yade-dev team mailing list archive

[chareyre <bruno.chareyre@xxxxxxxxxxx>]

This is mainly for Vaçlav.

I have two worries with the current code for clumps in NewtonsDampedLaw.

1/ Forces are damped based on the motion of each body. As a consequence, 
different contact forces on the same clump will be damped independently. 
Its a bit like damping separately each individual force applied on a 
standalone body. The very bad effect of this is that a body at static 
equilibrium can be moved out of equilibrium by damping effect (i.e. the 
exact opposite of what damping is supposed to do...).
The correct way to damp is to damp the resultant force/moment on a clump 
based on the motion of the clump.

2/ From what I see in the code, if a clump has bodies "i" and "j", I 
fear the integration loop could make something like (depending on the 
ordering of bodies):
 
on body i : clump->acceleration += i->force/clump->mass
on clump : clump->velocity += clump->acceleration*dt
on body j : clump->acceleration += j->force/clump->mass

so that forces on clump member j are ignored in the motion of the clump...

Is there something to prevent that? Are clumps always at the end of the 
loop?


Bruno
 


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