yade-users team mailing list archive

["Chen, Feng" <fchen3@xxxxxxx>]

Hi, Václav:

Currently I think using unbalanced force is the best way to know whether your system is close to equilibrium. 

Using the "velocity norm" appears to be a direct quantity, however, the "velocities goes to zero, or kinetic energy goes to zero" does not equal to the equilibrium state. Consider a mass-spring vibration case, when the velocity is zero for the mass, the acceleration for the mass is the maximum. 

It might be similar to the simple problem when we study basic physics in high school. How to define an object is "static or equilibrium" (Newton's first law)?  Then you would think delta(vel_norm)/t_p = 0, where t_p = a period of time, but it might be difficult to determine your t_p in DEM?

Feng Chen
Graduate Student 
Department of Civil and Environmental Engineering
223 Perkins Hall
University of Tennessee, Knoxville, 37996
http://fchen3.googlepages.com/home



-----Original Message-----
From: yade-users-bounces@xxxxxxxxxxxxxxxx on behalf of Bruno Chareyre
Sent: Tue 3/25/2008 5:44 AM
To: yade-users@xxxxxxxxxxxxxxxx
Subject: Re: [Yade-users] staticity quantification
 
Hehehe.
You don't like the "UnbalancedForce" parameter? ;-)

It is exactly what you are looking for, and its already used the way you 
want to use it (switch between isotropic and axial compression)

TriaxialCompressionEngine :

if ( UnbalancedForce<=StabilityCriterion && 
abs((meanStress-sigma_iso)/sigma_iso)<0.005 ) {
if(currentState==STATE_ISO_COMPACTION && autoCompressionActivation){
doStateTransition(STATE_ISO_UNLOADING);

"UnbalancedForce" is a normalized sum of forces on all bodies.
It can be a bit higher than 1 when the system is really far from 
equilibrium (e.g. at the begining of the isotropic compression when only 
peripheral spheres are pushed by boxes), but it is generally between 0 
and 1.
At static equilibrium, it is exactly equal to 0, which of course never 
happen. A reasonable value to consider something is stabilised could be 
between 1% and 0.1%.

Bruno


Václav Smilauer a écrit :
> Hello,
>
> I would like to quantify how much has a simulation approached static
> state (provided such state exists). Has someone done that? I thought of
> summing velocity norms (but what should be the threshold here?) or
> perhaps observing whether global stiffness is almost-constant. (Bruno,
> you're expert on that, how would you do that?)
>
> The reson for that is to programatically stop simulation once desired
> state is reached, without user interaction, so that I cun say: run that
> until it is done.
>
> Regards,
>
> Vaclav
> _______________________________________________
> Yade-users mailing list
> Yade-users@xxxxxxxxxxxxxxxx
> https://lists.berlios.de/mailman/listinfo/yade-users
>
>   


-- 
 
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Chareyre Bruno
Maitre de conference

Institut National Polytechnique de Grenoble
Laboratoire 3S (Soils Solids Structures) - bureau E145
BP 53 - 38041, Grenoble cedex 9 - France
Tél : 33 4 56 52 86 21
Fax : 33 4 76 82 70 43
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