Hello everyone. I'm facing a problem with a scene here with houdini. I've imported a cached alembic animation, now i want to get fluids to interact with it. I created a box with the shape i wanted the fluid to have and converted the colliding geometry from alembic to polygons. I checked the normals and honestly i can't figure out why isn't the fluid colliding with the tupwerware. Tested the same settings from scratch in another scene and it works.. Can't figure out what am I doing wrong here. Can you guys help me? Thanks…
I'm attaching the file here so you can better help me. Thanks.

Collisions against Alembic delay load primitives doesn't work. You need to unpack the alembic archive with the Unpack SOP.

Import your alembic primitives using the main File > Import > Geometry option instead of the File > Import > Alembic option as you did.

By importing the alembic archive with the geometry import, it creates a single object with a single Alembic SOP making unpacking with the Unpack SOP trivial.

When you unpack the alembic archives in to polygons and polysoup primitives, you need to ensure that the Primitive Normals (not point but primitive) point outward by toggling the display of prim normals on. If they point inward, collisions won't perform correctly. Just apply a Reverse SOP to reverse the primitive winding and flip the primitive normals.

It is common when importing geometry from Soft/Maya/Max with their opposite winding order of primitives to cause inward facing Normals. Again just append a Reverse SOP.

Now you should have good collisions.

I am going to try that.. Thanks Jeff… Glad I learned something new today…
Houdini Rocks… XD

Almost there Jeff.. Or not.. I mean. What is the correct way to unpack this stuff.. If a import it as an alembic geometry and add an unpack sop under that, either i get the all thing in one object (converted i guess) or i pick the path for a specific one. Do I have to do it for every single object in the scene?
Also, picking just the Ice Cream Box didn't work, or did.. I mean. It's weird, because the fluid doesn't collide with the box unless i reverse the normals and then the collision is all wrong because it's colliding with the internal faces, not the opposite.. I'm getting stuck with this.. :C

Ahh ok it sounds like the alembic geometry is quite complex, with internal nested objects. If you can elaborate in more detail or provide a bit of the geometry as an example if you can. The attached scene file did not come with the .abc file…

The Alembic SOP which imports the hierarchy will by default bring in the entire hierarchy. There is an option on the Unpack SOP to also create Groups for the various packed primitives either by shape node or transform node. I guess use shape node for shorter names. Enable that.

When you unpack the alembic archive, you should have the various pieces retain their group membership. It's nice having packed primitives as you still have a collection of ploys in a single polysoup primitive. It depends on how it was authored originally.

In the end, good fluid collider geometry should be manifold or “watertight”. This means a single enclosed object with shared points, no holes, no self-intersections. You “can” construct sdf colliders from several manifold objects that intersect, even ones that envelop others. Inspect the sdf volume to make sure a proper surface is constructed. This can construct a nice sdf volume representation for the flip fluid to collide against. Flat surfaces never play nice as colliders. They will need to be extruded in to a volume such as ground planes or flat surfaces.

Again, always check the primitive normal direction of the poly faces to ensure they point outward. If not, fluid will enter your collider then do strange collisions once inside.

Hmm, still not getting it. Either I don't know how to work properly with the unpack SOP or there's something else I'm missing. Here's the Alembic file attached. Can you please look into it and help me? I'd be most thankful….
Note the animation only starts on frame 343 and lasts approximately to frame 760 or so… Thank you so much in advance…