yade-users team mailing list archive

[Janek Kozicki <janek_listy@xxxxx>]

Andreas Plesch said:     (by the date of Fri, 21 Oct 2005 16:47:47 -0700 (PDT))

> Hi Janek,
> 
> yes, of course, my question was hard to address. I
> should mention that we are using PFC2d right now for
> geodynamic problems, and are looking into 3d. So I 
> am familiar with DEM, and concepts such as shear and
> normal contact stiffness, walls and friction, or
> particle bonding and bond breaking.

in yade you will find them in persistentInteractions,
volatileInteractions. Also we currently have 'modified mohr coulomb'
criterion but it is curretnly implemented in dirty manner and soon
should be separated from ElasticContactLaw to CoulombCriterion. This
will allow to add and mix with other criterions.

> The most similar
> model for us to start expanding on would
> be the "spheres settling on a plane" model. 

so - I suggest you to modify SDECSpheresPlane.cpp, by simply adding
another vertical plane, and attach it to a TranslationEngine (so it will
apply a kinetic movement to that plane). And observe the results. If you
want to record a force or anything during the simulation - have a look
at how classes ForceRecorder, VelocityRecorder, AveragePositionRecorder
are used in some filegenerators (eg. SDECImpactTest).

> For
> example we would like to explore sand which very
> slowly piles up in front of a moving vertical wall.
> In particular we would interest in the formation
> of cracks and faults in the sand structure.

without bonds and bond breaking this simulation is currently possible,
simply by modifying SDECSpheresPlane.

> 
> As a practical matter, one element which would be
> essential would be the option to save the state of
> a simulation, 

you should have a look at NullGUI - it's a command line interface to
yade. You can start a simulation without opening a graphical window, and
without losing CPU time for display. You can also configure it to save
simulation when it is running.

In fact QtGUI is unable to save simulation when it's running - it's easy
to add, but there were lot of more important things to do ;) And also
because we were using NullGUI when we needed simulation snapshots. Run:

./yade -n -H

to see help for NullGUI. btw, I just noticed that ./yade -n doesn't
print help, which is bad, because no one has a way to discover -H to see
the help. I should fix it quick.

> modify or add/substract elements and
> then restart. 

currently the only way to do that is by modifying .xml file by hand.
When you change the number of elements in the container, remember to
change the container size (on the top). In the future I hope there will
be a way to do such modifications using graphical interface, by clicking
on the elements.

Also when you save and later load the simulation you should check if the
results (eg. force on the bottom plane, or whatever) are simular if
simulation runs uninterrupted. That is because I don't remember now if
'save' actually saves all the data required later to restore the
simulation. It's possible that shearing force may be accidentally reset
to zero. Maybe that problem was fixed - I don't remember now, so better
you will check that anyway.

> I suppose this would be
> serialization/deserialization in the yade language ?

yes, exactly. At minimum we will add binary frontend, then probably yaml.

> 
> Does the DEM allow for bonding and bond breaking
> between elements currently ?

I replied in other post to that matter ;)

https://lists.berlios.de/pipermail/yade-users/2005q4/000042.html


> In the end, I would like to use other tools in
> addition to the FileGenerators to generate input files
> to the actual simulator and also be able to look at
> the state of the model with other tools at any stage.

you can add another class similar to ForceRecorder that will record to
file any value you need, when the simulation is processing. In such a
way you can easily prepare any input needed by other programs.

You can also write another file generator, that instead of asking the
user to input data - will load a given file, and from data inside it -
create .xml for simulation. In fact this is how FEM works - there is a
file that contains FEM mesh inside, and this mesh is loaded
(in yade-examples)

-- 
Janek Kozicki                                                         |
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