yade-dev team mailing list archive

[noreply@xxxxxxxxxxxxx]

------------------------------------------------------------
revno: 3666
committer: Raphael Maurin <raph_maurin@xxxxxxxxxxx>
timestamp: Tue 2015-06-02 19:39:01 +0200
message:
  Law2_ScGeom_ViscElPhys_Basic: complete the documentation
  Add a more precise documentation of the law integrating the last commit.
  I didn't complete the formulation associated with Pournin2001 (precising en,es,tc) as I am not using it and I do not know it much.
modified:
  pkg/dem/ViscoelasticPM.hpp


--
lp:yade
https://code.launchpad.net/~yade-pkg/yade/git-trunk

Your team Yade developers is subscribed to branch lp:yade.
To unsubscribe from this branch go to https://code.launchpad.net/~yade-pkg/yade/git-trunk/+edit-subscription

=== modified file 'pkg/dem/ViscoelasticPM.hpp'
--- pkg/dem/ViscoelasticPM.hpp	2015-06-02 17:09:57 +0000
+++ pkg/dem/ViscoelasticPM.hpp	2015-06-02 17:39:01 +0000
@@ -98,7 +98,7 @@
 		virtual bool go(shared_ptr<IGeom>&, shared_ptr<IPhys>&, Interaction*);
 	public :
 	FUNCTOR2D(ScGeom,ViscElPhys);
-	YADE_CLASS_BASE_DOC(Law2_ScGeom_ViscElPhys_Basic,LawFunctor,"Linear viscoelastic model operating on :yref:`ScGeom` and :yref:`ViscElPhys`. The model is mostly based on the paper for For details see Pournin [Pournin2001]_ .");
+	YADE_CLASS_BASE_DOC(Law2_ScGeom_ViscElPhys_Basic,LawFunctor,"Linear viscoelastic model operating on ScGeom and ViscElPhys. The contact law is visco-elastic in the normal direction, and visco-elastic frictional in the tangential direction. The normal contact is modelled as a spring of equivalent stiffness $k_n$, placed in parallel with a viscous damper of equivalent viscosity $c_n$. As for the tangential contact, it is made of a spring-dashpot system (in parallel with equivalent stiffness $k_s$ and viscosity $c_s$) in serie with a slider of friction coefficient $\\mu  = \\tan \\phi$.\n The friction coefficient $\\mu  = \\tan \\phi$ is always evaluated as $\\tan(\\min(\\phi_1,\\phi_2))$, where $\\phi_1$ and $\\phi_2$ are respectively the friction angle of particle 1 and 2. For the other parameters, depending on the material input, the equivalent parameters of the contact ($K_n$,$C_n$,$K_s$,$C_s$,$\\phi$) are evaluated differently. In the following, the quantities in parenthesis are the material constant which are precised for each particle. They are then associated to particle 1 and 2 (e.g. $kn_1$,$kn_2$,$cn_1$...), and should not be confused with the equivalent parameters of the contact ($K_n$,$C_n$,$K_s$,$C_s$,$\\phi$). \n - If contact time (tc), normal and tangential restitution coefficient (en,et) are precised, the equivalent parameters are evaluated following the formulation of Pournin [Pournin2001]_.\n - If normal and tangential stiffnesses (kn, ks) and damping constant (cn,cs) of each particle are precised, the equivalent stiffnesses and damping constants of each contact made of two particles 1 and 2 is made $A = 2*(a_1 a_2)/(a_1 + a_2)$, where A is $K_n$, $K_s$, $C_n$ and $C_s$, and 1 and 2 refer to the value associated to particle 1 and 2. \n - Alternatively it is possible to precise the Young modulus (young) and poisson's ratio (poisson) instead of the normal and spring constant (kn and ks). In this case, the equivalent parameters are evaluated the same way as the previous case with $kn_x = E_x d_x$, $ks_x = v_x*kn_x$, where $E_x$, $v_x$ and $d_x$ are Young modulus, poisson's ratio and diameter of particle x. \n - If Yound modulus (young), poisson's ratio (poisson), normal and tangential restitution coefficient (en,et) are precised, the equivalent stiffnesses are evaluated as previously:  $K_n = 2*(kn_1 kn_2)/(kn_1 + kn_2}$, $kn_x = E_x d_x$, $K_s = 2*(ks_1 ks_2)/(ks_1 + ks_2)$, $ks_x = v kn_x$. The damping constant is computed at each contact in order to fulfill the normal restitution coefficient $e_n = (en_1 en_2)/(en_1 + en_2)$. This is achieved resolving numerically equation 21 of [Schwager2007]_ (There is in fact a mistake in the article from equation 18 to 19, so that there is a change in sign).  Be careful in this configuration the tangential restitution coefficient is set to 1 (no tangential damping). This formulation imposes directly the normal restitution coefficient of the collisions instead of the damping constant. \n");
 	DECLARE_LOGGER;
 };
 REGISTER_SERIALIZABLE(Law2_ScGeom_ViscElPhys_Basic);