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Inconcistency between 2D axisymmetric and 3D model

Posted Mar 24, 2011, 11:07 a.m. EDT Structural Mechanics Version 4.1 2 Replies

John Smith
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I have a very simple model : A cantilevered cylinder, radius = 0.4m, length = 10m, fixed contraint at the bottom, free everywhere else.

In 2D axisymmetric geometry this cylinder is modeled by a r=0.4m x z=10m rectangle with it's bottom left edge at (0,0).
The 2D axisymmetric eigenfrequency solver only returns the hight frequency compression modes (see image attached), the lower frequency rocking modes are not computed.
The exact same cylinder computed in 3D returns the wanted lower frequency rocking modes (see image attached)

How to computed those rocking modes in 2D axisymmetric geometry.

Thanks,

John Smith.
2 Replies Last Post Feb 8, 2022, 10:12 a.m. EST
Nagi Elabbasi Facebook Reality Labs
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Posted: 1 decade ago Mar 24, 2011, 1:49 p.m. EDT
In 2D axisymmetric analysis both the geometry and the deformation must be not vary in the circumferential direction. The displacements of the cylinder’s low frequency bending modes are not axisymmetric so they cannot be picked up in an axisymmetric frequency analysis.

Nagi Elabbasi
Veryst Engineering
In 2D axisymmetric analysis both the geometry and the deformation must be not vary in the circumferential direction. The displacements of the cylinder’s low frequency bending modes are not axisymmetric so they cannot be picked up in an axisymmetric frequency analysis. Nagi Elabbasi Veryst Engineering
Jeff Hiller COMSOL Employee

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Posted: 3 years ago Feb 8, 2022, 10:12 a.m. EST

Starting at version 6.0, the bending eigenmodes of an axisymmetric object can be computed in the 2D axisymmetric interface by selecting the "Circumferential mode extension" option and specifying an azimuthal mode number. Read this blog post for more information on this topic.

Best regards,

Jeff

-------------------
Jeff Hiller
Starting at version 6.0, the bending eigenmodes of an axisymmetric object can be computed in the 2D axisymmetric interface by selecting the "Circumferential mode extension" option and specifying an azimuthal mode number. Read [this blog post](https://www.comsol.com/blogs/axisymmetric-solid-mechanics-with-a-twist/) for more information on this topic. Best regards, Jeff

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