yade-users team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

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

>
> 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?
>>
>>
> If you assume small variations per step (i.e. no 2-steps bouncings with
> Hert-Mindlin), you can compute dt exactly the same way. All you need is to
> define dt with tangent stiffness : dfn/dun and dfs/dus for the current state
> of the contact.
>

I don't remember, did you write your law with tangent or secant stiffness (I
> hope french maths translate well...)?
>

Actually I defined the normal stiffness as secant and the shear one as
tangent. This because I was following PFC manual. But I see it is better to
get both stiffnesses as tangent (I will modify it). So once I do that I can
just pass those values to the GST, right?


>
> If you use tangent stifness, you have stritcly nothing to do to get
> Hert-Mindlin handled by GSTimestepper.
>
> If you use secant stiffness, you can still exploit the old useless
> intitialKn/Ks that remains in interactionPhysics, and which is currently
> redundant with kn. Let kn be the tangent and be used by timestepper, and use
> intialKn in you law  (and rename initialKn to say what it is in your law, no
> engine is using that anyway).
>
> How is HM working for you a.t.m.?
>


> Bruno
>
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