yade-users team mailing list archive

[Chiara Modenese <question159394@xxxxxxxxxxxxxxxxxxxxx>]

Question #159394 on Yade changed:
https://answers.launchpad.net/yade/+question/159394

    Status: Answered => Open

Chiara Modenese is still having a problem:
Hi Bruno,

thanks for answer.

On 30 May 2011 19:01, Chareyre <question159394@xxxxxxxxxxxxxxxxxxxxx>
wrote:

> Your question #159394 on Yade changed:
> https://answers.launchpad.net/yade/+question/159394
>
>     Status: Open => Answered
>
> Chareyre proposed the following answer:
> 1/ This equation is formally correct, I don't see how a gain could be
> introduced.

This equation is very similar to the servo-control we use with rigid
boundaries; with the difference that there we also have a gain parameter
(let me call it that way, for me it does not matter if it is split into two
parameters other than one). So, why here the formula is correct but with
rigid walls we need the gain parameter?


> Actually, I'd keep calling 1/mass the "inverse inertia"
> rather than "gain", since it explains the two methods: one is static,
> the other is dynamic. It is better to have two methods, since different
> users will prefer one or the other.

It is not good to have two methods if one of them does not work (at least to
my experience, but I would be happy to hear from others that I am wrong). Am
referring here to what you call "static" method (in PeriIso file). If you
ever try to use it, you will see that it does not properly work. This is why
my question about gain parameter.
Mass is not mass, given its current unit of measure which can be derived
from the equation. As I see it, it is really a gain parameter (and I still
do not see the advantage to use 1/mass when this could simply be called
gain, unless you have a method which estimates the mass parameter from a
physical point of view, do you?).


> The only problem in dry granular
> materials is that there is no simple derivation of stiffness (unlike
> cemented materials with 12 interactions per body or more => no rolling).
>
Ok.

>
> 2/ The comment is about this cycle :
> resetForces->integrateAndUpdate->contactLaw->PeriCompressor->NewtonsLaw.
> The simplest way to understand what id does is to rewrite it differently
> (it's a cycle, so I can start anywhere) :
> - compute forces at time "t" (contactLaw)
> - define a new velGrad on the basis of computed forces
> - integrate bodies motion based on forces at time "t" and corresponding
> velGrad
> - integrate cell deformation using the same velGrad (we reseted forces
> in between, it doesn't matter)
>
> It should be correct if I don't miss something: forces(t) are used to
> define velGrad(t+dt/2) and body.vel(t+dt/2). I was not 100% sure when I
> wrote the code, so I added this note. The "else" would be using forces
> at time t to define velGrad at t+3dt/2.
>
Ok, thanks a lot.

Chiara

>
> Bruno
>
> --
> 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/159394/+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/159394
>
> You received this question notification because you asked the question.
>

-- 
You received this question notification because you are a member of
yade-users, which is an answer contact for Yade.