Developer's-corner/Boundary-Conditions.md

@@ -30,14 +30,24 @@ When a 3D simulation is done by considering only one disk hemisphere (in case of
 is automatically introduced at disk midplane. The vertical boundary condition will be then  applied only to the gridcells having $`\phi =`$ Opening. 
  
 Possible boundaries are: 
-1. ``open`` valid both for 2D and 3D disc. An open boundary will
+1. ``open`` is a radial boundary condition valid both for 2D and 3D disc. An open boundary will
 let the gas flowing out at the innermost and outermost radial
 gridcell by copying the density of the first active layer
 into the ghost one. The sign of the radial velocity controls the
 outflow condition.
-2. ``reflectingR`` and ``reflectingZ`` (3D case only) are commonly used boundaries.
-All the quantities are copied from the active cell  
-
+2.  ``reflectingZ`` for the 3D case only, is a mandatory choice for the 3D case unless the user set his own vertical boundary condition.
+All the quantities are copied from the first active layer into the
+ghost one except the component of the velocity normal to the layer
+that is reflected (copied changing the sign).
+3. ``reflectingR`` is a radial boundary condition (2D and 3D simulations). As for the vertical  condition ``reflectingZ`` all the hydro dynamical quantities are copied from the first active layer into the ghost one a part the radial component of the velocity which is reflected.
+3. `` evanescent `` is probably the most used radial boundary condition. The aim is to damp waves that propagates and reflect at the ghost cell creating annoying reflections phenomena in the whole
+disk. The damping function is described in : de Val-Borro M., Edgar R.~G., Artymowicz P., Ciecielag P., Cresswell P., D'Angelo G., Delgado-Donate E.~J., et al., 2006, MNRAS, 370, 529. 
+This condition is active in a specific radial domain (whose size in
+the code is set according to  Benitez-Llambay P., Ramos X.~S., Beauge C., Masset F.~S., 2016, ApJ, 826. 
+This condition requires to provide azimuthally averaged values for
+the whole set of hydrodnamical quantities in the damping domain.
+In general such values are provided by initial conditions. The idea
+is that the disc is unperturbed  at the innermost and outermost radial layers. The damping domain ensures convergence to unperturbed conditions.
 
 ## Adding new boundaries conditions