How to add Cohesion command?

Submitted by laudari on Fri, 09/03/2021 - 10:50

Hello LIGGGHTS forum.

Really thank you for your help. You guys have been amazing in my research journey.

I have one more question regarding cohesion.

I am trying to add cohesion model in my simulation. Right now I am using following model as mentioned below:

pair_style gran model hertz tangential history #Hertzian without cohesion

Right now I am using inclined surface with atom style granular.
I went through liggghts tutorial regarding `gran cohesion sjkr model`. But couldn't find the exact way to apply cohesion with value.

My question can I apply cohesion model and give some value when I use atom style granular?
Any example related to cohesion command would help me.
And is there any boundary for the cohesion value like coefficient of restitution 0 to 1?

Any help would be appreciated.

Thank you so much.

Forums:

mschramm | Fri, 09/03/2021 - 16:22

Say I wish to add the cohesion model sjkr to my simulation. I would use the following command to declare my pair_style
pair_style gran model hertz tangential history cohesion sjkr #Hertzian with cohesion

Notice that no values have been given. This is because you apply values the same way as with the coefficients of restitution or coefficients of friction, via a property/global command.
fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.45
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.9
fix m4 all property/global coefficientFriction peratomtypepair 1 0.05
fix m5 all property/global characteristicVelocity scalar 2.
fix m6 all property/global cohesionEnergyDensity peratomtypepair 1 300000 # <--- This is the coefficient for cohesion energy density

laudari | Thu, 09/16/2021 - 13:00

Hi @mschramm Need small help to calculate cohesionEnergyDensity.
Why do we need charactristicvelosity ?

One more thing

right now I am dropping particles from small height to inclined surface,
so particles properties are

fix m1 all property/global youngsModulus peratomtype 5.e6
fix m2 all property/global poissonsRatio peratomtype 0.4
fix m3 all property/global coefficientRestitution peratomtypepair 1 0.6
fix m4 all property/global coefficientFriction peratomtypepair 1 0.6
fix m5 all property/global k_finnie peratomtypepair 1 1.0

with radius 0.01 and density 2000.
inclined surface angle is 40 to 45 degree.

Is it okay to use 300000 value for cohesionEnergyDensity??
Actually I couldn't get this value.

Thank you

mschramm | Sun, 09/19/2021 - 20:15

Hello
charactristicvelocity is needed for the hooke model (i believe). I do not set this when using the hertz model. I simply copied and pasted...

As for the cohesion energy density... This is very much a calibration needed value.
I do remember seeing a paper that tried to compare the JKR model cohesion value with the SJKR used in LIGGGHTS but I do not remember the name of it.

Kumarikiran@93 | Mon, 08/21/2023 - 13:56

I'm inserting same mass particles of both 6mm sphere and prolate shape but it's seems during post visulation in paraview that very less number of spherical particles generated as compare to prolate. Why it happen? Also in generated log files there are equal numbers of particles in both shapes. Also can you tell me what modifications I need to do in LIGGGHTS script and code to accurately apply it for cohesive materials?

Kumarikiran@93 | Thu, 08/24/2023 - 09:28

I'm filling cohesion binary mixture into vibrating packed bed and providing vibration energy. After mixing in the final state particles become spread throughout the bed(not settling)?? why? What modification is required to settle the particles.

attractalderman | Tue, 02/20/2024 - 04:58

geometry dash lite I'm introducing particles of the same mass in both prolate and 6 mm sphere shapes, however it appears that less spherical particles were formed in Paraview during post-visulation than prolate particles.