how can set shear viscous damping ratio betas in yade in linear elastic model?

Hi,

this contact law was designed for a specific purpose (see [1]) where no tangential viscous damping was needed. In fact, in that case it is assumed that energy is dissipated in tangential direction via friction only. It could easily be added but, depending on your objective, you might be better off using another contact law. BTW, what's your objective?

Klaus

[1] https://www.researchgate.net/publication/261219119_A_3D_discrete_element_modelling_approach_for_rockfall_analysis_with_drapery_systems

I'm trying to simulate a triaxial test of sand. I've read some papers in which both beta_n and beta_s are used. I really can't judge in which senario beta_s should be used. Can you give me an answer? Thank you very much.

Dr Thoeni,
        Thank you very much for your answer. It really helped me a lot in undestanding the use of viscous damping ratio.
        However, I still have one more question. I'm trying to simulate a triaxial test of sand. I've read some papers in which both beta_n and beta_s are used. I really can't judge in which senario beta_s should be used. Can you give me an answer?
        Thank you very much.
Long Xue

At 2016-09-12 18:13:36, "Klaus Thoeni" <email address hidden> wrote:
>Your question #392660 on Yade changed:
>https://answers.launchpad.net/yade/+question/392660
>
> Status: Open => Answered
>
>Klaus Thoeni proposed the following answer:
>Hi,
>
>this contact law was designed for a specific purpose (see [1]) where no
>tangential viscous damping was needed. In fact, in that case it is
>assumed that energy is dissipated in tangential direction via friction
>only. It could easily be added but, depending on your objective, you
>might be better off using another contact law. BTW, what's your
>objective?
>
>Klaus
>
>[1]
>https://www.researchgate.net/publication/261219119_A_3D_discrete_element_modelling_approach_for_rockfall_analysis_with_drapery_systems
>
>--
>If this answers your question, please go to the following page to let us
>know that it is solved:
>https://answers.launchpad.net/yade/+question/392660/+confirm?answer_id=0
>
>If you still need help, you can reply to this email or go to the
>following page to enter your feedback:
>https://answers.launchpad.net/yade/+question/392660
>
>You received this question notification because you asked the question.

Hi,

in most of the cases I know only normal viscous damping is used. This makes sense since friction is dissipating energy in tangential direction but additional tangential viscous damping could be used to dissipate more energy. Isn't there a specific justification in the papers you are referring to?

Klaus

Thank you very much for your answer !
Friction really dissipate the main part of the energy in the tangential direction, but wouldn't it be better if beta_s is added to this model, after all the energy may dissipate in the tangential direction even if the friction doesn't happen ? And in the model Ip2_FrictMat_FrictMat_MindlinPhys, the beta_s can be adjusted.
It is really really hard for me to add the tangential viscous damping ratio to YADE.
So can you add beta_s to the model ? Can we see the new model in the next released YADE ?
Thank you very much !
Long Xue

At 2016-09-12 20:47:30, "Klaus Thoeni" <email address hidden> wrote:
>Your question #392660 on Yade changed:
>https://answers.launchpad.net/yade/+question/392660
>
> Status: Open => Answered
>
>Klaus Thoeni proposed the following answer:
>Hi,
>
>in most of the cases I know only normal viscous damping is used. This
>makes sense since friction is dissipating energy in tangential direction
>but additional tangential viscous damping could be used to dissipate
>more energy. Isn't there a specific justification in the papers you are
>referring to?
>
>Klaus
>
>--
>If this answers your question, please go to the following page to let us
>know that it is solved:
>https://answers.launchpad.net/yade/+question/392660/+confirm?answer_id=3
>
>If you still need help, you can reply to this email or go to the
>following page to enter your feedback:
>https://answers.launchpad.net/yade/+question/392660
>
>You received this question notification because you asked the question.

Hi,

I still think this is not the contact law you want to use for triax tests as it was designed for rock impacts. Other contact laws provide much more features. In the case of a triax test you would also be able to use Newton.damping as it is shown in the example [1].

By saying that, it is also possible for me to implement betas. It might just take some time as I have to set up everything from scratch.

Another question, why do you want to use this contact law? What feature is crucial?

Klaus

[1] https://github.com/yade/trunk/blob/master/examples/triax-tutorial/script-session1.py#L94

Thank you very much for your answer !
I really used the numerical damping in my model .
The reason why I want to use this contact law is that the contact law is very simple but it can reflect the most important feature ---friction--- of sand. In the meantime, I have made a lot of numerical tests about it and I have gain a lot of experience in specifying the parametres of it .
Yesterday, I checked my codes again and found a big bug in it and thus the problem I faced was solved.
Many thanks for your time !
However, in PFC, there really do exist beta_s in the linear elastic model and I am really not sure about whether the beta_s should be added or not. In my mind, the "collision" in the tangential direction is really the same as the collision in the normal direction. So why there shouldn't be a mechanism of dissipating energy when the sliding don't happen but the "collision" in the tangential direction takes place.

Long Xue

At 2016-09-14 19:22:52, "Klaus Thoeni" <email address hidden> wrote:
>Your question #392660 on Yade changed:
>https://answers.launchpad.net/yade/+question/392660
>
>Klaus Thoeni posted a new comment:
>Hi,
>
>I still think this is not the contact law you want to use for triax
>tests as it was designed for rock impacts. Other contact laws provide
>much more features. In the case of a triax test you would also be able
>to use Newton.damping as it is shown in the example [1].
>
>By saying that, it is also possible for me to implement betas. It might
>just take some time as I have to set up everything from scratch.
>
>Another question, why do you want to use this contact law? What feature
>is crucial?
>
>Klaus
>
>[1] https://github.com/yade/trunk/blob/master/examples/triax-tutorial
>/script-session1.py#L94
>
>--
>You received this question notification because you asked the question.

This question was expired because it remained in the 'Open' state without activity for the last 15 days.

Dear Klaus Thoeni,

you mentioned, "I still think this is not the contact law you want to use for triax tests as it was designed for rock impacts. Other contact laws provide much more features."

Do you have any recommendation for triaxial tests? Since this contact model is used in the expample provided by YADE Instruction.

Thanks in adavance

This question was expired because it remained in the 'Open' state without activity for the last 15 days.