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<p>Dear all,</p>
<p>apologies, I just realized I crossed the subjects of two
different (related questions). Following up using the previous
geometry, though.</p>
<p>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:</p>
<p><i>**************************************************************************************************</i><br>
</p>
<p><i>*Heading</i></p>
<p><i>*NODE</i></p>
<p><i><bunch of coordinates and labels></i></p>
<p><i>*ELEMENT, type=CPS3, ELSET=Surface1 </i><i><b> -> This is
bad </b></i><i>(in my application, of course)</i><i><br>
</i></p>
<p><i><bunch of labels and connectivity></i></p>
<p><i>*ELEMENT, type=C3D4, ELSET=Volume1</i></p>
<p><i><bunch of labels and connectivity></i></p>
<p>**************************************************************************************************</p>
<p>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).</p>
<p><br>
</p>
<p>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,</p>
<p><br>
<i>**************************************************************************************************</i></p>
<p><i>*ELSET, </i><i><i>ELSET</i>=test-surface_S6, generate</i><i>
<b>-> This would generate an element set of 16 elements whose
facets are in the boundary of interest</b><br>
</i><i> 1, 61, 4</i><i><br>
</i><i>*SURFACE, type=ELEMENT, name=test-surface</i><i> <b>->
This would generate the surface using the previous element 6
and facet S6 of the hexahedra </b>(there is a convention in
Abaqus for this)<br>
</i><i>test-surface_S6, S6</i></p>
<p>**************************************************************************************************</p>
<p>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).</p>
<p><br>
</p>
<p>So, finally, my question: <b>is there any way of retrieving
elements (*ELSETS) and nodes (*NSETS) of ONLY a volume mesh in
Gmsh? </b>Take as an example the enclosed INP files (geometries
in line with my previous email):<br>
</p>
<p>1) thin-lens-duplicate-geo.inp: this file was exported after
meshing the volume and without a physical group -> "Wrong" file
definition<br>
</p>
<p>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. <i><b>-> Can we obtain
this information somehow in Gmsh?</b></i><br>
</p>
<p><i><b>Note:</b></i> the *.geo files and the *.STL correspond to
the ones used for generating the INP files.</p>
<p><br>
</p>
<p>This topic also raised an additional question for me:</p>
<p>1) <b>Can we have internal boundaries if there is, for example,
an inclusion inside a lens?</b> E.g., bubble of air. This would
help defining internal contacts or pressures or the like.<br>
</p>
<p><br>
</p>
<p>Best regards and apologies for the crossed subject once again,</p>
<p>MA<br>
</p>
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