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[Jan Stránský <question703901@xxxxxxxxxxxxxxxxxxxxx>]

Question #703901 on Yade changed:
https://answers.launchpad.net/yade/+question/703901

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hello,

> whats the difference between “GlobalStiffnessTimeStepper”and "O.dt"

GlobalStiffnessTimeStepper sets the time step (O.dt actually) "automatically" based on simulation conditions.
It can be very handy e.g. if you insert particles with different material etc., you just add them and do not take care of O.dt, which is set to a safe value.

Apart from letting GlobalStiffnessTimeStepper to set O.dt automatically,
you can set it manually.

You can combine both approaches (e.g. part of simulation this, part
that).

> It takes a long time to run the whole simulation.

yes, large-scale simulations might take long time..

> I wonder if I can set the dt equals to maybe 4e-6 or 1e-5 or even a
larger dt to save some time?

Yes, you can.
But probably it is not a good idea. You would save time in exchange for (possibly, likely) non-sense results.
Higher value than determined by the GlobalStiffnessTimeStepper could (most likely would) make the simulation unstable.

> Would it affect the stability or the data such as the contact force
between the particles?

Most likely yes.


To make the simulation faster, you can try to run it in parallel (multi-core).

Critical time step is determined by mass/density, stiffness and size of particles [1].
Based on your problem*, you can do some mass/stiffness/size tricks, but each of them changes the physics (!!!). Some more, some less..

* please provide more information, e.g. what particle size distribution
you use, what materials and laws, ...

Cheers
Jan

[1] https://yade-dem.org/doc/formulation.html#stability-considerations

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