LIGGGHTS® - User Forum

Hello all,

I am trying to simulate the isotropic compression of a spherical wall/bounding box along the negative 'r' direction in spherical coordinates. Can anyone direct me towards the approach to edit mesh_module_stress_servo.cpp(/h) and/or fix_deform.cpp(/h) so that these modules work in spherical coordinates? Thank you very much!

Hi
I am using servo wall to maintain constant force on wall. And I have some doubts.

1. The formula referred in documentation for PID controller
output = kp * error + ki * errorsum + kd * errorchange
I want to print or save the output, error, errorsum and errorchange values. How can I do this in LIGGGHTS.

2. Is there any thumb rule for selecting kp, ki, and kd values.

3. How can I change a variable value in every step.

Hi
I am new to LIGGGHTS and modeling an impact problem. As shown in attached figure, impact is happening between a web and fixed wall. I want to compute the total impact force with time (sum of contact force for all contact points). Please note that the contact points change as the simulation progresses. Please help me by suggesting a suitable command for that.

Thanks

Hi

it's regarding storing the variables at particular timestep,
Then need to use those variables in the next loop

The script is like this

#####################################################
start of the program
>> Scripts intitiates
>> define varaibles
>> variables are changing at every timestep

>> ran for ten timestep
run 10
unfix the all the fixes
>> save the varables at 10

Hi,

i m trying to run my first simple simulation but an error comes

ERROR: Mesh error: dimensions too small - use different unit system (../multi_node_mesh_parallel_I.h:584)

I actually used SI unit and stl. file in ASCII file.

I can post some codes of mein and look forward to get some advices:

#Definition of boundaries
variable xmin equal -0.0102
variable xmax equal 0.0102

variable ymin equal -0.042
variable ymax equal 0.042

variable zmin equal -0.042
variable zmax equal 0.042

Hi
I want to fill the bonded particles in a region, as shown in attached figure. I am using lattice command for the same, however I am getting thr following error:
ERROR on proc 0: Neighbor list overflow, boost neigh_modify one (../neigh_gran.cpp:188)

I belive, it is related to the line# 135& 136 of the attached input script.
I am using 'nsq' instead of 'bin' since I was unable to insert the particles using bin.

Please suggest a way aroung the above problem.

Thanks
Shubham

Hi
I have two questions:
(i)
I am trying to model a problem as attached in the figure. A soft web is bonded to a rigid substrate which is moving at constant speed. Whwn web hits the wall, it should delaminate. However as shown, in my case particles are penetrating the wall. I have tried increasing the contact stiffness, but its not helping.
Can someone please help me with this, I have also attache the input file.

Hello
I am using "Flexible fiber" version and have a general question. In the 'lib' folder I found several ANCF beam libraries. I am wondering whether they can be used in Discrete method, or FE by importing a CAD file.

Thanks
Shubham

Hi
I am trying to break granular tupe bonds, by using the command:
fix bondbr3 all bond/break 1 2 ${adh_crit_dist}
2- bondtype
${adh_crit_dist} - critical distang to break the bond

I have also tried fix bondbr3 all bond/break/gran 1 2 ${adh_crit_dist}
But I am getting the following error:
Invalid fix style: "bond/break"

Can we model bond breakage for granular bonds?

Thanks

Hi
I wan to simulate a system very close to as shown in attached figure.
A discrete plastic web is bonded to a non-deformable but movable substrate. As the web his the wall, web should de-laminate from the substrate depending on the bond strengths.
How can the above problem modeled in LIGGGHTS?
How can we create breakable bonds between particle and non-deformable substrate?

Requesting for help, I am struggling a lot, as I am new to the environment

Thanks