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# RE: [femm] Define contour

- To: "'femm@yahoogroups.com'" <femm@yahoogroups.com>
- Subject: RE: [femm] Define contour
- From: Finlay Evans <finlay.evans@renishaw.com>
- Date: Thu, 25 Jul 2002 08:50:06 +0100

Hello Roman, What I do in this situation is to subdivide the airgap between static and moving parts with lines that trace a contour right round the moving part. I can then control the element size within the airgap to ensure that I get an accurate force result. (read the part in the manual that recommends using at least two elements between a line integral and a change in material boundary:- it is important!) See the attached femm model that I used to plot the force on a steel block as it moves into the gap between an electromagnet. (I have also used other lines to subdivide the air into different areas, so that I can control the element size where necessary.) These lines can then be picked in the post processor. I use the Lua lines below in my post-processor script; -- obtain forces clearcontour() seteditmode("point") ncpts = getn(cpts.x) for k = 1,ncpts do selectpoint(cpts.x[k],cpts.y[k]) end selectpoint(cpts.x[1],cpts.y[1]) fx, fxi, fy, fyi = lineintegral(3) The x and y coordinates of the line end points are stored in 'cpts.x' and 'cpts.y' which I define in my preprocessor model script, and read in from a file at the beginning of my post-processor script. You dont actually need to draw lines in your femm model, but you need the points there to use the method described. Furthermore, I use this line midway in the airgap to help define my element size within the airgap (using the line properties). This way I ensure that I only have really small elements where I need them (this is useful if you have a model with a lot of travel, or a very small airgap). The important obvious thing is to move these contour points with the moving geometry within your Lua pre-processor script (the model attached was designed with static contour lines but this is an exception to what I usually do) This works well for me, and results agree well with physical systems (to date Femm has predicted forces to within 10-15% of the actual measured forces for 3-4 systems that I have built, which I consider to be excellent for 2D - FEA) Regards, Finlay Evans Finlay Evans Senior Design Engineer Group Engineering - Renishaw Plc -----Original Message----- From: Roman Beresik [mailto:beresikr@valm.sk] Sent: 24 July 2002 14:26 To: femm@yahoogroups.com Subject: [femm] Define contour Hello femm group I have a simple simulation of electromagnet. I made program for motion of the core in the electromagnet by the lua script language. I defined segments and nodes selected as a group 1 near to core sufrace. I don't know how to define contour for this group in the post processor for the calculation of line integral. I found only commands which need to define co-ordinates of points for contour. However, the motion is programed by loop. I have a question. How to define the contour automatically for each step of loop ? Roman Beresik `Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.` `------------------------------------------------------------------------ This email and any attachments are confidential and are for the use of the addressee only. If you are not the addressee, you must not use or disclose the contents to any other person. Please immediately notify the sender and delete the email. Statements and opinions expressed here may not represent those of the company. Email correspondence is monitored by the company. The parent company of the Renishaw Group is Renishaw plc, registered in England no. 1106260. Registered Office: New Mills, Wotton-under-Edge Gloucestershire, GL12 8JR, United Kingdom. Tel +44 (0) 1453 524524 -----------------------------------------------------------------------`

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