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[mohsen <question295810@xxxxxxxxxxxxxxxxxxxxx>]

Question #295810 on Yade changed:
https://answers.launchpad.net/yade/+question/295810

mohsen posted a new comment:
Let start from the end:

>side note: I don't understand the physical relevance of this weighted
average you suggest.

It is the question for me also what is the meaning of for example arithmetic average?! Why before the modification in "Ip2_CpmMat_CpmMat_CpmPhys" (as described in question) arithmetic average was default way of computing 'E' (as it is for friction angle now)?
I do not know does it have a physical meaning or it is just an engineering simplification since finding contact stiffness is a hard job? 

As discussed in [1] absolutely in some situation (e.g soft to rigid
contact) arithmetic average is a wrong approach and therefore new method
'E' was added. In the following i have tried to clarify:

suppose that there is a contact between two spheres  with E1=1 and
E2=100. That is clear that most of deformation is due to softer sphere
(sphere 1) and Therefore stiffness of sphere1 should contribute more in
E (Or K) computation.

So how can we capture this reality in our modelling? May be weighted E
computation. Although undoubtedly there are some points that should be
answered specially when more than 2 materials has been defined.

> In (C1* E1+C2*E2)/(C1+C2) the problem I see is that you have a
dependency on 4 parameters instead of 2.

That is right in some way. But is it possible to define new algo  in
such a way that C1 refers to smaller E? If it was possible, so in each
contact always C1 works with smaller E and C2 with greater one and just
two parameters is enough.

>If it is really what you need C1 and C2 will have to be additional
material parameters, hence new classes.

Based on what i discussed above this approach is useful when just there
are two different material and wrong when more than two materials used
since we do not know in a contact which sphere is softer.

>Or new data is added to the MatchMaker itslef to define those constants
(but then someone will want to have >different values of C1,C2 for
different types of materials, not possible with only one MatchMaker, it
is a circular loop).

As you mentioned may be for a particular case it works but not a general
solution.

>Isn't it possible to compute the constant (C1* E1+C2*E2)/(C1+C2) once
in your script and use the "val" algorithm?

It is true just For two materials and just two defined particles . For
more than 2 particles this approach causes problems.

Regards

Mohsen Asadi Zeidabadi





[1]: https://answers.launchpad.net/yade/+question/290372

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