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Modal Analysis contact issues and Material specifications

Posted Jun 16, 2011, 11:42 a.m. EDT Materials, Studies & Solvers, Structural Mechanics Version 4.1, Version 4.2 0 Replies

Danielle Lower
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I am currently working on a modal analysis of a pipe within a pipe. The modal is fairly simple, two long, concentric cylindrical pipes, constrained at the top, subject to only a body load.

My first issue is establishing contact pairs. I set it up so that the outside surface of the inner pipe is not able to cross through the inside surface of the outer pipe, yet, when I run the analysis I still get modes where the interior pipe passes through the exterior pipe. Any thought?

Also, I have another model of the same system, except for this time I place a small rubber seal in between the two pipes, close to the top. I can get the model to run if I keep all of the components the same material (i.e. model the seal as steel just like the two pipes) but, when I try to change the seal material to a rubber the model is not able to run giving an error:
Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 30 equations giving NaN/Inf in the matrix rows for the variable mod1.u
at coordinates

Any input would be greatly appreciated.

Thanks
0 Replies Last Post Jun 16, 2011, 11:42 a.m. EDT
COMSOL Moderator

Hello Danielle Lower

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