[Feature] Sand (granular) simulation: loose grains that roll and pile

[ryichando]

Motivation

The solver currently handles shells, solids, and rods, but not granular media. Sand, gravel, and similar piling/pouring effects are common in animation and product visualization, and there is no way to produce them today. Adding a granular body type would let users simulate grains falling, rolling, and piling under gravity with frictional contact, while still interacting with the existing shell/solid/rod objects in the same scene.

Proposal

Add a sand body type: a collection of loose spherical grains (a faceless point cloud) that the solver advances under gravity with grain-grain, grain-wall, and grain-object frictional contact. Grains should roll, not just slide, so piles form at realistic angles of repose.

Suggested user-facing surface:

• A SAND group / object type.
• A way to turn a closed mesh into a particle cloud (volume seeding), or to feed a point cloud directly.
• Tunable parameters: grain radius, particle mass, and friction.
• Grains collide with existing shells, solids, and rods in the same scene.

Alternatives Considered

• Approximating grains with many small solid/shell bodies. Impractical at grain counts and does not capture rolling/piling cleanly.
• Doing granular effects in a separate package and compositing. Loses the two-way contact with the cloth/solid objects already in the scene.

Additional Context

Requested as a granular capability to complement the existing shell/solid/rod support, with two-way coupling to those object types.

Contribution Agreement

• I confirm that any code, patches, scripts, attachments, or other copyrightable material I include in this issue may be used, reproduced, modified, and distributed by this project under the Apache License 2.0 or as otherwise described in CONTRIBUTING.md.
• This is a feature request from the community (please provide a reference below).

Community Reference

No response

[ryichando]

This is implemented. Will be available in the next release.

sand-50.mp4

[recappingdude-code]

Ryoichi is doing god's work with this project.

I suppose this is done using the SPH granular solver, if yes, I would like to ask if it will support clumping of grains as an adjustable option (sort of like the attached image)

[ryichando]

This is not a SPH sim. It's a purely point-point contact model known as DEM. We chose this model because it's a straightforward extension.

Clumping is left for future work, but probably needs advanced research unless we switch to MPM (needs extra cost, exact point-point interaction could be compromised).

[ryichando]

A follow-up: I attempted to have a recent LLM implement this, including fully autonomous, unattended research. It did not succeed.
At this point, I believe active research is required. That would require explicit permission from the company, and that permission is not likely to be granted.

[ryichando]

Deployed in https://github.com/st-tech/ppf-contact-solver/releases/tag/addon-2026-07-01-0327 and https://github.com/st-tech/ppf-contact-solver/releases/tag/2026-06-30-20-45

[recappingdude-code]

Deployed in https://github.com/st-tech/ppf-contact-solver/releases/tag/addon-2026-07-01-0327 and https://github.com/st-tech/ppf-contact-solver/releases/tag/2026-06-30-20-45

legend, can we perhaps get some documentation on how to use this? preferrably in the video documentation as it's the best way to convey information?

[ryichando]

I plan to create a formal tutorial video. For the time being, please use this a quick demo:

sand-box-quick-80.mp4