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[Nima Goudarzi <question647543@xxxxxxxxxxxxxxxxxxxxx>]

New question #647543 on Yade:
https://answers.launchpad.net/yade/+question/647543

Dear All, 

I am trying to implement a new contact model into YADE. The model has some common features with HM but is different in some ways. I need to implement 8 responses in 4 directions [Normal, Tangential, Rolling and Twisting] (for of which are related to contact response and the rest to damping response). The model has 7 free parameters (E, ξ, ξ_c, β,μ,c_n,c_s)
>From above parameters, two are almost new comparing to classical DEM models:
	a) ξ_c which is a local crushing parameter describing the effects of local asperity crushing (in rolling direction) and related to the hardness of the particle mineral material
	b) β which is dimensionless shape parameter which has been introduced to link the contact radius R ̅ and the radius of the contact spheres (β can be regarded as a shape parameter, used to consider the effects of particle shape on the overall mechanical behavior of granular materials.
R ̅=βr
r=(2r_i* r_j)/(r_i+r_j )
In addition, K_n  (Normal stiffness) is different from HM. Here K_n=2rE . E represents the modulus of the particle material
And K_s=K_n/ξ.  ξ is the ratio of the normal to the tangential contact stiffness. (It seems to be an input parameter)

The model also proposes to calculate c_n as follow:
c_n=(2*sqrt(K_n* m) ln⁡(η))/sqrt(ln^2 (η)+π^2 )

 
For responses please see page 153 of this paper  (A novel three-dimensional contact model for granulates incorporating rolling and twisting resistances )
www.sciencedirect.com/science/article/pii/S0266352X14002390

(I can send you the paper if required)

Actually, I am trying to modify HM to capture all the behavior I need. 


I have some questions:

1- Do I need to write a new class of material for introducing parameter described above? (I need  ξ_c for the peak resistance in rolling direction) (I need β for calculating  R ̅ which directly incorporates in the calculation of rolling stiffness [K_r], twisting stiffness  [K_t], rolling damping coefficient [c_r], twisting damping coefficient [c_t] and peak resistances in rolling and twisting directions. I need ξ for calculating  K_s. If yes, can FrictMaterial be the base class? If not, is it possible to define them outside the .hpp file somewhere in .cpp?

2- Can I still use MindlinPhys (by some modification) or I need to define a new physics too?


3- Do I need to include the functions for counting the number of adhesive contacts, returning ratio between the number of sliding contacts to the total number, calculating the normal elastic potential energy of the system and calculating adhesion energy of the system as implemented in HM.

4- Do I need to define new Law or the existing in HM can be employed? 

I have some other questions I will ask after getting the response.


Sincerely Yours,

Nima

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