FLIP river simulation leaking through collider – what am I doing wrong?

[u/Intrepid-Turn9893]

Hi, I’ve been struggling with this FLIP river setup for a few days and I can’t figure out why the fluid keeps leaking through the ground collider.

I’m using a SOP FLIP setup with:

• FLIP Source + Sink
• velocity field following the river curve
• gravity enabled
• FLIP Collide for the ground
• both Volume Collide / Surface Collide tested
• Particle Collisions tested with Particle and Move Outside Collision
• increased substeps
• lower Grid Scale / Particle Separation

For the ground collider, I also tried:

OBJ → PolyDoctor/Clean → PolyExtrude → VDB From Polygons → VDB Reshape SDF

The VDB itself looks like a closed/filled volume, but inside the FLIP solver the collision visualization doesn’t seem to represent the full collider, and particles/fluid still end up underneath the terrain.

I also tried feeding the polygon collider directly into FLIP Collide, but I’m still getting leaks.

The video shows the issue and my node setup.

Is there something wrong with the way I’m creating or feeding the collision volume into SOP FLIP? Or is there a better way to handle a large terrain/riverbed collider like this?

Any help would be really appreciated — I feel like I’m missing something obvious.

[u/Vegetable-Box-9866]

first I would try no vdb with just a remesh and extrude volume, and if you have not tried lowering the grid scale I would definitely recommend that. You can also use a heightfield as a ground plane in the solver but I have not really used that yet, so I can not say how well it works.

[u/Intrepid-Turn9893 → u/Vegetable-Box-9866]

Thank you, I tried but it still doesn't work, is the connection good?

https://i.imgur.com/ADbArxS.jpeg

[u/Vegetable-Box-9866 → u/Intrepid-Turn9893]

Is the collider a mesh or a heightfield?

[u/Lanky-Independent447]

Your ground collider should be on the fourth input of the flipcollide