yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 28 April 2010 17:39, chiara modenese <c.modenese@xxxxxxxxx> wrote:

>
>
> On 28 April 2010 16:44, chiara modenese <c.modenese@xxxxxxxxx> wrote:
>
>>
>>
>> On 28 April 2010 16:19, chiara modenese <c.modenese@xxxxxxxxx> wrote:
>>
>>>
>>>
>>> 2010/4/8 Václav Šmilauer <eudoxos@xxxxxxxx>
>>>
>>> > I need the incremental formulation for the normal force in the contact
>>>> > law. Could you tell me how to do that? Should I simply used the
>>>> > normalVelocity component computed at contact as we do for the shear
>>>> > force? What about the sign convention? Should it remain the same,
>>>> > right?
>>>> Using relative velocity (it will be much easier than for shear, since it
>>>> is 1D) would be the simplest, it seems.
>>>>
>>>> Or if you want to go more precise, you could store previous normal
>>>> deformation, then compute the current one (total formulation), divide by
>>>> Δt to get increment and add it to previous incremental normal
>>>> deformation... Perhaps too complicated...
>>>>
>>>
>>> Hi,
>>> if I get the incremental displacement in the normal direction as
>>>
>>> dU(t+dt) = U(t+dt)-U(t)
>>>
>>> where U(t+dt) and U(t) are total formulation, it is fine or should I take
>>> into account the rotation of the normal?
>>> (btw, it is the incremental formulation that will permit me to calculate
>>> the potential elastic energy for the non linear elastic Hertz formulation in
>>> the normal direction..)
>>>
>>> thanks, Chiara
>>>
>>
>> Suggestion (x Bruno). Why do not we add the incremental formulation for
>> the normal direction (say as optional) in the FrictPhys_Basic law so that
>> the potential energy can be computed directly inside the go functor instead
>> of having an external loop as you did? Moreover as elastic energy is
>> computed now, it would be fine for the normal direction but you are also
>> adding the component due to the shear force without considering that sliding
>> could occur (so in that case you cannot more compute E simply as Fs*us, you
>> need the difference between the total energy and the plastic one). One more
>> reason to compute the incremental formulation in the normal direction.
>>
>
> Sorry sorry, the potential energy is computed in the right way (in fact I
> just realize now that if sliding occurs, the shear force would be simply
> equal to the maximum one). Anyway with an incremental formulation we could
> compute that energy into the go function, I think this is still possible.
>

To be more precise, we could compute incrementally the work done by the
springs in the systems more than the elastic energy. Almost in the same way
as we get the dissipated energy due to friction (it is not too difficult to
make distinction between work and energy if we think that work is defined as
a variation of energy, hence we get it incrementally). I just guess which
one should be monitored, if the work done or the energy..



> cheers, Chiara
>
>
>
>> Energy computations are not superfluos since they can help to understand
>> how the system evolves..
>>
>> Chiara
>>
>>
>>
>>>
>>>>
>>>> Cheers, v.
>>>>
>>>>
>>>>
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>>>
>>>
>>
>