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# Re: [femm] single wire -magnetic potential A problem

- To: dcm3c@aol.com
- Subject: Re: [femm] single wire -magnetic potential A problem
- From: rm1176@messiah.edu
- Date: Wed, 17 Oct 2001 21:10:24 -0400 (Eastern Daylight Time)
- Cc: femm@yahoogroups.com
- In-reply-to: <3e.13021d29.28ff0a16@aol.com>

    Hello,
    My name is Robert Marshall from Messiah College in Pa. My senior project
    is design a passive magnetic bearing system. We are wondering if there is any
    way to simulate a coil of wire in FEMM. We are also looking for a decent
    magnet supplier and any possible leads on finding information on this topic.

    On Wed, 17 Oct 2001 dcm3c@aol.com wrote:

    > In a message dated 10/16/01 10:09:23 PM Eastern Daylight Time,
    > tborzic@yahoo.com writes:
    >
    >
    > > Hello everybody, My name is Tomislav and as You may assume
    > > I'm new here and I am looking for some help regarding FEMM.
    > > I am trying to solve some "simple" problem.It goes like this:
    > > 1. Round wire,copper, infinite lenghth,we look at cross section
    > > ,r=0.075m =7.5cm, I= 100 + j0 A,f= 50Hz, relative
    > > permeability is 1.Working with old "pen and paper" i got some results
    > > which are sure correct.Point is to get same thing in FEMM.
    > > What I do is called "numerical callculations of eddy current in round
    > > conductor".I nedd to obtain values of "A" in points r1=0, r2=0.25,
    > > r3=0.5 and r4= 0.75. (In point r4 A = 0, boundary conditon,allready
    > > given).
    > > So what I need is that some one helps me to solve this,tell me
    > > how to define parameters for my problem in FEMM,keeping in mind that I
    > > am new here,but in near future i intend to use FEMM rather often.
    > > My results are:
    > > A1=0.9999951 x10-5 -j0.2109364 x10-7
    > > A2=0.8888852 x10-5 -j0.1666658 x10-7
    > > A3=0.5555543 x10-5 -j0.6510389 x10-8
    > > A4=0.5169879 x10-22 -j0.6638621 x10-19 ( this should be 0 but
    > > this is good enough)
    > > So I need to obtain this rezults with FEMM.
    > > Thanks
    > >
    > This problem is really similar to the example at <A HREF="http://femm.berlios.de/tube/tube.htm";>
    > http://femm.berlios.de/tube/tube.htm</A> Following a similar chain of reasoning
    > to this example, one can show that the solution for tangentially-directed H
    > as a function of radius r is:
    >
    > H = i/(2 Pi R) BesselI[1,a*r]/BesselI[1,a*R]
    >
    > where a=(1+j)/d, and skin depth d is d = Sqrt[1/(Pi*freq*mu_o*sigma)] where
    > freq is the frequency in Hz, mu_o is permeability of free space, and sigma is
    > electrical conductivity. R is the outer radius of the wire, and i is the
    > total current carried by the wire. In my notation, j = Sqrt[-1] and
    > BesselI[1,x] is the modified Bessel function of order 1 of the first kind.
    >
    > I've attached a .fem solution for the same problem. The agreement with the
    > analytical solution is pretty good.
    >
    > > P.S. To mr. David Meeker:
    > > i am translating User's manual to Crotian,for my personal needs,and
    > > for other students on University of Split, who may need it.When I am
    > > done (about 20 days i guess), I can convert it to *.pdf and send it to you
    > > if you want,and make it available for everybody on internet?
    > >
    > > Tomislav Borzic
    > > tborzic@yahoo.com
    > >
    >
    > Great! When you finish it, I'll post it on the web site.
    >
    > Dave
    > --
    > David Meeker
    > <A HREF="http://members.aol.com/_ht_a/dcm3c";>http://members.aol.com/_ht_a/dcm3c</A>
    >

- References:
  - Re: [femm] single wire -magnetic potential A problem
    - From: dcm3c@aol.com

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