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6 Replies
Last post: November 26, 2011 11:21am UTC
January 12, 2011 12:24pm UTC
2-D plate model
Hi,
I am trying to build simple model to analyse the eigenfrequencies of a freely vibrating irregularly-shaped 2-D plate. I have selected the plate model in the structural mechanics module. The shape I have imported from a .dxf CAD file. I have around 8000 elements, an amount which I believe to suffice.
When I try to solve my model all I get is an error of undefined value in the stiffness matrix. For a 3-D square plate with the same settings, everything seems to be working fine.
Can someone help me detect what have I forgotten in this model, because it does not work?
Yours,
Henna from snowy Finland
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January 12, 2011 3:01pm UTC in response to Henna Tahvanainen
Re: 2-D plate model
Hi
I have some problems too to run your file too, try to redefine a fresh model.
You must know by now that v4.0 is sensitive to model changes and modifications, you should get hands on the latest 4.1 its much smoother :)
If I extract your geometry and remake a plate model it works OK for me
--
Good luck
Ivar
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January 12, 2011 3:28pm UTC in response to Ivar Kjelberg
Re: 2-D plate model
Hi,
and thanks for a swift reply. I did not think of redefining the model before. I exported the geometry, and made a new model. Yet, I get the very same problem persisting; an undefined value found (in the stiffness matrix). I have also tried simply restarting COMSOL..Debugging one's models is very difficult in COMSOL.
It might be that I am missing something very simple in my model. There is nothing in particular that I should do to the imported geometry, before meshing? Is it possible for you to post the plate model online, so that I can make a comparison?
However, since you managed to run the model, I think the problem could also be my computer, or my version of the software.
Thanks again.
Henna
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January 12, 2011 3:57pm UTC in response to Henna Tahvanainen
Re: 2-D plate model
Hi,
The problem is that the model uses a Poisson's ratio that is exactly 0.5, which leads to a division by zero in the computation (and hence an error for Inf in the matrix rows) for a linear elastic material model. That material model uses a factor (1-2*nu), where nu is Poisson's ratio, in the denominator for the elasticity matrix, so a value of 0.5 is not allowed.
Try using a Poisson's ratio that is smaller than 0.5. Then the computation should run just fine.
Best regards,
Magnus Ringh, COMSOL
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January 13, 2011 6:45am UTC in response to Magnus Ringh
Re: 2-D plate model
Hi
I missed that one ;), as I redefined the material
--
Good luck
Ivar
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January 13, 2011 11:47am UTC in response to Ivar Kjelberg
Re: 2-D plate model
Oh, yes, indeed. That is the little thing that I missed. I had just selected some of the material properties wrong after reducing the material from orthotropic to isotropic , and the model dimensions from 3D to 2D. One should be careful to remember the actual physics behind!
Thank you very much!
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November 26, 2011 11:21am UTC in response to Henna Tahvanainen
Re: 2-D plate model
Hi,
I am also facing the same difficulty for microwaves heating model. Initially, I was simulating a layer of oil lying over a layer of oil and was getting some results, although not convinced.
Then I defined another layer of oil below the layer of water and tried to simulate it but it gave me the following error:
Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1160 equations giving NaN/Inf in the matrix rows for the variable mod1.E10
at coordinates: (0.0016633,0.00180792), (0.00332659,0.00361583), (0.00382242,0), (0.00714901,0.00361583), (0.00764484,0), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E20
at coordinates: (0.00548572,0.00180792), (0.0016633,0.00514125), (0.00469918,0.00847458), (0.0085216,0.00514125), (0.0191354,0.00333333), ...
There are 290 equations giving NaN/Inf in the matrix rows for the variable mod1.E21
at coordinates: (0.00548572,0.00180792), (0.0016633,0.00514125), (0.00469918,0.00847458), (0.0085216,0.00514125), (0.0191354,0.00333333), ...
There are 871 equations giving NaN/Inf in the matrix rows for the variable mod1.Ez
at coordinates: (0,0), (0.0114673,0), (0.00573363,0), (0.00249494,0.00271187), (0.00498989,0.00542375), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns
I have not even changed any other material, BC or property of the model and there is no red flag in the material section either but still I am facing this error, why???
Can you please help!
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