the flip object guides - if that is stairstepping, then you need to either smooth your collision volume or sample it at a higher resolution (collision separation on the flip object). You can also try decreasing the grid size for more accurate solves, with respect to particle motion, but this comes with a large hit to performance. If your collision volume is smooth, and you still see those lines, it could be a substepping issue...

[kleer001]

Sounds like some good ideas.

How do I smooth my collision volume? Do I need to crack open my object and insert a volume smooth SOP ?

[bandini]

If you are using vdb, just use a vdb smooth sdf sop. Do all smoothing before bringing your collision into DOPS. Remember that your collision volume is sampled into the collision field, which is built at the grid resolution specified by collision separation. Having a great collision volume, but high collision separation will downsample your collision representation. Conversely, having a low res collision field from SOPS and then sampling it with a low collision separation will give you a very stair-stepped collision volume in DOPS.

[kleer001]

The solution is just use a higher rez collision object.

[ryew]

Yeah, but as Adam advises, probably best to go with VDBs to make it quicker. 

 

VDBs have become my go-to for Pyro sims, so I'd definitely recommend trying them out in your FLIP sim.  I read them in as proxy volumes for Static Objects plugged into a Static Solver.  Much faster than using the old fluid source nodes.

[kleer001]

I hear yah, it sounds great, but I never got VDBs to work correctly for an animated object. I need the particles to stick, and with an animated surface you don't get that.

 

 

Yeah, but as Adam advises, probably best to go with VDBs to make it quicker. 

 

VDBs have become my go-to for Pyro sims, so I'd definitely recommend trying them out in your FLIP sim.  I read them in as proxy volumes for Static Objects plugged into a Static Solver.  Much faster than using the old fluid source nodes.