Question #267566 on Yade changed:
https://answers.launchpad.net/yade/+question/267566
Status: Open => Answered
Raphaël Maurin proposed the following answer:
Hi,
The spring-dashpot law is a contact law with an equivalent spring-viscous
damper system (+ tangential friction) and is called in yade
Law2_ScGeom_ViscElPhys_Basic. The possible differences with what you call the
spring-dashpot law stand in the way you are evaluating the equivalent
spring-viscous damper constants. In a way, it is then up to you to know how you
want to compute these equivalent constant. In Yade, there is different
possibilities depending on what you precise in the material you define:
- If you precise the contact time (tc) and the normal and tangential
restitution coefficient (en and es), it is computing the equivalent stiffnesses
and viscous damping from the formulation of Pournin 2001 (see in yade ref).
This is not what is usually called spring-dashpot law.
- If you precise the normal and tangential stiffnesses (kn, ks) and damping
constant (cn,cs) of each particle, it is computing the equivalent stiffnesses
and damping constant of each contact made of two particles 1 and 2 according to
kn = 2*kn1*kn2/(kn1+kn2), and the same for ks, cn and cs. This is probably the
nearest from spring-dashpot law except that you do not precise directly kn and
the restitution coefficient.
- Another alternative (more practical when dealing with polydisperse sample) is
to precise the young modulus (E) and poisson's ratio(v), and the damping
constants of each particle. The equivalent damping constant of the contacts are
calculated as the previous case, and computing the spring constant is evaluated
considering kn1 = E1*R1 and kn2 = E2*R2 (R: radius), while ks1 = v1*kn1 and ks2
= v2*kn2.
-With Francois Kneib, we developed another alternative (which is not commited
for now) where you can precise directly the young modulus, poisson's ratio, and
restitution coefficient. If necessary, this can be commited quickly.
Here are more or less the details about this contact law, for more precisions,
look at the source code
(https://github.com/yade/trunk/blob/master/pkg/dem/ViscoelasticPM.cpp).
Concerning your question, to resume my answer would then be that the contact
law you are looking for is Law2_ScGeom_ViscElPhys_Basic, and that depending on
how you want to evaluate the equivalent constants of the contact, you can use
the different inputs for the material, or develop another way in the contact
law.
I hope it is clear, don't hesitate to ask question if it is not the
case.
Raphaël
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