Re: Circuits in FEMM

[frank.e.lenning@xxxxxxxxxx]

--- In femm@xxxx, dcm3c@xxxx wrote:
> In a message dated 9/5/01 12:52:32 PM Eastern Daylight Time, 
> frank.e.lenning@xxxx writes:
> 
> 
> > 
> > Thanks Dave. What is the equation that FEMM solves for the time 
> > harmonic case and where does it do it in the FEMM source code?
> > 
> > 
> > 
> I've put a brief note in the "files" section on the extra equation 
that the 
> program solves associated with each current constraint:
> <A 
HREF="http://groups.yahoo.com/group/femm/files/currentconstraint.pdf";>
http://groups.yahoo.com/group/femm/files/currentconstraint.pdf</A>
> 
> The source code associated with it lives (for the 2d planar case) in 
the 
> prob2big.cpp and (for the axisymmetric case) prob4big.cpp files of 
fkn. The 
> code that enforces it is sort of strewn around, because the extra 
equation 
> really gets built implictly. Only the upper diagonal of the matrix 
is 
> stored, because of the symmetry of the problem, so the extra 
equation gets 
> built by adding extra forcing terms associated with the unknown 
gradient to 
> the elements that live in the regions associated with the circuit. 
Look for 
> the comments that show where the circuit parts live (e.g. lines 
> 78-89,294-302, 335-340 in prob2big, similar implementation in 
prob4big) . In 
> the source code, the voltage gradients are included in the vector of 
unknowns 
> right after the nodal values of potential. The voltage gradients 
also get 
> written to disk in the .ans file.
> 
> Dave.


Way cool Dave. Thanks. What I was really trying to do was understand 
better how FEMM solved this problem to tell if I could get another 
code, Quickfield, to do the same problem (I've been using FEMM but 
some others in my workgroup already own Quickfield). By your fine 
writeup, I believe the answer is no since Quickfield doesn't exactly 
have the same circuits capability and without setting up and solving 
the equations with the unknown potentials, you have nothing better to 
do but to guess at them and iterate...ugly. Your open source is great. 
I had already found the place in prob2big and your note will help me 
understand what I'm seeing better. BTW, your support of this group is 
nothing short of amazing. Microsoft could take some product support 
lessons from you.

On a related subject, I'm interested in a 3D FEM as well. Is there a 
public domain 3D mesher out there like triangle (or can triangle do 
it)?? I assume one could use the same solver engine as FEMM but the 
mesher and visualizations would need to change.