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<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 b 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>
<br>
<br>
<br>
<br>
</font>
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