The meaning of alphaKr and alphaKtw in CohFrictMat

Asked by Chen Lifan on 2020-09-02

Hello:
I'm using CohFrictMat to define the material of the rock issue. And I have some questions in the coefficients of alphaKr and alphaKtw. In the tutorial guide, it says alphaKr and alphaKtw are dimensionless rolling(bending) stiffness and twisting stiffness, respectively. I wonder what does than mean and I have no idea how much the values are proper for granite as there seems no reference.
I will appreciate any kind of help.
Thanks!

Question information

Language:
English Edit question
Status:
Solved
For:
Yade Edit question
Assignee:
No assignee Edit question
Solved by:
Robert Caulk
Solved:
2020-09-03
Last query:
2020-09-03
Last reply:
2020-09-03
Best Robert Caulk (rcaulk) said : #1

> it says alphaKr and alphaKtw are dimensionless rolling(bending) stiffness and twisting stiffness, respectively.

Imagine a beam connecting your two particles. If both particles roll along their shared axis, we install a spring that will resist this motion. alphaKr is the stiffness of that spring. Similarly, if the two particles twist along their shared axis, we install a spring that will resist this motion. alphaKtw is the stiffness of that spring.

> I have no idea how much the values are proper for granite

Unless you can find a paper that has calibrated these parameters for a similar material and similar scale (super important) that you are after - they don't directly correspond to any macroscopic conintuum mechanics parameters. Thus, these are calibrative. Like most DEM microparameters :-).

You are welcome to look at the source code to see exact implementation, if it will help you understand [1].

Cheers,

Robert

[1]https://gitlab.com/yade-dev/trunk/-/blob/master/pkg/dem/CohesiveFrictionalContactLaw.cpp#L199

Chen Lifan (chenlifan) said : #2

Thanks Robert Caulk, that solved my question.