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[Chareyre <question204014@xxxxxxxxxxxxxxxxxxxxx>]

Question #204014 on Yade changed:
https://answers.launchpad.net/yade/+question/204014

Chareyre proposed the following answer:
Hi Christian,

As long as the facets are not dynamic, you don't need to consider facets
in timestep definition.

PWaveTimeStep can't be directly compared to GlobalStiffnessTimeStepper
as you.
You can consider PWaveTimeStep as an order of magnitude of the expected
critical timestep (it at least scales correctly with sizes, modulus,
density). Since it is only an order of magnitude, it's usually
multiplied by a safety factor after trial and error for each type of
simulation.

GlobalStiffnessTimeStep computes the exact critical timestep for current
configuration, but it gives nothing as long as there is no contact, so
that it can't be used to define dt in the early steps of most simulations.

So there is not to choose between them, most scripts use both: the first
for early steps, the second to set dt to its maximum acceptable value in
the rest of the simulation (hence save time). Both work equally well
with facets.

Last note: nothing can replace your own tests. It is not uncommon to
read a "no it doesn't work" answer in this list when the thing actually
works (Yade code is so huge that nobody knows the entire code now). So,
when you wonder if something works, the best is to try it before asking.

Bruno


 


On 24/07/12 12:45, Christian Sommerfeld wrote:
> New question #204014 on Yade:
> https://answers.launchpad.net/yade/+question/204014
>
> Hi,
>
> i'm not sure if i have to use the utils.PWaveTimeStep() in my case. I want to simulate a facetbox which is rotating around the z-axes and enclosed by a pack of spheres . Therefore i want to record the force which acts on the facetbox. 
> The ducumentation says that the utils.PWaveTimeStep() makes some simplifications, like 
> • all particles are spherical and have the same radius R;
> • the sphere’s material has the same E and ρ
>
> All of my spheres have the same radius, but i use a facet as well. And i have seen that the utils.PWaveTimeStep() in some examples with facets and spheres. So i'm still wondering if i can use the utils.PWaveTimeStep() in my case? Or should i use GlobalStiffnessTimeStepper because i use a facet? 
>
>


-- 
_______________
Bruno Chareyre
Associate Professor
ENSE³ - Grenoble INP
Lab. 3SR
BP 53
38041 Grenoble cedex 9
Tél : +33 4 56 52 86 21
Fax : +33 4 76 82 70 43
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