I’m struggling with a FLIP sim where the water volume keeps shrinking over time.
I start with ~6 million particles and they slowly disappear as the simulation progresses.
I’ve already tried many things but nothing seems to stop the volume loss.

Here’s what I’ve tested so far:

Increased substeps (global/substeps 1–2)

Enabled Enforce Particle Separation (different iterations, rates, scales)

Tried different Velocity Transfer modes

Disabled Particle Reseeding and tested with/without oversampling

Checked VDB resolution on FLIP Collide to avoid leaky collisions

Tried using Ground Plane vs. FLIP Collide for terrain

Adjusted Narrow Band settings

Tested with/without Fluid Compress SOP

Disabled particle filtering / culling in Fluid Compress (Cull Bandwidth = 0)

Despite all this the FLIP still gradually loses volume or particles simply disappear.
It’s a waterfall hitting a still water pool, and the pool visibly shrinks over time.

Does anyone know what typically causes this kind of progressive volume loss, or have suggestions on what else to debug or check?

Thanks! using houdini 20.5.278

maybe this will help

https://www.tokeru.com/cgwiki/HoudiniDops.html#flip [www.tokeru.com]

You might try increasing your max substeps on your flip solver. Having fast collision objects in a flip sim will sometimes result in volume loss. More substeps can help with this. In your case it could be because the water is moving quickly when it hits the collision object.