yade-users team mailing list archive

[Jan Stránský <question295810@xxxxxxxxxxxxxxxxxxxxx>]

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

Jan Stránský proposed the following answer:
Hi Mohsen,

In general CPM mat was not really designed for different materials (or at
least not drastically different material), therefore many of assumptions
(like arithmetic average of stiffness or friction angle) are written "just
in case". If you want to compute the resulting IPhys parameters
differently, it is possible to modify the source code and you can:
- implement MatchMaker for some standard ways of combining two values
- use some more sophisticated formula directly in Ip2::go function

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.


I am not sure if I got this correctly, but for the stiffnesses, existing
MatchMaker and harmonic average is the correct approach to use. Or do you
get some wrong results with it?

cheers
Jan


2016-07-01 21:47 GMT+02:00 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
>
> --
> You received this question notification because your team yade-users is
> an answer contact for Yade.
>
> _______________________________________________
> Mailing list: https://launchpad.net/~yade-users
> Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~yade-users
> More help   : https://help.launchpad.net/ListHelp
>

-- 
You received this question notification because your team yade-users is
an answer contact for Yade.