[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

# Re: [femm] Asymptotic boundary condition

- To: femm@yahoogroups.com
- Subject: Re: [femm] Asymptotic boundary condition
- From: David Meeker <dmeeker@foster-miller.com>
- Date: Tue, 05 Feb 2002 10:34:46 -0500
- References: <20020205080840.1994.qmail@web10902.mail.yahoo.com>

    marco valcavi wrote:

    > Hello
    > I tried to make a simple simulation to verify the
    > asymptotic b.c.
    > I take a coil with a current and I simulate the B
    > field at 1 m on axis (B1) and 90° off axis (B2). In
    > the field produced by a dipole the ratio between B1
    > and B2 should be 3 but with the mixed b.c. and the
    > appropriate c0 I find that the ratio is nearly 2.
    > I make an error somewhere?

    A smoothing scheme is used in femm to smooth out the flux density which would
    otherwise be piece-wise constant in each element. One of the points that you
    examined (1 m on axis) is in a corner, where the smoothing scheme isn't so
    accurate--not enough information to do really good smoothing. Flux density is
    also less accurate on exterior boundaries than in the middle of the domain
    (but not as bad as corners). You are just seeing areas where the smoothing
    algorithm doesn't perform so great. If you want to turn off the smoothing
    algorithm for comparison, you can do it by unchecking View|Smoothing from the
    main menu of the post-processor.

    At points that aren't right on the boundary, the field is as you might expect.
    The field from a loop of current viewed from far enough away so that it looks
    like a dipole is:

    {Br,Bz} = {{(3*a*ni*r*uo*z)/(4*Pi*(r^2 + z^2)^(5/2)), -(a*ni*uo*(r^2 -
    2*z^2))/(4*Pi*(r^2 + z^2)^(5/2))}}

    where a is the loop's area, ni is the amp-turns carried by the loop, uo is the
    permeability of free space.

    For an example interior point, we could pick {0.6 m, 0.6 m}. At that point,
    the program returns:
    Br = 1.835e-006 Tesla
    Bz = 6.192e-007 Tesla
    if we take ni= 784.4017 and a=Pi*0.055^2 to match the problem geometry, the
    analytical formula yields:
    {1.830232623614073*^-6, 0, 6.10077541204691*^-7}
    which seems like a reasonable match.

    Dave.

    begin:vcard
    n:Meeker;David
    tel;fax:781-890-3489
    tel;work:781-684-4070
    x-mozilla-html:TRUE
    url:http://www.foster-miller.com
    org:Foster-Miller, Inc.;Electrical and Electronic Systems Group
    adr:;;350 Second Avenue;Waltham;MA;02451;USA
    version:2.1
    email;internet:dmeeker@foster-miller.com
    title:Senior Engineer
    fn:David Meeker
    end:vcard

- References:
  - Asymptotic boundary condition
    - From: marco valcavi <mvalca@yahoo.com>

- Prev by Date: Asymptotic boundary condition
- Next by Date: Lua zoom & grid
- Previous by thread: Asymptotic boundary condition
- Next by thread: Re: [femm] Hello
- Index(es):
  - Date
  - Thread