erodding vdbs with pops

[rich_lord]

I'm trying to set up an erosion effect using vdbs. I've found a few example files and have managed to set up the effect. It uses a vdb combine in a sop solver. This cuts away the surface and updates the collision of the vdb.

However, I'm not getting any run-off. The particles just cut straight through the vdb and make holes. I don't know what to change to stop the particles doing this and make them flow down the surface.

I can achieve this effect with polys, by pushing the geo along its normal, but id like to get it to work with VDBs also.

Any idea what I need to do to make my setup work better? Thanks!

erode.hip

Edited June 25, 2016 by rich_lord

[BRZ32]

The normal you're looking for is called the volume gradient. 
https://www.sidefx.com/docs/houdini14.0/nodes/vop/volumegradient

If you calculate the volume gradient each frame you should be able to do exactly the same thing you did with the poly version.

 

[rich_lord]

Thanks BRZ32. Yeah, I could grab that and use it as a force. I was hoping the particles would automatically run down the surface, like they do before I start eroding it. 

Alot more points with much smaller diameters worked a little better.

I'll keep experimenting!

[BRZ32]

The solver you have going is exactly right but there isn't a force strong enough pushing them along the surface to keep it from just sinking. if you used the cross product of that gradient, it would be a force pushing along the surface rather than just away from it.

[TheDude]

I haven't looked at your hip, but if you want 0 resistance to make the particles flow then you could try using a projected path erosion from the particles velocity