I've come across some strange results when trying to simulate fractured wood in H14's bullet solver. Compared to H13 it seems something might have gone awry in H14.

The geometry I am providing bullet is fractured wood fragments that explode when running through the solver. It appears collisions are interpenetrating and sending fragments flying off with high levels of velocity. I've tried adjusting scene scale, collision padding, substeps in bullet, and reducing the scale and number of the individual fractured pieces with no success.

I set up a test in H13 and the sim results are good considering it is handling long and thin geometry.

Attached are two simple test cases in both H14 and H13. H13 seems to handle the geometry not perfectly but with predictable results. H14 explodes the scene. I've checked over the collision hulls and can't find any issues.

Video results of tests:
H13 wood fracture results [drive.google.com]

H14 wood fracture results [drive.google.com]


I've been banging my head here for a couple days. Is there something I've overlooked in H14?

Any help is much appreciated! Thanks!

Please disregard this post. I realize now that I was only experiencing this issue on Houdini Daily Build 14.0.231. Works fine on the latest production build.

The H14 file crashes on me when I open it; if I disable all of the DOP nodes, and the assemble2 in the screenshot (which I have to do by opening Houdini in ‘Never Cook’ mode) I can view the scene.

Did those nodes get copied from the H13 file? Maybe they have some sort of corruption saved on some of the nodes, if they were indeed copied?

Thanks for taking a look Goldleaf.

Both networks were created from scratch in their respective environments. Not sure what is going on here but when I boot it up in the latest production build (14.0.201.13) everything works as expected.

Ah, I forgot to add, I was using build 223, linux-gcc-4.6

If a problem exists in the latest daily build but not in the production build, please submit a bug. Use the Support > Submit Bug link above.

The behaviour you're seeing appears to have been caused by a change made in 14.0.207:

Houdini 14.0.207: Fixed a bug in the Bullet library where angular momentum was not correctly conserved. This sometimes caused objects to exhibit unexpected behavior, such as a tall and thin object being unable to topple over.

I've reverted that change in tomorrow's build, since it caused some stability issues in certain situations (such as your attached file) that are more severe than the original bug.