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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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