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<div class="moz-cite-prefix">I had a look at your .geo and I found a
small error. Your three line loops are not defined in the same
way. The first is counterclokwise, the second is clockwise and the
third one is counterclockwise. All should be defined
counterclockwise.<br>
So you need to change Line Loop(13) = {3, 5, 6, 7}; to Line
Loop(13) = {-3, -5, -6, -7};<br>
and it will work. I checked<br>
<br>
Best regards<br>
<br>
Paul Cristini<br>
<br>
Le 06/09/2012 16:41, <a class="moz-txt-link-abbreviated" href="mailto:giuseppe.digiulio@ingv.it">giuseppe.digiulio@ingv.it</a> a écrit :<br>
</div>
<blockquote
cite="mid:20120906164109.17880dcqnwkrm0aw@webmail.rm.ingv.it"
type="cite">I am a new user of specfem2D and I am trying to
generate an external simple 2D mesh using gmsh; this seems one
nice external fe grid generator as indicated by specfem2d user
manual (version 7, page 10).
<br>
<br>
My question is about Jacobian as returned by the script
xcheck_quality_external_mesh.
<br>
<br>
I built using gmsh a simple geometry file composed of three
uniform layers (see the attached *geo file).
<br>
<br>
I performed a 2D mesh using allquads following the example shown
in specfem2D manual (fixing a minimum element size of 20 because
dimension of my model is relatively big).
<br>
<br>
gmsh 3UFscale_allquad.geo -2 -clmin 20 -order 2
<br>
<br>
I set the absorbing conditions with the python script
<br>
python ../LibGmsh2Specfem.py 3UFscale_allquad -t A -b A -r A -l A
<br>
<br>
obtaining the Mesh* Material* Nodes* Surf_abs_* and Surf_free*
files.
<br>
<br>
Now my problem is in the quality of my mesh as returned by
xcheck_quality_external_mesh because it returns negative jacobian.
<br>
<br>
xcheck_quality_external_mesh
<br>
:::::::
<br>
start reading the external node file: Nodes_3UFscale_allquad
<br>
start reading the external mesh file: Mesh_3UFscale_allquad
<br>
NPOIN = 12663
<br>
NSPEC = 12462
<br>
done reading the external files
<br>
<br>
start checking if any element with a negative Jacobian is found
<br>
element 6251 has a negative Jacobian
<br>
STOP negative Jacobian found
<br>
::::::
<br>
<br>
I do not know how can I improve my mesh to pass this check; I try
to delete the element 6251 with negative Jacobian but this is not
the only one. I tried different options in the 2D meshing, but
still obtaining negative jacobian.
<br>
<br>
And it is also strange that the Jmin seems 0.497 when I use
Tool/plugins og gmsh to analyseCurveMesh (see picture in attach).
If I understood well from gmsh manual (pa. 66) Jmin should be the
minimum Jacobian and this seems not negative.
<br>
<br>
I also attached the output files output_mesher.txt and
output_solver.txt obtained by xmeshfem2D and xspecfem2D,
respectively.
<br>
Of course xspecfem2D crashs, and all elements with negative
Jacobian are reported into output_solver.txt.
<br>
<br>
So my question is: how can I improve my external 2D mesh built by
gmsh for having positive jacobian everywhere ?
<br>
<br>
If someone of developpers has any suggestions to improve my mesh
deleting elements with negative jacobian in my mesh, these are
welcome!!!
<br>
<br>
The file *tar.gz contains my trial of mesh
<br>
<br>
Best regards and thank you in advance!
<br>
<br>
Giuseppe Di Giulio
<br>
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<br>
<br>
<pre class="moz-signature" cols="72">--
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--------
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