measure force in periodic boundary

Hi,

For the periodic boundary, how does it measure the forces on each surface?

James

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Jan Stránský
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2019-02-23
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2019-02-23
2019-02-23
 Jan Stránský (honzik) said on 2019-02-22: #1

Hi James,

using periodic boundary conditions (I prefer to call it periodic contact detection), the sample is periodic and there is no surface..
You can compute average stress [1] and using periodic cell dimensions [2], you can extract something like "surface force":
###
stressTensor = getStress()
s_xx = stressTensor[0,0]
s_yy = stressTensor[1,1]
s_zz = stressTensor[2,2]
dx,dy,dz = O.cell.refSize
a_xx = dy*dz
a_yy = dx*dz
a_zz = dx*dy
f_xx = s_xx / a_xx
f_yy = s_yy / a_yy
f_zz = s_zz / a_zz
###

but **personally** I would use just the stress values..

cheers
Jan

 jamespaul (jamespauljames) said on 2019-02-23: #2

Thanks Jan,

> **personally** I would use just the stress values..

Do you means you would use triax.stress[]?

>A second question:

For a periodic cube, according to Newton's second law, the forces on the opposite sides should be the same.Why set six goals instead of three as PeriTriaxController.Did I misunderstand the meaning of these 6 values?

 Jan Stránský (honzik) said on 2019-02-23: #3

> Do you means you would use triax.stress[]?

yes, for example.

> A second question:

next time, please open a new question for a new question.
Apart form 3 normal components, Peri3dController also controls 3 shear components, therefore in total there are 6 values.

cheers
Jan

 jamespaul (jamespauljames) said on 2019-02-23: #4

Thanks Jan Stránský, that solved my question.