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[Jan Stránský <question274242@xxxxxxxxxxxxxxxxxxxxx>]

Question #274242 on Yade changed:
https://answers.launchpad.net/yade/+question/274242

Jan Stránský proposed the following answer:
Hi Jabrane,

well, this is a good situation in my point of view :-) comming to our
previous discussions: Is gravity really important in your compression test?
If not (my opinion), just don't introduce it. The work done by gravity (for
normal materials) is (or at least should be) negligible to other kinds of
energies and works.

Concerning energies. Even if you run explicit dynamic simulation, I would
say experimentally the situation is almost static. Therefore the
contribution of kinetic energy should also not be very high. Usually also
such test is simulated without gravity (as it has almost zero effect).

To get feeling about different energies, you can create a mental
experiment, just one mass point (with mass m) on a vertical spring
(stiffness k) oscilating with certain amplitude "a" around equilibrium
position. After a short simple math you ends with maximum difference in
gravity potantial energy 2*m*g*a, maximum difference in potential elastic
energy of the spring k*a^2 and maximum kinetic energy (1/2)*k*a^2. For the
same amplitude a and for increasing stiffness, you wil get less and less
contribution of gravity. Normaly for triaxial test of usual materials,
"stiffness is much higher than displacements" and gravity basicle has no
effect.

Similar experiment you can do for static loading applying force F=k*u, u
being spring elongation. Then the change of gravity potential energy is
m*g*u and change of spring elastic potential energy is (1/2)*k*u^2. Again,
for higher stiffness the contribution of gravity derceases..

cheers
Jan


2015-11-16 13:46 GMT+01:00 Yor1 <question274242@xxxxxxxxxxxxxxxxxxxxx>:

> Question #274242 on Yade changed:
> https://answers.launchpad.net/yade/+question/274242
>
> Yor1 posted a new comment:
> Hi Jan,
>
> In fact when i delete the gravity from the code
> NewtonIntegrator(gravity=g,damping=DAMP,label="newton") ------>
> NewtonIntegrator(damping=DAMP,label="newton")
>
> it runs well and i don't have the oscillation.
>
> The question is how can i integrate the gravity in the code (without
> having oscillations) to calculate potential energy.
>
> Jabrane.
>
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