Beam with circular cross section frequency analysis

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  • Last Post 01 October 2018
Yazan Thaqakha posted this 27 September 2018

Hello,
I am using Modal in Ansys Workbench 19.0.

I have drawn a beam with a circular cross section, and set the constraint "fixed" on one end (on the surface).

After that I apply "Total deformation" in the solution section after that I solve it and produce the mode shapes and frequencies.

I have 2 questions;    1- I always get 2 similar frequencies in a row as shown in the picture below, why is that and how can I fix it?
2- When I play the mode shapes, the beam moves in 2 dimensions at a time, how can I fix it and let it move only in 1 dimension"

Note: When I draw a beam with rectangular cross section, when I play the mode shapes, the beam moves in 1 dimension only.

Thank you very much for the help!

Beam frequency

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SandeepMedikonda posted this 01 October 2018

Hi Yazan,

  It looks like you have a symmetric structure. When you do it is expected to have linear independent model shapes for identical frequencies. These are typically called degenerate modes and depending on the symmetry several frequencies can have this.

  I am not sure what you mean by moving in 2-Dimensions? Isn't the mode shape dependent on the Eigen Vector? Can you alternatively just 2-D analysis? You can set this in the Properties tab in Workbench under Analysis Type.

Regards,
Sandeep
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peteroznewman posted this 01 October 2018

Hi Yazan,

Your circular beam is symmetric, so you can eliminate the duplicate frequency results by splitting your geometry in half through the center of the beam and using a Symmetry Region. That way, your beam will stay in the plane.

Regards,

Peter

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