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# Re: [femm] Re: number of points in material defintion

- To: femm@yahoogroups.com
- Subject: Re: [femm] Re: number of points in material defintion
- From: Alexandru Andrei <alinixovici@yahoo.co.uk>
- Date: Wed, 5 Feb 2003 03:34:08 -0800 (PST)
- In-reply-to: <004b01c2cc6a$a05acc60$55755142@robertmacy>
- Reply-to: alinixovici@yahoo.co.uk

Can you send me the points tooked by you and the manufacturer' s curve?

Robert Macy <macy@california.com> wrote:

> `I took points from manufacturer's data curve. When femm plotted the data,
> the curve did not follow the data points.
> Yet, the original data was monotonic and "made sense". Please explain.
> - Robert -
> ----- Original Message -----
> From: mailto:David Meeker <dmeeker@ieee.org
> To: femm@yahoogroups.com
> Sent: Tuesday, February 04, 2003 6:47 AM
> Subject: [femm] Re: number of points in material defintion
> --- In femm@yahoogroups.com, "Michael Salloker
> <michael.salloker@f...>" <michael.salloker@f...> wrote:
> > Hello,
> >
> > I wonder how many points un B-H-curve are necessary to get a good
> > description of a ferromagnetic material.
> >
> > I found out, that increasing the number of points also increase the
> > speed of the calculation, so its necessary to find a sufficient large
> > number of data points.
> >
> > So imagine I have a material with a saturation of about 1T, i could
> > do a spacing of 0.1 T, or 0.05T aso. In general I believe its better
> > to make aquidistant points for B and for H, due the nonlinearity.
> >
> > Whats is the experts opnion?
> >
> > Thanks
> >
> > Michael
> The program interpolates the entered points using cubic splines.
> Cubic splines are twice continuously differentiable, so you don't need
> an excessive number of points to get a smooth BH curve.
> Generally, it is good to have more points around the "knee" of the BH
> curve. If there are not enough points around the knee, the program
> can't fit a monotonically increasing BH curve through the points. The
> program then smooths the data points repeatedly until the fit becomes
> monotonic--the cost for this smoothness is that the curve doesn't pass
> exactly through the defined points.
> If you push the "plot BH curve" button on the BH point entry dialog,
> the program plots up the fitted curve, along with the data points. If
> the program had to smooth, the fitted curve doesn't exactly pass
> through the data points. You can add more points (typically around
> the knee) to get things so that the program doesn't have to do any
> smoothing--although the smoothed curve that doesn't exactly pass
> through the defined points might be good enough for your purposes
> without having to add in extra points.
> Another consideration is that you'd typically want to make sure that
> you extend out the BH curve far enough so that you aren't
> extrapolating the BH curve at any of the points in your solution.
> Typically, I try to make the points somewhat evenly spaced in sort of
> a line integral sense. For example, if dB and dH are the differences
> in B and H respectively between successive points on the BH curve, and
> Bmax and Hmax are the last point on the curve, I try to make:
> sqrt((dB/Bmax)^2 + (dH/Hmax)^2)
> be sort of constant. However, this is just sort of a rule of thumb.
> Typically, most of the points in the materials library have about 15
> or so points.
> Dave.
> --
> David Meeker
> http://femm.berlios.de/dmeeker
> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
> `
> `Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.`

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  - Re: [femm] Re: number of points in material defintion
    - From: "Robert Macy" <macy@california.com>

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