yade-dev team mailing list archive

[Vincent Richefeu <richefeu@xxxxxxxxx>]

Hi,

I think that:

(1) if you consider the negative/positive force decomposition, so the negative viscous forces are to be taken into account like any other negative force. So just test the sign and it's ok (in my opinion, but it depends on why you want to do this decomposition)
(2) if you consider adhesive (negative) forces and contact (positive, elastic or not) forces, so you need to use the forces given by the force laws (and not the balanced force).

For instance. if you have f_n = f_elas + f_coh + f_visc, you can say:

(1) f_n is even positive or negative, so sigma = sigma^+ + sigma^-
(2) f_n results in 3 contributions, so sigma = sigma^elas + sigma^coh + sigma^visc (and I guess sigma^visc is about 0...)

Vincent 

Le 1 mars 2011 à 12:21, Chiara Modenese a écrit :

> Ok, then I would have a new question for you. I was thinking to apply Vincent's suggestion to plot fabric tensor considered as the sum of two contributions (which is already in code), one due to negative forces and the other to positive ones. The distinction could be made if one uses cohesive contacts, for instance. Say that you also include viscous damping, then you will not be able to distinguish between the contribution only due to cohesion since also damping, in fact, could change the sign of the forces. Vincent, do you have any other hint in this regard? Or maybe I could store the viscous and the spring force into two distinct vectors and play with that?
> 
> Thanks. Chiara
> 
> 
> On 1 March 2011 09:49, Chiara Modenese <c.modenese@xxxxxxxxx> wrote:
> Ok, I think I know why now. I mean, since I have viscous forces stored into normalForce that could be the cause.
> Cheers. Chiara
> 
> 
> On 28 February 2011 21:02, Chiara Modenese <c.modenese@xxxxxxxxx> wrote:
> Hi Guys,
> 
> small question. I was trying to plot normal force versus overlapping of all my interactions. For the normal force I want to keep the sign and so I simply project it onto the corresponding normal vector something like: Fn=i.phys.normalForce.dot(i.geom.normal). The problem is that, without adhesion and according to a certain convention, I expect forces all of the same sign whereas I sometimes record opposite ones. A problem in my script or why does that happen?
> 
> Thanks, Chiara
> 
> 
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