yade-dev team mailing list archive

[Chiara Modenese <c.modenese@xxxxxxxxx>]

There is NO bug here and no shear force (it is numerically zero). It is
clear to me that PFC computes contact stiffness in a different way. Do you
know how it is computed in PFC then? Do you know which formula they actually
implement? In Yade you can easily check it yourself in the code
(seeIp_FrictMat_FrictMat_MindlinPhys). It simply follows Hertz formulation
(I have just checked it once again and it is correct).

Chiara


On 14 July 2011 11:11, Christian Jakob <806944@xxxxxxxxxxxxxxxxxx> wrote:

> Ok, so this bug (?!) seems to be more important, than I thought...
>
> I compared the first 10 steps of the previous model and created 2 output
> files (force-disp-pfc.txt and force-disp-yade.txt) and 2 force-displacement
> plot files (force-disp-pfc.bmp and force-disp-yade.png).
> Note, that coordinate systems are different: z-axis in pfc is in the
> opposite direction!
>
> The txt-files are structured as follows (only z-components are
> examined):
>
> column 1 -> step number
> column 2 -> time
> column 3 -> overlap (un)
> column 4 -> velocity (upper particle)
> column 5 -> normal force (Fn or Fn_z)
> column 6 -> shear force (Fs or Fs_z)
>
> There are 3 basic differences:
>
> 1.) PFC starts output with step 1, YADE with step 2
> -> so step 1 in yade equals step 2 in pfc!
>
> 2.) normal forces are completely different for both programs (see column
> 5)
>
> 3.) in Yade a shear force occurs after the 6. step
>


>
> I will come back on you soon with results of linear model...
>
>
> Christian.
>
> ** Attachment added: "viscoelastic-test-step-by-step.tar.gz"
>
> https://bugs.launchpad.net/yade/+bug/806944/+attachment/2207404/+files/viscoelastic-test-step-by-step.tar.gz
>
> --
> You received this bug notification because you are a member of Yade
> developers, which is the registrant for Yade.
> https://bugs.launchpad.net/bugs/806944
>
> Title:
>  different behavoir of Hertz model while comparing PFC and YADE
>
> Status in Yet Another Dynamic Engine:
>   Confirmed
>
> 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
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/yade/+bug/806944/+subscriptions
>
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-- 
You received this bug notification because you are a member of Yade
developers, which is the registrant for Yade.
https://bugs.launchpad.net/bugs/806944

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

Status in Yet Another Dynamic Engine:
  Confirmed

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

To manage notifications about this bug go to:
https://bugs.launchpad.net/yade/+bug/806944/+subscriptions