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eigenfrequency analysis in ansys

Preml

New member
Hello
I am doing a Modal analysis on a structure made up of 3D-Beam4, Mass21 and Shear panel 28. To be more clear, the structure looks like a cube made up of Beam element on all 12 edges with Mass21 element at all corners of the cube and also with shells (shear panel 28) at all six faces of the cube.

I first constructed the beam structure with keypoints and lines, then i added the point masses and meshed them, then i created the shell element using Modelling-create-area and meshed it. Finally i merged them using "NUMMRG, ALL" in the command field.

After solving, the Eigen frequency i obtain is about 0.24271e-5 Hz. But the same problem when solved using ABAQUS gives the Eigenfrequency as 27 Hz which is the correct value.

Somebody please let me know where i went wrong.... Couldn't proceed any futher....

Thanks in advance
Prem
 
Try setting the minimum frequency to 1 Hz and run again (in the Range Minimum field in Workbench). There are always 6 rigid body modes for avery unconstrained analysis, and I guessing that you have found these. Alternatvely make sure you ask for 7 modes and look at the last one.

Regards,

Rod
 
Hi Rod
Sorry for not having mentioned about the boundary condition. It s a fixed support at all four corners of a face. Moreover i am working on Ansys classic and not in work bench.
I cud find a field where it asks for "initial frequency" and"end frequency" and i tried entering initial frequency as 1 Hz but it shows the same result as before.

Any other possibilities?

Regards
Prem
 

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