====== Create progressive 2D structured mesh with Z-set mesher ======
{{:recherche:softs:derafinee.png?400|}}

When simulating large domains with structured mesh (to avoid border effects for instance), it could be usefull to use the NG_extension mesher function of Z-Set (which - of course - is not even mentioned in Z-Set documentation).

This function allows to extend a 2D quadrilateral mesh, divinding the mesh size by two. 
The function takes the following parameters:
  * *bset _bset_ : the border set to extend
  * *length _float_ : total length of the extension
  * *nb\_extension _int_ : number of extension (2 will for instance consists of two extension floor divinding th initial size by 4)
  * *direction _x y z_ : direction of extension

The following example computes a simple 2D extension

<Code:shell>
****mesher
	***mesh deraf
		**mesh_lin_rectangle
			*ncutx 20
			*ncuty 1
			*sizex 1
			*sizey 0.05
		
		**bset toExtend
			*use_nset y0
		
		**NG_extension
   		*bset toExtend
   		*length 0.05
   		*nb_extension 1
   		*direction (0. -1.)
		**translate 0. 0.1 0.
	***mesh deraf
		**mesh_lin_rectangle
			*ncutx 10
			*ncuty 1
			*sizex 1
			*sizey 0.05
		**union 
			*add deraf.geof
****return
</Code>

====== What about 3D ? ======
{{:recherche:softs:double_deraf.png?400|}}

For 3D meshes, a simple way to use the above function is to combine two extension planes as follows: 

<Code:shell>
****mesher
	***mesh deraf
		**mesh_lin_rectangle
			*ncutx 20
			*ncuty 1
			*sizex 1
			*sizey 0.05
		
		**bset toExtend
			*use_nset y0
		**elset toDel 
			*add_elset ALL_ELEMENT
			
		**NG_extension
   		*bset toExtend
   		*length 0.05
   		*nb_extension 1
   		*direction (0. -1.)
		
		**delete_elset toDel
		
		**extension 
			*distance 1.
			*num 20
			*dir (0. 0. -1.)
	***mesh deraf
		**mesh_lin_rectangle
			*ncutx 20
			*ncuty 1
			*sizex 1
			*sizey 0.05
		
		**bset toExtend
			*use_nset y0
		**elset toDel 
			*add_elset ALL_ELEMENT
			
		**NG_extension
   		*bset toExtend
   		*length 0.05
   		*nb_extension 1
   		*direction (0. -1.)
		
		**delete_elset toDel
		
		**extension 
			*distance 1.
			*num 10
			*dir (0. 0. -1.)
		**translate 0. -0.05 0.
		**rotate 
			x1 0. 0. -1.
			x3 1. 0. 0.
		**translate 1. 0. 0. 
		**union
			*add deraf.geof	

****return
</Code>