# GetDP

robin.cornelius robin.cornelius at btinternet.com
Fri Mar 17 18:02:47 CET 2000

```I am currently experimenting with GetDP in order to use it on some magnetics
problems I am doing some research into. I was hoping if you could give some
advice on using GetDP for the problem I will now describe:-

I am involved in pulsed field magnotometry, that is we expose samples of
magnets to a sinusoidal pulse that is of high enough field strength to
ensure the magnet will completely saturate during both the positive and
negative parts of the pulse. (We achieve this using capacitor banks
discharging in to large coils). We measure the applied field and also deduce
the M-field of the magnet to produce MH and BH plots.

I am currently trying to simulate this process so we can look at the effects
of eddy currents with in the magnet.

The problem could initially be looked at in 2D. I do however wish to use
transient analysis (not time harmonic);

The domains would consist of Air with some source conductors with in it and
The Permanent Magnet.

1.
My first main question is how to introduce a source current density that is
time dependent. I have tried adjusting the examples but do not seem to find
a way of making it work. In your examples you use the source current density
as a constraint in the inductor region, but it doesn't seem possible that
the constraint can be time dependent. How can I get a time varying source ?

I have seen a situation in a commercial FEA package ( using magnetic scalar
potential formulation) where a boundry condition was set to be time step
dependent, so at each time step the magnetic scalar potential was calculated
for the boundary thus producing a homogenous field. If this was possible it
would be good but I would really like to be able to set time dependent
current densities.

2.
I need to be able to model non linear materials. I have looked at using M =
Atan (B)  and mu = differential of (Atan(B) models of material
characteristics. I have introduced this for mu in the time domain example
given, but I would like to know if it is possible to use a different mu[]
for different time steps so that I could use mu[a] for 0 < time <0.25 ,
mu[b] for 0.25 <time <0.75 and mu[a] for 0.75<time<1. (Where time varies
from 0-1). The reason I would like to do this is so I can use two Atan
models ie Atan(x+c) and Atan(x-c)  so that hysterysis of the material is
taken into account.

3. I would like to introduce into the formulation the ability to have eddy
currents in the permanent Magnet and have the M field of the permanent
Magnet included in the simulation as well. Do you have any advice for doing
this .

Thankyou very much for you help

Best Regards

Robin Cornelius
Robin.cornelius at btinternet.com

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