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<p><font face="Times New Roman, Times, serif">Hello Profs Christophe
Geuzaine and Jean-François Remacle, or others<br>
<br>
I have been experimenting with gmsh-getdp electromagnetic
simulation, focusing on magnetostatic cases involving 3D
solenoidal inductors with permeable cores. Overall, I am greatly
impressed with gmsh/getdp's capabilities and organization, but I
have run into some difficulties I can't seem to get past. <br>
<br>
My objective is to design a complicated magnetic flux collector
for an alternating magnetic field sensor in a borehole. I am
working only with your compiled software, as I am not a C
programmer. Since there is no built-in provision in gmsh-getdp
for creating an external (uniform) field and observing the
voltage it induces in the solenoid, I have been trying to do the
inverse EM problem of finding the distant b magnetic field
generated by current in the inductor (as modified by the core).<br>
<br>
<b>Problem 1</b> I can run your Inductor (3d) model with no
difficulty, and also a very simple test model (SensTest) of a
cylindrical inductor with cylindrical core. However, when I
have tried to incorporate a more complicated flux collector
system (my model sensor), the model seems to mesh and display
properly, but getdp provides a physically wrong source current <i>js</i>
even though <i>js0</i> is correct. <br>
<br>
Although the stranded inductor current density <i>js0</i> is
(correctly) a simple, unidirectional, cylindrical current, </font><font
face="Times New Roman, Times, serif"><font face="Times New
Roman, Times, serif">along the inner boundary of the inductor,
</font>the <i> js</i> derived from it is directed in the correct
annular direction but flows in the wrong (opposite) direction in
all outer parts of the inductor. The resulting b field seems
correct for this<i> js</i>, but it is incorrect for the provided
<i>js0</i>.<br>
<br>
I have likely caused this problem by some misunderstanding or
simple coding error; but I cannot find the bug</font><font
face="Times New Roman, Times, serif"><font face="Times New
Roman, Times, serif"> after many hours of experimenting</font>.
Can you give me any suggestions?<br>
<br>
<b>Problem 2</b> In both sensor and senstest, I have used the
spherical extension to infinity </font><font face="Times New
Roman, Times, serif"><font face="Times New Roman, Times, serif">of
the external field </font>that is employed in your Inductor
example. I have no difficult in displaying the vector field
using your graphics GUI, but I want quantitatively </font><font
face="Times New Roman, Times, serif"><font face="Times New
Roman, Times, serif">to </font>analyze the b vector flux
density near the radius of the inner sphere. I can read the <i>_.res</i>,
<i>_.pre</i> and <i>_.pos</i> output files in Matlab, but have
had difficulty interpreting the vector components in the file;
especially in relating them exactly to what I see in the gmsh
GUI vector plots and to the mesh nodal coordinates. Are the
gmsh-plotted vectors already interpolated from the edge element
values of <b>A</b> onto a different grid? The GUI<i> b</i>
vector plots seem to provide one vector per tetrahedron, (as
best I can tell), but the data output file<i> b.pos</i> etc.,
provides 6 components per tetrahedron, suggesting something
different.<br>
<br>
Can you direct me to any documentation about how to relate the
field values </font><font face="Times New Roman, Times, serif"><font
face="Times New Roman, Times, serif">in <i>b.pos</i> </font>to
the mesh node location for the EM case where edge elements are
employed in the analysis.<br>
<br>
I feel badly asking for this much support from a freeware
provider. If what I am asking is too onerous, I might be able to
provide modest remuneration to a person, or make a contribution
to an organization for this effort. Please don't hesitate to
ask.<br>
<br>
I append the file tree I have used with gmsh-getdp. I have
worked with versions 2.14 to 2.16.<br>
<br>
With sincere thanks<br>
<br>
Gordon West <br>
Retired Prof of Physics (geophysics), Univ of Toronto<br>
Consulting geophysicist<br>
</font></p>
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