Hello,

I´m having a bit of a problem getting the Spray component of a whitewater
simulation to collide with geometry. Foam and Bubbles work well but
spray will just go through the defined geometry. For collision I used a
popcollision detect. See attached screenshot. The red particles are those from
the foam and bubbles that collide, but you also can see how the spray particles pass through. Any pointer in the right direction is much appreciated.

POP Collision Detect and Collision Behaviour DOPs just detects collisions and can be set to a few behaviours but as the tip below that parameter states, you need to use RBD objects to get bouncing.

So bypass or remove the Collision Detect and from the RBD shelf tool, use the Static Object tool and select your collision geometry object and Enter.

This will bring in a Static Object DOP and a Static Solver merged in to your POPs to get collisions.

Note that POPs will interact with the collision volume. Make sure that your Static Object DOP is constructing proper collision geometry. You may have to make the object a watertight manifold volume. Or adjust the resolution of the collision sdf volume to get more accurate collisions.

Took me a while to find some time playing with Houdini. Thank you, this
does the trick. It works now as expected. Actually I just coppied the static
solver and corresponding nodes from the fluid sim to the whitewater sim
wich is basically the same as you suggested. Thanks again !