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postprocessing

Posted Jan 12, 2010, 1:10 p.m. EST 4 Replies

Rahul Dhopeshwarkar
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Hi.

I am calculating sagging (-Z displacement) of a membrane (.25 mm thick) using 3D solid, stress-strain module. After computation, the 3D or 2D (XZ or YZ) slice plots show a much much bigger -Z displacement (> twice the membrane thickness) than that denoted by the scale bar (~24 microns). Why are these two different?
4 Replies Last Post Jan 13, 2010, 1:22 a.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 12, 2010, 2:00 p.m. EST
Hi

To now I have never taken COSMOL yet to show a wrong display values, but a couple of times I noticed that I got fooled by a few extreme points.

Have you done a boundary Z plot direct on the lower surface , with min max display on boundaries ?

What I iften use is to play with the scale gain, auto adjsut to everything min max found, by setting a limited value you can reduce the displayed values.

Your case seems to be very smooth and regular.

sometimes displaying w*(w>limit) allows you to pintpoint also certain regions
Hope this can help

Good luck
Ivar

PS which version are you using ?
Hi To now I have never taken COSMOL yet to show a wrong display values, but a couple of times I noticed that I got fooled by a few extreme points. Have you done a boundary Z plot direct on the lower surface , with min max display on boundaries ? What I iften use is to play with the scale gain, auto adjsut to everything min max found, by setting a limited value you can reduce the displayed values. Your case seems to be very smooth and regular. sometimes displaying w*(w>limit) allows you to pintpoint also certain regions Hope this can help Good luck Ivar PS which version are you using ?
Rahul Dhopeshwarkar
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Posted: 1 decade ago Jan 12, 2010, 2:41 p.m. EST
Ivar,

Thanks for your reply.

I took a line plot (XZ) on the lower surface and the value I get match the values on the colorbar. However, limited values of 'w' do not seem to change the 3D/2D display plots. I'm using version 3.4.

Rahul

Ivar, Thanks for your reply. I took a line plot (XZ) on the lower surface and the value I get match the values on the colorbar. However, limited values of 'w' do not seem to change the 3D/2D display plots. I'm using version 3.4. Rahul
Ozgur
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Posted: 1 decade ago Jan 12, 2010, 5:06 p.m. EST
Not sure if this applies here but this might be due to numerical error arising from need to compute with very small numbers: You are trying to resolve microns in SI system (1e-6m). It might help to rescale your problem, go to a different built in unit system (CGS?) or use a non-dimensional representation. I remember encountering a similar issue although it was in a different type of problem.
hope this helps


Ivar,

Thanks for your reply.

I took a line plot (XZ) on the lower surface and the value I get match the values on the colorbar. However, limited values of 'w' do not seem to change the 3D/2D display plots. I'm using version 3.4.

Rahul


Not sure if this applies here but this might be due to numerical error arising from need to compute with very small numbers: You are trying to resolve microns in SI system (1e-6m). It might help to rescale your problem, go to a different built in unit system (CGS?) or use a non-dimensional representation. I remember encountering a similar issue although it was in a different type of problem. hope this helps [QUOTE] Ivar, Thanks for your reply. I took a line plot (XZ) on the lower surface and the value I get match the values on the colorbar. However, limited values of 'w' do not seem to change the 3D/2D display plots. I'm using version 3.4. Rahul [/QUOTE]
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 13, 2010, 1:22 a.m. EST
Hi

By comparing your two jpg I see the same value !,
your sag is negatif so its in the "blue" lower part of the color bar that you have -2.4e-5=-25e-6=-25um.

I have been cought a couple of times expecting to read on the top and not from the bottom, is it simply that ?

By the way you can always have your 3D graphs in um too, you have the choice of the units, just underneath the variable in the postprocessing plot window

Good éluck
Ivar
Hi By comparing your two jpg I see the same value !, your sag is negatif so its in the "blue" lower part of the color bar that you have -2.4e-5=-25e-6=-25um. I have been cought a couple of times expecting to read on the top and not from the bottom, is it simply that ? By the way you can always have your 3D graphs in um too, you have the choice of the units, just underneath the variable in the postprocessing plot window Good éluck Ivar

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