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# Multiple group membership for nodes

- To: femm@yahoogroups.com
- Subject: Multiple group membership for nodes
- From: "niallcaldwell" <niall.caldwell@ed.ac.uk>
- Date: Fri, 05 Sep 2003 01:15:11 -0000
- User-agent: eGroups-EW/0.82

    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

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  - Re: Multiple group membership for nodes
    - From: "David Meeker" <dmeeker@ieee.org>

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