Calculating Unbalanced force within LIGGGHTS script

Submitted by Rahul Kumar on Sat, 09/19/2020 - 11:04

Hi everyone,
I am doing triaxial test simulation. I want to compute the Unbalance force index (Formula is attached with this post), and change the strain rate accordingly within the script. I have tried to compute contact force and total force on particle and the reduce them to scaler value. But it seem there is a problem.

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compute fc all pair/gran/local pos force
compute fc1 all reduce sum c_fc
compute force all property/atom fx fy fz
compute fc2 all reduce sum c_force
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ERROR
Compute reduce compute does not calculate a local vector (../compute_reduce.cpp:243)
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Image icon triaxial.png33.04 KB

mschramm | Mon, 09/21/2020 - 22:03

The compute force all property/atom fx fy fz command provides 3 lists where fx values are accessed via force[1].

You will need to reduce each component to add them together.
compute fc2_x all reduce sum c_force[1]
compute fc2_y all reduce sum c_force[2]
compute fc2_z all reduce sum c_force[3]
variable fc2 equal c_fc2_x+c_fc2_y+c_fc2_z

wuhudasi's picture

wuhudasi | Fri, 11/06/2020 - 03:59

Hi, Rahul Kumar
I am a new user of Liggghts. I want to simulate a triaxial test. But I don't know how to keep the pressure constant when the sample is compressed in consolidation.
Because the sample area is changed. What command can detect area change? Could you please share your triaxial test scripts with me?
My email: 201916131103@cqu.edu.cn
Best wishes
wuhudasi