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[Fu zuoguang <question245062@xxxxxxxxxxxxxxxxxxxxx>]

Question #245062 on Yade changed:
https://answers.launchpad.net/yade/+question/245062

    Status: Answered => Open

Fu zuoguang is still having a problem:
Dear Bruno Chareyre and Jan Stránský:

      I think I can get some of your opinions a little more than before.
So I should give all my comprehension of these questions as follow.

     (1) As I said last time, reference frame can be introduced here just only for helping to understand the absolute motion of two spheres system in global space and the relative motion in reference frame. But it can offer almost no 
help to the formulas of calculation of shear strain since its development is uniquely depended by relative motion and 
the calculation values of it may not change no matter what the configuration is chosen. So the global system can entirely replace the reference frame to quantify relative motion of the two spheres.

     (2) Relative motion of the two can be decompose into two parts: the
first one is linear motion, which is completely due to the relative
linear velocity of the two and the other is angular motion, which is
determined only by relative angular velocity. These two parts joint
together to generate the shear strain of the two spheres.

     (3) Shear strain of the two spheres at the contact point caused by the first part above can be calculated just from the formula (1) to (7), the process is as follow:
Formula (1) to (7) : http://imageshack.com/a/img541/7540/8qsj.jpg
This part has nothing different from what I just described last time.

     (4) Shear strain of the two spheres at the contact point caused by the second part above need to be discussed here. Firstly, I should say sorry for my serious misunderstanding of this part last time, just in formula (8) to (10), I thought that both the linear and the angular motion of contact point, respectively represented by linear displacement and rotation of reference frame, can effect the shear strain but the fact is not, the latter can but the former can not. The details are just in [Luding 2008], in which the reference frame is empolyed for calculation.
Fig 4 : http://imageshack.com/a/img22/1277/dvxq.jpg 

     My questions today are
(1) Are there somethings wrong in detail (1) to (4) described above?
(2) If not, I think in Yade document, (delta_Ut)1 + (delta_Ut)2 may the same thing as (11)+(12), but just calculate in global space.

Seek your help!

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