yade-dev team mailing list archive

[chiara modenese <c.modenese@xxxxxxxxx>]

On 28 April 2010 19:44, Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx> wrote:

>
>
>> 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..
>>
>>  We could compute incrementally. However, I don't see any advantage while
> I see two drawbacks.
> (1) It would take more time : incrementing MUST be done at each step, or
> you miss some work done and all subsequent results will be missing this
> part. OTOH, you can compute elastic energy only on demand (say, each N
> iterations) with total equations.
> (2) It would result in accumulating rounding errors, so better avoid it IF
> possible.
>
> For me, monitoring energy or work is almost the same. Like if you were
> studying motion, you could monitor velocities or positions, they are just
> different orders derivatives of the same function.
>

Elastic energy is fine as it is computed now, but it is not the same as the
work done. It would be the case only if the system was conservative. It is
not because we introduce approximations integrating numerically the
equations of motion. Of course, as the time step reduces the work done
becomes much closer to the elastic energy stored in the system. The
difference between work and energy, in this case, can explain why the system
could become unstable (e.g. it could explode) if no energy dissipation
(through friction or damping) is present.

Chiara




> Bruno
>
>
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