Self-collisions & mutiple-object collisions

[Ch0veS0uris]

Hello,

1. Is there some ways (or it is planned) to add self-collisions detection for a deformable object? Like for the torsion.py example, but with a rotation of 360°?

2. It is possible (or planned) to simulate multiple objects (rigid or non-rigid) with collisions?

Best

[gertjanvanzwieten]

Physical collisions are not planned as a built-in feature, as Nutils operates at the slightly lower level of numerical toolbox. But it does have some instruments that may be useful in the implementation of a collision strategy, such as locate. Multiple objects would involve maintaining multiple independent topologies, but you would need to program a strategy for these topologies to interact.

[Ch0veS0uris]

Thank you very much @gertjanvanzwieten. In addition, for one object (2D or 3D), could we define several domains (or "patches") with different materials properties (young modulus, Poisson coefficient, or thermal parameters)?

[gertjanvanzwieten]

Certainly! You can do this either by splitting your integral into several integrals to differentiate the integrands, or use your topology's indicator method to form parameters that take different values over the subdomains, so you can still write your weak form as a single integral. I notice that indicator lacks documentation, but it takes a single argument, either the name of the subdomain or the subdomain as a topology, and returns a function that evaluates to 1 on the subdomain and 0 outside of it.

Edit: in case your question pertains to the subdomains themselves, these can be defined using slice operations if your topology is structured (see the coil example), or using the select method (see adaptivity, note that the selection is element-wise) or if you use gmsh via physical groups in the .geo file.

[Ch0veS0uris]

Thanks again @gertjanvanzwieten for the tips :) . My question is indeed to define the subdomains on a 3D deformable object. So it would also be great to have a variation of the examples (platewithhole-nurbs.py or/and torsion.py) without hole, but rather with the materials properties defined for each subdomain.

[gertjanvanzwieten]

We're working towards a new release so that's absorbing time but I'll see if we can add an example of that kind, I agree it would be useful.