yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/4/20 Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>

> On the same line : the energy dissipated by Cundall's damping in
> quasi-satic conditions is negligeable. You find that the work input from
> boundaries equals more or less plastic+elastic work at contacts (tests with
> pfc3D, damping~0.2, frictional contacts, ~50k iterations in a triaxial
> test). It corresponds with the fact that Cundall's damping looks useless in
> _some_ quasi-static conditions, after Yade simulations and discussions with
> Gaël, Vincent, and Vaclav.
>

I was thinking, in fact, only to investigate the dissipation due to local
damping.

>
> |Δε|*|σ| sounds straightforward, but with du and df, and non-linear
> elasticty on both normal and shear, and plasticity for fun, I have no
> initial guess... Computing the energy dissipated in
> Law2_ScGeom_FrictPhys_basic is straightforward, for sure.
> On the top of that, there is the case when plasticity==true at time "t",
> and plasticity==false at time "t+dt". You have to decompose |Δε| into
> plastic and elastic on one timestep. Straightforward again with the *_basic
> law, but with Hertz? I have no clue yet.
>

No idea as well. At least I can start doing that with elastic law to see how
it works.
BTW, we mention here only damping and friction. But what about the elastic
potential energy? In the process of loading/unloading we actually increase
the energy of the system since we consider normal and shear contact forces
as constant at each time step (due to numerical approximation). I do not
know if this has an effect or can be investigated. Maybe it does not matter
too much, but it is still an energy contribution (although not really a
dissipation).

Chiara

>
>
>
> Bruno
>
> Václav Šmilauer a écrit :
>
>  Put a "Real plasticWork" in the functor. Compute the energy dissipated at
>>> one contact on time increment dt, and include  a "plasticWork+= ..." in the
>>> if(plasticityCondition) bracket of the functor.
>>> Don't ask me how to define plastic work at contact with an elasto-plastic
>>> Hertz-based law... ;)
>>>
>>>
>>
>> I think since the formulation is incremental, you can use |Δε|*|σ| for
>> energy dissipated in plastic slip by Δε at plastic stress σ...?
>>
>> Generally, there is no unified function for dissipation. You could,
>> though, sum kinetic energy of particles, potential energy (if there is
>> some potential field), and subtract cummulative external work (boundary
>> conditions). That should give you pretty good image of system energy
>> evolution, including damping, plasticity and dissipation by numerical
>> entropy ;-)
>>
>> Cheers, v.
>>
>>
>>
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>
>
>
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