[Gmsh] About *Surface sets in Gmsh - Abaqus

[MA Ariza-Gracia]

Dear all,

apologies, I just realized I crossed the subjects of two different 
(related questions). Following up using the previous geometry, though.

The problem is that when you create a volume mesh from some STL surfaces 
and export it to an Abaqus INP, the structure of the INP file is as follows:

/**************************************************************************************************/

/*Heading/

/*NODE/

/<bunch of coordinates and labels>/

/*ELEMENT, type=CPS3, ELSET=Surface1 //*-> This is bad *//(in my 
application, of course)//
/

/<bunch of labels and connectivity>/

/*ELEMENT, type=C3D4, ELSET=Volume1/

/<bunch of labels and connectivity>/

**************************************************************************************************

The main problem here is that a 2D triangular mesh is generated on top 
of the 3D solid mesh which is not the goal. The goal is, for example, to 
have a *SURFACE definition in which to apply a pressure boundary 
condition / contact definition WITHOUT adding an additional 2D mesh on 
top. This *SURFACE definition should be done with the facets of the 
elements that belong to the volume but are on the surface (hopefully, it 
was clear).


In Abaqus, the surface definition can be Element-based or Node-based. 
For the Element-based, the *SURFACE is defined as a group of element 
sets and the facet that should be used for defining the surface. For 
example,


/**************************************************************************************************/

/*ELSET, ///ELSET/=test-surface_S6, generate//*-> This would generate an 
element set of 16 elements whose facets are in the boundary of interest*
//  1,  61,   4//
//*SURFACE, type=ELEMENT, name=test-surface//*-> This would generate the 
surface using the previous element 6 and facet S6 of the hexahedra 
*(there is a convention in Abaqus for this)
//test-surface_S6, S6/

**************************************************************************************************

Yesterday, I delved a bit in the source code and I think there is not 
such an option (only NSETS and ELSETS) but, if we would be able to 
retrieve (somehow) those elements with facets on the surface of 
interest, we could actually build the surface with a bit of 
post-processing (tedious but doable).


So, finally, my question: *is there any way of retrieving elements 
(*ELSETS) and nodes (*NSETS) of ONLY a volume mesh in Gmsh? *Take as an 
example the enclosed INP files (geometries in line with my previous email):

1) thin-lens-duplicate-geo.inp: this file was exported after meshing the 
volume and without a physical group -> "Wrong" file definition

2) thin-lens-volume-geo.inp: this file was exported after meshing WITH a 
physical group for the volume. Here, there is no wrong additional 2D 
elements, but we do not have any information about elements or nodes in 
a target surface. /*-> Can we obtain this information somehow in Gmsh?*/

/*Note:*/ the *.geo files and the *.STL correspond to the ones used for 
generating the INP files.


This topic also raised an additional question for me:

1) *Can we have internal boundaries if there is, for example, an 
inclusion inside a lens?* E.g., bubble of air. This would help defining 
internal contacts or pressures or the like.


Best regards and apologies for the crossed subject once again,

MA

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