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AiyaPK

Setting up for FEM destruction

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Hi,
Quite new to using solids for destruction.
I have a flying torus smashing into a stationary nuclear cooling tower (a modified tube) that's seated on the Y plane (no points below 0).
Used the shelf tools 'fracture solid object' on both, and set up initial velocity on the torus.
Things smash and collide, all cool....

My question is, what is a typical workflow for setting up objects for FEM destruction. More specifically:

1) The solid embed sop remeshes the tube, but some of the points are now below the ground plane collider. So at the start of the shot, the ground plane bumps the bottom row of points (or tets I suppose) upwards. How could I have it setup so the points at the bottom just start at y=0?

2) The tower just collapses as the time goes. The stiffness doesn't really do much to stop it either. Is this a matter of setting up target constraints and turning them off right at the point when the collision happens?.... but wouldn't that just cause the tower to start collapsing on itself from that point onwards?

3) Unrelated to this specific setup, but say I wanted to sim a car collision w/ curmpling handled by fem. Not every piece of the car is suppose to crumple, so lets say the wheels and the axles, how would I keep them w/ the deforming car? Is this also a case for constraints?

W/ RBD constraints/destruction, we could manually set up constraints and such (thus setup takes a lot of time), I was under the impression from other people that setup time for FEM destruction should be a lot quicker? I know that sounds like a harsh over generalization, but I kinda want to see exactly where in the spectrum FEM falls into since I haven't had much experience setting it up

Thanks!

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Kinda figured out the answer to #2 by changing the fracture threshold and also varying up shapestiffness attribute.
However, in doing so, I noticed that adding shapestiffness as a primitive attribute doesn't work. But adding it as a point attribute does?.... From the docs I was under the impression that shapestiffness should be a prim attribute....

Still haven't worked out the answer to #1 yet... though still messing around w/ my test scene. I initially tried wrangling the points below the ground plane to just have a @P.y of 0, but that ends up screwing up the sim entirely.... not sure what's going on there yet...

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So for the ground plane collision issue (#1), my solution so far seems to be manually setting the 'pin to animation' value to 1 for the 'base' points so they just don't move...
Using this as my equivalent for "active" attribute for RBD packed prims.
Seems to work so far... 
Originally I was trying to manually crank up "targetstrength" point attribute but it doesn't seem to do anything, which is when I decided to just use the pin to animation.
Will look into targetstrength some more later to see why it's not working...

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