What is the value of a in JKR model

satri

Hey your documentation says

What is the value of a that i shoudl consider for JKR V2 model. you say its a place holder and have used it in equation 1 and 2

satri

also what is the difference between alpha_f and alpha?

satri

also why do you have same names for upper case gamma and lower case gamma12?

satri

Please tell me if this is how EDEM computes the value of lowercase_a to be used for equation 1.

it equates equation number 2 to normal contact overlap which is given by lowercase_delta_n and then it solves for a numerically.

Once this is solved, the value of lowercase_a is used in equation 1.

Please tell me if this is how it works in the background?

I still want to know what the difference is between alpha_f and alpha.

satri

please tell me if this is how altair calculates lowercase_a in the background

→ equates the alpha value from equation 2 to lowercase_delta_n (normal contact overlap). Solve the equation 2 numerically to get the value of lowercase_a. Use this value in equation 1 to determine the value of Fn.

Please let me know if this is how altair evaluates the value of lowercase_a?

also i still want to know what is the difference between alpha_f and alpha?

Stephen Cole

Hi Satri,

You can checkout the source code of the model here:

https://community.altair.com/community/en/edem-api-contact-model-example-jkr-v2-cohesion-contact-model?id=kb_article&sysparm_article=KB0121837

Which may help answer your questions and gives the calculations in detail. CJKRV2.cpp is the main file with the force calculations.

For 'a' it's important to differentiate between the two definitions of contact radius. In EDEM we set a contact radius to determine if a particle is in contact or not (shown in the screenshot below) however the contact radius a used in equation 1 is not this. It's defined in:

Thornton C. (2015) Granular Dynamics, Contact Mechanics and Particle System Simulations: A DEM Study. Vol. 24. Springer.

Or as a snapshot from the API code:

EDEM Contact Radius definition; To allow for a contact force to be calculated when the particles are not in contact we set a particle Contact Radius in the EDEM GUI which is larger than the particle physical radius:

Aplha_f is the "particle contact radius" - "particle radius", which would be 0.2 mm in the case above.

Regards

Stephen

satri

Ok I get it the contact radius is not what we set in the GUI. But i am still not able to understand which equation are you solving to determine a in the code.

In the reference above, I recognize the if part.

But i still do not know which equation you are solving (fourth order equation) from Thornton C (2015) to determine the nContactRadius (in line 212)

Stephen Cole

Hi Satri, It uses the NUtilitiesFourthOrderPolynomial function listed in the code. The code is also available in the above link, which also includes some references.

Regards

Stephen

satri

Yes i saw the code. But which is the base equation you are solving with the code

I do not see this equation anywhere in the textbook Thornton C (2015)

even if i square this equation from the textbook

I do not get the equation you are solving with the code. So, I am not sure which is the fourth-order equation that you are solving.

satri

I believe this is for this equation.

satri

Hello Stephen

Please tell me which is this equation you are solving

a[0]*a^4 + a[1]*a^3 + a[2]*a^2 + a[3]*a + a[4]*a

I do not see this equation in the documentation at all nor in the textbook

Stephen Cole

Hi Shyam,

I believe it's following the method outlined in:

Parteli, Eric & Schmidt, Jochen & Blümel, Christina & Wirth, Karl-Ernst & Peukert, Wolfgang & Pöschel, Thorsten. (2014). Attractive particle interaction forces and packing density of fine glass powders. Scientific reports. 4. 6227. 10.1038/srep06227.