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[Anton Gladky <question253045@xxxxxxxxxxxxxxxxxxxxx>]

Question #253045 on Yade changed:
https://answers.launchpad.net/yade/+question/253045

    Status: Open => Answered

Anton Gladky proposed the following answer:
Hi Dominik,

double-check of the code is always welcome.

2014-08-13 15:46 GMT+02:00 Dominik Boemer
<question253045@xxxxxxxxxxxxxxxxxxxxx>:
> I have been reading the reference paper [Pournin2001] of the constitutive law "Law2_ScGeom_ViscElPhys_Basic".  I have two questions about it:
>
> 1.  In equation (22) [Pournin2001], cn and ct should have similar expressions as these are the solutions of similar differential equations with similar conditions.  Thus, there seems to be missing a factor 2 in the expression of ct.  Is that right?  If yes, has the eventual bug been fixed?

It looks like the equation are implemented according to the paper [1].

[1]
https://github.com/yade/trunk/blob/master/pkg/dem/ViscoelasticPM.cpp#L191

> 2. In the documentation (Release 2014-08-08.git-b1621bc, August 10, 2014) on page 457, some formulas are given for the conversion between en, et and tc, and kn, kt, cn in order to replace the deprecated function "yade._utils.getViscoelasticFromSpheresInteraction".  These formulas should be the simplified version of equation (22) in [Pournin2001] for spherical bodies.  This is why, 1/mref = 1/m + 1/m.  Thus, mref = m/2.  Furthermore, I1 = I2 = I = 2/5mr^2.  If these variables are replaced in equation (22)[Pournin2001], I get:
>
> kn = m/(2*tc^2) * (pi^2 + ln(en)^2)
> cn = -m/tc * ln(en)
> kt = m/(7*tc^2) * (pi^2 + ln(et)^2)
> cn = -m/(7*tc) * ln(en)
>
> These expression are different from those given in the documentation (p. 457).  Which version is correct?  And where does the error come from?

const Real massR = 2*mass1*mass2/(mass1+mass2); [2]

[2]
https://github.com/yade/trunk/blob/master/pkg/dem/ViscoelasticPM.cpp#L173

That is how we calculate meff. Please, check the code and let us know
your opinion.

Cheers

Anton

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