General Flip Theory

Flip (standing for Fluid Implicit Particle) is a hybrid solver in Houdini. It calculates the movement of liquid using both volumes and particles.

Basic Flip Configure

You can download my FLIP configure HIP here:

KKConfigureFlip.hiplc

To create the basic DOP-level flip setup you will need the following:

1. Flip Source - flip source SOP
2. Collision Source - collision source SOP
3. DOP network
   1. Flipsolver
      1. Create “Voxel Size” parameter = particle separation * grid scale
   2. flip object - (also used for single emission)
   3. volume source - (for continuous emission)
      1. reference source from flip source SOP
   4. gravity
   5. static object for collisions
      1. set to volume sample
      2. put geo SOP into SOP input
      3. put VDB SOP into proxy volume
4. Particle fluid surface
   1. turn on smoothing filters
   2. transfer over UVs to mesh

Inside the FLIP solver I almost always turn on the age and id attributes, I don’t understand why these are off by default.

Substeps are key to getting a good-looking FLIP sim. I usually set my minimum and maximum substeps to around 10. This will take longer, but the results will be far better than those of lower substeps.