I've been playing around with the finite element solver, and I can't figure out a couple of things:

- What do ‘shell’ and ‘solid’ prefixes refer to in the attributes? Is ‘shell’ for all of the tetrahedra exposed to air, and ‘solid’ are the interior ones?

- How do I get different properties in different parts of the object? In my hip file, I'm trying to vary materialuvw across a small block, but it doesn't seem to be picking up the differing values.

Thanks!

The “shell” prefixes are for 2d geometry, such as polygons, that have area but don't have any volume.
The “solid” prefixes are for truly 3d geometry such as tetrahedra, which do have volume.
So the attributes with the “shell” prefix won't affect tetrahedra, only attributes with the “solid” prefix affect tetrahedra.

Your setup is correct. But the values you're putting in “materialuvw” won't work; they're set to (0.5, 0.5, 0.5) for all points. If you play the sim forward to frame 2, you'll see that the solver has a warning: “ignored 3602 tetrahedrons with degenerate rest or uvw coordinates”.

I'm guessing you're trying to set the directions directly, rather than setting uvw coordinates. However, the coordinates that you put into “materialuvw” should vary from point to point. That way, they're similar to UV coordinates, except that they're 3D. So you're not directly setting the directions, but you're specifying a different set of coordinates that determine the direction vectors that are shown by the UVW visualization.

I've attached a tweaked version of your file, where I've made material uvw coordinates that go around in circles around the z-axis. I hope this clarifies things.

Michiel

Great, thanks for the explanations; that makes much more sense!

Is there something that needs to be toggled in order for per-point, sop-level attributes to be used by the solver? I can set v for all points, but not on just certain ones. And whenever I set attrs like solidstretchstiffness or solidshearstiffness, it doesn't change the behavior of the results (whether I'm setting all or just some).

There isn't some sort of toggle I have to set right? I've tried setting it on points before and after the tetrahedralize sop, but in both cases, I don't see any changes. I must be missing something simple, but I can't figure out what it could be.

In the attached file, I'm setting attributes to 1 all over, and to 0 on parts, since it's a multiplier, as I understand it.

Thanks so much for the help michiel!

Figured it out: I needed to set the attributes before the tetrahedralize sop (I had them after). And I'd also set them to be point attrs, when they should have been primitive attributes.

Thanks for the help Michiel!