yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

2010/3/25 Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>

>
>  (As said, I never used that code; what I was driving at was to get
>> comparison of critical timestep given by PWaveTimeStep and
>> GlobalStiffnessTimeStepper.)
>>
>>
>>
>>
> This is another interesting discussion I wish we could have when you were
> here...
> Actually, the relation between the two is relatively weak.
> In short, they scale the same way, but the factor between them depends on
> (always the same set) porosity, contact anisotropy, PSD,...
> 8 contacts per grain or 4 contacts per grain really means different
> critical timesteps for the explicit scheme. It is accounted for explicitely
> in GlobalStiffness since it is a sum on all contacts (you will find a factor
> sqrt(2) betwween the dt's), in PWave it is just ignored.
>
> The good point of global stiffness is it is dynamic (changing with packing
> state), so it can really be as close as possible as the exact current
> critical value. Even if GS gives dt only 10% higher than PWave (it is in
> fact more based on what you put as default factor in dt=0.5*PWave), it is
> worth using, since GS doesn't take more than 10% in cpu time. The weak point
> is GS gives nothing when there is no contact, thats why I use both in
> scripts now. PW gives an initial value, and GS adjusts it dynamicaly once
> contacts are created.
>
> Bruno
>
>
BTW, Bruno do you know if this method to get the timestep that varies with
the global stiffness can be well applied also when we have a non linear
relationship between forces and displacements at contact? As in the
Hertz-Mindlin formulation, for instance. Do you think that in such a case
the critical time step should change or should be taken differently than
having a linear relationship?

Thanks for your opinion,
Chiara

>
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>
> --
> _______________
> Bruno Chareyre
> Associate Professor
> Grenoble INP
> Lab. 3SR
> BP 53 - 38041, Grenoble cedex 9 - France
> Tél : 33 4 56 52 86 21
> Fax : 33 4 76 82 70 43
> ________________
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