Great, thanks for the helpful explanation!
Thanks,
David
On Friday, June 10, 2022 at 5:50:41 PM UTC-7 Ruochun Zhang wrote:
> Hi David,
>
> For your first question: I guess the short answer is that the 2015 paper
> prevails. At the implementation level, both Chrono and Chrono::GPU have the
> effective mass \bar{m} in the damping term, therefore in both places the
> input \gamma is the damping coefficient only. In the 2021 paper, it's
> mainly because Chrono::GPU deals with monodispersity only, therefore
> \bar{m} is constant, so we absorbed it into \gamma which is also a
> constant. But I guess this writing may have created confusion.
>
> And the GPU module uses Hertzian contact.
>
> About the static/sliding coefficient, right now Chrono::GPU assumes they
> are numerically the same. So via SetStaticFrictionCoeff methods you set
> both. So this number is used to both determine the clamping condition and
> model the frictional force of persistent sliding contacts (where you might
> argue they should be separately modelled by static and sliding
> coefficients). I think the name static friction was originally chosen, so
> that when (in the future) kinetic friction coefficient is added, the API
> naming is more cohesive.
>
> Again the new generation of Chrono DEM solver I mentioned before would
> make the force model completely transparent to and modifiable by the user.
> It still needs some time to be out though, perhaps not before the end of
> summer.
>
> Thank you,
> Ruochun
>
> On Friday, June 10, 2022 at 3:47:51 PM UTC-5 [email protected] wrote:
>
>> Hello,
>>
>> I have been reading through some of the papers about granular flow in
>> Chrono and have a few questions about the implementation.
>>
>> Just to clarify, I will mostly be referencing these two papers, which I
>> will refer to by as the 2015 and 2021 papers
>>
>> 2015: Chrono: An open source multi-physics dynamics engine
>> 2021: Chrono::GPU: An open source simulation package for granular
>> dynamics using the discrete element method.
>>
>> Firstly, I have a question about the equations for the normal and
>> tangential forces. In the 2015 paper, there is an mbar term in the damping
>> portion of the normal and tangential forces equations (equation 2). In the
>> 2021 paper, this mbar is not seen (equations 3 and 4). Which of these
>> papers is correct and why?
>>
>> Secondly, I have a question regarding the friction factor. In both
>> papers, for the calculation of u_t and to enforce the Coulomb friction law,
>> mu_s is used. Is mu_s the static or sliding friction coefficient? I have
>> noticed that in the GPU module, there is only the option to set the static
>> coefficient or rolling coefficient, but if particles are moving past each
>> other, this should be the sliding coefficient, right? (I noticed in table 2
>> of the 2021 paper, sliding coefficient is used).
>>
>> Lastly, I’m a bit confused as to whether the GPU module uses Hookean or
>> Hertzian contact by default.
>>
>> Sorry for all the questions, just want to make sure I have a good
>> understanding of my Chrono simulations.
>>
>> Thanks!
>> David
>>
>
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