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[Jan Stránský <question673023@xxxxxxxxxxxxxxxxxxxxx>]

Question #673023 on Yade changed:
https://answers.launchpad.net/yade/+question/673023

Jan Stránský proposed the following answer:
Hello,

> i set O.iter < 2 in way to have this velocity (18 m/s) only for the
first two iteractions, but even at 200 iters i still have the same
velocity.

if you set velocity and there is no need to change it (no contact or external force), it just remains constant (the case O.iter >= 2)
Also, the velocity remains constant in the case of contact if the body has blocked degrees of freedom or is not dynamic (default for facets)

> the surface pass through the soil without changing his velocity.
> I see the soil's spheres moving due to the impact, but the surface doesn't "feel" it. I already set the contact sphere-sphere and Facet-sphere, so i think Yade is setting at each iteraction the same velocity.
> IS it a problem with contacts? or is it a problem with the velocity definition?

Because facets in your simulation are not dynamic. To fix it, you have to do something like
###
f = facet(...,dynamic=True,fixed=False)
f.state.mass = 123 # (!)
f.state.inertia = (1,2,3) # (!)
###
I this case, each facet would move independently, so probably you should clump them together.
Also note that facet is considered as zero-thick element, so its mass and inertia is zero by default, you should assign a nonzero value.

Repeating Bruno, you could have find this behavior with a few spheres and a few facets. Consider first to build a very simplified simulation to understand all these Yade "gotchas"..
Also next time please try to provide a MINIMAL working example. E.g., saveFacets part of your script is not used at all..
Also next time please name your question according to your real problem, because "setting initial velocity" works ok according to your description :-)

cheers
Jan

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