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[Christian Jakob <806944@xxxxxxxxxxxxxxxxxx>]

Hello again,

Thank you for your answers. It helps me very much.

I compared PFC and YADE again with another simple test. Again there are two spheres and the upper one gets an initial velocity. During contact velocity, distance and forces are monitored. Unfortunately I could not catch the forces right now... any idea, how to do this?
Configurations, parameters and time steps are the same in both programs.

Nevertheless the velocity indicates, that PFC and YADE do not behave the same way (even without any damping). 
You can see that, when you compare velocity-time-no-damping-yade.png (from yade) with velocity-time-no-damping.bmp (from pfc) and velocity-time-visc-0-1-yade.png (from yade) with velocity-time-visc-1.00000000000e-001tension0.bmp (from pfc). Please note, that I increased number of cycles in yade in the damped case (visc_damp_normal = 0.1, line 14) to 700 to see the effect of tension force.

So my conclusion is, that both programs behave different and can lead to
different output. Therefore this is not a bug and I will set the status
of to 'fixed'.

Regards,

Christian

** Attachment added: "viscoelastic-test.tar.gz"
   https://bugs.launchpad.net/yade/+bug/806944/+attachment/2205401/+files/viscoelastic-test.tar.gz

** Changed in: yade
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/806944

Title:
  different behavoir of Hertz model while comparing PFC and YADE

Status in Yet Another Dynamic Engine:
  Fix Released

Bug description:
  Hello,

  During verifiing my model I compared output from PFC 4.0 with the
  output from YADE (bzr2877 on Debian Squeeze 64bit). There I found a
  different behavior between these two programs. I dont know if this is
  a bug or not, but I hope someone can explain the different behavior.

  The model itself is very simple. There are two spheres, an upper one and a lower one. The lower one is fixed and the upper one is falling down to the lower one, collides and jumps back. The value of interest is the flyback height of the upper particle.
  In PFC I measure higher values of flyback height, then in YADE (see log-files in the attachment).

  Can someone tell me why there is a difference in the flyback height?
  (input parameters are the same for both programs ... see caller_two-spheres-jumping.dat for PFC and two-spheres.py for YADE)

  Regards,

  Christian Jakob

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