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[Jan Stránský <question238696@xxxxxxxxxxxxxxxxxxxxx>]

Question #238696 on Yade changed:
https://answers.launchpad.net/yade/+question/238696

    Status: Open => Answered

Jan Stránský proposed the following answer:
Hi Lingran,

this is a famous problem of explicit DEM methods :-) in general it is not
possible to decrease time step "while not change the physics". The critical
time step depends on particle size, mass, and stiffness, so changing these
parameters can change the critical time step. If it "change the physics"
always depends on what you want to simulate, what results you expect etc.
etc. For example for quasi-static simulations, the particle mass should not
influence very much the results, so you can increase particle mass to
increase time step and the quasi-static physics is almost not influenced by
the mass change.

If the problem is only for sample preparation, you can try
pack.randomDensePack with spheresInCell parameter [1]. In this case, a
periodic sample is prepared and copied in the required space. So it is
relatively quick method, but resulting in different packing than gravity
deposition.

cheers
Jan

[1] https://yade-dem.org/doc/yade.pack.html#yade.pack.randomDensePack



2013/11/5 lingran <question238696@xxxxxxxxxxxxxxxxxxxxx>

> New question #238696 on Yade:
> https://answers.launchpad.net/yade/+question/238696
>
> Hi, all,
>
> About 15 years ago, a girl did an impact experiment of a boulder impacting
> onto a soil layer, now I want to reproduce her experiment by using yade.
> The problem is that her soil layer is quite big, to respect the reality,
> the numerical sample will have millions of particles, and the time step
> will be as small as 1e-8, thus the sample might never be prepared by
> gravity deposition.
>
> So my question is: how could we increase the time step while not change
> the physics? I did some two particles impact tests, it turns out playing
> with radius and density (keep mass constant) could increase time step, but
> the contact forces will also be changed, not good. So, any other ideas?
>
> Second question: Does somebody use viscous damping of
> Law2_ScGeom_MindlinPhys_Mindlin()? This contact law is said to be mature,
> but is it proper to be used in dealing with dynamic problems?
>
> Thanks.
> Regards.
> Lingran
>
>
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