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[Jan Stránský <question280376@xxxxxxxxxxxxxxxxxxxxx>]

Question #280376 on Yade changed:
https://answers.launchpad.net/yade/+question/280376

Jan Stránský proposed the following answer:
Hi Mohsen,

1-1: It is better to use JCF model for modelling an elastic beam than Cpm.
> am i right? Is there any example script?


As already suggested by Jerome, in the elastic regime, the two models are
equivalent. They differ in the inelastic regime, since both are developed
to model different phenomena.

1-2: In [1], #10 Jérôme said that "... so that distant particles may be
> bonded". It is really a good feature. this provides a tool to a potato by
> distant particles not filling with particles. the advantage is decreasing
> number of particles in the simulation. so how it possible? can you help me?


see below and [2]


2-1- Why at the first step the Young modulus is decreased?
>         I tried this two and in both the particles positions got infinite:
>         i. first young modulus: 10e6; second young modulus: 10e6
>         ii. first young modulus: 10e10; second young modulus: 10e10
>         And I tried below set of youngs and the potatoes explode but
> particle's positions were not infinite
>         iii. first young modulus: 10e2; second young modulus: 10e6.
>         can you explain me why such results happened?


When I tried the same modulus, the potatoes had too big overlap. So in the
first stage, 1e6 was defined, which affects elastic bonds inside the
potatoes. The value 1e10 then defines modulus of newly created contacts,
resulting in reasonable overlap of potatoes.

Exploding and/or NaN or infinite particles position is often the result of
too large time step. I tried 1e6/1e6 combination with "O.dt =
.1*PWaveTimeStep()" and it worked OK.


2-3- Any suggestion or previous experiences about calibrating?


the macroscopic stiffness is proportional to the microscopic one, so
calibrating stiffness is an easy task. Poisson's ratio is a bit more
tricky, but in general the lower 'poisson' parameter, the higher is
macroscopic Poisson's ratio.

So now, in Yade my simulations include 'n' particles(also a potato). Can i
> create a bond between specific particles (e.g. particles i and j) with no
> overlap ? In [3] i don't know where i should specify the particle id?


[1] ([3] in you original message) presents a concept of automatic distant
bonds creation, controled by parameter intRadius. In this case, **all**
particle whose distance is less then (intRadius*their diameter) will be
bonded, so non-touching particles as well.

You can also create interaction between arbitrary particles, see [2]. In
the case of Cpm, such bond is cohesive and stress free by default.

cheers
Jan

[1] https://yade-dem.org/doc/user.html#creating-interactions
[2] https://yade-dem.org/doc/user.html#individual-interactions-on-demand

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