Multiple group membership for nodes

["niallcaldwell" <niall.caldwell@xxxxxxxx>]

Firstly, many thanks to David for his advice over the slotted 
armature problem I had. I was not aware that the "lamination" feature 
essentially did this BH scaling that I was trying to do. The point 
about radial gap is well taken- this is the case in most of my 
designs. I presume that, if the material is working in the linear 
portion of its BH curve, and the gap is small in comparison with the 
major dimensions of the armature and the slot circumferential width, 
then a good approximation to obtain the same gap reluctance is to 
increase the radial gap by the same ratio as the "lamination factor" 
at the outside of the armature? 

One other point which has come up. I often want to parameterise 
models so that I can sweep through a design space to find an optimum 
of two or more variables. I want to use Lua with nested "for" loops 
to do this, for instance generating armature force for a range of 
diameters and lengths of the armature. 

To do this from the starting point of existing geometry I need to 
select nodes by group in Lua- all the nodes on the outside diameter 
are in group 1, while all the nodes at the top end are in group 2. 
The trouble is, there is always at least one node which wants to be a 
member of both groups (ie the outer top corner). Is there any way to 
assign multiple groups to entities?

The other option is to build up the entire problem in the lua script, 
bypassing the GUI, creating keypoints with coordinates calculated by 
functions of defined parameters. That way individual nodes 
coordinates can be a function of many parameters. This is the most 
powerful and general way of parameterising, and the way I used to 
work with Ansys becuase its GUI is such a dog compared to femm's, but 
really.... life is too short! 

BTW this same nested loop technique can be used to generate lookup 
tables of force and inductance at a range of currents and armature 
positions, for export to dynamic simulation packages (AmeSim, Easy5, 
Simulink) This allows the complete dynamic simulation of a solenoid 
taking into account damping, spring, inertia, colomb friction, 
electric circuit switching... I have heard that transient phenomena 
eg. eddy currents can be taken into account by running a frequency 
analysis in FEMM and inserting parasitic lumped parameters into the 
dynamic model.

Niall