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# transient analysis

- To: FEMM Discussion <femm@yahoogroups.com>
- Subject: transient analysis
- From: William Brodie-Tyrrell <wfbrodie@smug.adelaide.edu.au>
- Date: Fri, 13 Jun 2003 16:59:02 +0930 (CST)

    /me is yet another coilgun idiot, something that FEMM appears to be plagued
    with :) I'm the one slashdotted a few months ago for collecting flash
    capacitors from disposable cameras; my simulation efforts are resuming now
    that I've got hold of some suitable SCRs.

    I'm trying to do transient analysis of a thompson coilgun (coil induces
    current in conductive ring, currents are opposite due to Lenz's law and
    therefore repel). By careful placement of iron, I hope to maintain force on
    the armature over non-trivial distances, more than "the length of the
    solenoid" that is available from dragging a ferromagnetic armature into a
    coil. Therefore I can have longer pulse lengths for a given muzzle velocity,
    bigger Cs, lower currents, cheaper switching and more efficiency. I hope :)

    I wrote a lua script which measured lorentz force between the coils for
    different armature position, size, current, etc, but what I haven't figured
    out is how to determine the coupling between the coils and therefore the
    actual current that would be induced in the armature. The currents are
    currently hardwired in and give me a {F, L} cf position cf I profile for the
    structure. Then I plug those values into matlab to simulate an actual
    discharge.

    So, is there a handy block integral in FEMM that can tell me something like
    voltage gradient induced in the ring based on dI/dt (therefore dB/dt) from the
    driver coil? I'm using an axis-symmetric model.

    for those playing with solenoids,
    http://users.on.net/gbt/coilgun/solenoid-9-6-03.tgz
    contains yet another solenoid sim. Included is .FEM models, lua scripts,
    femm/lua output data and matlab source for simulating a discharge (output is
    I, F & velocity graphs). Consider it to be in the public domain.

    William Brodie-Tyrrell

    --
    "There is no God and Dirac is his prophet"
    -- Wolfgang Pauli

    <wfbrodie@smug.adelaide.edu.au>
    http://www.cs.adelaide.edu.au/~william

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