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# Re: [femm] New FEMM user

- To: <femm@yahoogroups.com>
- Subject: Re: [femm] New FEMM user
- From: "Eric Vogels" <eric.vogels@telia.com>
- Date: Mon, 18 Nov 2002 15:27:29 +0100
- References: <ar5ago+1n0e@eGroups.com> <3DD888A9.9010403@ieee.org>

> Thank you. I started learning to use the program and I started collecting as many as examples with PM as possible. In case someonein this list wants to share one (or more) examples with PM, please send this to eric.vogels@telia.com Thanksin advance. Eric Vogels ----- Original Message ----- From: David Meeker To: femm@yahoogroups.com Sent: Monday, November 18, 2002 7:28 AM Subject: Re: [femm] New FEMM user eavogels wrote: `Dear Mr. Meeker. My name is Eric Vogels and I will try to learn FEMM. I followed this group almost half a year and I must admit that the level where everyone is discussing models is too high for me to understand. Unfortunately I have not the right education but since many years I'm experimenting with magnets. Now I want to learn FEMM in order to be able to build my models in the program first, before building in real live. Do you think there is a change that I can use FEMM by only reading the manual and looking at examples or is fysics education neccesary. Please advice me. I only use permanent magnets, mounted on wheels. I wonder is examples with permanent magnets are available. I'm good in cutting and pasting other peoples work. In case you want to see where I work with in my spare time look at: <http://fdp.hemsida.net> Thanks (and thank you for the nice program). Eric Vogels.` Configurations of permanent magnets can be modeled by femm, but they must be configurations that can well-approximated by a 2D planar geometry or configurations that are rotationally symmetric (e.g. like a typical speaker design). I know of many users who have been able to set up and analyze programs and get OK results without much of a formal background in magnetism. For example, I've seen some pretty good simulations that have been created by high school students who where interested in modeling coil guns. However, as has been pointed out in several messages in the "FEMM Vs. commercial code" thread, without a fairly good understanding of the physics behind the program, itis possible to make models that aren't reasonable. Since the finite element is only an approximate method of solving the differential equations that are usually employed to model magnetic phenomena, it is possible to create geometries or meshes that give bad results if you don't have some understanding the numerical methods behind the program (and their shortcomings). Most importantly, it can be especially difficult to understand the results of the program without a good theoretical understanding of what the program is supposed to be doing. In some sense, the program is really just like any calculator--it crunches the numbers, but doesn't have any intrinsic understanding of the problem that it's solving--that's the user's job. Anyhow, I guess that I have been sort of remiss in putting up permanent magnet examples on the website. As an example, a fun PM configuration to look at is a Halbach array, which is an array of permanent magnets that tends to concentrate the PM flux on one side of the array. Since it's only about 1K, I've attached a sample of a wavelength's worth of such an array. It's a good example in the sense that it shows how permanent magnets can be been defined and oriented in the program. There have also been some pretty good threads that had to do with specific PM machine modeling problems on the mailing list. (e.g. the collection of messages that was spawned by http://groups.yahoo.com/group/femm/message/1229 having to do with small brushless DC motors). Dave.
>     --
>     David Meeker
>     dmeeker@ieee.org
>     http://femm.berlios.de/dmeeker
`Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.`

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