====== DG shell interactions ======

Once [[doc:user:elements:shells:shell|shell interactions]] are defined, they must be completed with (Discontinuous Galerkin) interface interactions, following the well-known material-element-interaction pattern.
 

===== Materials =====

First, the material is defined as:

  materialno = materialset.define (number, type)
  materialno = materialset(number)
  materialno.put(param, value)
  materialno.depend(param, fct, Key(Lock)))
  ...

|''number'' | material number (must be unique with respect to all elements in ''materialset'', not to shells)  |
|''type'' | shell type (for example ''DgShellMaterial'') |
|''param'' | name of the shell parameter (for example ''STABILIZATION_PARAMETER'') |
|''value'' | value of the corresponding parameter ''param''|
|''fct'' | function which characterizes the dependency of the property (optional: no fct if no dependency) |
|''Lock'' | [[doc:user:general:locks|Lock]] which defines the dependency variable of the property (compulsory if there is a dependency) |

====  DgShellMaterial ====

=== Description ===

DG law for shell interface elements.

==== Parameters ====
^   Name            ^     Metafor Code     ^  Dependency ^
| Stabilization parameter (>1)                   |   ''STABILIZATION_PARAMETER''    |              |

===== Elements =====

After defining the [[#Materials|material]], it must be associated to an ''[[doc:user:elements:general:def_element_properties|ElementProperties]]'':

  prp = ElementProperties(typeEl)
  prp.put(param1, value1)
  prp.depend(param1, fct1, Lock1)) #facultatif
  ...

where

|''type'' | desired type of element (for example ''DgShellFirstDegreeElement'') |
|''param1''| name of the property associated to the element (for example ''MATERIAL'' to associate the desired material)|
|''value1''| value of the corresponding property |
|''fct1''| function which characterizes the dependency of the property (optional: no fct if no dependency) |
|''Lock1''| [[doc:user:general:locks|Lock]] which defines the dependency variable of the property (compulsory if there is a dependency) |

====  DgShellFirstDegreeElement ====

DG interface element to insert between shells. These are 2-nodes linear lines, but they are interfering over all neighboring dofs. 

By default, stresses are integrated over ''dim*2'' integration points. The material used is  [[doc:user:elements:shells:interface#dgShellMaterial]].



====  DgShellSecondDegreeElement ====

Same as ''DgShellFirstDegreeElement'', but 8-nodes second order shell element.


====  DgShellNineNodeSecondDegreeElement ====

Same as ''DgShellSecondDegreeElement'', but 9-nodes second order shell element.

====  DgShellSixteenNodeThirdDegreeElement ====

Same as ''DgShellNineNodeSecondDegreeElement'', but 16-nodes third order shell element.


==== Parameters of shell DG interface elements ====
^   Name            ^     Metafor Code     ^  Dependency ^
| ''MATERIAL''    | Number of the material to consider              |  -  |
| ''STIFFMETHOD'' | Method used to compute the stiffness matrix \\ = ''STIFF_ANALYTIC'' : analytic matrix (default) \\ = ''STIFF_NUMERIC''  : numerical matrix            |  -  |
| ''BENDING_NPG''  | Number of integration points along one direction for bending solving \\ = 2 classical solving  (second order)\\ = 3 EAS solving with 22 or 7 added modes (8 or 9-nodes second order)\\ = 4 solving without EAS (16-nodes third order)  |  -  |


===== Interactions =====

[[doc:user:elements:shells:interface#Eléments|DG shell interface elements]] are generated at the start of the simulation by a ''DgShellInteraction'' [[doc:user:general:glossaire#Interaction]], defined over desired entities. 

  dg = DgShellInteraction(number)
  dg.push(gObject1)
  dg.push(gObject2)
  ...
  dg.addProperty(prp)
  interactionset.add(dg)                 # the interaction is added in InteractionSet 

or

  dg = interactionset.add( DgShellInteraction(number) )
  dg.push(gObject1)
  dg.push(gObject2)
  ...
  dg.addProperty(prp)


| ''number'' | User number of the interaction|
| ''gObject1'', ''gObject2'' | mesh geometric entities where the finite elements are applied |
| ''prp'' | [[doc:user:elements:general:def_element_properties|Properties]] of[[doc:user:elements:shells:interface#Elements|DG interface elements]] to generate |

Careful, for now if two entities have common nodes, to many elements will be generated.